After many wild years in the wind power business, clearer targets are now being set. Most of the players have realized that instead of having the most sophisticated turbine, the more important goals are to reach a levelized cost of energy (LCOE) and higher amount of annual energy produced (AEP).
The industry standard has been to use totally enclosed (IP54) generators in the turbines, mainly to avoid the risk of corrosion in its different forms and also to improve the lifetime of the components. Offshore turbines face additional challenges from the sea environment in which the components in both offshore and near-shore turbines are exposed to salt water.
IP54 protection in practice means one or two loops of cooling circuits that contain the same amount of heat exchangers, a lot of piping, fans, pumps and a control system, and so on. Each cooling loop increases the internal generator temperature too. Looking at the list, it is not difficult to see that the “additional” cost is huge.
What this also means is that the final generator coolant, whether air or liquid, has a remarkably higher temperature compared with the environment due to the thermal difference in heat exchange systems. This leads to either oversizing the machine, spending more money for material thermal grading, de-rating the power, or something else to get the same result. All this again means spending more money in comparison to the actual MWh produced.
It doesn’t have to be like this. And the most expensive unit doesn’t always have to be the best. Why?
The answer is a combination of proper corrosion protection and filtering. Basic corrosion protection to the outer parts has to be arranged in any case. So, why not do the same for the inner parts?
In all of The Switch generators, at the heart is the magnet, which always has double or even triple protection against the environment. How? All magnets have their own coating, which has already passed hard temperature and chemical tests, including salt spray. Plus, the magnet is embedded and finally impregnated in high-speed machines. Medium-speed machines have a mechanical cover on top. And the magnet in direct-drives is hermetically sealed inside the metal casing. So, no chance for corrosion in any of these cases.
The other critical component is the winding system. Vacuum-pressure impregnation (VPI) fills all the gaps, saturates the insulators and arranges a protective film on top. The coil ends may also be treated with an additional layer of resin specially meant for this purpose. If you think of traction motors, for instance in trains, they are often totally open and survive the conditions under the train. The Switch also has unique verified experience in medium-voltage insulations for electric machines that operate in conditions much tougher than the normal sea environment in the oil and gas industry.
We can also add filtering to the cooling air. For example, filtering with Goretex® to remove particles even in the range of mircometers prevents even humidity from penetrating through.
So let’s throw away old prejudices and make wind even more competitive against the polluting forms of energy. Let’s get smart about working towards the true end goals of LCOE and AEP!
Panu Kurronen, Product Manager, Generators
This story is featured in Switching on Frequently 01/2013.
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