Electric Motors/old GE motor

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Question
I have an old GE motor that will not start under load.

Model 44417
TYPE KT 740-4-3
Form C
3ph  3hp
220 volts
no. 3975125

circa 1920

The motor has four un-marked leads.
No diagram on motor.
It will run with one lead to neutral.
Direction will change when two specific (not any two) leads are reversed.

The windings were inspected by motor shop for additional leads or evidence of manipulation which were not found.

Video of motor running:
http://www.youtube.com/watch?v=oYy7kX4V8pQ

Any help on this would be great.

Thank you,

Don

Answer
The motor shop would have done a surge comparison test to identify which 3 leads are the phase ends, and which lead is the neutral coming from the internal star point.

Do not connect the neutral ie star point lead to anything. Cap it off.
Supply 3 phases into the 3 phases. motor should run.
Check the voltage per phase and current per phase. Should be all the same readings per phase.

It seems like one phase is open circuit from the lead, thats why when power is suppled from the neutral it runs.

I would first identify which lead is the neutral.
Then tape it off.
Test the 3 phase winding by supplying low voltage per line and measure current draw. It should be all balanced.
Otherwise the winding is either open circuit or shorted.

Electric Motors

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Harcharan Singh Diocee

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Electric motor winding redesign, AC and DC. Troubleshooting, motors controls generators. Vibration analysis, dynamic balancing, root cause analysis: electrical and mechanical.

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thirty five years electro-mechanical and Senior Management

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Journeyman Motor Rewinder, Millwright, Industrial Electrician, Vibration Analyst level II. Certified Electrical Technician ASTTBC, FSR Class B, in BC. Laser alignment specialist. Marine machinery repairs. Business Management Certificate. Last 19 yrs as Plant Manager

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