Q. Describe the principle of energy conversion. Show that the reaction of coupling magnetic field on the electrical or mechanical system is essential for the electro - mechanical energy conversion.

Sol.   Principal of energy conversion:

When energy is converted from one form into another., the principal of conversion energy can be invoked. According to this principle, energy can neither be created nor destroyed; it can merely be converted from one form into another.

The energy balance eq. must include these four energy terms and for a motor, it can be written as:

      (Total electrical energy input) = (Mechanical energy output) + (Total energy stored) + (Total energy dissipated)

And for a generator:

     ( Total mechanical energy output ) = ( Electrical energy input ) + (Total energy stored) + ( Total energy dissipated )

The various forms of energy involved for an electromechanical energy conversion devices, are now described below :

(i)                 Total electrical energy input from the supply main is W_ei.

(ii)               Total mechanical energy output is W_mo.

(iii)             Total energy stored in any device = energy stored in magnetic field, W_es + Energy stored in mechanical system , W_ms.

(iv)              Total energy dissipated = energy dissipated in electric circuit as ohmic losses + Energy dissipated as magnetic core loss ( hysteresis and eddy current losses ) + energy dissipated in mechanical system ( friction and windage losses etc. )

Thus the energy balance can be written in more specific form as :

             W_ei = W_mo + ( W_es + W_ms ) + (  ohmic energy losses + coupling field energy losses ) + Energy losses in mechanical system.

                   The subscripts e, m, i, s and o stands for electrical, mechanical, input, stored and output respectively.