ELE 1001 Basic Electrical Technology Lecture 5 Inductor

ELE 1001: Basic Electrical Technology Lecture 5 Inductor Department of Electrical & Electronics Engineering

Overview of topics Ø What is an Inductor? Ø Transient behavior of an Inductive circuit Ø Inductor as an energy storage element. Department of Electrical & Electronics Engineering

Inductors Ø Inductor is a passive electric device that stores energy in its magnetic field when a current flows through it Ø A coil of wire wound on a core Ø Air core Inductor, iron core inductor Ø Circuit representation is Department of Electrical & Electronics Engineering

Inductive Circuit Ø Inductance (L) : Property which opposes the rate of change of current. Ø The voltage induced in the inductor is proportional to the rate of change of current flowing through it L Ø Unit is Henry (H). i + Ø e. L = L (di/dt) v L Ø This proportionality constant is the self inductance or inductance (L) Department of Electrical & Electronics Engineering

Equivalent Inductance Ø In series Ø In Parallel Department of Electrical & Electronics Engineering

Growth of current in an Inductive Circuit Ø Department of Electrical & Electronics Engineering

Growth of current in an Inductive Circuit Ø Time Constant, = L/R Ø Time taken by the current through the inductor to reach its final steady state value, had the initial rate of rise been maintained constant Department of Electrical & Electronics Engineering

Decay of current in an Inductive Circuit Ø Initial current is through inductor is I 0 = V/R Ø At t =0, switch is moved from position a to b Department of Electrical & Electronics Engineering

Decay of current in an Inductive Circuit Department of Electrical & Electronics Engineering

Energy Stored in an Inductor Ø Department of Electrical & Electronics Engineering

Summary Ø Department of Electrical & Electronics Engineering

Illustration 1 An R-L series circuit is designed for a steady current of 250 m. A. A current of 120 m. A flows in the circuit at an instant 0. 1 sec after connecting the supply voltage. Calculate i) time constant of the circuit ii) the time from closing the circuit at which the circuit current has reached 200 m. A. Ans: (i) Time constant = 0. 1529 s (ii) t= 0. 2461 s Department of Electrical & Electronics Engineering

Illustration 2 A coil of resistance 8Ω and inductance of 0. 5 H is connected to 110 V d. c supply through a switch. The switch is closed at t=0 seconds. Find Ø Rate of change of current at the instant of closing of switch. Ø Final steady value of current. Ø Time constant of the circuit Ø Time taken by the circuit to rise to half of steady state value of current. Ans: (i) 220 A/s ; (ii) 13. 75 A (iii) 0. 0625 seconds (iv) 0. 04332 seconds Department of Electrical & Electronics Engineering