High Voltage Square Wave Generator for Motor Coil Insulation Testing

Applications of solid state driver for medium or high voltage motor are widespread. However, due to high switching frequency as well as high dV/dt, increased dielectric stresses and thermal stresses are applied on the insulation system; thus leading to the insulation failure of the motor. In order to test the insulation performance of the motor under the above stress conditions, a motor insulation testing facility which can generate high voltage and high frequency square waveform is developed. In the paper, low voltage solid state switches are used to generate high voltage square wave. The generator consists of several cascaded stages and each stage is made of IGBT stacks, capacitor, and wave shaping resistors. With specially designed charging and discharging circuits, each stage can generate square wave independently. Several stages can be cascaded to generate higher output voltage; the rise time can be as short as 200 ns, and the pulse width can be up to several milliseconds. Cascade connection methods are discussed and experimental results are presented in the paper. It has been shown that the cascade connection can make it possible to generate high voltage output by using low voltage solid state switches without any problem related to voltage division and synchronism of the cascaded stages.