The correct answer is: A shunt generator can self-excite only if the resistance of the field circuit is less than critical value.
A shunt generator is a type of DC generator in which the field winding is connected in parallel with the load. The field winding is responsible for creating the magnetic field that induces an emf in the armature winding. The amount of current that flows through the field winding determines the strength of the magnetic field.
If the resistance of the field circuit is too high, the current that flows through the field winding will be too low. This will result in a weak magnetic field, and the generator will not be able to self-excite.
If the resistance of the field circuit is too low, the current that flows through the field winding will be too high. This will result in a strong magnetic field, and the generator may be damaged.
The critical value of resistance is the value of resistance at which the generator will self-excite. The critical value of resistance depends on the design of the generator.
To self-excite, a shunt generator must have a field current that is greater than the critical value. The field current can be increased by decreasing the resistance of the field circuit.
The following is a brief explanation of each option:
- Option A: A shunt generator can self-excite only if the resistance of the field circuit is less than critical value. This is the correct answer.
- Option B: A shunt generator can self-excite only if the resistance of the field circuit is greater than critical value. This is incorrect. A shunt generator can self-excite only if the resistance of the field circuit is less than critical value.
- Option C: A shunt generator can self-excite irrespective of the value of the resistance in the field circuit. This is incorrect. A shunt generator can self-excite only if the resistance of the field circuit is less than critical value.
- Option D: None of the above. This is incorrect. The correct answer is option A.