Influence of High Frequency Stress of Waveforms on Life of Polymeric Enamel Insulation

Insulation breakdown in electrical motors has been observed in recent years as a result of adjustable speed drives driven by power electronic converters. These converters generate impulse waveforms with a high slew rate as a result of IGBTs' high switching frequencies. This paper focuses on high switching frequency stress in low voltage electrical motors for adjustable speeds. To examine the motor winding insulation under such stress twisted-pair samples were developed from enameled wires. A single- coated Polyester of enamel with a thickness of 40 microns is used for this work. The test results show that the insulation fails earlier for the square waveform compared to the square- spike and square-rising waveforms. In this paper the Weibull distribution and the shape parameter is analyzed for life of enamel insulation at high-frequencies, high voltages of square, and square-rising, square-spike waveforms of 10 to 30kHz.