V-A Characteristic Measuring of Stress Grading Tapes in the End-winding of Synchronous Generators

Abstract In every electrical machine operating above 6 kV the partial discharges may occur on the surface of the stator bars or coils either between stator core or in the end-winding near the end of the stator core. The PD activity at the slot exit of the stator causes surface discharges which lead to a damage of the insulation and potential breakdown ending in shutdown of the machine. This can be prevented by applying stress grading materials such as semiconductive tapes or varnish. These materials with SiC particles used for this protection have nonlinear voltage - current characteristic which lowers the gradient of increasing voltage along the sruface. The paper describes surface discharges and deals with measurement of V-A characteristic of end-winding corona protection.

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