What would be the magnitude and direction of average voltage induced across the field coils of a 6-pole DC generator each having 500 turns if there is a magnetic flux of 0.03 Wb/pole when the field is excited and residual magnetism of 0.003 Wb/pole after the field circuit is opened in 0.02 second? Consider the field coils to be connected in series.

Correct option is D

Given
P= Number of poles =6
N= Total turns =6×500=3000 (since 500 turns per pole in series)
Total initial flux =6×0.03=0.18 Wb. (since number of poles is 6)
Total residual flux =6×0.003=0.018 Wb
Change in flux, dϕ=0.18-0.018=0.162 Wb
Time of opening of circuit, dt=0.02 second
From concept,
Induced EMF

=24300 V
Its direction is the same as the initial direction of the exciting current.