Qualification and acceptance testing of large motor high voltage insulation systems for the petrochemical industry

The insulation system of a large high voltage industrial motor stator winding experiences various and significant stresses while in service. Motor manufacturers are responsible to design and execute detailed test programs to ensure the proven reliability of an insulation system before its use in production. Qualification programs are designed to prove an insulation system for its anticipated usage stress, and typically employ a rigorous series of tests of purpose-built samples, including system characterization, electrical breakdown, accelerated life tests and detailed laboratory analysis. In contrast, factory acceptance testing of a new rotating machine stator winding must be non-destructive but apply sufficient stress to assure that its insulation system has been manufactured per the design. This paper describes typical insulation system components used for a multi-turn form wound coil design, and the stresses that various parts of the system will face while in service. It presents a recommended qualification plan using industry-standard test methods to evaluate long-term reliability of a vacuum-pressure impregnated (VPI) insulation system under sinusoidal voltage supply. It describes the diagnostic- and withstand electrical tests for the “routine” and “special” acceptance tests, especially employed for petrochemical industry, where data may be used to establish a baseline condition assessment unique to the machine.