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CHAPTER NO.:-2ELECTROMAGNETIC INDUCTION MR.KARTIK K. PATEL (B.E.-ELECT. ENGG.) (LECT. IN EE DEPT.-VPMP POLYTECHNIC)
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TOPICS:-INTRODUCTIONFARADAY’S LAWS OFELECTROMAGNETIC INDUCTION.DYNAMICALLY INDUCED EMFFLEMING’S RIGHT HAND RULESTATICALLY INDUCED EMF 1. SELF INDUCED EMF 2. MUTUALLY INDUCED EMF
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The Histor y of Induction:“In 1831 Joseph Henry discovered magnetic induction.” Joseph Henry“ Michael Faradays ideas about conservation of energy led (1797-1878) him to believe that since an electric current could causea 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 Michael Faraday (1791-1867)
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1. INTRODUCTION: THE PHENOMENA OF ELECTROMAGNETIINDUCTION ARE VERY IMPRTANT FOR THESTUDY OF THE WORKING PRINCIPLE OF THEELECTRICAL MACHINES. THE ELECTRICAL M/C LIKE DCMOTOR, DC GENERATOR, INDUCTIONMOTOR, TRANSFORMER, ALTERNATORWORKS ON INDUCTION PRINCIPLE.
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ELECTROMAGNETIC INDUCTION:How to Induce an EMF?An emf can be induced whenever there is achange in flux.
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Relative motion between a magnetand a coilConductor moving in the magnetic field
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FARADAY’S LAWS:- THERE ARE TWO LAWS OF FARADAY’S RELATED TO ELECTROMAGNETIC INDUCTION AS STATED BELOW:
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FARADAY’S FIRST LAW:-“WHEN A CONDUCTOR CUTS THE MAGNETICFIELD, THE EMF INDUCED IN THATCONDUCTOR.’’
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2.FARADAY’S SECOND LAW :“THE MAGNITUDE OF EMF INDUCED IN ANYCONDUCTRO IS EQUAL TO THE RATE OFCHANGE OF FLUX LINKAGES WITH IT.”
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FARADAY’S LAW:-If we change the magnetic flux through a coil of Nturns, an induced emf appears in every turn and thetotal emf induced in the coil is the sum of theseindividual induced emfs.
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F araday’s Law for a SingleLoop : dΦ E =ε=− dt
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Faraday’s Law for a coilhaving N turns : dΦ E = ε = −N dt
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Examples of Induced Current:- Any change of current in primaryinduces a current in secondary.
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Direction of Induced CurrentBar magnet moves through coil S N Current induced in coil vReverse pole Induced current changes sign N S vCoil moves past fixed bar magnet Current induced in coil S NBar magnet stationary inside coil N S No current induced in coil
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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
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3.1 DYNAMICALLY INDUCED EMF:Definition:-“T he EMF Induced in the coil due to thephysical movement of the magnetic fieldor coil is known as Dynamicall y InducedEMF.”
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Consider a conductor A of length L meters placed in uniform magnetic field of flux density B wb/ m2 area =l*dx flux difference=BldxE=Bldx / dtBut velocity,V =dx/dtSo ,E=Blv volt.E=Blv*sinO
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CONDITIONS FOR PRODUCTIONOF DYNAMICALLY INDUCED EMF:-• FOLLOWING THREE CONDITION :-•Presents of magnetic fields•Presents of conductor•Relative movement of magnetic field and conductor
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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 inthe coil. This emf is called statically induced emf.”There are two types of statically induced EMF:-1)Self induced emf2)Mutually induced emf
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1) Self induced EMF:-Definition:- “ The emf induced in the coil dueto change its own flux linked with is knownas self induced emf.”-Conductor remains stationary and fluxlinked with it is changed. (the current whichcreates the flux changes i.e increases ordecreases).-
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Consider a coil having N turns as shown in fig, when the currentflowing through is, a flux will produced in the iron core. So theflux link with coil changes from its initial value of Φ 1 to finalvalue of Φ2 wb in time t second.
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self inductance:-“ The property of the coil oppose the change in current or flux iscalled self inductance.”Co-efficient of self inductance:-“The co-efficient of self inductance is defined as the ratio of fluxlink with the coil to the current flow in coil.”It is denoted by L.Its unit is Henry (H).
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B(t) i ~Consider a coil having N turns. When the current Iflowing through it, it will produced the flux. ΦHence B co-efficient of self inducance is given by, L ≡ the di I ε ε = −L L≡− (dI / dt ) dtL = µ o n A = µ o n V 2 2
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2) Mutually induced EMF:-“ The emf induced in one coil due to the change in flux of anthercoil linked with it. Is called mutually induced emf.”if current changes in coil #1, an emf is induced in coil #2 ε 2 = −N d Φ1 dt Φ∝B B ∝ I1 rewrite as: ε 2 = −M dI1 dt M is the “mutual inductance”
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2) Mutual induction:-“ The property of the coil to produce the emf inanther coil placed nearer to them when the currentflowing through the first coil changes is known as themutual inductance.•It is denoted by M.•Its unit is Henry(H).
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Compare the dynamicallyinduced emf with staticallyinduced emf:-Dynamically emf: Statically emf:“the emf induced in the coil “ the emf induced in coil due to physical movement due to the flux linked with of the magnetic field or coil the coil changes is called is called dyamically emf. statically emf.”E=Blv sino volt In this type of emf there is In this type of emf there is physical motion of no any physical motion of conductor. conductor.Example: alternator, d.c Example:- induction generator. motor, transformer.
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