high current draw on low speed start

[randy1948]

A newly rewound 2 speed ac motor with a single winding has a 40 amp draw at start. The high speed has 12 amps and settles back to 5.2. The rewinder took it back and checked it over claiming it is OK. what else should I be looking at or for? Using 208v. and 3 phase power. The system has a manual switch to change the speed on the fly. I have disconnected it for now and am making the connections directly until the issue is sorted out.does the connection of the line to windings become critical for phase? IE: L1 has to be connected to winding 1? etc. I am not sure if the 120 degree phase can be fighting itself?
Thanks

 

[bigbillnky]

Randy
I will try and help as much as I can, but I need more information. Nameplate HP, RPM, voltage, and amps. Is it true 2 speed, or is it wye start-delta run?

Bigbillnky,C.E.F.....(Chief Electrical Flunky)

 

[Marke]

Hello randy1948

Most two speed motors that I have been involved with have a higher power rating at high speed than at low speed. I would expect that the start current at high speed would be higher than at low speed. I think you are correct to question this.

As bigbillnky suggests, more information on the motor ratings connetions etc may shed some light on the subject.

How are you measuring the start current? becarful not to be caught out by the reaction times of the metering.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[aolalde]

One Winding dual speed motors can be:

A- CONSTANT TORQUE (common). Low speed is Delta 1, high speed Wye 2. The HP at low speed is half of those at high speed and the inrush current follows the HP’s. (Higher amps at high speed).

B- VARIABLE TORQUE. Low speed is Wye 1, high speed Wye 2. The HP at low speed is one quart of those at high speed and the inrush current follows the HP’s. (Higher amps at high speed).

C- CONSTANT POWER. Low speed is Wye 2, high speed Delta 1. The HP at low speed are same as those at high speed and the inrush and full load currents are regularly higher for the low speed due to a very low power factor (PF).

Again, you should provide the Name Plate Data to have a better answer.