Question

For a d.c. shunt generator to self excite, the conditions to be satisfied are that there must be some residual magnetism in the field magnet, it must be in the proper direction and the shunt field resistant must be
1. Above the critical field resistance
2. Equal to the critical field resistance
3. Less than the armature resistance
4. Less than the critical field resistance

Answer 1

Correct Answer - Option 4 : Less than the critical field resistance

The following conditions must be satisfied for voltage build-up in a self-excited DC generator.

• There must be a sufficient residual flux in the field poles.
• The field terminals should be connected in such a way that the field current increases flux in the direction of residual flux.
• The field circuit resistance should be less than the critical field circuit resistance.

 

Note: If there is a no residual flux in the field poles, disconnect the field from the armature circuit and apply a dc voltage to the field winding. this process is called Flashing the field. It will induce some residual flux in the field poles.