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Concentrated power for new performance levels

With the generator for its more powerful E-175 EP5 model, ENERCON is starting a new chapter in its technology and product strategy. The permanent magnet generator with its innovative division concept increases the nominal power of ENERCON’s top model to 7.0 MW in the standard configuration. Moreover, its future-oriented design creates additional potential for future turbine generations.

When assembling a jigsaw puzzle, there is the moment when the pieces start to come together almost by themselves and the overall picture becomes clearly recognisable to anyone. A similar thing is happening in ENERCON’s technology and product strategy. In parallel with the company’s business reorientation, the Research & Development team has rigorously advanced ENERON’s technology and product roadmap and gradually moved new technologies into series production. This includes the E-nacelle with built-in power equipment; more efficient power electronics for the specific needs of onshore wind applications; smarter turbine control systems for the EP3 and EP5 platforms; and much more.

ENERCON’s top model, the E-175 EP5, is the first wind turbine to combine all these individual elements in one product. The introduction of the new generator for the E-175 EP5 – another crucial technology component from ENERCON’s technology and product roadmap – completes the overall picture. The permanent magnet generator increases the nominal power of ENERCON’s flagship model to 7.0 MW.

Greater nominal power for E-175 EP5

High nominal power was the main requirement for the development team, says Matthias Bartsch, Director of Generator Development at ENERCON. ‘In the standard configuration, we run the generator at 7.0 MW, which is a significant power gain compared to the basic version of the E-175 EP5 with 6.0 MW. In addition, this greater power permits achieving significantly higher energy yields.’

In order to achieve this performance level in combination with ENERCON’s tried-and-tested direct drive concept and the low speed of the WEC rotor, the developers worked on maximising the air gap diameter. The air gap is the space between the stationary part (stator) and the rotating part (rotor) of the generator, measuring just centimetres. The air gap diameter is thus the diameter of this air gap circle. The larger the diameter, the stronger the torque of the generator. ‘We need as much torque as possible in order to achieve high electrical power outputs even at our low rotor speed’, explains Matthias Bartsch. ‘For this reason, we designed the new generator with an external rotor.’

External rotor for larger air gap diameter

In contrast to ENERCON’s generator models so far, in this new model the stator of the generator is located on the inside, and the rotor is turning around the stator on the outside. This increases the air gap diameter from 5.5 metres in the basic version of the generator to 9.5 metres in the generator of the more powerful E-175 EP5 model.

‘Another benefit of the external rotor design is that the rotor rim can be kept relatively narrow, thanks to the permanent magnets. In addition, we are able to reduce the length of the active parts by almost 50 per cent. This has a direct effect on material efficiency: we are also reducing the required magnet mass by more than 40 per cent’, explains Mr Bartsch.

Optimal design for transport

Another essential factor for defining the technical specifications was ease of transport. In order to make the deliveries of the generator components to the construction site as efficient as possible, the engineers set out to achieve low transport weights and a maximum size inside the permissible range for abnormal load transports without police escort. ‘We knew that the generator would need a divided design. A component of this type cannot be transported on the road in one piece’, says Mr Bartsch. ‘In Germany, the maximum width for transports without police escort is 4.99 metres. Because of this, 9.9 metres was the maximum total diameter for the new generator.’

The total weight of the generator is 124 tons, so that each half weighs only 62 tons. ‘This means that deliveries to the construction site can run as regular abnormal load transports. And another benefit is that no special equipment is needed for installation’, says Mr Bartsch. ‘The installation of the partial components of the generator at the construction site uses standard 750-ton installation cranes.’

Optimised for transport: the developers based themselves on the permissible transport weights and maximum size for abnormal load transports without police escort.

Efficient division concept

For now, the technical details of how the generator is divided remain a trade secret. To illustrate the division concept, the engineers will only describe the steps in general terms: the new generator is fully assembled (stator and rotor) at the factory and is then adjusted, tested and locked. Then, the component is divided into two halves that are transported to the construction site. Each half includes the already assembled stator and rotor. After the installation of the machine house at the construction site, the bottom part of the generator is installed first, followed by the top part. The bearing and the hub are installed in a third step. Finally, the locking device is removed from the rotor and stator.

‘Another benefit of this concept is that at the construction site, the partial components only require minimal bolt connections to secure them, which reduces the length of time the crane is needed’, explains Matthias Bartsch.  ‘The installation team performs the final installation and tightening of the bolt connections from inside the wind energy converter, and they don’t need the installation crane for that.’

Last but not least, the new concept simplifies service and maintenance during the operating stage. ‘Maintenance becomes easier’, says Mr Bartsch. ‘When maintenance is due, service technicians cross through the stationary part into the front of the turbine and can walk through the main carrier and the generator all the way into the hub. Inside the component, too, there is more room for service operations, and sub-components such as fans are easier to access. This is a boon for occupational health and safety.’

Successful proof of concept

While the series version of the new generator is currently in the advanced stage of development, the development team is already performing extensive testing on a technology prototype. This generator has already successfully passed proof-of-concept testing with numerous test sequences at ENERCON’s major component test station in Aurich as well as at the test station of the Fraunhofer IWES in Bremerhaven. These tests have taken the generator performance to its thermal limits, tried out various power curves in operation, and validated the overall generator behaviour. On top of that, testing covered the optimisation of the grid performance and of the grid-friendly characteristics of the generator-converter combination.

‘This extensive testing and validation programme, which we will soon continue with our close-to-production generator prototype of the next evolutionary stage, is part of our portfolio of measures that ensure the ENERCON Quality of our series products for our customers’, says ENERCON CTO Jörg Scholle.  

Sustainability in mind

Because ENERCON is already considering sustainability even during the development process, the technology prototype was also used to test end-of-life processes. The rare-earth elements from which the magnets are made represent valuable raw materials that should be returned to the relevant recycling streams when wind turbines are dismantled. For this reason, the development team used the technology prototype to investigate a method for separating the magnets built into the rotor of the PM generator. ENERCON is taking steps towards making the discovered processes more concrete in cooperation with industry partners.

Future-oriented concept

The development team is proud of its new generator that has raised the performance of ENERCON’s top model E-175 EP5 to another level, but they have still bigger plans, says ENERCON CTO Jörg Scholle: ‘With our external rotor generator, we are pursuing a future-oriented design. This new generator concept makes the E-175 EP5 extremely attractive for our customers in highly competitive markets – even more so in combination with our newly available hub height of 175 metres. Market analyses have shown that these features also enhance customers’ advantages in terms of direct marketing, for which our E-175 EP5 is already an excellent fit. Apart from the E-175 EP5, this generator concept holds a great deal of potential for future turbine generations and more demanding customer requirements.’