Udo Fromm

Solid insulation covering of conductors improves air insulation systems

In laboratory set-ups, polymer covering of the electrodes has resulted in the reduction of the insulating distances by a factor two. One of the problems with covered conductors is however that of creeping discharges on the surface of the covering. The aim of this work was to investigate how creeping discharges develop under lightning impulse (1.2/50 /spl mu/s) on two covered conductors at a 90-degree angle to each other. Furthermore, the aim was to investigate how to stop the propagation of a creeping discharge. This was achieved by inserting at least one cable termination, e.g. the type of termination used for high voltage cables, into the discharge path. The experiments showed that a set-up with two crossing cables can withstand very high voltages without any shed or termination of the creeping discharges. Further tests show a considerable increase of the breakdown voltage in other arrangements comprising covered electrodes. This was accomplished by using two cable terminations at each cable end to stop the propagation of creeping discharges.

Termination of Creeping Discharges on a Covered Conductor

Under laboratory conditions, a polymer covering of electrodes has resulted in a reduction of the insulating distances, under impulse stress, by a factor of two. One problem is creeping discharges on the surface of the covering.

Polymer/air interface space charge determined by a pressure wave propagation technique

The application of high DC voltage to a polymer/air insulation system can result in space charges on the interface. The space charges can cause significant distortions of the electric field distribution, which may trigger a surface flashover or breakdown in the insulation system. In the present investigation, an attempt has been made to measure the space charge on a polyester/air and PTFE/air interface by using a pressure wave propagation technique (PWP) under DC voltage.