Basic Concept of Rotating Electrical Machines by Dr. P.S. Bimbhra

1. Basic Concept of Rotating
Electrical Machines

2. Principal of Electro-mechanical Energy Conversion
Flow of energy in Electromechanical devices:-
Energy conservation principal-
“ Energy can neither be created nor it can be
destroyed, it can only be converted from one useful
form to another.”

3.  In an energy conversion device, out of the total
input energy, some gets converted into the
required form, some gets stored & rest is
dissipated.
Eqn-(1)
 The principal of energy conservation is based on
the above equation.
Total input
energy
Mechanical
Energy output
Total
energy
stored
Total
energy
dissipated

4. The various forms of energies involved in the above
equation(1) are described below:-
1. Total electrical energy input is ‘Wei’.
2. Total mechanical energy output is ‘Wmo’
3. Total energy stored = Energy stored in magnetic field ‘Wes’
+ Energy stored in mechanical system ‘Wes’.
4. Total energy dissipated = Ohmic loss + magnetic core loss
(hysteresis & eddy current loss) + friction and windage losses etc.

5. Thus energy balance equation (1) can be written
as:-
• Wei = Wmo + (Wes + Wms) + (ohmic loss + coupling loss) +
energy loss in mechanical system.
• Rearranging the above equation we have:-
• Wei-ohmic loss = (Wmo+Wms+Mech.energy loss) + Wes
+ coupling loss
Welec = Wmech + Wfld
Eqn(2)

6. From the above fig. it is clear that electrical loss & mechanical
losses though always present, plays no basic role in the energy
conversion process.
If we apply Eqn (2)for the fig(a) we have:
dWelec = dWmech + dWfld
dWelec = (Vt – I.R)Idt = Vt Idt – Ohmic loss
dWelec = E.Idt
Therefore
E.Idt = dWmech + dWfld ------Eqn(3)

7. From the above fig. it is clear that electrical loss & mechanical
losses though always present, plays no basic role in the energy
conversion process.
If we apply Eqn (2)for the fig(a) we have:
dWelec = dWmech + dWfld
dWelec = (Vt – I.R)Idt = Vt Idt – Ohmic loss
dWelec = E.Idt
Therefore
E.Idt = dWmech + dWfld ------Eqn(3)