J. Fleszyński

Effect of shape of insulator housings and positions of composite insulators on ageing resistance under high voltage and precipitation

This paper outlines the results of investigations on the ageing deterioration of model composite insulators where the slope angles of their sheds equal 0, 10 and 30 degrees. It also describes how their vertical, horizontal and oblique working positions affect the manner of their surfaces moistening under conditions of simulated rain and fog water precipitation. It is demonstrated that how the surfaces of insulator sheds are moistened substantially affects time-dependant variations in leakage currents and the energy of electric discharges on the insulator surfaces. Proof is provided that deviations of insulators from their vertical working positions towards the horizontal lead to a growth in leakage currents of insulators. It was also found out that a steeper slope angle of the insulator shed substantially improves the ageing resistance of the devices operated at various working positions under conditions of high voltage and rainwater or fog precipitation.

Influence of composite insulator inclination on its properties degradation in rain conditions

Results of ageing tests of composite insulators exposed to AC (50 Hz) high voltage and cyclic water precipitation in a rain chamber were presented. The subject of the investigation were composite insulators destined for 20 kV rated voltage with their housings made of HTV silicon rubber. The insulators were tested in horizontal, vertical and inclined position. During the tests, the leakage currents were recorded and surface hydrophobicity was estimated. Photo and video registration of the behavior of water drops on the tested surfaces were made. The following phenomena were described: non-uniform loss of insulator surface properties, merging of water drops which caused creation of conduction current paths, development of surface electric discharges. Essential influence of insulator operating position on the way of its surface wetting during rainfall and development of ageing process was described.

Steep-front impulse voltage in diagnostic studies of composite insulators

Laboratory studies of composite insulators by means of steep-front impulse voltage tests are presented. The tests were performed on four groups of insulators, i.e. on newly manufactured insulators, on insulators removed from service, on insulators earlier exposed to mechanical fatigue test and on insulators with intentionally introduced technological defects. Extensive results of these investigations indicate that application of steep-front impulses of 4 kV/ns provides a better diagnostic efficiency as compared with the standard testing by means of impulses with steepness of 1 kV/ns. It is shown that the application of 4 kV/ns impulses do not cause any damage to healthy insulators, while defected insulators are identified reliably. A new methodology allowing to assess the status of internal insulation in insulators removed from service is proposed based on the performed studies.

Test method of composite insulators aged in high voltage rain chamber

Rainfall can be a dangerous hazard for outdoor composite insulators. In the paper, a laboratory method of testing of ageing resistance of aerial composite insulators exposed to high voltage and water, simulating heavy rainfall, is presented. The method is illustrated by the results which show the impact of shed profile of the composite insulator with the housing made from silicone rubber on their aging resistance.