Analysis of Off-Line and On-Line Partial Discharge in High Voltage Motor Stator Windings

Abstract

-The off-line and on-line partial discharge (PD) in the stator winding of three high-voltage (HV) motors (1,400 HP, 6.6 kV) is measured and analyzed in this paper. The off-line PD is measured at high values between 24,300～36,100 pC after 18 years of motor operation. Spare replacement motors were not available for testing the degree of deterioration of the stator windings in standstill status. Therefore, on-line periodic analysis was conducted to monitor the trend of PD after installing a ceramic sensor (110 pF, 6.6 kV) in the terminal box for each phase of each motor. In the stator winding of the No.1 and No.2 HV motors, which showed high magnitudes of off-line PD and low magnitudes of on-line PD, defects are expected to appear in the neutral end of the winding. On the contrary, in the stator windings of the No.3 HV motor, which exhibits high off-line and on-line PD magnitude, defects are expected to appear in the terminal end of the winding where a voltage close to the phase voltage is applied.

Characteristics of Indicators for Insulation Deterioration in 26 kV Generator Stator Windings

“…Through the partial discharge test, the magnitude and pattern of the maximum void inside the insulation materials can be easily determined [9][10][11]. Therefore, the information about the maximum void that cannot be determined by the AC current and dissipation factor can be verified by the partial discharge test for online as well as offline [12][13][14]. Shown in Figure 8 is the test circuit diagram for offline PD estimation.…”

“…Sudden insulation failure of generator stator windings in operation reduces the reliability of power supply and makes rapid repair difficult, causing considerable economic loss. Accordingly, besides the US and Canada, South Korea has conducted research on insulation integrity assessment through off-line and on-line insulation diagnosis tests in generator stator windings [3][4][5].…”