Analysis of Traction Motor Bearing Voltage and Bearing Current Considering Whole-train Grounding and Suppression Measures

Abstract

Objective Most urban rail transit trains use PWM (pulse width modulation) variable frequency drive system, which often leads to bearing corrosion problems due to the excessive bearing voltage and bearing current during operation. Therefore, it is necessary to conduct in-depth research on the problem of excessive traction motor bearing voltage and bearing current considering whole-train grounding conditions. Method The formation mechanism of traction motor bearing voltage and bearing current is briefly analyzed. The bearing current paths of two typical vehicle models adopting different grounding schemes are analyzed separately. Based on this, a high-frequency equivalent circuit model containing vehicle grounding loop and traction system is established. The characteristics of bearing voltage and bearing current under two grounding schemes are simulated and analyzed. The effectiveness of different measures to suppress bearing voltage and bearing current is compared, and a circuit optimization design scheme is proposed from the perspective of whole-train grounding. Result & Conclusion The grounding system optimization scheme effectively reduces the grounding cable lengths, thereby diminishing the cable inductance. This optimization scheme can not only avoid the impact of electrostatic shielding method on traction motor efficiency and the impact of carbon brush grounding method on protective grounding, but also be compatible with the internal optimization schemes for these two traction drive systems. Simulation results verify that this optimization scheme can effectively reduce bearing voltage and bearing current while improving the return flow and potential of carbody.

Keywords

• urban rail transit
• train
• traction motor
• bearing voltage
• bearing current
• suppression measure
• whole-train grounding