Excerpt from
http://www.skf.com/files/690979.pdf
As well if you type Surge test theory for motors you will come up with a bunch of info...just have to weed through till you find what you need...
4. Surge Test
A Surge test is performed of each phase of the motor, again using an appropriate test
voltage based on the operating voltage of the machine and the appropriate
standards/company guidelines. Look for a jump to the left of the surge waveform pattern.
This is the signature of the turn – to – turn short. If a jump is observed, an inspection of
the motor should be made to look for damaged insulation between adjacent conductors.
The insulation may be hard to see visibly, so the motor may have to be disassembled to
find the problem. If no jump in the wave patterns is observed, the likelihood of motor
failure due to insulation failure is greatly reduced.
