Explainer video · TEMISA

Impulse (surge) test on form-wound coils: turn insulation and IEEE 522

Short answer

The impulse test checks turn insulation in a new form-wound coil, which a megger can't see. Each coil has several turns separated by very thin tapes. IEEE 522 calls for an impulse of 3.5 times the phase-to-ground peak voltage on each new coil, before it goes into the stator. Testing the loose coil doesn't replace testing the complete winding.

Key points

The weak point of a new coil is turn insulation, not copper.
Damage between turns can't be seen.
IEEE 522: 3.5 times phase-to-ground peak voltage per new coil.
The impulse finds weak spots before the coil goes into the stator.
Coil tests don't replace the complete winding test.

Transcript

Why isn't a new coil for a medium voltage motor any good until you test it? It's not the copper, it's the turn insulation. Each form-wound coil has several turns separated by very thin tapes, and damage there can't be seen. Like a new tire with a hidden defect: it looks perfect until you load it on the highway. IEEE 522 calls for applying each new coil an impulse of 3.5 times its phase-to-ground peak voltage. If there's a weak spot, the impulse finds it before it goes into the stator. But careful, testing the loose coil doesn't replace testing the complete winding. So it's not trusting, it's testing every coil. Does your repair include an impulse test? Comment IMPULSE and we'll tell you what to check.

Frequently asked questions

Why isn't a megger enough?

It measures conductors to ground; a fault between turns of the same coil doesn't show.

What level does IEEE 522 call for?

For new coils, 3.5 times the machine's phase-to-ground peak voltage.

Does TEMISA make and test form-wound coils?

Yes, at the Tlajomulco shop. Email ventas@temisa.mx.

Video with images and narration generated with AI.

See the service: Medium-voltage motor repair

Request a quotation by email: ventas@temisa.mx. Phone: +52 33 3614 2460.