"Condition and performance monitoring should be viewed as complementary approaches"

Wind turbines are increasingly being equipped with Condition Monitoring Systems (CMS) to provide operators with all the data concerning the condition of wind turbines.

With this, production stops can be avoided via early information about any changes in the operating environment. CMS focuses on foreseeing potential danger to components, restricting the damages and, thus, avoiding subsequent damaging of other components.

That way, maintenance procedures can be planned which help to avoid shutdown periods. Consequently, the availability is improved and maintenance costs can be reduced.

Providing an insight into the existing condition monitoring methods, their importance in turbine maintenance and how important it is in predicting turbine life spans, Jochen Ziehmann, Technical Consultant, 8.2 Consulting AG says the main intention of condition monitoring is to detect failures before its leads to serious damages. Another goal is to get an idea about the remaining life span of components in the wind turbine.

"Today, the most CM systems supervise the drive train including the main bearing, the gear box and the generator. But there are also systems available to check the condition of the tower and the blades. These systems are needed when more turbines are going off-shore. Several methods are used to monitor the condition," said Ziehmann, who is scheduled to speak during windenergyupdate.com's Wind Energy Performance Optimisation Summit (to be held on 11th - 12th February 2009 in Hamburg, Germany).

In most cases, the vibration is measured. From the vibration signals some scalar values and spectra are calculated. Every possible defect in the bearings, the gears or the shafts has it's own characteristic fingerprint.

"So an experienced analyst can tell the condition of each component. Other methods used today are visual and acoustical inspections, video endoscopy, temperature measurements and particle counters. Trained personnel can see or hear the status of gears and bearings by opening the gear box and having a look on the gears or listening to the bearings with a stethoscope. The video endoscopy is used for looking at components in the gear box that are not visible from the aperture. Particle counters are used to monitor the number of metal particles in the oil stream of the gear box. An increase in the number of particles could be an indication for a defect. The monitoring of temperatures is usually already part of the main turbine controller," Ziehmann told windenergyupdate.com.

On major trends in this arena, Ziehmann said in the last few years the number of installed "online" CM systems has grown rapidly.

"Instead of performing manual measurements in certain intervals, the systems are installed permanently on the turbines and measure the vibration at all times. The online systems are usually connected via a network to a central server where trained analysts can have a deeper look on the signals. The big advantage of online systems is the possibility to calculate statistical trend values. Some of the systems are able to measure not only vibration but also are able to count particles in the oil," pointed out Ziehmann.

Difference between performance monitoring and condition monitoring

According to Peter Clive, technical development officer, SGURR Energy Ltd, a key distinction needs to be made between performance monitoring and condition monitoring.

Condition monitoring involves the installation of special instrumentation to measure vibrations, pressure, temperature and other phenomena. This will incur downtime and may have warranty implications. The assessments associated with condition monitoring can be characterised by the time scales typical of the measurements the instruments make, Clive told windenergyupdate.com.

He added that these conditions are typically trended over time.

On the other hand, performance monitoring requires no additional instrumentation and utilises for its analyses only those data that are already being routinely acquired by the SCADA system.

"Condition monitoring is focused on the condition of individual components, subsystems and their planned maintenance whereas performance monitoring is based on assessments of the performance of the system as a whole with a more operational focus. As such performance monitoring and assessment entails a greater emphasis on statistical analysis of power curves for the characterisation of anomalous performance and the integration of event data with time series data for the attribution of variance. The time scales performance monitoring represents are therefore those associated with the accumulation of performance statistics. Condition monitoring and performance monitoring should be viewed as complementary approaches," said Clive.   

Initially, an arrangement needs to be made to allow those conducting the performance assessment to access and retrieve the SCADA data.

"This can generally be achieved in a manner most convenient to the client. Once it is in place, routine analysis of the SCADA data can commence and weekly bulletins and monthly reports are issued detailing performance, accurately attributing revenue variance, identifying key issues and making recommendations for remedial action, pre-emptive interventions and the most effective configuration of O&M infrastructure," concluded Clive. 

Wind Energy Performance Optimisation Summit

Jochen Ziehmann, Technical Consultant, 8.2 Consulting AG and Peter Clive, technical development officer, SGURR Energy Ltd are scheduled to speak during windenergyupdate.com's Wind Energy Performance Optimisation Summit (to be held on 11th - 12th February 2009 in Hamburg, Germany).

For more information, click here: http://www.windenergyupdate.com/performance09/programme.shtml


contact Tom Evans by email: tom@windenergyupdate.com