department of electrical & electronics engineering ele 1001: basic electrical technology lecture...
TRANSCRIPT
Department of Electrical & Electronics Engineering
ELE 1001: Basic Electrical Technology
Lecture 5
Inductor
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What is an Inductor?
Transient behavior of an Inductive circuit
Inductor as an energy storage element.
Overview of topics
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Inductors Inductor is a passive electric device that stores
energy in its magnetic field when a current flows through it
A coil of wire wound on a core Air core Inductor, iron core inductor
Circuit representation is
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Inductive Circuit
Inductance (L) : Property which opposes the rate of
change of current. The voltage induced in the inductor is proportional to the
rate of change of current flowing through it
eL = L (di/dt)
Unit is Henry (H).
This proportionality constant is the self inductance
or inductance (L)
L
+i vL
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Equivalent Inductance
In series
In Parallel
𝑳𝒆𝒒=𝑳𝟏+𝑳𝟐+……+𝑳𝒏
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Growth of current in an Inductive Circuit
Applying KVL,
Initial Conditions,
Final current & voltage equation,
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Growth of current in an Inductive Circuit
Time Constant, = L/R Time taken by the current through the inductor to reach its
final steady state value, had the initial rate of rise been maintained constant
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Decay of current in an Inductive Circuit
Initial current is through inductor is I0 = V/R
At t =0, switch is moved from position a to b
Lv
R0t
LV
ab i
Applying KVL,
Using initial conditions and solving,
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Decay of current in an Inductive Circuit
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Energy Stored in an Inductor
Instantenous power ,
Energy absorbed in ‘dt’ time is
Energy absorbed by the magnetic field when current is increased from 0 to I amperes, is
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Summary
Inductor stores energy in its magnetic field.
When a series RL circuit is connected to a d.c voltage source, there is an exponential growth of current through the inductor and the current decays exponentially when the voltage source is removed.
Time constant of a series RL circuit is
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Illustration 1
An R-L series circuit is designed for a steady current of 250mA. A current of 120 mA 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 mA.
Ans: (i) Time constant = 0.1529 s(ii) t= 0.2461 s
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Illustration 2
A coil of resistance 8Ω and inductance of 0.5H is connected to 110V d.c supply through a switch. The switch is closed at t=0 seconds. Find Rate of change of current at the instant of closing of
switch. Final steady value of current. Time constant of the circuit 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