Failure of equipment in a substation can lead to serious consequences resulting in unscheduled downtimes and potential loss of revenue. Maintenance testing can be carried out on equipment during scheduled outages taken at regular intervals of time. It is also important, however, to keep track of the equipment condition during operation by monitoring certain parameters based on the type of equipment. One parameter that can be monitored on a lot of electrical components is partial discharge activity. The term "partial discharge" refers to low energy discharges which occur in a dielectric. These discharges don't completely break down the dielectric and hence are called partial discharges. Partial discharge is not indicative of failure, but continuous PD activity deteriorates the insulation condition thereby, reducing the reliability of the electrical component and increasing the risk of equipment failure. Hence, online partial discharge testing can serve as a very important part of a predictive maintenance program. This paper dwells on how online PD testing can serve as an important tool in detecting and tracking deterioration in equipment insulation. This paper looks at the theory of partial discharge and covers the various sensing techniques that are used to detect online partial discharge. Sample PD plots obtained from lab measurements corresponding to different types of partial discharge have been shared in this paper. Some case studies have also been included to highlight the importance of online partial discharge testing.
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