There are two types of windings in DC machine;
- Armature Winding
- Field Winding
According to the connection of armature and field winding, the DC motors are classified into three types;
- Series motor
- Shunt motor
- Compound motor
In this article, we will discuss the DC shunt motor.
Connection Diagram of DC Shunt Motor
In the DC shunt motor, the armature winding and field winding is connected in parallel. The connection diagram of the DC shunt motor is as shown in the figure below.
DC power supply is connected between these two windings.
The resistance of shunt field winding (Rsh) is always higher than that of armature winding (Ra). Because the number of turns of field winding is greater than the number of turns in the armature winding.
In the field winding, the cross-section area of the wire is smaller than the armature winding.
Voltage and Current Relationship
The current passes through the armature winding is Ia and current passes through the shunt winding is Ish.
The total supplied current from the DC source is I. And this current is divided in to both windings.
As shown in the connection diagram;
Shunt field current;
V = Supplied DC voltage
Rsh = Shunt field resistance
The supply voltage is given by;
If we neglect the bush drop, the supply voltage is given by;
The field current depends on the supplied voltage V and shunt field resistance Rsh. Both quantities are constant. Hence, the shunt field current is also constant.
The flux produced in the motor depends on the field current. In the shunt motor, the field current is constant. Therefore, the flux produced in the motor is also constant. So, this motor is also known as a constant flux motor.
Torque Equation of DC Shunt Motor
Torque produced in the DC motor is proportional to the current passing through the armature winding and flux.
For the DC shunt motor, the field current is constant. And hence, the flux is also constant.
So, the torque produced in the shunt motor is proportional to the armature current only.
Speed Equation of DC Shunt Motor
For DC motors, the speed depends on the below equation,
For the DC shunt motors, the field current is constant. Hence the speed of this motor depends on the equation below,
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