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Surge Test
A Surge test is performed on each phase of the motor, using a test voltage based on the motor's operating voltage
and the appropriate standards/company guidelines.
Look for a jump to the left of the surge waveform pattern; this is the signature of a turn-to-turn short. If a jump is
observed, inspect the motor. Look for damaged insulation between adjacent conductors.
The insulation might be hard to see, so you might have to disassemble the motor to find the problem. If you do not
observe a jump in the wave patterns, the likelihood of motor failure due to turn insulation failure is greatly reduced.
Recommended Test Voltages for Insulation Resistance Testing
The following table provides guidelines for DC voltage applied during insulation resistance test. Test voltage should
be applied for one minute. (See IEEE 43, sections 5.4 and 12.2.)
Winding Rated Voltage (V)
< 1000
1000–2500
2501–5000
5001–12,000
> 12,000
a Rated line-to-line voltage for 3-phase AC machines, line-to-ground for single-phase machines, and rated direct
voltage for DC machines or field windings.
Recommended Test Voltages for HiPot and Surge Tests
The general recommended voltages for HiPot and Surge testing a motor, generator, or transformer are twice the
nominal rated line voltage (from nameplate; represented as v below) plus 1000 volts.
2 x v + 1000 volts = test voltage
This test voltage is consistent with NEMA MG-1, IEEE 95-1977 (for test voltage greater than 5000 volts), and IEEE 43-
2000 (test voltages less than 5000 volts).
For example, the test voltage for a 480-volt AC motor would be:
2 x 480V + 1000V= 920 + 1000 = 1960 V
Likewise, the test voltage for a 4160-volt AC motor would be:
2 x 4160V +1000V = 8320 + 1000 = 9320 V
For new windings or rewound motors, the test voltage is sometimes increased by a factor of 1.2 or even 1.7. This
provides for a higher level of quality control on the work performed. For example, for the 480-volt motor, the test
voltage would be:
1960V * 1.2 = 2352V
Or
1960 * 1.7 = 3332V
For additional information on recommended test voltages, refer to "Appendix C—Recommended Test Voltages."
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Insulation Resistance Test Direct Voltage (V)
a
Test Procedures
500
500–1000
1000–2500
2500–5000
5000–10,000
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