Page 242 - Basic Electrical Engineering

This shows that as time increases, the current practically becomes very
very small to ultimately becoming zero.

Example 2.51 A coil of resistance 5 Ω and inductance 0.1H is switched on

to a 230 V, 50 Hz supply. Calculate the rate of rise of current at t = 0 and at t
= 2τ where τ = L/R. What is the steady-state value of the circuit current?

Solution:

For the rise in current

Substituting values,

or, i = 46(1 − e −50t )

The rate of change of current,

= 2300 e −50t

at t = 0

at t equal to two times the time constant,