Achieving high voltage dielectric breakdown of turbine generator stator coils using capacitors

High surface electric field gradients are generated between the stator half-coil straight section grounding and the coil involute region. Surface flashover at electric stresses typically less than the dielectric strength of the groundwall often occurs. Oil or SF/sub 6/ immersion to prevent surface flashover is not feasible for these very large size of stator half coils. The surface flashover voltage has been used as a lower estimate of performance capability by Westinghouse. To determine the capability of Westinghouse Thermalistic/sup (R)/ groundwall, an electrical circuit has been devised to suppress the intensity of the surface voltage gradient across the involute region. The test circuit using high voltage capacitors allows the dielectric strength of the Thermalistic/sup (R)/ groundwall to be measured. The new testing circuit can be used to prevent over-design and the associated added cost to stator coil bars. The author will introduce the application of using capacitors to achieve dielectric breakdown of stator coil groundwall.