68846090-protection-settings

8/13/2019 68846090-protection-settings

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ELEC 4302/7311

POWER SYSTEM PROTECTION:PROTECTION SETTINGS

Dr. Ramesh a!sa"

S#h$$" $% I!%$rma&'$! Te#h!$"$() a!* E"e#&r'#a"E!('!eer'!(+ ,-$! "*(+ 47/212

The !'ers'&) $% ee!s"a!*+ S& L#'a+ 4072,s&ra"'a

a!sa"'&ee..e*.aPh: 561 0783369334

;a-: 561 078 336 94

1
mailto:[email protected]:[email protected]


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Contents

Introduction

Functions of Equipment Protection

Functions of Protective Relays

Required Information for Protective Setting Protection Settings Process

Functional Elements of Protective Relays

Operating Characteristics of Protective Relays

Overcurrent and Directional Protection Elements Distance Protection Function

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PROTECTIO SETTI!S"ITROD#CTIO

$ po%er system is composed of a num&er ofsections 'equipment( such as generator)transformer) &us &ar and transmission line*

These sections are protected &y protective

relaying systems comprising of instrumenttransformers 'ITs() protective relays) circuit&rea+ers 'C,s( and communication equipment*

In case of a fault occurring on a section) itsassociated protective relays should detect thefault and issue trip signals to open theirassociated C,s to isolate the faulted sectionfrom the rest of the po%er system) in order toavoid further damage to the po%er system* 3


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4

Below Fig. 1 is an typical example of power system sections with their

protection systems. Where:G1 is a generator. T1 is a transformer. B1,...,B5 are bus bars. !5 is

a transmission line "T#.$G is a generator protecti%e relay. $T is a transformer protecti%e

relay. $B is a bus protecti%e relay. $&!,...,$&' are T protecti%e

relays. (1,..., (' are (Bs.

)rotection *ettings: +ntrouction

Fig. 1 )rotection of power system sections


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PROTECTIO SETTI!S"ITROD#CTIO

-a.imum fault clearance times are usuallyspecified &y the regulating &odies and net%or+service providers*

The clearing times are given for local and remote

C,s and depend on the voltage level and aredetermined primarily to meet sta&ilityrequirements and minimi/e plant damage*

The ma.imum clearance times of the &ac+upprotection are also specified*

e*g* the clearing times for faults on the linesspecified &y one net%or+ service provider in$ustralia are presented in Ta&le I 'ne.t slide(*

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T,LE I: ;,LT CLE,R,NCE TIMES

-oltagele%el /-0

(B operate correctlyms0

(B fail ms0

ocal $emote ocal $emote

5 2 1 135 13544 1 1 5 5

35 1 1 5 5

1 1! !4 !4

14 1 16 !4 !411 1 16 !4 !4

66 1 16 !4 !4

7 44 116 & 15 &6


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F#CTIOS OF PROTECTI2E RE3$4S

The protection functions are considered adequate%hen the protection relays perform correctly in termsof"

De


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6F#CTIOS OF PROTECTI2E RE3$4S

Se"e#&''&) D's#r'm'!a&'$!8"The a&ility to detect a fault %ithin a specified /one of anet%or+ and to trip the appropriate C,'s( to clear thisfault %ith a minimum distur&ance to the rest of thatnet%or+*

S'!("e %a'"re #r'&er'$!:

$ protection design criterion %here&y a protectionsystem must not fail to operate even after one

component fails to operate*7ith respect to the protection relay) the single failurecriterion caters primarily for a failed or defective relay)and not a failure to operate as a result of aperformance deficiency inherent %ithin the design of

the relay*

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6F#CTIOS OF PROTECTI2E RE3$4S

The setting of protection relays is not a definitescience*

Depending on local conditions and requirements)setting of each protective function has to &eoptimi/ed to achieve the &est &alance &et%eenrelia&ility) security and speed of operation*

Protection settings should therefore &ecalculated &y protection engineers %ith vast

e.perience in protective relaying) po%er systemoperation and performance and quality of supply*

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RE0#IRED IFOR-$TIO FOR PROTECTI2ESETTI!

L'!e Parame&ers:

For a ne% line" final total line length as %ell as thelengths) conductor si/es and to%er types of eachsection %here different to%er types or conductors have

&een used*This information is used to calculate the parameters

'positive and /ero sequence resistance) reactance andsusceptance( for each section*

-a.imum load current or apparent po%er '-2$(corresponding to the emergency line %hich can &eo&tained from the ta&le of standard conductor rating'availa&le in each utility(*

The num&er of conductors in a &undle has to &e ta+en

into consideration*

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6RE0#IRED IFOR-$TIO FORPROTECTI2E SETTI!

Tra!s%$rmer Parame&ers:The manufacturer8s positive and /ero sequence

impedance test values have to &e o&tained*

The transformer nameplate normally provides the

manufacturer8s positive sequence impedancevalues only*

Term'!a" E'


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;a"& S&*'esResults of fault studies must &e provided*

The developed settings should &e chec+ed onfuture cases modelled %ith the system changes

that %ill ta+e place in the future 'e*g* %ithin 9years(*

#se a ma.imum fault current case*

CT = >T Ra&'$s:

O&tain the CT ratios as indicated on theprotection diagrams*

For e.isting circuits) it is possi&le to verify theratios indicated on the diagrams &y measuringthe load currents on site and comparing %ith a

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Che#?'!( ;$r CT Sa&ra&'$!: Protection systems are adversely affected &y CT

saturation* It is the responsi&ility of protection engineersto esta&lish for %hich forms of protection and under %hatconditions the CT should not saturate*

CTs %$r Tra!s%$rmer D'%%ere!&'a" Pr$&e#&'$!: -2) :2 and 32 CTs must &e matched as far as possi&le

ta+ing into consideration the transformer vector group)tap changer influence and the connection of CTs*

CTs %$r Tra!s%$rmer Res&r'#&e* Ear&h ;a"&RE;8 Pr$&e#&'$!:

$ll CT ratios must &e the same 'as %ith the &us/one protection() e.cept if the relay caninternally correct unmatched ratios*

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PROTECTION SETTINGS PROCESS

The Protection Settings team o&tains all theinformation necessary for correct setting calculations*

The settings are then calculated according to thelatest philosophy) using sound engineering principles*Pre;%ritten programs may &e used as a guide*

$fter calculation of the settings) it is important thatanother competent person chec+s them*

The persons %ho calculate and %ho chec+ the settings&oth sign the formal settings document*

The flo%chart in Fig* < indicates information flo%

during protection setting preparation forcommissioning of ne% Transmission plant*

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)ro9ect lea,er of the )rotection

*ettings team ,etermines scope

of work and target dates

*ummary an, comparison of inputs

+:; manufacturers pro%i,e bayspecific +:; ,etails

:ngineering team pro%i,es bay

specific proformas an, ,rawings

(orrecti%e actions an, re&issue of

,rawings

*tu,y new protection an, create

necessary setting templates in

liaison with engineering team an,

+:; manufactureres

ot


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;NCTION,L ELEMENTS O;PROTECTI>E REL,YS

To achieve ma.imum fle.i&ility) relays is designed using theconcept of functional elements %hich include protectionelements) control elements) input and output contacts etc*

The protection elements are arranged to detect the systemcondition) ma+e a decision if the o&served varia&les are

over=under the accepta&le limit) and ta+e proper action ifaccepta&le limits are crossed*

Protection element measures system quantities such asvoltages and currents) and compares these quantities ortheir com&ination against a threshold setting 'pic+up

values(* If this comparison indicates that the thresholds are crossed)

a decision element is triggered*

This may involve a timing element) to determine if thecondition is permanent or temporary* If all chec+s are

satisfied) the relay 'action element( operates*

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18

Fault)ic/up of

protection element


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OPER,TING C@,R,CTERISTICS O;PROTECTI>E REL,YS

Protective relays respond and operate according todefined operating characteristic and applied settings*

Each type of protective relay has distinctive operatingcharacteristic to achieve implementation o&5ective"

sensitivity) selectivity) relia&ility and adequate speed ofoperation*

,asic operating characteristics of protective elements isas follo%s"

Oer#rre!&


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AOPER,TING C@,R,CTERISTICSO; PROTECTI>E REL,YS

D's&a!#e


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O2ERC#RRET $D DIRECTIO$3PROTECTIO E3E-ETS

$n overcurrent condition occurs %hen the ma.imumcontinuous load current permissi&le for a particularpiece of equipment is e.ceeded*

$ phase overcurrent protection element continuouslymonitors the phase current &eing conducted in thesystem and issue a trip command to a C, %hen themeasured current e.ceeds a predefined setting*

The &iggest area of concern for over;currentprotection is ho% to achieve selectivity*

Some possi&le solutions have &een developed)including monitoring current levels 'current grading()introducing time delays 'time grading( or com&iningthe t%o as %ell as including a directional element todetect the direction of current flo%*

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C#RRET !R$DI!

Current grading %ill achieve selectivity &ydetermine the location of a fault using purelymagnitude of current*

It is difficult to implement this in practice unlessfeeder sections have sufficient differences inimpedance to cause noticea&le variations in faultcurrent*

In a net%or+ %here there are several sections of

line connected in series) %ithout significantimpedances at their 5unctions there %ill &e littledifference in currents) so discrimination orselectivity cannot &e achieved using current

grading*

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TI-E DE3$4S

$n alternate means of grading is introducing time delays

&et%een su&sequent relays* Time delays are set so that the appropriate relay has

sufficient time to open its &rea+er and clear the fault on itssection of line &efore the relay associated %ith thead5acent section acts*

:ence) the relay at the remote end is set up to have theshortest time delay and each successive relay &ac+ to%ardthe source has an increasingly longer time delay*

This eliminates some of the pro&lems %ith current gradingand achieves a system %here the minimum amount of

equipment is isolated during a fault* :o%ever) there is one main pro&lem %hich arises due to

the fact that timing is &ased solely on position) not faultcurrent level*

So) faults nearer to the source) %hich carry the highestcurrent) %ill ta+e longer to clear) %hich is very

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DIRECTIO$3 E3E-ETS

Selectivity can &e achieved &y using directional elementsin con5unction %ith instantaneous or definite;timeovercurrent elements*

Directional overcurrent protection schemes respond tofaults in only one direction %hich allo%s the relay to &e setin coordination %ith other relays do%nstream from therelay location*

This is e.plained using e.ample in Fig* >*

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DIRECTIO$3 E3E-ETS

,y providing directionalelements at the remote endsof this system) %hich %ouldonly operate for faultcurrents flo%ing in one

direction %e can maintainredundancy during a fault*

This is in line %ith one of themain outcomes of ensuringselectivity) %hich is to

minimi/e amount of circuitrythat is isolated in order toclear a fault*

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Fig. !: Cse of irection elementexample


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DIRECTIO OF C#RRET F3O7

In $C systems) it is difficult to determine the direction ofcurrent flo% and the only %ay to achieve this is to performmeasurements %ith reference to another alternatingquantity) namely voltage* The main principle of ho%directional elements operate is &ased on the follo%ingequations for torque"

If current is in the for%ard direction) then the sign of thetorque equation %ill &e positive and as soon as thedirection of current flo% reverses) the sign of the torqueequation &ecomes negative* These calculations are

constantly &eing performed internally inside directionalelement*

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)cos( ABCABCA IVIVT =

)cos( BCABCAB IVIVT =

)cos( CABCABC IVIVT =


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DIST$CE PROTECTIO F#CTIO

$ distance protection element measures thequotient 2=I 'impedance() considering thephase angle &et%een the voltage 2 and thecurrent I*

In the event of a fault) sudden changes occurin measured voltage and current) causing avariation in the measured impedance*

The measured impedance is then comparedagainst the set value*

Distance element %ill trip the relay 'a tripcommand %ill &e issued to the C, associated%ith the relay( if the measured value of theimpedance is less then the value set*

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6DIST$CE PROTECTIO F#CTIO

In Fig* 9 the impedance measured at the relay point$ is ) %herexis the distance to the fault'short circuit() and R and L are transmission lineparameters in per unit length* The line length is l

in the fig**

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Fig. 5 ;istance protection principle of operation.

( )inZ R j L x= +


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7e can see that the impedance value of a faultloop increases from /ero for a short circuit at thesource end $) up to some finite value at the remoteend ,* 7e can use this principle to set up /ones of

distance protection as %ell as to provide feed&ac+a&out %here a fault occurred 'distance to fault(*

Operating characteristics of distance protectionelements are usually represented using R;?

diagrams* Fig* @ sho%s an e.ample of -ho R;? operating

characteristic* The relay is considered to &e at theorigin* 29


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30

$egion ofoperation

Done 1

$egion of

non&operation

outsi,e the circle

oa,

region

$

E

Done 5

B

2

15

ine )

ine G

R SZ

Fig. 6 Aho positi%e&se@uence $&E operating

characteristic of a istance element.


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6DIST$CE PROTECTIOF#CTIO

The need for /ones sho%n in Fig* @ arises fromthe need of selective protection1 i*e* the distanceelement should only trip faulty section*

7e can set the distance element to only trigger a

trip signal for faults %ithin a certain distancefrom the relay) %hich is called the distanceelement reach*

The setting impedance is represented &y

) %here A3 is the line impedance* The distanceelement %ill only trip %hen the measuredimpedanceZRis less than or equal to the setting

impedance hsZL*31

RS s LZ h Z=


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Typically hsis set to protect B of the line &et%een t%o

&uses and this forms protection Aone * Errors in the 2Ts and CTs) modeled transmission line data)

and fault study data do not permit setting Aone for of the transmission line*

If %e set Aone for of the transmission line)un%anted tripping could occur for faults 5ust &eyond theremote end of the line*

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6DIST$CE PROTECTIOF#CTIO

Aone < is set to protect

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