DC series motor is widely used for high inertia loads like Hoists, cranes, Rotary Kiln, and Traction that require high initial torque at the start. Various types of motors are used for a particular type of application. The DC motors- shunt DC, separately excited DC motor, and DC series motor are suitable for delivering the high starting torque. However, the DC series motor can deliver the highest starting torque among all types of DC motors. We will now discuss how the DC series motor delivers high torque to the driven equipment.
The torque of the DC motor is proportional to the product of the main flux and the armature current. The field winding is connected in the series with the armature winding in the DC series motor. The diagram of the DC series motor is given below.
The torque of the DC motor is proportional to the flux and armature current.
The field winding of the DC series motor is connected in the series with the armature winding, therefore the current in both winding is the same.
From above, it is lucid that in the DC series motor torque is proportional to the square of the armature current. The DC series motor draws a large armature current as there is no back EMF present at the start. Therefore, the DC series motor is capable of producing the highest starting torque. The torque(Ta) armature current(Ia) characteristics of the DC series motor are as given below.
From the above characteristics of the DC series motor, the torque increase in the square of the armature current. The torque can increase up to the point till the saturation of the field magnet. After saturation, the armature and field current will not increase and thus the torque will not increase.
