Load Cutoff Switch Upon Over and Under Voltages

8/19/2019 Load Cutoff Switch Upon Over and Under Voltages

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CHAPTER 1

INTRODUCTON

1.1 OVERVIEW:

The Project Entitled “LOAD CUTOFF SWITCH UPON OVER AND

UNDER VOLTAGES” dei!ned "ith Peri#her$l Inter%$ce Controller &Utilit' co(#$nie

h$)e enor(o* $(o*nt o% (one' in)eted in tr$n%or(er o% $ll t'#e+ incl*din!

ditri,*tion $nd #o"er tr$n%or(er& O#er$tin!+ ($int$inin!+ $nd in#ectin! $ll #o"er

tr$n%or(er $re not $n e$' "or-& In order to red*ce ,*rden on ($inten$nce o% *ch

tr$n%or(er $ ne" ide$ h$ ,een dico)ered&

Thi #roject i ($inl' *ed to #rotect the tr$n%or(er %ro( !ettin! "orn o*t

d*e to electric$l dit*r,$nce& The electric$l #$r$(eter li-e c*rrent+ )olt$!e o% the

tr$n%or(er $re %ed $ ,$e )$l*e+ *in! $ -e'#$d to the Peri#her$l Inter%$ce Controller

$nd the o*t#*t i!n$l i #ro)ided to o#er$te $ rel$' ,' co(#$rin! the ,$e )$l*e "ith the

o#er$tin! electric$l #$r$(eter& The $##lic$tion conit o% $ ,o$rd o% electronic

co(#onent incl*i)e o% $ AT./S01 (icrocontroller "ith #ro!r$(($,le lo!ic& It h$

,een dei!ned to "or- "ith

hi!h $cc*r$c'& The electric$l #$r$(eter o% the #o"er

tr$n%or(er *ch $ )olt$!e $nd c*rrent $re %ed to the Peri#her$l Inter%$ce Controller $

,$e )$l*e& The )olt$!e $nd c*rrent )$l*e d*rin! the o#er$tion o% the #o"er tr$n%or(er

i (onitored $nd %ed to the controller& Thee )$l*e $re (onitored *in! $ LCD di#l$'&

2' co(#$rin! thee )$l*e the Peri#her$l Inter%$ce Controller #rod*ce $ tri# i!n$l

"hich o#er$te the rel$' $nd in t*rn the connecti)it' ,et"een ($in *##l' $nd the #o"er

tr$n%or(er i c*t o%%+ th* #rotectin! the #o"er tr$n%or(er %ro( ($l%*nctionin!&


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CHAPTER 2

PROTECTION SYSTEM OF TRANSFORMER

2.1 INTRODUCTION:

The #rotection 'te( o% tr$n%or(er i ine)it$,le d*e to the )olt$!e %l*ct*$tion+

%re3*ent in*l$tion %$il*re+ e$rth %$*lt+ o)er c*rrent etc& Th* the %ollo"in! $*to($tic

#rotection 'te( $re incor#or$ted&

1. Buchholz !"#c!$4

A 2*chhol5 rel$'+ $lo c$lled $ !$ rel$' or $ *dden #re*re rel$'+ i $

$%et' de)ice (o*nted on o(e oil6%illed #o"er tr$n%or(er $nd re$ctor+

e3*i##ed "ith $n e7tern$l o)erhe$d oil reer)oir c$lled $ coner)$tor& The

2*chhol5 Rel$' i *ed $ $ #rotecti)e de)ice eniti)e to the e%%ect o%

dielectric %$il*re inide the e3*i#(ent& It $lo #ro)ide #rotection $!$int $ll

-ind o% lo"l' de)elo#ed %$*lt *ch $ in*l$tion %$il*re o% "indin!+ core

he$tin! $nd %$ll o% oil le)el&

2. E%&'h (%ul' &!l%)$:

An e$rth %$*lt **$ll' in)ol)e $ #$rti$l ,re$-do"n o% "indin! in*l$tion to

e$rth& The re*ltin! le$-$!e c*rrent i conider$,l' le th$n the hort circ*it

c*rrent& The e$rth %$*lt ($' contin*e %or $ lon! ti(e $nd cre$te d$($!e

,e%ore it *lti($tel' de)elo# into $ hort circ*it $nd re(o)ed %ro( the 'te(&

U*$ll' #ro)ide #rotection $!$int e$rth %$*lt onl'&

*. O"!& cu&&!+' &!l%)$:


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An o)er c*rrent rel$'+ $lo c$lled $ o)erlo$d rel$' h$)e hi!h c*rrent

ettin! $nd $re $rr$n!ed to o#er$te $!$int %$*lt ,et"een #h$e& U*$ll'

#ro)ide #rotection $!$int #h$e 6to6#h$e %$*lt $nd o)erlo$din! %$*lt&

,. D#((!&!+'#%l $)$'!-:

Di%%erenti$l 'te(+ $lo c$lled $ circ*l$tin!6c*rrent 'te( #ro)ide

#rotection $!$int hort6circ*it ,et"een t*rn o% $ "indin! $nd ,et"een

"indin! th$t corre#ond to #h$e6to6#h$e or three #h$e t'#e hort6circ*it

ie+ it #ro)ide #rotection $!$int e$rth $nd #h$e %$*lt&

The co(#lete #rotection o% tr$n%or(er **$ll' re3*ire the co(,in$tion o%

thee 'te(& 8ot o% the tr$n%or(er $re **$ll' connected to the *##l'

'te( thro*!h erie %*e inte$d o% circ*it ,re$-er& In e7itin! (ethod the

tr$n%or(er doe not h$)e $*to($tic #rotecti)e rel$' %or #rotectin! the

tr$n%or(er&


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2.2 TRANSFORMER DEFINITION

A de)ice *ed to tr$n%er electric ener!' %ro( one circ*it to $nother+ e#eci$ll' $ #$ir o% (*lti#le "o*nd+ ind*cti)el' co*#led "ire coil th$t $%%ect *ch $ tr$n%er "ith $

ch$n!e in )olt$!e+ c*rrent+ #h$e+ or other electric ch$r$cteritic&

F#/ 2.1 B%$#c T&%+$(o&-!&


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2.* THE UNIVERSA0 EMF EUATION

I% the %l*7 in the core i in*oid$l+ the rel$tionhi# %or either "indin! ,et"een it

n*(,er o% t*rn+ )olt$!e+ ($!netic %l*7 denit' $nd core cro6ection$l $re$ i !i)en ,'

the *ni)er$l e(% e3*$tion 9%ro( F$r$d$': L$";4

E=2πfNaB

√ 2=4.44 fNaB


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A co(#$red "ith !ener$tor+ in "hich ($n' $,nor($l condition ($' $rie+

#o"er tr$n%or(er ($' *%%er onl' %ro(4

=& O#en circ*it

1& O)erhe$tin!

>& Windin! hort6circ*it

2..1 O3!+ c#&cu#' F%ul'$:

An o#en circ*it in one #h$e o% $ >6#h$e tr$n%or(er ($' c$*e *ndeir$,le

he$tin!& In #r$ctice+ rel$' #rotection i not #ro)ided $!$int o#en circ*it ,ec$*e thi

condition i rel$ti)el' h$r(le& On the occ*rrence o% *ch $ %$*lt+ the tr$n%or(er c$n ,e

diconnected ($n*$ll' %ro( the 'te(&

2..2 O"!&h!%'#+/ F%ul'$:

O)erhe$tin! o% the tr$n%or(er i **$ll' c$*ed ,' *t$ined o)erlo$d or hort

circ*it $nd )er' occ$ion$ll' ,' the %$il*re o% the coolin! 'te(& The rel$' #rotection i

$lo not #ro)ided $!$int thi contin!enc' $nd ther($l $cceorie $re !ener$ll' *ed to

o*nd $n $l$r( or control the ,$n- o% %$n&

2..* W#+#+/ Sho&'4c#&cu#' F%ul'$:

Windin! hort6circ*it 9$lo c$lled intern$l %$*lt; on the tr$n%or(er $rie %ro(

deterior$tion o% "indin! in*l$tion d*e to o)erhe$tin! or (ech$nic$l inj*r'& When $n

intern$l %$*lt occ*r+ the tr$n%or(er (*t ,e diconnected 3*ic-l' %ro( the 'te(

,ec$*e $ #rolon!ed $rc in the tr$n%or(er ($' c$*e oil %ire& There%ore+ rel$' #rotection

i $,ol*tel' nece$r' %or intern$l %$*lt&


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2.5 PROPOSED METHOD

In #ro#oed (ethod+ (onitorin! $nd #rotectin! the #o"er tr$n%or(er %ro(

o)er)olt$!e $nd o)er c*rrent $re #er%or(ed $*to($tic$ll' ,' *in! PIC (icrocontroller&

2.5.1 Co-3o+!+'$ o( 'h! 3&o6!c':

The #rotection o% #o"er tr$n%or(er th$t "e h$)e i(#le(ented $ o*r #roject

e7cl*i)el' cont$in the %ollo"in! $ ho"n in the Fi!& 1&1

Recti%ier+ %ilter $nd Re!*l$tin! circ*it 9Po"er circ*it;

?e'#$d $nd LCD di#l$'

Dri)er circ*it $nd $ Rel$'

AT./01 (icrocontroller ,o$rd

POWER SUPPLY

Power supply is a reference to a source of electrical power. A deviceor system that supplies electrical or other types of energy to an outputload or group of loads is called a power supply unit or PSU. The

term is most commonly applied to electrical energy supplies, lessoften to mechanical ones, and rarely to others.

Here in our application we need a 5v DC power supply for all

electronics involved in the project. This requires step down

transformer, rectifier, voltage regulator, and filter circuit for generation

of 5v DC power. Here a rief description of all the components are

given as follows!

TRANSFORMER:


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A transformer is a device that transfers electrical energy from one

circuit to another through inductively coupled conductors " the

transformer#s coils or $windings$. %&cept for air'core transformers, the

conductors are commonly wound around a single iron'rich core, or

around separate ut magnetically'coupled cores. A varying current in

the first or $primary$ winding creates a varying magnetic field in the core (or cores) of the

transformer. This varying magnetic field induces a varying

electromotive force (%*+) or $voltage$ in the $secondary$ winding.

This effect is called mutual induction.

f a load is connected to the secondary circuit, electric charge will flow

in the secondary winding of the transformer and transfer energy from

the primary circuit to the load connected in the secondary circuit.

The secondary induced voltage -, of an ideal transformer, is scaled

from the primary -/ y a factor equal to the ratio of the numer of

turns of wire in their respective windings!


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0y appropriate selection of the numers of turns, a transformer thus

allows an alternating voltage to e stepped up " y ma1ing 2 more

than 2/ " or stepped down, y ma1ing it.

AS!" PARTS OF A TRANSFORMER

n its most asic form a transformer consists of!

A primary coil or winding.

A secondary coil or winding.

A core that supports the coils or windings.

3efer to the transformer circuit in figure as you read the following

e&planation! The primary winding is connected to a 4'hert6 ac

voltage source. The magnetic field (flu&) uilds up (e&pands) and

collapses (contracts) aout the primary winding. The e&panding and

contracting magnetic field around the primary winding cuts the

secondary winding and induces an alternating voltage into the

winding. This voltage causes alternating current to flow through the

load. The voltage may e stepped up or down depending on the

design of the primary and secondary windings.


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TH% C7*/72%2T 7+ A T3A2+73*%3

Two coils of wire (called windings) are wound on some type of core

material. n some cases the coils of wire are wound on a cylindrical or

rectangular cardoard form. n effect, the core material is air and the

transformer is called an A3'C73% T3A2+73*%3. Transformers

used at low frequencies, such as 4 hert6 and 8 hert6, require a

core of low'reluctance magnetic material, usually iron. This type of

transformer is called an 372'C73% T3A2+73*%3. *ost power


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transformers are of the iron'core type. The principle parts of a

transformer and their functions are!

The C73%, which provides a path for the magnetic lines of flu&.

The /3*A39 :2D2;, which receives energy from the ac source.

The %C72DA39 :2D2;, which receives energy from the

primary winding and delivers it to the load.

The %2C


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According to the conventional model of current flow originally

estalished y 0enjamin +ran1lin and still followed y most engineers

today, current is assumed to flow through electrical conductors from

the positi%e to the ne&ati%e pole. n actuality, free electrons in a

conductor nearly always flow from the ne&ati%e to the positi%e pole.

n the vast majority of applications, however, the actual direction of

current flow is irrelevant. Therefore, in the discussion elow the

conventional model is retained.

n the diagrams elow, when the input connected to the left corner of

the diamond is positi%e, and the input connected to the ri&'t corner is ne&ati%e, current flows from the upper supply terminal to the right

along the re( (positive) path to the output, and returns to the lower

supply terminal via the )lue (negative) path.


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:hen the input connected to the left corner is ne&ati%e, and the

input connected to the ri&'t corner is positi%e, current flows from thelower supply terminal to the right along the re( path to the output,

and returns to the upper supply terminal via the )lue path.

n each case, the upper right output remains positive and lower right

output negative. ince this is true whether the input is AC


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or DC, this circuit not only produces a DC output from an AC input, it

can also provide what is sometimes called $reverse polarity

protection$. That is, it permits normal functioning of DC'powered

equipment when atteries have een installed ac1wards, or when

the leads (wires) from a DC power source have een reversed, and

protects the equipment from potential damage caused y reverse

polarity.

/rior to availaility of integrated electronics, such a ridge rectifier

was always constructed from discrete components. ince aout

>?5, a single four'terminal component containing the four diodes

connected in the ridge configuration ecame a standard commercial

component and is now availale with various voltage and current

ratings.

OUTPUT SMOOT*!N$

+or many applications, especially with single phase AC where the full'waveridge serves to convert an AC input into a DC output, the addition of a capacitor

may e desired ecause the ridge alone supplies an output of fi&ed polarity ut

continuously varying or $pulsating$ magnitude (see diagram aove).


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The function of this capacitor, 1nown as a reservoir capacitor (or smoothing

capacitor) is to lessen the variation in (or #smooth#) the rectified AC output voltage

waveform from the ridge. 7ne e&planation of #smoothing# is that the capacitor

provides a low impedance path to the AC component of the output, reducing the

AC voltage across, and AC current through, the resistive load. n less technical

terms, any drop in the output voltage and current of the ridge tends to e

canceled y loss of charge in the capacitor. This charge flows out as additional

current through the load. Thus the change of load current and voltage is reduced

relative to what would occur without the capacitor. ncreases of voltage

correspondingly store e&cess charge in the capacitor, thus moderating the

change in output voltage @ current.


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The simplified circuit shown has a well'deserved reputation for eing

dangerous, ecause, in some applications, the capacitor can retain a

lethal charge after the AC power source is removed. f supplying a

dangerous voltage, a practical circuit should include a reliale way to

safely discharge the capacitor. f the normal load cannot e

guaranteed to perform this function, perhaps ecause it can e

disconnected, the circuit should include a leeder resistor connected

as close as practical across the capacitor. This resistor should

consume a current large enough to discharge the capacitor in a

reasonale time, ut small enough to minimi6e unnecessary power

waste.

0ecause a leeder sets a minimum current drain, the regulation of

the circuit, defined as percentage voltage change from minimum to

ma&imum load, is improved. However in many cases the

improvement is of insignificant magnitude. The capacitor and the load resistance have a typical time constant B 3C where

C and 3 are the capacitance and load resistance respectively. As long as the

load resistor is large enough so that this time constant is much longer than the

time of


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one ripple cycle, the aove configuration will produce a smoothed DC

voltage across the load.

n some designs, a series resistor at the load side of the capacitor is

added. The smoothing can then e improved y adding additional

stages of capacitorresistor pairs, often done only for su'supplies to

critical high'gain circuits that tend to e sensitive to supply voltage

noise.

The ideali6ed waveforms shown aove are seen for oth voltage and current

when the load on the ridge is resistive. :hen the load includes a smoothing

capacitor, oth the voltage and the current waveforms will e greatly changed.

:hile the voltage is smoothed, as descried aove, current will flow through the

ridge only during the time when the input voltage is greater than the capacitor

voltage. +or e&ample, if the load draws an average current of n Amps, and the

diodes conduct for > of the time, the average diode current during conduction

must e >n Amps. This non'sinusoidal current leads to harmonic distortion and

a poor power factor in the AC supply.


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n a practical circuit, when a capacitor is directly connected to the output of a

ridge, the ridge diodes must e si6ed to withstand the current surge that

occurs when the power is turned on at the pea1 of the AC voltage and the

capacitor is fully discharged. ometimes a small series resistor is included efore

the capacitor to limit this current, though in most applications the power supply

transformer#s resistance is already sufficient.

7utput can also e smoothed using a cho1e and second capacitor.

The cho1e tends to 1eep the current (rather than the voltage) more

constant. Due to the relatively high cost of an effective cho1e

compared to a resistor and capacitor this is not employed in modern

equipment.

ome early console radios created the spea1er#s constant field with

the current from the high voltage ($0 E$) power supply, which was

then routed to the consuming circuits, (permanent magnets were then

too wea1 for good performance) to create the spea1er#s constant

magnetic field. The spea1er field coil thus performed F jos in one! it

acted as a cho1e, filtering the power supply, and it produced the

magnetic field to operate the spea1er.


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RE$ULATOR !" +,-../

t is a three pin C used as a voltage regulator. t converts unregulated DC current

into regulated DC current.

2ormally we get fi&ed output y connecting the voltage regulator at

the output of the filtered DC (see in aove diagram). t can also e

used in circuits to get a low DC voltage from a high DC voltage (for

e&ample we use G5 to get 5- from >F-). There are two types of

voltage regulators >. fi&ed voltage regulators (G&&, G?&&) F. variale

voltage regulators (G) n fi&ed voltage regulators there is

another classification >. Eve voltage regulators F. 've voltage

regulators /7T-% -7


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regulators. The most commonly used ones are G5 and G>F. G5

gives fi&ed 5- DC voltage if input voltage is in (G.5-, F-).

T*E "APA"!TOR F!LTER

The simple capacitor filter is the most asic type of power supply

filter. The application of the simple capacitor filter is very limited. t is

sometimes used on e&tremely high'voltage, low'current power

supplies for cathode ray and similar electron tues, which require

very little load current from the supply. The capacitor filter is also

used where the power'supply ripple frequency is not criticalJ this

frequency can e relatively high. The capacitor (C>) shown in figure

8'>5 is a simple filter connected across the output of the rectifier in

parallel with the load.

+ull'wave rectifier with a capacitor filter.


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:hen this filter is used, the 3C charge time of the filter capacitor (C>)

must e short and the 3C discharge time must e long to eliminate

ripple action. n other words, the capacitor must charge up fast,

preferaly with no discharge at all. 0etter filtering also results when

the input frequency is highJ therefore, the full'wave rectifier output is

easier to filter than that of the half'wave rectifier ecause of its higher

frequency.

+or you to have a etter understanding of the effect that filtering has

on %avg, a comparison of a rectifier circuit with a filter and one without

a filter is illustrated in views A and 0 of figure 8'>4. The output

waveforms in figure 8'>4 represent the unfiltered and filtered outputs

of the half'wave rectifier circuit. Current pulses flow through the load

resistance (3


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The value of the capacitor is fairly large (several microfarads), thus it

presents a relatively low reactance to the pulsating current and it

stores a sustantial charge.

The rate of charge for the capacitor is limited only y the resistance of

the conducting diode, which is relatively low. Therefore, the 3C

charge time of the circuit is relatively short. As a result, when the

pulsating voltage is first applied to the circuit, the capacitor charges

rapidly and almost reaches the pea1 value of the rectified voltage

within the first few cycles. The capacitor attempts to charge to the

pea1 value of the rectified voltage anytime a diode is conducting, and

tends to retain its charge when the rectifier output falls to 6ero. (The

capacitor cannot discharge immediately.) The capacitor slowly

discharges through the load resistance (3


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A comparison of the waveforms shown in figure 8'>4 (view A and

view 0) illustrates that the addition of C> to the circuit results in an

increase in the average of the output voltage (%avg) and a reduction in

the amplitude of the ripple component (%r ) which is normally present

across the load resistance.

2ow, let#s consider a complete cycle of operation using a half'wave rectifier, a

capacitive filter (C>), and a load resistor (3


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through the load resistor (3 produces the downward

slope as indicated y the solid line on the waveform in view 0. n contrast to the

arupt fall of the applied ac voltage from pea1 value to 6ero, the voltage across

C> (and thus across 3G0. ' Capacitor filter circuit (positive and negative half cycles).

NE$AT!0E *ALF1"Y"LE


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ince practical values of C> and 3. The charge on C> is the cathode potential of the

diode. :hen the potential on the anode e&ceeds the potential on the

cathode (the charge on C>), the diode again conducts, and C> egins

to charge to appro&imately the pea1 value of the applied voltage.

After the capacitor has charged to its pea1 value, the diode will cut off

and the capacitor will start to discharge. ince the fall of the ac input

voltage on the anode is consideraly more rapid


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than the decrease on the capacitor voltage, the cathode quic1ly

ecome more positive than the anode, and the diode ceases to

conduct.

7peration of the simple capacitor filter using a full'wave rectifier is

asically the same as that discussed for the half'wave rectifier.

3eferring to figure 8'>, you should notice that ecause one of the

diodes is always conducting on. either alternation, the filter capacitor

charges and discharges during each half cycle. (2ote that each diode

conducts only for that portion of time when the pea1 secondary

voltage is greater than the charge across the capacitor.)

+igure 8'>. ' +ull'wave rectifier (with capacitor filter).


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Another thing to 1eep in mind is that the ripple component (% r ) of the

output voltage is an ac voltage and the average output voltage (%avg)

is the dc component of the output. ince the filter capacitor offers

relatively low impedance to ac, the majority of the ac component

flows through the filter capacitor. The ac component is therefore

ypassed (shunted) around the load resistance, and the entire dc

component (or %avg) flows through the load resistance. This

statement can e clarified y using the formula for LC in a half'wave

and full'wave rectifier. +irst, you must estalish some values for the

circuit.


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Load Cutoff Switch Upon Over and Under Voltages

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Transcript of Load Cutoff Switch Upon Over and Under Voltages