Evaluation of Field Insulation of Turbine-Generators with Higher Thyristor Excitation

Application of a thyristor excitation system with high ceiling voltage to the turbine-generator field has required precise evaluation on field insulation, especially against spiky voltage. This paper reports on the investigation of breakdown through and over the surface of field insulating components for thyristor voltage. Particular emphasis is placed on the method for estimating voltage endurance characteristics for thyristor voltage in hydrogen. We established a simple evaluating method on the rotor slot armor by using the relation of voltage endurance characteristics between ac and thyristor voltages. Estimation tests have proved that hazardous points are (a) the surface flashover of the creepage block for initial-stage characteristics and (b) degradation of the slot armor due to partial discharge for long-term characteristics.