The process of field weakening
When a rheostat is placed in series with the field winding, it reduces the field current which leads to a reduction in flux in the air gap. As speed and flux are inversely proportional to each other, the motor speed goes up. This is accompanied by a reduction in torque because flux and torque are directly proportional to each other. Although there is a slight decrease in speed when the load is increased, this is so small as to be insignificant.
With a fixed voltage, the speed of the shunt wound motor is almost constant. The torque sees an increase with an increase in current, without any significant lowering of speed. The shunt wound electric DC motor is similar to the series wound motor in that it can be reversed with a reverse in either field or rotor winding connections. Regenerative braking is one of its many characteristics and it is able to maintain the field even with a reverse in rotor current, with self-excitation.
These electric DC motors find uses in fans, motorised wipers and other appliances which have fixed speeds. Wherever precise control of speed is required, shunt motors find a place. Teco Electric Co. Ltd. are manufacturers of DC and AC motors of all kinds to fit everybody’s requirements.