Cyndi Nyberg
Former EASA Technical Support Specialist

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. 

For this article, we will only focus on three-phase windings. The surge test is typically run by applying a high voltage across each of two phases of a three-phase motor. The decaying resonance patterns of the two phases are superimposed upon one another on an oscilloscope. If the two phases are identical, as they should be, then the patterns will be identical. A perfect match will yield only one apparent pattern (Figure 1a) while a variance or difference, as shown in Figure 1b, represents an apparent problem. Testing continues until all phases have been compared to one another – 1 to 2, 2 to 3 and 3 to 1. 

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