通过对MT56型牵引电动机故障的调查，查明了引起牵引电动机故障的主要原因是换向器的阶梯磨损。因为换向器的阶梯磨损引起电刷的异常磨损，使电动机换向不良，最终导致环火。为了解决换向器的阶梯磨损，对牵引电动机的换向器表面进行车上研磨。利用实际统计数据、座标图表明，车上研磨对减少牵引电动机的故障有良好的效果，同时节约了大量维修费用。 Through the investigation of MT56 traction motor fault, it is found that the main cause of the traction motor fault is the ladder wear of commutator. Because the commutator ladder wear abnormal brush caused wear and tear, poor motor commutation, and ultimately lead to ring fire. In order to solve the ladder wear of the commutator, the commutator surface of the traction motor is ground on-board. Using actual statistics, the plot shows that on-board grinding has a good effect on reducing traction motor faults while saving a lot of maintenance costs.