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Difference between DC Series Motor and Shunt Motor
A dc motor is a most basic type of electric motor that works on direct current supply. A typical dc motor consists of two main parts namely, magnetic field system and an armature. DC Machines are used in various applications such as toys, computers, printers, industrial machinery, and more. Based on the construction, the dc motors can be classified in three types namely, dc series motor, dc shunt motor, and dc compound motor.
In this article, I will explain what are the dc series and shunt motors and what are the key differences between them. So, let’s get started with the basics of DC series and shunt motors.
What is a DC Series Motor?
A dc series motor is one in which the armature winding and the field winding are connected in series as shown in the following figure.
Since the field winding and armature winding are connected in series, therefore, the current flowing in the field winding is equal to the armature current. This armature current when passes through the series field winding, it produces a working magnetic field in the machine.
DC Series motors are known for their extremely high starting torque. Hence, they are mainly used in applications where very high starting torque is required such as in cranes, hoists, locomotives, lifts, etc.
What is a DC Shunt Motor?
A dc shunt motor is a type of dc motor which has field winding connected in parallel to the armature winding as shown in the following figure.
Since the armature winding and field winding in a dc shunt motor are connected in parallel, hence, the field winding receives the same supply voltage as the armature winding. Also, the voltage across and current through the shunt field winding remains the same. Thus, the dc shunt motor operates at a constant speed.
DC shunt motors also provide a simple speed control mechanism by varying the field current by changing the field winding resistance. However, the starting torque of dc shunt motor is lower than that of the dc series motor. For this reason, they are used in applications where medium starting torque and constant speed is desired like in elevators, printers, toys, etc.
After getting a brief overview of DC series motor and DC shunt motor, let us now discuss the key differences between them.
Difference between DC Series Motor and DC Shunt Motor
The following table highlights all the significant differences between dc series motor and dc shunt motor −
| Parameter | DC Series Motor | Shunt Motor |
|---|---|---|
| Basic | In a dc series motor, the field winding is connected in series with the armature winding. | In a dc shunt motor, the field winding is connected in parallel with the armature winding. |
| Field current | In dc series motors, the field current is same as the armature current. | In dc shunt motors, the field current is not equal to armature current. |
| Voltage across armature and field windings | In dc series motors, the voltages across armature and field windings are different depending on their resistance. | In dc shunt motors, the voltage across the armature winding and field winding is same and is equal to the supply voltage. |
| Field winding design | A dc series motor has a field winding design with few turns of thick conductor wire. | The field winding of a dc shunt motor is designed with large number of turns of fine wire. |
| Resistance of field winding | The field winding of a dc series motor has very low resistance as it carries full armature current. | The field winding of a dc shunt motor has a very high resistance, so that it draws a very small current. |
| Staring torque | A dc series motor develops very high starting torque. | A dc shunt motor develops low and constant starting torque. |
| Torque-current relation | In dc series motors, the torque is directly proportional to the square of the armature current i.e., | In dc shunt motors, the torque is directly proportional to the armature current i.e., |
| Starting current | High starting current due to combined field and armature winding in series. | Lower starting current due to the parallel winding arrangement. |
| Speed | The dc series motors are variable speed dc motors. | The dc shunt motors are approximately constant speed motors. |
| Starter | To start dc series motors, the four-point starter is used. | To start dc shunt motors, three-point starter is used. |
| Speed-load characteristics | DC series motors have low speed at high loads, whereas dangerously high speed at low loads. | There is not significant change in the speed of dc shunt motor with the change in load. |
| Speed regulation | Poor speed regulation | Its speed regulation is better as compared to the DC Series motor. |
| Dynamic response | DC series motors have a faster dynamic response due to high starting torque. | The dynamic response of dc shunt motors is lower as compared to dc series motors. |
| Rotor design | The design of rotor of dc series motors is optimized for high starting torque. | In dc shunt motors, the rotor design is optimized for constant speeds. |
| Energy efficiency | DC series motors have lower energy efficiency at high speeds and light loads. | DC shunt motors provide better energy efficiency at a wide range of speeds and loads. |
| Field current adjustment | In dc series motors, it is not possible to adjust the field current independently as it has same field and armature currents. | In dc shunt motors, the field current can be adjusted independently without affecting the armature current. |
| Need of load balancing mechanism | DC series motors require a load balancing mechanism to prevent over speeding. | There is no need of this kind of mechanism as they have almost constant speed. |
| Applications | DC series motors are used for applications where high starting torque is required like in electric locomotives, hoists & cranes, electric bikes and cars, etc. | DC shunt motors are used in applications where constant speed is required like in fans, blowers, elevators, centrifugal pumps, lath machines, etc. |
Conclusion
A DC motor is an electric machine that converts direct current electricity into mechanical energy. DC motors can be of three major types namely, dc series motors, dc shunt motors, and dc compound motors. The dc series and shunt motors are widely used in variety of applications and they are completely different in terms of their construction and operating characteristics. DC series motors have a field winding connected in series with the armature winding and known for their high starting toque. On the other hand, dc shunt motors have a field winding connected in parallel with the armature winding and known for their constant speed and good speed regulation properties. In this comprehensive article, I have explained the basic theory of dc series and shunt motors along with the key differences between them.
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