o7 to 17th lecture

8/8/2019 O7 to 17th Lecture

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07th LECTURE 28-07-2010

MAGNETIC MATERAILS1:-FERROMAGNEETIC MATERAILS

2:-DIAMAGNETIC MATERAILS

3:-PARAMAGNETIC MATERIALS

1> FERROMAGNETIC MAERIALS:-These materials has high & positive

susceptibility to a magnetic field.

These contains a strong attraction to a magnetic field and retain this property

after external field has been removed.

The materials whose permeability thousand times greater then the free space

are called ferromagnetic materials

Iron, nickel & cobalt etc.

2> DIAMAGNETIC MATERILS:-very week & negative susceptibility to amagnetic field .

It repelld slightly by a magnetic field and does not retain this property afterthe external field has been removed

Materials have less permeability than the free space is called diamagnetic

materials

Copper ,gold & silver etc

3> PARAMAGNETIC MATERIALS:-small and positive susceptibility to themagnetic field.

It attracts slightly by a magnetic field and does not retain this property

after the external field has been removed

Permeability slightly breaker than the free space

Magnesium ,molybdenum,& lithium

CHAPTER NO#___01___ 8th lecture 29-07-2010

TRNASFORMER

Transformer is a static machine/device.

It transfer electrical power from one ckt to another ckt

During transfer of power there is no change occur in the frequencyWORKING PRINCIPLE

The T.F work on mutual induction action b/w the two ckt coils ( Michael

Faraday ) Tow circuit are combined by a common magnetic flux.

Its simple form, it consist of two inductive coils which are electrically

isolated ( speratily ) but magnetically inter link to each other.

If two coils placed near to each other and if one is connected to a A.C

Supply, the EMF will be induced in the coil. The EMF induced will be

according to the turn of the secondary coil


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PRIMARY WINDINGThat winding which is connected to the A.C Suppaly or that winding which is energized

with the source.

SECONDARY WINDING

The winding which is connected with the load OR that winding from which we takeoutput.

If we increase or decrease the magnitude of voltage that will no effect on

frequency

Due to system frequency the frequency on other ckt remains same and also small

turning ( 0.025 ) effects.

CONSTRUCTION OF T.F

Magnetic core and winding are the two basic pars of the t.fCORE

The T.F core is made of nonagon and coldroled ,high permeability silicon

steel of this lamination

Each lamination is insulated with variation or oxide coating to reduce eddy

cuurent losses

The thickness of each lamination various 0.35mm to 0.5mm

The shape of each strip is E I and L 7(INVERSE L) as shown in figure


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E I L 7 0.35mm for a frequency 50Hz

0.5mm for a frequency 25Hz

E I types used for shell type T.F

L 7 types used for core type Core may be either in square or rectangular in shape

It has two parts vertical and horizontal

The vertical portion is called limp

The horizontal portion is called yoke

Two coils are wondeon on the limb or on the the central limb

One coil is called primery winding and secondary is called secondary

winding

The winding which is connected to the source is called primery

winding

The winding from which we take output or connected the load is calledsecondary winding

CLASSIFICATION OF T.F

1/ ACCORDING TO THE CORE

a > core type transformerb > shell type transformer

2/ ACCORDING TO THE VOLTAGE

a > step up transformer

b > step down transformer3/ ACCORDING TO THE PHASE

a > single phase transformer

b > three phase transformer4/ ACCORDING TO THE COOLING

10TH LECTURE 03-08-2010

1 > ACCORDING TO THE CORE


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a

In the core type T.F windings surround a considerable part of the

core

Core inside the winding

Winding around the core

High voltage level/high capacity

B > SHELL TYPE T.F

In shell type T.F the core surrounds a considerable portion of the winding

Small capacity

2 _ACCORDING TO THE VOLTAGE

A > STEP UP T.F

The T.F which increases the output voltage means low voltage into high voltage

The number of turns in the secondary side is more than the primary side

N2 > N1N1 > N2


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B > STEP DOWN T.F

The T.F which change the high voltage level into low voltage level

The number of turns in the secondary side is less than the primary side

Step down T.F are used for secondary transmission & distribution

Step up T.F are used in Generation station

3_ACCORDING TO THE PHASE

A > Single Phase T.F

B > Three Phase T.F4_ACCORDING TO THE COOLING

A > Oil filled self cooled

B > Oil filled water CooledC > Air force cooled forecey oil cooled with air or water

D > Air blast type

E > Naturally air cooling system

11th LECTURE 04-08-2010

EMF EQUATION OF THE T.F

OR

VOLTAGE EQUATION OF THE T.F

Let

N1 = no: of turns on the primary side

N2 = no: of turns on the secondary sidef = supply frequency

=maximum core flux in Webers = ( Bm*A )


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we know that when a.c supply is connected to the winding flow gets its maximum value1/4 cycle

i.e 1/4f sec time period

average value of flux

consider that flux is changing sunsiodully the emf will be sinusoidal then sin wave

FORM FACTOR= R.M.S/AVERAGE VALUE=1.11

=0.707 MAX: VALUE/0.637 MAX: VALUE =1.11

F.F=1.11

: . Per turn induced EMF

=1.11*4f

=4.44f volt

EMF induced in primery winding having number of turns ( N1 ) Np

Ep=E1=4.44f Np volts

Similarly Emf induced in the secondary winding having no: of turns N2,Ns

Es=E2=V2=4.44f Ns

=Bm*A


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E1=4.44f N1 volts=4.44f BmaxN1*A volts

E2=4.44f N2 voltsE2=4.44Bmax*AN2 volts

12th LECTURE 05-08-2010

Transf


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Continue lec

Continu


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Continue le

Contine l


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13TH AND 14TH LECTURES ARE ON PROBLEMS( NUMRICALS )

15TH LECTURE 11-08-2010

ADVANTAGES OF T.F The transformer is a static device or machinery and there is no wear and tear ,it

has no friction losses

No attention or little attention is required for operation so its maintains is low

As , there is no rotating part in it an extra high voltage or high power can be

transferred easily by providing a good insulation to its winding

T.F ideally changes one A.C level to another A.C level without the effectingactual power supplied

If a transformer step up the voltage to the level of circuit it must decrease the

current to keep the power into the device equal to the power output

Electrical power can be generated at one central location ,its voltage stepped up to

the transformation over long distance at very low losses & its voltage steppeddown again for final value

IDEAL TRANSFORMER

Ideal transformer is one which has no losses i.e its winding have no Ohmic

losses , there is no magnetic leakage and hence which has no (I^2R) and corelosses

An ideal transformer is less losses device with an input winding and output

winding

The relationship b/w input voltage and output voltage & input current and

output current


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16th LECTURE 12-08-2010

TRANSFORMER CONNECTED AT NO LOAD An ideal T.F there is no core losses and copper losses

In practical transformer these two losses can not be neglected

At no load condition , the primery current is not fully reactive and it

supplies

i. Iron losses in the core ,that is hysteresis and eddy current losses

ii. Very small amount of copper losses in the primary windingiii. There is no copper losses in the secondary winding

iv. The no load current lags behind V1 by angle which is less than

90.

v. The no load input power is given by W0=V1I1COS ,

COS =no load P.F at no load condition


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I. Active component Iw, In phase with the primary voltage v is called power

component-supply the iron losses ( hystrsis & eddy current losses )

Iw=I0COSII. Magnetizing component Iju.

It is WATT less component and its function is maintain the alternating flux in the

core with the sets up EMF induced E2 and nearly equal to V.

Im=I0SIN

The no load current is 1 to 5% of full load current.

TRANSFORMER CONNECTED AT LOAD


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When transformer is connected with load , secondary current will set up its own

flux due to its own EMF

opposes the main

N2I2 known as demagnetizing

E1 will decrease by the magnitude of decrease.

V1 > E1 and primary winding draw pure current I2

I2 step up its own EMF

which opposes the and direction as .

N1I2=N2I2

I2=(N2/N1)I2

I2/I2=N2/N1

IW & IM are constant where T.F is connected at load or no load.

The P.F and T.F at no load is very small ,i.e negligible

Basically there are three fluxes, main flux

The losses occur in T.F are called Core Losses.


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17TH LECTURE 16-08-2010

LEAKAGE FLUX AND MUTUAL FLUX

When the primary winding is excited ,magnetic flux is build up throughthe core

All the flux does not round the core link with the secondary winding

MUTUAL FLUX

The flux linking both primary and secondary is called mutual or

magnetizing flux denoted by

The flux which remain in the core of the T.F and link with both

primary and secondary winding is called magnetic flux.

LEAKAGE FLUX

The portional flux that goes through one of T.F coil not the otherone is called leakage flux ,

OR

Which passes through the primary winding but return through theair ,by passing the secondary winding.


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o7 to 17th lecture

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