Wind turbine gearbox technologies 

INTRODUCTION

Operational experience reveals that the gearboxes of modern electrical utility wind turbines at the MW level of rated power are their weakest-link-in-the-chain component. Small wind turbines at the kW level ofrated power do not need the use ofgearboxes since their rotors rotate at a speed that is significantly larger than utility level turbines and can be directly coupled to their electrical generators.

The typical design lifetime of a utility wind turbine is 20 years, but the gearboxes, which convert the rotor blades rotational speed of between 5 and 22 rpm to the generator-required rotational speed of around 1,000 to 1,600 rpm, commonly fail within an operational period of 5 years, and have to be replaced. That 20 year lifetime goal is itself a reduction from an earlier 30 year lifetime design goal.

EXPERIENCE WITH TURBINE TRANSMISSIONS

Among insurers, who joined the market in the 1990s, wind power is currently considered a risky sector. German industry giant Allianz was faced with around 1,000 damage claims in the year 2006 alone. Gearboxes had to be replaced in large numbers according to the German Insurance Association.

On average, an operator has to expect damage to his facility every four years, excluding malfunctions and uninsured breakdowns.

Many insurance companies now are writing maintenance agreements requiring wind producers to write the replacement of vulnerable components such as gearboxes every five years directly into their contracts. A gearbox replacement can cost up to 10 percent of the original construction cost, enough to cut deep into the projected profits.

Wind gusts lead to misalignment of the drive train and gradual failure of the gear components. This failure interval is disturbing, as it creates a significant increase in the capital and operating costs and downtime of a turbine, while greatly reducing its profitability and reliability. Existing gearboxes are a spinoff from marine technology used in shipbuilding. …

Proceedings of the 1st International Nuclear and Renewable Energy Conference, Amman, Jordan, March 21-24, 2010

Adam Ragheb and Magdi Ragheb, University of Illinois, Urbana

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