Page 7 - Energize January 2022

COVER STORY

Added to this the estimated life costs are therefore key drivers to the economic and technical viability of wind turbines
span of wind turbines is about 20 years, becoming a primary renewable energy source in South Africa.
compared to conventional steam turbine The adequate functioning of most utility-scale conventional wind turbines depends to
generator units that have averaged 40 a large extent on the performance of the gearbox. These gearboxes transform slow speed,
years. The failure rate of wind turbines high torque wind turbine rotor rotations to the higher speed required by the generator,
is about 3 times higher than that of which converts the mechanical power to electricity. They are typically configured to have
conventional generators. Therefore, planetary gearsets and bearings that require special attention due to their extreme operating
reliability is essential to the success of conditions and high lifetime expectations.
wind energy systems and this requires The wind turbine gearbox is the most critical component in terms of high failure rates
appropriate condition monitoring. and down time. These premature gearbox failures are a leading maintenance cost driver that
As a result of external variants, wind can substantially lower the profit margin of a wind turbine operation as they typically result
turbines undergo constantly changing in component replacement.
loads, unlike conventional power plants. According to a study published by the National Renewable Energy Laboratory (NREL) the
Due to these highly mutable operational mean downtime for gearbox failure was in the range of 6 to 15 days for a study performed
conditions, the mechanical stress placed on European on-shore wind turbines over a 13-year time period. The mean downtime could
on wind turbines is unmatched in any be even longer if a spare gearbox is not available and crane availability is an issue. The same
other form of power generation and they study also looked at data representing about 27 000 turbines ranging from 500 kW to 5 MW
consequently require a high degree of over a six-year period and found that the cumulative downtime caused by gearbox failures
maintenance to provide cost effective and was more than 150 000 hours.
reliable power output throughout their Further analysis found that 76% of gearbox failures were bearing-related and mostly due
expected 20-year life cycle. to high-speed shaft (HSS) and intermediate-speed (IMS) bearing axial cracks.
Ensuring long-term asset reliability and Despite significant advancements in gearbox design, they remain an operation and
achieving low operation and maintenance maintenance cost driver due to the very high associated repair costs coupled with a high

Figure 3: WearCheck uses sophisticated equipment to obtain accurate,
Figure 2: Samples of gearbox oil being analysed by WearCheck reliable results

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