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

         dW_elect = ( dW_mech + dW_f + dW_loss  ) ..... Motor

         dW_mech = ( dW_elect + dW_f + dW_loss ) ..... Generator

         Where

         dW_elect = Change in electrical energy

         dW_mech = Change in mechanical energy

         dW_f = Change in field energy

         dW_loss = 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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