Electrical Engineering ⇒ Topic : Speed of d.c shunt motor by Field rheostatic control

Shunt Motors :

The flux of a D.C. shunt motor can be changed by changing shunt field current (I_sh) with the help of a shunt field rheostat as shown in Fig.(a). Since the field current is very small, the power wasted in the controlling resistance is very small.

In non-interpolar machines the speed can be increased by this method in the ratio 2: 1. In machines fitted with inter poles a ratio of maximum to minimum speeds of 6: 1 is fairly common.

                                                                                 fig (a)

                                        Field rheostatic control for a D.C. shunt motor