Electrical Machines
which of the following type of brush and their application is/are correct

 copper graphite → low voltage high current density
 electro graphite → large ratings
 carbon brush → normal ratings
All of these

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Electrical Machines
A DC shunt generator builds up to a voltage of 220 V at no load while running at its rated speed. If the speed of the generator is raised by 25% kepping the circuit conditions unaltered, then the Voltage to which the machine would build up will

 increase to value lying between 220 V and 1.25 times 220 V
 increase to a value greater than 1.25 times 220 V
 increase to 1.25 times 220 V
 not change and remain at 220 V

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Electrical Machines
Compensating windings are used in DC generators

  to neutralize the cross magnetizing effect of the armature reaction.
  mainly to reduce the eddy currents by providing local short circuit.
None of these
  to provide path for the circulation of cooling air.

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

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