Correct Answer - Option 3 : Zero
Concept:
- Residual magnetism is the small magnetic field left in the iron cores of the shunt fields when the generator is at rest
- Without it, the fields would have to be flashed with a DC current in order to start the generator generating; Hence to start the generator, it is necessary for the DC shunt generator
- Once it is destroyed, it can be restored by connecting its field finding to a DC source for a short time to magnetize the poles
- So, we need to connect the field winding to a battery (DC source)
Explanation:
In dc generators, induced emf is given by
\({E_b} = \frac{{\phi ZNP}}{{60A}}\)
Induced emf is directly proportional to speed, it will be zero at zero speed.