Transformers and Impulse Testing

If well designed, just verify the air gap at critical points don´t change due to coils treatment. The main cause of failure in impulse testing is a wrong air gap by deformations while coils are in the oven.

Kind regards

what air gaps are u talking about?

As some other colleagues have pointed out, impulse testing (lightning type is the hardest one) consist in applying a high voltage impulse to the windings. The most possible failure is arcing between conductors/earth due to dielectric weakness.

Even in the case of oil filled transformers, previously to close the head and pouring the oil. is very important to control the shortest distances (air gaps) in which arcing may occur.

I've witnessed some failures in impulse testing in high power transformers (hundreds MW) and all have been because of that.

Kind regards

Transformer impulse test, is to inject certain limit of high voltage in to the transformer winding and to ensure that the transformer winding can withstand the impulse voltage.

Unless, if you are a transformer tester and you know what to test and what to expect after the test is completed, otherwise, for us as a technician, we can only look at the print out graph and see if the test for the impulse is O.K. or not.

Just ask them what is the test voltage applied. You got to pretend that you know what they are doing.

This is a specialized test. There are standards for the test and the results. IEEE and a variety of engineering companies offer test methods and specs, to members. If your equipment is not passing, look to those organizations and what has been published. Doble Engineering is one such company, which primarily helps contracted member companies. I would have to know how your stuff is failing and then research the answer in the published record of 'papers'.

David