Evgeni Volpov and Anatoly Shkolnik
Off-line partial discharge diagnostic tests, dielectric dissipationfactor, Tan (delta), phase-resolved pattern, pulse-height histogram, partial discharge inception voltage
The paper presents some results of off-line partial discharge (PD) tests, which were conducted on stator windings of 3.2-kV, 6.6-kV, and 11.5-kV rated motors. The primary goal of the study was to examine a relationship between a motor’s rated voltage and its PD activity concerning the machine operating period. By implementing a simultaneous PD and dielectric dissipation factor (DDF) measuring technique, some important stator insulation problems and defects were diagnosed. Typical and most representative phase-resolved PD patterns were analysed in view of their connection with Tan (delta) and Volt-Coulomb trends. The obtained data clearly indicate that appreciable or even significant partial discharges indeed do occur in stator insulation. These concerns not only motors rated 6.6-kV and above, but also motors rated 3.2-kV (the latter are, normally, not recommended for PD testing, because of their low-operating voltage). It is shown that the reasons for this lie in the specificity of the stator insulation defects, but do not relate to the machine-rated voltage. Thus, the decision regarding PD diagnostic tests should be made by considering motor availability requirements and cost savings, but not its rated voltage.
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