A couple of developments, recently reported by media, have highlighted the ongoing challenges related to crashing of the blades and the overall safety of turbine.
In one of the instances, involving Suzlon Energy and breakage of v2 blades on its s.88 turbine in the US, it was shared that the entire energy production at a small wind-scale farm southwest of Wyanet had come to a halt following the blade rash. The blades measuring 140 feet long and 15 feet wide crashed with a loud sound and recovery was 100 to 150 feet away from the structure. The blades were reportedly installed in June 2007. For its part, Suzlon informed the National Stock Exchange that there had been no shut down of turbines in the US and dismissed media reports as "baseless and speculative". It acknowledged that there had been an accidental breakage of a single V2 blade on a Suzlon S.88 turbine but this was an extremely rare and unusual incident. "The cause of this incident is presently under detailed investigation," it said.

In another incident, it was reported that turbine #10 at the Searsburg wind energy facility in Searsburg, Vermont experienced a catastrophic failure when one of the blades came in contact with the turbine's tower causing it to buckle during high winds. This turbine's 28-ton nacelle and 3-blade rotor assembly crashed to the ground scattering debris several hundred feet from the structure. Approximately 20-gallons of heavy oil spilled from the unit when its fluid reservoirs were damaged. A comment related to this development was as follows: "The Searsburg towers are located at an elevation of nearly 3000-feet in some of the harshest weather conditions in New England. Performance issues and blade failures have plagued this project for some time."

Such developments underscore the importance of timely assessment of the external factors, which can adversely impact the operations of such sites. And one of such factors is weather.

According to Toby King, COO, Insensys Limited, ice, strong turbulent winds and lightning can all cause blade damage and thus blade imbalances can then cause early wear in the drive train, leading to a premature failure.

Specifically, on problems related to ice build up on blades and the damage caused, King told windenergyupdate.com that ice build up causes two main problems. 

"Firstly, there is a significant safety issue if the ice is 'thrown' from a blade tip, typically as it starts to melt, if the turbine is close to a populated zone. This causes most operators to shut turbines down in icing conditions.  They then have to visually inspect the turbine to verify that it is safe to restart. This takes time and effort, and means there is increased lost revenue caused by the downtime being extended whilst waiting for an inspection," shared King, 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).

"The second reason for shutting down is that ice can cause an imbalance (either in terms of mass or aerodynamic performance) between the blades, which can rapidly lead to a premature wear of the bearings and gearbox.  Most current methods for assessing such imbalances are very rudimentary (typically an accelerometer on the gearbox.)  These measure a symptom, not the cause.  Our system measures the imbalances in the blades themselves, so a more informed decision can be taken, automatically, on whether to keep generating, reduce power or shut down.  This leads to a longer turbine life through reduced wear, less maintenance and better overall energy output," added King.

In terms of a pro-active approach to combat such threats, the impact of weather conditions can be recorded and analysed at an early stage, thus increasing reliable operation.

According to King, by monitoring the loads on the blades caused by high winds, icing etc., operators can reduce the high loads on their blades and drivetrain by changing their operating strategies (for example, correcting blade imbalances, shutting down when the ice on the blades reaches a dangerous level, or when the wind loads cause large blade imbalances, or simply reducing output power under high mechanical load conditions) and thus protect the blades, bearing and gearboxes.

Referring to a positive development, King says operators are opting for a more sophisticated approach towards condition monitoring, and are beginning to consider the whole life cost of the turbine, rather than just maximising short-term revenue.

Wind turbines work in different operating conditions, and therefore blade pitch activity is different for each wind turbine. Consequently, grease required for each wind turbine mechanism is also different and usually this is not optimised.

Considering this, on how can one work on blades to combat different weather conditions, King said, "Our view is that by using blade monitoring equipment, and sophisticated operating strategies, the blade loads and the drive train loads can be kept within the design envelope, thus achieving the turbine design life and avoiding costly secondary failures."

And on what can be done or to improve the overall turbine performance in the context of adverse weather conditions, he said by monitoring the blade loads, it is possible to control both blade and drivetrain load, even during adverse weather conditions, to keep them within the design envelope and prevent premature failures. 

"This leads to much higher overall availability, lower maintenance costs, less lost revenue and improved turbine life," shared King.

Wind Energy Performance Optimisation Summit

Toby King, COO, Insensys Limited is 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

Or

contact Tom Evans by email: tom@windenergyupdate.com