Abstract: Overvoltage is one of the main causes of damage in the isolation of inverter-fed traction motors. To solve this problem, the mechanism and influencing factors were analyzed with the transmission line theory and simulation on the equivalentcircui.t The analyses show thatovervoltage is a function of the rise time of the converter output pulse and the lengths of the traction motor cables, and that its magnitude can be as large as 1. 9 times of the pulse voltage. The magnitude can be decreased to 1. 1 times of the pulse voltagewith a shuntR-C reactor.