On-line PD detection, requirements for practical use

Because the energy market liberalisation forces utilities to cut costs, delayed replacement and smaller maintenance budgets have become goals for many utilities. Competing with this demand is the increased risk of liability for unexpected nondelivered energy. These two forces have stimulated research into the field of onsite and online diagnosis in order to determine the condition of a transformer at the least possible cost. One of the fields that has attracted attention is partial discharge measurements, as they are seen as a good indicator for local defects and incipient failure caused by such. This paper describes two onsite partial discharge methods that both use frequency information to to deal with noise and enable online measurements. One method uses VHF frequencies, the other uses UHF frequencies. Based on this comparison, a questionnaire was sent to several Dutch utilities asking them to specify how the see the relevance of partial discharge measurements and how they would implement it. The paper presents the conclusions from this questionnaire and the direction of development desired by the utilities.