Evidence emerges from gear box failures

Stories of gear box failures after only 21 months of operation were among those circulating at the recent European wind energy conference in Kassel. The commonly held view of industry members is that as wind turbine size increased so did the demand for lighter (cheaper) components. Responding to the pressure, gear box manufacturers delivered a light but under-engineered and immature product. "Germany needs its DEM 0.17/kWh for wind to pay for its exceptionally fast development. Everyone wants the largest turbine available but these aren't sufficiently tested," was the comment of one observer.

"All gear box manufacturers and all turbine builders have been affected by component failures," says Martin Hoppe-Kilpper of the Institute for Solar Energy Technology (ISET) in Kassel. He draws his evidence from the detailed performance reports of the 1557 turbines installed under the state-supported 250 MW wind energy program between 1989 and 1996. The reports, mainly from 500 kW and 600 kW turbines in operation for five to six years, are monitored by ISET. It is this size group which so far has proved most vulnerable to gear box trouble.

For 1999 alone, statistics in the ISET annual wind energy report for 1999/2000 reveal gear box failures on 25 machines, blade failures on 25, hub failures on nine, and generator failures on 19 machines. The Enercon turbine crops up often in the failure reports, mainly because it was the most popular make of turbine in the support program; 325 Enercon machines are included among the database of 1557 turbines. Thirteen of the early Enercon 32/33 turbines were among the 25 gear box failures. Enercon's E40 turbine does not have a gear box. Other companies hit by one to three gear box failures last year were the former GET Danwin, Lagerwey, Micon, Seewind, Tacke and Vestas.

The Enercon E32/33 and E40 machines also accounted for 16 of the 25 blade failures last year. Lagerwey and Nordex were hit on this front with three sets of blade failures each, while AN Bonus, Fuhrländer, and a GET 41 machine all had one rotor blade failure.

The figures for the first half of 2000 reveal a continuation of the gear box problems in the database turbines. Six more of the early Enercon E32/33 turbines were hit along with two Micon M4607530/570 machines, four Vestas V25/27/29 turbines and one WindWorld W2500/2700 turbine.

Blades show up again as the other main problem during the first half of this year. Six Enercon E40 machines and five E32/33 turbines had blade problems as did one NEW 100 machine, one Vestas 25/27/29, one Vestas 39/42/44 and one WindWorld W2500/2700 turbine. Generator failures were experienced in two E32/33 machines, one E16/17/18/ machine and one Vestas 39/42/44, ISET reports.

"While insurance companies claim that as a rule gear boxes must be replaced after ten years, we have not observed this," says Bertholt Hahn of ISET. But there is time yet for this to happen. "Only now are most of the 500 kW and 600 kW machines included in the 250 MW program approaching their tenth birthday," he adds.