Q. In every electromagnetic conversion device, both generator and motor action take place simultaneously. Explain.
The case the output is mechanical as in a motoring mode, the coupling field must react with the electrical system as to absorb electrical energy from electrical system. In such a case i.e. in a motoring mode this reaction is counter emf e , similar to the emf induced in the primary winding of a transformer the coupling field extracts energy proportional to ei from the electrical system, converts it into mechanical from and delivers energy proportional to T? to the mechanical system.
In case the output is electrical as in a generating mode, the coupling field must react with mechanical system so as to absorb mechanical energy from mechanical system. In such a case ei, in a generating mode, this reaction is the counter torque T developed due to interactions of current i and the coupling field. Thus coupling field extracts mechanical energy proportional to T? from the mechanical system converts into electrical form and delivers energy proportional to ei to the electrical system.
Example
A coil with an axial length of 25 cm and diameter of 20 cm has 200 turns. It is placed in a uniform radial flux of 0.002 web/m2/ (a) If the coil is rotated at 25 rev. per sec., find the voltage induced in the coil. (b) What will be the force on each conductor and torque acting on the coil, if it carries a current of 10 Amps.
l = 25 cm
d = 20 cm
N = 200 turn
Φ = 0.002 ?b/m2
V = 25 rev. per sec.
e = T
e = Blv
B = Φ/a
a = π/4 (d2) = π/4 × (20 × 10-2)2 = 0.0314 m2
B = 0.002/0.0314 T
B = 0.06269 T
e = 0.06363 × (25 × 10-2) × 25
e = 0.398
e = 0.4 volts
f = BIl
F = 0.06369 × 10 × 25 × 10-2 = 0.159225 newtons
T = 2 IBRl
= 2 × 10 × 0.06369 × 20/2 × 10-2 × 25 × 10-2 = 0.031845 N-m