PI test on Y-Delta motors

[testtech]

A client wants polarization index testing done on 18 motors that use Wye Delta starters. When the motor is off, the phases are not interconnected. Thus, ordinarily, each phase of the motor would be tested to ground individually. This is time consuming. I propose to place jumpers on the starters as follow: T1-T6, T2-T4 and T3-T5. I believe this will give me a delta motor configuration so that I can test all three phases to ground at once, as with a normal delta wound motor. Does anyone see a problem with this approach?

 

[busbar]

An approach may be to conduct the test with windings jumpered, but if a low result is obtained, split the coils and retest individually. On the North American continent, many motors are internally connected and so tested.

 

[Dopler]

The connection that will result is delta, the procedure of PI will indicate if the motor is in good or bad condition.

 

[aolalde]

If you want to test only the motor winding insulation you have to disconnect the motor from the starter switchgear, other way you will test the whole system motor-starter.

The connection you are providing is for delta connection. A general condition of the insulation to ground will be analyzed.

Individual test of the phases will give information of ground and the phase to phase insulation condition.

 

[testtech]

Thanks to you all for your input.

Aolalde: The test will be conducted from load side of the contactors, which, of course will be open during the test. Thus the starters will be out of the circuit.

 

[jbartos]

Suggestion: Adhere to some industry standards, e.g.
2003 NETA Acceptance Testing Specifications
7. INSPECTION AND TEST PROCEDURES
7.15.1 Rotating Machinery, AC Motors and Generators
Section:
2.1 Electrical Tests – AC Induction Motors and Generators

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