Insulation breakdown of field winding in turbine-generator fed from static exciter

The paper is concerned with the additional voltage stress in the field winding of turbine-generator produced by a thyristor exciter. In few cases, the insulation of field winding was damaged within a short time (some months) after commissioning the static exciters, although previously these rotors were in service with a DC rotating exciter without any trouble for many years. The current paper describes the experimental results of the study searching for a possible reason for the failure.