Application Note
Early detection of wind turbine electrical generator damage reduces downtime
Gill Sensors & Controls WearDetect identifies the first stages of failure in wind turbine electrical generators in time for maintenance scheduling
Background
Renewable energy is forecast to account for almost half the world’s electricity generation by 2026 (up from ~40% in 2023) and global offshore wind is estimated to increase 6-fold in the next 10 years.
Wind turbines are increasingly important for power generation and efforts are focusing on reducing the levelized cost of energy (LCoE) over the lifetime of equipment. Reducing downtime, optimising asset performance and extending asset life all contribute positively to this measure.
The electrical generator within a wind turbine is one of a number of key components with high failure rates that when experiencing issues contribute significantly to overall downtime. Wind turbine electrical generators, housed within the nacelle of a wind turbine, typically suffer from stator wedge failure and early detection can allow for planned maintenance to take place, which in turn protects ancillary equipment and extends asset life.
Challenge
Wind turbine maintenance is particularly challenging because of their remote or off-shore location. In addition, much of the equipment requiring maintenance, including the generator, is housed in the nacelle at the top of the wind turbine tower. As a consequence, maintenance is difficult to carry out, dangerous and expensive.
Wind turbine electrical generators are prone to failure and commonly this is caused by the ejection of stator wedges. Unlike regular generators, wind turbine generators are not operated under steady load conditions. The stochastic nature of the (natural variable) loads – from wind speed and direction change to temperature variation from weather conditions – can impact failure modes and make prediction of wear more difficult. This contrasts with the steady operation of generators used in other applications. The loading unpredictability experienced by wind turbine generators makes prediction of the rate of wear far more uncertain.
As a consequence, wind turbine servicing is not only more difficult due to remoteness of the location, inaccessibility of the nacelle and unpredictable nature of the weather conditions, but there is also the reduction in effectiveness of traditional time based prediction techniques for driving the service schedule.
When a generator does fail, total repair costs are extremely high, including specialist teams to access remote, and potentially hazardous locations, possibly off-shore. This can lead to a delay in arranging repairs resulting in increases in overall downtime costs.
Solution
Early detection of wear or damage in a wind turbine electrical generator can increase asset effectiveness in many ways as identified earlier. A WearDetect sensor can be used to continuously monitor ferrous wear within the electrical generator housing. Measuring the wear debris in the housing provides an early indication of the first stages of wear which is typically triggered by the loosening of the stator assembly and deterioration of a stator wedge before it is ejected.
The sensor is located in the closed airflow of the electrical generator. When it detects an acceleration in the rate of debris build up, this is an indicator that a fault is developing. The sensor can be set to create an automatic alert to notify maintenance teams that wear is beginning to occur. The alternative of manually testing the wedges when the generator is out of service is not feasible in a wind turbine electrical generator.
If a wedge is left to deteriorate and eventually ejects, it leaves unsupported winding which can become damaged, may cause flashover and ultimately failure of the generator.
Monitoring iron levels and alerting maintenance teams to very early changes in the electrical generator allows steps to be taken to schedule maintenance and prevent further, more significant damage, occurring.
Monitoring occurs while the generator is in operation and, due to the early nature of the measurement, the generator can keep running until the maintenance activity is implemented. Crucially, continuous monitoring allows maintenance activity to be focused on the areas that require it, based on having ‘visibility’ through the sensor of the actual wear occurring.
Implementation of continuous monitoring measures, such as wear debris measurement, all contribute to increased wind turbine up-time and ultimately to improvement of the LCoE.
