On-Line Continuous Partial Discharge (PD) measurements of medium voltage substations are an excellent way to determine the overall health of the equipment. Partial discharge measurements can provide maintenance alerts to allow scheduling of equipment outages based on actual condition data as opposed to scheduling based on time intervals. PD measurements provide information about the insulation system that is impossible to extract with other methods. Remote monitoring adds additional value to continuous monitoring by relieving customers of the burden of data analysis, readily involving remote experts. This paper discusses the effectiveness of PD measurements using multiple sensors. Multiple sensors provide additional noise reduction and the ability to localize PD activity for measurements made in higher frequency bands. The importance of continuous PD monitoring vs. periodic walk in PD measurements for switchgear is also discussed. PD activity in switchgear can be unstable and dependent on ambient conditions. Negative periodic PD tests in switchgear can result in a false sense of security. Case studies from field experience are presented to support the discussions.
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