ABSTRACT
A DC machine is a versatile machine that can be used both as a generator and as a motor. The use of DC machines as DC generators to produce bulk power has rapidly disappeared due to the economic advantages involved in the use of AC generation, transmission, and distribution. This is partly due to the high efficiency and relative simplicity with which transformers convert voltages from one level to another. Today, the need for DC power is often met by the use of solid state-controlled rectifiers or renewable generation. However, DC motors are used extensively in many industrial applications because they provide constant mechanical power output or constant torque, adjustable motor speed over wide ranges, precise speed or position control, efficient operation over a wide speed range, rapid acceleration and deceleration, and responsiveness to feedback signals. Such machines can vary in size from miniature permanent-magnet motors to machines rated for continuous operation at several thousand horsepower. This chapter discusses the principles of operation (including commutation), equivalent circuit, and different motor characteristic curves. It also discusses starting and braking of DC motors.
