Measurement and analysis of partial discharge in high voltage motor stator windings

Online partial discharge monitoring system (PDMS) was developed to assess the condition of stator winding in high voltage motors. 80 pF capacitive couplers were connected to a 6.6 kV motor stator coil terminal. The voltage applied to stator coils were at 3.81 kV, 4.76 kV and 6.6 kV, respectively. These stator coils have various types of artificial insulation defects such as large voids, semi-conductive coating damage and strand insulation fault. On-line PD monitoring system, digital PD detector (PDD) and turbine generator analyzer (TGA) were used to measure PD activity. Most of the defect mechanisms of a large motor can be associated with PD patterns such as internal, slot and conductor surface discharges. PD patterns coincide with on-line PD monitoring system, PDD and TGA. These instruments have an input bandwidth of 100 kHz-50 MHz, 40-400 kHz and 0.1350 MHz. Continuous on-line PD monitoring system was measuring the discharge activity of large motors that were installed with 80 pF capacitive couplers at the terminal box.