What are the otches and ransitions of the traction motors?
There are typically several (4 or 6) traction motors in a locomotive, depending on the number of bogies and the number of motors per bogie. They can be grouped in the electrical circuits in various ways, such as being all in series, a series combination of pairs in parallel, or all parallel, etc. These combinations provided a few different ranges of power/torque and speed. Within each such combination, finer control over the speed and power is possible by resistive (rheostatic) control, chopper (SCR – semiconductor switches) control, or by frequency control as in the 3-phase AC locos. Most older locos used resistive control with a large array of resistive elements that could be progressively added into or taken out of the circuit to limit the current drawn by the motors. Each step in this is a ‘notch’. E.g., the WCAM-3 loco operates with its 6 motors in series, with notches numbered 1 to 22; at a higher speed it can use either 2 series sets of 3 paralleled motors or 3 series sets of 2
