MR.KARTIK K. PATEL(B.E.-ELECT. ENGG.)

(LECT. IN EE DEPT.-VPMP POLYTECHNIC)

CHAPTER NO.:-2ELECTROMAGNETIC

INDUCTION

TOPICS:-INTRODUCTIONFARADAY’S LAWS OF ELECTROMAGNETIC INDUCTION.DYNAMICALLY INDUCED EMFFLEMING’S RIGHT HAND RULESTATICALLY INDUCED EMF 1. SELF INDUCED EMF 2. MUTUALLY INDUCED EMF

The History of Induction:

“In 1831 Joseph Henry discovered magnetic induction.”“ Michael Faraday's ideas about conservation of energy led him to believe that since an electric current could cause a magnetic field, a magnetic field should be able to produce an electric current. He demonstrated this principle of induction in 1831.’’

So the whole thing started 180 years ago

Joseph Henry(1797-1878)

Michael Faraday(1791-1867)

1. INTRODUCTION:1. INTRODUCTION:

THE PHENOMENA OF ELECTROMAGNETI INDUCTION ARE VERY IMPRTANT FOR THE STUDY OF THE WORKING PRINCIPLE OF THE ELECTRICAL MACHINES. THE ELECTRICAL M/C LIKE DC MOTOR, DC GENERATOR, INDUCTION MOTOR, TRANSFORMER, ALTERNATOR WORKS ON INDUCTION PRINCIPLE.

ELECTROMAGNETIC ELECTROMAGNETIC INDUCTION:INDUCTION:

How to Induce an EMF?An emf can be induced whenever there is a change in flux.

Relative motion between a

magnet and a coil

Conductor moving in the magnetic field

2. FARADAY’S LAWS OF 2. FARADAY’S LAWS OF ELECTROMAGNETIC ELECTROMAGNETIC INDUCTION:INDUCTION:

Michael Faraday

(1791 – 1867)

THERE ARE TWO LAWS OF FARADAY’S RELATED TO ELECTROMAGNETIC INDUCTION AS STATED BELOW:

FARADAY’SFARADAY’S LAWS:-LAWS:-

FARADAY’S FIRST LAW:-FARADAY’S FIRST LAW:-

“WHEN A CONDUCTOR CUTS THE MAGNETIC FIELD, THE EMF INDUCED IN THAT CONDUCTOR.’’

2.FARADAY’S SECOND 2.FARADAY’S SECOND LAWLAW::

“THE MAGNITUDE OF EMF INDUCED IN ANY CONDUCTRO IS EQUAL TO THE RATE OF CHANGE OF FLUX LINKAGES WITH IT.”

FARADAY’S LAW:-

If we change the magnetic flux through a coil of N turns, an induced emf appears in every turn and the total emf induced in the coil is the sum of these individual induced emfs.

FFaraday’s Law for a Single araday’s Law for a Single LoopLoop::

dt

dE

Faraday’s Law for a coil Faraday’s Law for a coil having N turnshaving N turns::

dt

dNE

Examples of Induced Current:- Any change of current in primary induces a current in secondary.

Bar magnet moves through coil Current induced in coil v

S N

Reverse pole Induced current changes sign v

N S

Coil moves past fixed bar magnet

Current induced in coil

S N

Bar magnet stationary inside coil

No current induced in coil

N S

Direction of Induced Current

3. TYPES OF INDUCED EMF:-3. TYPES OF INDUCED EMF:-

THERE ARE TWO TYPES OF INDUCED EMF:-1.DYNAMICALLY INDUCED EMF2.STATICALLY INDUCED EMF SELF INDUCED EMF MUTUALLY INDUCED EMF

3.1 DYNAMICALLY INDUCED 3.1 DYNAMICALLY INDUCED EMF:EMF:

Definition:-“The EMF Induced in the coil due to the physical movement of the magnetic field or coil is known as Dynamically Induced EMF.”

Consider a conductor A of length L meters placed in uniform magnetic field of flux density B wb/ m2

area =l*dxflux difference=Bldx

E=Bldx / dt But velocity, V =dx/dtSo ,E=Blv volt.E=Blv*sinO

CONDITIONS FOR PRODUCTION OF DYNAMICALLY INDUCED EMF:-

• FOLLOWING THREE CONDITION :-FOLLOWING THREE CONDITION :-•Presents of magnetic fields•Presents of conductor•Relative movement of magnetic field and conductor

2) Statically induced Emf:-2) Statically induced Emf:-

Definition:-“ There is no physical motion of conductor but due the flux, the flux link with the coil is changed and so emf induced in the coil. This emf is called statically induced emf.”There are two types of statically induced EMF:-1)Self induced emf2)Mutually induced emf

1) Self induced EMF:-1) Self induced EMF:-

Definition:- “ The emf induced in the coil due to change its own flux linked with is known as self induced emf.” -Conductor remains stationary and flux linked with it is changed. (the current which creates the flux changes i.e increases or decreases).-

Consider a coil having N turns as shown in fig, when the current flowing through is, a flux will produced in the iron core. So the flux link with coil changes from its initial value of to final value of 2 wb in time t second.

self inductance:-self inductance:-

“ The property of the coil oppose the change in current or flux is called self inductance.”Co-efficient of self inductance:-“The co-efficient of self inductance is defined as the ratio of flux link with the coil to the current flow in coil.”It is denoted by L.Its unit is Henry (H).

Consider a coil having N turns. When the current I flowing through it, it will produced the flux. Hence the co-efficient of self inducance is given by,

B(t)

~

i

dt

diL

VnAnL oo22

2) Mutually induced EMF:-2) Mutually induced EMF:-

“ The emf induced in one coil due to the change in flux of anther coil linked with it. Is called mutually induced emf.” if current changes in coil #1, an emf is induced in coil #2

12

dNdt

BB I1 rewrite as:

12

dIMdt

M is the “mutual inductance”

2) Mutual induction:-2) Mutual induction:-

“ The property of the coil to produce the emf in anther coil placed nearer to them when the current flowing through the first coil changes is known as the mutual inductance.

•It is denoted by M.•Its unit is Henry(H).

Compare the dynamically Compare the dynamically induced emf with statically induced emf with statically induced emf:-induced emf:-Dynamically emf:“the emf induced in

the coil due to physical movement of the magnetic field or coil is called dyamically emf.

E=Blv sino voltIn this type of emf

there is physical motion of conductor.

Example: alternator, d.c generator.

Statically emf:“ the emf induced in

coil due to the flux linked with the coil changes is called statically emf.”

In this type of emf

there is no any physical motion of conductor.

Example:- induction motor, transformer.

Thanks all of you….