This part of IEC 61377 applies to the combinations of motor(s), chopper and their control, and its object is to specify: - the performance characteristics of electric drives consisting of a chopper, direct current motors, and the related control system; - methods of verifying these performance characteristics by tests. In traction drives, a combined system with chopper and direct current motor(s) without any control between the mechanical output and the chopper is not usual. It is not, therefore, considered in this standard.