Author Topic: Efficiency, Delta vs Wye  (Read 1555 times)

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TDC

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Efficiency, Delta vs Wye
« on: December 19, 2014, 08:37:18 PM »
Is the efficiency the same for axial flux alternators?

joestue

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Re: Efficiency, Delta vs Wye
« Reply #1 on: December 19, 2014, 09:19:36 PM »
its basically the same.
In delta, third and 9th harmonics flow round and round in circles, causing no load losses to be higher, but they are canceled out at the terminals--because they got eaten up by the winding resistance.
For WYE, third and 9th harmonics are subtracted from the terminal volts. so there is no circulating current, however the open circuit rms voltage is reduced.
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Flux

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Re: Efficiency, Delta vs Wye
« Reply #2 on: December 20, 2014, 09:18:40 AM »
For conventional motors the losses are similar and dual voltage machines rely on the interchangeability.

When the basic phase voltage is much more distorted the delta scheme suffers from a significant circulating harmonic current. This can add drag near cut in and reduce the low wind performance.

With axials the open circuit waveform depends on many things and if you really need to use delta it is worth looking at the proportions between magnet and coil to get a reasonable waveform.

With distributed coils in an air gap without iron teeth the waveform usually tends to be reasonable as long as you avoid extreme geometry. if you follow the normal suggested magnet and coil dimensions the phase voltage tends to triangular and is not bad enough to be a big problem in delta. Spacings which tend to push the harmonics towards square wave can potentially be problematic in delta.

One thing to watch is accuracy of turns/phase, star will not be bothered by significant variation and some machines used unmatched phases as a way of load matching. Delta will circulate heavy currents with any significant phase unbalance.

Flux