Electrical Engineering ⇒ Topic : Rise of Current in an inductive circuit

RISE OF CURRENT IN AN INDUCTIVE CIRCUIT

Let i = current at any instant,

      I_m = maximum steady value of current (= V/R),

     R = resistance,

      L = inductance, and

      λ= time constant of the circuit (= L/R)

Then, important relations are:

(a) Rise of Current

                                               .......(1)

                                ........ 1(a)

                             fig (a)                                                                                         fig (b)

Hence the time constant X of an R-L circuit may be defined as the time during which the current actually rises to 0.632 of its maximum steady value Fig.(b):

The delayed rise of çurrent in an inductive circuit is utilized in providing time lag in operation of electric relays and trip coils etc.

(b) Decay of Current

                                          ......... (2)

 Putting t = λ in eqn. (2), we get

                                         ........... 2 (a)

Hence time constant (X) of an R-L circuit may be defined as the time during which current falls 0.37 or 37% of its maximum steady value while decaying Fig.(b)

                                                  Fig.(b) Decay of current in an R-L circuit