Speed Control of DC Shunt Motor - Easy Methods.

Speed Control of DC Shunt Motor.

The electrical machine is one of the most important subject in Electrical Engineering. If you are a student of Electrical Engineering then you should know that "Speed Control of DC Shunt Motor". Of course, before going to know Speed control of DC Shunt Motor we will learn what is DC Shunt Motor. So let's know What is DC Shunt Motor and Speed Control of DC Shunt Motor.

What is DC Shunt Motor?

DC Shunt Motor is a DC Motor whose field coil is connected in parallel with the Armature coil. As the Field coil is connected in parallel(or as a shunt) with the armature coil that is why it called DC Shunt Motor. 

Speed Control of DC Shunt Motor Formulas:

Are you know what is speed control. Speed control means a change in rotation of the motor by us. Now there is a question that how speed control is possible of a DC Shunt Motor. 

At first, let's see the EMF Equation of the DC Motor;

E= (P�NZ)/60A

Here, 

E= EMF

N= Speed
�= Flux per pole

Z= No. of Conductors
A= Parallel path

As the P, Z, A,60 are constant so we can write,

 E=N�K               where K=PZ/60A

So the speed equation is N=E/K�

According to the above equation, the speed of the DC motor can be changed by changing the Flux and Terminal voltage of the Armature.

Flux can be changed by changing the field current. So we will discuss the two methods of  Speed Control of DC Shunt Motor-

1. Field Current Control Method
2. Armature Voltage Control Method

Speed Control of DC Shunt Motor by Field Current Control Method:

Speed control of DC Shunt Motor by Field Current Control Method is Very Easy. From the equation, we know that if we decrease the current in the field coil speed will be increased and vice-versa.

Apparatus Required:

1. Rheostat.
2. Ammeter.
3. Voltmeter.

Procedure: 

1. Find the terminals A1, A2, F1, F2 in terminal box of the motor.
2. Find the terminals L, LC(or N), A, F in the four-point starter.
3. Connect the DC power supply to the L and LC terminals of the starter.
4. Connect the A2, F2, LC terminals together.
5. Connect the A1 terminal of the motor to the A terminal of the starter.
6. Connect the one terminal of the rheostat to the F terminal of the starter and another terminal to the F1 terminal of the motor.
7. If you measure the current and voltage then you can use ammeters and voltmeter.
8. For better understanding see the Circuit diagram carefully.
9. Now move the slider of the rheostat to get your desired speed.

Circuit diagram for Speed Control of DC Shunt Motor by Field Current Control Method:

click on the image to enlarge

Note: By using this method you can increase the speed of the motor above the rated speed.

Speed Control of DC Shunt Motor by Armature Voltage Control Method:

Generally, as the supply voltage is constant the armature voltage also constant. If we decrease the voltage across the armature by increasing a variable resistance in series with the armature the back emf will be decreased hence the speed will be decreased.

Apparatus Required:

1. Rheostat.
2. Ammeter.
3. Voltmeter.

Procedure:

1. Find the terminals A1, A2, F1, F2 in terminal box of the motor.
2. Find the terminals L, LC(or N), A, F in the four-point starter.
3. Connect the DC power supply to the L and LC terminals of the starter.
4. Connect the A2, F2, LC terminals together.
5. Connect the F1 terminal of the motor to the F terminal of the starter.
6. Connect the one terminal of the rheostat to the A terminal of the starter and another terminal to the A1 terminal of the motor.
7. If you measure the current and voltage then you can use ammeters and voltmeter.
8. For better understanding see the Circuit diagram carefully.
9. Now move the slider of the rheostat to get your desired speed.

Circuit diagram for Speed Control of DC Shunt Motor by Armature Voltage Control Method:

click on the image to enlarge

Note: By using this method you can Decrease the speed of the motor below the rated speed.

Read Also:

• Change the direction of rotation of 9V DC motor easily
• How Three phase motor runs on Single phase supply in Train?
• How EMF is induced? Types of induced EMF.

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