DC Shunt Motor
Shunt-wound DC motor or DC shunt motor is a self-excited DC motor that operates on direct current, and the field winding connects in parallel to the armature winding. Both windings are exposed to the same power supply voltage, and this motor can 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. This motor can be self-excited from the armature windings, which 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 connects in parallel with the armature, and this motor also 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. To be clear, we will explain it with equations.
Considering the following variables:
The current passes through the circuit is:
And as we have a constant power source, the shunt current will be:
To get the general voltage equation of the shunt motor:
In another way:
When the motor runs with the constant supply voltage, the Shunt field current will be:
And as we know, the shunt field current is proportional to the field flux (Qα Ish).
The flux will approximately remain constant and proportional to a constant item, so this motor is a constant flux motor.
Construction of the DC Shunt Motor
Of course, the shunt motor has the same construction as the 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 a very high current.
The armature can support a higher current because it has a higher gauge wire. This high current passes through the armature during the motor’s starting up 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 equations:
Self-Speed Regulation of a Shunt Wound DC Motor
Eb: back EMF.
Q: total produced flux.
P: number of poles.
Z: number of coils.
N: rotational speed.
Be aware; We mention the number of coils that affect the back EMF.
And as we said, the net voltage increases when the back EMF decreases at a constant voltage supply, so;
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:
The increase in torque will increase motor speed, and the motor will become able to compensate for the slowdown due to loading, so the motor becomes able to self-regulate its speed, so we say that the Shunt-wound motor is a constant speed motor.
Characteristics of the 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.
- Boring mills.
- 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.