Characteristics of surface spark-over voltage for several waveforms on solid insulators in cryogenic coolants

The surface spark-over voltages on solid insulators in liquid nitrogen and helium are studied under alternating current voltage of 50 Hz, direct current voltage and impulse voltage. The insulator structure used in experimental studies is a model of a power cable end. In the structure, static capacitance is formed between outer surface and inner conductor of insulator. The spark-over voltages for several insulators were measured versus gap length, below 6 cm, under different voltage waveforms. The spark-over voltages increase slightly with increase of gap length. The spark-over voltage for the insulator with the larger static capacitance is lower than that with the smaller capacitance. The relation between the surface spark-over voltage and the capacitance can be expressed by an experimental equation for each of the applied voltage waveforms.