6 September 2017

Energy - Balance Theory

  • The electric motor receives the energy at the input terminal and delivers it at the mechanical output terminals. 
  • The mechanical energy is given at the input terminal whereas the electrical energy produces at the output terminals in the case of generator. 
  • Energy – balance equation : Motor
        Electrical Input energy = Mechanical Output energy + Change in stored energy
  • Energy – balance equation : Generator
         Mechanical Input energy = Electrical Output energy + Change in stored energy
  • The energy balance equation can also be written in following way

         dWelect = ( dWmech + dWf + dWloss  ) ..... Motor
         dWmech = ( dWelect + dWf + dWloss ) ..... Generator
         Where
         dWelect = Change in electrical energy
         dWmech = Change in mechanical energy
         dWf = Change in field energy
         dWloss = Change in energy losses
  • The transferred energy are always taken as positive ( + Ve ) but change in stored energy in the coupling field may be either positive or negative in the energy balance equation. 
  • Its value can be taken as positive for increase in the stored energy and negative for decrease in the stored energy. 
  • If the losses in the electro – mechanical systems are neglected, the energy balance equation can be written in general form
             Input energy = Output energy + Change in stored energy

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