Looking more closely at offshore wind turbines
The estimated costs for the operation of offshore wind farms located at remote sites under harsh conditions are significantly increased by unexpected failures leading to corrective maintenance work. A reduction in the number of these unexpected failures could be achieved if adequate condition monitoring (CM) techniques were applied, both for early failure detection and fault tolerance control. Experience with CM techniques in offshore wind farms was limited before the launch of the CONMOW project and showed the numerous difficulties in ensuring their successful application. Moreover, little information was available on operation conditions as wind turbine designs have changed rapidly over previous years and larger differences exist between different wind farms. Researchers at the Prüftechnik Dieter Busch Condition Monitoring Gmbh & Co Kg thus focused on the integration of CM systems into the Supervisory control and data acquisition (SCADA) systems. Valuable information such as temperature, pressure and status signals could then be used without the need of a clear alarm from the SCADA system. A vibration monitoring system, equipped with acceleration sensors was installed for this purpose at multiple turbines within the test facilities of the Energy Research Centre of the Netherlands. Prüftechnik VIBROWEB XP® collected operation data as well as load measurements through dedicated web interfaces for further analysis and algorithm development. On the other hand, Prüftechnik VIBNODE® systems that use displacement sensors were installed at the low speed section of the drivetrain and were proven to be superior to vibration sensors. Analysing electrical power measurements could trace increased vibration levels due to misalignment of the generator shaft which indicated mechanical abnormalities or even premature faults. Continuously measuring the vibration behaviour and performing preliminary evaluations over the whole range of operation conditions resulted in reduced amounts of data for later offline analysis in the diagnostic centre. To facilitate the generation of reports and access for non-specialists to these reports, the Prüftechnik reporting tool OMNITREND® was further developed.
