Controlled Overvoltage DC Testing as a Diagnostic Tool for Low-Voltage Three-Phase Motors: A Case Study

Procedures for continuous high-voltage testing for stators rated at 2.3kV or higher are outlined in IEEE Std 95; however, there is no equivalent standard for testing low-voltage machines, especially for field testing. Nevertheless, multiple maintenance departments implement controlled overvoltage DC tests as a tool to detect defects in the groundwall insulation system of low-voltage motors and to evaluate the effects of various aging mechanisms that occur during normal operation. This article presents a case study demonstrating that, for low-voltage motors, the controlled overvoltage DC test is an excellent tool for detecting insulation defects that will inevitably lead to ground faults.