A New Approach to Make the Electric Field Uniform Along the Stress Grading System of A Form-Wound Coil under Square Waves

Surface partial discharges on the stress grading system of a medium voltage form-wound coil fed by an inverter can lead to insulation failure. Reducing the maximum surface electric field is therefore essential for prolonging insulation life. Under square waves in simulations using COMSOL Multiphysics, this work studies how floating metal foils added to the stress grading tape (SGT) affect electric field and temperature distributions. The results show that the metal foils make the electric field uniform but increase the temperature, due to increased current density in the stress grading tape. However, the temperature rise is below that considered to be detrimental to the insulation.