Electric generators

  • An electric generator is essentially the opposite of a motor.
  • A motor turns Electrical Potential Energy to Mechanical Energy.
  • A generator turns ME to EPE

Average EMF induced in a coil

Is the same as the Faraday’s law.

Max EMF induced

EMFaverage = 2NlvB

Instantaneous induced EMF

EMF instantaneous  = 2NlvBsinθ

Where θ = angle that the normal from the coil makes with the flux

Substitute cosθ if θ = angle the armature makes with the flux

RMS induced EMF

rms emf

That is, EMFmax divided by root 2.

DC generator

  • Very similar in design to a DC motor
  • Converts mechanical energy to electrical energy
  • A mechanical torque is applied to the coil, and it rotates
  • This rotation cuts through flux, so induces a voltage
  • The EMF produced is always positive, because of the split ring commutator

AC generator

  • Similar to DC
  • Coil is fixed to two slip rings which allow the armature to rotate, resulting in an AC
  • Since the coil first moves up then down, the EMF switches direction every half turn
  • Results in a sine wave if you plot EMF against time

 

 

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