Shunt Motor

Basic diagram of shunt motor.

The shunt motor is different with the series motor in shunt motor the field winding is connected in parallel with the armature instead of in series. And from the basic of electrical theory a parallel circuit is often stated as a shunt. Based on the field winding that is placed in a parallel connection with the armature, it is called a shunt winding while the motor is called a shunt motor. Figure 1.0 and 1.2 shows a diagram of a shunt motor.

Shunt motor operating characteristic

In theory shunt motor has slightly different operating characteristics compare with series motor. A shunt motor cannot produce large current for starting like the series field. This is because its shunt field coil is made of fine wire. And this means that the shunt motor has very low starting torque, which requires that the shaft load be rather small.

When voltage is applied to the motor, the high resistance of the shunt coil will keeps the overall current flow to become low. The armature for the shunt motor operating system is similar to the series motor and it will only draw current to produce a magnetic field that is strong enough to cause the armature shaft and load to start turning. When the armature begins to turn, it will produce EMF. The EMF will cause the current in the armature to begin to diminish to a very small level. The amount of current the armature will draw is directly related to the size of the load when the motor reaches full speed. Since the load is generally small, the armature current will be small. When the motor is at its full rpm, its speed will remain fairly constant.

Speed of shunt motor

When the motor is at its full rpm, its speed will remain fairly constant. This is happen due to the load characteristics of the armature and shunt coil.

The shunt motor's speed can be controlled. The ability of the motor is to maintain a set rpm at high speed when the load is changes and it is due to the characteristic of the shunt field and armature. Since the armature begins to produce the back EMF as it is starts to rotate, it will use the back EMF to keeps its rpm at high speed. If we increases the load slightly and it will causes the armature shaft to become slow down, small back EMF will be produced. This will allow the difference between the back EMF and applied voltage to become larger, which will cause increasing its current. The extra current provides the motor with the extra torque which is required to regain its rpm when this load is increased slightly.

To control shunt motor's speed can be used in two different ways. Such as with varying the amount of current supplied to the shunt field and controlling the amount of current supplied to the armature. Controlling the current to the shunt field allows the rpm to be changed when the motor is at full rpm. Second way to control regulation of motor speed is by increasing or decreasing the voltage applied to the field.

Torque characteristic

The torque is increasing as the motor gains the speed due to the fact that the shunt motor's torque is directly proportional to the current. When the motor’s speed is at very low, the motor has very little torque. And after the motor is at full rpm, its torque is at its fullest potential. In fact, if the shunt field current is reduced slightly when the motor is at full rpm, the rpm will increase slightly and the motor's torque will also increase slightly.