MRO Magazine

Vibration monitoring effective on wind turbine

This case study is a concrete example of the benefit of a vibration monitoring system with remote access on an isolated machine. A wind turbine is an excellent example of such an isolated machine, wit...


November 1, 2010
By Fr襩ric Champavier

This case study is a concrete example of the benefit of a vibration monitoring system with remote access on an isolated machine. A wind turbine is an excellent example of such an isolated machine, with difficult access as well.

The equipment is a wind turbine with a rated power of 600 kW that was commissioned in 2000 on a wind farm near Narbonne, France. It is a Stall Control type of machine, using an asynchronous generator with a double winding, running at two fixed speeds, 1,000 rpm and 1,500 rpm, depending on the wind speed.

Since 2006, this machine has been equipped with a OneProd Wind System, a continuous vibration monitoring system. The measurements are remotely processed by a local service provider that specializes in the monitoring of rotating machines, with the assistance, when required, of the system provider, 01dB-Metravib.

On April 21, 2009, after an alarm was issued by the instrumentation on the generator, the operator of the wind farm requested the results of the analyses of the latest vibration measurements from the service provider. It also requested a diagnosis of the problem, along with recommendations for maintenance actions.

In parallel, the operator also consulted the subcontractor in charge of the maintenance of the machines, who recommended replacing the bearings of the generator.

On April 22, the service provider and 01dB-Metravib sent the conclusions of their analyses to the operator, along with their diagnosis hypotheses. The study of the most recent vibration signals collected on the generator, as well as the analysis of their time history, showed a few problems with the equipment, including:

• the existence of a very marked periodic shock at the rotation frequency of the generator (1,500 rpm) on the last measurements collected at high speed on the bearing located opposite the coupling

• progressive occurrence of shocks throughout the month of March 2009, and development of these shocks during the month of April 2009

• a strong and concomitant increase of the Kurtosis parameter collected in March and April 2009

• the existence of a similar but less intense phenomenon when the turbine was operating at slow speed (1,000 rpm)

• a notable increase of the vibration components corresponding to the notch frequencies of the generator, which are electromagnetic vibrations generated by the presence of notches on the rotor, these notches hosting the windings or bars that make up the rotor electric circuit.

The conclusions and diagnosis hypotheses were as follows:

• No fault -scaling, wear or defective lubrication -was identified on the bearings

• Possible -but not likely -air gap change (rotor/stator distance) resulting from radial backlash

• Possible temperature phenomenon, which may result from a ventilation problem on the generator, leading to stator distortion and rotor/stator contact

• Hypothesis of a secondary element generating shocks at the rotation frequency.

Accordingly, the following corrective actions were recommended: immediate visual inspection of the generator; verification of the fixing of the generator fan, which is mounted along the rotor axis on the opposite side of the coupling, and driven by an independent motor; and control of the bearing backlash.

On April 23, 2009, based on these elements, the machine was inspected, while the electric parameters were controlled. The on-site operations by the technicians showed that the fixing devices of the generator fan were broken, hence the air flow was no longer correctly oriented, which generated abnormal heating of the machine at the origin of the observed phenomena.

The fan was set back into place during the operation (which lasted three hours), after which the machine could be restarted. The bearing replacement scheduled for the next day was cancelled.

In this example, the diagnostic capabilities offered by the system proved very useful, allowing for a targeted, quick and relevant maintenance action, thus avoiding a costly and useless operation (changing the bearings).

No degradation of the machine was observed, while operating losses were limited to the maintenance time. Furthermore, the operator benefits from the experience of getting feedback on the machine.

Frdric Champavier is a CMS expert with 01dB-Metravib. The company is represented in Canada by Alliance Predictive, Sherbrooke, QC. For more information, visit www.alliancepredictive.comand www.oneprod-system.com,or use the reply number below at mromagazine.com/rsc.

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