Download Basic Electrical Engineering C L Wadhwa Pdf

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Contents:

• D.C. Circuits
• Electromagnetic Induction 
• A.C. Circuits 
• Network Theory 
• Three Phase Supply 
• Basic Instruments 
• Transformer 
• D.C. Machines 
• Three-Phase Synchronous Machines 
• Three-Phase Induction Motors 
• Single Phase Induction Motors 
• Power System 
• Domestic Wiring
• Multiple Choice Questions
• Reference
• Index

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It's more important to know about the Faraday's laws of electromagnetic Induction .

Faraday's laws of electromagnetic Induction :

We have two laws mainly

First Law :

It states : Whenever the magnetic flux linked with a circuit changes, an e.m.f. is always induced in it.

or

 Whenever a conductor cuts magnetic flux, an e.m.f. is induced in that conductor.

Second Law :

It states : The magnitude of the induced e.m.f. is equal to the rate of change of flux-linkages.

Induced EMF e = -NdΦ/DT

Please Comment Below If You Have Any Suggestions Or Doubts Regarding This Topic

Production of Induced EMF And Current

Production of Induced EMF And Current


In Fig.  is shown an insulated coil whose terminals are connected to a sensitive galvanometer
G. It is placed close to a stationary bar magnet initially at position AB (shown dotted). As seen, some
flux from the N-pole of the magnet is linked with or threads through the coil but, as yet, there is no
deflection of the galvanometer. Now, suppose that the magnet is suddenly brought closer to the coil in
position CD (see figure). Then, it is found that there is a jerk or a sudden but a momentary deflection
in the galvanometer and that this lasts so long as the magnet is in motion relative to the coil, not
otherwise. The deflection is reduced to zero when the magnet becomes again stationary at its new
position CD. It should be noted that due to the approach of the magnet, flux linked with the coil is
increased.

Next, the magnet is suddenly withdrawn away from the coil as in Fig. 7.2. It is found that again
there is a momentary deflection in the galvanometer and it persists so long as the magnet is in
motion, not when it becomes stationary. It is important to note that this deflection is in a direction
opposite to that of Fig. 7.1. Obviously, due to the withdrawal of the magnet, flux linked with the coil
is decreased.

The deflection of the galvanometer indicates the production of e.m.f. in the coil. The only cause
of the production can be the sudden approach or withdrawal of the magnet from the coil. It is found
that the actual cause of this e.m.f. is the change of flux linking with the coil. This e.m.f. exists so long
as the change in flux exists. Stationary flux, however strong, will never induce any e.m.f. in a station￾ary conductor. In fact, the same results can be obtained by keeping the bar magnet stationary and
moving the coil suddenly away or towards the magnet.

Relation Between Magnetism And Electricity

Hey I am Here to discuss about the Small Topic  Relation between Magnitism And Electricity

Relation Between Magnetism And Electricity

It is well known that whenever an electric current flows through a conductor, a magnetic field is

immediately brought into existence in the space surrounding the conductor. It can be said that when

electrons are in motion, they produce a magnetic field. The converse of this is also true i.e. when a

magnetic field embracing a conductor moves relative to the conductor, it produces a flow of electrons

in the conductor. This phenomenon whereby an e.m.f. and hence current (i.e. flow of electrons) is

induced in any conductor which is cut across or is cut by a magnetic flux is known as electromagnetic

induction. 

The historical background of this phenomenon is this :

After the discovery (by Oersted) that electric current produces a magnetic field, scientists began

to search for the converse phenomenon from about 1821 onwards. The problem they put to them￾selves was how to ‘convert’ magnetism into electricity. It is recorded that Michael Faraday* was in

the habit of walking about with magnets in his pockets so as to constantly remind him of the problem.

After nine years of continuous research and experimentation, he succeeded in producing electricity

by ‘converting magnetism’. In 1831, he formulated basic laws underlying the phenomenon of elec￾tromagnetic induction (known after his name), upon which is based the operation of most of the

commercial apparatus like motors, generators and transformers etc.

Force on a Current-carrying Conductor Lying in a Magnetic Field & Fleming left hand rule

Hello I am Here to present an important topic and most exciting topic

Electromagnetism

Force on a Current-carrying Conductor Lying in a Magnetic Field

It is found that whenever a current-carrying conductor is placed in magnetic field, it experiences a

 force which acts in a direction perpendicular both to the direction of the current and the field. In Fig

. is shown a conductor XY lying at right angles to the uniform horizontal field of flux density B Wb

/m2

 produced by two solenoids A and B. If l is the length of the conductor lying within this field and

 I ampere  the

current carried by it, then the magnitude of the force experienced by it is

the BIl = µ0 µr HIl newton

Using vector notation

F

= I l B

F = IlB sin θ where θ is the angle between l

which

is 90º in the present case

or F = Il B sin 90º = Il B newtons (∵ sin 90º = 1)

The direction of this force may be easily found by Fleming’s left-hand rule.

Hold out your left hand with forefinger, second finger and thumb at right angles to one another.
If the forefinger represents the direction of the field and

the second finger that of the current, then thumb gives the direction

 of the motion. It is illustrated in Fig.

shows another method of finding the direction of force acting on a current carrying conductor. It is
known as Flat Left Hand rule. The force acts in the direction of the thumb obviously, the direction of motor of the

conductor is the same as that of the force. It

 should be noted that no force is exerted on a con￾ductor when it lies parallel to the magnetic field. In general, if the conductor lies at an angle θ with the direction

of the field, then B can be resolved into two components,
B cos θ parallel to and B sin θ perpendicular to the con￾ductor. The former produces no effect whereas the latter is
responsible for the motion observed. In that case,

Fleming left hand rule

F = BIl sin θ newton, which has been expressed as
cross product of vector above.

Absolute & Relative Permiability & Flux Density

Absolute Permeability (μ) and Relative Permeability (μr) 

Magnetic lines

 a bar of a magnetic material, say, iron placed in a uniform field of strength H N/Wb. Suppose, a flux density of B Wb/m2

 is developed in the rod.

Then, the absolute permeability of the material of the rod is defined as
μ = B/H henry/metre 
or 
B = μH 
    = µ0 µr H Wb/m2 ...(i)
When H is established in air (or vacuum), then corresponding flux density developed in air is

B0 = µ0 H

Now, when iron rod is placed in the field, it gets magnetised by induction. If induced pole strength in the rod is m Wb, then a flux of m Wb emanates from its N-pole, re-enters its S-pole and continues from S to N-pole within the magnet. If A is the face or pole area of the magentised iron bar, the induction flux density in the rod is


Bi = m/A Wb/m2

Hence, total flux density in the iron rod consists of two parts 

(i) B0 –flux density in air even when rod is not present
(ii) Bi–induction flux density in the rod


B = B0 + Bi
 = µ0 H + m/A


Eq. (i) above may be written as 
B = µr . µ0 H 
    = µr B0

µr =B/B0

Hence, relative permeability of a material is equal to the ratio of the flux density produced in that material to the flux density produced in vacuum by the same magnetising force.

Flux Density (B) 

 It is given by the flux passing per unit area through a plane at right angles to the flux. It is usually designated by the capital letter B and is measured in weber/meter2 . It is a Vector Quantity. It ΦWb is the total magnetic flux passing normally through an area of A m^ 2
, then
B = Φ/A      Wb/m^2  or tesla (T)

Intensity of Magnetisation (I)

It may be defined as the induced pole strength developed per unit area of the bar. Also, it is the magnetic moment developed per unit volume of the bar.

Let


 m = pole strength induced in the bar in Wb
A = face or pole area of the bar in m^2

Then
 I = m/A    Wb/m^2
Hence, it is seen that intensity of magnetisation of a substance may be defined as the flux density
produced in it due to its own induced magnetism.

If l is the magnetic length of the bar, then the product (m × l) is known as its magnetic moment M.

I= m/A
  = m×l / A×l
  = m/V
  = Magnetic Moment / Volume