Parts of Transformer - Electrical Diary

What is DC Shunt Motor?

DC shunt motor is a motor in which field winding is connected parallel to the armature. In this motor field winding consists of a large number of enameled copper wires to provide a high resistance as shown in the figure. the value of field flux and field current is constant. Thus the speed of the shunt motor remains almost constant and is not affected by the load variation. this motor can not be started if a heavy load is connected to it. it is suitable for a stable and light load.

Characteristics of DC Shunt Motor

The characteristics of any machine provide some useful information about the machine and a relation between the two different parameters of the machine.

Torque Load Characteristics OF DC Shunt Motor

Torque is directly proportional to the armature current and magnetic flux in the air gap, But the flux in the air gap is constant hence developed torque only depends on the armature current. while trying to draw a  torque load characteristic it is a straight line passes through the origin. The starting torque of the motor is equal to about 1.5 times full load torque.

Speed Load Characteristic 

The speed of the DC shunt motor depends on applying

• Terminal Voltage
• Armature Current 
• Armature Resistance
• Air gap Flux
• Back EMF

But in a shunt motor, the value of applied terminal voltage, armature resistance, and flux remains constant. hence the speed of the shunt motor depends only on the armature current. This means armature current is only variable for the speed of the shunt motor. At no load armature current is very small and the motor speed is maximum. The speed load graph of the DC Shunt motor is given below

From the above-given speed load graph, it is very clear that when a load of a machine increase then the speed of the machine reduces but also from the graph it is shown that a change in speed is very low for a large change in load and hence practically shunt motor is motor of constant speed.

Speed Torque Characteristic

the relation between the speed and torque of the shunt motor is given above. The speed of the motor depends on the torque and torque depends on the load current. The torque increase with a rise of load current and the speed remains constant for any load but it slowly decreases as a result of armature voltage drop.

Application of DC Shunt Motor

DC shunt motor is used where constant speed is required like

• line shaft
• Lathe Machine
• Constant speed head centrifugal pumps
• laundry washing machine
• Milling Machine
• Grinder
• Small Printing press
• Paper making machine
• metal cutting machine

Also, Read

How induction motor work?

What is squirrel cage induction motor?

How DC compound motor work?

How Separately excited dc motor work?