Principle of energy conversion, Mechanical Engineering

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.

Posted Date: 7/23/2012 1:14:09 AM | Location : United States

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