Final Report Summary - WETMATE (WETMATE – a 33kV Subsea Wet-MateableConnector for Offshore Renewable Energy)
Executive Summary:
Most European offshore wind farms are currently installed within 20 km of the coast in shallow water depths up to 20m. The next generation will be developed at distances of 40 km in sea depths up to 80m. These new locations present technical challenges for engineering and the possibility of new synergies between all marine renewable energy resources including wave, tide and wind. The WetMate consortium delivered a prototype 33kV hybrid wet-mate connector with a connectivity monitoring system and future-proof features for higher voltage connector technologies.
This will lead to efficient power transmission, reduced installation and maintenance costs and precision remote monitoring that reduces routine maintenance and intervention by divers, benefitting health, safety and affordability.
The operational requirements for the WetMate connector have been quantified. It is concluded that the nominal current carrying capability of the mating construction is to be increased from 500A to 650A at 33kV.
A variety of candidate insulating and conducting materials for use within the WetMate connector were evaluated to determine the electrical properties of the insulators. The conclusion was that to ensure the health of the insulation system, it will be a requirement to include a moisture level monitoring system, to ensure a low content of water in the apparatus during operation.
A new strategy for environmental monitoring and wireless communications has been considered and a health monitoring system has been developed in a very low power form maximising the chances of being able to both scavenge sufficient power from the electric field and as such simplify the installation without impacting on the end users cable, maintaining the pass through ideal of the connector.
A prototype connector has been manufactured to prove it’s mating and demating capabilities and a standalone flushing rig to mimic the design in the final connector has also been designed, built and tested.
Laboratory tests suitable for high voltage test of the connector in dry condition were carried out. The occurrence of PD just above nominal voltage means that high voltage withstand tests at slight or high over voltages at this time are not recommended. After modifications in design or mating procedure the connector should be PD free.
Two different environmental monitoring and wireless communications have been developed and one has been tested with the communication web platform whilst the other has been tested underwater to prove that the communication is possible at depths of 50 metres.
A number of dissemination activities have been completed by the partners and an exploitation plan and agreement formulated has been accepted by the SME partners.
The project partners in this exciting collaborative project are:
Hydro Bond Engineering Ltd
Nordic Seal AS
Fortis Mechanical Design Ltd
Marine Signals
The UK Intelligent Systems Research Institute Ltd
Technical University of Denmark
Project Context and Objectives:
The European electricity generation sector is moving towards a single integrated supply and demand market in which it hopes to generate 20% of electricity needs from renewable energy sources by 2020. Offshore renewables are a key way of achieving this target and the Atlantic Arc (Iceland, Norway, UK, Ireland, France, Spain and Portugal) has some of the most favourable wave and wind resources in the world, representing 150-240TWh/year. Consequently, there is a strong drive to increase off-shore tidal, wave and wind energy activities in the EU.
A €30Bn project involving nine north-western European countries will see a 100GW underwater energy ‘super grid’ in the North Sea linked to wind farms, tidal power stations and hydroelectric plants over the next decade. The Desertec Industrial Initiative aims to provide 15% of Europe's electricity by 2050 or earlier via power lines stretching across desert and the Mediterranean. Coal (28.7%) currently accounts for the largest share of capacity, but a fast growing wind market (7.9%) has recently overtaken the market share of fuel oil (6.9%). By the end of 2008, installed wind capacity had reached 55GW compared to the total installed capacity of 800GW. Investment in the offshore market in 2009 was significant amounting to €1.5 billion. Further investments are expected with the implementation of EU policies favouring offshore production to meet the EWEA 40GW by 2020 and 150GW to meet 2030 targets.
Wind power is currently in the vanguard of the movement towards offshore renewable energy. Today’s offshore farms are mostly installed in relatively shallow water less than 20 km from the coast. However, the next generation of offshore energy farms will be developed at distances around 40 km requiring investment to overcome the problems of operating in depths up to 80m.
The transmission and distribution of electrical energy requires high capacity cabling. This is partly achieved through bigger conductor cross-sections and thus heavier cables, but also higher transmission voltages incur lower energy losses. A saving of just 1% on the electrical energy produced by a power plant of 1GW means transmitting 10MW more to consumers, sufficient to supply > 4000 homes. Increasing the transmission voltage is one way of reducing these losses. Over land, long distance transmission is typically done with overhead lines at voltages of 115kV to 1,200kV at up to 200Hz.
Voltages range from 6kV (coastal) to 145kV (subsea networks). In offshore subsea applications raised transmission voltages are also desirable but their adoption is hindered by the harsh environment and the ability to make reliable connections between generators and cabling infrastructure.
Cabling for offshore power generation involves a multitude of connections to be made to each generating device. These cables can be run to shore individually or connected to a subsea hub. A single, higher power cable can then be run to shore for termination into an onshore grid. Given the technical challenges associated with high voltages in the presence of sea water around connection points, the voltage generated by offshore devices has traditionally been limited to 11kV-33kV. According to Scottish Enterprise figures, the cost of building a 500MW wind farm is estimated to be around €1.5Bn 5% of which is normally attributable to connectivity. With over 800 such farms in operation or planned globally, the value of the market opportunity for cabling and associated components is estimated to be in excess of €60Bn by 2020. Although less progressed, the investment in other ocean power sources is also enormous. It is estimated that the worldwide wave resource is 6,000 TWh per year, twice as much as global nuclear production and 700 TWh/year for tidal power . Worldwide the market potential for the wave industry is about US$1 trillion of which about €50Bn will again be spent on connectivity.
Connecting devices need to be capable of efficiently conducting electrical power as well as allowing disconnection for inspection and maintenance of the connector. There are two categories of such devices:
• Dry-mate. Used for connecting on board ships for subsequent subsea deployment
• Wet-mate. Used primarily for subsea connections and installed by remotely operated vehicles (ROVs) or divers
Dry-mate connections are made above the surface onboard or on land prior to cable laying. Dry-mate splicing is conducted onboard a ship before the cable is deployed to the seabed. Splicing is a time consuming process which relies on the use of a large vessel capable of handling the cables without risk of capsizing, a good weather window and a highly trained workforce. This can mean that the ship has to be on location for up to 3 weeks. Dry-mate connectors rated at 11kV are already manufactured by Hydro (figure left) and the joining operation can be carried out in one day, but a large ship is still required. Splicing is the method currently used for 33kV connections. With day rates for large ships around €100K-€200K, this is very costly.
Subsea (wet-mateable) connectors are desirable: the mechanical connection can be made quickly using subsea remote operated vehicles (ROVs) operating from much smaller ships. Wet-mate connection implemented with ROVs is less sensitive to weather restrictions as heavy cables do not need to be hauled up to the deck of the ship. The costs of wet-mating each generator are therefore greatly reduced and reliable 33kV wet-mate connectors are in increasing demand by the industry. However, there are significant challenges in designing and building such a connector that are the focus of this project.
Low voltage wet-mate connectors (6-11kV) have historically been used in the oil & gas industry to simplify cable handling and allow easy maintenance or replacement. However, their low voltage specification means that they have only low power capacity and are not generally suitable for use in shallower waters. It should be noted that the renewables environment is far more severe in spite of the lower water pressures involved. The connectors are subject to variable power levels (zero to maximum twice per day for tidal), pressure variations, warmer and highly-oxygenated water that promotes corrosion and marine growth, sand and silt accumulation and cable flexing. In addition, products for oil and gas are developed as customised one-off equipment that does not address the mass market. They are prohibitively expensive (10x higher than our solution).
There are major technical challenges that need to be addressed to develop a wet-mate 33kV connector related to voltage breakdowns such as partial discharge (PD) and water treeing which are compounded at higher voltages. PD is usually the result of localised dielectric breakdown of the solid or fluid electrical insulation under high voltage stress. It generally begins at 6kV in voids or cracks or at conductor-dielectric interfaces within a solid insulators, or in bubbles within liquid dielectrics. The phenomenon causes progressive deterioration of insulating materials, ultimately leading to electrical breakdown. The cumulative effect of PD within solid dielectrics is the formation of numerous branching, partially conducting, discharge channels - a process known as treeing. Over time the insulation to earth or between phases is so weakened that it breaks down completely.
There have been a few initiatives conducted by marine engineering companies to develop 33kV wet-mate connectors. Where such work has been undertaken, they are project specific designs and are not flexible enough to serve as technology platforms across sectors. Oil & gas sector products are bespoke solutions and too costly. Some self-monitored solutions exist in development with poor optical connectivity achieved across power connectors due to external links. The commercial market for the renewables sector is generally patchy and products are ad-hoc solutions compared to our purpose designed technology.
This project provided an exciting opportunity to advance the current state-of-the-art in subsea connectors. The fact that there is an increasing number of 33kV-ready subsea cables being laid demonstrates that the market has already recognised the benefits of such a solution. The medium term goal is to increase subsea transmission voltages to 33kV so as to make systems such as subsea hubs and grids serviceable and facilitate flexible demonstrator projects. Long-term there is a clear need for a proven technology that can form a platform for a range of higher voltage wet-mate connectors within the renewables industry.
The project developed a proof of concept solution for a 33kV 3-phase subsea connector that has several highly desirable innovations that will result in reliable operation and reduced offshore energy industry costs. To remove any need for interventional routine maintenance, we propose a connector solution that will monitor its own long-term performance and health by utilising power cables’ integrated optical fibre element to transmit data. A suite of sensors will provide real time data on humidity, internal pressure, and crucially, PD activity within the connector joint (via temperature, noise and trace gas measurements). Our innovations are:
• High electrical integrity 33kV wet-mateable conductivity (10 year MTBF)
• Reliable hydrostatic pressure mating mechanism (mates on first attempt)
• High mechanical long-term stability (>10 years)
• Integrated connector performance sensing of Partial Discharge
• Multiplexed optical performance data / control signal communications
• Internal protected optical connectivity
• Predictive health analysis/fault prognosis system
• Built in design for future higher voltage extension
This connector will confer multiple real world benefits on end users. A pluggable connector rated for higher voltages will enable infrastructure to be easily and relatively cheaply reconfigured or upgraded to optimal operation without the preventive high costs of splicing – development projects will be accelerated by this facility. Integrated remote sensing and monitoring will also eliminate the need for costly routine maintenance and reduce intervention by divers thus offering health, safety and additional financial benefits: cable installers will be able to streamline their existing procedures of employing divers and ROVs without the requirement for large, expensive ships to maintain the infrastructure.
A STRATEGIC objective is to engineer our technology as a platform for future higher voltage rated designs.
The SMART objectives are:
• To research the electrical requirements for the connector
• To gain new knowledge in relation to partial discharge sensing and monitoring
• Understand the requirements for the mechanical aspects of the wet-mate connector
Associated TECHNICAL objectives are:
• The connector design will have a max. external diameter of 600mm, mass of <800kg, corrosion resistance of 25 years, a rated time to failure (MTBF) of 30 years, tilt misalignment tolerance of 2.5°, rotational misalignment tolerance of 5° (using self-correcting alignment guides), drop test rating of 2m, external pressure rating of 2.6MPa (250m water depth), the ability to close via hydrostatic pressure in >15m water depth (0.25Mpa) operating temperature tolerance of -10°C to 32°C, effective re-sealing after 20 mating/de-mating cycles.
• Electrical performance requirements 33kV (up to 36kV), 650A rated to 1500 MWdays. Contact Resistance < 2.5mOhm and insulation resistance >10GOhm. To withstand 40kV for 4 hours and demonstrate a rapid ramp breakdown average of 49kV. Connector must meet the requirements of IEC 60502-2 and RA-SNO-00183.
• The connector electrical integrity sensing and monitoring system must consume <25W, powered from induction coils located within the connector to eliminate the potential for insulation breakdown and short circuit via the sensing hardware. Sensor must be capable of operating at temperatures from -15° to 40°C. Data will be transmitted along the optical communication lines via an interface incorporated into the sensor. A backup battery system will power the hardware for a minimum of 30mins in the event of loss of transmitted cable power. This will provide fault diagnosis to the onshore station in the event of connector failure locally or elsewhere in the system.
• The design concept proposes a 2 stage flushing cycle that will remove any impurities and moisture. The filtered de-ionised flushing cycle will remove impurities and sea water, ensuring that the inner connector cavity is free from contaminants. This flushing cycle must be carried out at whilst the connector is held in position by the ROV. The dry hot gas flushing cycle (>60°C for 90 minutes) will ensure that the electrical components are completely dry before pressure is reduced and the connector is allowed to close.
Project Results:
Electrical Concept Development and Design Criteria
The operational requirements for the WetMate connector were quantified. Critical electrical and mechanical parameters were defined for further developments on the WetMate connector. A fully prepared document on the product specifications was prepared by Hydro Bond Engineering in collaboration with the participants of WP1. It is concluded that the nominal current carrying capability of the mating construction is to be increased from 500A to 650A at 33kV.
A variety of candidate insulating and conducting materials for use within the WetMate connector were evaluated to determine the electrical properties of the insulators. The conclusion was that to ensure the health of the insulation system, it will be a requirement to include a moisture level monitoring system, to ensure a low content of water in the apparatus during operation.
Electric field FEA analysis - According to IEC 60502-2 and IEC 60502-4, typical electrical tests consist of AC-voltage tests, lightning impulse tests, partial discharge (PD) tests and thermal and dynamic short-circuit tests. Usually, PD tests are the most critical when determining the nominal voltage for the proposed connector design. Also, lightning impulse voltage test can reveal weaknesses in the connector design.
Simulation models and initial simulations were performed on provided HRC240 connector design. The geometry provided for the analysis was simplified and preconditioned for electric field distribution calculation, and several assumptions were made due to a lack of information.
Simulation results - Since the analysis simulates the partial discharge test, the electric field strength within the air region was investigated. Breakdown electric field strength in homogenous field distribution inside dry air at 1 bar is ideally around 3 kV/mm. Since the field analysed is not homogenous due to the impurities in the air, a more realistic value would be 2 kV/mm.
But, regarding partial discharges, it is important to consider the conditions in free gas and along surfaces. In all high voltage constructions, you need to distinguish between 2 situations.
a) The applied field and the breakdown field in free gases. In this case, the mentioned peak value of 2 kV/mm breakdown field would apply.
b) The applied field and the breakdown field along the interface (tangential) between solid and gas. In this case, the breakdown field is about half of the value in free gas. Therefore the dimensioning criteria for this case would be under realistic conditions 1 kV/mm peak. In connectors, you will always have interfaces exposed to electrical fields and in general, the tangential field at these interfaces should be minimised.
Tests were conducted and, based on the results it was decided to focus on pd-behaviour of the connector.
The test platform was validated as being able to identify connection issues under dry conditions. Also the connector internal sensors performed correctly, though with lower sensitivity than the laboratory setup made possible.
Regarding testing of the next connector design, the occurrence of pd at slight overvoltage emphasises the necessity of pd-monitoring in wet-matable solutions. Pd inception at voltages 1.05 pu and higher in dry condition, must be considered as not quite sufficient. Design and/or mating process should be optimised aiming at pd free conditions at all relevant overvoltages.
Thereafter the tests should be repeated under wet controlled conditions, including the flushing and drying process. Also recommend are pd-measurements with a functional prototype under real conditions, including pressure and temperature.
Partial discharge detection and environment
Occurrence of partial discharges - Electric discharges that do not fully bridge an electrode is called partial discharge, acronym PD. The magnitude of these usually is small. However, in AC systems, these can cause progressive deterioration of insulation and thus leading to ultimate failure. PD is then essential to detect and locate in HV components. The occurrence of PD can vary, and depending on the insulating material, the safe operating limit determined. PD is classified by four different definitions, explained in the subsections below.
Internal Discharges - Gas filled cavities formed during the extrusion or moulding process of insulating materials have lower permittivity than the solid insulation material which surrounds it. Due to this low permittivity of the gas and depending on the shape of the cavity, an enhancement of the electric field occurs. Due to the switching polarities of the discharge of an AC system, local heating is generated in the cavity, which over time leads to the breakdown of the insulation.
Surface Discharges - In the case of an electric stress component existing parallel to a dielectric surface then surface discharges may occur. This is often the case when sharp edges are a part of the structure, resulting in excessive field enhancement over the insulation surface. These types of discharges apply to bushings, cable ends, etc.
Corona Discharges - Corona discharges occur when sharp edges and protrusions occur in an electric field. These usually occur at the high voltage side; however, corona can also be caused at earth potential where sharp edges exist. Even though large distances can be between the electrode and earth potential, the concentrated field in the corona leads to partial breakdown of the surrounding gas. This partial breakdown of the surrounding gas should be taken into extra consideration when dealing with sulphur hexafluoride gas (SF6), as the degradation product of SF6 is extremely poisonous and aggressive.
Treeing - Treeing forms in a solid insulation medium as a result of internal discharges. After treeing has progressed over time, the stem and larger branches growing outwards become hollow. Due to the sharp form of these hollow spaces in the direction of the field, considerable discharges occur; these discharges are very unstable in nature. When treeing sets in, discharges become increasingly visible, growing rapidly and in an extremely short period can in some cases lead to breakdown within a few seconds.
Methods of Partial discharge detection
Nonelectrical PD detection methods
Gas detection - A very simple method of detection is in the form of gas pressure measurements. This method is most often applied to transformers with impregnated paper insulation. In the case of discharges occurring in the insulation, a gas is produced which is then detected with a Buchholtz relay. Drawbacks of the gas detection method are that the discharge measurement is not quantitative and usually damage has started to occur on the grounds of discharges when the fault is detected.
Acoustic detection - Discharges such as corona and surface discharges can be detected and located using acoustic methods in air and oil insulation. With an ultrasound, narrow bandwidth microphone of 30 to 50 kHz in combination with a parabolic reflector with a directional beam of 10° or a more precise audio tube a discharge can be located. Discharges of only several pC can be detected using this method. However, the amplitude of the discharges cannot be quantified and therefore this technique can only be used as a locator of PD.
Light detection - External discharges can be detected by light detection. This can effectively be achieved by photography, given that a complete shield of ambient light is present. The location of the discharge can be very effectively located using this technique, however it requires the discharge to be in visual range of the optical sensor and a quantitative measurement is not possible.
Electrical PD detection methods
Two main methods of PD detection exist. Using the Classic detection method displays the discharges as short impulses superimposed on a 50Hz time-base. Using the Time resolved detection the true shape of the discharge is displayed on a trigger based time-base. Using these techniques, the discharge impulses are amplified with a bandwidth of around 100-500 kHz.
Different variations of measurement circuits can be used in order to detect discharges:
1) A high voltage source which preferably is free from discharges.
2) The sample to be measured for discharges
3) The impedance Z across which the voltage impulses are caused by the discharge in the sample
4) The coupling capacitance k which allows the passage of the impulses of high frequency. This must be in the same order of magnitude as sample a.
5) Signal amplifier A.
6) Observation unit O, in the form of a crest voltmeter, oscilloscope, pulse sampling device etc.
7)
The classical method of PD detection can be divided into two different subcategories; Straight detection and Balanced detection.
Straight detection - The advantage of the straight detection method is its simplicity and as a result it is widely used for routine tests of standard products. The disadvantage of the straight detection method is that it is not possible to distinguish the sample discharge signals from external disturbances.
Balanced detection - Balanced detection is common in laboratory testing where external disturbances can be controlled in a sufficient manner. Detection can be achieved either by using a basic circuit or with the sample earthed.
It is easy to create a balanced circuit using two samples, preferably of the same insulation material are measured. The preferred setup is by using samples composed of the same material and thus the loss factors are equal over large frequency spectra. Ideally the two samples have the same capacitance, however this is not necessary.
With this configuration the external discharge pulses can be suppressed while still detecting the discharges originating in the samples ‘a and a’. By injecting large discharges between high voltage and earth and adjusting the capacitive and resistive components to minimal response, the bridge is balanced.
With the use of electronic processing, a more practical configuration of the balanced circuit can be constructed with the use of a pulse discriminator.
Pulses occurring on both sides of the bridge are processed in the pulse discriminator. Pulses having the same polarity and arriving at the pulse discriminator at the same time, originate outside the bridge circuit. These common-mode signals can then be rejected, suppressing signals originating outside the bridge. Opposite polarity pulses originating in the samples are accepted and can then be assessed and analysed. The disadvantage of this method is that the rejection ratio is smaller compared to the balanced detector; however this method has the advantage that no balancing is required resulting in fixed impedance values.
By applying the balanced detection method on complicated samples, the discharge location can be assessed. By interrupting the earth screen at several locations, the discharge can be located.
Earthing interruptions can be made where the earth electrodes are made to overlap. However, this method is sensitive to measuring faults in the case of the insulation ring not being perfect, resulting in unwanted discharges occurring in that region. These are preferably made where a semi-conductive layer is placed between the two interrupted ground electrodes. With this configuration, sufficiently high impedance is formed to separate the electrodes, while still being sufficiently low not to interfere with the electric field in the insulation. This longitudinal resistance created between the electrodes should be in the order of a few kΩ.
As quantitative measuring is not possible with non-electrical detection methods, the preferred measuring method is electrical detection.
With the straight detection method, it is not possible to discriminate external signals from signals originating from the measured sample. Thus, the potential risk of external pulses corrupting the measurements makes it impossible to utilize the straight detection method as a practical measuring technique.
The balanced detection method technique is the preferred measuring technique as it is possible to discriminate external signals from signals originating from the measured samples. In addition, this technique allows for the possibility for discharge locating, which is essential as the WetMate connector PD measurements will need to be separated from the discharge signals originating in the joined power cables. This technique however is only possible to apply if the ground armouring of the joined cables can be interrupted from the grounded parts of the WetMate construction.
Design of sensor system and amplifiers
The requirements and schematic and PCB have been produced for the environmental sensing and PD detection. The design consists of environmental sensors to monitor the atmosphere within the connector housing during and after mating. This will provide details regarding any possible leaks or degradation within the connector from pressure, humidity and temperature. Further to the environmental sensing, Partial Discharge sensing has been designed to detect if the connector is starting to fail electrically.
The unit is powered by scavenged power from the electric field around the cables. This placed a high level of importance on designing the health monitoring unit to meet very low power requirements.
Due to the limited amount of power that can be scavenged from the electric field, low power consumption is critical to the design. The processor has been selected for its very low power consumption, all the ancillaries will be connected via power switches to enable the shutting down of all sub systems while they are not in use, this is controlled by the processor which is the only device permanently connected to the power.
PCB’s have been produced to a production standard and have been tested, programmed and evaluated.
Communications and power supply
The original intention was to use the optical fibre within the cable to send information about the state of the connector back to the shore. From a commercial point of view, special, possibly additional features would be required within the shore-bound cable. This was considered to discourage the selection of this connector style due to the requirement not to affect any of the cable interfaces which are owned by the customer. Alternative approaches were evaluated and the best option from this was the use of an ultrasonic modem between the connector housing and the energy convertor on the surface. This solution is ideal due to its low power and lack of interference with existing infrastructure. Should any data be required to be sent to the shore, this can then be integrated into the energy convertor data system.
This report details the design of the communications between the connector on the sea bed and the receiver on the surface as well as the power scavenging technique being employed. The chosen technology for the communications is an ultrasonic modem.
This translates the digital data into ultrasonic sound waves using an FSK modulation technique in the 48 to 52 kHz region which is then received at the surface with a matching receiver where it is decoded and translated back into the digital data.
A complete off the shelf modem was not available due to the ultra-low power requirements required by the power scavenging supply, so a low power design was implemented taking advantage of the short range and low baud rate required for the project.
The Modem is required to transmit over 100m from the sea bed vertically to the surface, once per day, and transmit around 200 bytes per day.
The communications system has been reviewed and the method going forward has been agreed amongst the project partners. The preferred option is to use a custom built, low power, ultrasonic modem. This is due to the very limited power available to the modem and the short range and low data rate required.
With this in mind, the design of the modem has been completed based upon an off-the-shelf transducer and standard transmitter concepts that have been improved upon to reduce power consumption at the cost of reduced data rate and range.
Further to this, the communications protocol has been defined with data redundancy included to reduce the need to retransmit erroneous packets.
Electronics design and sensor system prototyping
The schematic and PCB design have been divided into two sections, the first for the power and sensor circuits and the second for the ultrasonic modem.
Power and Sensor Schematic Design
The design is broken down into 4 sections:
1. Partial discharge input and protection
2. Partial discharge amplification, noise cancellation and interrupt generation
3. Power supply and storage
4. Processing and environmental sensors
Power and Sensors PCB Design
The PCB has been laid out in a modular fashion, this means that each sub circuit on the board has a distinct area allowing easy access to the different circuits and making the process of debugging easier.
Ultrasonic Modem Schematic Design
The design breaks down into 3 main parts:
1. Transducer Power amplifier. Takes the low current, low voltage signal from the MSP430 and increases it in both current and voltage to drive the transducer. It also has the option to include a transformer to further boost the voltage if needed
2. Receiver gain amplifier Amplifiers the very small signal from the transducer to a level compatible with the FSK demodulator
3. FSK demodulator Takes the received signal from the transducer and turns the FSK modulated signal and transforms it back into serial digital
Ultrasonic Modem PCB Production
The ultrasonic modem has been spread-out in a similar manor to the sensor board. The board has been subdivided by function to allow easy debugging.
4. Transducer Power Amplifier
5. Receiver Gain Amplifier
6. FSK demodulator
Ultrasonic Modem Testing
After discussions with our End user, some additions were suggested, varying in complexity to add:
Motion detection to detect any disturbance caused by trawlers or shipping anchors etc. that could disrupt the position of the connector and as a result possibly reduce the performance of any seals etc. This could be achieved by the addition of accelerometers to the design, these are available in very low power devices and have wake on motion options. The selected accelerometer is the ADXL362. This uses just 270nA in motion activated wakeup mode allowing for a simple integration with virtually no impact on power usage
Temperature monitoring on the cable itself, this would be possible but would require the installation of many sensors within the main body of the connector, each pin would have to be individually monitored as well as the conductors leading to 9 sensors to make it worthwhile. This would be easily integrated into the sensor board design.
Photographs of any bio-fouling on the connector. This would be impractical with the power available to the device and the bandwidth available for transmission. This could be achieved if power is supplied from the surface, but not on the scavenged power available. Otherwise an ROV of sort would be required in much the same way as connectors can be inspected at present.
After discussions with Marine Signals, it was decided to investigate the addition of a real time clock to enable more accurate timing between the surface and connector to allow the surface device to sleep for prolonged periods and conserve power.
A sensor board capable of detecting pressure, humidity and partial discharge has been produced and tested. The board has been shown to run at under 700uA during sleep mode and is capable of communicating with the sensors to check the Pressure, Humidity, temperature and also detect Partial Discharge events. The board has been demonstrated running off a capacitive charge circuit scaled proportionately from the 33kV system down to a 415V industrial connection to demonstrate the ability to run off the scavenged power.
Receiver-based DAQ and processing design and prototyping
The DAQ2 connects to the internet via GPRS modem which can be changed to any internet device for reconfigurable deployment options. The DAQ2 also uploads all the data received from the health monitoring unit to a cloud based server. The web based interface on the DAQ2 displays the results to the system administrator responsible for maintaining the remote devices. The cloud server website provides the interface to the end user displaying the condition of all the different sensors and trends for each unit. The cloud interface also sends out alerts if conditions at any location exceed defined limits. The cloud interface is able to produce standard reports for each sensor detailing the trends on each sensor over time so that the end user can inspect the unit quickly for any signs of deterioration and schedule any required maintenance in advance of a failure.
The DAQ2 system connects to a network to connect to the internet and upload the data, the network can be selected from any number different infrastructure types, either directly to a Network connect, Wi-Fi, Mobile Telephone Network, Satellite etc.
This provides flexibility for the installation allowing the appropriate method to be selected for the environment and location.
The DAQ2 will be configured to listen for the data at a pre-determined time of day which can be altered and is set to coincide, but exceed the time when the health monitoring board transmits the data, this allows the DAQ2 to remain in sleep mode while it is not receiving data to help it conserve power. The DAQ2 is not as power critical as the monitoring hardware on the sea bed.
The DAQ2 is the local surface monitoring equipment. It sits on the surface, either on the WEC/TEC or on a separate buoy, depending on the requirements of the installation, and relays the information from the health monitoring equipment to the server. The DAQ2 has an internet connection that will be defined based on the installation requirements and what is available at that location, and will have a web interface to allow configuration of the system remotely.
The Web Interface starts with a page detailing the software version of the DAQ2, its serial number and the last successful communications with the health monitoring unit.
This provides a single page check on the state of the unit.
The front page of the website for each sensor provides an overview of the received data. This page can be configured to display different sets of data over varying time periods as per the end users preferences. Currently, the pages are in Spanish but translations will be made at the end of the project. The system displays the location of the device for reference, this location is defined within the setting for the sensor and doesn’t represent information from the sensor, if the sensor was moved the settings would have to be updated to reflect the new location.
The DAQ2 provides a flexible surface installation that can be configured for different installations in different areas with differing connectivity options. This allows the system to be easily tailored to the end users requirements and site conditions with minimal impact on the performance of the system.
The web interface provides a comprehensive tool for interrogating the different sensors, investigating alarms, and analysing trends over time. This provides the user with the maximum amount of information to judge the state of the different connectors and plan for any down time ahead of connector failures.
WetMate Technical Solution
Material Selection
As a term, covers more aspects of the design than simply the grade of material used for each component. It will be demonstrated that Material Selection includes a description of each component selected, and why.
The design uses some large bespoke components that will be fabricated and surface treated, and some proprietary components that will come ready for use in this application. All of these components, proprietary and bespoke, will be the materials selected for this project.
This is a subsea application hence the primary consideration is corrosion resistance and seal integrity over the full operational life.
Sub-categories of WetMate design.
The WetMate design is made up two main design areas: Electrical and Mechanical
Mechanical Design
The mechanical design is dominated by the physical motion of moving the “Carousel” a distance of over 2m and making the electrical connection. The motion of this will be courtesy of hydraulic or pneumatic cylinders that receive their services from a “Smart Tool”.
Electrical Design
Considering this project is fundamentally an electrical connector one, the monitoring system for the electrical connector's performance is remarkably simple. The basic premise is the monitoring of the damaging phenomenon known as Partial Discharge. This can cause catastrophic breakdown in the connector. Monitoring of this is by measuring the leakage that is collected by the metal shield surrounding the connector itself. A single wire connects the measurement module to each of these shields. There are three cables but because of the Carousel system, the number of connections is six. Therefore six connecting wires need to be routed through the system.
The non-permanent re-makeable nature of this electrical connector means that these signal cables will need to make & break also. This will be through the use of co-axial SMB connectors.
As with any proprietary component that is made up of multiple parts (such as a cylinder or gearbox) it is not necessary to list the actual material grade used for each individual part as it is the entire assembly itself that forms the ‘material selected’ and so will be treated as an object in itself.
Environmental Conditions for the WetMate connector as defined by Hydro Bond Engineering Ltd in their product specification document No PS010 are:
The cable supplied shall be suitably designed for sealed installation, operation and multiple recovery and deployment, throughout its designed life, based on the following prevailing environmental conditions. The Contractor shall be responsible for ensuring that the final agreed specification is adequate to meet these environmental conditions:
• Maximum water depth: 100 meters
• Air Temperature (Storage): -20ºC to +60ºC
• Sea Temperature: -4ºC to +30ºC
• Typical Tidal current velocity: 3.23 m/s @ 23.27m above seabed (Or approx. 10m below surface)
• Impact force: Drop test 2m
Along the length, the cable will be surface laid direct onto the seabed. Although, some sections of the route may expect movement with sand and large-grain sediment which may result in shallow cable burial or even complete cable exposure on the sea floor. There is also the possibility of some localised bio fouling, mussel beds, rocky / cobble / boulder irregular formations which may occur in some sections along the route. It is difficult however to define bio fouling as depending upon the site of the WetMate connector, different marine environments will have an effect.
The concept of Biofouling is usually used to describe the settlement and growth of the animals and plants on submerged structures including ship’s hulls, piers, piling and oil rigs. However the WetMate connector, modem and cables will also be subjected to Biofouling
The fouling organisms observed in the deep sea are smaller than those observed at shallow depths. During the first 40 meters of depth because there are more light and plankton the Macro fouling is more developed and is more important than in the deep sea. Most algae are photosynthetic and can only survive in these regions having adequate light. However mussels, barnacles, tubeworms, ascidians, and hydrozoans which take their energy from nutrients present in the sea and do not need light and may cause fouling at great depths. Thus, the consequences of increasing depth are usually a modification of the dominant species and a reduction in thickness. At depths below 150 m, the physico-chemical parameters of seawater (nutrients, salinity and temperature) are generally the same in any ocean. Hence, the same organisms are often observed at such depths as long as the bottom is geologically similar.
Geographical distribution:
There are three typically risk zones that are related with the sea water temperature:
Polar zones: <5°C, low fouling risk.
Fouling will occur for a short time period, typically either side of mid-summer.
Temperate zones: 5-20°C, medium fouling risk.
Fouling will occur throughout the year peaking in spring to early summer.
Tropical/sub-tropical zones: >20°C high fouling risk.
Fouling continues throughout the year with a multiplicity of species.
Sensor Anti- Fouling
During the last 20 years, marine monitoring stations have been developed to collect data for calibration of satellite observations and coastal water quality assessment. Most are surface buoys or subsurface moorings, and are now equipped with sophisticated sensing equipment, which is subject to biofouling. The long-term quality of measurements may therefore be questionable due to biofouling issues in the short-term.
The protection of the sensing area of the sensor is a concern that has been addressed during the last decade, and operational solutions are now implemented on commercial equipment used for long-term deployments.
Conclusion
From a materials point of view the most challenging aspect of the design is corrosion resistance from salt water corrosion as a by-product of the long term exposure to sea bed that this machine will experience. Fortunately for this project, this challenge is not a new one for the marine industry and there is a wealth of proven technology and techniques in this area that can be directly transferred to the WetMate project.
Structurally and from a sealing point of view (to protect the electrical elements) there are some challenges; the loads from the pulling of the cable are significant and so place large loads on the structure of the assembly. Similarly the pressure of 10 bar at 100m depth is significant and presents the challenge of creating sufficiently capable seals.
These challenges however, are quantifiable, whether it is a load - or pressure that need to be resisted. As far as materials go that leaves one challenge - that of corrosion, which as mentioned previously is able to draw from a significant wealth of relevant knowledge that supports the content of this report.
Flushing system
The wet-mate connector requirement is for the base assembly to be installed onto the floor of the sea bed and fixed in position for later use when a wet-mateable connection is required to be made.
To protect the base assembly whilst lying dormant on the sea bed, an environmental cap will be fitted over ball valves to prevent significant ingress of sea debris and sea life, which may cause opening and closing problems on the movable ball area of the ball valve during prolonged unprotected exposure to underwater sea environment.
When a connection is ready to be made, it is at this point that the environmental cap is opened with the smart-tool. Obviously, when the cap is lifted and opened sea water and tidal debris can rush into the void area, and it is this area, which is required to be flushed through before the electrical connection can be safely made.
This process is designed to be repeated for approximately 5 mates and demates, and a service lifespan of 10 years.
Design
The design and dimensional geometry for the simulated flushing chamber is the same as the fully designed wet-mate’s full assembly, meaning that sufficient simulation of the flushing can be achieved, albeit with some assumptions being made for the design of the flushing chamber to commence, which are highlighted below.
As there is a need to ‘flush’ the sea water void, there needs to be fresh water fed into the void to flush through to clear and clean the area. It has been proposed by the consortium that hoses can be fed down with the connectable component to enable the flushing and cleaning aspect, and that the hoses can be disconnected easily with the use of a smart tool-pack.
It is proposed that clean water is an allowable method to flush the chamber up to 50m in water depth using the associated hoses, and this is the focus of the flushing chamber technique in this deliverable. Although outside the scope of this project the consortium have proposed that a smart tool-pack would be used to disconnect the hoses, as per the smart tool-pack option required for the upper portion aspects of the wet-mate assembly.
Drying Process
The process will utilise dried compressed air to purge through the chamber to ‘dry’ the region to an acceptable level for the next phase which is to open the large CORT ball valves to commence the electrical connection.
The air being fed from the ship deck, and in the flushing simulation, is dry air to ensure that the air sent to the chamber does not contain any water vapour (as per water vapour in the air in the atmosphere), as this may cause further condensate to form on the chamber walls. Dry air has the ability and capacity to take up the remaining water vapour within the chamber and can be evacuated through the hoses back to deck, thereby drying the chamber.
Methods of Coupling and Uncoupling
The complete connection of the WetMate connector is defined by two separate operations. The first being the physical or mechanical coupling of the WetMate connector halves and the second being the electrical connection and disconnection of the enclosed connector internal elements.
The obvious connection methods using divers and ROV’s were considered and then discarded:
1. The use of divers is very expensive given the support systems required to allow them to decompress safely. In addition the strong tides typical of the WEC and TEC installations mean that dive times are limited to very short windows of slack tide.
2. Larger work class ROV's to aid with deployment but as with divers these typically require a reasonable amount of costly infrastructure and support personnel on the vessel.
3. There are opportunities to use alternate techniques such as down wire transfers in conjunction with much smaller observation class ROV's. These operate with significantly smaller cost and infrastructure overhead. This is our preferred choice
The mechanical connection and disconnection process can be broken down into a number of stages. The “Approach Stage” is the gross translation of a connector half through the ambient surrounding water to the area of the static mating half. “The Mechanical Alignment Stage” and the Final “Alignment and Coupling Stage”. These are described in further detail below.
Approach Stage
The approach taken by the free connector half to the corresponding static connector half is entirely governed by the type of renewable energy appliance. The appliances generally fall into two categories for shallow water applications with unique characteristics as described below.
Wave Energy Converters (WEC)
These typically operate on the surface and are mechanically tethered to a ballasted structure located on the seabed. An array of WEC’s may connect back electrically to a central hub which in turn connects to the main seabed power umbilical. Power generation normally occurs within the surface structure and is transmitted to the seabed umbilical via a dynamic umbilical which may also form the tensile tether. The appliances are generally free to align to the prevailing current and wave direction. The WetMate connector fixed half would typically be sited on the seabed and integrated into the sea bed ballast or hub structure. The appliance side connector would be on the end of the appliance dynamic umbilical or interconnect. WEC’s are typically located in shallow waters and in this application the appliance side connector could be lowered into place via the vessel crane during slack water.
Tidal Energy Converters (TEC)
These typically operate submerged and are the marine equivalent to a wind turbine. Depending on the location and tidal flow conditions they may operate with a fixed orientation or be free to pivot to suit varying tidal flow directions. As with WEC’s they normally feature a fixed ballasted sea bed structure or piling. The appliance would typically dock directly onto the seabed structure and be removable by lifting onto a support vessel for regular maintenance operations. As with WEC’s the static seabed umbilical would terminate at the fixed seabed structure and feature the static half of the WetMate connector. The other half of the connector would be integrated into the appliance structure. A degree of positional compliance may be included in the connector fixing to accommodate the coarse Mechanical Alignment stage. For these applications the connector would be deployed with the appliance typically from a vessel by crane.
Coarse Mechanical Alignment Stage
Once the appliance side connector is within several meters of the fixed half a means of coarse mechanical alignment is used to control the position of the connector mating features as the connector halves come together. Subsea production systems face very similar deployment, location and coupling challenges and for this reason standardised approaches are followed.
The connector halves would each be fixed within a steel superstructure. The fixed side would feature a pair of parallel guide posts either side of the WetMate connector and protrude well in front of it. The appliance side connector superstructure would feature a similarly positioned pair of sleeves and guide cones.
Once satisfied that the appliance connector is positioned roughly above the guide posts it is lowered and an initial element of radial alignment achieved. When lowered further the geometry of the mating posts and sleeves further improve alignment such that at the point where the connector flange halves meet they approach and couple within their own positional tolerance.
For deployments in deeper locations or those where current conditions make alignment of the appliance an issue a down wire approach could be adopted. Using this technique a pair of wires are lowered from the vessel and connected to the top of the guide posts on the seabed structure. A small observation class ROV can be used for this task. Once the downwires are in place then they are tensioned and the appliance side connector runs down these guided to the sea bed posts. When the coupling process is complete the small observation ROV is used to release the guide wires and they are recovered back to the vessel.
Final Mechanical Alignment and Coupling Stage
The final stage of mechanical connection is controlled by features present on the mating halves of the WetMate connectors, the connection is based around a Grayloc type split half coupling. Chamfered lead in features and diameter registers on the mating flanges couple to provide shear restraint and the surrounding split coupling provides tensile load and moment resisting capacity. Several O-Ring seals are retained in dovetail grooves on the flange faces to form a seal between the two halves isolating the connector enclosure from the surrounding ambient sea water.
Conclusion
The original connection concept was using divers and ROV’s. These were considered and then discarded due to costs and the issues of time and strong tidal currents. An alternate concept using down wire transfers in conjunction with much smaller observation class ROV's that operate with significantly smaller cost and infrastructure overhead is proposed.
The complete connection of the WetMate connector is defined by two separate operations. The first being the physical or mechanical coupling of the WetMate connector halves and the second being the electrical connection and disconnection of the enclosed connector internal elements.
Integration of WetMate prototype components
The specific aims of the prototype are to prove that the technologies and concepts generated in previous work packages (WP’s 1 to 3) can be incorporated to create a connector capable of being deployed underwater and providing a sufficiently dry and clean environment for the power carrying elements to be mated to carry the necessary electrical loads.
The prototype has two main elements:
• Connector
• Flushing rig
The connector prototype enables the method of making the electrical connection to be tested and proved and incorporates all the elements, movements and design features required to create an electrical connector that will fit through standard undersea ball valves.
The prototype system aims to mimic the functionality of the carousel and the upper and lower pins to create a working full scale electrical connection. Incorporated into the prototype are the additional elements required to enable the partial discharge monitoring system to be implemented.
All components for the WetMate prototype were manufactured/procured and fully assembled at ISRI. Trials have been carried out on the connector rig to confirm that all hydraulic actuators function as predicted and that each of the moving parts of the prototype move within the required limits and constraints. All aspects of the prototype function as expected and it is ready for installation and high voltage testing of the electrical connector elements.
The flushing rig has been assembled and connected to water and gas supplies to conduct draining, flushing and drying trials. These trials showed that a typical sea water sample containing sand and other bio-fouling common in sea water could be successfully drained, flushed and dried.
A training workshop was held with the SME partners on Thursday 30th July 2015 demonstrating the operation of the carousel and flushing rig.
WetMate Demonstration
In the original proposal it was stated that a wave/wind farm site would be selected during the project to provide the details of the environmental conditions with which to test WetMate. Accelerated environmental testing using computer models will be used to assess wear, damage and deterioration. The models will use the selected site conditions. Mating and de-mating for the full–function system will be performed to ensure reliable sealing, Compatibility with the Tooling range will be assessed in Lab based, mock sea trials. Pressure differentials achieved using the flushing system will be tested to define operating conditions; the mating and de-mating process will be evaluated to analyse the closing and opening of the pressure seal under appropriately specified simulated conditions. We will demonstrate seal integrity and managed water ingress/expulsion for a finite number of mating operations and submerged time in typical sub surface conditions.
It soon became apparent that the original objective was not feasible and this was discussed at the project review meeting in Brussels, September 2014. The prototype that was developed as agreed at the project review meeting has been designed to demonstrate and prove the new ideas that have been generated in the WetMate project and as such is not a prototype connector designed to be utilised underwater due to the prohibitive costs of the parts i.e. ball valves and rental of the ship and rig for testing.
The Environmental Conditions for the WetMate connector has been defined by Hydro Bond Engineering Ltd and reported in previous deliverables
The concept of Biofouling is usually used to describe the settlement and growth of the animals and plants on submerged structures including ship’s hulls, piers, piling and oil rigs. However the WetMate connector, modem and cables will also be subjected to Biofouling
Relation of fouling with depth:
The fouling organisms observed in the deep sea are smaller than those observed at shallow depths. During the first 40 meters of depth because there are more light and plankton the Macro fouling is more developed and is more important than in the deep sea. Most algae are photosynthetic and can only survive in these regions having adequate light. However mussels, barnacles, tubeworms, ascidians, and hydrozoans which take their energy from nutrients present in the sea and do not need light and may cause fouling at great depths. Thus, the consequences of increasing depth are usually a modification of the dominant species and a reduction in thickness. At depths below 150 m, the physico-chemical parameters of seawater (nutrients, salinity and temperature) are generally the same in any ocean. Hence, the same organisms are often observed at such depths as long as the bottom is geologically similar.
Geographical distribution: There are three typically risk zones that are related with the sea water temperature:
• Polar zones: <5°C, low fouling risk. Fouling will occur for a short time period, typically either side of mid-summer.
• Temperate zones: 5-20°C, medium fouling risk. Fouling will occur throughout the year peaking in spring to early summer.
• Tropical/sub-tropical zones: >20°C high fouling risk. Fouling continues throughout the year with a multiplicity of species.
It was agreed that Biofouling needs to be approached from a holistic perspective rather than being focused on just one aspect of the problem and the consortium have agreed at this stage not to target Biofouling too specifically as the product is required to be robust across various international waters at different water temperatures.
During the workshop the carousel ‘jumped’ significantly during its operation thus not allowing a smooth transition during the mating process and the pins and conductor holes did not align well also the electric conductor had not arrived.
Although the SME’s were happy with the workshop a partner asked that the carousel after the modifications were made went through 10 mate/demate cycles to prove it works. To facilitate this the assembly was dismantled to alter the alignment.
When the electrical conductor (1 lead) arrived it was installed onto 1 of the 3-pins. The alignment was re-checked and confirmed; however a full connection was attempted. The connection was successful, except for the upper connection which was short by 10mm. to resolve this a 10mm spacer was manufactured and installed onto the assembly, completing the assembly.
Significant modifications were made prior to electrical testing
The flushing rig was then tested. The rig was filled with a simulated ‘sea water’. Although the rig drained it was extremely slow and it was thought that there was a build-up of sand at the bottom (from previous trials) that was causing the problem. A partner suggested that we reversed the flushing procedure and actually pump in the flushing water at the bottom. The pipes were reversed and the process was carried out a second time and this improved the drainage.
High Voltage Testing
The carousel was dismantled and transferred to the high voltage testing laboratory at DTU.
The laboratory tests conducted were suitable for high voltage test of the connector in dry condition. Utilization of the built-in sensors allowed for condition monitoring in all situations, both in the laboratory and onsite. The occurrence of PD just above nominal voltage means that high voltage withstand tests at slight or high over voltages at this time are not recommended. After modifications in design or mating procedure the connector should be PD free.
The Health Monitoring system
Two sensors were manufactured. The first was capable of linking to the PLAMASI web based software that Marine Signals use. The system allows the monitoring of temperature, pressure and humidity.
A second system was designed suitable for the deep water trials, this sensor was sealed in a waterproof can with eyelets attached to allow the sensor to be lowered in the water. The container was sent to Marine Signals for their trials. A number of deep sea trials took place from a platform and proved that communication was possible from 50M to the surface; however the communication system needs extra work post project.
A small integrated sensor incorporating both of the PCB units was designed and the schematic sent to the partners for future use. The sensor has also been designed to incorporate an accelerometer (to check for impact whilst stationary subsea) and a real time clock to allow for integration of communication from the surface to the health monitoring unit.
Conclusion
The UK leads the Rest of the World in the development of Wave & Tidal Energy. The number of blue chip companies such as Alsthom, Andritz, Atlantis etc. is evident in the financial investment to accelerate the Development & Demonstration of Tidal and Wave sub-system technologies.
When the technology finally matures using this ‘proof of concept project’ as the catalyst then the requirements for array installation is required. To allow this to take place effectively & efficiently a device such as WetMate will be required to be fitted within the infrastructure of the Tidal Array. Hydro Group commitment to develop the WetMate was seen as a critical element of the long term commercialisation of Wave & Tidal array projects. Hydro are now further committed to building a commercial WetMate for installation in a marine energy project over the next 2 years. Maygen’s Inner Sound Project in the Pentland Firth in Scotland is currently under construction and several other projects similar to this are in early stages of development. With a political will to deliver around 20% of the UK’s current electricity needs from Wave & Tidal Stream energy WetMate has a crucial commercial role to “Plug & Play”.
Potential Impact:
The European electricity generation market is consolidating and continues towards a single European market. The EU hopes to generate 20% of its electricity needs from renewable energy sources by 2020. A €30Bn project involving nine north-western European countries will see a 100GW underwater energy ‘super grid’ in the North Sea linked to wind farms, tidal power stations and hydroelectric plants over the next decade. A North Sea grid could link into grids proposed for a much larger German-led plan for renewables called the Desertec Industrial Initiative (DII). This aims to provide 15% of Europe's electricity by 2050 or earlier via power lines stretching across desert and the Mediterranean.
The offshore renewables sector, incorporating wind, wave and tidal energy is central to delivering renewable energy to meet global and European targets. It is now recognised that a step change in the development of offshore renewable energy is essential if we are to move towards a low carbon energy world. The WetMate project will contribute significantly to the above objectives, as well as helping meet the aims of the Commission’s Strategic Energy Technology Plan (SET-plan) for competitive and secure energy, as current cable connector systems for offshore renewables are unable meet the growing demand of higher power distribution voltages.
This new market offers the potential to support a new electricity supply network infrastructure which can allow the incorporation of mass renewable technologies which can eventually replace fossil fuels. Grid requirements of mass scale renewable technologies mean that a new infrastructure is required that can deal with the intermittent supply and varied geographic dispersal of the natural resources relied upon for energy generation. European targets of international trade instigate that each EU member state meets a minimum of 10% electricity interconnection levels, a figure that most member states are not currently achieving. Several models have already been proposed to address this but in reality the massive requirement of infrastructure needed to provide the capacity to meet energy consumption from renewables will likely require an interconnected European electricity system.
Cabling for offshore power generation involves a multitude of connections to be made to each generating device. These cables can be run to shore individually or connected to a subsea hub. A single, higher power cable can then be run to shore for termination into an onshore grid. Given the technical challenges associated with high voltages in the presence of sea water around connection points, the voltage generated by offshore devices has traditionally been limited to 11kV-33kV. According to Scottish Enterprise figures, the cost of building a 500MW wind farm is estimated to be around €1.5Bn 5% of which is normally attributable to connectivity. With over 800 such farms in operation or planned globally, the value of the market opportunity for cabling and associated components is estimated to be in excess of €60Bn by 2020. Although less progressed, the investment in other ocean power sources is also enormous. It is estimated that the worldwide wave resource is 6,000 TWh per year, twice as much as global nuclear production and 700 TWh/year for tidal power. Worldwide the market potential for the wave industry is about US$1 trillion of which about €50Bn will again be spent on connectivity.
The project proposes to create a high-electrical integrity 33kV wet-mateable connector, closed and locked by sea hydrostatic pressure with built in performance sensors communicating to the shore station through an optical fibre link. This connector will be affordable, cheap to operate and provide remote monitoring of power links for smart preventive maintenance.
To aid dissemination of the WetMate project a secure website was created in M3 of the project which gives the public information on the Project Goal, Partners, Project Objective and Press Releases. The website is located at www.wetmate.eu. The website also has a secure partner login facility controlled by individual project participant each having their own unique password.
The member’s portal has additional section for Documents, Dissemination & Exploitation, Contacts and Project news as well as a recent change section on the home page which allows the partners to ‘click’ on the change and be transferred to the document in question.
The documents section is broken down into:
• Meetings
• Contractual documents
• Deliverables
• Meetings
The contacts section has all the key contact details for each partner to enable all partners to have efficient communication.
A dissemination presentation was produced describing the project and this is available on the project website.
A pop up banner was produced for the partners to use at exhibitions and conferences.
15 conferences/exhibitions were attended where the WetMate concept was disseminated.
3 Press Releases were issued one in a global magazine.
1 conference publication was produced.
1 networking event was attended.
List of Websites:
www.wetmate.eu
The project partners in this exciting collaborative project are:
HydroBond Engineering Limited (SME - Coordinator)
Telephone: +44 1224 822996
Website: http://www.hydrogroupplc.com/
Contact Person: Doug Whyte dwhyte@hydrogroup.plc.uk
Nordic Seal AS
Website: www.nordicseal.com
Telephone: +47 33140570
Contact Person: Per Stokkan, ps@nordicseal.com
Fortis Mechanical Design Ltd
Telephone: +44 1229 716689
Website: www.remote-technology.co.uk
Contact Person: Darren Ball, darren.ball@fortis-design.co.uk
Marine Signals
Telephone: +34 (928) 454 953
Website: www.marinesignal.com
Contact Person: paco@marinesignal.com
The UK Intelligent Systems Research Institute Ltd
Telephone: +44 1664 501 50
Website: www.uk-isri.org
Contact Person: David Cartlidge, david.cartlidge@uk-isri.com
Technical University of Denmark
Telephone: +45 45 25 35 15
Website: www.dtu.dk
Contact Person: Joachim Holboell, jh@elektro.dtu.dk
Most European offshore wind farms are currently installed within 20 km of the coast in shallow water depths up to 20m. The next generation will be developed at distances of 40 km in sea depths up to 80m. These new locations present technical challenges for engineering and the possibility of new synergies between all marine renewable energy resources including wave, tide and wind. The WetMate consortium delivered a prototype 33kV hybrid wet-mate connector with a connectivity monitoring system and future-proof features for higher voltage connector technologies.
This will lead to efficient power transmission, reduced installation and maintenance costs and precision remote monitoring that reduces routine maintenance and intervention by divers, benefitting health, safety and affordability.
The operational requirements for the WetMate connector have been quantified. It is concluded that the nominal current carrying capability of the mating construction is to be increased from 500A to 650A at 33kV.
A variety of candidate insulating and conducting materials for use within the WetMate connector were evaluated to determine the electrical properties of the insulators. The conclusion was that to ensure the health of the insulation system, it will be a requirement to include a moisture level monitoring system, to ensure a low content of water in the apparatus during operation.
A new strategy for environmental monitoring and wireless communications has been considered and a health monitoring system has been developed in a very low power form maximising the chances of being able to both scavenge sufficient power from the electric field and as such simplify the installation without impacting on the end users cable, maintaining the pass through ideal of the connector.
A prototype connector has been manufactured to prove it’s mating and demating capabilities and a standalone flushing rig to mimic the design in the final connector has also been designed, built and tested.
Laboratory tests suitable for high voltage test of the connector in dry condition were carried out. The occurrence of PD just above nominal voltage means that high voltage withstand tests at slight or high over voltages at this time are not recommended. After modifications in design or mating procedure the connector should be PD free.
Two different environmental monitoring and wireless communications have been developed and one has been tested with the communication web platform whilst the other has been tested underwater to prove that the communication is possible at depths of 50 metres.
A number of dissemination activities have been completed by the partners and an exploitation plan and agreement formulated has been accepted by the SME partners.
The project partners in this exciting collaborative project are:
Hydro Bond Engineering Ltd
Nordic Seal AS
Fortis Mechanical Design Ltd
Marine Signals
The UK Intelligent Systems Research Institute Ltd
Technical University of Denmark
Project Context and Objectives:
The European electricity generation sector is moving towards a single integrated supply and demand market in which it hopes to generate 20% of electricity needs from renewable energy sources by 2020. Offshore renewables are a key way of achieving this target and the Atlantic Arc (Iceland, Norway, UK, Ireland, France, Spain and Portugal) has some of the most favourable wave and wind resources in the world, representing 150-240TWh/year. Consequently, there is a strong drive to increase off-shore tidal, wave and wind energy activities in the EU.
A €30Bn project involving nine north-western European countries will see a 100GW underwater energy ‘super grid’ in the North Sea linked to wind farms, tidal power stations and hydroelectric plants over the next decade. The Desertec Industrial Initiative aims to provide 15% of Europe's electricity by 2050 or earlier via power lines stretching across desert and the Mediterranean. Coal (28.7%) currently accounts for the largest share of capacity, but a fast growing wind market (7.9%) has recently overtaken the market share of fuel oil (6.9%). By the end of 2008, installed wind capacity had reached 55GW compared to the total installed capacity of 800GW. Investment in the offshore market in 2009 was significant amounting to €1.5 billion. Further investments are expected with the implementation of EU policies favouring offshore production to meet the EWEA 40GW by 2020 and 150GW to meet 2030 targets.
Wind power is currently in the vanguard of the movement towards offshore renewable energy. Today’s offshore farms are mostly installed in relatively shallow water less than 20 km from the coast. However, the next generation of offshore energy farms will be developed at distances around 40 km requiring investment to overcome the problems of operating in depths up to 80m.
The transmission and distribution of electrical energy requires high capacity cabling. This is partly achieved through bigger conductor cross-sections and thus heavier cables, but also higher transmission voltages incur lower energy losses. A saving of just 1% on the electrical energy produced by a power plant of 1GW means transmitting 10MW more to consumers, sufficient to supply > 4000 homes. Increasing the transmission voltage is one way of reducing these losses. Over land, long distance transmission is typically done with overhead lines at voltages of 115kV to 1,200kV at up to 200Hz.
Voltages range from 6kV (coastal) to 145kV (subsea networks). In offshore subsea applications raised transmission voltages are also desirable but their adoption is hindered by the harsh environment and the ability to make reliable connections between generators and cabling infrastructure.
Cabling for offshore power generation involves a multitude of connections to be made to each generating device. These cables can be run to shore individually or connected to a subsea hub. A single, higher power cable can then be run to shore for termination into an onshore grid. Given the technical challenges associated with high voltages in the presence of sea water around connection points, the voltage generated by offshore devices has traditionally been limited to 11kV-33kV. According to Scottish Enterprise figures, the cost of building a 500MW wind farm is estimated to be around €1.5Bn 5% of which is normally attributable to connectivity. With over 800 such farms in operation or planned globally, the value of the market opportunity for cabling and associated components is estimated to be in excess of €60Bn by 2020. Although less progressed, the investment in other ocean power sources is also enormous. It is estimated that the worldwide wave resource is 6,000 TWh per year, twice as much as global nuclear production and 700 TWh/year for tidal power . Worldwide the market potential for the wave industry is about US$1 trillion of which about €50Bn will again be spent on connectivity.
Connecting devices need to be capable of efficiently conducting electrical power as well as allowing disconnection for inspection and maintenance of the connector. There are two categories of such devices:
• Dry-mate. Used for connecting on board ships for subsequent subsea deployment
• Wet-mate. Used primarily for subsea connections and installed by remotely operated vehicles (ROVs) or divers
Dry-mate connections are made above the surface onboard or on land prior to cable laying. Dry-mate splicing is conducted onboard a ship before the cable is deployed to the seabed. Splicing is a time consuming process which relies on the use of a large vessel capable of handling the cables without risk of capsizing, a good weather window and a highly trained workforce. This can mean that the ship has to be on location for up to 3 weeks. Dry-mate connectors rated at 11kV are already manufactured by Hydro (figure left) and the joining operation can be carried out in one day, but a large ship is still required. Splicing is the method currently used for 33kV connections. With day rates for large ships around €100K-€200K, this is very costly.
Subsea (wet-mateable) connectors are desirable: the mechanical connection can be made quickly using subsea remote operated vehicles (ROVs) operating from much smaller ships. Wet-mate connection implemented with ROVs is less sensitive to weather restrictions as heavy cables do not need to be hauled up to the deck of the ship. The costs of wet-mating each generator are therefore greatly reduced and reliable 33kV wet-mate connectors are in increasing demand by the industry. However, there are significant challenges in designing and building such a connector that are the focus of this project.
Low voltage wet-mate connectors (6-11kV) have historically been used in the oil & gas industry to simplify cable handling and allow easy maintenance or replacement. However, their low voltage specification means that they have only low power capacity and are not generally suitable for use in shallower waters. It should be noted that the renewables environment is far more severe in spite of the lower water pressures involved. The connectors are subject to variable power levels (zero to maximum twice per day for tidal), pressure variations, warmer and highly-oxygenated water that promotes corrosion and marine growth, sand and silt accumulation and cable flexing. In addition, products for oil and gas are developed as customised one-off equipment that does not address the mass market. They are prohibitively expensive (10x higher than our solution).
There are major technical challenges that need to be addressed to develop a wet-mate 33kV connector related to voltage breakdowns such as partial discharge (PD) and water treeing which are compounded at higher voltages. PD is usually the result of localised dielectric breakdown of the solid or fluid electrical insulation under high voltage stress. It generally begins at 6kV in voids or cracks or at conductor-dielectric interfaces within a solid insulators, or in bubbles within liquid dielectrics. The phenomenon causes progressive deterioration of insulating materials, ultimately leading to electrical breakdown. The cumulative effect of PD within solid dielectrics is the formation of numerous branching, partially conducting, discharge channels - a process known as treeing. Over time the insulation to earth or between phases is so weakened that it breaks down completely.
There have been a few initiatives conducted by marine engineering companies to develop 33kV wet-mate connectors. Where such work has been undertaken, they are project specific designs and are not flexible enough to serve as technology platforms across sectors. Oil & gas sector products are bespoke solutions and too costly. Some self-monitored solutions exist in development with poor optical connectivity achieved across power connectors due to external links. The commercial market for the renewables sector is generally patchy and products are ad-hoc solutions compared to our purpose designed technology.
This project provided an exciting opportunity to advance the current state-of-the-art in subsea connectors. The fact that there is an increasing number of 33kV-ready subsea cables being laid demonstrates that the market has already recognised the benefits of such a solution. The medium term goal is to increase subsea transmission voltages to 33kV so as to make systems such as subsea hubs and grids serviceable and facilitate flexible demonstrator projects. Long-term there is a clear need for a proven technology that can form a platform for a range of higher voltage wet-mate connectors within the renewables industry.
The project developed a proof of concept solution for a 33kV 3-phase subsea connector that has several highly desirable innovations that will result in reliable operation and reduced offshore energy industry costs. To remove any need for interventional routine maintenance, we propose a connector solution that will monitor its own long-term performance and health by utilising power cables’ integrated optical fibre element to transmit data. A suite of sensors will provide real time data on humidity, internal pressure, and crucially, PD activity within the connector joint (via temperature, noise and trace gas measurements). Our innovations are:
• High electrical integrity 33kV wet-mateable conductivity (10 year MTBF)
• Reliable hydrostatic pressure mating mechanism (mates on first attempt)
• High mechanical long-term stability (>10 years)
• Integrated connector performance sensing of Partial Discharge
• Multiplexed optical performance data / control signal communications
• Internal protected optical connectivity
• Predictive health analysis/fault prognosis system
• Built in design for future higher voltage extension
This connector will confer multiple real world benefits on end users. A pluggable connector rated for higher voltages will enable infrastructure to be easily and relatively cheaply reconfigured or upgraded to optimal operation without the preventive high costs of splicing – development projects will be accelerated by this facility. Integrated remote sensing and monitoring will also eliminate the need for costly routine maintenance and reduce intervention by divers thus offering health, safety and additional financial benefits: cable installers will be able to streamline their existing procedures of employing divers and ROVs without the requirement for large, expensive ships to maintain the infrastructure.
A STRATEGIC objective is to engineer our technology as a platform for future higher voltage rated designs.
The SMART objectives are:
• To research the electrical requirements for the connector
• To gain new knowledge in relation to partial discharge sensing and monitoring
• Understand the requirements for the mechanical aspects of the wet-mate connector
Associated TECHNICAL objectives are:
• The connector design will have a max. external diameter of 600mm, mass of <800kg, corrosion resistance of 25 years, a rated time to failure (MTBF) of 30 years, tilt misalignment tolerance of 2.5°, rotational misalignment tolerance of 5° (using self-correcting alignment guides), drop test rating of 2m, external pressure rating of 2.6MPa (250m water depth), the ability to close via hydrostatic pressure in >15m water depth (0.25Mpa) operating temperature tolerance of -10°C to 32°C, effective re-sealing after 20 mating/de-mating cycles.
• Electrical performance requirements 33kV (up to 36kV), 650A rated to 1500 MWdays. Contact Resistance < 2.5mOhm and insulation resistance >10GOhm. To withstand 40kV for 4 hours and demonstrate a rapid ramp breakdown average of 49kV. Connector must meet the requirements of IEC 60502-2 and RA-SNO-00183.
• The connector electrical integrity sensing and monitoring system must consume <25W, powered from induction coils located within the connector to eliminate the potential for insulation breakdown and short circuit via the sensing hardware. Sensor must be capable of operating at temperatures from -15° to 40°C. Data will be transmitted along the optical communication lines via an interface incorporated into the sensor. A backup battery system will power the hardware for a minimum of 30mins in the event of loss of transmitted cable power. This will provide fault diagnosis to the onshore station in the event of connector failure locally or elsewhere in the system.
• The design concept proposes a 2 stage flushing cycle that will remove any impurities and moisture. The filtered de-ionised flushing cycle will remove impurities and sea water, ensuring that the inner connector cavity is free from contaminants. This flushing cycle must be carried out at whilst the connector is held in position by the ROV. The dry hot gas flushing cycle (>60°C for 90 minutes) will ensure that the electrical components are completely dry before pressure is reduced and the connector is allowed to close.
Project Results:
Electrical Concept Development and Design Criteria
The operational requirements for the WetMate connector were quantified. Critical electrical and mechanical parameters were defined for further developments on the WetMate connector. A fully prepared document on the product specifications was prepared by Hydro Bond Engineering in collaboration with the participants of WP1. It is concluded that the nominal current carrying capability of the mating construction is to be increased from 500A to 650A at 33kV.
A variety of candidate insulating and conducting materials for use within the WetMate connector were evaluated to determine the electrical properties of the insulators. The conclusion was that to ensure the health of the insulation system, it will be a requirement to include a moisture level monitoring system, to ensure a low content of water in the apparatus during operation.
Electric field FEA analysis - According to IEC 60502-2 and IEC 60502-4, typical electrical tests consist of AC-voltage tests, lightning impulse tests, partial discharge (PD) tests and thermal and dynamic short-circuit tests. Usually, PD tests are the most critical when determining the nominal voltage for the proposed connector design. Also, lightning impulse voltage test can reveal weaknesses in the connector design.
Simulation models and initial simulations were performed on provided HRC240 connector design. The geometry provided for the analysis was simplified and preconditioned for electric field distribution calculation, and several assumptions were made due to a lack of information.
Simulation results - Since the analysis simulates the partial discharge test, the electric field strength within the air region was investigated. Breakdown electric field strength in homogenous field distribution inside dry air at 1 bar is ideally around 3 kV/mm. Since the field analysed is not homogenous due to the impurities in the air, a more realistic value would be 2 kV/mm.
But, regarding partial discharges, it is important to consider the conditions in free gas and along surfaces. In all high voltage constructions, you need to distinguish between 2 situations.
a) The applied field and the breakdown field in free gases. In this case, the mentioned peak value of 2 kV/mm breakdown field would apply.
b) The applied field and the breakdown field along the interface (tangential) between solid and gas. In this case, the breakdown field is about half of the value in free gas. Therefore the dimensioning criteria for this case would be under realistic conditions 1 kV/mm peak. In connectors, you will always have interfaces exposed to electrical fields and in general, the tangential field at these interfaces should be minimised.
Tests were conducted and, based on the results it was decided to focus on pd-behaviour of the connector.
The test platform was validated as being able to identify connection issues under dry conditions. Also the connector internal sensors performed correctly, though with lower sensitivity than the laboratory setup made possible.
Regarding testing of the next connector design, the occurrence of pd at slight overvoltage emphasises the necessity of pd-monitoring in wet-matable solutions. Pd inception at voltages 1.05 pu and higher in dry condition, must be considered as not quite sufficient. Design and/or mating process should be optimised aiming at pd free conditions at all relevant overvoltages.
Thereafter the tests should be repeated under wet controlled conditions, including the flushing and drying process. Also recommend are pd-measurements with a functional prototype under real conditions, including pressure and temperature.
Partial discharge detection and environment
Occurrence of partial discharges - Electric discharges that do not fully bridge an electrode is called partial discharge, acronym PD. The magnitude of these usually is small. However, in AC systems, these can cause progressive deterioration of insulation and thus leading to ultimate failure. PD is then essential to detect and locate in HV components. The occurrence of PD can vary, and depending on the insulating material, the safe operating limit determined. PD is classified by four different definitions, explained in the subsections below.
Internal Discharges - Gas filled cavities formed during the extrusion or moulding process of insulating materials have lower permittivity than the solid insulation material which surrounds it. Due to this low permittivity of the gas and depending on the shape of the cavity, an enhancement of the electric field occurs. Due to the switching polarities of the discharge of an AC system, local heating is generated in the cavity, which over time leads to the breakdown of the insulation.
Surface Discharges - In the case of an electric stress component existing parallel to a dielectric surface then surface discharges may occur. This is often the case when sharp edges are a part of the structure, resulting in excessive field enhancement over the insulation surface. These types of discharges apply to bushings, cable ends, etc.
Corona Discharges - Corona discharges occur when sharp edges and protrusions occur in an electric field. These usually occur at the high voltage side; however, corona can also be caused at earth potential where sharp edges exist. Even though large distances can be between the electrode and earth potential, the concentrated field in the corona leads to partial breakdown of the surrounding gas. This partial breakdown of the surrounding gas should be taken into extra consideration when dealing with sulphur hexafluoride gas (SF6), as the degradation product of SF6 is extremely poisonous and aggressive.
Treeing - Treeing forms in a solid insulation medium as a result of internal discharges. After treeing has progressed over time, the stem and larger branches growing outwards become hollow. Due to the sharp form of these hollow spaces in the direction of the field, considerable discharges occur; these discharges are very unstable in nature. When treeing sets in, discharges become increasingly visible, growing rapidly and in an extremely short period can in some cases lead to breakdown within a few seconds.
Methods of Partial discharge detection
Nonelectrical PD detection methods
Gas detection - A very simple method of detection is in the form of gas pressure measurements. This method is most often applied to transformers with impregnated paper insulation. In the case of discharges occurring in the insulation, a gas is produced which is then detected with a Buchholtz relay. Drawbacks of the gas detection method are that the discharge measurement is not quantitative and usually damage has started to occur on the grounds of discharges when the fault is detected.
Acoustic detection - Discharges such as corona and surface discharges can be detected and located using acoustic methods in air and oil insulation. With an ultrasound, narrow bandwidth microphone of 30 to 50 kHz in combination with a parabolic reflector with a directional beam of 10° or a more precise audio tube a discharge can be located. Discharges of only several pC can be detected using this method. However, the amplitude of the discharges cannot be quantified and therefore this technique can only be used as a locator of PD.
Light detection - External discharges can be detected by light detection. This can effectively be achieved by photography, given that a complete shield of ambient light is present. The location of the discharge can be very effectively located using this technique, however it requires the discharge to be in visual range of the optical sensor and a quantitative measurement is not possible.
Electrical PD detection methods
Two main methods of PD detection exist. Using the Classic detection method displays the discharges as short impulses superimposed on a 50Hz time-base. Using the Time resolved detection the true shape of the discharge is displayed on a trigger based time-base. Using these techniques, the discharge impulses are amplified with a bandwidth of around 100-500 kHz.
Different variations of measurement circuits can be used in order to detect discharges:
1) A high voltage source which preferably is free from discharges.
2) The sample to be measured for discharges
3) The impedance Z across which the voltage impulses are caused by the discharge in the sample
4) The coupling capacitance k which allows the passage of the impulses of high frequency. This must be in the same order of magnitude as sample a.
5) Signal amplifier A.
6) Observation unit O, in the form of a crest voltmeter, oscilloscope, pulse sampling device etc.
7)
The classical method of PD detection can be divided into two different subcategories; Straight detection and Balanced detection.
Straight detection - The advantage of the straight detection method is its simplicity and as a result it is widely used for routine tests of standard products. The disadvantage of the straight detection method is that it is not possible to distinguish the sample discharge signals from external disturbances.
Balanced detection - Balanced detection is common in laboratory testing where external disturbances can be controlled in a sufficient manner. Detection can be achieved either by using a basic circuit or with the sample earthed.
It is easy to create a balanced circuit using two samples, preferably of the same insulation material are measured. The preferred setup is by using samples composed of the same material and thus the loss factors are equal over large frequency spectra. Ideally the two samples have the same capacitance, however this is not necessary.
With this configuration the external discharge pulses can be suppressed while still detecting the discharges originating in the samples ‘a and a’. By injecting large discharges between high voltage and earth and adjusting the capacitive and resistive components to minimal response, the bridge is balanced.
With the use of electronic processing, a more practical configuration of the balanced circuit can be constructed with the use of a pulse discriminator.
Pulses occurring on both sides of the bridge are processed in the pulse discriminator. Pulses having the same polarity and arriving at the pulse discriminator at the same time, originate outside the bridge circuit. These common-mode signals can then be rejected, suppressing signals originating outside the bridge. Opposite polarity pulses originating in the samples are accepted and can then be assessed and analysed. The disadvantage of this method is that the rejection ratio is smaller compared to the balanced detector; however this method has the advantage that no balancing is required resulting in fixed impedance values.
By applying the balanced detection method on complicated samples, the discharge location can be assessed. By interrupting the earth screen at several locations, the discharge can be located.
Earthing interruptions can be made where the earth electrodes are made to overlap. However, this method is sensitive to measuring faults in the case of the insulation ring not being perfect, resulting in unwanted discharges occurring in that region. These are preferably made where a semi-conductive layer is placed between the two interrupted ground electrodes. With this configuration, sufficiently high impedance is formed to separate the electrodes, while still being sufficiently low not to interfere with the electric field in the insulation. This longitudinal resistance created between the electrodes should be in the order of a few kΩ.
As quantitative measuring is not possible with non-electrical detection methods, the preferred measuring method is electrical detection.
With the straight detection method, it is not possible to discriminate external signals from signals originating from the measured sample. Thus, the potential risk of external pulses corrupting the measurements makes it impossible to utilize the straight detection method as a practical measuring technique.
The balanced detection method technique is the preferred measuring technique as it is possible to discriminate external signals from signals originating from the measured samples. In addition, this technique allows for the possibility for discharge locating, which is essential as the WetMate connector PD measurements will need to be separated from the discharge signals originating in the joined power cables. This technique however is only possible to apply if the ground armouring of the joined cables can be interrupted from the grounded parts of the WetMate construction.
Design of sensor system and amplifiers
The requirements and schematic and PCB have been produced for the environmental sensing and PD detection. The design consists of environmental sensors to monitor the atmosphere within the connector housing during and after mating. This will provide details regarding any possible leaks or degradation within the connector from pressure, humidity and temperature. Further to the environmental sensing, Partial Discharge sensing has been designed to detect if the connector is starting to fail electrically.
The unit is powered by scavenged power from the electric field around the cables. This placed a high level of importance on designing the health monitoring unit to meet very low power requirements.
Due to the limited amount of power that can be scavenged from the electric field, low power consumption is critical to the design. The processor has been selected for its very low power consumption, all the ancillaries will be connected via power switches to enable the shutting down of all sub systems while they are not in use, this is controlled by the processor which is the only device permanently connected to the power.
PCB’s have been produced to a production standard and have been tested, programmed and evaluated.
Communications and power supply
The original intention was to use the optical fibre within the cable to send information about the state of the connector back to the shore. From a commercial point of view, special, possibly additional features would be required within the shore-bound cable. This was considered to discourage the selection of this connector style due to the requirement not to affect any of the cable interfaces which are owned by the customer. Alternative approaches were evaluated and the best option from this was the use of an ultrasonic modem between the connector housing and the energy convertor on the surface. This solution is ideal due to its low power and lack of interference with existing infrastructure. Should any data be required to be sent to the shore, this can then be integrated into the energy convertor data system.
This report details the design of the communications between the connector on the sea bed and the receiver on the surface as well as the power scavenging technique being employed. The chosen technology for the communications is an ultrasonic modem.
This translates the digital data into ultrasonic sound waves using an FSK modulation technique in the 48 to 52 kHz region which is then received at the surface with a matching receiver where it is decoded and translated back into the digital data.
A complete off the shelf modem was not available due to the ultra-low power requirements required by the power scavenging supply, so a low power design was implemented taking advantage of the short range and low baud rate required for the project.
The Modem is required to transmit over 100m from the sea bed vertically to the surface, once per day, and transmit around 200 bytes per day.
The communications system has been reviewed and the method going forward has been agreed amongst the project partners. The preferred option is to use a custom built, low power, ultrasonic modem. This is due to the very limited power available to the modem and the short range and low data rate required.
With this in mind, the design of the modem has been completed based upon an off-the-shelf transducer and standard transmitter concepts that have been improved upon to reduce power consumption at the cost of reduced data rate and range.
Further to this, the communications protocol has been defined with data redundancy included to reduce the need to retransmit erroneous packets.
Electronics design and sensor system prototyping
The schematic and PCB design have been divided into two sections, the first for the power and sensor circuits and the second for the ultrasonic modem.
Power and Sensor Schematic Design
The design is broken down into 4 sections:
1. Partial discharge input and protection
2. Partial discharge amplification, noise cancellation and interrupt generation
3. Power supply and storage
4. Processing and environmental sensors
Power and Sensors PCB Design
The PCB has been laid out in a modular fashion, this means that each sub circuit on the board has a distinct area allowing easy access to the different circuits and making the process of debugging easier.
Ultrasonic Modem Schematic Design
The design breaks down into 3 main parts:
1. Transducer Power amplifier. Takes the low current, low voltage signal from the MSP430 and increases it in both current and voltage to drive the transducer. It also has the option to include a transformer to further boost the voltage if needed
2. Receiver gain amplifier Amplifiers the very small signal from the transducer to a level compatible with the FSK demodulator
3. FSK demodulator Takes the received signal from the transducer and turns the FSK modulated signal and transforms it back into serial digital
Ultrasonic Modem PCB Production
The ultrasonic modem has been spread-out in a similar manor to the sensor board. The board has been subdivided by function to allow easy debugging.
4. Transducer Power Amplifier
5. Receiver Gain Amplifier
6. FSK demodulator
Ultrasonic Modem Testing
After discussions with our End user, some additions were suggested, varying in complexity to add:
Motion detection to detect any disturbance caused by trawlers or shipping anchors etc. that could disrupt the position of the connector and as a result possibly reduce the performance of any seals etc. This could be achieved by the addition of accelerometers to the design, these are available in very low power devices and have wake on motion options. The selected accelerometer is the ADXL362. This uses just 270nA in motion activated wakeup mode allowing for a simple integration with virtually no impact on power usage
Temperature monitoring on the cable itself, this would be possible but would require the installation of many sensors within the main body of the connector, each pin would have to be individually monitored as well as the conductors leading to 9 sensors to make it worthwhile. This would be easily integrated into the sensor board design.
Photographs of any bio-fouling on the connector. This would be impractical with the power available to the device and the bandwidth available for transmission. This could be achieved if power is supplied from the surface, but not on the scavenged power available. Otherwise an ROV of sort would be required in much the same way as connectors can be inspected at present.
After discussions with Marine Signals, it was decided to investigate the addition of a real time clock to enable more accurate timing between the surface and connector to allow the surface device to sleep for prolonged periods and conserve power.
A sensor board capable of detecting pressure, humidity and partial discharge has been produced and tested. The board has been shown to run at under 700uA during sleep mode and is capable of communicating with the sensors to check the Pressure, Humidity, temperature and also detect Partial Discharge events. The board has been demonstrated running off a capacitive charge circuit scaled proportionately from the 33kV system down to a 415V industrial connection to demonstrate the ability to run off the scavenged power.
Receiver-based DAQ and processing design and prototyping
The DAQ2 connects to the internet via GPRS modem which can be changed to any internet device for reconfigurable deployment options. The DAQ2 also uploads all the data received from the health monitoring unit to a cloud based server. The web based interface on the DAQ2 displays the results to the system administrator responsible for maintaining the remote devices. The cloud server website provides the interface to the end user displaying the condition of all the different sensors and trends for each unit. The cloud interface also sends out alerts if conditions at any location exceed defined limits. The cloud interface is able to produce standard reports for each sensor detailing the trends on each sensor over time so that the end user can inspect the unit quickly for any signs of deterioration and schedule any required maintenance in advance of a failure.
The DAQ2 system connects to a network to connect to the internet and upload the data, the network can be selected from any number different infrastructure types, either directly to a Network connect, Wi-Fi, Mobile Telephone Network, Satellite etc.
This provides flexibility for the installation allowing the appropriate method to be selected for the environment and location.
The DAQ2 will be configured to listen for the data at a pre-determined time of day which can be altered and is set to coincide, but exceed the time when the health monitoring board transmits the data, this allows the DAQ2 to remain in sleep mode while it is not receiving data to help it conserve power. The DAQ2 is not as power critical as the monitoring hardware on the sea bed.
The DAQ2 is the local surface monitoring equipment. It sits on the surface, either on the WEC/TEC or on a separate buoy, depending on the requirements of the installation, and relays the information from the health monitoring equipment to the server. The DAQ2 has an internet connection that will be defined based on the installation requirements and what is available at that location, and will have a web interface to allow configuration of the system remotely.
The Web Interface starts with a page detailing the software version of the DAQ2, its serial number and the last successful communications with the health monitoring unit.
This provides a single page check on the state of the unit.
The front page of the website for each sensor provides an overview of the received data. This page can be configured to display different sets of data over varying time periods as per the end users preferences. Currently, the pages are in Spanish but translations will be made at the end of the project. The system displays the location of the device for reference, this location is defined within the setting for the sensor and doesn’t represent information from the sensor, if the sensor was moved the settings would have to be updated to reflect the new location.
The DAQ2 provides a flexible surface installation that can be configured for different installations in different areas with differing connectivity options. This allows the system to be easily tailored to the end users requirements and site conditions with minimal impact on the performance of the system.
The web interface provides a comprehensive tool for interrogating the different sensors, investigating alarms, and analysing trends over time. This provides the user with the maximum amount of information to judge the state of the different connectors and plan for any down time ahead of connector failures.
WetMate Technical Solution
Material Selection
As a term, covers more aspects of the design than simply the grade of material used for each component. It will be demonstrated that Material Selection includes a description of each component selected, and why.
The design uses some large bespoke components that will be fabricated and surface treated, and some proprietary components that will come ready for use in this application. All of these components, proprietary and bespoke, will be the materials selected for this project.
This is a subsea application hence the primary consideration is corrosion resistance and seal integrity over the full operational life.
Sub-categories of WetMate design.
The WetMate design is made up two main design areas: Electrical and Mechanical
Mechanical Design
The mechanical design is dominated by the physical motion of moving the “Carousel” a distance of over 2m and making the electrical connection. The motion of this will be courtesy of hydraulic or pneumatic cylinders that receive their services from a “Smart Tool”.
Electrical Design
Considering this project is fundamentally an electrical connector one, the monitoring system for the electrical connector's performance is remarkably simple. The basic premise is the monitoring of the damaging phenomenon known as Partial Discharge. This can cause catastrophic breakdown in the connector. Monitoring of this is by measuring the leakage that is collected by the metal shield surrounding the connector itself. A single wire connects the measurement module to each of these shields. There are three cables but because of the Carousel system, the number of connections is six. Therefore six connecting wires need to be routed through the system.
The non-permanent re-makeable nature of this electrical connector means that these signal cables will need to make & break also. This will be through the use of co-axial SMB connectors.
As with any proprietary component that is made up of multiple parts (such as a cylinder or gearbox) it is not necessary to list the actual material grade used for each individual part as it is the entire assembly itself that forms the ‘material selected’ and so will be treated as an object in itself.
Environmental Conditions for the WetMate connector as defined by Hydro Bond Engineering Ltd in their product specification document No PS010 are:
The cable supplied shall be suitably designed for sealed installation, operation and multiple recovery and deployment, throughout its designed life, based on the following prevailing environmental conditions. The Contractor shall be responsible for ensuring that the final agreed specification is adequate to meet these environmental conditions:
• Maximum water depth: 100 meters
• Air Temperature (Storage): -20ºC to +60ºC
• Sea Temperature: -4ºC to +30ºC
• Typical Tidal current velocity: 3.23 m/s @ 23.27m above seabed (Or approx. 10m below surface)
• Impact force: Drop test 2m
Along the length, the cable will be surface laid direct onto the seabed. Although, some sections of the route may expect movement with sand and large-grain sediment which may result in shallow cable burial or even complete cable exposure on the sea floor. There is also the possibility of some localised bio fouling, mussel beds, rocky / cobble / boulder irregular formations which may occur in some sections along the route. It is difficult however to define bio fouling as depending upon the site of the WetMate connector, different marine environments will have an effect.
The concept of Biofouling is usually used to describe the settlement and growth of the animals and plants on submerged structures including ship’s hulls, piers, piling and oil rigs. However the WetMate connector, modem and cables will also be subjected to Biofouling
The fouling organisms observed in the deep sea are smaller than those observed at shallow depths. During the first 40 meters of depth because there are more light and plankton the Macro fouling is more developed and is more important than in the deep sea. Most algae are photosynthetic and can only survive in these regions having adequate light. However mussels, barnacles, tubeworms, ascidians, and hydrozoans which take their energy from nutrients present in the sea and do not need light and may cause fouling at great depths. Thus, the consequences of increasing depth are usually a modification of the dominant species and a reduction in thickness. At depths below 150 m, the physico-chemical parameters of seawater (nutrients, salinity and temperature) are generally the same in any ocean. Hence, the same organisms are often observed at such depths as long as the bottom is geologically similar.
Geographical distribution:
There are three typically risk zones that are related with the sea water temperature:
Polar zones: <5°C, low fouling risk.
Fouling will occur for a short time period, typically either side of mid-summer.
Temperate zones: 5-20°C, medium fouling risk.
Fouling will occur throughout the year peaking in spring to early summer.
Tropical/sub-tropical zones: >20°C high fouling risk.
Fouling continues throughout the year with a multiplicity of species.
Sensor Anti- Fouling
During the last 20 years, marine monitoring stations have been developed to collect data for calibration of satellite observations and coastal water quality assessment. Most are surface buoys or subsurface moorings, and are now equipped with sophisticated sensing equipment, which is subject to biofouling. The long-term quality of measurements may therefore be questionable due to biofouling issues in the short-term.
The protection of the sensing area of the sensor is a concern that has been addressed during the last decade, and operational solutions are now implemented on commercial equipment used for long-term deployments.
Conclusion
From a materials point of view the most challenging aspect of the design is corrosion resistance from salt water corrosion as a by-product of the long term exposure to sea bed that this machine will experience. Fortunately for this project, this challenge is not a new one for the marine industry and there is a wealth of proven technology and techniques in this area that can be directly transferred to the WetMate project.
Structurally and from a sealing point of view (to protect the electrical elements) there are some challenges; the loads from the pulling of the cable are significant and so place large loads on the structure of the assembly. Similarly the pressure of 10 bar at 100m depth is significant and presents the challenge of creating sufficiently capable seals.
These challenges however, are quantifiable, whether it is a load - or pressure that need to be resisted. As far as materials go that leaves one challenge - that of corrosion, which as mentioned previously is able to draw from a significant wealth of relevant knowledge that supports the content of this report.
Flushing system
The wet-mate connector requirement is for the base assembly to be installed onto the floor of the sea bed and fixed in position for later use when a wet-mateable connection is required to be made.
To protect the base assembly whilst lying dormant on the sea bed, an environmental cap will be fitted over ball valves to prevent significant ingress of sea debris and sea life, which may cause opening and closing problems on the movable ball area of the ball valve during prolonged unprotected exposure to underwater sea environment.
When a connection is ready to be made, it is at this point that the environmental cap is opened with the smart-tool. Obviously, when the cap is lifted and opened sea water and tidal debris can rush into the void area, and it is this area, which is required to be flushed through before the electrical connection can be safely made.
This process is designed to be repeated for approximately 5 mates and demates, and a service lifespan of 10 years.
Design
The design and dimensional geometry for the simulated flushing chamber is the same as the fully designed wet-mate’s full assembly, meaning that sufficient simulation of the flushing can be achieved, albeit with some assumptions being made for the design of the flushing chamber to commence, which are highlighted below.
As there is a need to ‘flush’ the sea water void, there needs to be fresh water fed into the void to flush through to clear and clean the area. It has been proposed by the consortium that hoses can be fed down with the connectable component to enable the flushing and cleaning aspect, and that the hoses can be disconnected easily with the use of a smart tool-pack.
It is proposed that clean water is an allowable method to flush the chamber up to 50m in water depth using the associated hoses, and this is the focus of the flushing chamber technique in this deliverable. Although outside the scope of this project the consortium have proposed that a smart tool-pack would be used to disconnect the hoses, as per the smart tool-pack option required for the upper portion aspects of the wet-mate assembly.
Drying Process
The process will utilise dried compressed air to purge through the chamber to ‘dry’ the region to an acceptable level for the next phase which is to open the large CORT ball valves to commence the electrical connection.
The air being fed from the ship deck, and in the flushing simulation, is dry air to ensure that the air sent to the chamber does not contain any water vapour (as per water vapour in the air in the atmosphere), as this may cause further condensate to form on the chamber walls. Dry air has the ability and capacity to take up the remaining water vapour within the chamber and can be evacuated through the hoses back to deck, thereby drying the chamber.
Methods of Coupling and Uncoupling
The complete connection of the WetMate connector is defined by two separate operations. The first being the physical or mechanical coupling of the WetMate connector halves and the second being the electrical connection and disconnection of the enclosed connector internal elements.
The obvious connection methods using divers and ROV’s were considered and then discarded:
1. The use of divers is very expensive given the support systems required to allow them to decompress safely. In addition the strong tides typical of the WEC and TEC installations mean that dive times are limited to very short windows of slack tide.
2. Larger work class ROV's to aid with deployment but as with divers these typically require a reasonable amount of costly infrastructure and support personnel on the vessel.
3. There are opportunities to use alternate techniques such as down wire transfers in conjunction with much smaller observation class ROV's. These operate with significantly smaller cost and infrastructure overhead. This is our preferred choice
The mechanical connection and disconnection process can be broken down into a number of stages. The “Approach Stage” is the gross translation of a connector half through the ambient surrounding water to the area of the static mating half. “The Mechanical Alignment Stage” and the Final “Alignment and Coupling Stage”. These are described in further detail below.
Approach Stage
The approach taken by the free connector half to the corresponding static connector half is entirely governed by the type of renewable energy appliance. The appliances generally fall into two categories for shallow water applications with unique characteristics as described below.
Wave Energy Converters (WEC)
These typically operate on the surface and are mechanically tethered to a ballasted structure located on the seabed. An array of WEC’s may connect back electrically to a central hub which in turn connects to the main seabed power umbilical. Power generation normally occurs within the surface structure and is transmitted to the seabed umbilical via a dynamic umbilical which may also form the tensile tether. The appliances are generally free to align to the prevailing current and wave direction. The WetMate connector fixed half would typically be sited on the seabed and integrated into the sea bed ballast or hub structure. The appliance side connector would be on the end of the appliance dynamic umbilical or interconnect. WEC’s are typically located in shallow waters and in this application the appliance side connector could be lowered into place via the vessel crane during slack water.
Tidal Energy Converters (TEC)
These typically operate submerged and are the marine equivalent to a wind turbine. Depending on the location and tidal flow conditions they may operate with a fixed orientation or be free to pivot to suit varying tidal flow directions. As with WEC’s they normally feature a fixed ballasted sea bed structure or piling. The appliance would typically dock directly onto the seabed structure and be removable by lifting onto a support vessel for regular maintenance operations. As with WEC’s the static seabed umbilical would terminate at the fixed seabed structure and feature the static half of the WetMate connector. The other half of the connector would be integrated into the appliance structure. A degree of positional compliance may be included in the connector fixing to accommodate the coarse Mechanical Alignment stage. For these applications the connector would be deployed with the appliance typically from a vessel by crane.
Coarse Mechanical Alignment Stage
Once the appliance side connector is within several meters of the fixed half a means of coarse mechanical alignment is used to control the position of the connector mating features as the connector halves come together. Subsea production systems face very similar deployment, location and coupling challenges and for this reason standardised approaches are followed.
The connector halves would each be fixed within a steel superstructure. The fixed side would feature a pair of parallel guide posts either side of the WetMate connector and protrude well in front of it. The appliance side connector superstructure would feature a similarly positioned pair of sleeves and guide cones.
Once satisfied that the appliance connector is positioned roughly above the guide posts it is lowered and an initial element of radial alignment achieved. When lowered further the geometry of the mating posts and sleeves further improve alignment such that at the point where the connector flange halves meet they approach and couple within their own positional tolerance.
For deployments in deeper locations or those where current conditions make alignment of the appliance an issue a down wire approach could be adopted. Using this technique a pair of wires are lowered from the vessel and connected to the top of the guide posts on the seabed structure. A small observation class ROV can be used for this task. Once the downwires are in place then they are tensioned and the appliance side connector runs down these guided to the sea bed posts. When the coupling process is complete the small observation ROV is used to release the guide wires and they are recovered back to the vessel.
Final Mechanical Alignment and Coupling Stage
The final stage of mechanical connection is controlled by features present on the mating halves of the WetMate connectors, the connection is based around a Grayloc type split half coupling. Chamfered lead in features and diameter registers on the mating flanges couple to provide shear restraint and the surrounding split coupling provides tensile load and moment resisting capacity. Several O-Ring seals are retained in dovetail grooves on the flange faces to form a seal between the two halves isolating the connector enclosure from the surrounding ambient sea water.
Conclusion
The original connection concept was using divers and ROV’s. These were considered and then discarded due to costs and the issues of time and strong tidal currents. An alternate concept using down wire transfers in conjunction with much smaller observation class ROV's that operate with significantly smaller cost and infrastructure overhead is proposed.
The complete connection of the WetMate connector is defined by two separate operations. The first being the physical or mechanical coupling of the WetMate connector halves and the second being the electrical connection and disconnection of the enclosed connector internal elements.
Integration of WetMate prototype components
The specific aims of the prototype are to prove that the technologies and concepts generated in previous work packages (WP’s 1 to 3) can be incorporated to create a connector capable of being deployed underwater and providing a sufficiently dry and clean environment for the power carrying elements to be mated to carry the necessary electrical loads.
The prototype has two main elements:
• Connector
• Flushing rig
The connector prototype enables the method of making the electrical connection to be tested and proved and incorporates all the elements, movements and design features required to create an electrical connector that will fit through standard undersea ball valves.
The prototype system aims to mimic the functionality of the carousel and the upper and lower pins to create a working full scale electrical connection. Incorporated into the prototype are the additional elements required to enable the partial discharge monitoring system to be implemented.
All components for the WetMate prototype were manufactured/procured and fully assembled at ISRI. Trials have been carried out on the connector rig to confirm that all hydraulic actuators function as predicted and that each of the moving parts of the prototype move within the required limits and constraints. All aspects of the prototype function as expected and it is ready for installation and high voltage testing of the electrical connector elements.
The flushing rig has been assembled and connected to water and gas supplies to conduct draining, flushing and drying trials. These trials showed that a typical sea water sample containing sand and other bio-fouling common in sea water could be successfully drained, flushed and dried.
A training workshop was held with the SME partners on Thursday 30th July 2015 demonstrating the operation of the carousel and flushing rig.
WetMate Demonstration
In the original proposal it was stated that a wave/wind farm site would be selected during the project to provide the details of the environmental conditions with which to test WetMate. Accelerated environmental testing using computer models will be used to assess wear, damage and deterioration. The models will use the selected site conditions. Mating and de-mating for the full–function system will be performed to ensure reliable sealing, Compatibility with the Tooling range will be assessed in Lab based, mock sea trials. Pressure differentials achieved using the flushing system will be tested to define operating conditions; the mating and de-mating process will be evaluated to analyse the closing and opening of the pressure seal under appropriately specified simulated conditions. We will demonstrate seal integrity and managed water ingress/expulsion for a finite number of mating operations and submerged time in typical sub surface conditions.
It soon became apparent that the original objective was not feasible and this was discussed at the project review meeting in Brussels, September 2014. The prototype that was developed as agreed at the project review meeting has been designed to demonstrate and prove the new ideas that have been generated in the WetMate project and as such is not a prototype connector designed to be utilised underwater due to the prohibitive costs of the parts i.e. ball valves and rental of the ship and rig for testing.
The Environmental Conditions for the WetMate connector has been defined by Hydro Bond Engineering Ltd and reported in previous deliverables
The concept of Biofouling is usually used to describe the settlement and growth of the animals and plants on submerged structures including ship’s hulls, piers, piling and oil rigs. However the WetMate connector, modem and cables will also be subjected to Biofouling
Relation of fouling with depth:
The fouling organisms observed in the deep sea are smaller than those observed at shallow depths. During the first 40 meters of depth because there are more light and plankton the Macro fouling is more developed and is more important than in the deep sea. Most algae are photosynthetic and can only survive in these regions having adequate light. However mussels, barnacles, tubeworms, ascidians, and hydrozoans which take their energy from nutrients present in the sea and do not need light and may cause fouling at great depths. Thus, the consequences of increasing depth are usually a modification of the dominant species and a reduction in thickness. At depths below 150 m, the physico-chemical parameters of seawater (nutrients, salinity and temperature) are generally the same in any ocean. Hence, the same organisms are often observed at such depths as long as the bottom is geologically similar.
Geographical distribution: There are three typically risk zones that are related with the sea water temperature:
• Polar zones: <5°C, low fouling risk. Fouling will occur for a short time period, typically either side of mid-summer.
• Temperate zones: 5-20°C, medium fouling risk. Fouling will occur throughout the year peaking in spring to early summer.
• Tropical/sub-tropical zones: >20°C high fouling risk. Fouling continues throughout the year with a multiplicity of species.
It was agreed that Biofouling needs to be approached from a holistic perspective rather than being focused on just one aspect of the problem and the consortium have agreed at this stage not to target Biofouling too specifically as the product is required to be robust across various international waters at different water temperatures.
During the workshop the carousel ‘jumped’ significantly during its operation thus not allowing a smooth transition during the mating process and the pins and conductor holes did not align well also the electric conductor had not arrived.
Although the SME’s were happy with the workshop a partner asked that the carousel after the modifications were made went through 10 mate/demate cycles to prove it works. To facilitate this the assembly was dismantled to alter the alignment.
When the electrical conductor (1 lead) arrived it was installed onto 1 of the 3-pins. The alignment was re-checked and confirmed; however a full connection was attempted. The connection was successful, except for the upper connection which was short by 10mm. to resolve this a 10mm spacer was manufactured and installed onto the assembly, completing the assembly.
Significant modifications were made prior to electrical testing
The flushing rig was then tested. The rig was filled with a simulated ‘sea water’. Although the rig drained it was extremely slow and it was thought that there was a build-up of sand at the bottom (from previous trials) that was causing the problem. A partner suggested that we reversed the flushing procedure and actually pump in the flushing water at the bottom. The pipes were reversed and the process was carried out a second time and this improved the drainage.
High Voltage Testing
The carousel was dismantled and transferred to the high voltage testing laboratory at DTU.
The laboratory tests conducted were suitable for high voltage test of the connector in dry condition. Utilization of the built-in sensors allowed for condition monitoring in all situations, both in the laboratory and onsite. The occurrence of PD just above nominal voltage means that high voltage withstand tests at slight or high over voltages at this time are not recommended. After modifications in design or mating procedure the connector should be PD free.
The Health Monitoring system
Two sensors were manufactured. The first was capable of linking to the PLAMASI web based software that Marine Signals use. The system allows the monitoring of temperature, pressure and humidity.
A second system was designed suitable for the deep water trials, this sensor was sealed in a waterproof can with eyelets attached to allow the sensor to be lowered in the water. The container was sent to Marine Signals for their trials. A number of deep sea trials took place from a platform and proved that communication was possible from 50M to the surface; however the communication system needs extra work post project.
A small integrated sensor incorporating both of the PCB units was designed and the schematic sent to the partners for future use. The sensor has also been designed to incorporate an accelerometer (to check for impact whilst stationary subsea) and a real time clock to allow for integration of communication from the surface to the health monitoring unit.
Conclusion
The UK leads the Rest of the World in the development of Wave & Tidal Energy. The number of blue chip companies such as Alsthom, Andritz, Atlantis etc. is evident in the financial investment to accelerate the Development & Demonstration of Tidal and Wave sub-system technologies.
When the technology finally matures using this ‘proof of concept project’ as the catalyst then the requirements for array installation is required. To allow this to take place effectively & efficiently a device such as WetMate will be required to be fitted within the infrastructure of the Tidal Array. Hydro Group commitment to develop the WetMate was seen as a critical element of the long term commercialisation of Wave & Tidal array projects. Hydro are now further committed to building a commercial WetMate for installation in a marine energy project over the next 2 years. Maygen’s Inner Sound Project in the Pentland Firth in Scotland is currently under construction and several other projects similar to this are in early stages of development. With a political will to deliver around 20% of the UK’s current electricity needs from Wave & Tidal Stream energy WetMate has a crucial commercial role to “Plug & Play”.
Potential Impact:
The European electricity generation market is consolidating and continues towards a single European market. The EU hopes to generate 20% of its electricity needs from renewable energy sources by 2020. A €30Bn project involving nine north-western European countries will see a 100GW underwater energy ‘super grid’ in the North Sea linked to wind farms, tidal power stations and hydroelectric plants over the next decade. A North Sea grid could link into grids proposed for a much larger German-led plan for renewables called the Desertec Industrial Initiative (DII). This aims to provide 15% of Europe's electricity by 2050 or earlier via power lines stretching across desert and the Mediterranean.
The offshore renewables sector, incorporating wind, wave and tidal energy is central to delivering renewable energy to meet global and European targets. It is now recognised that a step change in the development of offshore renewable energy is essential if we are to move towards a low carbon energy world. The WetMate project will contribute significantly to the above objectives, as well as helping meet the aims of the Commission’s Strategic Energy Technology Plan (SET-plan) for competitive and secure energy, as current cable connector systems for offshore renewables are unable meet the growing demand of higher power distribution voltages.
This new market offers the potential to support a new electricity supply network infrastructure which can allow the incorporation of mass renewable technologies which can eventually replace fossil fuels. Grid requirements of mass scale renewable technologies mean that a new infrastructure is required that can deal with the intermittent supply and varied geographic dispersal of the natural resources relied upon for energy generation. European targets of international trade instigate that each EU member state meets a minimum of 10% electricity interconnection levels, a figure that most member states are not currently achieving. Several models have already been proposed to address this but in reality the massive requirement of infrastructure needed to provide the capacity to meet energy consumption from renewables will likely require an interconnected European electricity system.
Cabling for offshore power generation involves a multitude of connections to be made to each generating device. These cables can be run to shore individually or connected to a subsea hub. A single, higher power cable can then be run to shore for termination into an onshore grid. Given the technical challenges associated with high voltages in the presence of sea water around connection points, the voltage generated by offshore devices has traditionally been limited to 11kV-33kV. According to Scottish Enterprise figures, the cost of building a 500MW wind farm is estimated to be around €1.5Bn 5% of which is normally attributable to connectivity. With over 800 such farms in operation or planned globally, the value of the market opportunity for cabling and associated components is estimated to be in excess of €60Bn by 2020. Although less progressed, the investment in other ocean power sources is also enormous. It is estimated that the worldwide wave resource is 6,000 TWh per year, twice as much as global nuclear production and 700 TWh/year for tidal power. Worldwide the market potential for the wave industry is about US$1 trillion of which about €50Bn will again be spent on connectivity.
The project proposes to create a high-electrical integrity 33kV wet-mateable connector, closed and locked by sea hydrostatic pressure with built in performance sensors communicating to the shore station through an optical fibre link. This connector will be affordable, cheap to operate and provide remote monitoring of power links for smart preventive maintenance.
To aid dissemination of the WetMate project a secure website was created in M3 of the project which gives the public information on the Project Goal, Partners, Project Objective and Press Releases. The website is located at www.wetmate.eu. The website also has a secure partner login facility controlled by individual project participant each having their own unique password.
The member’s portal has additional section for Documents, Dissemination & Exploitation, Contacts and Project news as well as a recent change section on the home page which allows the partners to ‘click’ on the change and be transferred to the document in question.
The documents section is broken down into:
• Meetings
• Contractual documents
• Deliverables
• Meetings
The contacts section has all the key contact details for each partner to enable all partners to have efficient communication.
A dissemination presentation was produced describing the project and this is available on the project website.
A pop up banner was produced for the partners to use at exhibitions and conferences.
15 conferences/exhibitions were attended where the WetMate concept was disseminated.
3 Press Releases were issued one in a global magazine.
1 conference publication was produced.
1 networking event was attended.
List of Websites:
www.wetmate.eu
The project partners in this exciting collaborative project are:
HydroBond Engineering Limited (SME - Coordinator)
Telephone: +44 1224 822996
Website: http://www.hydrogroupplc.com/
Contact Person: Doug Whyte dwhyte@hydrogroup.plc.uk
Nordic Seal AS
Website: www.nordicseal.com
Telephone: +47 33140570
Contact Person: Per Stokkan, ps@nordicseal.com
Fortis Mechanical Design Ltd
Telephone: +44 1229 716689
Website: www.remote-technology.co.uk
Contact Person: Darren Ball, darren.ball@fortis-design.co.uk
Marine Signals
Telephone: +34 (928) 454 953
Website: www.marinesignal.com
Contact Person: paco@marinesignal.com
The UK Intelligent Systems Research Institute Ltd
Telephone: +44 1664 501 50
Website: www.uk-isri.org
Contact Person: David Cartlidge, david.cartlidge@uk-isri.com
Technical University of Denmark
Telephone: +45 45 25 35 15
Website: www.dtu.dk
Contact Person: Joachim Holboell, jh@elektro.dtu.dk
