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Machines Measurements EMT

Machines Measurements EMT
Question:-
Option (A)
field resistance was higher than critical resistance
Option (B)
there was no residual magnetism in the field circuit
Option (C)
field winding was wrongly connected
Option (D)
there was a break in the armature circuit
Correct Option:
C
Question Solution:
The small voltage due to residual magnetism, should circulate current in the field coils in such a direction as to produce flux lines aiding the residual flux. If the field connections are incorrect, the flux produced by small field current opposes the residual flux and the generated voltage decreases to zero.
Question:-
Option (A)
the interpoles produced additional flux to augment the developed torque
Option (B)
the flux waveform is improved with reduction in harmonics
Option (C)
the inequality of air-gap flux on the top and bottom halves of the armature is removed
Option (D)
a counter-emf is induced in the coil undergoing commutation
Correct Option:
D
Question:-
Option (A)
(ii) and (iii)
Option (B)
(iii) and (iv)
Option (C)
(i) and (ii)
Option (D)
(i) and (iv)
Correct Option:
C
Question Solution:
According to Lenz' law, direction of current in secondary will be such that flux due to secondary current will oppose the flux due to primary current.

Due to primary, the flux set-up in the core is in anti-clockwise direction.