Electrical Machines
To have sparkless commutation, the armature reaction effect in a DC machine is neutralized by

  compensating winding and commutating poles.
 fixing the brush axis inline with the pole axis.
 shifting the brush axis from GNA to MNA.
 increasing field excitation.

ANSWER DOWNLOAD EXAMIANS APP

Electrical Machines
The results of a slip test for determining direct axis (Xd) and quadrature axis (Xq) reactances of a star connected salient pole alternator are given below Phase values: Vmax = 108 V ; Vmin = 96 V Imax = 12 A ; Imin = 10 A Hence the two reactances will be

 Xd = 9.6Ω and Xq = 9Ω
 Xd = 8Ω and Xq = 10.8Ω
 Xd = 10.8Ω and Xq = 8Ω
 Xd = 9Ω and Xq = 9.6Ω

ANSWER DOWNLOAD EXAMIANS APP