Large-Motor High-Voltage Insulation Systems Testing: Qualification and Acceptance for the Petrochemical Industry

The insulation system of a large, high-voltage (HV) industrial motor stator winding experiences various and significant stresses while in service. Motor manufacturers are responsible for designing and executing detailed test programs that ensure the proven reliability of an insulation system before its use in production. Qualification programs are designed to certify whether an insulation system is designed well enough to sufficiently handle its anticipated usage stress. These programs typically employ a rigorous series of tests for 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 nondestructive yet still apply sufficient stress to ensure that its insulation system has been manufactured per the design. This article describes the typical insulation system components used for a multiturn form-wound coil design and the stresses that various parts of the system will face while in service. A recommended qualification plan is presented using industry-standard test methods to evaluate the long-term reliability of a vacuum pressure impregnated (VPI) insulation system under sinusoidal-voltage supply. It describes the diagnostic and withstand electrical tests for routine and special acceptance tests, especially those employed for petrochemical industry, where data may be used to establish a baseline condition assessment that is unique to the machine.