Surge Testing

Surge testing is not the only test that can detect weakened insulation between phases or coils in a connected winding. IEEE 43-2000 is the standard that applies to insulation testing in the field at industrial plants. The guideline it provides is for DC voltages at or below nameplate voltage (ref Table 1 in the standard). Surge testing is not considered an optimal technology for regular testing to be applied in the field on in service motors for several reasons: Danger to personnel; potential damage to the motor; and conditions required for surge testing are rarely valid in the field. Anyone involved in the condition assessment of insulation on motors in the field, is encouraged to carefully read IEEE 43-2000. It is frequently mis-quoted.

IEEE 43 covers only the recommended practice for insulation resistance testing. IR is an excellent test for detecting certain issues with aging, moisture and surface contamination. But, it is not the only recommended field test for insulation. IR can not detect weak ground, phase and turn insulation in every case. The more rigorous hipot, surge and PD tests are also necessary to properly test an insulation system. These tests are routinely used to test insulation systems in motors, transformers, cables, etc. in the factory and in the field.

The recommended standard practice is to start with the least stressful tests (winding resistance, inductance and capacitance). If these tests pass, next perform the IR and PI tests. If these tests pass, then perform the most rigorous tests (hipot, partial discharge and surge tests). If all these tests pass, only then can you have high confidence in the integrity of an insulation system.

The surge test works very well in the field. It is not dangerous to personnel. And it does not damage motors with a good insulation systems.

I personally have used the hipot and surge tests to identify motors with failed insulation systems immediately after a PdMA tester said it was okay. In my experience, 10-20% of insulation failures will go undetected if the hipot and surge tests are not performed.

When I test for a customer, I honestly explain the benefits and the risks of using the over voltage tests and let the customer decide which combination of tests we should perform. This is a better approach then to tell the customer that the over voltage tests should never be performed. Most of my customers decide that we should conduct the over voltage tests. And when we find a problem, they are glad we found it.