IEC TS 6081 5 4 Edition 1 0 201 6 1 0 TECHNICAL SPECIFICATION Selection and dimensioning of high voltage insulators intended for use in polluted conditions – Part 4 Insulators for d c systems IE C T S[.]
I E C TS 6081 5-4 ® Edition 201 6-1 TE CH N I CAL SPE CI FI CATI ON colour i n si de Sel ecti on an d d i m en si on i n g of h i g h -vo l tag e i n su l ato rs i n ten d ed for u se i n pol l u ted d i ti on s – IEC TS 6081 5-4:201 6-1 0(en) Part 4: I n su l ato rs fo r d c system s TH I S P U B L I C AT I O N I S C O P Y R I G H T P R O T E C T E D C o p yri g h t © I E C , G e n e v a , S w i t z e rl a n d All rights reserved Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either IEC or IEC's member National Committee in the country of the requester If you have any questions about IEC copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or your local IEC member National Committee for further information IEC Central Office 3, rue de Varembé CH-1 21 Geneva 20 Switzerland Tel.: +41 22 91 02 1 Fax: +41 22 91 03 00 info@iec.ch www.iec.ch Ab o u t th e I E C The International Electrotechnical Commission (I EC) is the leading global organization that prepares and publishes International Standards for all electrical, electronic and related technologies Ab o u t I E C p u b l i ca t i o n s The technical content of IEC publications is kept under constant review by the IEC Please make sure that you have the latest edition, a corrigenda or an amendment might have been published I E C Catal o g u e - websto re i ec ch /catal o g u e The stand-alone application for consulting the entire bibliographical information on IEC International Standards, Technical Specifications, Technical Reports and other documents Available for PC, Mac OS, Android Tablets and iPad I E C pu bl i cati on s search - www i ec ch /search pu b The advanced search enables to find IEC publications by a variety of criteria (reference number, text, technical committee,…) It also gives information on projects, replaced and withdrawn publications E l ectroped i a - www el ectro ped i a o rg The world's leading online dictionary of electronic and electrical terms containing 20 000 terms and definitions in English and French, with equivalent terms in additional languages Also known as the International Electrotechnical Vocabulary (IEV) online I E C G l o ssary - std i ec ch /g l o ssary 65 000 electrotechnical terminology entries in English and French extracted from the Terms and Definitions clause of IEC publications issued since 2002 Some entries have been collected from earlier publications of IEC TC 37, 77, 86 and CISPR I E C J u st Pu bl i sh ed - websto re i ec ch /j u stpu bl i sh ed Stay up to date on all new IEC publications Just Published details all new publications released Available online and also once a month by email I E C Cu stom er Servi ce Cen tre - websto re i ec ch /csc If you wish to give us your feedback on this publication or need further assistance, please contact the Customer Service Centre: csc@iec.ch I E C TS 6081 5-4 ® Edition 201 6-1 TE CH N I CAL SPE CI FI CATI ON colour i n si de Sel ecti on an d d i m en si o n i n g o f h i g h -vol tag e i n su l ators i n ten d ed for u se i n po l l u ted d i ti on s – Part 4: I n su l ators fo r d c system s INTERNATIONAL ELECTROTECHNICAL COMMISSION ICS 29.080.1 ISBN 978-2-8322-3704-5 Warn i n g ! M ake su re th a t yo u o btai n ed th i s pu bl i c ati o n fro m an au th ori zed d i stri bu to r ® Registered trademark of the International Electrotechnical Commission –2– I EC TS 6081 5-4:201 © I EC 201 CONTENTS FOREWORD I NTRODUCTI ON Scope N orm ati ve references Term s, defi n iti ons and abbrevi ated term s Term s and defi n i ti ons Abbreviated term s Pri nci pl es General Overal l desi gn process Materials 1 Site severity determ i nation I n put data d c poll uti on accum u lation correcti on : Kp Ch em ical com position of th e poll u ti on layer (Type A pollu ti on) Correctin g for NSDD (Type A pol lu ti on) Correctin g for CU R (Type A pol lu tion , cap an d pin i nsu lators) 6 Effect of diam eter on the pol luti on accum u lation Kd Correction for th e n u m ber of sim i lar insu l ators i n paral l el: Ks Determ i nation of th e reference d c site severity Determ i nation of th e reference d c U SCD Correction of th e RU SCD for each can didate insu l ator Correction for th e effect of di am eter on pol lu ti on withstan d perform ance C d Correction for altitu de Ca Determ i nation of th e requ ired U SCD for each can didate Ch eckin g the profi le param eters 1 General Alternatin g sh eds defin ed by sh ed overh an g Spaci n g versu s shed overhan g 20 M in im um distance between sheds 20 Creepag e distance versu s cl earance 21 Shed an gl e 22 Creepag e factor 22 1 Design verificati on 23 1 General 23 1 Operatin g experi ence 23 1 Laboratory testin g 23 Ann ex A (inform ati ve) H ydroph obicity transfer m ateri als 24 A Qu al itative fl ashover beh aviou r 24 Ann ex B (inform ati ve) Dependence of U SCD on poll u ti on severity 26 B Pol l uti on type A 26 B Pol l uti on Type B 28 Bibl i ographic References 29 I EC TS 6081 5-4:201 © I EC 201 –3– Figu re – Overall desi gn process for d c i nsu lati on – determ i nation of d c Si te Pol l uti on Severi ty Fig u re – Overall desi gn process for d c insu lati on – determ i nation of th e requ ired USCD dc for candidate i n su latin g sol uti ons 1 Fig u re – RUSCD dc as a function of d c si te pol l u ti on severi ty Fig u re – Correcti on for th e effect of di am eter on d c pol lu tion withstan d perform ance Fig u re A – Dependency of specific flash over vol tag e over du ctivity of an electrol yte (param eter: wettabil ity of surface) 24 Fig u re B – d c overhead l i nes Coll ected field experi ence on n on H TM in su lators (u ncoated g lass an d porcelain i nsu lators) 26 Fig u re B – d c overhead l i nes Coll ected field experi ence on H TM i nsu l ators (com posite li ne insu l ators) 27 Fig u re B – Com posite i nsu l ators: Exam pl e of th e i nfl uence of CF on U SCD (l aboratory tests) , see CI GRE Broch ure [1 ] for m ore details 28 Tabl e – Typical ran g es of Kp accordin g to cl im atic ditions –4– I EC TS 6081 5-4:201 © I EC 201 I NTERNATI ON AL ELECTROTECH NI CAL COMMI SSI ON SELECTION AND DIMENSIONING OF HIGH-VOLTAGE INSULATORS INTENDED FOR USE IN POLLUTED CONDITIONS – Part 4: Insulators for d.c systems FOREWORD ) Th e I n ternati on al El ectrotechn i cal Com m i ssi on (I EC) i s a worl d wi d e org an i zati on for stan dardi zati on com pri si n g al l n ati on al el ectrotech ni cal com m i ttees (I EC N ati onal Com m i ttees) The obj ect of I EC i s to prom ote i n ternati on al co-operati on on al l q uesti on s concern i n g stand ardi zati on i n th e el ectri cal an d el ectron i c fi el ds To thi s en d and i n addi ti on to other acti vi ti es, I EC pu bl i sh es I n ternati on al Stan dards, Tech n i cal Speci fi cati ons, Tech ni cal Reports, Pu bl i cl y Avai l abl e Speci fi cati ons (PAS) an d G u i des (h ereafter referred to as “I EC Publ i cati on (s) ”) Th ei r preparati on i s entru sted to tech n i cal com m i ttees; an y I EC N ati on al Com m i ttee i nterested i n th e su bj ect deal t wi th m ay parti ci pate i n th i s preparatory work I nternati on al , g overn m ental an d n on g overn m ental org an i zati ons l i si n g wi th th e I EC al so parti ci pate i n thi s preparati on I E C col l aborates cl osel y wi th th e I n tern ati onal Org an i zati on for Stan d ardi zati on (I SO) i n accordan ce wi th di ti on s determ i ned by ag reem en t between th e two org an i zati ons 2) The form al deci si on s or ag reem en ts of I EC on tech ni cal m atters express, as n earl y as possi bl e, an i n ternati on al sensu s of opi ni on on th e rel evan t subj ects si n ce each tech n i cal com m i ttee has representati on from al l i n terested I EC N ati on al Com m ittees 3) I EC Pu bl i cati ons h ave th e form of recom m en dati ons for i ntern ati on al u se an d are accepted by I EC N ati onal Com m i ttees i n th at sense Whi l e al l reasonabl e efforts are m ade to en sure that th e tech n i cal content of I EC Pu bl i cati on s i s accu rate, I EC cann ot be h el d responsi bl e for th e way i n whi ch th ey are used or for an y m i si n terpretati on by an y en d u ser 4) I n order to prom ote i n tern ati onal u n i form i ty, I EC Nati on al Com m i ttees u nd ertake to appl y I EC Pu bl i cati on s tran sparen tl y to the m axi m um extent possi bl e i n th ei r nati on al an d reg i on al publ i cati ons An y d i verg ence between an y I EC Pu bl i cati on and the correspon di ng n ati on al or reg i on al pu bl i cati on sh al l be cl earl y i n di cated i n the l atter 5) I EC i tsel f d oes n ot provi de an y attestati on of form i ty I n depen d en t certi fi cati on bodi es provi de conform i ty assessm ent servi ces and, i n som e areas, access to I EC m arks of form i ty I EC i s not respon si bl e for an y servi ces carri ed out by i nd epen den t certi fi cati on bodi es 6) Al l u sers shou l d en su re th at th ey h ave the l atest edi ti on of th i s publ i cati on 7) N o l i abi l i ty sh al l attach to I EC or i ts di rectors, em pl oyees, servan ts or ag ents i ncl u di n g i n di vi du al experts an d m em bers of i ts tech ni cal com m i ttees an d I EC N ati on al Com m i ttees for an y person al i n j u ry, property d am ag e or oth er dam ag e of an y n ature wh atsoever, wh eth er di rect or i ndi rect, or for costs (i ncl u d i n g l eg al fees) and expen ses ari si n g ou t of the publ i cati on , u se of, or rel i an ce u pon , thi s I EC P u bl i cati on or any other I EC Publ i cati on s 8) Atten ti on i s drawn to th e N orm ati ve referen ces ci ted i n th i s pu bl i cati on U se of th e referenced publ i cati on s i s i n di spen sabl e for the correct appl i cati on of thi s pu bl i cati on 9) Atten ti on i s drawn to th e possi bi l i ty that som e of th e el em en ts of th i s I EC Publ i cati on m ay be the su bj ect of patent ri g h ts I EC shal l n ot be hel d respon si bl e for i den ti fyi n g an y or al l su ch patent ri g hts The m ain task of I EC techn ical com m ittees is to prepare I ntern ati onal Stan dards I n excepti onal circum stances, a tech n ical com m ittee m ay propose th e publ icati on of a tech n ical specification wh en • th e requ ired su pport can not be obtain ed for th e pu bl ication of an I n tern ati onal Stan dard, despite repeated efforts, or • th e subj ect is stil l u nder tech n ical developm en t or wh ere, for an y oth er reason , th ere is th e future but no im m edi ate possi bi lity of an agreem ent on an I ntern ation al Standard Techn ical specificati ons are subj ect to review wi thi n th ree years of publicati on to decide wh eth er th ey can be tran sform ed in to I n tern ati onal Stan dards I EC 6081 5-4, wh ich is a tech n ical specification, has been prepared by tech n ical com m ittee 36: I nsu lators I EC TS 6081 5-4:201 © I EC 201 –5– The text of th is tech n ical specification is based on th e fol l owin g docum en ts: DTS Report on voti n g 36/382/DTS 36/390/RVC Fu l l inform ation on th e voti ng for the approval of this techn ical specificati on can be fou n d in th e report on votin g i ndicated in th e above table This docum en t h as been drafted i n accordance wi th th e I SO/I EC Directi ves, Part A l ist of al l parts in th e I EC 6081 series, publ i shed u nder the g en eral title dimensioning of high-voltage insulators intended for use in polluted conditions , on th e I EC websi te Selection and can be foun d The com m ittee h as deci ded that th e ten ts of th is docum en t wi ll rem ain u nch ang ed un til the stabi li ty date indicated on th e I EC websi te un der "http://webstore i ec ch " i n th e data rel ated to th e specific docum ent At th is date, the docum en t wi ll be • reconfi rm ed, • wi thdrawn , • repl aced by a revised edi ti on, or • am ended A bi l in g ual versi on of th is pu bl icati on m ay be issu ed at a l ater date IMPORTANT – The 'colour inside' logo on th e cover pag e of th is publ ication indicates that it contai ns colours which are consi dered to be u sefu l for the correct understanding of its contents Users shou ld therefore print this docum ent u sin g a colou r printer –6– I EC TS 6081 5-4:201 © I EC 201 I NTRODUCTI ON Work has been g oin g on in CI G RE C4 303 an d th e I EC to produce d c pol lu ti on desi g n g u ides th at represen t th e current state of the art The CI G RE work h as resu l ted in an H V d c Poll ution Appl ication G u i del i nes broch u re [1 ] and th e I EC work in th is fin al part of I EC 6081 – Selection and dimensioning of high-voltage insulators intended for use in polluted conditions – Part 4: Insulators for d.c systems The work represents a h ug e accum u lati on of pol l uti on perform ance kn owl edg e from various sources (both pu blish ed an d u n pu bl ish ed) n ever before collated i n to a sin g l e opus Contrary to th e parts of I EC 6081 deal in g with a c , this tech n ical specificati on covers both pol ym eric an d g l ass an d porcelain insu lators for d c system s in a si n gl e pu blication I t also covers h ybri d insu lators (th e ceram ic core is fu ll y covered by a pol ym er) NOTE Th e presen t docu m en t does n ot appl y to i n sul ators wi th coati ng s, du e to th e vari ety of coati n g s to be si dered Thi s m ay be reconsi dered at th e n ext revi si on of th i s techn i cal speci fi cati on , after g n i n g m ore knowl edg e an d experi ence and a better defi n i ti on of th e coati ng characteri sti cs an d requ i rem ents The approach for d c insu lator desi g n an d selecti on wi th respect to pol l uti on g iven in th is part is different to that used for a c Th e key differences are: • A sim pl ifi ed approach is presented wh ich is i nten ded for prelim inary desig n However, si nce u nder d c poll uti on bui l d-up an d its effects can be m ore severe th an u nder a c , the fin al desig n sh ou ld be based as m uch as possi bl e on a direct poll ution severity m easured un der d c for th e si te being stu died Equal l y direct eval uation of th e insu lators sel ected by th is process sh ou ld be considered (A statistical desi gn approach is avail able i n th e CI G RE g u i deli n es for d c poll ution [1 ]) ; • Two approaches are considered to estim ate poll ution severity: on e usi n g pri or d c site severity experience, th e other usin g site severity m easurem en ts on a c or u nen ergised i nsu lators; • Correcti on of si te severi ty for specific param eters th at h ave an i nfl u ence un der d c (e g pol l ution u n iform ity rati o, effect of di am eter on poll u tion accum ul ation , N SDD) are considered; • Direct transfer from corrected site pol lu tion severi ty to necessary U SCD wi thou t an y use of discrete site severity classes (as m ade in I EC 6081 Parts an d 3) ; • Recogn i ti on is m ade of th e im proved perform an ce of H ydrophobicity Transfer M aterials (HTM) as a practical solu ti on for m an y desi gns, notabl y at UH V, wh il e taking into accou nt poten tial h ydroph obici ty l oss; • I m portance of the influ en ce of al titu de; • Distinct diam eter correcti on for fl ash over perform ance Alth ou g h there is som e positi ve experi ence with vali dati on by testi n g of tradi tion al g lass and porcel ain insu lators, th e ful l translati on of such test resu l ts to service ditions is sti ll u n der consi deration An y such experience is m n l y l ackin g for com posite i n su lators, si nce an agreed stan dardised testin g procedure is n ot yet avai l abl e Th e probl em is accentu ated to porcel ain /g l ass as wel l com posite techn olog y by the conti nu in g rise in system voltag es wh ere over-desig n m ay resu lt i n u nreal istic insu l ator leng ths or h eig h ts H ence for this first edition th e verificati on of a chosen insu lator solu ti on by testing is entirel y subj ect to agreem ent For pol ym eric, n otabl y H TM, th e pol lu tion withstand m ay not be the on l y necessary desig n inform ation The desi g n stress sh ou ld be selected n ot on l y to avoid fl ashover, bu t also to assure a l im ited ag ei n g of th e insu l ators in servi ce Th is item is however ou t of the scope of th e presen t specification Appl ications with troll ed i n door en vironm ent are n ot inclu ded in the scope of th is docum en t I EC TS 6081 5-4:201 © I EC 201 –7– SELECTION AND DIMENSIONING OF HIGH-VOLTAGE INSULATORS INTENDED FOR USE IN POLLUTED CONDITIONS – Part 4: Insulators for d.c systems Scope This part of I EC 6081 5, wh ich is a Tech nical Specificati on, is applicabl e as first approach for th e determ ination of the requ ired d c U n ified Specific Creepag e Distance for i nsu l ators wi th respect to pol lu tion To avoid excessi ve over or un der desi gn , existin g operation experience shou l d be com pared and even tu all y additi on al appropriate tests m ay be perform ed by agreem ent between su ppl ier an d custom er I t is appl icable to: • G l ass and porcelai n insu lators; • Com posi te an d h ybrid insu lators wi th an HTM or n on-H TM h ou si n g This part of I EC 6081 g i ves specific g u i del i n es an d princi pl es to arri ve at an i nform ed judg em ent on the probabl e beh aviour of a g iven in su lator in certain pol l uti on en vironm ents The structure an d approach of th is part of I EC 6081 are sim il ar to th ose expl ain ed in Part , bu t adapted for th e speci fic issu es encou ntered with pol lu ted H V d c insu l ation The aim of th is Techn ical Specificati on is to gi ve the user sim pl ifi ed m eans to: • I dentify i ssu es specific to d c applications th at can affect the choice and desig n process; • Determ i ne th e equ ival en t d c Site Pol lu tion Severity (SPS) from measurements, correcting for electrostatic effects, diameter, pollution distribution and composition; • Determ i ne th e reference U SCD for differen t can didate insu latin g solu ti ons, takin g in to accou nt m ateri als, dim en si ons an d risk factors; • Eval u ate the su itabi l ity of differen t insu lator profil es; • Discuss th e appropri ate m ethods to verify th e perform ance of th e sel ected insu lators, if requ ired; This sim plified process i s in ten ded to be used when com parable operati onal experience from existing d c system is i n com plete or n ot avai l abl e The sim pl ified desi gn approach m ig ht resu lt i n a solu tion that exceeds th e ph ysical constrai nts of th e proj ect M ore refin ed approach es for such cases, e g using a statistical approach, are g iven in th e CI GRE d c gu idel ines [1 ] I n extrem e cases, e g for exception al l y severe si te ditions, al tern ative solu tions such as ch an g i ng th e lin e rou te, relocation of verter stations or usi n g an in door d c yard m ay n eed to be consi dered Normative references The foll owi n g docum ents are referred to i n th e text in such a way that som e or al l of their ten t constitutes requ irem ents of th is docum ent For dated references, on l y th e edition cited appl i es For u ndated references, th e latest edition of the referenced docum en t (incl udin g an y am endm en ts) appli es –8– I EC TS 6081 5-4:201 © I EC 201 I EC TS 61 245, Artificial pollution tests on high-voltage ceramic and glass insulators to be used on d.c systems Selection and dimensioning of high-voltage insulators intended for use in polluted conditions – Part 1: Definitions, information and general principles I EC TS 6081 5-1 : 2008, Selection and dimensioning of high-voltage insulators intended for use in polluted conditions – Part 2: Ceramic and glass insulators for a.c systems IEC TS 6081 5-2, Selection and dimensioning of high-voltage insulators intended for use in polluted conditions – Part 3: Polymer insulators for a.c systems IEC TS 6081 5-3, IEC TS 62073, 3.1 Guidance on the measurement of hydrophobicity of insulator surfaces Terms, definitions and abbreviated terms Terms and definitions For th e purposes of th is docum en t, th e term s and defi n iti ons gi ven i n I EC 60050-471 : 2007 an d the fol lowi n g appl y I SO an d I EC m ain tai n term in olog ical databases for u se i n stan dardi zati on at th e fol l owing addresses: • I EC Electropedi a: avai labl e at h ttp://www el ectropedia org / • I SO On lin e browsi n g platform : avai l abl e at http://www iso org/obp 3.1 Unified Specific Creepage Distance USCD creepage distance of an insu lator di vi ded by the m axim um operatin g voltag e across th e insu l ator I t is g en eral l y expressed i n m m /kV Note to entry: For d c the m axi m u m operati n g vol tag e i s th e d c system vol tag e as defi n ed i n I EC 60071 -5 3.1 Reference d.c Unified Specific Creepage Distance RUSCDdc valu e of U n ifi ed Specific Creepag e Distance for a d c system at a pol lu ti on si te determ in ed from ESDD an d N SDD valu es corrected for N SDD, CU R, etc accordin g to th is docum ent Note to entry: Th i s i s g en eral l y expressed i n m m /kV 3.1 Contamination Uniformity Ratio CUR rati o of th e pol l uti on deposi t densi ty on th e l ower surface of insu l ators to that of th e u pper surface Note to entry: Referred to as Pol l uti on U ni form i ty Rati o (P U R) i n som e cou ntri es Note to entry: Th i s i s referred to as Contam i nati on U n i form i ty Rati o i n som e coun tri es 3.1 Hydrophobicity Transfer Material HTM pol ym er m aterials wh ich exh i bit h ydroph obicity an d th e capabil ity to transfer h ydrophobicity to th e layer of pol lu ti on I EC TS 6081 5-4:201 © I EC 201 Cd – 18 – ,7 ,6 ,5 ,4 ,3 ,2 ,1 0, 0, 200 400 600 800 000 200 Averag e di am eter (m m ) IEC Key N on-H TM H TM wi th risk of parti al h ydroph obicity l oss H TM wi th no risk of h ydroph obicity l oss Figure – Correction for the effect of diameter on d.c pollution withstand performance For diam eters sm al ler th an 250 m m , th e correcti on factor agreem ent) [1 ] 9.2 Cd m ay be l ower than (su bj ect to Correction for altitude Ca I n d c it m ay becom e n ecessary to correct th e RU SCD for alti tu de by th e factor Ca NOTE Th i s su bj ect i s cu rren tl y u n der stud y by CI G RE D1 44 Un til th e CI G RE resu lts are avail able, th e proposed correcti on (based on I EC 60071 -1 ) is: Ca = e n( H ) 81 Where H is th e h eigh t above sea-level in m etres The current desig n practi ce in in dustry is to use H – 0 i nstead of H in th e above form u la and to on l y appl y the correcti on above 000 m Since th e altitu de correcti on m ay depen d on i nsul ator ch aracteristics an d pol l ution severi ty it is appl ied on a per can didate basis U nti l further i nform ation is avai lable, a valu e of 0, 35 is sug g ested for n This correcti on is also u sed to correct test resu lts obtained at h ig h alti tu de to th eir sea- l evel valu e 9.3 Determination of the required USCD for each candidate The requ ired U SCD (U SCD req ) for each candi date is determ in ed as fol lows: I EC TS 6081 5-4:201 © I EC 201 – 19 – USCDreq = RUSCD × Cd × Ca Checking the profile parameters 0.1 General Profi l e param eters are i m portan t for avoiding rai n bridg i n g, preventi ng l ocal sh ort circui tin g between sh eds, aiding self-clean i ng , avoi di n g pol lu tion “traps” and controll in g local electric field stress Stu d y of the effect of profil e param eters un der d c [1 ] h as revealed that som e param eters, notabl y Creepage Factor, can h ave a far g reater effect th an u nder a c This clause follows the ph il osoph y of I EC 6081 5-2 an d -3 H owever, i n these two techn ical specifications for a c , the inform ation was su pported by a sig n ifican t fi el d and laboratory experi ence, wh ich is m u ch less for d c case of th is docu m en t I t is to be clarified th at the present inform ation is a picture of th e insu lators curren tl y used, wi th out a suffici en t consol idated an d l on g field experience (see also th e case of insu lators wi th extrem el y hi g h creepag e factors) I n the fol l owing th e typical val u es currentl y used i n practice for each profil e param eter are g i ven , along with lim its if th ese are known An optim al profi l e can be i nfl uenced by too m an y param eters, so th e fol l owing can be used to select th e m ost appropri ate profi l e: • Consul t data from servi ce or test station experi ence to confirm th e perform ance of th e profile; • Fi nd an altern ati ve profi l e or i nsul ator techn ol og y; • Verify th e perform ance of th e profi le by appropri ate com parati ve testi n g (e g order of m erit com parison with other profiles) NOTE Th e fi g ures i n the Su bcl auses 1 to are i nten d ed sol el y to i l l u strate th e di m ensi on al param eters used to d eterm i n e profi l e param eters They are n ot i n ten d ed to represent opti m um sh ed shapes 0.2 Alternating sheds defined by shed overhang The classificati on of a profil e as bei n g al tern ati n g or n ot is based on difference i n shed overh ang m easured from the i nsul ator trunk to th e ti ps of th e largest an d sm allest sh eds p1 Shed overhang alone is not an important parameter, as long as the shed angle is not essentially flat (< 5°), or excessive (> 35°) The parameter is useful for defining uniform shed diameter profiles compared to alternating shed diameter profiles However larger values of difference in shed overhang may be beneficial for vertical insulators in ice, snow and heavy rain conditions p2 IEC N ot applicabl e to cap an d pin i nsu lators or m ulti-sh ed pin i nsu l ators Parameter Glass and Porcelain Insulators Composite & Hybrid Insulators, non-HTM Composite & Hybrid Insulators HTM Overh ang N on -al ternati n g : N on -al tern ati n g : Non -al ternati n g : p1 -p2 < 20 m m p1 -p2 < m m p1 -p2 < m m Al tern ati ng : Al tern ati n g : Al tern ati ng : p1 -p2 ≥ 20 m m p1 -p2 ≥ m m p1 -p2 ≥ m m – 20 – I EC TS 6081 5-4:201 © I EC 201 0.3 Spacing versus shed overhang p Spaci n g versu s sh ed overh an g is rati o of th e vertical distance between two sim ilar poi nts of successive sh eds of th e sam e diam eter (spaci ng ) an d the m axim um shed overh an g s s p IEC Un iform sh eds IEC Alternatin g sh eds This parameter, as well as those described in clauses 10.4, 10.5 and 10.6, involve shed-to-shed spacing and are important for the avoidance of “shorting out” creepage distance bridged by a shed-to-shed arc especially under heavy rain conditions N ot appl icabl e to cap an d pin i nsu l ators or m u ltished pi n insu lators Parameter Glass and Porcel ain Insulators Composite & H ybrid Insulators, non-HTM Composite & H ybrid Insulators HTM s/p U su al l y ≥ U su al l y ≥ U su al l y ≥ 0, 80 General l y never bel ow 0, General l y never General l y never bel ow 0, 85 bel ow 0, 70 0.4 Minimum distance between sheds c c is th e m inim um distance between adj acen t sheds of th e sam e di am eter, m easured by drawi n g a perpendicu lar li n e from the lowest point of rim of th e u pper sh ed to the n ext shed below of the sam e diam eter c IEC IEC c Minimum distance between sheds is one of the more important characteristics for insulator profile evaluation Shed-to-shed arcing for small shed spacing can negate any effort to improve performance by adding creepage distance N ot applicable to cap and pi n insu l ators or pi n i nsu l ators IEC Un iform sh eds Alternatin g sh eds I EC TS 6081 5-4:201 © I EC 201 Parameter – 21 – Glass and Porcelain Insulators c Composite & Hybrid Insulators, non-HTM Composite & Hybrid Insulators HTM Typi cal m i n i m um : 60 m m Typi cal m i n i m um : 45 m m (70 m m for i n su l ators wi th u n d erri bs) Rarel y l ess than 40 m m Rarel y l ess than 60 m m For averag e di am eters >250 m m rarel y l ess th an 55 m m * *N OTE On l y for su rg e arresters, posi ti ve servi ce records wi th c = 46 m m and averag e di am eters of up to 31 m m are avai l abl e 0.5 Creepage distance versus clearance l d is the straig h t air distan ce between two d l1 d1 l2 d2 IEC IEC Pl n sh eds d3 l d Parameter l /d d2 l2 l3 IEC Cap and pi n Creepage distance versus clearance is a more localised check of the risk of bridging by arcs when dry bands or uneven hydrophobicity occur It is also important in avoiding localised pollution build-up in deep and narrow sections of the profile l1 d1 poi nts on th e i nsu l ati n g part or between a poi nt on th e insu l ati n g part an d an other on a m etal part l is th e part of th e creepage distance m easu red between th e above two poi nts l/d is th e h ig h est ratio fou nd on an y section, for exam ple on the u n dersi de of a cap and pin insu lator IEC Al tern ati n g sh eds Glass and Porcelain Insulators Typi cal m axi m um : Rarel y m ore than 4, Composite & Hybrid Insulators, non-HTM Composite & Hybrid Insulators HTM Usual l y i n accordance wi th I EC TS 6081 5-3 – 22 – I EC TS 6081 5-4:201 © I EC 201 0.6 Shed angle For rou n ded sh eds, α i s m easu red at th e m i d -poi n t α Open profiles allow for more efficient natural washing of insulator surfaces, provided the shed angle is not so low as to impede excess water run-off N ot appl i cabl e to pi n i n su l ators IEC Parameter Composite & H ybrid Insulators, non-HTM Glass and Porcel ain Insulators Composite & H ybrid Insulators HTM Typi cal l y 0° to 25° α Rarel y m ore th an 30° For h ori zontal i n su l ators wi th α