W. Bretuj

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 non-ceramic insulators' shed inclination on their long-term behaviour in cyclic rain and fog conditions

The paper presents the results of comparative tests of model composite insulators with housings made of HTV silicon rubber and sheds inclined at different angles (0deg, 10deg, 30deg). The main aim of the tests was to acquire experimental data for an assessment of the effect of the shed inclintion angle on the ageing degradation of composite insulators under high voltage in rain and fog conditions. The insulators were exposed to AC (50 Hz) voltage and water precipitation in a rain chamber and in a fog chamber. The tests showed clear differences in ageing times between insulators, leading to increased leakage current and surface electric discharges. It was found that the insulators with a large shed inclination angle (30deg) have a higher ageing resistance, particularly in rain conditions.

Influence of composite insulator operating position on the development of aging process under AC high voltage and water precipitation

Results of ageing tests of model composite insulators in rain and fog chambers are presented. The influence of different operating positions of the insulators: vertical, inclined and horizontal, on the development of leakage currents on their surfaces during the leakage tests is discussed. An important role of sheds inclination of the insulators in the leakage currents restriction is emphasized.

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.

Capacitance changes in degraded metal oxide varistors

ZnO based ceramics show a highly nonlinear current-voltage (I-V) characteristic due to intergranular layers at the boundaries of ZnO grains. This research indicates that the junctions formed on the border between ZnO grains and the intergranular phase are responsible for the creation of potential barriers which control the flow of current through the bulk of such a ceramic. Having polycrystalline nature and a large number of intergranular barriers, and so a high energy absorption capability, ZnO ceramics are used as active components in overvoltage protection devices. However, as a result of charge transport the height of the barriers decreases and varistor degradation occurs. The degradation seems to affect mainly the prebreakdown region of the I-V curve and it results in increased leakage current. This paper presents a part of research aimed at assessing the effect of ageing on the capacitance characteristic of ZnO varistors.

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.