Electrical Engineering MCQs XYZ
If field current is decreased in shunt dc motor, the speed of the motor:
- Increases
- Decreases
- Remains same
- None of these
Correct answer: 1. Increases
Explanation: In a shunt DC motor, the field winding is connected in parallel (shunt) with the armature winding. The speed of a DC motor is given by the formula:
N ∝ {(V−Ia⋅Ra)/Φ}
where:
- N is the speed of the motor
- V is the applied voltage
- Ia is the armature current
- Ra is the armature resistance
- Φ is the flux produced by the field winding
When the field current is decreased, the flux (Φ) produced by the field winding also decreases. According to the formula, if ΦΦ decreases, the speed (N) increases, assuming that the armature current (Ia) and the applied voltage (V) remain constant.
So, in summary, if the field current is decreased in a shunt DC motor, the speed of the motor increases.