Maintaining the wind turbines

Generator service technicians take care of the key component of a wind energy converter: the generator – the component that converts the kinetic energy of the rotor into electric energy. ENERCON currently employs 40 such generator technicians worldwide, just a fraction of its entire Service staff.

In order to keep up with the expansion of its installed base, the company plans to create more such teams. For most of the year, generator service technicians do the same type of work as the regular Service electronics technicians. If, however, a wind power converter within their Service area suddenly indicates voltage drops or excessive temperatures at the generator, it is their chance to apply their specialised know-how. International Support’s generator service teams are deployed worldwide for assignments in their special field.

Daniel Onnen and Matthias Meiners have already prepared their equipment for a troubleshooting assignment on the generator of an E-40 wind turbine in the village of Hagermarsch in Northern Germany. On this morning in May, the wind turbine located at a site that affords a view of the North Sea island of Borkum is standing still. The wind turbine’s control system displays status “Error: temperature measurement”.

Onnen and Meiners have already carried out all measurement checks that can be done from the ground. “Now we continue at the top,” says Onnen. Two red bags are ready, containing crimping pliers, multimeter, wire cutters, ratchet set, heat-shrink tubing, blow-dryer, generator paint, cleaning rags, and a set of temperature sensors. “We also take a compressor along, in case we need to use the gun for the generator paint,” says 28-yearold Onnen.

He climbs up the tower in order to manoeuvre the bags through a hatch into the nacelle, using a winch. Once the tools have arrived safely in the nacelle, Meiners also climbs up.

“To verify whether the fault may be with the sensors, we need to do a measuring check on them,” explains Onnen. When a sensor is working properly, its electrical resistance is of a certain quantity – depending on generator temperature. Any deviations point to a malfunction.

“With most defects, the resistance moves into the high-ohmic range,” says Matthias Meiners, who is also 28 years old. Through measurements at generator details, the technicians can identify the exact location of the fault. Sometimes however, Meiners and Onnen may even need to take the complete measurements of all temperature sensors in a generator area.

“If we find a defective temperature sensor, we replace it,” explains Meiners. He uses heat-resistant glue to affix a new sensor to a generator winding of the E-40 machine. Then he strips the cables that are attached to the new sensor and crimps them to two ends of a cable strand on the generator. After some more measurements and checks, Meiners, who is a qualified equipment and systems technician, pulls a piece of heat-shrink tubing over the transition point. He uses the blow-dryer to make the tube shrink and tighten around the joint.

The “generator overtemperature” message is one of the control system messages where the specialist teams are called into action. “We are also called when the excitation current in the generator deviates from the target value,” says Onnen. The turbine’s control system constantly monitors this value; if deviations occur, the Service Dispatch centre receives a notification. “If this happens, the team must check different areas of the generator systematically in order to assess whether values are still plausible.” Measuring points are set in a manner that enables the technicians to narrow down the location of the fault step by step. “Once the fault has been exactly identified, one possible way to fix it may be to replace a pole shoe.”

“Our work requires the ability to work very precisely and thoroughly as well as a lot of creativity, physical fitness, and strength,” says Onnen. Creativity is needed e.g. during troubleshooting and for the upgrading of operating equipment, but also when devising interim solutions for problems until required spare parts arrive on site. And regarding the need for strength, one only needs to consider the fact that one pole shoe of an ENERCON turbine may weigh up to several hundreds of kilograms. Of course, chain hoists and other lifting equipment are used to make the replacing of components easier, but some heavy manual work remains.

Onnen and Meiners also perform routine maintenance work: Typically, this is preceded by a report from a Service electricians team who has carried out a visual in spection of the generator. The generator service experts then look for dirt and flaking paint on rotor and stator and work such spots with a brush before applying new paint to patch any defective spots.

“You need a lot of electrical know-how to be able to repair an annular generator. We used to acquire this special knowledge through ‘learning by doing’ within the team, but nowadays ENERCON provides special training for staff to teach them in this field,” says Onnen. He is a qualified electric machine mechanic and had already gained experience with generators before joining ENERCON six years ago: He did his apprenticeship at an electric motor manufacturing company in East Frisia. “In addition, you need to enjoy travelling,” adds Meiners. About five or six times a year, the two generator specialists from the ENERCON Service team for Northwestern Germany travel on international support assignments. “We get a few days’ notice, and then we’re off to France, Sweden, Taiwan, or New Zealand.” Such deployments may take anywhere be tween five days and four weeks.

Generator service technicians specialise in the repair and maintenance of ENERCON wind turbines. Their tasks range from visual inspections to cleaning and the repairing of paint defects to the bridging or – in extreme cases – replacement of coils, pole shoes, or windings. A prerequisite for the job is a sound foundation in electrics, gained for example during vocational training as electric machine mechanic, as well as the ability to work at height and physical fitness. Currently, new generator service teams are being formed for France, Canada, Italy, and Scandinavia. 

Key qualifications: Vocational training in electrotechnical engineering. Enthusiasm for wind energy; physical fitness; ability to work at heights. Tasks and responsibilities: Service & maintenance of electronic components of WEC, esp. generator. Advantages: + Various tasks pertaining to the maintenance of wind turbines. + Practical introduction to all aspects of the job. + Highest standards of safety. + Career opportunities within the ENERCON Service organisation.