A Novel Breakdown Protection Circuit for Endurance Tests under Repetitive Impulsive Voltages

Different from conventional three-phase asynchronous motor working at sinusoidal voltages, the inverter-fed motors are stressed by high frequency semi-square wave voltages generated by inverters. Due to the over-voltages at the motor terminals and the voltage uneven distribution in winding, the electrical field in insulation may reach partial discharge inception voltage (PDIV) and PD will occur with high probability. For the insulation systems of Type II motors, whose insulation is composed of corona-resistance materials, moderate PD activities are allowed. The endurance (lifetime) tests, however, under repetitive impulsive voltages should be carried out to evaluate the insulation performance. One of the problems needed to be solved for the endurance tests at impulsive voltages is how to design a reliable breakdown protection circuit used to remove the samples (in several microseconds) from the whole system when breakdown occurs and record the endurance time. Conventional over-current hardware used under AC and DC voltages cannot be used anymore because the peak magnitude of the normal charging and discharging current at rising and falling flanks of impulsive voltages and the breakdown current are similar. This paper aims to report a novel breakdown protection circuit specially designed for the endurance tests at impulsive voltages. The current at impulsive voltages will be measured by HALL sensors and processed by FPGA in real time to distinguish the possible breakdown current from the normal charging-discharging current and responds to the generator in several micro-seconds when breakdown occurs.