The position of partial discharges (PD) with respect to power frequency phase position has long been known to provide useful information on the nature of deterioration of electrical insulation. In the past, virtually all such data has been from PD tests performed in the laboratory on static models or equipment. Improvements in the past 15 years in noise elimination technology have made it possible to monitor the PD activity (number, magnitude and phase position) in the HV stator windings of operating motors and generators. Over a two year period, the PD activity was recorded on more than 100 motors, hydrogenerators and turbine generators, and the pulses analyzed with respect to the ac phase position, with a resolution of 3.6/spl deg/. In the majority of stator windings, the PD pulses occurred in the expected portion of the ac phase, i.e. Between 0 and 90/spl deg/ as well as between 180 and 270/spl deg/. However a significant number of instances were recorded where the pulses appeared to be shifted /spl sim/30/spl deg/. This is probably due to the phase-to-phase electric stress which occurs in the endwinding portion of a three phase stator winding. In many other machines, the PO phase positions were very different from the expected patterns determined from static tests. In some of these cases, such results were obtained on machines with suspected loose stator windings. It seems reasonable to conclude that the unusual PD patterns may be due to the influence of moving stator coils on the PD patterns. Such an influence is not easy to simulate in static laboratory tests. PD pulse phase analysis is shown to be a useful means of helping to determine the main deterioration mechanisms of stator insulation systems of operating motors and generators. >
[1]
R. Bartnikas,et al.
A Simple Pulse-Height Analyzer for Partial-Discharge-Rate Measurements
,
1969
.
[2]
H. G. Sedding,et al.
A new sensor for detecting partial discharges in operating turbine generators
,
1991
.
[3]
J. K. Nelson,et al.
Assessment of deterioration in epoxy/mica machine insulation
,
1992
.
[4]
T. Okamoto,et al.
Novel Partial Discharge Measurement Computer-Aided Measuremnet Systems
,
1986,
IEEE Transactions on Electrical Insulation.
[5]
W. McDermid,et al.
Practical online partial discharge tests for turbine generators and motors
,
1994,
IEEE Power Engineering Review.
[6]
J. S. Johnson,et al.
Detection of Slot Discharges in High-Voltage Stator Windings During Operation
,
1951,
Transactions of the American Institute of Electrical Engineers.
[7]
M. Kurtz,et al.
Generator Insulation Diagnostic Testing
,
1979,
IEEE Transactions on Power Apparatus and Systems.
[8]
Toshikatsu Tanaka.
PD pulse distribution pattern analysis
,
1994,
Proceedings of 1994 4th International Conference on Properties and Applications of Dielectric Materials (ICPADM).