Electrical Machines
A part an alternator winding consist of eight coils in series, each having an emf of 20 V rms induced in it. Coils are placed in successive slots and between each slot and the next, there is an electrical phase displacement of 30°. Find the emf of eight coils in series

  66.91 V.
 76.91 V.
 86.91 V.
 56.91 V.

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Electrical Machines
Two 3-phase AC generators are such that one has twice the linear dimensions of the other. The field windings of each are excited to give identical sinusoidal air-gap flux density waveform. Both have the same number of stator slots and identical winding patterns. The conductor/slot in a big generator is K times that of the smaller one. The value of K to get equal no load voltage at same frequency is

 4.
 8.
  1/2.
 1/4.

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Electrical Machines
A 3-φ alternator has negligible stator resistance. A short circuit test is conducted on this alternator. At a particular speed, a field current of If1 is required to drive the rated armature current. If the speed of the alternator is reduced to half, the field current required to maintain rated armature current

 Would be equal to If1/2.
 Woud be equal to 2If1.
 Would be equal to If1.
  Cannot be predicted due to insufficient data.

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Electrical Machines
For satisfactory parallel operation of two transformers which of the following conditions is most essential,

 MVA rating of all transformer inversely proportional to impedance.
  polarities of all transformers must be same.
 percentage impedance of all transformers must be same.
 voltage ratio of all transformers must be same.

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