01dB-Metravib (AREVA Group)

Gearing up for Condition Monitoring

Lyon, May 2011. With growing wind energy capacity, every hour counts for existing turbines, especially in high wind seasons. Condition Monitoring is a powerful way to avoid downtime and plan maintenance optimally. The stakes are high, and the degree of customization needed for Condition Monitoring Systems is also very high.

How can wind farm operators manage assets with condition monitoring?
Let’s take an example …A 1,5 MW wind turbine generates a turnover of approx. 300,000 € every year (in France). This represents 5,750 € a week on average. Opposite to this income, the cost of changing a gearbox for this kind of wind turbine is also in the surrounding of 300,000 €, and the cost of changing a generator 80,000 €.
These quick numbers help realize that if a significant failure happens in a given year, the profitability of the wind turbine is gone for that year. You realize easily how important it is to detect in advance the failure of various elements (pinions, bearings …), in order to reduce the cost of maintenance and plan the maintenance work. The planning part is crucial in the wind industry, where delays for replacement parts can be long. The timing is also critical for major work because of the heavy seasonality.
Condition Monitoring Systems (CMS) come at play to provide monitoring and diagnostic, so that operators can anticipate problems. Vibration analysis technology is particularly well suited, as it can lead to very targeted diagnostics. Still, machine design and operating conditions are unique in the wind industry: they very much differ from what can be found in traditional industrial machinery, and require specific monitoring methodologies. The main bearing or the gearbox for example could simply not be effectively monitored by a classic monitoring system.

The case
The OneProd service team monitors a 25 machine windfarm in the North of France. The wind turbines are equipped with vibration analysis through the OneProd Wind System solution. In one of the gearboxes, we recently identified a faulty sun pinion in the epicyclical shaft … which is to say a failure in the heart of the gearbox. We quickly sent out an alert to the operator.

Analysis of the failure
This pinion had a broken tooth and generated an impulsive phenomenon for each revolution. Given the very low rotation speed of this pinion – about 100 RPM - the classic indicators can’t pick up the energy of the failure in the signal and detect the failure. It takes a special indicator to lead to a correct diagnostic. Our service teams use the ShockFinder indicator for this kind of situation. They know it well because they have put their very own know-how into the indicator!
The principle is simple: the indicator detects shocks within a time wave, and counts the periodic shocks. This leads to a relevant piece of information because on one hand, even low energy phenomena get detected, and on the other, random shocks are discarded.
Let’s get back to our sun pinion. After the alert was given, the maintenance team performed a borescope inspection and confirmed the diagnostic. The next step was to plan the repair work on the gearbox. Had the gearbox run to failure, it would not have been possible to repair it.
In this only case, the operator was able to save 60K€, which is the difference between a brand new gearbox and the repaired gearbox.

“C’est la révolution !”
Here is another probing example. The CMS helped us monitor a failing bearing on the gearbox high speed shaft. We found out the bearing had surface irregularities and monitored the failure. This close monitoring helped the operator pick the optimal moment to repair, according to the bearing condition and the weather conditions.
The gain here is estimated to 3 weeks of production, or 16K€, without counting the catastrophic possibilities.

A system that pays for itself
In the end, condition monitoring proves itself quite useful and profitable when well adapted. Bear in mind that it only takes one identified failure to pay for the system! Also, experience shows that a gearbox will encounter 1 to 2 major failures in its 10 year lifetime.
Time to gear up for condition monitoring!
01dB-Metravib (AREVA Group)

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