Updated: Mar 2, 2021
The high inertia loads like Hoist, Crane, Rotary Kiln and Traction require high torque initially at start. Various types of motors are used for particular type of application. The DC motors- shunt DC, separately excited DC motor, DC series motor are good for delivering the high starting torque. However, the Dc series motor can deliver the highest starting torque among all types of DC motor. We will now discuss how the DC series motor deliver high torque to 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 DC series motor. The diagram of the DC series motor is as given below.
Torque of DC motor is proportional to the flux and armature current.
The field winding of DC series motor is connected in the series with the armature winding, therefore the current in both the 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 large armature current as there is no back EMF present at start. Therefore, the DC series motor is capable of producing highest starting torque. The torque(Ta) armature current(Ia) characteristics of the DC series motor is as given below.
From above characteristics of the Dc series motor, the torque increase in 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.