Speed Regulation

Author: E.E. Kimberly

When a shunt motor is loaded, the speed decreases because the no-load current can produce only that torque required at no load. Since Eg is a function of rate of cutting of a constant magnetic field, its value decreases when the speed decreases. In equation (11-3) both V and Ra are constant; and, therefore, to maintain a balanced equation with a decreased value for Egj the value of Ia must increase. The torque is proportional to /a, and so increases as Ia increases. This related action of speed decrease and torque increase continues until a stable condition is reached, when the current corresponding to a certain speed is just sufficient to drive the motor and its load at that speed. The change in speed corresponding to a change in load from zero to full load is called speed regulation. Speed regulation is usually expressed as a per cent of full-load speed. Thus,