Electrical Engineering Interview Questions And Answers: Determine the efficiency & characteristic of a Shunt wound DC motor.

Objective:-To Determine the efficiency & characteristic of a Shunt wound DC motor.

Theory:- The field coil and the armature windings are connected in shunt or parallel across the power source. The armature winding consists of relatively few turns of heavy gauge wire. The voltage across two windings is the same but the armature draws considerably more current than the field coil. Torque is caused by the interaction of the current caring armature winding with the magnetic field produced by the field coil. If the DC line voltage is constant, the armature voltage and the field strength will be constant. The speed regulation is quite good; the speed is a function of armature current and is not precisely constant. As the armature rotates within the magnetic field, an EMF is induced in its wining. This EMF is in the direction opposite to the source EMF and is called the counter EMF, which varies with rotational speed. Finally, the current flow through the armature winding is a result of the difference between source EMF and CEMF. When the load increases, the motor tends to slow down and less CEMF is induced, which in turn increases the armature current providing more torque for the increased load. Motor speed is increased by inserting resistance into the field coil circuit, which weakens the magnetic field. Therefore, the speed can be increased from “basic” or full-load, full-field value to some maximum speed set by the electrical and mechanical limitations of the motor.

The shunt motor is constant speed, medium starting torque & high running torque.

Equipments Required:-

1. Power supply

2. DC Motor/generator

3. DC Voltmeter/Ammeter

4. Electrodynometer (fixed 240V ac)

5. Connection Leads

6. Tachometer

7. Timing belt

Connection Diagram:-