Review of Partial Discharge and Dielectric Loss Tests for Hydropower Generator Bars

Abstract

Condition assessment of hydropower generators is important to ensure high serviceability of power stations. Many of the in-service generators are old and current load operation schemes demands more than the design load, which makes the remaining lifetime of the generators uncertain. The reviewed literature shows many works regarding identifying signature PRPDA patterns for different relevant defects in the generator. Calibration is however impossible, due to variable signal propagation in the generator from the partial discharge source. The results regarding complex permittivity as function of frequency as a measure on water ingress are promising. However, the field grading paint at the ends of the bars are affected by the low frequency and gives a variable capacitance. The literature is still focused on qualitative measurements without giving quantitative answers.