Fundamental study of electrical insulations for superconduucting power system apparatuses

研究了50Hz交流电压、直流电压和冲击电压下固体绝缘子在液氮和氦气中的表面放电电压。实验研究中使用的绝缘子结构是电力电缆端部的模型。在该结构中，绝缘体的外表面与内导体之间形成静电电容。由于在比火花放电电压低的电压下放电而产生串音。然而，实验和计算证实，气泡不影响火花放电电压。测量了几种绝缘子在不同电压波形下的放电电压随间隙长度（小于6cm）的变化。火花放电电压随间隙长度的增加略有增加。具有较大静电电容的绝缘子的放电电压低于具有较小静电电容的绝缘子。液氦中的放电电压比液氮中的放电电压低，静电电容对放电电压的影响更大。表面火花放电电压与电容之间的关系可以由每个施加电压波形的实验方程表示。对于给定介电常数和绝缘子厚度的绝缘子，可由该方程估算其火花放电电压。

The surface spark-over voltages on solid insulators in liquid nitrogen and helium were studied under alternating current voltage of 50Hz, 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. Babbles are generated due to discharge at a lower voltage than that of spark-over. However, it was experimentally and computationally confirmed that the bubbles do not influence the spark-over voltage. The spark-over voltages for several insulators were measured versus gap length, below 6cm, under different voltage waveform. The spark-over voltages increase slightly with increase of gap length. The spark-over voltage for the insulator with the larger static caacitance is lower than that with the smaller capacitance. The spark-over voltage in in liquid helium is lower than that in liquid nitrogen and more largely influenced by the static capacitance. The relation between the surface spark-over voltage and the capacitance can by expressed by an experimental equation for each of applied voltage waveforms. The spark-over voltage for insulator, whose permittivity and thickness are given, can be estimated from the equation.