Page 492 - Handbook of Electrical Engineering
P. 492
482 HANDBOOK OF ELECTRICAL ENGINEERING
Figure 20.1 Mutually coupling and leakage fluxes in coils that share a common magnetic iron core.
is called the flux linkage ψ. An emf is induced in the winding when the current is changed and
therefore when the flux linkage is changed in sympathy with the current. The emf e induced is:-
dψ
e =
dt
dψ dI dI
= · = L (20.1)
dI dt dt
which opposes the applied voltage at the terminals of the winding.
Where L is the inductance of the winding in henrys (or flux linkages per ampere). If I varies
sinusoidally then the emf is induced in a co-sinusoidal manner,
d(I sin ωt)
ˆ
ˆ
e = L = ωLI cos ωt volts
dt
ˆ
= XI cos ωt
where X = ωL is the inductive reactance at the frequency ω.
When the emf is induced in one winding by the current changing in a second winding the
process is called ‘induction by transformer action’ or ‘transformer induced emf’.
The rate of change of flux linkages can be brought about by rotating one winding with respect
to a second winding, as is the fundamental situation in a motor or generator. If the current that
