Effect of High Harmonic Voltage on Long-term Dielectric Properties of Crosslinked Polyethylene Insulated Cable

In the superconducting MAGLEV system using a linear synchronous motor (LSM), the power converter for driving LSM is installed above ground. As one useful power converter, a PWM (pulse width modulation) inverter has been developed. The output voltage of the PWM inverter contains much harmonics caused by the PWM controller. Crosslinked polyethylene insulated cable (CV cable) has been adopted as a feeder cable for the MAGLEV power supply system, and accordingly the voltage with much harmonics, which is produced by the PWM inverter, loads on the CV cable.The dielectric strength of CV cable under the voltage with much harmonics, which has never been reported so far, has come to be recognized as a very important issue in the development of MAGLEV. The authors have examined the output voltage waveform of PWM inverter and have found that it can be simulated by an AC voltage of commercial frequency upon which high frequency AC voltage is superimposed. Using a special generator capable of generating this particular voltage, the harmonic-superimposed voltage for long-term aging test has applied to CV cables and the dielectric properties of the cables have been investigated.