Characteristics of speed torque

The torque is proportional to armature current, the nature of these characteristics. At no load,T_a is no load speed.

As the load is increased, torque also increases. To generate more torque, armature current also increased due to this speed decreases.

However reduction in speed is not too large from no load to full torque. Therefore DC shunt motor is called constant speed motor.

For the cumulative compound motor, the shunt field, and series field fluxes and to each other. So total flux increase. so it can develop large torque at low speed just like dc series motor.

Theses motor run at moderately high speed even at no load. This is an advantage over dc series motor.

For the differential compound motor, the shunt and series field fluxes cancel each other. So total flux decrease. With the increase in load, speed increases. At full load, speed becomes so high that motor operates in the unstable region. Due to this region differential compound motors are not practically used.