Random Thought Thread

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Delta 3 phase won't generate current on ground on any regular three-phase motor that I have ever worked with but you would certainly generate current on a wye wound motor using a neutral center tap like a generator.

If you were to take this Delta 3 phase and run it through a wye Delta transformer with a center tap bonded to ground I think you would probably generate about 138 volts to ground if I'm remembering right. And yeah, a set up like that would generate power on ground. Neutral actually, but they're the same here.

Delta 3 phase does not have a neutral and the ground is just to the frame. The vast vast majority of three-phase motors do not use a fourth wire (except externally as a chassis ground) but I guess there is probably some such as generators that do?

But still, I would expect that kind of a generator to have a separate neutral and chassis ground.
 
A regular three phase motor will have three different legs and each leg is attached to two windings each (3) winding is attached to two different legs. Ground is not attached to a winding and can not receive current unless there is a fault. This is why you can drive a motor with unbalanced legs (relative to ground) as long as they're balanced to each other (through phasing) However, you could design a motor where each leg is attached to one winding and the other side of each winding is attached to a common neutral. This neutral would be bonded to ground in the main power distribution panel. That neutral would be capable of carrying current. Motors are not normally designed this way because the amp draw would be double (due to half the voltage potential) so you'd need much more copper for a given power output, but it would probably be necessary for a power generator.
 
Nathan the Machinist said:
Delta 3 phase does not have a neutral and the ground is just to the frame. The vast vast majority of three-phase motors do not use a fourth wire (except externally as a chassis ground) but I guess there is probably some such as generators that do?

But still, I would expect that kind of a generator to have a separate neutral and chassis ground.
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Yes and Yes, Nathan. Tesla’s 3-Phase 4-Pole AC Induction Motor, for instance. Not so important in machine shops I guess, but important for electric trains, cars, etc.
 
Wherever yoko yoko goes...this tends to happen...

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