Energy - Balance Theory

Energy Balance Theory

In this article, the energy balance theory is given which is given to the most of rotating machines. 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 Theory: Motor

  • Electrical Input energy = Mechanical Output energy + Change in stored energy

Energy Balance Theory: Motor

  • Mechanical Input energy = Electrical Output energy + Change in stored energy

Energy Balance Theory Equation

The energy balance equation can also be written in following way

dWelect = ( dWmech + dWf + dWloss  ) ..... Motor

dWmech = ( dWelect + dWf + dWloss ) ..... Generator


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

You may also like to read these articles:

Law of conservation of Energy

Single Excited System – Doubly Excited System

How voltage is built up in Generator?

Armature Reaction in the DC Generator

Current harmonic – Voltage harmonic


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