Manual on Prot Gen & Gts

8/7/2019 Manual on Prot Gen & Gts

http://slidepdf.com/reader/full/manual-on-prot-gen-gts 1/30

Manual on

Q 'rECT ION OF

'GENERAT 'O RS , G ENERATOR

TRAN SFORMERS AD

220 kVA 0 400 kV

NETWORKS



" _~

",:

. ~';:T.""'-:-,~~::."'.._", _:

CENTRAL BOARD OF IRRIGATION AND POWER

The, Central Board of Irrigation and .Pc?':Y.e.re~tablished in 1927.has

rendered over sev'en decades' of cledkciled services to professlonal

engineers in th~ twill disciplines 6f:WatetResbhrces and Energy to

facilitate -optimal developmenf.of Wat er \ai}.a;Energy Resources by

applic~tip~ of modern technologies le~~l~gt o ~a:cceierat~deeonomicdevelopment' c i t ' the country. ., , · r , , • . ~ . : ' .,

o'b) ~C:~iyes~'.' .

• :~~l1deri:ngExpertise ohW~tE1rResources' ~ .Energy a:ndAlliedE¢lds.. ',' .', r '.' <:.:, " .' '

• Psomoting Research itnd :p.~ofess.ionalEk~el1ence.

•, . .~p,;g~.i~~L~agepto Iridiql\E~giiu~~r~;~aAag~rs~d Scientists'" 5 : ' i1 t tl i~hef r .:Counte rp~hs ': i \ iV9 i idClh'd,tntem.ationalOrg~nis~tioi:iU;i

• ' ,g ~ ~ c ) l 1 ii i sh i n gKnow l e c i g ' e D a ' t ~ base '~hd . :;P tOViP ing Infor~~tion.'. ~~yl~es. .' : . ,

• .':T.;c~~logical Forecasting.": -r,

MANUAL ON

PROTECTION OF GENERATORS,

GENERATOR TRANSFORMERSAND

220 kV AND 400kV NETWORKS

PUBLICATION NO. 274

(Revised)

Editors

C.V.J. VARMA

P.K. LAL

Chairman

Committ,!e to Study Protection System

BHANU BHUSHAN

CENTRAL BOARD OF IRRIGATION & PO\VER

Malcha Marg, Chanakyapuri, New Delhi-Ll O021

E-Mail; [email protected]

Phone: 91-11-611 5984,6876229;

Fax; 91-11-611 3647

.Website: www.cbip.org

mailto:[email protected]

http://www.cbip.org/

http://www.cbip.org/

mailto:[email protected]



L IST OF CONTENTS

Foreword

Introduction

Section 1 Generator and Generator Transformer Protection

Section 2 Line Protection

Section 3 Auto Reclosure

Section 4 T ransformer Protection

Section 5 Reactor Protection

Section 6 Bus Bar Protection

Section 7 Local Breaker Back-up (Breaker fail) Protection

Section 8 Fault Locator, Disturbance Recording and Event Logging Equipment

Section 9 Guidelines for Protection System Engineering

Section 10 CT, CVT Locations

Section 11 Commissioning Tests & Maintenance Recommendations

Sect ion 12 Tes t Equ ipments

Section 13 Reference Standards

." . " , ': d : "

Page

iii

1

2

19

23

26

29

31

33

35

38

41

48

52

53 '

FOREWORD

High availability and reliable operation of large generating plants with EHV network assume

tremendous importance in susta ining huge grids connect ing number of uti li ties from the view

point of meeting ever increasing demand and maintaining power system stability for better gridopera tion. Large plants, therefore , cannot be allowed to be out of service for long t ime as the

same may resul t i n heavy load shedding to sus tai n no rma l g rid f requency. It is, therefore,

necessary to reduce outage t ime with minimum damage to the machines a t reduced costs.

Protection Scheme isa very important component ofthe Power System. Protection Scheme

has to be reliable, efficient, fast in operation, maintainable, flexible, compact and dependable

with self-checking features to protect the system against all types of faults.

The Protect ion phi losophy of large generators, generator t ransformer and EHV Networks

varies from uti li ty to uti li ty . For large machines general ly redundant protect ions are provided

such tha t f ai lu re o fone set o f p rot ec ti on does not h inder t he prote ct ion ope rat ion at any par t

of time.

In a Workshop organi sed by CBIP on "Mode rn T rends i n the Pro tect ion Phil osophy of

Electric Power Apparatus and Systems" itwas recommended that a Working Group with expert

member s d rawn f rom CEA, NTPC, Power Grid , a f ew Util it ie s, Academic Ins ti tu ti ons and

ieading manufacturers, be constituted to standardise the technical specifications for Protection

System for EHV lines 220 kV and above, bus bars and inter-connect ing grid t ransformers,

keep ing in vi ew the sys tem needs and presen t day p rac ti ce s. Acco rdingly, a Commit te e was

const ituted by CBIP under the Chairmanship of Shri Bhanu Bhushan, Direc tor (Operat ion) ,

Power Grid Corpora tion of India Ltd., who deliberated over the subject for more than one year

and made recommenda ti ons on al l a spect s o f Prot ec ti on for EHV Sys tem of 220 kV and 400

kV. The composi tion of Committee and task Force is given in this publica tion.

_ This Publication inthe form of manual on Protection of Generators, Generator Transformer

and 220 kV and 400 kV Networks fi rs t publ ished in Octobe r 1998 found wide acceptance

from all uti li ties and manufacturers. There were lot of feedbacks/suggest ions. Since copies of

this edition had also exhausted, ithas decided to incorporate the suggestions in the new edition.

The Cent ral Boa rd o f I rr igat ion and Power Pla ce s on reco rd i ts g rate ful t hanks t o Shr i

Bhanu Bhushan , Chairman of the Commi ttee , ot her members o f the Commi ttee , Convenor

and member s of t he o ther Task Force fo r the e ffor ts put in by them. Iwould particularly like to

thank Sarvshri Bhanu Bhushan, Vikas Saksena of Power Grid, R.N. Kaul of NTPC, S.P. Singh

of CEA and B.S. Palki ofABB, who formula ted the draft of this manual and then incorpora ted

laboriously suggest ions made by other members of the Committee on Protect ive Systems for

EHV Systems.Sh. B.S. Palki , DGM, ABB Ltd., took great pains to incorpora te suggest ions/feedback in

the revised version.

It is hoped , th is Manual wil l serve a s a very useful gu ide t o mee t the. needs o f u til it ie s,

engineers and manufacturers.

Irj~(c.v,i. Varma)

Member Secretary

Central Board of Irrigation & Power



INTRODUCTION

Recommendations contained herein for protection of E.H.V. system of 220

kV and 400 kV are intended to be used by utilities in India, as a gUide for

minimum provisions at different voltage levels. The manual also contains a

section on Generator and Generator Transformer protection. Additional or

superior provisions can always be made by concerned utili ties at their discretion.

Detailed specifications of each protection will have to be drawn by individual

utili ties while framing purchase specifications. Major functional requirements

and general sett ing criteria for various protections have also been deal t wi th in

this document. It may be noted that wherever setting ranges of relays have

been ment ioned inthis manual, these are intended to be indicat ive . The manual

does not recommend any specific technology namely Electromechanical, Static

or Numerical . Ut ili ties may decide on this at their d iscretion .

Following considerations have been taken into account while making these

recommendations:

(i) Prevai ling practices of various ut ili ties in India and informat ion about

practices followed elsewhere in the world.

[ii) Experiences with the prevailing protection practices.

( i i i ) The state-of-art in the protection field and features of the presently

available relays such that the specified requirements may be complied

with, by reputed manufacturers wi th their proven products without any

deviation and at reasonable cost.

1



Section 1

GENERATOR AND GENERATOR TRANSFORMER

PROTECTION

1.0 GENERAL

1.1 Generators are designed to run at a high load factor for a large number of years and

permit certain incidences of abnormal working conditions. The machine and its auxiliaries

are supervised by mon ito rin g d evices to k eep t he i ncide nces of abnormal wo rki ng

condi tions down to a .m in imum. Despi te the monitor ing, e lect ri ca l and mechanica l

faults may occur , and the generators must be provided with protective relays, which, in

case of a f au lt , quick ly ini ti at e a d is connec tion of the machine f rom the system and , if

necessary, initiate a complete shut down of the machine.

1 .2 Recommendat ions con ta ined her ein f or e lect ri ca l p ro tect ive sys tems of genera to r and

gener ator t rans fo rmer a re intended to be used for genera to rs of 10 MVAand above . It

descri bes th e requi rements of v ario us protect ions, sp ecial comments t o help i n

determining application of these protections , for units of var ious types and sizes , setting

criteria and tripping principles.

The protection requirements of machines used in pumped storage schemes need further attention

and the recommendations given below do not cover these details .

1 .2 .1 Genera to r can be connected to the primary t ransmiss ion sys tem info llowing two ways:

I. Unit Sch eme

In thi s scheme no swit chgear i s prov ided b etween the generator and generator

transformer which are treated as a unit. A unit auxil iary transformer is tapped off at

the inter connec tion , fo r the supp ly of power to the aux il ia ry p lant .

I I. Generator Circuit Breaker Scheme

In thi s s cheme , a genera to r c ir cu it b reaker i s p rovided between the genera to r and genera to r

transformer:

1 .3 I n v iew of genera to r uni t being a complex sys tem, var ious e lect ri ca l hazar ds - requ ir e

consideration. These are given below:

Stator insulation failure

Overvoltage

Rotor faultsLoss of synchronism

Over/under frequency

Overload

Unbalanced loading

Loss of excitation

Reverse power

Inadvertent energisation of generator

2

1.4 Following are the var ious protections recommended for the generator and generator

transformer protection.

Type of Fault ANSI Device No. Protection Functions

GENERATOR STATOR

Short Circuits 87 G Generator differential87 GT Overall differential

21 G Minimum impedance (alternatively

51/27 G Over current/under voltage)

Asymmetry 46 G Negative sequence

Stator overload 51 G Overload

Earth fault stator 64 G1 95% stator earth fault

64 G2 100% stator ear th fault

Loss of excitation 40 G Loss of excitation

Out of s tep 98 G Pole slip

Monitoring 32 G/37 G Low forward power/reverse power

(Double protection for large

generators)

Blade fatigue 81 G Minimum frequency

Inter turn fault 95 G Over voltage or over current

Mag. Circuits 99 G Overfluxing volt/Hz

Higher voltage 59 G Over voltage

Accidential energisation 27/50 G Dead machine

Monitoring 60 G PT fuse failure

GENERATOR ROTOR

Rotor ground 64 F Rotor earth fault

GENERATOR TRANSFORMER

Short circuits 87 GT Overall differential ..

51 GT Overcurrent

87 T Transformer differential

Ground fault 51NGT Earth fault over-current

87 NT Restricted earth fault

Overhang 87 HV HV Winding cum overhang

differential

UNIT AUXILIARY TRANSFORMER

Short circuit 87 UAT Transformer differential

51 UAT Over-current

Ground fault 51 NUAT Residual over-current

64 UAT Restricted earth fault

3



The transformer guards like Buchholtz protection, Winding temperature high, Oiltemperature high,

etc. are also important and shall be provided as per transformer manufacturer's recommendations.

1.5 Recommendations regarding selection of the generator protections for units of dif ferent

types and s izes a re summari sed in the tab le g iven below:

RECOMMENDED PROTECTIONS FORGENERATORS

Functions Steam/Gas Turbines Hydro Turbines

Small Medium Large Small Medium Large

« 10 (l0-100 (> 100 « 10 (10-100 (> 100

MVA) MVA) MVA) MVA) MVA) MVA)

Differential Y y Y y y y

95% Stator ElF Y y Y y Y y

100% Stator E /F N YI N Y N Y IN Y

Interturn Faults Y Y Y Y Y Y

Backup Impedance N y Y N Y y

Voltage

Controlled O/C y N N y N N

Negative Sequence . Y Y Y y Y Y

Field Failure Y Y Y y y y

Reverse Power Y Y Y Y Y Y

Pole Slipping N N Y N N y

Overload N N N Y Y Y

Over voltage y y y y y y

Under frequency y Y Y y y y

Dead Machine N N Y N N y

Rotor Ear th Fault Y Y Y y y y

Overfluxing N Y Y N Y y

2.0 DETAILED REQUIREMENTS

2.1 Generator Stator

2. 1.1 Generator Dif ferential Protection (87 G)

This i s a un it typ e p rot ectio n, instan taneous in op erati on, covering th e stato r wi nding fo r

phase to phase faults.

The gener ator d iff erent ia l r elay i sno t s ensi tive to s ingle phase to ear th f au lt s due to the h igh

neutral earthing resistance arrangement.

4

..~~:.;

As thi s pro tect ion ope ra te s fo r gener ator internal f au lt s, opening the gener ator breaker in

c1ass-Aeliminates the system infeed to the fault (if the unit is synchronised).

For all machines of ratings 10 MVAand above, this protection shall be provided.

Requirements:

(i ) Be triple pole type with individual phase indication(i i) Have ope ra ting t ime les s than 30 mil li seconds a t 2 t imes set ting

( ii i) Be high or low impedance principle based

( iv ) Opera ting cur rent 5 to 10% of nomina l curr en t

(v) High stabili ty against maximum through fault condition, CT saturation, harmonics and

DC transients

(vi) Be provided with suitable voltage dependent res is tors across the relay to limit the voltage

to sa fe level , in case of h igh impedance type r elay

2.1.2 Generator-Transformer differential protection (87 GT)

This isa unit type protection with coverage f rom the generator terminals up to the HV breaker

and the generator transformer HV terminals .

It wil lde tect phase f au lt s on both s ides of the gener ator t rans fo rmer and s ingle phase to ear th

faul ts o f the HV s ide only { theea rth f au lt cur rent on the LVside i sver y sma ll , due to the h igh

neutral earthing resistance}.

Generator transformer dif ferential relays have harmonic res traint circuits to prevent incor rectoperation when the generator and unit transformers are energised f rom the system.

This sh all be provid ed fo r a ll machine s of ratin g 10 MVAabove. The pro tecti on need not

include Unit Auxiliary Transformer (UAT)in its zone and UAT should be covered by a separate

protection.

Incase of breaker -and-half SWitchingscheme, the crs associated with main and tie breakers

sha ll be connected to separa te b ia s winding and these shal l not be par al le led in order to avo id

false operation due to dissimilar CT transient response.

Requirements.

(i) Be triple pole type with individual phase indication

( ii) Have through fault res traint features for external faults with an adjustable or multi-bias

setting( ii i) Have, magnetizing inrush res traint features and also be stable for inrush under normal

over f luxing conditions, magnetising inrush proof feature shall not be achieved through

any intentional t ime delay e.g. use of timers to block relay operation( iv ) Sha ll have unrest ra ined ins tantaneous h ighset ove rcur rent uni t ope ra tion which i s

unaffected by inrush

(v) Have one. b ias w indi ng per phase and per CT input (However UATCT need no t h ave

separa te input and may be para ll ed with the Genera to r CT)

(vi) Have an adjustable operating cur rent

(Vi i) Have an ope ra ting t ime not greater than 30 rnilli seconds at 5 times setting

(viii) Have facil ity for ratio and phase angle cor rection either through auxiliary transformer

or through in built provisions.

5



2.1.3 Backup Protect ions for Short Circuits

This shall be provided for a ll machines of 10 MVAand above. Vol tage restrained over current

r el ay may be used in pl ace o f min imum impedance rel ay in case of machines wit h rati ng le ss

than 10 MVA.

2 .1 .3.1 Backup impedance prot ect ion ( 21 G)

This opera tes for phase faults in the uni t, inthe HV yard or inthe adjacent t ransmission l ines,

with a sui table delay, for cases when the corresponding main protect ion fai ls to opera te .

The impedance measured bythe relay isinfluenced bythe relay connect ion, the fault type andgenerato r and sys tem sourc e impedance fo r fau lt s on the hjgh vo ltage s ide o f t he delt a- starconnected generator transformer. A circular characteristic the center of which corresponds to

connect ion posit ion of VT should be used for this reason.

The impedance relay shall have fuse-fail interlock.

Requirements

(I) Be triple pole type(ii ) Be of single step under impedance type(iii) Shall have two adjustable definite time delay relays of 0.5-5 seconds( iv ) Be sui tab le for measuri ng two and three phase fau lt s with in a set d is tance from the

point of installation(v ) Shal l be abl e t o ope ra te for fau lt cu rren ts down to 0 .3 In.

Setting Recommendations

The impedance relay shall have reach set ting to cover t he l onges t HV outgo ing l ineo r 70% ofrated generator load impedance.

Time relay of step 1-O.S sec.- T ime re lay of s tep 2 shall be set to coo rdinat e wit h th ird zone t ime of d is tance relay o r

back up o/c relay of the outgoing l ine

II

~..

2.1.3.2 Overcurrent/Undervoltage protection (51/27) G

Requirements

(i) Be triple pole type(i i) Shall be able to opera te when the fault current from the generator terminals becomes

low due to excitation system characteristic(iii) Shall have under voltage criteria(iv) Shall reset to de-energised position if under-voltage criteria disappears

2.1.4 Negative Phase Sequence Protection (46G)

The negat ive phase sequence protect ion safeguards the generator rotor against over heatingcaused by the induced doub le f requency (100 Hz) cur rent s when nega tive phase sequencecur rent s ar e p resent in the s ta to r. The nega tive phase sequence cu rr en t can appear due to .unbalanced single phase loads or transmission line unsymmetrical faults. This shall be provided'for all machines of ratings 10MVAand above

Requirements:

(i) Be triple pole type

6

I .. _".,

(i i] Have an ala rm un it and a tr ip un it

(i i i) Have a continuously adjustable negative sequence current setting

(iv) Have alarm unit range covering negative phase sequence current of 5-10% of generator

rated current continuously adjustable(v) Have a definite t ime set ting range of 1-10 secs. associa ted with an alarm uni t(vi) Have a trip unit with a variable time current characteristics matching with the generator

122t characteristic


The rel ays should be set to t he NPS capab il ity of the generato r. The NPS capabi li ty o f the

machine varies considerably from one machine to another.

Alarm unit shall be set at 50% of continuous withstand capability value of the machine and time

del ay for al arm can be 3 Secs.

2.1.5 Generator Overload Protect ion (SlG)

Overload relay is used as an additional check of the stator winding temperature.

This may be provided for hydro uni ts where there are high head varia tions and connected for

alarm. Itmay also be connected for run back.

In case o f t he rmal set the re is no chance o f thermal ove rl oad ing a s t he machine i s provided

with number of limiters and therefore is not recommended.

Requirements:

(i ) Be s ing le pol e type( it ) Be of definite time over-current type(iii) Have a continuously adjustable setting range of SO-200%(iv) Have a drop-off/pick-up rat io greater than 95%(v) Have an adjustable t ime set ting range of 2.S to 25 sec.

2.1.6 Generator Sta tor Earth Fault Protect ion

The high neutral earthing resistance arrangement limits the generator earth fault current to lessthan 10 amperes, thus minimising damage tothe core laminat ions. Although a single phase toearth fault i snot cri tica l, i t requires c learance within a short t ime, due to the fol lowi~g:

It may develop into a phase to phase fault (due to presence ofionised air).- If a second earth fault occurs the current isno longer l imi ted bythe earthing resistor.

- Fire may result from the earth fault arc.

Two different types ofstator earth fault relays are recommended both installed inthe secondary

circuit of the generator.

2.1.6.1 0 -9S% stator earth fault protection (64G1)

This protection zone islimited to approximately 9.5%of the stator winding due to the danger of

false tripping. This shall be voltage relay iIh:"nitori: '6 il.....~:.,;!~L,~2 U,-'. dup(.J acre __, 1 : ; . , : C;}(t! .;;;J

res is to r by the neut ral re tu rn cur rent . Thi s i snorma lly used as back up prot ect ion. I t a lsoCovers the generator bus, low vol tage winding of the uni t t ransformer and the high vol tage

winding ofthe UAT. When connected to open del ta winding of generator PT, the protect ion

shall be blocked for PT fuse failure.

7



For faults within 10% ofthe generator neutral . the resul ting current is not enough to opera te

the relay.

This shall be provided for a ll machines of rat ings 10 MVA and above.

Requirements:

( i) Single pole type

( ii) Shall have independently adjustable voltage and time setting

(ii i) Sui table to protect 95% ofstator winding(iv) Be suitable for operation from broken-delta voltage transformers or neutral grounding

transformer secondary

(v) Shall be insensi tive to 3rd harmonic voltage


Pick up vol tage of the relay - 5% of maximum neutral vol tage

Time delay - 0.3 to 0.5 sees.

2.l .6 .2 100% sta tor earth fault protect ion (64G2)

This protects the whole stator winding and the generator neutral. The relay generally operates

on the principle of low frequency signal injection into the secondary of the earthing transformer,

detecting the corresponding current ifan earth fault occurs. The relay isset interms of insulation

resistance. This is normally used as the main protect ion.

Alternatively, a protection based on change in magnitude/distribution of 3rd harmonic voltage

caused byan earth fault i sused. When provided, this shall have vol tage check or - current checkuni t as applicable, to prevent faulty opera tion of the relay at generator stand sti ll or during the

machine running down period.

This prot ecti on shal l a lways be prov ided fo r mach ine above 100 MVA. The op ti on is l ef t to

the uti li ty depending upon the importance of the machine for machines of smaller sizes. Low

frequency current injection based relays are recommended for machines of 200 MVAand above.

The 95-100% relay ifseparately available , may be connected for a larm and opera tor can take

the machine out .

Requirements:

(i) Be sui table to protect 100% of sta tor winding

[ ii) Be insensitive to external faults, transients and inherent harmonic currents.

(iii) Shall be based on low frequency current injection principle/alternatively shall operate

on the princ iple of detec ting change in the magni tude/distr ibut ion of 3rd harmonicvol tage caused by an earth fault .

(iv) Have continuously adjustable time delay range 1-10 seconds(v) If based on injection principle

shall continuously monitor ground circuit

- sha ll continuously moni tor injec tion signal and injec tion equipment

- shal l be in service at s tandstil l, s ta rt up and s top

(vi) If based on 3rd harmonic voltage principle

shall have under vol tage or over current check

8


100% stator earth fault relay (Injection Principle)

Pick up level of the relay = 500 ohms

t ime delay - 2 seconds (Greater than 3rd zone ofdistance relay)

100% stator earth fault relay (3rd harmonics principle)

Setting 0.45 V (should be checked w.r. t. 3 rd harmonic vo lt age

generated by the machine)

2.0 sec .

80% of rated vol tage

20% of rated current

Time delay

Voltage check unitCurrent check unit

2.1.7 Loss of Excitat ion Protect ion (40G)

A complete loss ofexcitation may occur as a result of unintentional opening of the field breaker,an open ci rcu it o r a shor t cir cu it of the main f iel do r a fau lt in AVR.

When a generator with sufficient active load loses the field current, itgoes out of synchronism

and starts to run asynchronously a t a speed higher than the system absorbing react ive powerfor the excitat ion from the system. Under these condi tions the sta tor end regions and part ofthe rotor get over heated.

This isrecommended for machines of a ll sizes above 10 MVA.

Requirements:

(i) Have mho charac ter is tic l yi ng in 3 rd and 4th quadrant of impedance d iag ram wi th

adjustable reach and off set. Alternatively, this protection shall be based on directional

current uni t with set ting range to match generator capabil ity curve

(ii) Shall have an under vol tage relay and/or over current relay as an addit ional check(iii) Shall have timer with adjustable range of 1-10 seconds to distinguish loss of excitation

from power swings

Setting Recommendations:

(i) For off set mho type relay

Diamet er of mho c ir cle - (xd - x' a/2

Off set of the mho circle from origin - X'd/2Time delay =1.0 sec.Under voltage relay = 70% .

.(Ii) For directional current type relay

Direction current relayis set to match with the generator capabilitycurve in4th quadrantTime delay 0.5 to 1 sec.

Under voltage 70%

Over current 110-115%

2.1.8 Pole Slipping Protect ion (98G)

The loss of f ie ld protect ion shall be supplemented by an addit ional out of step funct ion which

detects all pole slips.

9



Pole slipping ofgenera tors with respect to the ' system, can be caused bya number of condi tions

leading to an increase in rotor angular posit ion beyond the generator t ransient stabi li ty l imits.

Some of the causes o f po le s li pp ing are:

(a) Large network disturbances

(b) Faults on the elect rica l network close to the generator.(c) Weak t ie between the network and the generator ( tr ipping of transmission lines)

(d) Loss of generator f ie ld (fieldwinding or excitat ion supply fai lure)

(e) Opera ting the generator in an excessive under excited modeThis is recommended for machines of 100 fl.1VAand above. For hydro machines uti li ties can

decide depending on machine parameters.

Requirements:

(i) Shall be capable of detec ting a power swing which can lead to instabi li ty in addit ion to

be ing abl e to det ect an ac tual po le s lip(i i) Byvarying size of the character istic i t shal l be possible to ensure tha t a t rip command is

given to the circuit breakers in such a way that separation of the poles occurs at a

control led angle a t any t ime.


(a) If the source of osc il la tion l ies within a generator /t ransformer uni t, the machine has to

be isola ted from the network after the first slip.

Forward reach of relay characteristics shall cover generator/generator transformer. Tripping

in this zone shall be in the firs t pole slip. The reach of this zone is O . 7 ~ .

(b) If the source ofosci llat ion l ies outside the uni t in the network, the generator should not

be switched off or a tle.ast not unt il several pole slips have occurred.

2.1.9 Low forward power/reverse power interlock relays (32G/37G)

The low forward power i nter lock is r ecommended fo r therma l mach ines and reve rse powe r

protect ion may be used for hydro machines to protect against motoring.

When the steam flowthrough turbine isinterrupted byclosing the ESVs or the governor valves,

the rema in ing energy s to red in the set is del ivered to t he sys tem and the mach ine en te rs i nt o amotoring condi tion drawing power from the system to supply i ts losses whi le keeping the turbo

alternator shaft at synchronous speed.

The low forward power rel ay de te cts t hat the unit is mo to ring and must therefore be

shutdownTripping for mechanicai faults and abnormal conditions

For faults in the turbine or boiler, the turbine protection closes the ESVs. For abnormal

conditions, the generator protection closes the ESVs. When the generator develops low forwardpower, the relay after a short t ime delay t rips the generator breaker .

A protect ion fie ld suppression signal may also be required i f the AVR does not have a built-in

facilityto reduce the generator fieldcurrent as the speed decreases, to avoid over fluxing conditions.

Requirements:

(i) Be single phase power measuring type

1U

(ii) Have a'power setting of approximately 0.5% - 1%of rated active power ofgenerator unit

( iii) Have independent t ime delay relay with set ting range of 1-10 seconds and 0-20 secondsrespectively on p ick up

(tv) Have one more common timer with a pick up setting range 5-50 seconds for annunciationthat the Turbo generator set has started motoring

(v) Have sui table arrangement for prevent ing the opera tion of this protect ion during startup and synchronising of the uni t

(vi) Shall be provided with possibility of angle correction to facilitate measurement of poweraccurately


low forward power relay pickup < 0.05 x Pn- timer t1 - 2 seconds , t 2 - 2 seconds

2.1.10 Under-frequency protection (81G)

The under frequency protection

Prevents the steam turbine and generator from exceeding the permissible opera tingtime at reduced frequencies

Ensures that the generating unit is separated from the network at a preset value of

frequency that is less than the final stage of system load shedding

Prevents the AVR from excit ing the machine at reduced speeds when some protect iverelays may no t per form at allPrevent over f luxing of the generator . The over fluxing relay is used to protect against

small overfluxing for long periods while the over voltage and under frequency relays alsoprotect against large over f luxing for short t imes

The sta tor under frequency relay measures the frequency of the sta tor terminal vol tage

Though under frequency tripping is recommended by turbine manufactures, care should betaken bygrid opera ting personnel in ensuring that machines are not run at lower frequenciesand instead resort to means l ike load shedding in the event ofoverload.

Requirements:

(I) Have one alarm stage and two tripping stages(ii) Shall have set ting ofrange of 45 Hz - 55 Hz with a le as t coun t o f 0.1 Hz for each stage( ii i) T imer for al arm stage have a range o f 0.5 to 5 second with a least count of 0.5 second.

Timers for each tripping stage shall have range of1to 10 seconds with a least count of0.1 second

(tv) Shall have undervoltage blocking


- S ta to r under tr equency rel ay p ick up level = 48.5 Hz- Time delay for alarm - 2 Sec.

For time delay sattinq of tripping stages recommendations of turbir.e manufacturers rna}' be followed.

2.1.11 Inter turn fault protection (95G)

It is generally considered difficult to obtain reliable protection against short circuit of one turn

if the sta tor 'winding has large number of turns per phase .

11



Inter turn fault protect ion isrecommended only for machines where there isa spl it winding and

a ll t he s ix t ermina ls a re b rought out on the neutr al s ide.

For generator with spl it neutrals, convent ional inter-turn fault protect ive scheme comprises a

t ime de layed low set over -cu rrent r el ay whi ch senses t he cu rrent fl owing in t he connect ion

between the neutrals of the sta tor winding.

Alternatively a splitphase differential protection may be used.

Requirements

(i ) Over current relay with t ime delay

(ii) Over current relay shall have bui lt in f il te rs to rejec t higher harmonics

(iii) Range of over current shall be selected depending on maximum spill current for external

fault

Setting Recommendation

Overcurrent relay shall be set to maximum unbalanced current in case of external fault .

T ime delay 0 .2 - 0.4 seconds

2.1 ..12Genera tor Transformer Over Fluxing Protect ion (99 GT)

Overf luxing protect ion isprovided to safeguard the generator , generator t ransformer and uni tauxiliary transformer against operation at fluxdensities which may cause accumulative damage

to the core.

From the fundamental equat ion V = 4.44 x f x n x 4> , the level of f luxis proport ional to the

ratio of terminal voltage to frequency (v/f). This rat io ismoni tored by the protect ive relay.

An over fl uxing condi ti on i s more l ikel y t o occur whi le t he generato r is separated f rom thesystem and the speed is al lowed to d rop, but it can al so happen wit h the mach ine on load if the

tap changer of the generator t ransformer (H V s ide ) i s on a low tap position and the excitation

of the generator is manually increased. In this case the increased generator terminal vol tagemay cause over fluxing tripping at nominal frequency.

The over f luxing protect ion opera tes with a t ime delay after which the t ripping funct ions are

executed.

This protect ion must be provided for generator-t ransformers of size 10 MVAand above.

Requirements

(i) Shall be phase to phase connected.

( ii ) Shall opera te on the princ iple of measurement of vol tage to frequency rat io .

( ii i) Have inverse t ime character istics compatible with generator t ransformer over f luxing.withstand capability for tripping.

[iv) Provide an independent a larm with a definite t ime delay of value ofV/f between 100%to 130% of rat ed value.

(v) Have a h igh reset ti ng rat io o f 98% or better.


The overf luxing capabil ity of the t ransformer must be checked and the character istic matched '

accordingly for both alarm and trip.

12

.~';-,;.,,:....,:

2.1.13 Generator Over Voltage Protection (59G)

An over ~ol tage on the terminals of the generator can damage the insulat ion of the generator ,

bus duct inq , b reakers , generat or tr ans fo rmer and auxil ia ry equ ipment such a s vo ltagetransformers, excitation transformer etc.

This should be provided for machines of a ll sizes, hydro and thermal

Requirements:

(i) Be single pole type/or t riple pole type

( ii) Shall have two separately adjustable stages .

(i i i) Have a continuously adjustable set ting range of 100 - 140% of rated voltage( iv ) Have a d rop o ff t o pi ck up rat io g rea te r than 9S%

(v) Have a con tinuous ly var iab le t ime delay set ti ng range o f 0 .5 - S seconds for one rel ayand 2 to 20 seconds for the other relay.


Stage 1 Over volt age relay p ick up - 1.15 x VnTimers t1 - 10 seconds

Over volt age re lay p ick up - 1 .3 x Vn

Timer t2 - O.S seconds

Stage 2

2.1.14Dead machine protection (27/S0G)

Despi te existence of inter locking schemes, a number of generators have been inadvertent ly

energized while at stand ~titl or on tu rn ing gear . The generato r and roto r may get damaged?eyond repair unde r t hi s condit ion. Othe r prote ct ive rel ays li ke lo ss o f exci ta ti on, back up

Impedance , r ever se powe r would ope rat e wit h de lays and this i s not admi ss ib le. The deadmachine protection permits fast tripping.

,T~i~ should be insta lled in switchyard panel rather than in generator panel to ensure that

protection isavailableduring maintenance periods when the generator protection can be renderedinopera tive bySWitchingoff the DC supply to the panel .

!his protect ion isrecommended for a ll machines of size 100 MVAand above. The protect ionIS connected to t rip generator breakers, generator t ransformer breaker and the HV Bus.

Requirements;

(i ) Sha ll cons is t o f 3 high speed over current relays of range (0.02 - 20 In) to initiateinstantaneous tripping if generator terminal voltage is below set value. .

( ii ) Shall have under vol tage relays of range (0.2-1 Un ) to permit opera tion of over currentrelays when vol tage is low

(i i i) Shall have timer s wit h adjustabl e range (0 -605 ) to avoid operati on o f p ro tec ti on fornearby fault when the machine is in service .

(iv) Shall be secure against voltage transients at closing


Overcurrent relay

Under voltage relay

Activation of relay

For Weak System

1-2 pu

20% to 40% rated vol tage

20 Seconds after dead t ime

For Strong System

3-4 pu

SO%to 70% of rated vol tage

20 Seconds after dead time

13



2.1.15 Generator VT fuse fai lure monitor ing (60G)

This has to be provided for a ll the machines since i t i s required for blocking ofre lays which can

mal-opera te in the event of PT fuse blowing inprimary side or secondary side.

Requirements:

(i) Be triple pole type

[ ii) Be abl e t o det ect fu se fai lu re i nboth p rimary and seconda ry s ide of VT

(iii) Have a fixed setting of 70% of rated voltage and have a time delay of 40 to. 50 milli-seconds on p ick up

(iv) Be of vol tage balance or equivalent type

(v) Have sufficient contacts to block tripping of those relays which are vol tage dependent

and give alarm

2.1.16 Rotor ground fault protection

This protection shall be provided for machines ofallsizes. Itis recommended that the protection

isconnected only for alarm and the operator may take the machine out at the earliest opportunitya ft er the f ir st ear th fault has occur red . The tr ipping logic should a lso i nc lude uni t tr ipping incase fie ld c ircuit breaker opens when the machine is funning.

Requirements:

( i) Shall be based on DC injec tion princ iple or low frequency AC injec tion princ iple

(ii) Shall be single stage or two stages(i i i) Shall have bui lt -in t ime delay to prevent unwanted opera tion of the relay

Alternatively

A sensi tive vol tage funct ion opera ting on bridge measuring basis with auxil ia ry equipment .Thi s shal l have two l evel s, one for al arm and one for t rip .

Setting ranges : Alarm stage 100 ohm to 25 k ohm, Time delay 2-60 SecondsT rip stage 100 ohm to 25 K ohm, T ime delay 2-60 Seconds


alarm level - 25 K ohmpick up level - 5 K ohmtimer tl -1 secondstime r t 2 - 5 seconds

2.2 Generator-Transformer Protection

For short circuit protection, transformer-differential relay and over-current relay connected tod if fer ent groups a re r ecommended . For g round fau lt s, ea rth fau lt o /c re lays and res tr ic ted

earth fault relay connected to different groups are recommended.Incase a overhang pro tec ti on is r equ ired, t he same may be combined with REF prot ec ti on onHV side of generator transformer.

2.2.1 Generator Transformer Different ia l Protect ion (87 GT/87 T)

Requirements:

(i ) Be triple pole with individual phase indication

14

( l i ) Have unres tri ct ed in st an taneous h igh set over cur ren t unit s which sha ll no t operat e

during inrush

(ii i) Have an adjustable or mul ti bias set ting

( iv) Have second ha rmoni c o r o ther i nrush p roof fea tu res and al so sha ll be s tabl e under

normal over fluxing conditions. Magnetising inrush proof feature shall not be achieved

through any intentional t ime delay e .g. use of t imers to block relay opera tion or using

disc operated relays.

(v) Have one b ia s winding per pha se and per C. '] '. input

(vi) Have an adjustable operating current(vi i) Have an opera ti ng t ime not g rea te r t han 30 mi ll i seconds a t 5 t imes o f sett ing

(viii) Shall have facility for ratio and phase angle correction either through auxiliary transformeror through in built provisions.

2."2.2 Generator Transformer Backup Overcurrent Protect ion (51 GT)

Requirements:

( i) Be tr ip le pole t ype

(ii] Be of definite t ime over current type( iii ) Have an ad jus tab le sett ing range of 50-200% of rat ed cu rr en t and 0 .5 - 5 seconds t ime

delay

2.2 ..3 Generator Transformer Back Up Earth Fault Protect ion (51 NGT)

This relay monitors the current inthe generator t ransformer neutral . It can detec t faults in thet ransformer HV side or in the adjacent network.

Requirements:

( i) Be of s ingl e pol e type

( i i ) Be of definite time characteristic

( iii ) Have an adjus table set ti ng range of 10 to 100% of ra ted cur ren t( iv) Have a t ime r sett ing range o f 0.5 to 5 seconds

. 2 .2 .4 HV wind ing cum overhang d if fer en tia l prot ect ion (87 HV187 NT)

This isa uni t type protect ion which opera tes for earth faults on the generator t ransformer HVside and also covers a large portion of the HV winding and the HV terminals upto the HVcurrent transformers. ....

Requirements:

(i ) Be triple pole type (Single pole i fused as Restr ic ted El F Protection)

.o n Have opera ting t ime less than 30 mil li seconds at 2 t imes set ting

(ii i) Be high impedance or low impedance type

( iv) Operati ng cu rr en t sha ll be 0 .1 - 0 .4 In(v) High stabi li ty against maximum through fault condi tion, CT saturat ion, harmonics and

DC transients(Vi) Be provided with sui table non l inear resistors across the relay to l imit the peak vol tage

to 1000 vo lts , in c ase of h igh impedance type(Vii) Be provided with faulty phase identification

2.3 Unit Auxiliary TransformerProtections

For short circuit protection, unit auxiliary transformer differential relay, overload relay for alarm

15



and over current relay connected to different groups are recommended. However a uti li ty may

carry out an applica tion check and decide not to have a separate different ia l relay for UAT.

For ground faults residual O/c relay and Restr ic ted E/F relays connected to different groups

shan be provided. The type ofconnection may beeither current based or voltage based depending

on the grounding system.

'2.3.1 Uni t Transformer Different ia l Protect ion (87 UAT)

This isa uni t type protect ion covering the uni t t ransformer and the cable connect ion to the uni tboard. .

This protect ion opera tes for phase faults, but not for single phase to earth faults as this current

is limited by the neutral earthing resistance.

The unit transformer differential relay initiates a general trip and unit shutdown.

Requirements:

(I ) Be triple pole with individual phase indication(il) Have unrestricted instantaneous high set over current unit which shall not operate during

inrush(i i i) Have an 'adjustable or multi bias setting( I V ) Have second harmoni c o r o ther in rush p roo f fe atu res and al so should be s tabl e under

normal over fluxing conditions, magnetising inrush proof feature shall not be achieved

through any intentional t ime delay e .g. use of t imers to block relay opera tion or using

disc operated relays.

(v ) Have one bi as wind ing per phase and per C.T. i npu t(vi ) Have an adjustable opera ting current(vi i) Have an ope rati ng t ime not grea te r t han 30 mil li seconds at 5 t imes o f set ti ng(viii) Shall have facilityfor ratio and phase angle correction either through auxiliary transformer

or through in built provisions.

2.3.2 Uni t Transformer back up over current protect ion (51 UAT)Relay

(I) Be triple pole type( i j ) Be of definite t ime over current type(i i i) Have an adjustable set ting range of 50-200% of rated current and 0.5 to 5 seconds t ime

delay

2.3.3 Uni t Transformer back-up earth fault protect ion (51 NUAT)

(i ) Be single pole type

(i i) Be of definite t ime over current type(ii i) Have a set ting rage of 10-100% of rated current and t ime set ting range of0.5-5 seconds

2.3.4 Uni t t ransformer restr ic ted earth fault protect ion (64 UAT)

(i) Be single pole type(ii) Have opera ting t ime less than 30 mil li seconds at 2 t imes set ting

(ii i) Be high impedance or low impedance type

(iv) Opera ting current shall be 0.1- 0.4·1l1

(v) High stabi li ty against maximum through fault condi tion, CT saturat ion, harmonics and

DC transients

16

(vi ) Be provided with sui table non-l inear resistors across the relay to l imit the peak vol tage

to 1000 vol ts , in c ase o f h igh impedance type

(vii) Be provided with fault indication

3. ENGINEERING RECOMMENDATIONS

3.1 Redundancy

The prot ect ion funct ions shal l be subdiv ided into two groups each being independen t and

capable of providing uninterrupted protection even inthe event of one of the protection groups

fai ling. Given below is recommendat ion for dividing the protect ions in two groups:

GROUP A GROUP B

Generator

Generator differential

Minimum impedance

(or alternatively over

current/under voltage)

Negative sequence protection

Over load protection

100% stator earth-fault

Rotor earth fault

Reverse Power

Over voltage

Inter-turn fault

Generator Transformer

Transformer differential

Earth fault over current

Over-all differential

95% sta tor earth fault

Loss of excitation

Pole slip

Under frequency

Reverse power

Over fluxing

Over current

Restricted earth faultHV Winding cum overhang differential

UnitAuxiliary Transformer

Transformer differential

Ground fault over current

Over current

Restricted earth fault

3.2 Tripping Principles

1ngeneral, itis best ifgenerator protection relays initiate non-sequential trip mode (Class-A) for

unit isolation. However sequential trip;Jir:~ k..lass B}P;VViLks e Li.~~~.;r 11 ,-an~·.0; U;;'! i:1J-'

steam turbine generator on some abnorrna: Gpera till!:) cI..JndiliO;1S w1h:~r'-.!delayed tripping of llie

generator wil l not resul t in increased damage: to the turbine , gCl l. .. :rator or other e lect rica l

eqUipment . The reason for sequent ia lly t ripping a steam turbine generator is to avoid the over-

speed condi tion that resul ts when the generator main breaker ist r ipped whi le steam isappliedto the turbine.

17



Proper control logic iscr it ical to the design of a sequent ia l t ripping scheme and requires some

sort of mechanica l "Turbine Tripped" indicat ion (i.e. steam stop valve l imit swi tches, t rip oil

system pressure swi tches e tc .) which is supervised by an elect rica l reverse power relay. This

relay is normally set to detec t very low power levels and incorpora tes a brief t ime delay of the

order of several seconds for added security.

It has been recommended that generator protective relays, initiate non-sequential trip mode for

isola tion of the uni t due to elect rica l faults. Only devices protect ing uni t from 'an abnormal

mechanical operating condition or an abnormal (not faulted) electrical condition or normal shutdown should ini tiate a sequent ia l t rip.

18

Section 2

LINE PROTECTION

1.0 GENERAL

The l ine protect ion relays are required to protect the l ine and clear a ll type offaul ts on i twithin

shortest possible time with reliability, selectivity and sensitivity. The line protection relays shallbe suitable for use with capacitive voltage transformers having passive damping and transientresponse as per lf.C 186. .

Recommendation for provisions of line protection at different voltage levels are as follows:

1.1 400 kV Lines

There should be two independent high speed main protect ion schemes cal led Main-Iand Main-

I lwith a t least one of them being carrier a ided non-swi tched three zone distance protect ion.

The other protect ion may be a phase segregated current different ia l ( this may require digital

communication) phase comparison, directional comparison type or a carrier aided non-switched

distance protect ion. Further , i fM~in-Iand Main-Il a re both distance protect ion schemes, then

they should be preferably of different types. However, they need not necessarily be of different

make. Both the protect ions should be sui table for single and three phase t ripping. In addit ion

to above Iollowinq shall also be provided:

(i) Two stage over -vo ltage p rot ec ti on. However i n such cases whe re. sys tem has g rown

sufficiently or in case of short lines, utilities on their discretion may decide not to providethis protection.

(il) Auto redose re lay sui tabl e for 1 ph/3 ph (wit h deadl ine charg ing and synch ro check

facility) reclosure.

(i i i) Sensitive IDMT directional E/F relay

1.2 220 kV Lines

There should be atleast one carrier aided non-switched three zone distance protection scheme.

In addition to this another non-switched/switched distance scheme or directional over current

' andear th fau lt r el ays should be p rovided a s back up. Main p rot ec ti on should be suit ab le fo r

single and three phase t ripping. Addit ionally, auto-reclose relay sui table for 1 phf3 ph (with

dead line chargirig and synchro-check facility) rcclosure shall be provided. In case of both' line

protections being Distance Protections, IDMTtype E/F relay shall also be provided additionally.

2.0 REQUIREMENTS

2.1 Distance Protection

Distance Protection scheme shall have the following attributes:

(i) Three independent zones{ii) Non-switched type with separate mea suremen ts for al l phase to phase and phase to

ground faults.

( ii i) Capable of single and three phase t ripping

(iv) Direc tional (mho or quadrilateral or other sui tably shaped) character istics for zone 1,

zone 2 and zone 3

19



(v) Capable of opera tion for c lose-up three phase faults and switch on to faults

(vi) Adjustable characteristic angle to match line angle wherever applicable

(v ii ) Accuracy of bet ter than or equal to 5% of set val ue fo r re ach measuremen t in zone 1

and bett er than o r equal t o 10% of set val ue for zone 2 and zone 3

(vi ii ) Accuracy of bet te r than or equal to 5% ofse t value for t ime measurement ofzone 2 andzone 3 .

Ox) Variable residual compensation

(x) Shall include power swing detection feature for selectively blocking, as required.

(xi) Shall include suitable fuse-failure protection to monitor all types of fuse failure and block

the protection.

(x i i ) Maximum opera ting t ime under given set of condi tion shall be as fol lows:

SIR 4 15

Relay setting 10 Ohms 2 Ohms

Fault location (as % of relay setting) 60% 60%

Trip duty Contacts per phase" 4 4

Fault resistance Zero Ohms Zero Ohms

Max. Operating Times 45ms 45 ms for 3 phase faults

Including trip relays (if any) for all faults 60 ms for o the r f aul ts

and with CVT

* These t rip duty contacts can be provided either in-buil t in the distance relay or through

addit ional relay. Making capacity of t rip contrac ts shall be 30 A for 0:25 S with an'

inductive load of L/R > 10 ms

2.2

(il

( i j )

Directional Comparison Protection

Shall be a uni t system of protect ion

Shall be directional comparison type suitable for operation with one signalling channel,

e.g., PLCC

Shall have h igh speed fau lt dete cti on based on pr inci pl es l ike de tect ion o f post f au lt

travelling wave, superimposed components, etc. .

Shall have high sensi tivi ty for a ll types of faults

Shall be sui tab le for 1 and 3 pha se t ri pp ing

Shall not be affected byheavy load transfer, power swings, CT saturation, CVT transients,

VT fuse failure, line charging currents, distorted primary currents and voltages, external

switching activities, sudden power reversal, zero sequence, mutual coupling, shunt reactor

"in-zone" switching etc. and lightning strokes

Shall have fea tures l ikeswitch on to fault , weak end infeed, echo system

Shall have feat ure to cover nea rby faul t at h igh speed in the event o fchannel f ai l

(iii)

( i v)

(v)

(vi)

(vii)

(viii)

2.3 Phase Segregated Line Differentia1 Protection

(i) The relay shall be a ll digital mul ti microprocessor based, designed for use with modern

digital telecommunication system multiplexer conforming to ITU-T (CeITT) specifications

and Fibre Optic medium.

20

( i i ) Each phase current shall beseparately evaluated at both ends for both amplitude and phase.

( iii) Shall be suitable for single phase tripping and autoreclosing.

(iv) The message transmitted by the relay to other end shall include information on currents,

supervision information, CT saturation detection, synchronisation of terminals etc.

(v) The measurement shall be stabi li sed phase by phase for CT saturat ion.

(vi) The communication delay shall be continuously measured and automatically compensated

for in the differential measurement.

(vii) Communication telegram shall have error detection and correction feature.(viii) Suitable programmable evaluation algorithm will be provided to ensure proper security

and dependability of the message.(ix) The connection equipment from the relay to the communication shal! be a 64 kbps

Channel.(x) An opt ional e lect rica l or opt ical port shall be provided to direc tly connect the signal to

auxiliary channel of OLTE (optical line terminal equipment) by passing the multiplexer

or for redundancy purpose.(xi ) The relay shall have communica tion port for remote monitor ing, programmaing and

control.(x i i ) The direct intertrip signal also shall be transmitted as part of telegram.(xiii] The sampli ng fr equency for analog s igna ls shal l be minimum 2 kHz. Fi lt er ing and

measuring techniques shall be used to ensure correct performance during all operating

and transient conditions.

2.4 Phase Comparison Protection

(i) Shall be Current phase comparison type.( ii) Shall be suitable for operation with one signal channel.

(iii) Shall have high sensitivity for all types of faults.

( iv) Shall be capable of single and three pole t ripping.

(v) Shall have facility for blocking/permissive trip modes

(vi) Shall have facility for direct transfer tripping

(vii) Shall have comprehensive alarm and test facilities(vi ii ) Shall hot be affec ted by heavy load transfer, power swings, CT saturat ion,· CT phase

errors, Propagation delays, Capacitance current etc., as is typical of unit protections.

2.5 Over Voltage Protection

The relay shall have following features:

Have a h igh d rop of f t o p ickup ra tio

Have adjustable setting range for voltage and time

Have two stagesLow set stage shall monitor anyone phase to phase vol tage and shall have associa ted

timerHigh set stage shall monitor a ll three phase to phase vol tage and shall have associa ted

timer

3 ..0 SpCCi<l l Com n.ent.s

(t) If found necessary, a t cer ta in locat ions, out of step t ripping relays shall be provided for

islanding the system during disturbances

21



( i i ) For short line application distance relays should have shaped characteristics for ground

faults and be used in permissive over reach mode with weak end infeed logic . Further ,

i f i t i s a double c ircuit l ine, current reversa l logic should also be available .

( i i i ) ON relay for 400 kV lines shall be connected to t rip concerned l ine breakerls), sta rt

LBB, block auto rec losure and send direc t t rip command.

(iv) The direc tional ear th fault relay recommended along with the distance relay should be

seen as a supp lement to i t and no t a s a back up. It hel ps to dete ct ve ry high res is tance

fault which distance relay cannot.

(v) HVDC Systems connected to AC networks with low short c ircuit levelscan influence AC

line protect ions in i tvic inity. This aspect needs to be looked into on case to case basis.

4. 0

4.1

0 )

( ii)

SETTING CRITERIA

Reach Settings of Distance Protection

Zone-I: to be set to cover 80-85% of protected l ine length

Zone-II : to be set to cover minimum 120% of length of princ iple l inesect ion. However ,

in ca se of D/C lines 150% cove rage mus t be p rov ided to take care of , under reaching

due to mutua l coupli ng ef fe ct but , c ar e is to be t aken tha t it does not re ach int o nex t

lowe. voltage level.

Zone- II I: For 400 kV lines Zone -I II t o be set t o cove r 120% of pr inci pl e secti on plus

adjacent longest sec tion subject to a reach restr ic tion so that i tdoes not reach into next

lower vol tage level . For 220 kVlines, Zone-III reach may be provided to cover adjacent

longest section if there is no provision of LBB or all protect ion are connected to single

DC source at remote and substat ion.

Res is tive reach: Re sis tive reach should be set t o g ive max imum cove rage subj ect tocheck of possibi li ty against load point encroachment considering minimum expected

vol tage and maximum load. Also attention has to be given to any l imitat ions indicatedby manufacturer' in respect of resistive setting vis-a-vis reactance setting.

(iii)

4. 2 Time Setting of Distance Protection

A Zone-Il t iming of 0.3 second isrecommended. However , i fa long l ine isfol lowed bya short

li ne, then a h ighe r sett ing (say 0.5 sec) may be adopted on long l ine to avoid indi scr iminat e

t ripping through Zone-II opera tion on both l ines.

Zone- III timer shou ld be set so as to provide discrimination with the operating time of relays

provided in subsequent sections with which Zone-III reach of relay being set overlaps.

4 .3 O/V Protection

4.3.1 Low set stage may be set at llOo,.{) with a typical time delay ofS seconds. However , a

t ime grading of 1 second may be provided between relays of different l ines a t a sta tion.

Longest time delay should be checked with expected operating time of overfluxing relayof the t ransformer to ensure disconnection of l ine before t ripping of t ransformer.

4.3.2 High set s tage may be set at 150% with a t ime delay of 100 m.second.

4.4 PO\Vl.:l ' Jwing Blocking Function As soc iated with Distance Relays

Decisions perta ining to allowing which Zone to trip and which to block should be taken based

on system studies Oil case to case basis.

22

Section 3

AUTO-RECLOSING

1.0 GENERAL

The auto-reclosinq of power l ines has become a general ly accepted pract ice. Reports from

different parts of the world show that in certa in networks inregions subject to a high l ightningintensi ty only about 5 per cent of the faults are permanent . Auto-reclosing therefore provides

significant advantages. Outage t imes wil lbe short compared to where . sta tion personnel have

to re-energise the l ines after a fault. Additionally, in interconnected networks auto-reclosing

helps in maintaining system stability.

Following different arrangements of auto-reclosing are possible:

High speed single pole reclosing (HSAR)

High speed three pole rec losing (HTAR)

Delayed three pole reclosing (DAR)DAR with dead line (DL)and synchronism check(SC)

HTARwith DL and SCHTAR with parallel line check (PC)

Incase ofHSAR and HTAR without check, the two ends can be reclosed at about the same instant.

In case o fDAR and HTAR with DLand SC the C .B. at one end recl oses f ir st af ter the set dead

t ime and with a check of dead l ine condi tion. After a successful l inere-energizat ion from oneend the vol tage , phase angle and possibly frequency on the l ine and sta tion side are compared.

At acceptable synchronous in-phase condi tions the C.B. a t the second end isreclosed.

1.1 R.ecommendations for provisions of auto-reclosing.

Presently 1 phase high speed auto-raclosure (HSAR) at 400 kV and 220 kV level is Widely

practised including on lines emanating from Generating Stations and the same isrecommended

for adoption. If 3-phase auto-rcclosure is adopted infuture the applica tion ofthe same on l ines

emanating from generating stations should be studied and decision taken on case to case basis.

2.0 REQUIREMENTS

It shall have the following attributes:

(i) Have single phase and/or three phase reclosing facilities.

(il) Have a continuously variable single phase dead time.

(iii) Have continuously variable three phase dead time.

(iv) Have continuously variable reclaim time.(v) Incorporate a facility ofselecting single phase/three phase/single and three phase auto-

rcclose. and non-auto reclosure modes.(vi) H.-vc facilities for selecting cI ...:..:k:~·._>vli;~ins cr J~Jj li, .._;c:.c:·;;;":"> 7L;:,LUI,,- ':;.

(vi i) Be of high speed single shot type(Viii) Sui table relays for SC and OLC should be included in the overa ll auto-reclose scheme.

(ix) Should allow sequential reclosing of breakers in one and halfbreaker or double breaker

arrangement.

23



3.0 SPECIAL COMMENTS

3.1 Fas t s imu ltaneous t ri pping of t he b reake rs at both ends ofa fau lt y l ine is essential for

successful auto-reclosing. Therefore, availability of protection signalling equipment isa

pre-requisite.

Starting and Blocking of Auto-redose Relays:3.2

Some protections start auto-reclosing and others block. Protections which start AIR are Main-

r and Main-Il line protections.

Protections which block AIR are:

Breaker Fail Relay

Line Reactor Protections

O/V Protection

Received Direct Transfer trip signals

Busbar Protection

Zone 2/3 of Distance Protect ion

Carrier Fail Conditions

Circuit Breaker Problems.

When a re cl os ing relay re cei ves s ta rt and block AIR impulse simultaneously, block signal

dominates. Similarly, if itreceives 'start' for I-phase fault immediately followed by multi-phase

fault the later one dominates over the previous one .

3.3 Fol lowing commen ts are fo r mu lt i-bre aker a rr angement s of one and hal f b re aker o r

double breaker arrangement

3.3.1 In a mul ti -C.B. arrangement one C.B. can betaken out of opera tion and the l ine sti ll be

kept in servi ce . Af ter a li ne fau lt on ly t hose e .Bs which were cl osed before the faul t

shall be redosed.

3.3.2 In mul ti -C.B. arrangement i t i s desirable to have a prior ity arrangement so as to avoid

cl os ing of both the b reake rs in c ase of a pe rmanen t f au lt. Thi s wil l help in avo idi ng

unnecessary wear and tear.

A na tu ral pr ior it y is t ha t t he e.B. nea r the busba r is r ec lo sed f ir st . I n case of f au lts

on two li ne s on bo th s ides o fa ti e C .B . the t ie C.B. i s r ecl osed af te r t he oute r e.Bs .

The ou ter e .Bs. do not need a p rio rit ing with respect t o each other .

3.3.3 In multi-breaker arrangement it i snecessa ry t o tr ip two e.Bs . t o c lea r a li ne fau lt and

also au to redose these two .. Bas ical ly two types o f ar rar igemen t for C .B . a ssoc ia ted I

relays are possible i.e:

CB. OrientedLine Oriented

..

With CB. oriented arrangement co-operation between C.Bs, Synchrocheck relay etc. isstraight

forward and autorec lose mode can be selected scporately for each breaker . \ \" ith l i:'e. 0\ ic: ,L._J

arrangement interconnections between line r,~i·.:,:;_'and reclosure relay issimpler, l""'~cccpcr2lt:on

with cir cui t b reakers schemes becomes compl ic ated. For the above rea sons CB. o rient ed

arrangement is recommended.

24

3 .4 Incase of bus ba r confi gurat ion a rr angemen t hav ing a t ransfer breaker , a sepa ra te au to-

reclosure relay for transfer breaker is recommended.

4.0 SETTING CRITERIA

4.1 Dead Time

Auto-reclosing requires a dead t ime which exceeds the de-ionising t ime. The t ime required for

the de- ion is ing o f t he fault pat h depends on several f acto rs i nc luding the arcing time, faul tduration, wind conditions, circuit voltage, capacitive coupling to adjacent conductors, etc. The

circuit vol tage is the fac tor having the predominating influence on the de-ionising t ime.

S ingl e phase dead t ime of 1.0 sec. is r ecommended for both 400 kVand 220 kV sys tem.

4 ..2 Reclaim Time

The reclaim time isthe time during which a new start of the auto-reclosing equipment isblocked.

If redosing shot has been carried out and the l ine isenergised and a new fault occurs before the

reclaim time has elapsed, the auto-reclosing equipment is bl ocked and a s ignal for def in it e

tr ipping of the b reaker is obt ai ned. Aft er t he recl aim t ime has el apsed , t he au to- rec lo sing

equipment returns to the start ing posit ion and a new reclosing sequence can occur . The rec la im

time must not be s et to such a low value that the intended operating cycle of the breaker is

exceeded, when two fault incidents occur close together. If the breaker is closed manually, the

auto-reclosinq equipment isblocked and cannot start again unt il the rec la im t ime has e lapsed.

For the breaker to be used for auto-reclosing, i t i s essential tha t i thas the opera ting mechanism

and bre ak ing capac it y nece ssary fo r it t o be ab le to per fo rm the auto -r ecl os ing sequence s

required.

4.3 Circuit Breaker Requirement

According to lEe Publication 56.2, a breaker must be capable of Withstanding the fol lowing

operatinq cycle with fullrated breaking current:

0+ 0.3 s + CO + 3 min. + CO

The recommended opera ting cycle a t 400 kVand 220 kVis as per the IEC standard. Therefore ,

rec la im t ime of 25 Sec . is recommended.

25



~ - - - - - - - - - - - - ~ - - - - - - - - - - " " " I " " " ' ' ' ' ' - - - - . ~ - : ; - , - - - - - - - - - - - - - - - - - - - - - -. .- - ~ l

Section 4

TRANSFORMER PROTECTION

1.0 GENERAL

A Power Transformer is a very valuable and vital linkin a Power Transmission system. Reliable,

secure and fast protect ion system for the t ransformer is essential to minimise the damage incase of an in te rnal f au lt with sui tab le back up protection scheme to take ca re o f uncle aredsystem faults.

Faults occur in Transformer due to insulation breakdown, ageing of insulation, overheating due

to over excitat ion, oil contamination and leakage or reduced cooling. To give an early warning

and to minimise the damage in case of a fault it is necessary to equip it with monitors andProtective relays.

Recommendat ions for provision of protect ive and monitor ing equipment for t ransformers of

400 kV and 220 kV class are as fol lows:

1.1 Following are the various protections recommended for the transformer protection:

(a) Transformer differential protection

(b) Overfluxing protection

(cl Restricted earth-fault protection(d) Back up directional OIC + El F protect ion on HV side

(e) Back up directional OIC + El F protection on LVside

(f) Pro tect ion and mon it ors buil t in t o T ransfo rmer (Buchho lz re lay, Winding and Oi l

Temperature Indicators, Oil Level Indicator and Pressure Relief Device)(g) Protection for Tertiary Winding

(h) Overload Alarm

2.0 REQUIREMENTS

2.1 Differential Protection

(1 ) Triple pole with individual phase indication(i i) Have unrestrained instantaneous high set over-current uni ts which should not opera te

during inrush.

(i i i) Have an adjustable or mul ti bias set ting(iv) H,'Wesecond harmonic or other inrush proof fea tures and also should be stable under

normal overfluxing conditions, Magnetising inrush proof feature shall not be achieved

through any intentional t ime delay e .g. use of t imers to block relay opera tion or usingdisc operated relays.

(v) Have one b ia s winding pe r phase and pe r c.T. input(vi ) Have an adjustable opera ting current(vii ) Have an ope ra ti ng time not g reat er t han 30 milli seconds at 5 times of setting

(viii) The scheme shall have facilityfor ratio and phase angle correction either throllQh auxiliary

transf 01:ncr or through in-built provisior.. .

2.2 Over fluxing Protection

(i) Overfluxing protection shall be phase to phase connected.

26

[i i)

(iii)

(iv)

Opera te on the princ iple of measurement of vol tage to frequency rat io ..

Have inverse time characteristics compatible with transformer overfluxmg. 0

Provide an independent a larm with a definite t ime delay at value of v/f between 100 Y o

to 130% of rated value.(v) Have a h igh resett ing rat io o f 98% or better.

2.3 REFProtection

2.4

2. 5

(vi)

2. 6

(i)

(i i)

(i i i)

Shall be single pole . .Have an opera ting current sensi tivi ty of a t least 10% of.nominal current

Be tuned to the system frequency .Have a suitable non-linear resistor to limit the peak voltage during in-zone faults In case

of high impedance type(v) Shal l be h igh or low impedance principle type.

(1)

(ii)

(i i i)

(iv)

(i)

(i i)

(i i i)

(iv)

(v)

Back-up overcurrent protection relay (on HV side and MV side)

Be 3 pole typeHave lDMT characteristic (directional on MVside)

Have a variable set ting range of 50-200% of rated current

Have a characteristic angle. 30(l45( degrees lead . . .. 11

Shall include high unit having low transient over-reach and vanable settmg range typica y

500-2000% of rated currentInclude hand reset indicators per phase(vi)

0 )

(i i)

(i i i)

(iv)

(v )

Back up earth-fault protection relay

Shall be single pole typeHave IDMT characteristic (directional on MVside)Have a variable setting range of typically 20-80% of rated current

Shall have a character istic angle of 45/60 degree lag .Shall inc lude high set instantaneous uni t having low transient over-reach and vanable

setting range of typically 200-800% of rated current

Shall include hand reset indicators

(iv)

Overload Alarm relay

Shall be of single pole type

Shall be o f definite time overcurrent type f rated current andShal l have a con ti nuous ly va riab le cu rr ent r ange o f 50-200% 0

continuously variable timer setting range of 1-10 sec.Shall have a drop off to pick up ratio of 95% or better.

2.7 Tertiary Winding Protection

There are varia tions in the pract ices adopted for bringing out the .te rt ia ry ter~inall~" ~~I : ~ : s . ;Th

.. h t f. ~ .':-·-_.!··"I..,t·"rro t(' ct·on<:cl;:'l;l.~l.""." ... ; .ere ore, dcpenc inq upon t e y p > 2 a' '- r . n- . _• . v . . ' - C " , L,_I.....'I' .--.... _.. .-

in consultat ion with the manufacturer of t lIe transformer.

3.0 Special Comments

3.1 Dup li ca tion o f tr ansfo rmer p ro te ct ion i sno t cons ide red necessa ry bu t t he prote cti on

27



and monitors shall be divided in two groups viz. Gr A and Gr B at 400 kV. At 220 kV

level this is recommended depending on the importance of the substation and where it

is decided to go for two groups of protection with two station batteries.

Given be low i s one poss ib le way of g roup ing t he se p rot ect ions ;

Group A

Transformer biased

differential relay

Back up Pro tec ti on (HV)

Overf luxing Protect ion (HV)

Oil temperature high t ripping

Group B

R.E.F. Protection

Buchholz Protection

Back up Protection (MV)

Overf luxing Protect ion (MV)

Overload protect ion (Alarm only) winding

temperature high t ripping

OLTC Buchholz tripping

Oil level high/ low tripping

Pressure relief tripping

Delta winding protection

Group A and B prot ect ions shall be connected t o s epar at e DC sour ce /s epar ate ly f used suppli es.DC sources shall be supervised.

Both Gr A and Gr B prot ect ions shal l g ive out tr ipping impuls es to HV , MVand LV (i f applicable),circuit breakers.

3.2 The transformer overfluxing protection has been recommended on both sides for

interconnecting transformers. This is to cover all possible operating conditions, e.g.

the transformer may remain energised from either side. For other transformers

overf luxing relay shall be provided on the un tapped Windi ng o f the Transfo rme r.

3.3 In case of breaker and hal f swi tching schemes, the dif ferent ia l protect ion C.Ts. associa ted

with Main and Tie breakers should be connected to separate bias windings and these

shou ld not be para lle led i no r der to avoid fal se operation due to dissimi lar C.T, transientresponse.

3.4 Whenever s epara te pha se-wi se C.Ts ar e avai lable on neut ra l si de o f tr ans forme r, tr ip le

pole high impedance relay may be provided instead of single pole R.E.F. relay.


4.1 The current setting of the back up Ole r elay shall be s et above t he expect ed maximum

load current so as to allow possible overload on account of loss of one of the paralleltransformers.

4.2 Overload relay shall be set at 110% of rated current with delay of 5 seconds. This shall

be connec ted t o g .i ve on ly al arm and not fo r tr ipping.

28

Section 5

REACTOR PROTECTION

1.0 GENERAL

Shunt Reactors are used in EHV systems to limit the overvoltages due to capacitive VAR

Gene rat ion i n Long Transmis sion Lines,

The shunt re act ors a re norma ll y connect ed

(a) Through isolators to a line

(b) Through circuit breakers to a bus b ar

( c) Through c ircuit b re aker s to t he t er ti ar y of a I nte rconnec ting tr ansfo rme r.

Fau lts occu r in shunt re ac to rs due to in su la ti on b reakdown, agei ng o f in su la ti on, over~e .a ti ~g

due t o ove rexci ta ti on , o il contaminat ion and l eakage . To gi ve an earl y wa rn ing and , t o rruntrruze

the damage in case of a fault it is necessary to equip it with monitors and protective relays,

Recommendations for provision of protect ion and monitor ing equipment for Reactors are as fol lows:

(a) Reactor dif ferent ia l Protect ion

(b) Reactor REF Protect ion

(c) Reactor backup protection (Impedance type or definite time o/c & E/F)

(d) Protections and monitors built into reactor (buchholz, winding temperature, oil

t emperature , pressure rel ief, oil l evel , Fire protect ion)

2.0

2.1.

(i)

(i i)

( i i i )

(iv)

(v)

REQUIREMENTS

Differential Protection

Shal l be tr ip le pole type

Have an ope rat ing curr ent s ensi ti vi ty of a tl eas t 10% of nominal current.

Be tuned to system frequency

Have operating time not greater than 30 ms at 5 times of ~etti.ng .

Have suitable non-linear resistors to limit peak voltage dunng in-zone faults m case of

h igh impedance type

Shall be high or low impedance type.(vi)

2.2 Restricted earthfault protection

(i) Shall be single pole .

(i i) Have an ope rat ing curr ent s ensi ti ve ly o f a tl eas t 10% of nominal cur rent

( i i i ) Be tuned to syst em f requency( iv ) Have sui table non- li near re sis to rs to l im it peak voltage dur ing in-zone fault s

(v) Shall be high or low impedance type

2.3 Backup protection Relay

Either

(I ) Shall be triple pole type .,

(i i) Shal l be si ng le s tep pola ris ed 'mho ' or impedance d ist ance re lay SUIt abl e fo r measunng

phase to ground and phase to phase faults.

29



O i i )

(iv)

(v)

Or

(i )

(ii)

Shall grounds a character istic angle between 60-80 degrees

Shall have an adjustable definite t ime delay relay with set ting range of 0.2. to 2.0 Sec .Shall have a sui table range for covering 60% of reactor impedance

Shall be a single stage definite. time 3 pole, overcurrent relay with adjustable current andtime.

Sha ll be connect ed for 2 O/C and 1 E /F connec ti on and shal l be non-d ir ec ti ona l wit hhigh reset rat io and low transient overreach.

3.0 SPECIAL COMM.ENTS

3. T No duplica tion of reactor protect ions needs to bedone but the protect ions and monitorsshal l be divided in two group v iz. Gr. A and Group B.

Given below is one possible way of grouping these protect ions

Group A Group B

Reactor differential relay

Reactor back up relay

Buchholz trip

Reactor R. E/F relay

Oil temperature trip Winding temperature trip

Pressure relief trip Oil level high/low trip Fire protection trip

Gr. Aand Gr. B. protect ion shall be connected to separate DC Source/separa te ly fused suppl iesand DC sources shall be supervised.

Both Gr. A and Gr. B protect ions shall giveout t rip impulses to main breaker and also block autorec losing where they are direc tly connected to the l ine they should also t rip remote end CB.

3 .2 I tmay be no ted tha t the connec ti on o f Restr ict ed Eart h Fau lt prote ct ion on the neu tra l

side shall be from residually connected bushing CTs (in case of bus reactor) or from the

ground side CT in the neutral grounding reactor (for l ine shunt reactor). The lat te r isto

ensure tha t the protect ion covers the neutral ear thing reactor as wel l in the protectedzone.

3.3 The impedance o r overcur ren t backup pro tec ti on may not be ab le t o det ect in te r-t urn

fault in the reactor , for which the buchholz may be the only answer, unless the number

of turns involved isvery high. Manufacturers of reactor and relays may be consulted inthis regard.


The magnitude and nature of the SWitching-incurrents should be considered when determiningsettings of reactor protections.

4.1 Typical settings for ole relays are:

Current Setting - 1.3 x Rated current Time setting - 1 sec.

4-.2 Typical sett ing for impedance type of relays are _

Reach - 60% of Reactor Impedance Time setting - 1 s ec.

30

Section 6

BUS BAR PROTECTION

1.0 GENERAL

Bus bar protect ion isrequired to be provided for high speed sensi tive c learance ofbus bar faults

by tripping all the c ircuit breakers connected to faulty bus.

Recommendat ions for providing bus bar protect ion at different vol tage levels are as fol lows+

(i) Bus bar p rot ec ti on must be prov ided in a ll new 400 kV and 220 kVsubsta ti ons a swel l

as generating station switchyards.

( ii ) For exist ing substat ions, provision of bus bar protect ion isconsidered a must a t400 KV

leve l and a t 220 KVleve l i t is e ssen tia l at substa ti ons having multi ple f eed. In case o f

radia lly fed 220 KVsubstat ions, having more than one bus it i sdesirable to have bus bar

p ro te ct ion bu t is not a must .

2.0 REQUIREMENTS

Bus bar protection shall have following features.

(i) I t sha ll be o f 3 phase t ype and operat e sel ec ti ve ly for e ach bus bar sect ion.

(ii) It shall operate on differential principle and provide independent zones of protection for

each bus.

(iii)Itshall provide zone indication.( iv) I tshal l be stable for through fault condi tions upto maximum 40 kA fault level .

(v) For applica tions where bus different ia l protect ion sensi tivi ty has to be set below load

curr ent , as may be a ca se wit h use of concret e s tructu res , it is r ecommended that a

separat e check zone i s p rov ided o the rwise p rovi si on o f separat e check zone is not

essential . Check zone, i fprovided, shall be of high impedance tYPE! '( v i ) It shall incorpora te continuous supervision for C,T. secondaries against any possible

open ci rcuit s. I n case of dete cti on of any open ci rcu it ing o f C.'T, secondaries, a fter a

t ime delay, the affec ted zone of protect ion shall be rendered inopera tive and an alarm

will be initiated.

(vii) Itshall include D.C. supply supervision

(vi ii ) Inc lude adequate number of high speed tripping relays.

(ix) Whenever C.T.. switching isinvolved the scheme shall include necessary C.T. switching

.relays and have provision for C.T. switching incomplete alarm.

(x) I tshal l inc lude IN/OUT switching fac il ity for each zone.

I,


3 .1 The D.C. supply for bus bar prot ect ion shal l be from an independen t f eede r.

3 .2 Fau lt s l ying be tween C.B and C.T. shal l be cl ea red from one s ide by opening o fC .B on

busbar protection operation. However clearing of fault from other side shall be through

breaker failure protection/back up protccti on.

3 .3 3 Phase t rip r elays sha ll be p rovided for ea ch ci rcuit b reaker whi ch sha ll al so i nit ia te

B.F.P. of concerned breaker.

31



3.4 length of secondary leads should be kept as minimum as possible. Where lead runs are

excessive, an increase in wire size or use of parallel conductors are means to reduce

lead resistance.

3.5 In ca se of exis ti ng subst ations where curr ent t ransf ormer s a re of d iff er ent r at io s, b ia sed

type di ff erenti al p ro te ction i s re commended for use .


4.1 C.T wire supervision relays should be set with a sensitivity such that they can detect C.T,s econdar y open c ircuit even ih case of least loaded feeder.

4. 2 . Bus ba r d iff er ent ia l p ro te cti on shou ld have ove ra ll sensi ti vit y above heavi est l oaded f eede r

current unless a separate check zone has been provided. In cases where fault currents

are expected to be low as brought out in 2 (v) a bove, the protection should be sensitive

enough to take care of such expected low fault current.

4.3 In case of voltage operated high impedance type protection, the voltage setting should

be above expected voltage developed across the relay during maximum through fault

current condition. In case of current operated relays for stability under through fault

condition, external resistance is to be set such that voltage developed across relay and

res is tance combination isbelow the vol tage requi red for forcing requi red relay operating

current.

32

Section 7

LOCAL BREAKER BACK-UP PROTECTION

(BREAKER FAILURE PROTECTION)

1.0 GENERAL

In the event of any circuit breaker failing to trip on receipt of trip command from protection

relays, all circuit breakers connected to the bus section to which the faulty circuit breaker is

connected are required to be tripped with minimum possible delay through LBB protection.

This protection also provides coverage for faults between e.B and C.T. which are not cleared

by other protections.

Recommenda tions f or p rov id ing LBB pro te cti on at di ff erent vol tage level s a re as f ol lows :

(i) In all new 400 kV and 220 kV substations as well as generating stations switchyards, it

must be p rovi ded fo r each ci rcuit b reake r.

( ii) For existing swrtchyards, it is considered a must at 400 kV level and also at 220 kV

swi tchyar ds hav ing mult ip le f eed. I n case o f radia ll y f ed 220 kV substa tions, p rovis ion

o f LBB pro te ction i sde si rable but not e ssenti al .

2.0 REQUIREMENTS

LBB protect ion shall have fol lowing features:

(i) Have short operation and drop off times.

( ii) Have th ree phas e cur rent e lements wit h fa cil it y fo r pha se wis e i nit ia ti on.

(iii) Have current setting range such that these can be set at minimum 200 mA for line and

50 rnA fo r genera tor s ( fo r lA C.T, Seconda ry ).

(i v) Have one common as soc iat ed time r wi th adju st abl e s ett ing.


(i) The relay is separate for each breaker and is to be connected in the secondary circuit of

the CTs associated with that particular breaker. This CT secondary may be a separate

core, if available . Otherwise i t shall be clubbed with Main- lor Main- Il protect ion-core .

( ii ) For l ine breakers, direct t ripping of remote end breaker (s) should be arranged on operation

o f LBB prote cti on . For tr ans forme r b reaker s, di re ct t ri ppi ng o f br eaker( s) on the o ther

. side of the transformer should be arranged on operation of LBB protection.

(i i i) For lines employing single phase auto-reclosing, the LBB relays should be started on a

single phase basis from the trip relays. This is to avoid load currents in the healthy

pha se s, a ft er si ngl e pha se t ri pp ing, le ad ing to unwan ted ope ra ti on o f t he b reaker fa ilu rep ro te ct ion, si nce t he curr en t se tti ng i s no rma ll y [owe r than t he l oad cur rent.

(iv) It is considered a good practice to have DC circuits of Gr.A and Gr.B protections and

LBB rel ay i ndependen t. A sepa rat ely fu sed supply should be t aken for LBB rel ay i n t hi s

case.

( v) LBB canno t oper at e w ithou t p roper i nit ia ti on . It i s good pract ice to provide redundant

trip output and breaker fail input where other forms of redundancy does not exist. One

way of doing this is by providing separate aux. relay in parallel with trip unit and using

contact s of these for LBB ini tiat ion.

33



(vi)Separ at ion : ho~ ld be ma in tai ned between p rot ec ti ve re lay and CB t ri p co il DC c ircui t s o

that short ~Ircult or blown fuse in the CB circuit will not prevent the protective relafrom enerqising the LBB scheme. . Y

In addi~ion t~ other. fault sensing relays the LBB relay should be initiated by Busbar

pro~ech.on, since failure of CB to clear a bus fault would result in the loss of entirestation If LBB relay is not ini ti ated.

Whenever used in combination with busbar protection scheme, tripping logic of thesame shall be used for LBB protection also.

For .brea~er-fail relaying for low energy faults like buchholz operation, special

conslderatJ~n~ may have to be given to ensure proper scheme operation by using C.B.contact loqic 10 addit ion to current detectors .

(vii)

(viii)

(ix)

4. 0 SETTING CRITERIA

0 ) Cur.rent level de~ecto rs shou ld be ~et a s sens it ive a s t he mai n p rot ec ti ons. A general

se:tt~g of 0.2 A IS commonly practiced for lines and transformers. However, in case of

existinq schemes associated with lines having single phase autoreclosure and where

pha se wis .e in iti at ion i s not avail ab le , it is re commended that 2ph + 1E/F element may

be used WIt hpha se e lement s et above maximum expected load current whi le ElF elementmay be set sensi tively.

(i i) C I I(l

' t " l ) .urrent e~e detector for gener~tor.s may be set at 50 rnA (for lA C.T. secondaries). •

~lmer s et tmg shou ld be s et cons ider inq b reaker i nt err up ti ng t ime, curr en t det ect or r es et

time and a margin. Generally a timer setting of 200 ms has been found to be adequate.

34

I. .. .. J

Section 8

DISTURBANCE RECORDING AND FAULT

LOCATION EQUIPMENT

1.0

1.1

GENERAL

Disturbance Recorder

Provi de s bett er unders tandi ng o f the behavi ou r o f Powe r network a fte r a d is tu rbance

Gives use fu l in fo rmat ion to improve exis ti ng equ ipment and in planning/designing new

installations

Disturbance recorder shall be microprocessor based and shall be used to record the graphic

form of instantaneous values of voltage and current in all three phases, open delta voltage and

neutral current, open or closed positions of relay contacts and breaker during the system

disturbances.

Dis tu rbance reco rder s ar e r ecommended fo r a ll the 400 kV li ne s. At 220 kv level also they are

recommended for all interconnecting lines. In other cases utilities may decide depending on

their need.

It is also recommended that all the disturbance recorders in the station are synchronised with

GPS

1.2 Fault Locator

Distance to fault locator is recommended to be provided as a standard for all 400 kV and 220

kV lines on both ends. However for short lines of length upto 20 kms, fault locator can be

provided at one end only.

1.3 Event Logger

The Event l ogger i s u sed to reco rd the s tat e o f swit chya rd equ ipment and r el ays and occurr ence s

of al arms. The equ ipment a ls o r eco rds events r eco rded byd ist urbance r ecorder, a s al so changes

in digital inputs, i.e operation and resetting of relay contact and switching of primary plant

within the substation.

In case all required events can be accommodated in disturbance recorder no separate event

logging equipment is recommended.

2.0 REQUIREMENTS

2.1 Disturbance Recorder

Recording capacity

- Record minimum eight analogue inputs (8) and minimum 16 binary signals per bay orcircuit. .

Memory capacity

. - Minimum 5 sec of total recording time

Recording times

Minimum prefault recording time of 100 ms

35



- Minimum Post fault recording time of 1000 ms

Trigger

Any of d ig it al s igna ls can be programmed to act a s t rigger

Analogue channels should have programmable threshold levels for triggers. Selection

of over or under levels should be possible.

Time Tagging- Has built in real t ime clock and calendar to time tag recorded dis turbances. Drift of the

in bui lt clock shall not b e more th en 0.5 sec per day .

Sampling Rate

- 1KHz

Recording band width

- 5-250 Hz

Voltage Channel

- Dynamic range 0.0 1-2 x Nomin al Voltag e

- Resolution 0.1 %

Current Channel

- Dynamic range wi th fullDC offset

- .01-60 x Nominal Current

Printer

P rinter sha ll be sui table fo r tak ing print on p lane paper

2.2 Fault Locator

Be on line t ype

Have built in display unit

The display shall be directly in percent of linelength or kilometers without requiring any

further calculation

Be suitable for applicable breaker operating time

Have an accuracy of 3%or bet te r

Sha ll t ake care of

(a ) p re sence of r emote end infeed

(b) predominant DC. component in f au lt cur rent

(c) high' fault arc res is tance

(d) Severe CVT transient

Shall have mutual zero sequence compensation if faul t locator i s to be used on doublecircuit line.


3.1 Start function to disturbance recorder is to be provided by change in state of one or

mo re of t he event s connec ted and/ or by any ext ern al trig geri ng so that recordin g of

event s duri ng a faul t or system distu rba nce can b e obt ained . List of typ ical sign als

recommended to be recorded isgiven below:

36

(i) Recommended Analogue Signals

Fr om CT

From Line VT

V ' \ NVBNV

CN

From Aux. VT

Vo

( ii) Recommended Digital Signals(Typical)

Main 1 Carrier receive

Main 1 Trip

Li ne O /V Stag e l/Stag e II

Reactor Fault Trip

Stub Protection Optd.

Main IITrip

Main IICarrier Receive

Direct T rip CH A/BCB I S tatus A PH

CB I S tatus B PH

CB I S tatus C PH

CB II S tatus A PH

CB II S tatus B PH

CBI I S tat us C PH

Bus bar trip

Main/Tie CB LBB Optd.

Note : Th ese may need modificat ion depending upon Protect ion s chosen and t he ~ontact

availability for certain functions.

If dis turbance recorder function or fault locator functions are available as integral par t of

any of main protection, then separate stand alone units for this functions are.not required.

However both DR and Fault locator function, ' preferably should not be in the same unit.

In case of DR being par t o f main pro tect ion, i t s hould be pos sible to connect exter na l

binary inputs.

S tand alone DRwhich can cater to more than one bay/circuit can also be used. However

this should have minimum 8 analogue and 16 binary inputs per bay/circuit .

3.2

3.3

3.4

37



Section 9

GUIDELINES FOR PROTECTION SYSTEM ENGINEERING

1.0 GENERAL

Some broad gUideli nes fo r Eng ineeri ng of Pro tec tion Sys tem in add it ion to enginee ri ng

recommendations made invarious sections, are given below and could be refined iffeltnecessary

by the Utility according to its specific needs and practices.

2.1 Gr. A and Gr. B Protection

Wherever two se ts o f DC sources are avai lab le, t o ob tai n redundancy and to be ab le t o take

protect ion out for maintenance , whi le equipment is in service , the relays are e lect rica lly and

physica lly segregated into two groups. Grouping isdone to the extent possible in such a way

that each group can independently carry out protective functions with near equal redundancy.

Interconnection between these two groups shall not general ly be attempted. Ho~ever i ffound

absolutely necessary such interconnection shall be kept to the bare minimum.

Even incases when only one set ofbattery source isavailable segerat ion of protect ions and trip

c ircuits in two groups may be considered by giving DC suppl ies through separate fuses.

2.2 Trip Unit

In case o f segregati on be ing made as indic ated above, scheme associ ated wi th each ci rcu it

b re ake r i sp rov ided with two sets of t ri p un it s, one in GrA and one in Gr.B. Each set consis ts

o fone un it fo r 1 /3 phase t ri pp ing and ano ther for 3 phase tr ipping only. 1/ 3 phase t ri pp inguni t and 3 phase t ripping uni ts are ini tiated byfunctions asdescribed below. However , incase

the protect ion relay i tsel f i s having sufficient number of t rip duty contacts, then separate t ripunits will not be necessary. .

2.2. 1 1 p h & 3 ph trip (Protec tions which start auto rec loser)

Main 1 Line Protection

Main IILine Protection

These uni ts shall be applicable for l ine c ircuits only and shall be with sel f reset type contacts

2·.2.2 3 ph trip (Protec tions which block auto rec losure)

Direct trip receive

Line reactor protection

Bus bar protection

Transformer protection

Overvoltage protection

Back up protections

These uni ts shall be hand reset type

2 .2.3 Direct tr ip of r emot e end bre aker

In l ine wit h t he p re sent 400 KV pract ice i t is r ecommended tha t di re ct tr ip s ignal is sen t t o

remote end under following conditions.

38

(i ) When LBB relay operates

( i j ) Reactor protection and O/V protection

2.3 DC Distribution

Since the availabil ity of even the best engineered protect ion depends upon the integri ty ofthe

DC auxi li ary supp ly, conside rab le care has to be given to the des ign o f a sys tem which will

retain the rel iabi li ty of the protect ion system as a whole , under a ll condi tions. Secondly from

an operational point of view, itis essential that itis possible to work on any part of the protectionsystem with fullsecurity, while not disturbing the rest of the protective system.

Arising out of these considerations, following guidelines for designing a suitable DC distribution

system have been set for th.

2.3.1 For 400 kVsta tionsthere shall be two separate bat te ry systems available for protect ion,

cont ro l and tr ipping /cl os ing ope rat ions . For 220 kV stati ons where only one set of

battery source is available segregation of protection and trip circuits in two groups may

be considered by giving DC supplies through separate fuses.

2.3.2 Distr ibut ion of DC supply shall be done bay wise to feed the fol lowing,

(a) Protection

(b) CB functions

(c) Isolator/earth switch functions

(d) Annunciation/Indications(e) Monitoring functtons(Disturbance Recorder, Fault Locator, Event Logger etc.) when these

are not integral part of protection

2.3.3 (a) Protect ion Funct ionFor each group of protect ion(ie Group A and Group B relays) separate DC sources

are recommended.

(b) CB FunctionsTrip coi l 1&2 shall be fed from separate sources. Closing coi lcan be from either of

these two sources.

(c) Isolator/Earth switchThese associa ted with anyone circuit sha ll be fed from one of the two DCsources.

In the case of a 1 & 1/2 CB arrangement, the Isolator/Earth switch associated with

the tie CB can be fed from either Source 1 or 2.

(d) Annunciation & IndicationFor each bay , these funct ions can be fed from eit her one o f t he 2 sou rces . Each

function shall be fed however through separate feeds.

(e) Monitoring FunctionsThese shall be grouped in 3 groups

(i) Disturbance Recorders

( i i ) Fault Locators

( ii i) Event Loggers

All the three groups shall be fed through separate teeds from either ofthe two

sources. This is to enable the fullavailability of these equipment irrespective

of that of the protections.

39



2 .3 .4 General Not es :

1. As to how the separate D.C. feeds are to be taken from the sources, there are twoalternatives.

{a} Through separate f eeds f rom the boa rd to each c ir cu it panel

(b) Through a limi ted no of feeds t o a sepa rat e pane l o f t he relay o r cont ro l board

(Exclusively meant for marshalling the DC circuits for the various relay panels).

The choice between (a) or (b)is lef t to the uti li ties as per the ir individual pract ices.

2 . Sub -fus ing o f t he DC c ir cu its shal l bedone wit h ca re s ince b lowing of t he fuse will haveto be monitored. Also such sub-fusing shall bekept to the minimum and can be augmentedwith isolating links as required.

3. Selection of sources in the event of one supply to a function failing is to be done withcare, because i f the fault l iesdownstream one may lose both suppl ies.

4 . As a rule every DC supply gOing through fuse should be supervised with a no-volt relay.

For t rip ci rcuit s where separa te tr ip c ir cui t supe rv is ion re lays are p rovided i t is no tnecessary to provide separate DC supervision relays.

5 . MeBs of adequat e break -up capaci ty c an al so be used ins te ad o f fuses .

2.4 Cabling

I t i s recommended that:

(i) Separate cable s are used for AC & DC circuit

( ii) Separate cable s are used for DC 1 & DC 2 circuits

( ii i) For d if fer ent co res o f CT & CVT separate cables shall be used.

40

Section 10

LOCATION OF CTS AND VTS IN SUB-STATIONS

1.0 GENERAL

Instrument t ransformers (CTs and VTs)are used to obtain measured quant it ies of current and

vol tage in approp ri at e fo rm for use in cont ro l, p ro te ct ion and measur ing equipment such asEnergy meters, indicat ing instruments, protect ive relays, fault locators, fault recorders,

synchronizers. These are insta lled indifferent bays such as l ine, t ransformer, bus coupler bays

and al so at the busbar .

2.0 LOCATIONOF CTS AND VTS INDIFFERENT SUB-STATION

ARRANGEMENTS

2.1 Given below are some examples ofdi fferent bus configura tions showing sui table locat ion

o f CTs and VTs .

IC : ; - , : ' J ~ Ic : ; - . ' , ' , w

F PBus Sectionoliz.er T

.!-----f---_._--o" o--X rn 0 ,, 0- -- 1- - - - - -

r L: = = = = ' l : ' = = : I

Bus Coupler

hImfT'lm_ .~-PhOS9

Fig. 1 : Double busbar arrangement

41



I

r - }-PhaseWWW

pI

r -}-Pha se

www

p1

II 1

y yt<,

Fig. 2 : Double Main with Transfer bus arrangement

",3~3~ 3 1 ~'I~~

I I I ~~~O~1 1 WWlL

t ,P- - - - - - - - + I --J----------- - - r - - - - - - - - - -

bl~~~

Fig. 3 : Double breaker ';rrangement

42

, , ~ I Iyl ~3-Phos.

E/o-X rn O/T/~x----fPt--o/T/~*""/~ ,

drnmmll-Pho,.

Fig. 4 : One and a half breaker arrangement

Fig. 5 : One and a half breaker arrangement (alternative arrangement with 5 CTs)

43

",.:



z0

= i=0

V ') V ') ~: : : : : l : : : : : l I-m III 0

a : : :~ z c..<~ a : : :~~ -<> > m

V'); ,c : ; ,c :

=>00 m00 0'<t '<t . . . . .

r:-l

: ? - X T/ 11 -= -

/ ( )- -- jH t- j I I

'&.

/ to')

-l

: ? - x t/

/ 11 -

: ? - x T/ 11 ~

/ ( ) - - -j 1 -1I - - 111

"G o

/ I"l

l

..

r - - - - - - - - - - - - - - 4 ~ ~ - - - - - - - - - - - - ~. .It

'&.

"G o

/

l'

IIIw

O-----o/o-fl.

44

",'

III1--J

.,.

_ . . . .

cQ)

EQ)

enc0._._0

._0..0en

::J..0

._Q)

..:::,t;

0Q)._..0

-0J::

"'-

0

-0C

0

Q)

c0

._0-Q)

EQ)

J::(.)

U)

enc.>.

..2Q)

"':0:;:

Q)

>:;::;(.)

Q)_ . . . .0._a..

0

(.).0 .

>-I-

r-

enL . L :



2.2 Current Transformers

Some exp lanato ry no tes and commen ts wi th refe rence to above are given below regarding

location of CTs.

2.2.1 Double Bus Arrangement (Ref. Fig..4)

The CTs shall be pl aced near the cir cu it br eakers (CBs) and on the l ine s ide . The dete cti on

zones ofl ine relays and busbar relays start a t the CTs. It is advantageous ifthese two points are

dose to each other. In the improbable case of a fault between the CT and CB the busbarprotection willdetect and clear the fault.

2 .2 .2 Double Main and Transfer Bus Arrangement (Ref:Fig.5)

It isadvantageous to locate the CTs on the lineside ofthe disconnectors for Line and Transformer !

bays. Inthis way the protect ive relay connected to the CT wil l remain connected to the l ine or

Transformer when i t i s swi tched over to the t ransfer busbar.

A separate CT i s r equ ir ed to be p rovided in t he T ransfe r bus coupl er bay to obta in select ive

t ripping for faults on Transfer bus.

2.2.3 Bus Coupler and Bus Sectional izer Bays (Ref. Fig.4 and Fig.S)

A set of CT isnecessary to enable different busbar protection zones to be formed. The protection

can be arranged to give complete fault dearing with a short t ime-delay (LB.B. t ime) for faults

between CBand CT. Sometimes CTs on the two sides of CB are employed bysome uti li ties but

are usual ly not considered necessary. Therefore , only one set of CTs isrecommended.

2.2.4 Double Breaker Sta tion (Ref: Fig.1)

It i su sual t o l oca te the CTs on the line s ide a ft er the CBs. The two CTsshal l be ident ical . To

get the l ine current the secondary currents ofthe two CTs are summated.

2 .2 .5 One and a Half Breaker S tat ion (Re f. Fig. 2 and Fig.3)

L ike the doub le b re aker s tat ion , the CTs are l oca ted close t o the CBs. At t he cen tr al CB (Tie

CB) two CT sets are shown. This arrangement uti lizes 4 CTs however it i sa lso possible to use

a single set of C.T, with the t ie CBthus reducing number of CTs to 3 per diameter. The centreCT in this case will have to be a non-standard one and therefore 3 CT arrangement is not

recommended at present but can be reviewed at a later date.

Fig. 3 shows alternative way of locating the CT s. This arrangement requires 5 CTs. The

advantages with this arrangement are:

Pa ral lel ing o f two CTs to the main l ine p ro tec tion i s no t r equir ed . This gives be tte r

transient response.

Separate stub protection can be connected

Presen tl y there are many ins tall ati ons wit h 4 CT a rrangemen t and per fo rmance has been

satisfactory. Therefore, it i srecommended that 4 CT arrangement iscont inued to be adopted.

2.3 Voltage Transformers

2.3.1 Line CVTs

CVTs are used for meter ing, protect ion and synchroniza tion. Located at the l ine entry they

46

also enable indicat ion ofvoltage on a l ine energized from the opposite end. CVTs can also be

used as coupl ing capacitors for power l ine carrier (PLC). They are then to belocated at the l ine

side of the l ine t raps and l ine earthing switches, as shown in Fig..5 .

For 400 kV leve l i t i s re commended that each l ine bay is provided wi th CVTs al l t he t hree

phases . Even for 220 kV subs ta tions it is preferable t o prov ide th ree phase CVTs in each

phase for each l ine bay. However , depending on uti li ty pract ice CVTs in one phase may also

be provided in which case protect ions wil lhave to be connected to Bus VTs.

2. 3.2 Bus CVTs

Three phase VTs/CVTs on the busbars provide input for directional relays and reference voltage

for synchroniza tion. These VTs wil lhave to be selec ted by using vol tage selec tion scheme.

2.4 CTjVT Earthing

CT/VT secondary neutrals should be earthed at one point only. VT secondary neutral earthing

isdone at equipment i tsel f. However , i t i s preferable to earth the CT secondary neutral in the

controlz'protection cubicle in order to provide maximum security to the operating personnel.

2.5 CTPolarity

As a pract ice the P1 terminal of the CT shal l be towa rds the bus and P2 away f rom the bus .

3.0 EXAMPLESOF CT,VT LOCATION

Examples of a double main and Transfer bus configura tion showing l ine, Transformer, MainBus coupler and Transfer bus coupler bays and another of one and half bus configura tion for a

line with react or and T ransfo rmer d iamet er a re shown in fi gs . 6 & 7 to i llustrate locat ion of

CTs and CVTs and utilisation of various cores based on the above recommendations.

47





ensu re cor rect connecti on and impl emen tat ion o f logic between rel ay panel s and car rier

equipment.

1.5.8 Phasing Tests

It is necessary to prove correct phasing before a new piece of equipment can be put in parallel

with existing equipment.

When a circuit i sbe ing paral le led for the first t ime, the VT associa ted with tha t c ircuit must be '

energised from a known source and outputs should be compared with outputs of already provenVTs to prove that the VT connect ions are correct .

1.5.9 On-load Tests

(i) Standing Current in Relays

Having go t t he new equipmen t on load it i se ssent ial to do on load te st s. It should be checked

that there is negligible spi ll current in any residually connected relays and in any protect ion

working on the differential principle. Appearance of current in differential circuit should also

be chekced eit her by reve rs ing or sho rting and di sconnecti ng one o f the C.T, connections.

Before measuring current inthe CT circuits ofdifferential relays care should be taken to remove

the appropria te t rip l ink.

[ii) Directional Relays

On load tes ts ar e al so requ ir ed to prove the polar ity of the VT connect ion with respect to CT

connecti on . This wil l ensure that the schemes /rel ays are look ing in p roper d ir ecti on . The

manufacturers instruc tions are to be fol lowed to conduct this test. The types ofre lays tha t needto be tested this way are directional relays and distance relays/schemes.

2.0 ROUTINEMAINTENANCETESTS

Protect ive gear may stand quiescent for months and yet be required to opera te with precision if

fault occurs on i ts associa ted primary equipment . Routine maintenance tests on protect ive

gear are done to ensure that the equipment remains available to perform ina fullydiscriminative

manner the duty required of it.

There are two major fac tors whi le considering the maintenance act ivit ies of any equipment .

Theyare:-

(i)

(ii)

2.1

the human element

the equipment itself with its other associated paraphernalia

The following major points are to be considered in the human element i.e. the

maintenance personnel,

1. I thas to be recognised that handl ing protect ive relays isa special ised job. Therefore , i ti snecessary to depute sui table technical personnel who wil lbe retained in this f ie ld for

long periods in order to gain maximum benefit from their experience.

2. The personnel involved should be tccbnical ly sound and be aware of rno.Li I, j_T.::.ct:C~s.

Further , e lect ronics and computers are invading protect ion relay fie ld and the present

day relay maintenance personnel need to be wel lversed in this discipl ine - a need that

d id no t ex is t a f ew year s ago.

50

3 . They should be ful ly famil ia r with the equipments and systems theYkabrecalled upon

t.t~

handle. For this purpose periodic t ra ining inthe manufacturers wor s ecome ess~n ra .

4. They shou ld be ab le to at tend to most of the common fail ur es o f equipmen ts Without

waiting for instructions from the manufacturers. .5. The personnel involved should be innovative to develop test proced~lrebslw~tlchmda~.not

be mentioned by the manufac turers. This may benecessitated byavaia . e SI e can I Ions

and considerations of operational experience.

Maintenance Tests/Checks

Secondary injec tion tests should be carried out to check the relay performance .and if

possi ble t he relay shou ld be al lowed to tr ip t he cir cu it b re aker s. The n~cesslt y fo r

proper recording of result and logging of problems cannot be over-emphasised.

Check for t ightness and cleanliness of a ll fasteners and connect ions should be done.

Check for alarm and ind icat ion c ir cui ts shou ld be done. Thi s can be combined with

secondary injection testing.

Check all the concerned logics and interlocks.

Insulation tests of relay wiring to earth and between circuits sh.ould be ~im~d.out wit~ a

500 Volttester. After maintenance when the equipment is put into service, ItISessentI~1

to check that the relays are extended with the proper voltages and currents. T his

applies also to any auxiliary voltage.

2.3 Frequency of routine Maintenance

When determining a programme, the frequency ofmaintenance ins.pections.an~ tests will~epend

on the faul t h is to ry and fau lt li abi li ty of t he equipmen t. There ISno poin t m over t~ s~mg an

equiprnent, the programme should be. planned so that fault i~ the e .quipment are ant1~lpated,

not precipitated. The frequency of test will, however, vary WIdelyWIththe type of e~U1pment.Certain items are continuously monitored, some are checked several times a day, whilst others

may be tested weekly, monthly, yearly or even every two years. Recommended frequency of

tests and types of equipment are :

2.2

2 . 2 . 1

2 . 2 . 2

2 . 2 . 3

2 . 2 . 4

2 . 2 . 5

(i) Daily

- Relay fl ags i nspected on every shi ft

- Counte r re adings on carr ie r channe ls

(i i) Yearly

Check of tripping criteria of protectionInjec tion of gas actua ted relays with a ir or oil

Secondary injection tests on all relaysInsulation resistance tests

51

•.•.. ·1



Section 12

TEST EQUIPMENT

1.0 GENERAL

In order to ensure healthiness and maximum availabil ity of protect ive relays i t i s necessary to

carry out periodic testing. Presently, manual as wellas microprocessor based automatic testing

kits are available. While the manual kits have been in use byutility engineers in past, automatictest kits are relat ively recent int roduct ion. Apart from automat ic testing capabil ity, these kit s

are a lso capable of replaying the fault recordings captured by disturbance recorders as wel l as

t ransient simulat ion done using Elect ro MagnetiC Transient Programme (EMTP). Also, it is I

possible to do comprehensive end to end testing oftineprotections including protection signalling

with use of these automat ic kits in conjunction with Time synchronising cqutpment. Utilities I

may decide on requirement of manual or automat ic kits depending on size ofthei r network and I

testing practices.

2.0 REQUIREMENTS

2.1 Manual Test Kits

(a) Portable over current relays testing equipment . The input rat ing shall be between 200-

250 V. 50 Hz , AC supply and the cur ren t output r ange shal l be 0 .05-200 amps. wit h

negligible harmonic distort ion of less than 1%. A time interval meter shall be fit ted toread and display 0-10 seconds with an accuracy of + 10 mil li seconds.

(b) Portable test equipment for testing distance relays comprising supply unit, control unit

and fault impedance uni t. Sui table for Acvol tage from 380-440 V,three phase , 3 wiresystem 20 Ampere (short t ime rated) with built in safety devices.

2 ..2 Automatic Test K its

It sha ll be sui tab le t o t es t al l t ypes o f d is tance , overcu rr en t, g round relays , synch roni sing,

t ransformer, reactor and busbar protect ion relays of major manufac turers in automat ic as wel las manual mode.

It shall inc lude all the accessories required for making the complete test set up.

It shall have three phase current output range 0-30 amps. (rrns]and three phase vol tage range0-110 voltage (PH-G).

It shal l work on s ing le pha se 240 V, 50 Hz +·10% supply

Shall include necessary software and hardware

(a) To accept fault recordings available from fault data recorder/numerica l relay/EMTP

simulat ion and replay these on the relay under test.(b) To draw the relay characteristics

The accuracy of relay test kit sha ll be as fol lows:

1% for voltage and current output and resolution oftime measurement of 1ms orbetter.

52

..-'.~.."'~:

REFERENCE STANDARDS

01 lEC E lectrical Relays-AII-or-nothing electrical relays

255-1-00

02 lEC 255-3 Electrical Relays - Single input energising quantity measuring

relays with dependent or independent t ime

03 lEC 255-5 Electrical Relays - Insulation tests for electrical relays

04 IEC 255-6 Electrical Relays - Measuring relays and protection equipments

05 IEC 255-7 Electrical Relays - Test and measurement procedures for

electro-mechanical all-or-nothing relays

e n IEC255-8 Electrical Relays - Thermal electrical relays

(JJ IEC255-10 Electrical Relays -Application of the lEe quality assessment

system forelectronic components to all-or-nothing relays

C B lEC255-11 Elect rica lRelays- Interrupt ions to and alterna ting component

(Ripple) in DC auxiliaryenergising quantity of measuring relays

c e IEC255-12 E le ct ri ca l Re lays -Dir ecti ona l re lays and powe r relays wi t h two

input energising quantities

10 IEC25513 Electrical Relays - Biased (% ) differential relays

11 IEC255-16 Electrical Relays- Impedance measuring relays

12 IEC Electrical Relays- Vibration, shock, bump and seismic tests on

255-21-1 measuring relays a nd p rotection equipment (Vibration tests)

13 IEC Electrical R elays - Vibration, Shock bump and seismic t ests on

255-21~2 measuring relaysand protection equipment (Shock&Bump .tests)

14 lEC Electrical Relays- Vibration, Shock, bump and seismic tests on

255-21-3 measuring relays a nd protection equipment (Seismic tests)

15 IEC Electrical Relays- Electrical disturbance tests for measuring

255-221 re lays and pro te cti on equipment (1MHzbur st d is tu rbance t es ts )

16 IEC E lectrical Relays -E lectrical disturbance tests for measuring

255-22-2 relaysand protect ion equipment (Elec trosta tic discharge tests)

17 IEC Electrical Relays- Electrical disturbance test for measuring

255-22-3 relays and protection equipment (Radiated electromagnetic

fielddisturbance tests)

18 IEC E lectrical Relays - Electrical disturbance tests for measuringI d ,. . t (F t t ,. -:~.,~,1:-•."·~.pnrn I..,rts)255-22-4 re ays an protec .:r.1l CC]lnpmen a<: .ra '. '_. .. c> '., .v_·'· .

19 IEC Electrical relays - contract performance

255-23

53

Date post:	09-Apr-2018
Category:	Documents
Upload:	kamalanathan-rajeshkumar
View:	229 times
Download:	0 times

Manual on Prot Gen & Gts

Documents