Study on Construction of a Electrical Discharge Model for Developing Optimum Insulation Design of Compact UHV Transmission Line

为了实现超高压输电系统绝缘设计的高可靠性，需要建立一个能够预测绝缘强度的放电发展模型。要建立这样一个模型，必须对放电的发展进行精确的观察。利用激光诱导等离子体控制放电的起始和路径，成功地研究了影响放电发展的一些因素。由于放电发展主要受电场控制，因此研制了一种用于测量放电空间电场的Pockels传感器。将一束3.5J的CO2激光束传输到直流电应力下的棒面间隙中。放电的触发效应和导向效应通常是同时观察到的。放电的发生是由激光的照射触发的，随后它的路径沿着激光诱导等离子体被引导。结果表明，等离子体的存在降低了间隙的击穿电压。在本研究中，只有在施加较低的正电压到棒电极的情况下才观察到触发效应。放电路径并不沿着激光诱导等离子体。激光照射到间隙击穿之间的延迟时间从几百μ m到几μ m不等。通过对电场的测量发现，在激光诱导等离子体的正极侧出现了负电荷，并增强了等离子体附近的电场。激光诱导等离子体中产生的负离子漂移可引起触发效应。

A model of electrical discharge development by which electrical insulation strength can be predicted is required for realizing a high reliability of insulation design of a compact UHV transmission line system expected as a future promising system. To make such a model, the precise observation of the discharge development is strongly needed. Some factors affecting the discharge development was examined successfully by using a laser induced plasma which can control the initiation and the path of the discharge. A Pockels sensor was developed and used to measure electric field in the discharge space because the discharge development was controlled mainly by the electric field.A 3.5J CO2 laser beam was transmitted into a rod-to-plane gap which was dc electrically stressed. Trigger and guide effects of the discharge were usually observed simultaneously. The occurrence of the discharge was triggered by the irradiation of the laser and subsequently the path of it was guided along the laser induced plasma. It was found that the breakdown voltage of the gap was decreased by the existence of the plasma.In this study, only the trigger effect was observed under such a condition that a relatively low positive voltage was applied to the rod electrode. The discharge path did not lie along the laser induced plasma. The delay time between the irradiation of laser and the breakdown of a gap varied from several hundreds mus to several ms. From the measurement of the electric field it was found that negative charge appeared at the positive polarity side of the laser induced plasma and enhanced the electric field near the plasma. The trigger effect can be caused due to the drift of negative ions produced in the laser induced plasma.