Partial discharge - A valuable stator winding evaluation tool

This paper has been prepared to illustrate the value of partial discharge (PD) testing in assessing the condition of stator windings on operating generators and motors. Because of the magnitude of the data base accumulated by one particular PD system vendor during the last 15-20 years, this data base was chosen for study. It was felt that sufficient data had been accumulated to allow useful statistical analysis of the capabilities of PD testing. No attempt is made in the paper to provide technical background or details of the PD test/analysis processes. There are numerous technical papers and industry guides; the interested reader is referred to IEEE 1434, EPRI Reports [7, 8], and other documents in the Bibliography. In particular, this present paper is based on information presented in more detail in Reference 13. This paper is based somewhat narrowly on data from only one company; however, there are several other companies involved in PD testing and evaluation. As described below in this paper, these companies have also been successful in identifying stator winding problems through the use of PD equipment. PD monitoring systems appear to be finding conditions of concern on about 6% of generators where the equipment is installed. Probably no other generator monitoring system exceeds this rate of problem detection. Because of the power of PD testing, it is hoped and expected that use of PD monitoring will continue to expand at a significant rate in both utility and industrial power plants.