Three Phase Fault Analysis with Auto Reset on Temporary Fault and Permanent Trip Otherwise
ABSTRACT The project is designed to develop an automatic tripping mechanism for the three phase supply system The project output resets automatically after a !rief interruption in the event temporary fault while it remains in tripped condition in case of permanent fault The electrical su!station which supply the power to the consumers ie industries or domestic can have failures due to some faults which can !e temporary or permanent These faults lead to su!stantial damage to the power system e"uipment #n #ndia it is common to o!serve the failures in supply system due to the faults that occur during the transmission or distri!ution The faults might !e $% &$ine to %round'( $$ &$ine to $ine'( )$ &Three lines' in the supply systems and these faults in three phase supply system can affect the power system To overcome this pro!lem a system is !uilt( which can sense these faults and automatically disconnects the supply to avoid large scale damage to the control gears in the grid su!*stations This system is !uilt using three single phase transformers which are wired in star input and star output( and ) transformers are connected in delta connections( having input ++, volt and output at -+ volt This concept low voltage testing of fault conditions is followed as it is not advisa!le to create on mains line ... timers are used for handling short duration and long duration fault conditions A set of switches are used to create the $$( $% and )$ fault in low voltage side( for activating the tripping mechanism Short duration fault returns the supply to the load immediately called as temporary trip while long duration shall result in permanent trip
Chapter/ #ntroduction of Three Phase Fault Si0 num!ers of steps down transformers are used for forming star and delta secondary secondary s at at low voltage output output Fault condition condition is created with a set of switches to input $$( $%( )$ fault to the circuit This triggers a ... timer in monosta!le to reset after fault clearance in a short duration temporary fault or permanently trip the output in case of prolonged fault ‟
1e 2now that if the fault accurse then it creates many pro!lems to the load 3any times load is damaged So it is very important to protect the system again the faults 4ifferent type of fault in ) phase is/ $*$ fault &line to line fault' $*% fault &line to ground fault' +$*% fault &dou!le line to ground fault' 3ostly $*% fault &line to ground' fault is occurs in industries( su! station and any other places where three phase supply is used( other fault is occur in !ed condition compare to $*% fault This type fault is damage the load so we prepared the protection circuit which is introduce !elow5
Chapter/+ Bloc2 4iagram Fig/ +- Bloc2 4iagram
+- #ntroduction of Bloc2 4iagram 66#n prevention circuit si0 num!ers of steps down transformers are used for forming star6and delta secondary s at low voltage output 6 Fault condition is created with a set of switches to input $$( $%( )$ fault to circuit This triggers a ... timer in monosta!le to reset after fault clearance in a short duration temporary fault clearance in short duration temporary fault or permanently trip the output incase of prolonged fault 6 6 6 6 6 6 The electrical su!station which supply the power to the consumers ie industries or domestic can have failures due to some faults which can !e temporary or permanent These faults lead to su!stantial damage to the power system e"uipment #n #ndia it is common to o!serve the failures in supply system due to the faults that occur during the transmission or distri!ution The faults might !e $% &$ine to %round'( $$ &$ine to $ine'( )$ &Three lines' in the supply systems and these faults in three phase supply system can affect the power system To overcome this pro!lem a system is !uilt( which can sense these faults and automatically disconnects the supply to avoid large scale damage to the control gears in the grid su!*stations 6 6 6 6 6 6 This system is !uilt using three single phase transformers which are wired in star input and star output( and ) transformers are connected in delta connections( having input ++, volt and output at -+ volt This concept low voltage testing of fault conditions is followed as it is not advisa!le to create on mains line ... timers are used for handling short duration and long duration fault conditions A set of switches are used to create the $$( $% and )$ fault in low voltage side( for activating the tripping mechanism Short 6 ‟
duration fault returns the supply to the load immediately called as temporary trip while long duration shall result in permanent trip 6 #n an electric power system( a fault is any a!normal electric current For e0ample( a short circuit is a fault in which current !ypasses the normal load An open*circuit fault occurs if a circuit is interrupted !y some failure #n three* phase systems( a fault may involve one or more phases and ground( or may occur only !etween phases #n a 7ground fault7 or 7earth fault7( charge flows into the earth The prospective short circuit current of a fault can !e calculated for power systems #n power systems( protective devices detect fault conditions and operate circuit !rea2ers and other devices to limit the loss of service due to a failure 6 6 6 6 #n a poly*phase system( a fault may affect all phases e"ually which is a 7symmetrical fault7 #f only some phases are affected( the resulting 7asymmetrical fault7 !ecomes more complicated to analy8e due to the simplifying assumption of e"ual current magnitude in all phases !eing no longer applica!le The analysis of this type of fault is often simplified !y using methods such as symmetrical components 6 6 6 4esign of systems to detect and interrupt power system faults is the main o!jective of power system protection 6
Chapter/) 6 TRA9SFOR3:R 6 ;AR41AR: CO3PO9:9TS 6 6 6 6 6 6 6 6
6 6 R:S#STOR 6 6 CAPAC#TOR 6
)- Transformer A transformer is a static electrical device that transfers energy !y inductive coupling !etween its winding circuits A varying current in the primarywinding creates a varying magnetic flu0 in the transformer?s core and thus a varying the secondary winding This magnetic flu0 through varying magnetic flu0 induces a varying electromotive force &emf' or voltage in the secondary winding Transformers can !e used to vary the relative voltage of circuits orisolate them( or !oth Transformers range in si8e from thum!nail*si8ed used in microphones to units weighing hundreds of tons interconnecting the power grid A wide range of transformer designs are used in electronic and electric power applications Transformers are essential for the transmission( distri!ution( and utili8ation ofelectrical energy Fig/ )- Transformer Circuit The ideal transformer model assumes that all flu0 generated !y the primary winding lin2s all the turns of every winding( including itself #n practice( some flu0 traverses paths that ta2e it outside the windings Such flu0 is termed lea2age flu0( and results in lea2age inductance in series with the mutually coupled transformer windings $ea2age flu0 results in
energy !eing alternately stored in and discharged from the magnetic fields with each cycle of the power supply #t is not directly a power loss &see Stray losses !elow'( !ut results in inferior voltage regulation( causing the secondary voltage not to !e directly proportional to the primary voltage( particularly under heavy load Transformers are therefore normally designed to have very low lea2age inductance 9evertheless( it is impossi!le to eliminate all lea2age flu0 !ecause it plays an essential part in the operation of the transformer The com!ined effect of the lea2age flu0 and the electric field around the windings is what transfers energy from the primary to the secondary #n some applications increased lea2age is desired( and long magnetic paths( air gaps( or magnetic !ypass shunts may deli!erately !e introduced in a transformer design to limit the shortcircuit current it will supply $ea2y transformers may !e used to supply loads that e0hi!it negative resistance( such as electric arcs( mercury vapor lamps( and neon signs or for safely handling loads that !ecome periodically short*circuited such as electric arc welders The conducting material used for the windings depends upon the application( !ut in all cases the individual turns must !e electrically insulated from each other to ensure that the current travels throughout every turn For small power and signal transformers( in which currents are low and the potential difference !etween adjacent turns is small( the coils are often wound from enamelled magnet wire( such as Formvar wire $arger power transformers operating at high voltages may !e wound with copper rectangular strip conductors insulated !y oil*impregnated paper and !loc2s press!oard
Fig/ )+ Transformer ;igh*fre"uency transformers operating in the tens to hundreds of 2ilohert8 often have windings made of !raided $it8 wire to minimi8e the s2in* effect and pro0imity effect losses $arge power transformers use multiple*stranded conductors as well( since even at low power fre"uencies non*uniform distri!ution of current would otherwise e0ist in high*current windings :ach strand is individually insulated( and the strands are arranged so that at certain points in the winding( or throughout the whole winding( each portion occupies different relative positions in the complete conductor The transposition e"uali8es the current flowing in each strand of the conductor( and reduces eddy current losses in the winding itself The stranded conductor is also more fle0i!le than a solid conductor of similar si8e( aiding manufacture The windings of signal transformers minimi8e lea2age inductance and stray capacitance to improve high*fre"uency response Coils are split into sections( and those sections interleaved !etween the sections of the other winding Power*fre"uency transformers may have taps at intermediate points on the winding( usually on the higher voltage winding side( for voltage adjustment Taps may !e manually reconnected( or a manual or automatic switch may !e provided for changing taps Automatic onload tap changers are used in electric power transmission or distri!ution( on e"uipment such @
as arc furnace transformers( or for automatic voltage regulators for sensitive loads Audiofre"uency transformers( used for the distri!ution of audio to pu!lic address loudspea2ers( have taps to allow adjustment of impedance to each spea2er A center*tapped transformer is often used in the output stage of an audio power amplifier in a push*pull circuit 3odulation transformers in A3 transmitters are very similar 4ry*type transformer winding insulation systems can !e either of standard open*wound ?dip*and*!a2e? construction or of higher "uality designs that include vacuum pressure impregnation &
feed!ac2 control loops #t may use an electromechanical mechanism( or electronic components 4epending on the design( it may !e used to regulate one or more AC or 4C voltages :lectronic voltage regulators are found in devices such as computer power supplies where they sta!ili8e the 4C voltages used !y the processor and other elements #n automo!ile alternators and central power station generator plants( voltage regulators control the output of the plant #n an electric power distri!ution system( voltage regulators may !e installed at a su!station or along distri!ution lines so that all customers receive steady voltage independent of how much power is drawn from the line Fig/ ))
Other important parameters are/ Temperature coefficient of the output voltage is the change with temperature &perhaps averaged over a given temperature range' #nitial accuracy of a voltage regulator &or simply 7the voltage accuracy7' reflects the error in output voltage for a fi0ed regulator without ta2ing into account temperature or aging effects on output accuracy 4ropout voltage is the minimum difference !etween input voltage and output voltage for which the regulator can still supply the specified current A low drop*out &$4O' regulator is designed to wor2 well even with an input supply only a volt or so a!ove the output voltage The input*output differential at which the voltage regulator will no longer maintain regulation is the dropout voltage Further reduction in input voltage will result in reduced output voltage This value is dependent on load current and junction temperature A!solute ma0imum ratings are defined for regulator components( specifying the continuous and pea2 output currents that may !e used &sometimes internally limited'( the ma0imum input voltage( ma0imum power dissipation at a given temperature( etc Output noise &thermal white noise' and output dynamic impedance may !e specified as graphs versus fre"uency( while output ripple noise &mains 7hum7 or switch*mode 7hash7 noise' may !e given as pea2*to*pea2 or R3S voltages( or in terms of their spectra Guiescent current in a regulator circuit is the current drawn internally( not availa!le to the load( normally measured as the input current while no load is connected &and hence a source of inefficiency5 some linear regulators are( surprisingly( more efficient at very low current loads than switch*mode designs !ecause of this' Transient response is the reaction of a regulator when a &sudden' change of the load current &called the load transient' or input voltage &called the line transient' occurs Some regulators will tend to oscillate or have a slow response time which in some cases might lead to undesired results This value is different from the regulation parameters( as that is the sta!le situation definition The transient response shows the !ehaviour of the regulator on a change This data is usually provided in the technical documentation of a regulator and is also dependent on output capacitance
3irror*image insertion protection means that a regulator is designed for use when a voltage( usually not higher than the ma0imum input voltage of the regulator( is applied to its output pin while its input terminal is at a low voltage( volt*free or grounded Some regulators can continuously withstand this situation5 others might only manage it for a limited time such as , seconds( as usually specified in the datasheet This situation can occur when a three terminal regulator is incorrectly mounted for e0ample on a PCB( with the output terminal connected to the unregulated 4C input and the input connected to the load 3irror*image insertion protection is also important when a regulator circuit is used in !attery charging circuits( when e0ternal power fails or is not turned on and the output terminal remains at !attery voltage A simple voltage regulator can !e made from a resistor in series with a diode &or series of diodes' 4ue to the logarithmic shape of diode <*# curves( the voltage across the diode changes only slightly due to changes in current drawn or changes in the input 1hen precise voltage control and efficiency are not important( this design may wor2 fine Feed!ac2 voltage regulators operate !y comparing the actual output voltage to some fi0ed reference voltage Any difference is amplified and used to control the regulation element in such a way as to reduce the voltage error This forms a negative feed!ac2 control loop5 increasing the open*loop gain tends to increase regulation accuracy !ut reduce sta!ility &avoidance of oscillation( or ringing during step changes' There will also !e a trade*off !etween sta!ility and the speed of the response to changes #f the output voltage is too low &perhaps due to input voltage reducing or load current increasing'( the regulation element is commanded( up to a point( to produce a higher output voltageH !y dropping less of the input voltage &for linear series regulators and !uc2switching regulators'( or to draw input current for longer periods &!oost*type switching regulators'5 if the output voltage is too high( the regulation element will normally !e commanded to produce a lower voltage ;owever( many regulators have over*current protection( so that they will entirely stop sourcing current &or limit the current in some way' if the output current is too high( and some regulators may also shut down if the input voltage is outside a given range &see also/ crow!ar circuits'
)) Timer The ... Timer #C is an integrated circuit &chip' implementing a variety of timer and multivi!rator applications The #C was designed !y ;ans R Camen8ind in -E, and !rought to mar2et in -E- !y Signetics &later ac"uired !y Philips' The original name was the S:... &metal can'9:... &plastic 4#P' and the part was descri!ed as IThe #C Time 3achineJ #t has !een claimed that the ... gets its name from the three . KL resistors used in typical early implementations( M+@ !ut ;ans Camen8ind has stated that the num!er was ar!itrary The part is still in wide use( than2s to its ease of use( low price and good sta!ility As of +,,)( it is estimated that - !illion units are manufactured every year F#% )T#3:R #C 4epending on the manufacturer( the standard ... pac2age includes over +, transistors( + diodes and -. resistors on a silicon chip installed in an N* pin mini dual*in*line pac2age &4#PN' M@
Asta!le H free running mode/ the ... can operate as an oscillator =ses include $:4 and lamp flashers( pulse generation( logic cloc2s( tone generation( security alarms( pulse position modulation( etc Bista!le mode or Schmitt trigger/ the ... can operate as a flip*flop( if the 4#S pin is not connected and no capacitor is used =ses include !ouncefree latched switches( etc =sage The connection of the pins is as follows/ Pin 9ame - + ) . N %94 TR#% O=T Purpose %round( low level &, <' O=T rises( and interval starts( when this input falls !elow -)
... Basics The ... timer #C is a sim ple N pin 4#$ pac2age #C #t can/ 6 6 6 !e used as a monosta!le !e used as an asta!le source or sin2 -,,3a use supply voltages of .v to -.v disrupt the power supply* use a decoupling capacitor 6 =sing the ... as a !uffer A !uffer circuit allows an input circuit to !e connected to an ou tput circuit( it is li2e an interface !etween one cir cuit and another The !uffer circuit re"uires very little input current !ut should !e a!le to supply ade"uate output current The ... can supply in e0cess of -,,3a of current and so can !e used as a convenient !uffer for logic gates which cannot supply much current The ... can also Qsin2 a similar amount of current The circuit used is/ ‟
F#% / )N T#3:R AS A B=FF:R The circuit acts li2e an inverter or 9OT gate 1hen the input is held low( the output is high and will provide &source' current 1hen the input is held high( the output is low and will sin2 current Remem!er( for a !uffer for even higher power devices that re"uire even larger currents( the ... !uffer can !e used to drive a relay or a transistor circuit =sing the ... as a monosta!le 6 6 6 6 6 6 6 6 The ... can !e used as a monosta!le using the circuit shown/ The output is normally low !ut will go high for a short length of time depending on the values of the other components R and C determine the time period of the output pulse The input is normally high and goes low to trigger the output &falling edge triggered' The length of the input pulse must !e less than the length of the output pulse The =f capacitor decouples the supply to avoid affecting other parts of the circuit #t is standard to add a -,9f capacitor from pin. to gnd T -- R C T H seconds( R H ohms( C H Farads The minimum value of R should !e a!out -2 to avoid too much current flowing into the ... The ma0imum value of R should !e a!out -3 so that enough current can flow into the input of the ... and there is The minimum value also current to of C -,,Pf allow for the electrolytic capacitors lea2age current to avoid the timing e"uation !eing too far off The ma0imum value of C should !e a!out -,,,UF as any !igger capacitors will discharge too much current through the chip
These ma0imum and minimum values give a minimum period of ,- Us and a ma0imum period of -,,,s ) 4iode 4iodes are used to convert AC into 4C these are used as half wave rectifier or full wave rectifier Three points must he 2ept in mind while using any type of diode -3a0imum forward current capacity +3a0imum reverse voltage capacity )3a0imum forward voltage capacity Fig/ -9,, diodes The num!er and voltage capacity of some of the important diodes availa!le in the mar2et are as follows/ 4iodes of num!er #9,,-( #9,,+( #9,,)( #9,,( #9,,.( #9,, and #9,, have ma0imum reverse !ias voltage capacity of .,< and ma0imum forward current capacity of - Amp 4iode of same capacities can !e used in place of one another Besides this diode of more capacity can !e used in place of diode of low capacity !ut diode of low capacity cannot !e used in place of diode of high capacity For e0ample( in place of #9,,+5 #9,,- or #9,, can !e used !ut #9,,or #9,,+ cannot !e used in place of #9,,The diode B>-+.made !y company B:$ is e"uivalent of diode from #9,,- to #9,,) B> -+ is e"uivalent to diodes #9,, to ,, and B> -+ is e"uivalent to diode #9,,
Fig/ )-, P9 Vunction diode P9 V=9CT#O9 OP:RAT#O9 9ow that you are familiar with P* and 9*type materials( how these materials are joined together toform a diode( and the function of the diode( let us continue our discussion with the operation of the P9junction But !efore we can understand how the P9 junction wor2s( we must first consider current flow inthe materials that ma2e up the junction and what happens initially within the junction when these twomaterials are joined together Current Flow in the 9*Type 3aterial Conduction in the 9*type semiconductor( or crystal( is similar to conduction in a copper wire Thatis( with voltage applied across the material( electrons will move through the crystal just as current wouldflow in a copper wire This is shown in figure -*-. The positive potential of the !attery will attract thefree electrons in the crystal These electrons will leave the crystal and flow into the positive terminal ofthe !attery As an electron leaves the crystal( an electron from the negative terminal of the !attery willenter the crystal( thus completing the current path Therefore( the majority current carriers in the 9*typematerial &electrons' are repelled !y the negative side of the !attery and move through the crystal towardthe positive side of the !attery
Current Flow in the P*Type 3aterial Current flow through the P*type material is illustrated Conduction in the P material is!y positive holes( instead of negative electrons A hole moves from the positive terminal of the P materialto the negative terminal :lectrons from the e0ternal circuit enter the negative terminal of the material andfill holes in the vicinity of this terminal At the positive terminal( electrons are removed from the covalent!onds( thus creating new holes This process continues as the steady stream of holes &hole current' movestoward the negative terminal ). Relay A relay is an electrically operated switch 3any relays use an electromagnet to operate a switching mechanism mechanically( !ut other operating principles are also used Relays are used where it is necessary to control a circuit !y a low*power signal &with complete electrical isolation !etween control and controlled circuits'( or where several circuits must !e controlled !y one signal The first relays were used in long distance telegraph circuits( repeating the signal coming in from one circuit and re*transmitting it to another Relays were used e0tensively in telephone e0changes and early computers to perform logical operations A type of relay that can handle the high power re"uired to directly control an electric motor or other loads is called a contactor Solid*state relays control power circuits with no moving parts( instead using a semiconductor device to perform switching Relays with cali!rated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults5 in modern electric power systems these functions are performed !y digital instruments still called 7protective relays7 A simple electromagnetic relay consists of a coil of wire wrapped around a soft iron core( an iron yo2e which provides a low reluctance path for magnetic flu0( a mova!le iron armature( and one or more sets of contacts &there are two in the relay pictured' The armature is hinged to the yo2e and mechanically lin2ed to one or more sets of moving contacts #t is held in place !y a spring so that when the relay is de*energi8ed there is an air gap in the magnetic circuit #n this condition( one of the two sets of contacts in the relay pictured is closed( and the other set is open
Other relays may have more or fewer sets of contacts depending on their function The relay in the picture also has a wire connecting the armature to the yo2e This ensures continuity of the circuit !etween the moving contacts on the armature( and the circuit trac2 on the printed circuit !oard &PCB' via the yo2e( which is soldered to the PCB 1hen an electric current is passed through the coil it generates a magnetic field that activates the armature( and the conse"uent movement of the mova!le contact&s' either ma2es or !rea2s &depending upon construction' a connection with a fi0ed contact #f the set of contacts was closed when the relay was de*energi8ed( then the movement opens the contacts and !rea2s the connection( and vice versa if the contacts were open 1hen the current to the coil is switched off( the armature is returned !y a force( appro0imately half as strong as the magnetic force( to its rela0ed position =sually this force is provided !y a spring( !ut gravity is also used commonly in industrial motor starters 3ost relays are manufactured to operate "uic2ly #n a low*voltage application this reduces noise5 in a high voltage or current application it reduces arcing 1hen the coil is energi8ed with direct current( a diode is often placed across the coil to dissipate the energy from the collapsing magnetic field at deactivation( which would otherwise generate a voltage spi2e dangerous to semiconductor circuit components Some automotive relays include a diode inside the relay case Alternatively( a contact protection networ2 consisting of a capacitor and resistor in series &snu!!er circuit' may a!sor! the surge #f the coil is designed to !e energi8ed with alternating current &AC'( a small copper 7shading ring7 can !e crimped to the end of the solenoid( creating a small out*of*phase current which increases the minimum pull on the armature during the AC cycle M-@ A solid*state relay uses a thyristor or other solid*state switching device( activated !y the control signal( to switch the controlled load( instead of a solenoid An optocoupler &a lightemitting diode &$:4' coupled with a photo transistor' can !e used to isolate control and controlled circuits
Relays are used for/ Amplifying a digital signal( switching a large amount of power with a small operating power Some special cases are/ o o A telegraph relay( repeating a wea2 signal received at the end of a long wire Controlling a high*voltage circuit with a low*voltage signal( as in some types of modems or audio amplifiers( o Controlling a high*current circuit with a low*current signal( as in the starter solenoid of an automo!ile( 4etecting and isolating faults on transmission and distri!ution lines !y opening and closing circuit !rea2ers &protection relays'( Fig/ )-- Relay A 4P4T AC coil relay with 7ice cu!e7 pac2aging #solating the controlling circuit from the controlled circuit when the two are at different potentials( for e0ample when controlling a mains*powered device from a low*voltage switch The latter is often applied to control office lighting as the low voltage wires are easily installed in partitions( which may !e often moved as needs change They may also !e controlled !y room occupancy detectors to conserve energy( $ogic functions For e0ample( the !oolean A94 function is realised !y connecting normally open relay contacts in series( the OR function !y connecting normally open contacts in parallel The change*over or Form C contacts perform the WOR &e0clusive or' function Similar functions for 9A94 and 9OR are accomplished using normally closed
contacts The $adder programming language is often used fo r designing relay logic networ2s o The application of Boolean Alge!ra to relay circuit design was formali8ed !y Claude Shannon in A Sym!olic Analysis of Relay and Sw itching Circuits :arly computing Before vacuum tu!es and transistors( relays were used as logical elements i n digital computers See electro*mechanical co mputers such as ARRA &computer'( ;arvard 3ar2 ##( Xuse X+( and Xuse X) o o Safety*cri tical logic Because relays are much more resistant than semiconductors to nuclear radiation( they are widely used in safety*critical logic( such as the control panels of radioactive waste*handling machinery Time delay funct ions Relays can !e modified to delay opening or delay closing a set of contacts A very s hort &a fraction of a second' delay would use a copper dis2 !etween the armature and moving !lade assem!ly Current flowing in the dis2 maintains magnetic field for a short time( lengthening release time For a slightly longer &up to a minute' delay( a dashpot i s used A dashpot is a piston filled with fluid t hat is allowed to escape slowly The time period can !e varied !y increasing or decre asing the flow rate For longer time perio ds( a mechanical cloc2wor2 timer is installed
where # is the current through the conductor in units of amperes( < is the potential difference measured across the conductor in units of volts( and R is the resistance of the conductor in units of ohms The ratio of the voltage applied across a resistor?s terminals to the intensity of current in the circuit is called its resistance( and this can !e assumed to !e a constant &independent of the voltage' for ordinary resistors wor2ing within their ratings Resistors are common elements of electrical networ2s and electronic circuits and are u!i"uitous in electronic e"uipment Practical resistors can !e made of various compounds and films( as well as resistance wire &wire made of a high*resistivity alloy( such as nic2elchrome' Resistors are also implemented within integrated circuits( particularly analog devices( and can also !e integrated into hy!rid and printed circuits Fig/ )-+ Resistor The electrical functionality of a resistor is specified !y its resistance/ common commercial resistors are manufactured over a range of more than nineorders of magnitude 1hen specifying that resistance in an electronic design( the re"uired precision of the resistance may re"uire attention to themanufacturing tolerance of the chosen resistor( according to its specific application The temperature coefficient of the resistance may also !e of concern in some precision applications Practical resistors are also specified as having a ma0imum power rating which must e0ceed the anticipated power dissipation of that resistor in a particular circuit/ this is mainly of concern in power electronics applications Resistors with higher power ratings are physically larger and may re"uire heat sin2s #n a high*voltage
circuit( attention must sometimes !e paid to the rated ma0imum wor2ing voltage of the resistor 1hile there is no minimum wor2ing voltage for a given resistor( failure to account for a resistor?s ma0imum rating may cause the resistor to incinerate when current is run through it Practical resistors have a series inductance and a small parallel capacitance5 these specifications can !e important in high*fre"uency applications #n alow*noise amplifier or pre*amp( the noise characteristics of a resistor may !e an issue The unwanted inductance( e0cess noise( and temperature coefficient are mainly dependent on the technology used in manufacturing the resistor They are not normally specified individually for a particular family of resistors manufactured using a particular technologyA family of discrete resistors is also characteri8ed according to its form factor( that is( the si8e of the device and the position of its leads &or terminals' which is relevant in the practical manufacturing of circuits using them ) Capacitor A capacitor is a passiveelectronic component consisting of a pair of conductors separated !y a dielectric &insulator' 1hen there is a potential difference &voltage' across the conductors( a static electric field develops in the dielectric that stores energy and produces a mechanical force !etween the conductors An ideal capacitor is characteri8ed !y a single constant value( capacitance( measured in farads This is the ratio of the electric charge on each conductor to the potential difference !etween them The capacitance is greatest when there is a narrow separation !etween large areas of conductor( hence capacitor conductors are often called 7plates7( referring to an early means of construction #n practice the dielectric !etween the plates passes a small amount of lea2age current and also has an electric field strength limit( resulting in a !rea2down voltage( while the conductors and leads introduce an undesired inductance and resistance
Fig/ )-+ Capacitor An ideal capacitor is characteri8ed !y a single constant value( capacitance( which is measured in farads This is the ratio of the electric charge on each conductor to the potential difference !etween them #n practice( the dielectric !etween the plates passes a small amount of lea2age current The conductors and leads introduce an e"uivalent series resistance and the dielectric has an electric field strength limit resulting in a !rea2down voltage The properties of capacitors in a circuit may determine the resonant fre"uency and "uality factor of a resonant circuit( power dissipation and operating fre"uency in a digital logic circuit( energy capacity in a high*power system( and many other important aspects A capacitor &formerly 2nown as condenser' is a device for storing electric charge The forms of practical capacitors vary widely( !ut all contain at least two conductors separated !y a non*conductor Capacitors used as parts of electrical systems( for e0ample( consist of metal foils separated !y a layer of insulating film Fig/* )-) Capacitors
A capacitor &originally 2nown as a condenser' is a passive two*terminal electrical component used to store energy electrostatically in an electric field The forms of practical capacitors vary widely( !ut all contain at least two electrical conductors separated !y a dielectric &insulator'5 for e0ample( one common construction consists of metal foils separated !y a thin layer of insulating film Capacitors are widely used as parts of electrical circuits in many common electrical devices 1hen there is a potential difference across the conductors( an electric field develops across the dielectric( causing positive charge to collect on one plate and negative charge on the other plate :nergy is stored in the electrostatic field An ideal capacitor is characteri8ed !y a single constant value( capacitance This is the ratio of the electric charge on each conductor to the potential difference !etween them The S# unit of capacitance is the farad( which is e"ual to one coulom! per volt The capacitance is greatest when there is a narrow separation !etween large areas of conductor( hence capacitor conductors are often called plates( referring to an early means of construction #n practice( the dielectric !etween the plates passes a small amount of lea2age current and also has an electric field strength limit( the !rea2down voltage The conductors and leads introduce an undesired inductance and resistance Capacitors are widely used in electronic circuits for !loc2ing direct current while allowing alternating current to pass #n analog filter networ2s( they smooth the output of power supplies #n resonant circuits they tune radios to particular fre"uencies #n electric power transmission systems they sta!ili8e voltage and power flow
Chapter/ CO3PARATOR ;ow an op*amp can !e used as a comparatorY 4escriptions Potential dividers are connected to the inverting and non inverting inputs of the op*amp to give some voltage at these terminals Supply voltage is given to
Chapter/ . 1ORK#9%/ OP:RAT#O9 :WP$A9AT#O9 The project uses num!ers step*down transformers for handling the entire circuit under low voltage conditions of -+v only to test the ) phase fault analysis The primary of ) transformers are connected to a ) phase supply in star configuration( while the secondary of the same is also connected in star configuration The other set of ) transformers with its primary connected in star to ) phase have their secondary s connected in delta configuration The output of all the transformers are rectified and filtered individually and are given to relay coils push !uttons( one each connected across the relay coil is meant to create a fault condition either at star ie $$ Fault or )$ Fault The 9C contacts of all the relays are made parallel while all the common points are grounded The parallel connected point of 9C are given to pin+ through a resistor R. to a ... timer ie wired in monosta!le mode The output of the same timer is connected to the reset pin of another ... timer wired in asta!le mode $:4 S are connected at their output to indicate their status The output of the =) ... timer from pin) is given to an Opamp $3).N through wire -- and d-+ to the non inverting input pin)( while the inverting input is 2ept at a fi0ed voltage !y a potential divider R<+ The voltage at pin+ coming from the potential divider is so held that it is higher than the pin) of the Op*amp used as a comparator so that pin- develops 8ero logic that fails to operate the relay through the driver transistor G- This relay G- is Q)CO relay ie is meant for disconnecting the load to indicate fault conditions ‟
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OP:RAT#9% PROC:4=R:/ 1hile the !oard is powered from a )phase supply all the relay coils get 4C voltage and their common point disconnects from the 9C and moves on to the 9O points there !y providing logic high at pin+ of ... timer =- ie that is 2ept on monosta!le mode 1hile any push !utton across the relay is pressed it disconnects that relay and in the process in common contacts moves to the 9C position to provide a logic low at trigger pin of ... timer to develop an output that !rings the =) ... timer which is used in asta!le mode for its reset pin to high such that the asta!le operation ta2es place at its output which is also indicated !y flashing 4-- $:4 #f the fault is off temporary in nature ie if the push !utton pressed is released immediately the =-
monosta!le disa!les =) the output of which goes to 8ero in the event of any push !utton 2ept pressed for a longer duration the monosta!le output provides a longer duration active situation for =) the asta!le timer the output of which charges capacitor C-) through R-- such that the output of the comparator goes high that drives the relay to switch off three phase load The output of Op*amp remains high indefinitely through a positive feed!ac2 provided for its pin- to pin) through a forward !iased diode and a resistor in series This results in the relay permanently switched on to disconnect the load connected at its 9C contacts permanently off #n order to maintain the flow of 4C supply the star connected secondary set 4C S are paralleled through 4N(4E 4-, for uninterrupted supply to the circuit voltage of -+v 4C and .v 4C derived out of voltage regulator #C N,. ‟
Chapter Application 6 6 6 6 6 6 6 Su!station( 6 Transformer( 6 4rives Relay( 6 Transmission $ine 6
Chapter/ 6 6 6 6 6 6 6 6 6 3ore Relia!le 6 Reduce $osses 6 3ore :fficiency 6 1or2 Complete Time to Time 6 Safety :"uipment 6 Advantages
Chapter/N Reference 6 6 6 6 Power system protection !y dipa2 s!an2ar Analog and digital communication( tech ma0 pu!lication :lectrical machines !y !lthereja Swich gear and protection !y ssrao
