Skip to content

DC Shunt Motor

July 12, 2020

Shunt-wound DC motor or DC shunt motor is a self-excited DC motor that operates on direct current and the field winding is connected in parallel to the armature winding. So both windings are exposed to the same power supply voltage, and this motor is able to maintain a constant speed with any load.

Shunt motor is the most common type of DC motor where we connect the field winding parallel with the armature windings. So, this motor can be self-excited from the armature windings and this gives it the feature of greatest speed regulation, simplified reversing control, and low starting torque.

So, the Shunt motor is suitable for belt-driven applications in industrial and automotive applications. Also, the field winding is connected parallel with the armature, and this motor has the addition that it has a low starting torque but at the same time, it runs at a constant speed.

Shunt-wound DC motor is known as a constant flux motor because the field flux almost remains constant and that can be more clear with equations as:

The current passes through the circuit is:

Itotal = Ia + Ish.

And as we have a constant power source the shunt current will be:

Ish= E/Rsh.

So;

Ia=Itotal-Ish=E/Ra.

To get the general voltage equation of the Shunt motor:
E=Eb+Ia.Ra.

In another way:

E=Eb+(Itotal- Ish).Ra.

When the motor run with the constant supply voltage the Shunt field current will be:

Ish=E/Rsh.

And as we know the shunt field current proportional to the field flux (Qα Ish).

So, the flux will approximately remain constant as it proportional to a constant item so this motor is a constant flux motor.

Construction of DC shunt motor

Of course, shunt motor has the same construction of DC motor; the stator (field winding), the rotor (the armature), commutator, and so on. The shunt field winding is made of several turns on the coil and those turns are made of thin wire. Also, the shunt winding size is quite small and can’t carry very high current.

The armature can support higher current because it has a higher gauge wire. This high current passes through the armature during the starting up of the motor or when it runs at a slower speed.

The operation principle of DC shunt motor

When we apply a voltage to the motor, a current is produced in the armature and a strong magnetic field. This field interacts with the magnetic field and makes the armature rotates.

When the armature rotates it produces a back EMF. This EMF opposes the armature voltage and reduces the armature current if we increase the motor load. The armature will rotate slowly and the back EMF will reduce.

To be more accurate, let’s illustrate with relations:

Self-Speed Regulation of a Shunt Wound DC Motor
Eb=Q.P.Z.N/60

Where:

Eb: back EMF.

Q: total produced flux.

P: number of poles.

Z: number of coils.

N: rotational speed.

Take care; here we mention the number of coils and they affected the back EMF.

And as we said the net voltage increases when the back EMF decreases at a constant voltage supply so;

Enet= E-Eb.

When the net voltage increases the armature current increases and as the torque is proportional to the armature current it will also increase according to:

T=Q.P.Ia.Z/2.π.A.

While:

A: area.

The increase in torque will cause an increase in motor speed and the motor became able to compensate slowdown due to loading so the motor becomes able to self-regulate its speed so we say that Shunt-wound motor is a constant speed motor.

Characteristics of DC shunt motor

As a result of its advantages, we can use the Shunt Wound DC motor in many applications such as:

  • Lathe machines.
  • Centrifugal pumps.
  • Drills.
  • Boring mills.
  • Shapers.
  • Fans.
  • Blowers.
  • Conveyors.
  • Lifts.
  • Weaving machine.
  • Spinning machines, and everywhere where constant speed is required.

This because of its great advantages as:

  • Simple control performance.
  • High availability.
  • Smooth running.
  • Wide control range.
  • Low speeds.

Finally, I hope you like this article and you can follow our topics that will deepen more and more to illustrate DC motors.