Moire and superconductivity

if needed that can be done, but usually thr rotor retains enough magnetism to bootstrap enough voltage for the field current.

All power plant size generators have been three phase for at least a century.

It is true that you need two wires on each phase if you insist of using two phase with 90 degree phase shift. Tesla must have known that by combining the return wires of all three phases to a common neutral the return currents cancel out. So if there is no current flowing in the common neutral wire, why install it in the first place ?Thus a two phase (90 degree) system requires 4 wires, a balanced three phase system only three.

Two phases is the minimum number of phases which will produce a rotating magnetic field and hence an electric motor will always start and it will rotate in the well defined direction, either CW or CCW.

A motor can be run with a single phase, but it might not start and if it starts, might sometimes rotate in CW direction while at other times in CCW direction.

In practice current "single phase" motors are actually two phase motors with a big capacitor to feed the other winding with 90 degree phase shift. In old times before big starter capacitors, it was assumed that it was easiest to deliver the phase shifted voltage from the power plant as a separate phase.

No such issues with three phase motors, it will always start and rotate in a consistent direction. If you want to change the rotation direction, just swap two phase conductors and the motor will rotate in opposite direction.

snipped-for-privacy@downunder.com wrote in news: snipped-for-privacy@4ax.com:

You need to examine the difference between Delta and Wye configurations.

Now think about what happens if a phase gets shorted or opens in both configurations.

Which one can tolerate such a short and continue operating?

A lot of mission critical (data center) systems use Delta configured feeds. A lot of blade servers require 208V AC power.

Thanks, Three phase motors are fairly easy. I don't understand the single phase induction motors as well. (the phase slippage stuff.)

George H.