Electrical Engineering XYZ MCQs
The magnetic circuit of a dc shunt generator with negligible armature resistance and brush contact voltage drop remains unsaturated when it delivers full-load current at rated terminal voltage. The brushes are kept in the interpolar axis and speed is maintained constant. When the load is switched off, the terminal voltage would:
- Decrease
- Become zero
- Remain the same
- Increase
Correct answer: 3. Remain the same
Explanation: When a DC shunt generator delivers full-load current at rated terminal voltage, it means the generator is operating at its maximum capacity under steady-state conditions. In this scenario, the magnetic circuit of the generator is saturated to its fullest extent, ensuring efficient power generation.
Now, when the load is suddenly switched off while keeping the generator speed constant and the brushes in the interpolar axis, several factors come into play:
- No change in flux produced: Since the generator’s speed remains constant and the brushes are in the interpolar axis, there’s no change in the magnetic field strength or the flux produced by the field winding.
- No change in armature reaction: With negligible armature resistance and brush contact voltage drop, there’s no significant change in the armature reaction when the load is switched off.
- No change in terminal voltage: Given that there are no changes in the magnetic flux or armature reaction, the induced electromotive force (EMF) remains constant. Consequently, the terminal voltage of the generator remains the same even when the load is switched off.
Therefore, the terminal voltage would remain the same when the load is switched off.