Abstract :
Measurements of the properties of a number of the condenser parts of 132 kV bushings which have been in service for 20¿25 years have been made in the laboratory. Destructive examination of bushings with characteristics typical of clearly defined groups has been carried out. This has enabled particular power-factor/voltage and capacitance characteristics to be associated with definite defects, provided that either the original characteristics are known or a sufficiently large sample of bushings of the particular type has been tested to permit these properties to be inferred. The measurements have been extended to the field, the various difficulties encountered being discussed. It is shown that the properties of the other bushing components and fittings such as porcelain weathershed, arc shield, oil and breaker parts affect the measured properties to the extent that minor defects cannot be diagnosed as they can be on tests carried out on the condensers alone in the laboratory. A technique which permits the detection of major defects by nondestructive tests on installed bushings is described. These methods have been applied to over 1600 132kV oil-circuit-breaker bushings, with the result that approximately 4% defective bushings have been removed from service and another 3% classified as being in doubtful condition.
