Keep the blades turning

Wind turbines are making a major impact on the power generation market. However, as with any electromechanical equipment, they need to be properly maintained in order to remain reliable and continue delivering clean energy, even after the manufacturer’s warranty has expired. Ron Bridges reports

Electricity is essential to everyday modern life. Turning on the lights, watching television, getting a cold drink out of a refrigerator or riding a train – electricity is all around us and something we can’t imagine our day without. Even though it’s required for almost everything that we do, we won’t necessarily stop to think about where the electricity we’re using is coming from.

Over the past decades, the number of wind turbine installations has continued to increase as the need for renewable energy sources has grown and so too has the need for their maintenance. Specialist service providers are needed to make sure that the turbines keep turning and generate electricity.

Since wind turbines were first commissioned on an industrial scale, the technology and design of the components has progressed rapidly, enabling units over 1 MW to be installed with an expected working life of around 20 years.

Planning for warranty expiration
Wind turbine manufacturers offer a warranty period of five to ten years, where the original equipment manufacturer (OEM) has a contract with the owners to deliver maintenance and repair projects. When this expires, owners are able to seek out more cost-effective suppliers, but any savings must not be at the expense of quality or expertise.

Wind turbines built by the same OEM will contain many common components from the same manufacturers, but this is not always the case when it comes to the generator. Very often, two identical models of wind turbine will contain generators from different suppliers, which can make maintenance programs more complex.

Such a specialist field requires considerable expertise to be able to handle the numerous designs and offer upgrades that can improve reliability and efficiency. Sulzer has extensive experience in generator maintenance and repair, with many specialist engineers involved in the wind turbine industry. This expertise covers all manufacturers of generators, and the processes used to deliver a timely repair have been honed over many years.

Optimising availability
Once a generator has arrived at the service centre, it is important to establish the technical details of the machine and carry out a series of initial tests and discover the precise condition of the generator. These are followed by the tear-down and visual inspection, which offer additional information on the work that needs to be carried out. From here, the reliability and availability of the turbine will be determined. The choice of materials used to rewind a generator and the way in which they are installed can make all the difference between uninterrupted service for two years or ten years.

Modern insulation technology used in generator windings allows for thinner layers which can withstand greater dielectric stress and higher temperatures, which also allows more space for copper within the same slot area. This reduces the resistance of the stator winding, which runs cooler, allowing an increase in output.

Spares inventory
Most operators will hold at least one generator as a spare unit so that it can be installed at the same time the faulty component is removed from the nacelle. This optimises repair times and minimises costs by only requiring the specialist crane to be on site for one day.

However, the storage of generators needs some special mattention if these vital pieces of equipment are going to remain serviceable. Sulzer recommends that the generators are kept in a climate-controlled atmosphere that minimises moisture content and temperature fluctuations. It also suggests that the drive shafts are turned at least once a month to prevent bearings and seals ‘taking a set’.

If a spare component is not available, the time in the workshop becomes critical because every hour is lost generating time and this can be a significant loss. This is in addition to the extra crane costs that will be incurred due to the lifting equipment needing to return to site to install the repaired generator.

Minimising repair times
Depending on the make of the generator, Sulzer can turnaround a repair in just two weeks, but some designs are more complicated than others, so this time can extend in some cases. However, Sulzer has the expertise and facilities to minimise these times and ensure a high-quality repair. By using the latest CAD software, new bars or coils can be precisely formed to ensure an exact fit in the stator slot, making the installation process more efficient.

By using comprehensive testing techniques, the reliability of the new coils and the repair as a whole can be guaranteed. Testing at full voltage, with both the rotor and the stator being tested for insulation resistance as well as partial discharge provides evidence of the build quality of the project.

Planning ahead
Preserving the reliability of a wind turbine is essential for keeping it operational and cost effective. By working to prevent potential failures, condition monitoring and repair work can be planned ahead of time, ensuring that any downtime is minimised.

In addition, a greater breadth of experience, supported by expert design engineers, allows modifications to the original components to be introduced that will improve durability. By delivering these as part of a planned schedule, productivity can be maximised and component failures avoided.

Ron Bridges is Account Manager for Sulzer, the leading worldwide, independent service provider for the repair and mmaintenance of rotating machines including turbomachinery, pumps and electro-mechanical equipment.

Sulzer offers a specialist on-site wind turbine repair service that can react to unplanned maintenance issues, with a particular emphasis on generator repairs. With high turbine availability as a priority, Sulzer has dedicated resources capable of delivering preventative maintenance routines as well as comprehensive overhaul and repair services.
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