Coatings for electrical insulation

Monday, August 18, 2014

Tags :  coatings

At the top levels of motorsport power unit design, the current focus seems to be on making smaller engines and improving efficiency. Simply put, we want more performance from less fuel. This is true not only for our day-to-day motoring but for Formula One and Le Mans races. Given that there is a finite amount of oil in the world and that we have no viable replacement for it yet, we need to use it more frugally. This has not been lost on the rule-makers for Formula One and Le Mans – after all, what relevance is a high-speed V8 to the likes of Honda or Renault when its roadcar engines are becoming smaller and turbocharged?

A large part of the revolution in economy and efficiency is energy recovery, and most car companies and race teams have chosen the electric hybrid route. Also, electric racing is now with us, with some big names – teams as well as drivers – signed up to Formula E.

High-powered electric motorsport might prove exciting to watch, if not to listen to. However, for engineers there are challenges with moving from designing complex engine parts to assemblies with very few moving parts. Many adjacent components need to be separated by large gaps or electrical insulation. The problem is possibly most acute in the propulsion motors. The individual turns of the coils in the motor windings need to be separated from each other electrically; the same applies to the coils in each phase, and all the windings need to be insulated from the stator ‘iron’ and the motor’s casing.

In motorsport we want everything to be compact, so we try to make the windings small. We pull the windings around relatively sharp corners, and during winding the coils rub hard against each other, so it is very easy for the insulation on the winding wire to become damaged. A lot of electrical winding wire is coated in a polymer, and several layers of insulating coating may be used. There is a compromise here: more insulation is more robust and reliable, but it also increases the size of the bundle of conductors. There may also be additional insulation applied after winding, in the form of transformer varnish or lacquer.

Elsewhere in the stator of the electric motor, it is possible that insulating ceramic or polymer coatings could be applied to other components. The problem with coatings compared to much thicker separate insulating components is that coatings are far more easily damaged, and at the end of winding a motor a minor short can mean that the whole motor is scrap. The skill of the people winding the motor and assembling the stator into the case is as much a factor here as the integrity of the coating in many cases. The designer also needs to consider the lack of damage tolerance in any coating selected, and balance this against his or her desire to make everything as small and light as possible.

Written by Wayne Ward

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