A Novel Nonlinearly Equivalent Circuit Model for Calculating Electric Fields Along the Stator End-winding of HV Rotating Machine

In order to study the performances of electric potential or electric field distribution along the stator bar end-winding, a novel equivalent circuit model was proposed to calculate the electric field distribution along the surface of stress grading system in this paper. Compared with the conventional equivalent circuit which just described the stress grading tape (SGT) and groundwall insulation, this model was more complex and also took the air gap into account. Based on the proposed equivalent circuit, the transient potential and electric field distributions along the three-segment SGTs, usually named as medium, medium-high and high resistance coating respectively, of a rated 24 kV class hydro-generator stator bar end-winding were simulated. The simulation results show that the transient potential or electric field at each point along the three-segment SGTs has a significant phase or time difference (or delay) with any other location at a moment. This novel proposed equivalent circuit model should be adequate to optimize SG system of stator end-winding for the high voltage rotating machines.