A Machine Integrated Rogowski Coil for Bearing Current Measurement

Inverter driven machines are a vital part of electrical traction drives. They are subject to high-frequency parasitic currents, caused by the high-frequency components of the pulse width modulated (PWM) voltage. These currents can flow through the bearings of the machine and cause severe damage. They are usually measured by introducing a gap into the parasitic current path, bridging the gap and measuring the current through the bridge. This method and similar methods from the literature change the current path in the machine and thereby influence the measurement results. Therefore, in this work, a rogowski coil is developed, which is integrated into the machine and measures the current through the shaft of the machine. By placing such rogowski coils on the shaft inside and outside the machine and substractign the measured currents, the bearing current on either end of the machine can be measured without interfering in the current path. This work outlines how to design a Rogowski coil specifically for the bearing current measurements using a differential structure to achieve high common mode rejection.