Page 243 - Basic Electrical Engineering
P. 243
The steady-state value,
The larger the time constant is, the more is the time taken by the current to
rise or decay in a L–R circuit during transients. Current almost decays to zero
at five times the time constant. Beyond this time the magnitude of current is
less than one per cent of its steady-state value. When the circuit is switched
on, energy is stored in the inductor in the form of a magnetic field and during
switching off, the stored energy gets dissipated.
Example 2.52 A coil having an inductance of 1.4 H and a resistance of 1Ω
is connected to a 12 V dc source through a switch. What will be the value of
current after 400 m sec of switching on the supply? How much time will it
take for the steady-state current to drop to half its value after the switch is
turned on?
Solution:
We have,
Therefore,
