Energy Balance

Energy Balance

• According to the principle of conservation of energy, the energy cannot be created or destroyed but it can be transformed from one form to another. The process of energy transformation is reversible but there are certain losses due to practical devices. Hence in energy conversion process the entire energy cannot be transformed from one form to another. The loss in the process is called energy loss. In addition to the loss, some part of energy gets stored in the medium like magnetic field. This is called energy stored. There exists a perfect energy balance in the process of electromechanical energy conversion. Thus the input energy has three parts, transformed energy, energy loss and stored energy. The energy loss gets converted to heat energy in the electromechanical devices. Thus the energy balance equation for generating and motoring actions can be written as,

• In these energy balance equations, the transformed energy terms are always positive but change in energy stored may be positive or negative. If energy stored increases, it is positive while if it decreases it is negative. The energy dissipated in the form of heat can be because of copper loss (IPR) due to current flowing in winding, eddy current loss, hysteresis loss, mechanical friction etc. The energy balance equation can also be expressed interms of differential energy terms as,

dW_e = dw_m + dW_f + dW_loss                          ... (2.2.3)

dW_m = dW_e + dW_f + dW_loss                         ... (2.2.4)

and   

where dW_e = Differential electrical energy

dW_m = Differential mechanical energy

dW_loss = Differential energy loss or energy dissipated

dW_f = Differential stored energy in magnetic field        

• The analysis of the electromechanical device can be done using such energy balance equation. This is called energy method of analysis based on conservation of energy.

 Review Question         

1. Write a note on energy balance equation.