What is a DC Shunt Motor : Construction, Working Principle, Circuit Diagram

In electrical motors, series circuits and parallel circuits are commonly known as series and shunt. Therefore, in DC motors the connections of the field windings, as well as the armature, can be done parallel which is known as DC shunt motor. The main difference between DC series motor as well as DC shunt motor mainly includes the construction, operation, and speed characteristics. This motor gives features like easy reversing control, speed regulation, and starting torque is low. Thus, this motor can be used for belt-driven applications within automotive as well as industrial applications.

What is a DC Shunt Motor?

A DC shunt motor is a type of self-excited DC motor, and it is also known as a shunt wound DC motor. The field windings in this motor can be connected in parallel to the armature winding. So both windings of this motor will expose to the equal voltage power supply, and this motor maintains an invariable speed with any kind of load. This motor has a low starting torque and also runs at a constant speed.

Construction and Working Principle

The DC shunt motor construction is the same as any type of DC motor. This motor can be constructed with basic parts like field windings (stator), a commutator, and an armature (rotor).

The working principle of a DC Shunt Motor is, whenever a DC motor is turned ON, then DC flows throughout the stator as well as the rotor. This current flow will generate two fields namely the pole as well as the armature.

In the air gap between armature and field shoes, there are two magnetic fields, and they will respond with each other for revolving the armature.

The commutator overturns the armature current flow direction at ordinary gaps. So the armature field is repelled with pole field for all time, it keeps revolving the armature within an equal direction.

DC-Shunt Motor Circuit Diagram

The DC shunt motor circuit diagram is shown below, and the flow of current and voltage being supplied to the motor from the supply can be given by Itotal & E.

In case of the shunt wound DC motor, this current supply will divide into two ways like Ia,& Ish, where ‘Ia’ will supply throughout the ‘Ra’ resistance armature winding. In the same way, ‘Ish’ will supply through the ‘Rsh’ resistance field winding.

Therefore, we can write it as Itotal = Ia + Ish

We know that Ish = E/ Rsh

Otherwise Ia = Itotal- Ish= E/Ra

Generally, when the DC motor is in a running state & the voltage supply voltage is stable and the shunt field current given by

Ish = E/Rsh

But we know that the armature current is proportional to the field flux (Ish ∝ Φ). Thus the Φ remains more otherwise less stable, due to this reason; a shunt wound DC motor can be named as a constant flux motor.

Back EMF in DC Shunt Motor

Whenever the DC shunt motor’s armature winding rotates within the magnetic field which is generated by the field winding. Thus an e.m.f can be stimulated within the armature winding based on the Faradays law (electromagnetic induction). Although, according to Lenz’s law, the induced e.m.f can act within reverse direction toward the armature voltage supply.

Thus, this e.m.f is named as the back e.m.f, & it is represented with Eb. Mathematically, this can be expressed as,

Eb = (PφNZ) / 60A V

Where P = no. of poles

Φ = Flux for each pole within Wb

N = Motor’s speed in revolutions per minute

Z = No. of armature conductors

A = No. of parallel lanes

DC Shunt Motor Speed Control

The speed characteristic of a shunt motor is different compared with a series motor. As a DC Shunt motor attains its complete speed, then the armature current can be directly connected to the motor load. When the load is extremely low within a shunt motor, then the armature current can also be below. When the DC motor attains its complete speed, then it remains stable.

The DC shunt motor speed can be controlled very easily. The speed can be maintained constant until the load changes. Once the load changes, then the armature tends to delay, which will result in less back e.m.f. Thus, the DC motor will draw extra current, this will consequence in enhancing within torque to gain speed.

So, whenever the load enhances, the net result of load on speed in a motor is approximately nil. Similarly, once the load decreases, then the armature achieves speed & produces extra back e.m.f.

The DC shunt motor speed can be controlled in two ways

• By altering the sum of current flowing through the shunt windings
• By altering the sum of current flowing through the armature

In general, DC motors appear with a particular rated voltage & speed in (revolutions per minute. Once this motor functions under its complete voltage, then the torque will be reduced.

Brake Test on DC Shunt Motor

The brake test is the one kind of load test on the dc shunt motor. Generally, this test can be done for the low-rated DC machines. The main reason for doing this test is to identify the efficiency and also by using this test, the output of mechanical power can be calculated & separated the same by using electrical input. So this is the reason to calculate the efficiency of the DC motor, this test is used. Therefore, this type of test cannot be employed on superior-rated machines.

Characteristics of DC Shunt Motor

The characteristics of a shunt DC motor include the following.

• This DC motor works at a fixed speed once the voltage supply is set.
• This DC motor is upturned by the turn around the motor connections like a series motor.
• In this type of DC motor, by a rising motor current, torque can be improved without reducing in speed.

DC Shunt Motor Applications

The applications of shunt DC motor include the following.

• These motors are used wherever stable speed is required.
• This kind of DC motor can be used in Centrifugal Pumps, Lifts, Weaving Machine, Lathe Machines, Blowers, Fans, Conveyors, Spinning machines, etc.

Thus, this is all about an overview of the DC shunt motor. From the above information finally, we can conclude that these motors are ideal where exact speed control is needed due to their self-regulating speed capacities. The applications of this motor mainly comprise machines instruments like grinders, latches & industrial tools like compressors as well as fans. Here is a question for you, what are the Advantages and Disadvantages of a DC shunt motor?