Overvoltage Protection and Maintenance Testing of A-C Rotating Machines

Rotating machines supplied directly from utility distribution systems are subjected to various overvoltages. Depending on the power system in question, these overvoltages may or may not be hazardous to machine insulation. The magnitude of the overvoltages, whether of internal or external origin, can be limited by the protective devices commonly used for machine protection. An operator must satisfy himself, however, that the insulation in question has sufficient strength to be protected by these devices. This determination of insulation strength is readily accomplished by means of nondestructive direct high-voltage tests. How these tests are made has been discussed in considerable detail for the bene fit of those contemplating the incorporation of such tests in a preventive maintenance program.