Establishment and Verification of Detailed Analytical Models for Shaft Voltage and Bearing Current of Flat-Wire Motor

The bearing currents of alternating current motors are a common issue in the field of variable-frequency drives. When the bearing voltage exceeds the breakdown threshold of the oil film, the parasitic capacitance network of motor system components provides a pathway for leakage currents, ultimately endangering the metal ball bearings. It should be noted that the capacitance from the end winding to the rotor makes a significant contribution to the parasitic capacitance network. Therefore, a more detailed analytical model that considers the impact of the end winding is needed, but existing analytical models are not yet capable of achieving this. This paper establishes a detailed finite element model of the electric motor, focusing on the impact factors of variation of the proportion of the end winding to rotor capacitance <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\boldsymbol{Cwr},\boldsymbol{ew})$</tex>. Additionally, in this paper, the calculation formula for the capacitance in the equivalent circuit of the flat-wire motors is modeled. Building upon previous research, simplified analytical models for two types of bearing currents are established and verified through simulation, with the simulation results being essentially consistent with the analytical outcomes. Finally, the paper summarizes the impact of circulating bearing currents and EDM bearing currents on bearing electro-corrosion and calculates the electrical life of the motor bearings.