Company:
BC Hydro, British Columbia, Canada
Machine Description:
Air Cooled Hydro Generator, 239 MVA, 13.8 kV, 37 Years Old
Failure Mechanism Identification Through Condition Based Monitoring:
BC Hydro installed 6 epoxy mica capacitors (80pF) per phase connected to a continuous monitor measure the partial discharges on the Hydro Generator.
The continuous instrument detected high magnitudes of positive and negative partial discharge activity. The hump of high partial discharge magnitude for Phase C of the machine is shown in the 2D plot in Figure 1 below:
Figure 1: 2D PD Plot Showing Hump at High Magnitudes – Phase C
Corrective Maintenance Prior to Machine Failure
Maintenance activities were planned and implemented prior to machine failure. The winding was repaired by cleaning the 10 bars closest to the 80pF capacitive couplers and then coated with red glyptal epoxy.
After the repair, trending of partial discharge data showed a significant reduction in partial discharge levels. This is shown in figure 2
Figure 2. Trend of PD activity – Phase C
Reference:
Partial Discharge Measurements on Hydro Generator Stator Windings Case Studies”, by S. Li and M. Chow” in IRMC June 2006