code 1
DESCRIPTION
electrical code standarTRANSCRIPT
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SPLN 7A^ =197E'SiTAI\Itr|AFIPERUSAHAAN UMUM LISTRIK NEGARA
Lampiran Surat Keputusan Direksi PLN
No: O32 lOn/n Tanggal 14 Agustus 1978
IEc PUEILICATIG'N 71-1
Sixth Edi t ion 1976
INSULATICIN GcICtFItrIII\IATItf,I\I
Part 1 : Terms, Definitions, Principles and Rules
KGIGIFItrITNASiI ISIOLASil
Bagian 1 : lstilah, Definisi, Prinsip dan Ketentuan
D E P A R T E M E N P E R T A M B A N G A N D A N E N E R G I
PERUSAHAAN UMUM LISTRIK NEGARA
J L . T R U N O J O Y O M I / 1 3 5 . K E B A Y O R A N B A R U - J A K A R T A
W;r;J*-
SfrqnnmAtrtPERUSAHAAN UMUM L ISTRIK NEGARA
SFILN 7A' z 1g-78
Lampiran Surat Keput$an Direkri PLN
OgZlDlRt1g78 Tansgal 14 Agustut 1978
tEC Publication 71-1Sixth edition 1976
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I NSU LATTON CO.ORD I NATION
Part 1 : Terrns, definitions, principles and rules
KOORDINASI ISOLASI
Bagian 1 : lst i lah, definisi , pr insip dan ketentuan
ACKNOWLEDGEMENT
l . T h e E n g l i s h v e r s i o n o f | E c P u b | i c a t i o n T l _ l i s a d o p t e d a s
a PLN standart j accordinq to a decree of the PLN Board of
D i re ( r t o r No .032 /D lR l78 , 14 t h ' Augus t 1978
2. Tlr is Enqlish version of IEC Publication 71-1 is reproduced
irr 250 copies for use as company standard. by permission of
l n r e r n a t i o n a l E | e c t r o t e c h r r i c a l C o m m i s s i o n a s s t a t e d i n a I e t t e r
of rhr: General SecretarY dated 12th, July 1979'
CoPYright :
IN -TERNATIONAL ELECTROTECHNICAL COMMISSION
Geneve, 1976
lssued bY :
DEPARTEMEN PERTAMBANGAN & ENERGI
PERUSAHAAN UMUM L ISTRIK NEGARA
Jakarta, 1980
CONTENTS
l r o r c w o r d . . . ' .Prclucc
CI{APTER I : GENERAL CONSIDERATIONSScction One -Scope and Object
Clausel . Scope2. Objcct
Section Two - Definitions
3 . Nomina lvo l tageo fa th ree -phasesys tem . . . . $ . .4. Il ighest voltage of a three-plrase system5. tl igltcst voltage lbr equipnrent
6. I jx ternul i r rsulat ion
7 . l n t e r n l l i r r s u l a t i o n . . . .8. lndoor e x ternal insulatit-rn9. Outdoor e rte rnal insulationI 0. Scl l ' - rcstor ing insula l ion
I l . NoIr-sc l l - rcstor ing iusula l iun12. l 'ype test
1 3 . R o u t i r r c t c s t .
14. IsolatctJ ncutra l systcnl
15. l lcsonant carthcd systcrrt (system earthed through an arc-suppression coil).l ( ) . i iar thcd ncutra l systcrrr17. l ,ar th f 'aul t lactor
18. Overvol tagc19. Ilhass-to-carth per unit overvoltage (p.u.)
2{1. Phase-to-phasc per unit overvoltage (p.u.)
21. Slitching overvoltage
22. Lightning overvoltage
23 .S ta t j s l i ca l sw i t c I r i ng ( l i gh tn ing )overvo l tage24 . Convcn tional nra.r, furr u nr switching (ligh tning) overvol tage25. "fernporury ovcrvoltage26. Statistical srvitching (l ightnin g) inrpulse withs and voltage27. ConvsnLiorrul su'itchin g(lightning) inrpulse withstand voltage28. Rated swi tching ( l ightning) i rnpulsc wi thstand vol tage29. Il.ated slrort t luration powcr-lieq'ucncy withstand voltage . . ; .30. l la ted insulat ion levcl31. Stat is t ic l l saf 'ety factor32. Convent ional safety t lc tor33. Protectiun lcvel of a protectivc device34. Protect ion tactors o la protcct ive dcvice . . . ,
Section Three - Basic Principles of Insulation Co-Ordihation
35. Insulation co-ordination .36. Voltage stresses and other factors affecting insulation37 . ltanges of highest voltagcs for equiprnent .3 8. I)ielcctric tcsts
38.1 ' Iypcs of dielectr ic tcst38.2 Sclection of tlte dielectric tests .
39. Co-ordination for voltages under normal operatin gonditions and for temporary overyoltages . . .,10. Co-ord inat ionforswi tch ingandl ightn ingovervo l tages . . . . i .
40.1 Choice of the prccedure40.2 S tatistical procedure40.3Co nventional Lrrocedu re
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('llAlvl'l1R ll : S'l'ANl)ARl) INSULATION LTwELS FOR EQUIPMENT tN RANCE A(bs pagesf t. (icanl indications 11f Z
' t l t { ts ol 'sl :rrnlurd irrsulul ion icvcls . 11
(' l l^P' l ' l ' l t l l l : S IANI)ARD INSULATION LEVELS FOR EQUIPMENT IN RANGE B
43. (lcntral indications 13. l . | . . | . a l r | co | . s | l t t t t | : t rd i r t s t t l u t i t l n [ cvc |s
{5- ( ' l tu icc t r l ' t l rc iusul : l t ion h 'vc l 13
CIIAP'I'IR,lV : STANDARD INSULATTON LEYELS FOR EQUIPMENT IN RANCE C
46. Gencral irrdications17 -
'l'ablc ol' rtrttdrd insutrtion lcvcls lor highest voltage range for equipment equal to or greater than 300 KV. .
{8 . Ra tcd s rv i t c l r i l r g i l r rpu lsc r v i t l r s tand vo l tagc49- Ratcd l ig l r tn i r rg i rnpulsc s, i l l rs tarrd vol lags
CHAPTER V : GENERAL TESTING PROCEDURE
5(I General51. Switching lnd lightning irnpulsc witltstand test . .52. 507, disnrptivr: disclrargc tt'st53. ljifttr:n-iurPrrlsc s'ithstitnd lcstt l . ( 'onventiorral i rrrpulsc nithsttnd test . .55. Slrort rluration P1;syg1-1'rc(lucncy voltage withstand test . . . . . .
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INTERNATIONAL ELECTROTECHNICAL COMMISSION
INSULATION CO-ORDINATION
Part 1: Ternls, definitions' principles and rules
FOREWORD
l)ThcforEaldaidoosoragE.mc'aofthclEco!tcchnicalDafigr3'PrcFtrdbyTccbnicatcomEitrccsoawiiche||t}cNationalco'sittcas havi'S a spacral ,o*, ,t",";o
"r r"pr""-tcd, lxn,."a rs rcxrly gs po36iblc, a! iabrtatiolal con'cosus of opinioD o! lhc
suFs dc.alt with-
4 Thry b3vc tbc forE of rccomlortd.ti.ms forilt.rlrti'Eat rtsc ttd thty rre s?Ed by tbc N*iooel @oeittlcs b th'l $ds '
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*to *o-o," iatcraarioaal rroifcaliol" tbc IEc rsprEsrg thc gish thgt aIl Netiqasl codtDittcc' thouH adopr tb r!*t oflhc IEc
rccooacodariqa for tbck *o-" -ft Ji-fo * aeriiml conlitions witt FrEit Ary disfElcr bctrt.||! thc IEC rccoEEctdtrioo
-a ,U -.-"p".aitg Datiolel irlc! should' ts f'I as poBsiblc, b' cbaly ildicalld ilt tk Lfi'r'
PREFACE
This pBblicsrid has bc.|B prtDartd by I EC Tcchdcal [email protected] No' 28' IletLtioo co.ordis'rbn'
It fonne tbclixtl dlition ofIEC publicatiotr tl,.IrsnLtior co-ordiDation, arrd rrphc.. thc fffb cdirior'_ sbtishcd.in !r-2' wth,h dcalt only
eirh c{uipoer of higl"o ".r,"g"
r* ,i-iipfi, "q*r -no
o_. gr".to tb.!.100 }v, .!d rbc tourth cditi@, puuisui{ ir tgcz' tlir* ua
J*o}'""fia f* "qUp-*r
foi ,rli"l ti"L6Jvotigc for tbc-cquipmcot i! grcsrcrthan I kV dd tlss thFn 100 tV'
tt forros Prt I ofIEC Publication ?1.
IEC publicatiol ?l-2 (il Fcprretiod) wi[ cotstitErc tbe ippli:.tior Gui& for thc Insulition cootdinsfon of ElGctrical Eq
Dr.f,ts oEir ilircusr.d at thc lt|cqtirgl bcld in Tcl-Aviv ir 1966, in M.lbounc io 1969: iD Milar io I97l .rd i!-Aticdt io 1972' Ai a tcsult
of rhis hrt ,rcctiig, rh, a'|fl n*"-*, 2t-ac."urr on*xr, *T l!-i:g to rhc National comhittcls for_approrel undct th€ sr
Month!'RxlcinAugustlgT3'e-"oa..".'oo"'-""tzt1ccatr'tomcc)43'$ggsubmittrdtothoN'tio'5lcod|IliGaforryroraludc" tbc.Tsi Monibr' Ptdcrdurc iu Juty l9?4. ' - '
- Tb" fono*iog -uoaic! YoEd cxPlicitly iE favour ofprrblicatio-n:' Surcden
, S*itzerland
: ' - ' I - T u r k e yUnion of Soviet Socialist Rcpublics
United KingdomYugoslavia
E ptotflory ra? - :'l '
Thr coulcil of tb. Iutcmarn'.l Elccuotcchtric.l conrnircio'o lobg itcddcd, i! Jun. 193, thst 'trcono
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INSULATION CO.-OR DINATION
Part | : Terms, definitions, principles and rules
CHAPTER I: GENERAL CONSIDERATIONS
SECTION ONE - SCOPE AND OBJECT
I. Scope
This stanclard applies ro cquipment fior three-phase a.c. systems, having a highest voltage tor equipment aboveI k v
This standard covers only phase-to-earth insulation, except in respect of some definitions. Standards forinsulation other than phasc-to-carth insulation are under study.
2. Object
The object of this standlrd is to specify the insulation of the various items of equipment us€d in a giv€oinstall'ation. Eachr Apparatus Committee is responsible for specifying the insulation level and test proceduresuitable for its equipmcnt. taking into consideration the recommendations given in the following sections: inparticular, for the tests prescribed in this standard, the values of the rated withstand voltages shall be choseniiom the standardized insulation levels of this publication.
'l'his standard will be supplementerl by Publication 7l-2 (in preparation) which will constitule the Application
( i t r i t l c .
SECTION TWO DEFINITIONS
'l'he following definitions have been adopted for the purpose of this standard.
3. Noininal voltage of a three-phase system
The r.m.s. phase-to-phase voltage by which the system is designatedtcristics of the system are related.
,t. Highest voltage of a three-phase system
and to which certain operating charac-
The highest r.m.s. phase-to-phase volt4ge which occurs under normal operating conditions at !fly timc rtrd rtany Point of the system. It excludes voltage transients (such as those due to system switching) alrd tcmprrrryvoltage variations due to abnormal system conditions (such as those due to fault conditions or thc surldcndisconnection of large loads).
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i. I liqhcsl rollrgc for tquiPrncnl
Thc highcst r.nr.s. phlse-to+h se voltlrge lbr which the equipment is designul in rcspcct of its insulation as
*cll i|s orlrcr charactcristics which relatc to this voltage in the relevant equipment stundards'
i !rrs veltage is thc maxirnum value of the highest voltage of the system for which the equipment may be used.
ln rhis sranclard, the highest voltage fbr equipment wil l be represented by U-.
t ( . . In sysrcnrs wrrh highest vol t lge r i r l cquiprnent equal to or greater ! .han 123 kV, th is vol tage U* in generaldoes not mater ia l ly <t i f fer
lionr the highcsr value of' rhc systcrn operating voltage. Below 123 kV, the voitage U* may be higher than the highest system
vpl(a11c. sincc cuclr sran6arcl valuc ol'U", applies to differeni svstcms tlte nominal voltage of which may differ by as much as 209/o
( f - c r r n s r u n c c U ^ ' . 2 4 k V c o v r : r \ l ( ) k V r r n d 2 2 k V ) , e n d h a v i n g t h e r e f o r e d i f f e r e n t v a l u e s o f t h e h i g h e s t s y s l e m v o l t a g e .
(r 1,::tcrnrlinsulation
'flie riistances in lir and tire surlaces in contact with open air of solid insulation of the equipment which are
subjcci to diclechic srresses and 1() the ei'tects of atmospheric and other external conditions such as pollution,
hrrrliditv. vermin. etc.
?. hternal insulation
Thc internal solid. liquid or gaseous parts of the insulation of equipment which are protected from the effects
of ltmospheric and other external conditions such as pollution. humidity, vermin, etc.
\ )
Inrloor external insulafion
Extcrlal insulation which is,-lc'signed to operate inside buildings and ccnsequently not exposed to the weather.
Outcklor external insulation
F..rrcrnal insulation which is designed to operate outside buildings and consequently exposed to the weather.
l l) S('lf-restoring insulation
insulation which completely recovers its insulating prop€rties after a disruptive discharge caused by theanplicarion of ir test voltage; insulation ofthis kind is generally, but not necessarily, external insulatron-
l ! Non-self-restoring insulation
lnsulation which loses its insulating properties or does not recover them completely, after a disruptiverlischarge caused by the applicarion of a test voltage; insulation of this kind is generally, but not necessarily,in ternui insulat ion.
i2. 'fype test
A test made on one piece of equipment or on several similar pieces intended to show that all pieces ofrquipmcnt made to the same specification and having the same essentill details would pass an identical tcs.; it isusulllv not reoeated on different deliveries.
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13. Reiutine test
A test to which each piece of equipment is subjected.
14. lsoluted neutral system
A syst€m which has no intentianal connection to earth exoept through indicating, mcasuring or protcctivcdevices ofvery high impedance.
15. Resonant e:rrth€d system (system eadhed thruugh rn arc-suppression coil)
A system in which th€ neutral is earthad through a reaclor, the reactance having a value such that during asingle phase-to-earth fault, the power frequency inductive current passed by this reactor substantially neutraliasthe power-frequency capacitive component of'the earth fault currcnt.y'y'o.e. - With.caonant c lhing ofo systcm, thc rcsidual currcnt in thc foula is limitcd to s|rch aa cricnt that aD arcing fr tio.ir it ulu.lly
self+.rtingu$hing.
16- Earthed neutnl system
A system in which the neutral is connected to earth, eithcr solidly or through a resistance or reactance of avalue low enough to reduce materially any transieni oscillations and to improve the conditions for selective earthlault protection.
17. lrrrth frult frctor
At a selected location of a thr€e-phase system (generally the point of installation of an equipment) and for agiven system configuration, the ratio of the highest r.m.s. phase-to-earth power-frequency voltage on a soirndphase during a fault to earth (affecting one or more phases at any point) to the r.m.s. phase-to-earth power-liequcncy voltage which would be obtained at the selected location without the fault.
Norcs l. Thi6 f.ctor is a purc numcricrl r.tio (highcr tharr l) and charocnrias io gc[eral Erms th. canhing cotrditio[s of . iyttch asvicu/ed from th. s€hcrcd location, iodcpctr&ntly ofthc actual opcrrting value oflh€ volragc at thrt location.
Th. "earlh faulS factor" is thc producr of .1/' &rd thc -factor of.orthing" which hlr bccn 'rs.d in thc pas(
2. - TIlc carth tbult f&lors arc calculatcd from lhc pha&.scqucncc impedaicc compoocnts of the sy6tem, ar vicwcd froE rhc *Lctcd. location, using for any rolarirg niachinc! lhc Eubtransicnt rclctancs.
J. - If, for all crcdibh systcfi conngurations, thc zcro-scqucnca rcactance ir hls thro thr€e limes thc posilivc-saqucnca Gactaooc andif thc zcro-$cqucnca rcsistanc€ docs not excead thr positivc-sequc[ca aEactancc, ih€ earth fault factor will not cxc.cd'I.4.
lE. Overvoltage
Any time-dependent voltage between one phase and earth or between phases having a peak valuc or valucsc;rceeding the correspoirding pakvallrc(U*,fzlrBor U^ nE respectively) derived from the highest voltage forequrpment.
^lds. -- Ovcwoltagcs arc llways t.ansiory phcnarncna. A broed disiinclion may be mrd. bctrc.n highly damFd ow.voltagct of rclrdrllyiho.t drrrrdor (s€€ Clau!€s 2l and 22) .rd undamped or only wcakly dalnFd ovcrvoltryes of rclarivcly long du..lioo (*rCl{usc 25). The bordcr-line trctw€en thcae two groups cannot be clc|rly lixed.
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l ' , Phrse-to+arth pcr unit overvoltage (p.u.)
Thc ratio of the pcrk values o[ a phuse+o+arth ovcrvoltagc and of thc phase-to-earth volt.gp corrcspondingro thc highcst voltagc lbr er4uipmr:nt (i.e, Um JzlJ3J.
:0. Phlse-to-phasc per unit overyoltage (p.u.)
Thc rutio of the peak valucs ol a phasr-to-phasc overvoltage and of the phasc-to+arth voltage cbrrcspondingr(, thc hi!hcst voltlgu lirr cquipnrcnr (i.c. lgilin U^ utl Jl'1.
This ratio will bc cxprcsserl bv A ,,r, J, ,( being the ratio of the peak value of thc phase-o-phase ovcrvoltaga tothc pcuk value of thc highest voltagc lbr equipment (i.e. U..,/2).
Thc pcak value ol' the highest voltage for equipmenl (i.e. the lowesr per unit value of a phase-o-phaccovcrvoltagc) will thus be expresscd in p.u. value as I x J3..Vrre. - Thc p.u. ovcrvoltageJ defincd in Chuses 19 lnd 20, fo. ahc purpos. of insuhtion co-ordination srudi!.. arc rsfcrred !o alr Fat
valuc of thc phrs.-ro-€urth voltuBc corrcsponding to thc highest \,oltl8e for cquipmcnt ai a fxcd rcercnc! balis. Whctr oyqrcl3a$rarc nlcrsured in various conditions during tesls on a syslem or an cquivalcnt model, it may bc convaricnt to rcfar lhcsa owrvolt{ctlo thc phasc-to-clrth volt Bri rhcr prior to or irl'tcr tlrc swilching opcrarion, as appropriatc. ln sucb caics. Ihc tarm "ovcwoltag!factor" lhould be uv€d for thc riltro, Jrtd:rs thc overvoltages arc dot always proportional rc the syscm vohagc, ir i! Dcoalssry !ostrtc the latler !$ wcll as all condilt()ns ol the !est.
: l . Switching ovcrvoltagc
A phase-to-carth or a phase-to-phase overvoltage at a given location on a system due to onc specific switchingoperation, lallt or other cause, the shape of which can be regarded for insulation co-ordination purposcs as'iirnilar to that of the standard impuls€ (Clause 5l) used for s\r,itching impulse tests. Such overvoltages arcusrrally highly darnped and ol'short duration.
?3. l,ightningovcrvoltage
A phasc-to-earth or a phase-to-phase overvoltage at a given location on ii system. due to a lightning discharger.rr other cause, the shape of which can be regarded, for insulation co-ordination purpox, as similar to that of the:'ltr(l:rrd impulse (Clause 5l) used lor lightning impulse tests. Such overvoltages are usually unidirectional andt'f vcr y short duration.
,!orr' t'r Crdur'.r :, l,r/ lJ. - For thc purF)se of insulation co-ordinstion, swirching lrnd lithrning ev.rvoltdgca ilrr clasiificd .c.ordiog 10th,rjr shirfxj. rcgurdlcs$ o[ their ofl!'in. .\lthough, considerable deviations from the standa.d shapes occur od actusl st3lcms. i! thisrtandard it ir con$idered sullicicn! to dc.$jrtbe such overvokages by lhcir classificrlion rnd Ftk vtlue.
I 3. Statistical switching (tightning) overvoltage
Switching (lightning) overvoltage applied to equipm€nt as a result of an event of one specific type on thesystem (line energization, reclosing, fault occurrence, lightning discharge, etc.), the peak value of which has aprobability of being exceeded which is equal to a specified reference probability.
'l his reference probability is chosen as 27o in this standard.
14. Conventional maximum switching (lightning) ov€floltrge
The peak value of a switching (lightning) ov€rvoltage which is considered as the matimtrm overyoltage in theconventional procedure of insulation co-ordination.
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25. Temporaryovervoltagc
An oscillatory phase-to-earth or phase-to-phase oyervoltage at a given location of relatively long duration and
which is undamped or only weakly damped.
Temporary overvoltagrs usually originate from switching operations oi faults (e.9. load rejection, single-phase
faults) and/or tiom non-lineariries (ferro-resonance etTeits, harmonics). They may be characterized by their
amplitude, their oscillation frequencies, and by their total duration or their decrement.
26. Statistical switching (lightning) impulse withstud voltage
The peak value ofa switching (lightning) impulse test voltage at which .insulation exhibits under specified
conditions a probability of withstand equal to a specified reference probability-
This reGrence probabitity is chosen as 90% in this standard-
The concept of statistical withstand is at piesent applicable only to self-restoring insulation.
27. Conventional switching (lightning) imPdse withstrnd voltage
. The peak value of a switching (lightning) impulse test voltage at which an insulation shall not show any
disruptive discharge when subjected to a specified number of applications of this impulse, under specified
conditions.
This concept applies particularly to non-self-restoring insulations.
28. Rated switching (lightning) impulse withstand voltage
Thc prescribed peak value of the switching (lightning) impulse withstand voltage which charactcrizes the
insuLrtion of an equipment as regards the withstand tests-
rVrks ,/. - Depending on the kind of insulalion md complying to whai is specificd in the rclevant apparatus standards, dickctric t€sls arc
mfldc to vedfy that:.- thc sraiisrical swirching (lighhing iripulse withstaod voltage is equal to o. higher than the rated swiching (lightnind impuls.
w(hs(and voltage (see Subrlause 40.2):- rhc convcdrional switching (lighhing) impulse Dirhstand voltage is cqual to or higher than the rat d swilching (lighaning)
impulsc withsrand vokag€ (see Sub-clause 40.3).
,'. - The sl&d.rrd impulse shspes used for withstand les$ oo equipdent as u/€ll as thc test proc€duaes are defined in ChNptcr V.
29. Rated short duration power-frequency withsttnd voltlge
The prescribed r.m.s. value of sinusoidal power-frequency voltage that the equipment shall wirhstand during
tests made under specified conditions and for a specified time usually not exceeding I min.
10. Rated insulation level
a./ For equipment with highesr voltage for equipment equal to or greater than 300 kV: the rated switchingand lightning impulse withstand voltages.
D/ For equipmenr with highest voltage for equipment lower than 100 kV: the rated lightning impulse and
short duration power-fiequency withstand voltages.
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-11 St:raistical safcty factor
For a given type of eyenr, the ratio of the appropriat€ statistical switching (or lighufng) impubc withSred
volrxBc to rhe statisticirl overvoltage, established on the basis of a given risk of failure, taking inio acoount rhc.iratisticrl distributions of withstrnd voltagcs and overvoltages.
.!,r.. - Indicanons .cgffding rhe corrclxtir)n bctw!'en thc minimum value of the statistic.l safcty f0ctor and thc riiL of frihrc rc3 lo b.cxctcdcd will bc lbunrl in thc r,:trtrttl cdiliott ol tltc Applicttion Guid€ (l EC Publicltion 7l'21.
-i2. Conventionll sofety ftctor
The ratio of a conv€ntional swirching (or lightning) impulse withstand voltag€ to the corresponding conven-
tronal miximum overvoltage, cstlblished on the basis of experience and taking into account the possiblc
dcviarions ol'rhe actual withstand voltage and overvoltages liom their convenlionul values as well as any oaher
litctors.
13. Protection level ofr pmtective device
The highest p€ak voltage values which should not be exceeded at the terminals of a protectivc device when
rcspecrively switching impulses and lightning impulses of standard shlpes and rated values are applied under
spceified conditions.
,vr"r ,/. - Thc value lbr lighrning impulsrs is rhe highes( value ofany ofthe following:-' mirximurn sparkover voltagc with 1.2/50 irnpulse;- mirimum residualvohagB Jt lhc specified current;- mlximurn liont-ol-wave spurkover voluge divided by I l5.
:. - Eirhe. rhe srilistical or rhe coovenrioiral impulse protc.tive level can bc considercd. with the lamc rne.rring ar in Claulct 23,24,16 rnd 27.
J4. Protoction factors of a protective device
Tlrc prorection l'actors of a protective device are the ratios of the switching impulse and. lightning impulsc
valucs respectively of the proteclion level of a protective device to the peak value of the rated voltage of theprotcctive rlevice..\,,/..- ln rhc case ot sp$k g,.tps, lhe ph se-to{rrth voltlge correspondiflg to rhe highest voltrgc for cquiprhent is uscd conventionally as
thc rxred voltrge.
SECTION THREE -* BASIC PRINCIPLES OF INSULATION CO.ORDINATION
:15. lrsulationco-ordination
, Insulation co-ordination comprises the selection of the electric strength of equipment ahd its application, inrcliltion to the voltages which can appcar on the system for which the equipment is intended and taking intoaccount the characteristics of available protective devices, so as to reduce to an economically and bperationallyacceprable level the probability that the resulting voltage stresses imposed on lhe equipment will cause damagek) cquipmcnt insulation or aflect continuity of servic.e.
-16. Voltage strcslrcs xnd olhcr factols alTecting insulation
The followigg classes ofdielectric stresses may be encountered during the operation ofan equipment:- power-frequency voltages, under normal opefating conditions, i.e- not exceeding the highest volta'3e for
equrpment ;- temporary overvoltages;
7A:80
- 7
- switching overvoltages;- lightning overvoltgges.
For a given voltage stress, the behaviour of internal insulation may be influenced by its degrec of ageing, and
that ofexternal insulation by its degree of atmospheric contamination.
37. Ranges of highest voltages for equiPm€rt
For the purpose of this standard, the standardized values of the highest voltage for equipment arc divid€d into
three ranges:- range A: above I kV- range B: lrom 52 kV- range C:300 kV and
38. Dielectric tests
and less than 52 kV;
to less than 300 kV;
above.
38-l Types of dielectric tests
The following types ofdielectric tests are considered in this standard:- short duration (l min) power-frequency Gsts;- long duration power-frequency tests;- switching impuls€ tests;- lightning impulse tests.
Switching and lightning impulse tests may be either withstand tests, with a suitable number of voltage
impulses at rated impulso withstand voltage applied to the insulatiori (see Clauses 53 and 54), or 507o disruptive
discharge tests in which the abiliry ofthe insulation to withstand impulses at the rarcd impuls€ withstand voltage
is inferred from the measurement of its 507o disruptive discharge voltage (see Clause 52); this, of course, is only
possible in the case of self-restoring insulation.
Slrort duration power-frequency tests are withstand tests.
Recommended values of the short duration power-frequency test voltages and of the switching and lightning
impulse withstand voltages are given in this standard. For.long duration power-frequency tests, however, only a
gencrrl guidance is given in Clause I to ihe relevant Apparatus Committees.
38.2 Selection of the dielecrfic tusts'fhe
selection of the dielectric tests according to this standard is difflrent in voltage ranges A, B and C. It can
also be influenccd by the type ofequipment-
Rangcs A uml B
The performance under power-frequency op€rating voltage, temporary overvoltaggs and switching over-voltages is checked in general by-a short duration power-frequency test,
The performance under lightning overvoltages is checked by a lightning impulse test.
Ageing of internal insulation and contamination of external insulation, when they may affect performane
uncler power-frequency operating voltages and overvoltages, generally require long duration power-frequencyIests-
rvo.e. - Wiahin thcsc .anges of voltages, it is accepted that tlE traditionel I miE por€r-ftcqucncy tcst Seneaally providc! r tuiubb safllymargin wiih resp€cl to switchidg ovcrvoltages and thc highcst tempoa4ry ovcrvoltages (thc duration of which is much 5horl6 lhalrI min), as well as to Dormal opcratiBg voltagc br to mode.atc temporary overvoltages (rhc duration of rrhich may bc long€r burwilh a lo €r amplitude). This I min tcrt with lhc vollsge valBes in Tdblcs I, II and lll thus apFaas ds s comPromise, sinctovcrvoltages comparable bolh in dwation and amplitudc with tlrc valucs in lhe test rarely occur on normal systems. If for somerypes ofinternal insulation ihis test is shown to bc ituppropria(e. it will th€n be for the;clcvant Apparatus Commiltees to adrpr tlrcvoltage levcl und.the duration of(he rcst.
7 A : 8 0
- - - 8 -
R<tttgc C
ln this voltage range, tha perl'ormance of insulation under power-frequency operating voltags and t€mporary
ovcrvoltages on one hand, and unrler switching overvoltages on the other, is demonstrated by differcnt tests..
The perlbrmance under power-tiequency op€rating voltages and temporary overvoltages is chccked by long'
duration power-frequency t€sts, uirning at demonstrating the suiBbility of the equipment with resPect eithcr to
agcing or to contamin{tion, accortling to which is the case.
The pcrtbrmance under switching overvoltages is checked by switching impulse tests.
The peribrmance under Iightning ctvervoltages is checked by lightning impulse tests'
M,lc. "- tJp to rhis timc, thc v{lucs ot th€ lr dirional shorr duration po*tr-frequency withsrand te$t voltagcs har/c bcctt.hith ctough in thit
rrng€ lo rlkc somc ir(rount :rlso of (hc €lltc(s of srr/irching ovcrvohagcs and temporary ovcrvolltgls. Wirh- the intaoduclion of lcsts
spcclfic ro swilching impulsrs rbi equipmcn! having highesr vohage equal to or grentet th{n 100 kV lrnd the availability of tcsrr
spccrlic to parriol discharges, rhc valuesof thc power-frequency tesr voltages can bc r.duced, atrd lheir natu]e rcconsidcrad so as to
b. ,nu." ,"p..r"nruri"" ol ngrrnal opcraring voltug"a ond tapor".y overvoltages only; this rcvisiitn should rrow bc undcrtakctt by
the rclevant Appararus comnrrtlccs. until this can be donc, lhe power-frcquency tes6 al pres€n! prcscaibcd by thc rchvant
Apparatus Commirt€ca will corrlrlrue !o |rppl
39. Co-ordination for voltages undcr nrtrmal operating conditions and for temporary overvoltages
When the behaviour of equipment under normal operating voltages and temporary overvoltages has to be
demonstrated by a short-duraiion power-t'requency test, i.e. in voltage ranges A and B, the recommended values
ot the test voltage are to be found in Tables I, II and IlI.
Long-dur:iLtion power-t'rcquency tests, intended to demonstrate the behaviour of equipment with respect to
ageing of internal insulation or to contamination oi external insulation, should be prescribed by tbe re.levant
Apparatus Committees. The following general indications are given for their guidance'
ln specifying tests representative of stresses under normal operating conditions and temporary overvoltages, it
should be assumed thac:
a,/ As regards the voltage under normal oP€rating conditions, the insulation shall withstand permanent
opcration irt the highest voltage tbr equipment.
bJ l,ower-lirequency tests, rnten<ied to verity th€ ability to withstand surface contamination, should be carried
out at rhe apjropriate voltage, i.e. either U./.rA or U. in case of a system which may operate with a phase
carthed tbr long periods. The contamination conditions must be specihed in the approPriate I E C pubticarions'
c,l As reglrds re temporary phase-to-earth overvoltages in range c, their Peak value does not exceed 1.5 p.u.
iu usual cases and their duration does not exceed I s on each occasion; special consideration may be required
wh(:n system conditions are more severe.
/) power-frequency tests, lnrended to verify, as far as practicable, that there will be no significant deterio
ration ofthe insulation due to partial discharges during the expected working life ofequipment and that in the
most severe conditions the insulation is not liable to thermal instability, should be performed at some voltage
above U-/.rA phase-to€arth and for a duration appropriate to the system conditions, and in such a manner
that all elements are stiessed in the saine proportions as in service.
All srandards conc€rnrng the values of the test voltages, as well as the test procedure and the test conditions,
should be decided by the rel€vant Apparatus Comrnittees in compliance with these indications and the
requirements given in the differenc parts of I E C Publication 6Q High-voltage Test Techniques,
.10. Co-ordination for switching and lightning ovenoltages
In voltage ranges A and B, insulation co-ordination for switching overvoltages can g€ncrally be disregarded'
as indicared in Sub-clause 38.2, and no switching impulse test is required in this standard. In voltage range C, co-
ordination has to be considered tbr switching and for lightning overvoltages, which have to be trcated separat€ly.
7A :80
..f
- 9 -
ln every case, insulation co-ordination prcsupposcs some knowledge of the magnitude of the overvoltages to
bc cxpcctcd ut thc cquipnlsnt location. considcring credible S],st€m contingencies. the electrical charircteristics of
thc system and ol thc cquipmcnt and cxpcrience of comparable systcms as wcll irs thc linlitiug ellcct of any
protective devices.
Where surge arresters are installed, iheir choicc shall tak€ into considerarion the magnitude and duradon of
the temporary ovclloltages during which they may be required to operate satistactorily while conrinuing to
provide an adequate margin of protection (see also Clause 3 of IEC Publication 99-lA, First supplement topublication 99-l (1958): Recommendations for l-ightning Anesters, Part I : Non-linear Resistor Type Arresters)-
The insularion strength of equipmdnt for switching and lightning stresses shall then be chosen on
the predicted overvoltages to ensure that the requisites of insulation co-ordination are satisfied.
A statistical or a rion-statistical procedure may be considered. Some general rules for procedure
and conventional approaches to insulation co-ordination will be found in the second edition of the
Cuide ( I EC Publ icat ion 7l-2).
the basis t l f
in stat ist ical
App l ica t ion
40.1 Choice of the procedure
The need for thorough studies of system overvoltages, as well as the need to carry out tests based on the
application of a rather high number of impulses, set practical limits to the use of the statistical procedure of
insulation co-ordiuation.
A statistical approach is particularly valuable where there is a strong economic incentive towards a reduction
of insulation strength esp€cially when switching overvoltages are a problem. For these reasons, the statistical
procerlure is mrinly appropriate to voltage range C and is not usually ernployed in ranges A and B.
Furthermore, in all voltage r4nges, when the equipment insulation is essentially non-self-restoring, only a
small number o[ impulse applicntions (for instance, three for each test condition, as specified in Clause 54) can
often be acccpted to check that the withstand strength is ensured and therefore, at the Present stage of the art, it
is impossible to consider failure probability as a design variable subject to quantit&tive control. Thus, the use of
thq slatistical procedure is at present practically restricted to self-restoring insulatiqns.
40.2 Statisticalprocedure'I hc statistical procedure acknowledges the fact that iosulation failures may occur; it attempts to quantify the
risk of failure and to use it as a safety index ia insulation design'
r\ rigorous determination of the risk of failurc for a given category of overvoltages requires that both the
ovcrvoltage stresses of this category and the equipment withstand be described in terms of their respecttve
lieilucncy distributions.
ln a simplified form of this procedure, assumptions are made on th€ shapes of the probability curves (e-9.
normal frequency distribution and given standard deviation) which permil the representation of each curve by a
single point corresponding to a given value of probability. The ordinates of such points are designated as
"sratistical overvoltages" (Clause 23) in the case of overvoltage probability curves, and as "statisdcal impulse
wirhstand voltages" (Clause 25) in the case of withstand probability curves. The ref'erence probability tor
equipment impulse withstand voltages has been established as 90olo.
lnsulation co-ordination for a given category of overvoltages, in this simplified statistical context, consists in
the selection of a margin, characterized by the statistical safety factor, between the statistical impulse withstand
voltage and rhe statisrical overvoltage, which will result in a probability of lailure lcapable of numerical
expression) deemed to be acceptable from the point of view of system reliability and cost.
The minirnum acceptable values of th€ statistical switching and lightning impulse withstand v(tltagcl ll i lvlrr!
thus been determined, the rated switching and lightning impulse voltages will be selectcd from tbc stxrrrlxr(l
7 A : 8 O
--i- l0 _
al:1 r Ct4icr lV. Tcsts requiring a rather large number of impulse applications arc thcn nccdcd to veri$,rl r| -ptebb ttcgrcc of confidcnce. that the actual. statistical withstand voltages arc cqual to or higher thanrb dd iEFft3 withsrand voltages.
TL sifcerirn can bc done by means of a 50Yo disruptive dischargc voltage test, from which thc acturlcbl (90%) wirhsrard voltage can be derived with a good degree of confidence in the casc of sclf-rcsoring-hlil| rhich continues to bchave as such at the corresponding tcst voltages; thes€ are somc hat highcrtbl ric ratert wirhstand voltage.
'fhe same verification can be done iir case of such insulation that the prcibability
of denegc in these conditions, in spite of a relatively large number of impulses and an increased impulscrolu3c. can bc economically accepted (for instance, support-insulators, disconnectors)..
Tl: ncnfication has to be done rt the rated withstand voltage in the case of insulation which might not be sclf-resroring ar the 509o disruptive discharge voltage but is self-restoring at the rated withstand voltage, and forrhtch thc application of a number of impulses in such conditions to the non-self-restoring parts of the insulationan bc aoccpted (for instance, some types of bushing, some types ofinstrument transformer and swirchgear).
4O.3 Conventional orocedure
ln this procedur€, the criterion of insulation co-ordination for $piiching or lightning overvoltages is thcmargin between an overvoltage conventionally accepted, but not necessarily ascritained, as approximating thema.rimum value to be expected at the equipment location (Clause 24) and a withstand voltage the value of whichmay not bc rigorously demonstrable but derived from an impulse test (Clause 27).
This margin. determines a safety factor which should not be less than a value found to bc adcquarc fromcxJrerience. The Application Guide gives some usual values for the three voltage rangcs. The corrcspoirdinginrpulse test voltage has to be selecrcd from the standard values listed in the following chapters.
7A:80
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CHAPTER II: STANDARDFOR EQUIPMENT
INSULATION LEVELSIN RANGE A
ii l
41. Generrlindications
ai This chapter specifies insulation levbls associated with standard values ofthe highcst voltage for cquipmcnc
in range A.
bJ Two series of standard insulation levels arc givcn: Series I and Series II.
Series I is based on practice in most European and several other countries, while Scries II is mainty based on
practice in the United States of America and Canada. Only onb of these two series should be used in any one
country.
42. Tables of standarrd insulation levels
The standard insulation levels are given in Table I (Series I) and Table II (Series tI).
Tnsln IStandard insulation levels for I kY ( U- < 52 kV
Serres I (based on current practice in most European and several other cruntries)
Highest voltagefor
equipment U-(r .m.s.)
Ratedlightning irnpulsewithstand voltage
(peak)
Ratedpower-frequency short duration
withstand voltage(r.m.s.)
List I List 2
kv kv kv kv
3.61.2
t 217.52436
m40CI7595
145
,lO607595
t25r70
l0n28385070
ln addition to the rated power-frequenclr withstand voltage, two values of rated lightning impulse withstaodvolt4ges (lists I and 2) are given in Series I for each highest voltage for equipment. InErmediate tcst volt€es
should not be employed. Impulse lests arc included in order.to check the ability of insulation, and in particular
of windings, to withstand lighining overvoltages and st€ep switching overvoltages, particularly those which result
f'rom chopping due to restrikes aaross the arc gaps of switching devies.
Under special conditions of usage, the relevant Apparatus Co--itt"r, can decide to apply reduced restvoltages in power frequency and/or impulse tests, or even to delete impulse tests. But, in that case, it must beproved either by tests, or.by a combination of tests and calculation, thal insulation rEquirements are fulfilled for
the essential stresses in service.
The chqice betu/een lists I and 2 should.be made by considering the. dege€ of exposurc to lightdng ardswitching overvoltages. the type of system neutral earthing and, where applicable, the type of overvoltaSeprotective devic€. if/
7 A : 8 0
_ 1 2 _
Fiqurpmcnt clcsigncd to lisi I is suitablc lbr installations such as the following:
| ) ln systems and industrial installations not connecled to overhead lines:
4i where the system neutral is earthed either solidly or through an impedance which is low comparcd with
that of an arc-suppression coil. Surge protective devices, such as surge diveiters, are generally not rcquired;
,,1 wherc the system neurral rs earthed through an arc-suppression coil and adequate overvbltage protection
is provided in special systems, e.g. lrn extensive cable network where surge arresters capable of discharging
the cable capacitanct may be required.
2) ln systcms and industrial installations connected to overhead lines only through transformers where the
c:rpacirance to eilrth of cilblci r:onnected to the transformer lower voltage terminals is at least 0.05 pF per
phasc. When the cabla cirpacitlncc to earth is insutlicient, additional capacitors may be added on the
trtnsfonn€r si<Ie of the switchgcar, as close as possible to the transformer terminals, and so that the combined
capacimnce to earth of the cables plus the additional capacitors is at least 0-05 pF per phase.
Thls covcrs the cas€s :
aJ where rhe system ntjutral is earrhed either solidly or through an impedance which is low compared with
that of an arc-suppression c'oil. Overvoltage protection by means of surge arresters may be desirable;
,J where the system neutr:tt is earthed through an arc-suppression coil and where adequate overvoltagc
protection by surge arresters is provided'
3) In systems and industrial installations connected directly to overhead lines:
4.1 where th€ system neutral is earthed either solidly or through an impedance which is low compared with
that of an arc-suppression coil and where adequate overvoltage Protection by spark gaps or surge arresters
is provided depending on the probability of overvoltage amplitude and frequency;
b/ where ihe system neutral is earthed through an arc-suppression coil and where adequate overvoltage
protection by surge arresters is provided.
In all orher cascs. or where a very high degree of security is required, equipment designed to list.2 has to be
used.
TABLE IIStanfurd insulation levels for I ky < U- < 52 ky
Series II ( based on currcnr pructice in the LJnited States of Amerfua, Cunatkt and sotne other counties )
Highest voltagefor
equipment U-(r .m.s.)
Ratedtightning impulsewithstand voltage
(peak)
Ratedpower- frequency short duration
withstand voltase( r .m.s . )
500 kvAand bclow
Above500 kvA
kv KV KV kv
4.4013.20 ' l
13.e7 It4.s2 I26.416.5
60
95
75
u0
l 9
34
5070
150200
lJora. .- Test valucs listcd ara spccific to t'ull insularion lev€ls of transforraers, but arc rcprcsentative of othel equipment in common usagl
in U.S. and Canadian itandards as well. Panicular appamtus standards should be referrcd to lba exac! value6. Reduced insulation
levels may be applied wherc justified by the degrce of proreclion.
7A:80
I
;
- 1 3 -
CtlAlvl'ER III: STANDARD INSULATION LEVELSFOR EQUIPMENT IN RANGE B
43. Gcneml indicatio[s
This chapter gives the recommended combinations of the highest voltage for cquiprnent ir rangc B and thetwo {.'omponants of insulation level as statid in Clause 30:- rated lightning impulse withstand.voltage;- rated power-frequency short duration withstand voltage.
M. Table of standard insulation levels
Table III is based on the proposition that, in this range of voltages, lightning surges
the selection of insulation levels.
first consideration in
Tnsle IIIStandard insulation levels for 52 kV ( U- < 300 kV
l 2 3 4
Highest voltagetbr
equipment U-(r.m.s.)
Base for p.u. values
u^ y_+V J
(peak)
Ratedlightning impulsewithstand voltage
(peak)
Ratedpower-frequerrcy
short duration withsland voltage(r.m.s.)
kv kv KV kv
52-_
72.5 _
173 _
t45 _
170 ---
245 _
425 250 - 9 5
t40
185
230
275
325
360
395
f f i
59 f25
rtn 450
n 8
139
?.oo
550
650
750
- 850
-9s0
r 050
45. Choice of the insulation level
The table associates one or more recommended insulation tevels with each standard valuc of thc bigh€stvoltage for equipment.
Intermediate test voltag€s shall not be employed. When more than one insulation level is given, thc highesrlevel is appropriate for equipment located in sysiems wherc the earth fault factor is higher than 1.4 (s€eClause l7).
Several insulation levels may exist in the same system, appropriate to installations situated in differentlocations or to differing equipment situated in the same installation. A discussion of the selection of theinsulation level in relation to the particular conditions of the installatibn will be found in the second edition ofthe Application Guide (l EC Publication 7l-2).
7 A : 8 0
have
- 1 4 -
cljAPTER lV: STANDARD TNSULATTON LEVELSFOR EQUIPMENT TN RANGE C
J6. C,cneralindications
a/ This chapter specifies stantlurd insulation levels associated with standard values of the highcst voltage forcquipment in range C. 'l'hcsc lcvels ale lhe same whether the statistical or the conventional procedure fordetermining insulation levqls is adopted, depending on the type ofequipment under consideration.
6,) Thc standard values of rated impulse withstand voltages shall be taken from the following series, which isapplicable to both switching aud lightning impulse voltages:750 kv, 850 kv,950 kv, l0s0 kv, 75 kv, 1300 kv, t425 kv, t550 kv, 1675 kv, t800 kv, t950 kv,2 r00 kv, 2 250 kv, 2 400 kv, 2 550 kv, 2 700 kv, 2 900 kv.Intermediate values shall not be employed.
c) Table tV of Cladse 47 givcs recommended combinations of highest voltages for equipment and insulationlcvel. When, due to the design of the system or the methods chosen for the control of switching or lightningovervoltages, combinations other than those given in Table IV are technically and economically justifiable, thevalucs shall be selected from the series eiven above.
rf Scvera.! insulation levels may exist in the same system, appropriate to installations situated in differentlocations or to differing equipment situated in the same installation. A discussion of the selection of theinsulation level, in relation to the particular conditions of the installation will be found in the second editionol'the Appticetion Guide (l EC Pubtication 7l-2).
47. Table of stanrlard insulation leyels for highest voltage range lbr equipment equsl to or greater than 300 kY
't tble tV shows the recommended combinations of the highest voltage for equipment. and the two componensrrl tl)e insulalion levcl:- ratcd switching impulse withstand voltage;-- rlted lightning impulse withstand voltage.
'l he table is bascd on thc proposition that, in this range of voltages, switching overvoltages should have firstt:onsideradon in the selection of insulation level.
ln column 3, the per unit (p.u.) values of the rated switching imputse withstand voltage of column 4 areindicated lor convenience of comparison with p.u. sivitching overvoltages expected in the sysrcm for which theequipment is intended; these p.u, overvoltages must of cours€ always be less than the p.u. withstand voltage byan appropriate margin.
.18. Rlted switching impulse withstand voltage
'tn Table IV, the range of rated switching impulse withstand voltages associated with a parricular highcstvoltage for equiprnent hlrs been chosen in consideration of the following:
r.r,l For cquipmcnr protected against switching overvoltages by surge arresters:- the expected values of temporary ovewoltages;- the characteristics ofpresently available surge arresters:- the margins generally considered advisable between the protectiye level of thc surge affester aud the
switching impulse withst nd voltage of the equipment.
7 e : 8 0
- 1 5 -
Tl,st.e IV
Standard insulation levels for U- 3W kY
Retb bctuccnrated lightning and
switching impulsewithstand voltages
Rrrcd rwitrtinjimpukc withstand
volta3e (pcak)
Highestvoltage'forequipment'U*(r.m.s.)
300
7fi
8s$
l : ,1 3
t.27
l . t 2 '
r .24l . l l
t.24t . t 2
t .24t . 1 I
t .36r .2 ll . l 0
r.32t . r 91.09
I . 3 8
1.26
t . t 6
850
9fl1
10gl362 296
3.47
2.86
t-21
2.76
3.06
2.45
428 t l7s
1frn
525 429
1 r75 t{E
I 550
765 625 r 8${t
,.26
1.47
1.55
I 959
1rffi
2 dxl
7 A : 8 0
- 1 6 -
For equipment not protected against switching overvoltages by surge arresters:
the aceptutrlc risk of disruptive discharge considering thc probable range of ovcrvoltages o*urring at the
equipmcnt lmatisn; '
- the degrec'of ovdrvolrage cdnri:ol gencrasy rLe$cd :bonoqrizl aad obuinablc by crrcfrd *bction of the. switcAing dwier.and in thc'systeq dcsign. . , . .-
ccmd editiorA dircussion of thc scl€ction of rated svirching impulsc withltend vobaga rill bc foud b thc tof the Applhation Cuide (lEC ltblication 7l-2).
49. Rod lighbing fuilpBlsc wirh$ad vottegc
Th€ r gc of rared lightning impulse withsard volta€cs asciated, in Tabb IY, rirh r prrticuhr raed
switching impulse withstand voltage has ben choscn in consideration of thc folbwing:
ai For equipment protlc1qd by surge arrcsters, the tlui lo*cst vilrrsiof lighting i|[pub tiArbd reltrg6
are appliqrbb. Thcy ,*ere chosen by taking into account thb ratio of lightdqg impub poadiw lcrils .to
switchihg impuls prbtectiye level likely to be achievcd with s.urgc arresters, end by dding {Fopriatr rtrtrgoswhich may bc particularly ncccssary in vicw of tle greatrer effect of separatioo bctE fb $rge arrcstera aod
tha prote€tcd appiratus on the protection level achievabb fc fightning iophr .s @o&d with that forswitching impulses.|',rtFor €quipmenr not protected by surge arr€stcrs (or not cftCrivq SoC*d). mly tb highcst vahre oflightniirg impulse withstand voltages shouH be usd- Tb hi8tcat EfE & brd o tlp ratio thu isnormatly obtainal bet\r,em tlre lighming ad switdliog irytlkq silfd{EltrtF of ih? rr|cmd insularionofsppalags (e.g, circuit-breakers, discunectiag swilchi, irstns@t,trasfur*roiiie-)- lhcy wt chosen ie.soch al*ay thar the insut?Irion design wilt be determincd mainly by.thc ability bf th r*Gta8l insulation towithstand thc switching impulse test volttges.
c.l [n a few extreme cascs, provision hru to be mde for a higber value of lighming imPulsc rvithsrand voltage'This higher vatue sho{tt bechosen from the sedes otstandard values glv.!+, in ltem f/ of Claug a5-
7A.:80
,:
t 7 -
CHAPTER V: GENERAL TESTING PROCEDURE
50. General
This chapter sets out the procedures lor switching and lightning impulse tests; also, where maintained, theprocedure tbr a I min power-frequency withstand test. The procedure for all other tests at power frequency (seeClause 39) shall be specified by the relevant Apparatus Committees.
Thc purpose of the tests in this chapter is to verify that an equiprnent complies with the rated withstandvoltages that determine its insulation level.
{ For each type of test and each type of equipment, the I E C Technical Committee dealing with high-voltage
{ testing techniques or the appropriate Apparatus Committee shall spccify the methods of detecting insulationtailures and the criteria of failure of the insulation durins the tesrs.
So far as is practicable, the tests shall be made in accordance with the following standards. Minor deviationsare permissible in keeping with the special characteristics of a parricular type of equipment, provided that thestandard insulation levels are not modified.
51. Switching and lightning impulse withstand tests
The switching and lightning impulse test voltages shall be exprcssed by rhe prospective peak value of thestandard impulses of positive and negative polarities. In the casc of cxternal insulation, ref€rcnce is made tostandard atmospheric conditions and, for wet tests, to standardized rain conditions in t E C Publication 60.
The standard lightning impulse has a front time of 1.2 us and a time-to-half-value of50 ps as specified in IECPublication 60.
'fhe standard switching impulse has a time-to-crest of 250 us and a tim€-to-half-value of 2500 Fs, as specifiedin lttc Publication 60. The Apparatus Com;nittees may specify a different test impuls€ shape where it is shownthat this is necessary to establish the lowest withstand of a particular apparatus or where the standard impulseshapE cannot be achieved for a particular test object with test equipment available at present-
ln the following, three types of imputse test are recommended: the statistical tests referred to in Sub-clausc 40.2 being detailed in Clauses 52 md 53 and the conventional test referred to in Sub-clause 210.3 beingdctailed in Clause 54. The choice for application to particular apparatus is a maater for the relevant ApparatusCorirmittee to decide upon within the general guide lines set forth in this standard.
52. 50% disruptive discharge test
ai This test is made at voltages above the rated impulse withstand voltage, using a procedure and a number ofimpulses which will establish the 507o disruptive discharge voltage of the insulation with acceptable accuracy.
From this, it can be demonstrated with a high degree of assurance that the statistical withstand voltage is, asrequired, not less than the rated impulse withstarid voltage. Because many disruptive discharges are required,this test is only suitable for essentially self-restoring insulations (see penultimat€ paragraph in Sub-clause 40.2).
ivol.. - Thc.e arc a oumbe. of proctdurcs availablc. and any of thcse may bc used providing rhat thc accu.acl of rhc dctcrminatioo iswithin ooc-halfof rhe srandard deviation wirh a cootidence level oi 95yo.
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6/ Switching and lightning 507o <lisruptive dischargc tes6 shall bc mqdc as typc r.s6.
c,l Srvitching 507o disruptive dischlrge tests shall be madc with thc cqurpmenl dry lor iodoor cquipment; urettests ilnd dry tests shall be rnrdc lbr outdoor equipment. For the latter, ho$cvcr, yberc it is known whichcondition, wea or dry, gives thc lowcr disruptive voltage, it is sulhcient ro rGst wirh thet coodition-
dJ Lightning 507o disruptive disclurge tests shall be made with thc cquiprml dry, fo( both indoor andoutdoor equipmcnt.
e) The equipment shall bc tcstul by applying standard switching and tighr"ing impubcs of positive andnegative polarities, except whcre it is known which polarity will give rhc lortr disruFirc dischargc voltagc, inwhich casc it is suflicient to tcst with that polarity.
| ) The 50% disruptive dischargc voltage for any of thc above conditions, &tcroird il aordancc with I ECPublication 60, shall be not lcss than l/(l-1.3 o)* times the rated impuhc rithred voltagc, whcrc 6 is therclativc standard deviation ol thc disruptive discharge voltage probabiliry br. Udcss othcnrise rmmmcndedby the relevant Apparatirs Cornmittee, the following values will be assuracd for ai insuladon:
- switchihg impulse tests: o - 0.06:'- lightning impulse tests: o = 0.03.
53- l'ifteen-impulse withstard test
a,l The test is made at the rated withstand voltage with 15 impulses of standard sb.pc- lf tlE number ofdisruptive dischargcs in the self-restoring insulation does not exceed two and if no disrupriw discharge occursin thc non=self-restoring insulation parts of the equipment, the insulation of thc equipmcnt shall be @nsideredto have passed thc tesr successlully.'fhis test demonstrates that the true statistical withstand voltage of the self-restoring insulation of thecquipment is not less than the rated withstand voltage. but with a degree of assurance coniiderably lower than
i;J;,ffl;l.,.13:::l'J:Ji:"#iT,li'*11,T*,u"" orthe Apprication Guide (rEC pubrication 7r-2).l),1 Switching and lightning impulse tests shall be made as type tests-rJ Switching impulse tests shlll be made with the equipment dry lor indoor equipment. Wet and dry testsshnll be made fbr outdoor equipmert. For the latter, however, where it is known which condition, w€t or dry,gives the lower disruptive discharge voltage, it is sufficient to test with ihat condition.r,1,) Lightning impulse tests shall be made with the equipment dry, for both indoor and outdoor equipment.e./ The equipment shatl be tested by applying switching and lightning impulses of the standard shapes ofpositive or negative polarity or both- The polarity or polarities to bc used shall tr specified by the relevaltApparatus Committee.
54. Conventionel impulse withstard test
aJ -lhis
test, so called bccause it applies to the conventional procedure of insulation co-ordination, rcstrictsthc numbcr of impulses in order to avoid possible damage to non-self-restoripg insulation. It is considercdsurtable for apparatus in which this aspect predominates, in accordance with Sub-clause .10.1.
This value of the 50% disruptive voltage corresponds for the rated impulse voltage to th€ reference wirhsrand probability ($%) in aGaussian dist r rbut ion
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br Tk conventional switching and lightning impulse withstand voltages are vcrified by means of swirching]nd ltehtntng impulse withstand tests in which the test voltage applied shall be equal to the ratcd impuls€rr thstand voltage in qucstion.
c' S*itching and lightning impulses shall be of the standard shapes and of positive or negative polarity orborh. The polariry or porarities to be used phal be specified by the rerevani App"ratus co-mltt ..c' Unless otherwise specified by the relevant Apparatus Committee, the withsiand test shall be performed by'p9i].,rng three impulses fior each polarity required- The test shall be considered satisfactory if no indication off'rrrgrc rs found, using the methods of detection specified by rhe relevant Apparatus Committec or the IEcTccjrnrcal Committee dealing with high-voltage testing techniques.j' $*rtching and lightning impulse withstand tests shall be made as type tests. They may also.be so66fied aslolrlirr rcsrs by the relevant Apparatus Committee..t lisn rdditional chopped-wave lightning impulse withstand test is considered for transformers and rcactors,rlr spccirrcarion fbr such tests shal be laid down by the relevant Apparatus committee-
SS lilprf duration power-frequency roltage withstand tests
o ' The I min power-frequency test voltage is specified as the r.m.s. value of the voltage which the insulationshail be capable or withstanding for I min. If the test voltage is non-sinusoidal, the peak value dividei i; Jtrr Jeemed to be the test voltage.
5 The dry power-frequency withstand test shall be made as a routine test. except where otherwise specified by:hc !-elevant Apparatus Commitiee.
:n.ril be mitde as a type test.
short duration power-fiequency tests include tests at frequencies up to a few hundred hertz and of shorter duration than I min suchf! tnduced voltage tests on transfiormers with gradd insulation (see IEC publication 76. power Transformers, and IEcPublicarion I 86. Voltage Transformers).
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