Abstract :
The d.c. traction motor was used almost universally in traction drives until developments in power semiconductors made a.c. drives a practical alternative. The attraction of the dc machine for traction drives is the ease of control. In its simplest form, the controller is a manually operated rotary drum switch which progressively reduces the resistance connected in series with the machine and d.c. supply. Conversely, the developments in power converters and electronic control have produced control systems with high efficiency and wide control range incorporating several stages of automatic control.
