Quote:
Originally Posted by e*clipse
That's the thing that's bugging me... Even though I have the motor in many pieces, there isn't an obvious neutral connection. As far as I know (from looking at analyses of similar motor by the DOE, the motor is wired wye, not delta. I just can't find the magic center point. 
Acually, I'll test to see if there is any conductivity between any phase and the case. That would be interesting. |
Are you just interested in where the neutral point is?
As I understand it, you can find the 'neutral point' if you dig through the windings and find where the star point is. It's just a connection between the coils, and it is insulated after it is braised or bonded or whatever method they use to connect them. It should be on one of the ends, and there will be at least one longer insulated wire (from the coil that does not end up near there) coming to it.
That's different from the 'ground point'. The ground is there to help keep you safe if there is a failure in the motor. If Phase A wears through the insulation, and the frame is now at the same voltage as A phase .. there should be a fuse blow or a breaker trip because the ground is connected back to the source of the power - battery pack, transformer, etc.
If you have a .. I think it's a 12 lead motor .. you can wire it for 460V or 230V, Y or delta. Both ends of each coil, 6 coils total, 2 for each phase, are brought out to the motor junction box. Then finding the neutral is easy. The junction box is confusing just because there are so many terminals to deal with.
If you get a resistance reading between the frame and any of your three phases of less than about 1 mega ohm then there is a problem. The insulation on the motor should measure 10X or 100X that.
Y or Star connected has a bit higher voltage and a bit lower current. Delta has higher current but lower voltage. I think Delta has better torque .. but don't quote me. We have a couple of compressors that start up under load and have the first stage as delta and the second stage as Y. It matters to motor rewinders, and it matters when you are ordering a motor so you get what you need at the right voltage. The rest of the time no one seems to care.