Investigation of partial discharge signal propagation, attenuation and pattern recognition in a stator winding

Offline partial discharge measurements have been carried out on a 3.5 MVA, hydro-generator. Specific types of defects have been simulated at different locations of a phase winding. The resulting signal was monitored. A modified bar including a defect was either connected immediately at the winding terminal or on one of the coils end. The position of the connection was gradually moved away from the terminal, while monitoring the discharge activity from the external coupler. It was found that slot discharges and other simulated defects generated characteristic phase resolved partial discharge patterns (PRPD) easily distinguishable from internal discharge patterns. Results showed that discharge signal attenuation was significant even below 1 MHz. The severity of the defects created was not evaluated but it was found that PRPD recognition was a useful identification tool.