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The competitive environment recently created by free market electricity supply requires that electric utilities reduce capital and operating expenses and, at the same time, increase the overall quality of electricity. Underground distribution cable systems are particularly sensitive to this need, which can be effectively addressed by in-situ diagnostic tests. This paper discusses one such diagnostic method based on thelocation ofdiscrete partial discharge sites. The paper briefly reviews the conditions under which a cable service wou& produce partial discharges. It illustrates the fact that, although cable syskms undergo some overall deterioration, service failures occur at the sites of discrete defects, which in most instances can be identified by a partial discharge test. The principles of the test are reviewed and statistical data with significant case studies are presented. The effects of maximum test voltage and instrument sensitivity are discussed in the light ofstatistical field test data.

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