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 Wei.
(ii) Total mechanical energy output is Wmo.
(iii) Total energy stored in any device = energy stored in magnetic field, Wes + Energy stored in mechanical system , Wms.
(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 :
Wei = Wmo + ( Wes + Wms ) + ( 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.