## 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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