Electrical Machines
Which of the following methods are used to control the speed of DC motors is

 supply voltage control
All of these
 armature circuit resistance control
 field current control

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Electrical Machines
Compensating windings are used in DC generators

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

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