Voltage endurance testing

The medium-voltage ASD stator insulation systems operate under greater stress than those using the sine-wave power. The repetitive short rise-time pulses generated by most ASDs cause an additional stress. The pulses are often increased by the effect of the cable between the ASD and motor. It is incumbent on the user and ASD manufacturer to account for the magnitude, rate of rise, and repetition rate of these pulses. The medium-voltage machines powered by ASDs operate with some level of PD. The machine manufacturer must ensure that the insulation system will provide adequate life in the PD environment. VE testing is a well-understood and accepted method to qualify insulation systems. It is a reliable means to compare new insulation systems with the documented existing ones. The TS describes several qualification procedures based on the knowledge of the converter waveform. These will assure that all parts of the machine insulation system will present acceptable test life.