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液氮和氦气固体绝缘子表面的闪过电压。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容。气泡是由于放电电压低于火花放电电压而产生的。然而，实验和计算证实，气泡不影响火花过电压。在不同电压波形下，测量了几种绝缘子的闪过电压与间隙长度的关系，结果均在6cm以下。火花过电压随间隙长度的增加而略有增加。静电电容较大的绝缘子的火花过电压要低于静电电容较小的绝缘子的火花过电压。液氦中的火花过电压比液氮中的低，且受静电电容的影响更大。表面火花过电压与电容之间的关系可以用每个外加电压波形的实验方程来表示。在给定介电常数和绝缘子厚度的情况下，由方程可以估计出绝缘子的火花过电压。

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.