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Inductor

An inductor is a passive two terminal element designed to store energy in its magnetic field. Inductor also called reactor or coil. It consists of conductor like wire wound into a coil. When current passing through the coil, energy is stored temporarily into the magnetic field. Applications of inductor in our daily life are transformers, power supplies, TVs, radios, radars etc.

When current passes through a conductor then the conductor has inductive properties and we can regard it as an inductor. But the inductance may be little. To enhance the inductance of the inductor practically inductor is usually formed into a cylindrical coil with many turns of conducting wire as shown in below image.

 

inductor construction

                                                        photo by Windell H. Oskay

inductor picture

photo by Windell H. Oskay

 

The electric current passing through the conductor creates magnetic flux (Φ). If magnetic flux increases, inductance also increases. Relation between inductance and magnetic flux is

L = Φ / i

Equation shows inductance depends on magnetic flux created by circuit current. If current passes through the inductor coil, voltage induced by the inductor is directly proportional to its rate of change in current.

v  = dΦ / dt

From equation , v  =  L di / dt        ————- (i)

Here L is proportionality constant and known inductance of the inductor. Henry is the unit of inductance. 1 Henry equals 1 volt second per ampere.

Geometrically inductance depends upon many facts such inductor coil shape, cross section area, number of turn on coil, permeability of core material and spacing between turns.

Mathematically L = N2μA / l .

 

Equation (i) shows voltage current relationship in inductor. Below figure shows the graphical representation of this relationship when inductance is independent of current for an inductor.

voltage current relationship of an inductor in graphThis type inductor is known as a linear inductor. When current varies then inductance varies, in this situation the graph will not be straight line. That type inductor is non linear inductor.

Inductors are commercially available in many different shapes like capacitor. Practical inductor has values ranging from micro henrys (μH) to ten of henrys (H). Inductors can be fixed or variable like capacitor.

The core of inductor is made of steel, iron, plastic or air.

 

inductor symbol

Some practical inductors are shown in below image

 

inductors practical

 

Types of inductor

Inductor varies according to application.

Radio frequency inductor

 

 

Radio frequency inductors

photo by  wikipedia/F1jmm

 

Radio frequency inductor is known as RF inductor also. RF inductors are used in many sectors. In mobile communications, satellite TV receivers, filters, vehicle location system, matching networks, GPS etc.

Air core inductor

 

aircore inductor

photo by wikipedia

 Air core inductor coil wound on plastic, ceramic and other non magnetic materials. They have low inductance than magnetic core inductor. But they have high frequency. Because air core inductor has no core losses as they supply high frequency. A problem occurs in air core inductor when mechanical vibration forms it gives variations of inductance.

Ferromagnetic core inductor

 

Ferromagnetic core inductors

photo by wikipedia

 Iron core or ferromagnetic core is used in ferromagnetic core inductor. This type inductor gives high inductance. When current flows through ferromagnetic inductor causes two losses in core called eddy current loss and hysteresis loss.

 Laminated core inductor

 

Laminated core inductors

photo by wikipedia

 To prevent eddy current inductors are made with laminated core. So they give low frequency. Laminated core inductor has same construction as transformer. The core of laminated core inductor made with stacks of thin steel sheets.

Inductor application

Inductors are used hugely in AC circuits. They are used also as electric filter and signal processing. Inductors are commonly used in analogue circuits. In power section inductors are extensively used. They are used with the combination of capacitor.  In electrical transmission system inductors are used as reactors because they are used to limit switching and fault current. Inductor can store energy like capacitor to its magnetic field though it has limitation how long can store. Inductor is used in motor to convert electrical energy to mechanical energy. Most important uses of inductor are in transformer. Couple inductors are used in transformer.

Inductor construction

 

construction of inductor

photo by wikipedia

 Inductor made with a coil wound on a core. Copper wire is used as coil to wound on core. The core is made with ferromagnetic material either plastic or steel. Low frequency inductor such transformer with core electrical steel laminated. Lamination prevents eddy current.

Property of inductor

Inductor has following properties

i)    The voltage across an inductor is zero when the current is not changing remains constant. Thus an inductor acts like short circuit to dc. i.e. since di/dt  = 0 and v = L di/dt. Putting value v = 0 volt.

ii)  The current flowing through an inductor can not change instantaneously or suddenly. According to the equation v = L di/dt discontinuous change in the current through an inductor requires an infinite voltage which is physically impossible.  In this way current through an inductor can not down instantaneously.

The current may take the form of figure denoted possible through an inductor but can not take the shape of figure denoted not possible in real life situations due to the discontinuities.

 

Property of inductor

 

properties of inductor

iii)  Inductor is a passive device which store energy to its magnetic field surrounding the device.

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