400-hp Motor Amperage

The only way I know of that a single phase line an ever read higher than the other two combined phase lines is if you have a shorted winding taking power to the grounding system. Check your neutral and ground lines at the power source and see if it changes when the motor is running.

i do agree with you and recomend him to check the coil to coil insulation also , in normal every coil should be isolated from the others with open ends.

this problem seems the parralel coils togather.

and for this reason the internal resistance is droping and creating less or reverse

tourqe to all sets.

regards

The inbalance of current ( causing the over heating )while the motor is running could be due to improper neutral earth at the supply.That can be unconnected earth or resistive earth ( hot neutral cable if it is under size ).This can be checked with the phase to phase terminal voltages of the motor when it is running.One reading should be quite different from the other two.

The resistive ohm of the coils are quite equal but it cannot tell as thick conductor coil can have a few turns less or more and contribute to differences in reactance/impedence thus inbalance loading.

Kindly let us know the outcome,I wsh to learn more.

Regards,

Khor.

You should check coil to ground resistance on all coils with a megger- use nothing less than 1000 V test voltage for your 480 V system- higher would be better (i.e., 5000 V).

I think it is due to motor winding coils start and end connection not don properly. For Exmp: A1-a2,B1-b2,C1-c2 like all the 6 coils.

What sort of meter did you use to measure your OHMs?

Did you check for shorts to ground?

Did you seperate the leads before measuring?

Is it possible that one of the coils has been reconnected backwards?

Do you know how to check each coil's polarity? If yes, do that for each coil.....

Because the motor has 12 leads, it is possible they may been miss-labeled during the rebuild, causing you to place coils A & B in series, as in a 480V connection (normal amps), and C coils in parallel, as in a 240V connection. Or Jack could be correct, one or both are installed in the opposite direction. Take it back or get the shop to bring a motor analyzer to the site, which ever is easier.

I suspect that Spark Chaser is on the right track. This sounds like that one or more coils are reversed in polarity. If the wiring was changed inside the motor I would check this real close. The other option that I have seen is several loops of a set of coils being shorted.

If the motor has ever been repaired because it blew a hole in the rotor, it will always run hot as laminations were damaged. Make sure your check voltage at the motor and NOT the starter! I'm also assuming that you've checked connections for tightness. I'm also assuming you have ground detector lights or some sort of continuous insulation monitor. If your using a soft start, insure that the bypass contactor kicks in and that your not running below rated rpm. I don't really know why you mentioned that it was a 12 lead machine unless you suspect someone connected it wrong! That'll do it every time!