In the April 2007 issue of CURRENTS, we covered surge testing anomalies, specifically for AC windings. The surge test can be used for DC windings as well. It can be a useful tool for evaluating armatures and some DC fields. A note of caution: If a winding does not have a minimum insulation resistance per ANSI/EASA AR100-2006, it is not safe to apply an overpotential test (surge or high potential). Surge testing shunt fields may not provide meaningful results if the surge pulse decays too quickly - if it dissipates through only the first few hundred turns. To obtain a test voltage high enough to test every turn would require too high a voltage. That high voltage would overstress the groundwall insulation.

The surge test is used to detect winding faults in AC and DC windings. If there is a turn-to-turn short, the surge test will show that. The surge test is an important step in the initial inspection of a machine, as well as a final test to ensure a proper rewind.