Dielectric breakdown properties of low-density polyethylene under power-frequency voltages with high-frequency components

For magnetic levitation railway systems using linear synchronous motors, pulse-width-modulation inverters and polymer insulated cables are used for driving cars and feeding electricity, respectively. This implies that ac voltages with many harmonics induced by inverters are applied to cables. However, little is known about dielectric properties of polymers under such ac voltages. Therefore, breakdown characteristics have been investigated for low-density polyethylene using power-frequency ac voltages with high-frequency components. It was found that breakdown voltage decreases as the frequency component increases. However, the number of zero-crossings of the applied voltage, which is very influential in the water-tree length, does not seem to play an important role in the dielectric breakdown.