3-phase synchronous machine => 5-phase synchronous machine

[mad mathematician]

These power systems analysis books...

Anyhow, I was thinking just a few moments, can you have a five phases synchronous machine as opposed to the the three phases synchronous machines?

My reasoning is pure arithemetical-geometric, I mean a circle has 360 degrees so if we look to divide such a machine into odd phases there's 3,5,9,15,45.

So is it engineerical feasible to construct such a synchronous machine? (I just think of the number of equations increased... yuk).

 

[DaveE]

Yes. They exist, but are uncommon except in servo system motors.

Anyway, it has nothing to do with the arithmetic of dividing up a circle. The engineering world doesn't necessarily think 120^o is prettier than 72^o or 51.429^o. I'm sure there is a detailed cost benefit analysis that favors 5 phases over 3, 6, or 7 phases in each application.

Next step (usually it's my 1st, actually), Google: "5-phase synchronous motors"

 

[Averagesupernova]

If you have three phases it's reasonably easy to generate double the number of phases using transformers. But, three phase mostly shines with motors and motors are reasonably easy to build with many many poles. So, it accomplishes a similar thing.

 

[jrmichler]

Back in the late 1990's, I was involved in the development of a four phase permanent magnet servo motor. The EE who originated the design was convinced that four phases, and trapezoidal phase currents would develop more power in the same size package as three phases and sinusoidal phase currents. Since a 9.9 inch diameter by 16 inch long motor was conservatively rated at 225 ft-lbs continuous torque, and peak rated at 600 ft-lbs peak torque, nobody argued with him.