I E C TR 62 0 -2 ® Edition 201 6-07 TE C H N I C AL RE P ORT colour in sid e H i g h -vol tag e d i rect cu rren t (H VD C ) s ys te m s – G u i d an ce to th e s peci fi cati on an d d es i g n eval u ati on of AC fi l ters – IEC TR 62001 -2:201 6-07(en) Part : Perform an ce Copyright International Electrotechnical Commission TH I S P U B L I C ATI O N I S C O P YRI G H T P RO TE C T E D C o p yri g h t © I E C , G e n e va , S w i tze 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 Abou t th e I E C The International Electrotechnical Commission (IEC) 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 c a ti 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 C atal og u e - webs tore i ec ch /catal og u e E l ectroped i a - www el ectroped i a org 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 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 pu bl i cati on s s earch - www i ec ch /s earch pu b I E C G l os s ary - s td i ec ch /g l os s ary 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variety of criteria (reference number, text, technical committee,…) It also gives information on projects, replaced and withdrawn publications 65 000 electrotechnical terminology entries in English and French extracted from the Terms and Definitions clause of IEC publications issued since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 P u bl i s h ed - webs tore i ec ch /j u s u bl i s h 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 Copyright International Electrotechnical Commission I E C C u s to m er S ervi ce C en tre - webs tore i ec ch /cs c 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 TR 62 0 -2 ® Edition 201 6-07 TE C H N I C AL RE P ORT colour in sid e H i g h -vol tag e d i rect cu rren t (H VD C ) s ys te m s – G u i d an ce to th e s peci fi cati on an d d es i g n eval u ati on of AC fi l ters – Part : Perform an ce INTERNATIONAL ELECTROTECHNICAL COMMISSION ICS 29.200 ISBN 978-2-8322-3540-9 Warn i n g ! M ake s u re th at you obtai n ed th i s pu bl i cati on from an au th ori zed d i s tri bu tor ® Registered trademark of the International Electrotechnical Commission Copyright International Electrotechnical Commission –2– I EC TR 62001 -2: 201 © I EC 201 CONTENTS FOREWORD I N TRODU CTI ON Scope N ormative references Current-based interference criteria General Determining the necessity for telephone interference limits 3 Defining telephone interference limits 1 3 General 1 3 Mechanisms of interference 1 3 N oise performance coordination levels 3 I nfluence of power transmission lines 3 Determination of I T limits for a specific project 3 Pre-existing harmonics and future growth 23 3 Recommendations for technical specifications 25 Consequences for filter design 26 Telephone infrastructure mitigation options 27 Experience and examples 28 General 28 Review of design requirements 28 Measured current levels of schemes in service 30 Example of actual telephone interference problems 31 Experience in China, showing no interference problems 33 Conclusions 33 Field measurements and verification 34 Overview 34 Equipment and subsystem tests 34 General 34 2 Fundamental frequency impedance and unbalance measurement 34 Frequency response curve 34 System tests 35 4 Measuring equipment 35 4 Overview 35 4 AC filter energization 36 4 Verification of the reactive power controller 36 4 Verification of the specified reactive power interchange 36 4 Verification of the harmonic performance 37 4 Verification of audible noise 39 I n-service measurements 41 General 41 I n-service tuning checks 41 On-line monitoring of tuning 41 Monitoring of I T performance 41 5 Measurements of pre-existing harmonic levels for design purposes 41 Annex A (informative) Voltage and current distortion – Telephone interference 42 A Voltage distortion limits for H V and EH V networks 42 Copyright International Electrotechnical Commission I EC TR 62001 -2: 201 © I EC 201 –3– General 42 A A Recommended limits for H V or EH V networks 43 A H armonic current in generators 45 A Causes of telephone interference 45 A Definition of telephone interference parameters 47 A Discussion 50 A Coupling mechanism from power-line current to telephone disturbance voltage 51 Annex B (informative) Example of induced noise calculation with Dubanton equations 52 B General 52 B Residual I T 52 B Balanced I T 53 Annex C (informative) I llustration of the benefit of including a TI F requirement in the technical specification 54 Annex D (informative) Specification of I T limits dependent on network impedance 56 Annex E (informative) The impact of AC network harmonic impedance and voltage level on the filter design necessary to fulfil an I T criterion 60 E General 60 E Assumptions and pre-conditions 61 E H armonic impedance of AC network 63 E Filter design 65 E Explanation of the difference in impact of relative and absolute performance criteria on required filter Mvar 67 Bibliography 68 Figure – Conversion factor from positive sequence current at the sending end to positive sequence current at the receiving end, and input impedance of a 230 kV line, 24 km long, 000 Ω -m 21 Figure – Conversion factor from positive sequence current to residual current, and input impedance of a 230 kV line, 24 km long, 000 Ω -m 21 Figure – Simple circuit for calculation of harmonic performance taking into account pre-existing harmonics 23 Figure – Converter variables for harmonic performance tests 37 Figure – Example of measurements made during a ramp of the converters 40 Figure A – Contributions of harmonic voltages at different voltage levels in a simple network 42 Figure A – C-message and psophometric weighting factors 46 Figure A – Flow-chart describing the basic telephone interference mechanism 51 Figure D – Simplification of the detailed network used for telephone interference simulation 56 Figure D – I nduced voltage in telephone circuit vs network impedance, for unitary current injected 57 Figure D – I T limits as defined for different network impedances 58 Figure E – Converter harmonics un-weighted (A) and I T weighted (kA) on 240 kV base 62 Figure E – Converter Mvar absorption versus load 63 Figure E – I mpedance sector diagram and RL-equivalent circuit 64 Figure E – Simplified converter/system topology 64 Figure E – Simplified circuit including overhead transmission line 65 Copyright International Electrotechnical Commission –4– I EC TR 62001 -2: 201 © I EC 201 Table – Performance thresholds for metallic noise Table – Performance thresholds for longitudinal noise Table – Performance thresholds for balance Table – I llustrative maximum telephone line length to achieve the N orth American recommended longitudinal Ng level, as a function of balanced I T level, earth resistivity and separation distance Table – I llustrative maximum telephone line length to achieve the N orth American recommended longitudinal Ng level as a function of residual I T level, earth resistivity and separation distance Table – Some H VDC schemes – Specified telephone interference criteria 29 Table – Measured 95 % values of TH FF and Ipe of a 600 MW scheme (3 phases) 31 Table – Measured 95 % values of TH FF and Ipe of a 300 MW scheme (3 phases) 31 Table A – Voltage distortion limits from I EEE 51 9-1 992 43 Table A – Compatibility levels for harmonic voltages (in percent of the nominal voltage) in LV and MV power systems [based on Table of I EC TR 61 000-3-6: 2008] 44 Table A – I ndicative values of planning levels for harmonic voltages in H V and EH V power systems [based on Table of I EC TR 61 000-3-6: 2008] 44 Table E – Required total amount of installed filter Mvars to meet a I T limit of 25 kA for 600 MW transmission 61 Copyright International Electrotechnical Commission I EC TR 62001 -2: 201 © I EC 201 –5– I NTERNATI ONAL ELECTROTECHNI CAL COMMI SSI ON H I G H - VO L T AG E D I RE C T C U RRE N T ( H VD C ) S YS T E M S – G U I D AN C E T O T H E S P E C I F I C AT I O N DESIGN E VAL U AT I O N P a rt : AN D O F AC F I L T E RS – P e rfo rm a n c e FOREWORD ) The I ntern ati on al El ectrotechni cal Comm i ssi on (I EC) i s a worl d wi d e organi zati on for stan d ard i zati on com pri si ng al l nati onal el ectrotech ni cal commi ttees (I EC N ati onal Com mi ttees) The obj ect of I EC i s to promote i ntern ati on al co-operati on on al l q u esti ons concerni ng stand ard i zation in the el ectri cal and el ectroni c fi el d s To th i s end and i n ad d i ti on to other acti vi ti es, I EC pu bl i shes I nternati onal Stand ard s, Techni cal Speci fi cati ons, Techni cal Reports, Pu bl i cl y Avai l abl e Speci fi cati on s (PAS) and Gu i d es (hereafter referred to as “I EC Pu bl icati on(s)”) Thei r preparati on i s entru sted to techni cal commi ttees; any I EC N ati onal Com mi ttee i n terested i n the su bj ect d eal t wi th may parti ci pate i n th i s preparatory work I n ternati onal , g overnmental and non govern mental organ izati ons l i si ng wi th the I EC al so parti ci pate i n thi s preparation I EC col l aborates cl osel y wi th th e I nternational Organi zati on for Stand ard i zati on (I SO) i n accord ance with cond i ti ons d etermi ned by ag reement between the two organ i zati ons 2) The formal d ecisi ons or ag reements of I EC on techn ical matters express, as nearl y as possi bl e, an i ntern ati on al sensu s of opi n i on on the rel evan t su bj ects si n ce each techni cal commi ttee has representati on from al l i nterested I EC N ati onal Com mi ttees 3) I EC Pu bl i cati ons h ave the form of recomm end ati ons for i nternati onal u se an d are accepted by I EC N ati onal Com mi ttees i n th at sense Wh i l e al l reason abl e efforts are mad e to ensu re that the techn ical content of I EC Pu bl i cati ons i s accu rate, I EC can not be hel d respon si ble for the way i n wh i ch th ey are u sed or for an y mi si nterpretati on by any end u ser 4) I n ord er to promote i ntern ati onal u ni form ity, I EC N ati on al Commi ttees u n d ertake to appl y I EC Pu bl i cati on s transparen tl y to the maxi mu m extent possi bl e i n thei r nati onal and regi onal pu bl i cati ons Any d i vergence between any I EC Pu bl i cation and the correspond i ng nati onal or regi on al pu bl i cati on shal l be cl earl y i nd i cated i n the l atter 5) I EC i tsel f d oes n ot provi d e an y attestation of conformi ty I nd epen d ent certi fi cati on bod i es provi d e conformi ty assessment servi ces and , i n some areas, access to I EC marks of formi ty I EC i s not responsi bl e for an y servi ces carri ed ou t by i nd epend ent certi fi cati on bod i es 6) Al l u sers sh ou l d ensu re that th ey have th e l atest ed i ti on of th i s pu bl i cati on 7) N o l i abi l i ty sh al l attach to I EC or i ts d i rectors, empl oyees, servants or agen ts in clu d i ng i nd ivi d u al experts and mem bers of i ts tech ni cal com mi ttees an d I EC N ati onal Comm i ttees for any personal i n j u ry, property d amage or other d amage of an y natu re wh atsoever, whether d i rect or i nd i rect, or for costs (i ncl u d i ng l eg al fees) and expenses ari si ng ou t of the pu bl i cati on, u se of, or reli ance u pon, thi s I EC Pu bl i cati on or any oth er I EC Pu bl icati ons 8) Attention i s d rawn to the N orm ati ve references ci ted in thi s pu bl i cati on U se of the referenced pu bl i cati ons i s i nd i spensabl e for the correct appl i cati on of thi s pu bl i cati on 9) Attenti on i s d rawn to the possi bi l i ty that some of the el ements of thi s I EC Pu bl i cati on may be the su bj ect of patent ri g hts I EC shal l n ot be h el d responsi bl e for i d enti fyi ng any or al l su ch patent ri ghts The main task of I EC technical committees is to prepare I nternational Standards H owever, a technical committee may propose the publication of a Technical Report when it has collected data of a different kind from that which is normally published as an I nternational Standard, for example "state of the art" I EC TR 62001 -2, which is a Technical Report, has been prepared by subcommittee 22F: Power electronics for electrical transmission and distribution systems, of I EC technical committee 22: Power electronic systems and equipment This first edition of I EC TR 62001 -2, together with I EC TR 62001 -1 , I EC TR 62001 -3 and I EC TR 62001 -4, cancels and replaces I EC TR 62001 published in 2009 This edition constitutes a technical revision Copyright International Electrotechnical Commission –6– I EC TR 62001 -2: 201 © I EC 201 This edition includes the following significant technical changes with respect to I EC TR 62001 : a) b) c) d) e) expanded and supplemented Clause 9, and Annex B; new Clause on current-based interference criteria; new annexes on induced noise calculation with Dubanton equations; addition of a TI F requirement in a technical specification, specification of I T limits dependent on network impedance and on the impact of AC network harmonic impedance; and f) specification of voltage level on the filter design necessary to fulfil an I T criterion The text of this Technical Report is based on the following documents: En q u i ry d raft Report on voti ng 22F/41 0/DTR 22F/41 4/RVC Full information on the voting for the approval of this document can be found in the report on voting indicated in the above table This publication has been drafted in accordance with the I SO/I EC Directives, Part High-voltage direct current (HVDC) systems – Guidance to the specification and design evaluation of AC filters , A list of all parts in the I EC 62001 series, published under the general title can be found on the I EC website The committee has decided that the contents of this publication will remain unchanged until the stability date indicated on the I EC web site under "http: //webstore iec ch" in the data related to the specific publication At this date, the publication will be • • • • reconfirmed, withdrawn, replaced by a revised edition, or amended A bilingual version of this publication may be issued at a later date I M P O RT AN T – T h e ' c o l o u r i n s i d e ' l o g o o n th a t it co n ta i n s u n d e rs t a n d i n g c o l o u r p ri n t e r Copyright International Electrotechnical Commission of c o l o u rs i ts wh i ch co n te n ts a re U s e rs t h e c o ve r p a g e o f t h i s p u b l i c a t i o n c o n s i d e re d sh ou l d to t h e re fo re be u s e fu l p ri n t th i s fo r i n d i ca te s th e d ocu m en t c o rre c t using a I EC TR 62001 -2: 201 © I EC 201 –7– I NTRODUCTI ON The I EC 62001 series is structured in four parts: Part – Overview This part concerns specifications of AC filters for high-voltage direct current (H VDC) systems with line-commutated converters, permissible distortion limits, harmonic generation, filter arrangements, filter performance calculation, filter switching and reactive power management and customer specified parameters and requirements Part – Performance This part deals with current-based interference criteria, design issues and special applications, field measurements and verification Part – Modelling This part addresses the harmonic interaction across converters, pre-existing harmonics, AC network impedance modelling, simulation of AC filter performance Part – Equipment This part concerns steady-state and transient ratings of AC filters and their components, power losses, audible noise, design issues and special applications, filter protection, audible noise, seismic requirements, equipment design and test parameters Copyright International Electrotechnical Commission –8– I EC TR 62001 -2: 201 © I EC 201 H I G H - VO L T AG E D I RE C T C U RRE N T ( H VD C ) S YS T E M S – G U I D AN C E T O T H E S P E C I F I C AT I O N DESIGN E VAL U AT I O N P a rt : AN D O F AC F I L T E RS – P e rfo rm a n c e Scope This part of I EC 62001 , which is a Technical Report, provides guidance on the performance aspects and verification of performance of harmonic filters The scope of this document covers AC side filtering for the frequency range of interest in terms of harmonic distortion and audible frequency disturbances I t excludes filters designed to be effective in the PLC and radio interference spectra This document concerns the "conventional" AC filter technology and line-commutated highvoltage direct current (H VDC) converters N o rm a t i v e re fe re n c e s The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document For dated references, only the edition cited applies For undated references, the latest edition of the referenced document (including any amendments) applies High-voltage direct current (HVDC) systems – Guidebook to the specification and design evaluation of AC filters – Part 1: Overview I EC TR 62001 -1 : 201 6, I EC TR 62001 -4: 201 6, High-voltage direct current (HVDC) systems – Guidebook to the specification and design evaluation of AC filters – Part 4: Equipment 3 C u rre n t - b a s e d i n t e rfe re n c e c ri t e ri a G e n e l Permissible distortion limits and performance measures for limiting telephone interference, such as telephone interference factor (TI F), product of RMS current (A) and TI F (I T), (the definitions of these criteria are shown in 3 and Clause A 4), are discussed in details and summarized in I EC TR 62001 -1 : 201 6, Clause Where these measures are applied with strict limits, particularly current-based criteria such as I T, they can be a decisive or limiting factor for filter design Thus, these measures can directly affect the costs of filters and the concomitant effects of larger filters (extra station space, shunt reactors to compensate excess reactive power produced by the filters, etc ) On the other hand, a few H VDC projects have experienced high levels of telephone interference that caused problems during commissioning and early operation Reference [1 ] considers basic interference criteria, defines telephone interference limits and discusses consequences of the telephone interference for filter design Because these criteria, based on psophometric or C-message weighting of harmonics, are specific to evaluation of noise induced on telephone circuits electromagnetically coupled to AC lines, they should only be specified where significant coupling between AC transmission _ N u mbers i n sq u are brackets refer to the Bi bl i ograph y Copyright International Electrotechnical Commission – 58 – I EC TR 62001 -2: 201 © I EC 201 is shown in Figure and Figure where the current at the receiving end of a transmission line is dependent on the sending end impedance Therefore, to maintain the induced voltage at the acceptable level, for higher network impedances the permitted maximum I T is reduced A limit expressed as a weighted voltage, for example TI F, would tend to reproduce this behaviour, i e the higher the impedance, the lower the current H owever, for a given induced voltage level in telephone lines, the range of network impedance is rather large so that a limit expressed in TI F would be unnecessarily restrictive for many network configurations Considering that it is easier to filter effectively when connected to a network with a high harmonic impedance, a requirement that would be dependent on network impedance magnitude would probably result in a cheaper filter design For instance, preliminary studies showed that at the 1 th harmonic, an I T of 20 000 A would be required for the worst cases that happen for system impedances higher than around 30 Ω For system impedance higher than 82 Ω , the limit would be 26 000 A I n addition, for an impedance magnitude of 42 Ω and above, the limit would be 40 000 A and finally, for the minimum impedance and above, the limit would be 80 000 A Figure D shows the different limits associated with their specific impedance locus I T l i mi ts (kA) accord i ng to d i fferent n etwork i mped ances 250 200 50 Reactan ce (j * Ω ) 00 50 80 40 26 20 –50 –1 00 –1 50 –200 –250 50 00 50 Resi stan ce ( Ω ) 200 IEC F i g u re D – I T l i m i t s a s d e fi n e d fo r d i ffe re n t n e t w o rk i m p e d a n c e s Knowing for instance that an I T of 20 kA at the 1 th produces the same induced voltage as an I T of 80 kA when applied to their specific impedance loci, these values can be normalized to one reference value in order to simplify the calculations by the manufacturer They can also be normalized between the different characteristic harmonics to combine them in a total I T value representative of the expected induced voltage in the telephone lines Copyright International Electrotechnical Commission I EC TR 62001 -2: 201 © I EC 201 – 59 – Such a specification method was considered for the project in question, however the project was delayed and the specification studies postponed These results are given as information hoping that they can be used in some way to improve the specification of telephone interference I t is anticipated that such a method is not as conservative as a model with transmission line terminated by an large impedance locus, for example, because in the latter case there is a high probability of hitting severe combinations of transmission line and remote network impedances, whereas the proposed method considers only actual network conditions, with some tolerance This method could be used where preliminary studies show a convenient dependency between induced voltage and network impedance Copyright International Electrotechnical Commission – 60 – I EC TR 62001 -2: 201 © I EC 201 An n e x E (informative) T h e i m p a c t o f AC n e t w o rk h a rm o n i c i m p e d a n c e a n d v o l t a g e l e v e l o n t h e fi l t e r d e s i g n n e c e s s a ry t o fu l fi l a n I T c ri t e ri o n E.1 G e n e l This annex makes an assessment of the amount of filtering (Mvar) required to limit the I T-product to 25 kA for a line commutated converter, as calculated for different system voltages and different ways of representing AC network harmonic impedance The results are first summarized below in Table E , and then a more detailed description of the modelling and filter design is given The example is based on a 600 MW converter connected to a system with a short circuit level between to 20 times rated power, system voltage of 240 kV or 500 kV and system frequency of 60 H z All designs shown in the table contain shunt filters tuned to all characteristic harmonics, i e 1 th , th , … 36 th and 48 th I n the calculations, they are represented by single tuned band-pass and high-pass filters, although in an actual scheme they would be implemented as combinations of double or triple tuned branches in order to optimise capacitor bank designs The filter Mvar requirements as shown in Table E are very high compared to a design with no I T requirement (but a TI F limit of 40), which would have fewer tuned filter branches and would require an installed Mvar of only about 25 % of rated power I n addition, the Mvar distribution between tuning frequencies is such that an actual design would probably require a shunt reactor to restrict Mvar surplus for almost all designs I n some cases, the degree of installed Mvar would probably justify the use of series filters and possibly self-tuned or active filters For a given converter rating, one would typically expect the degree of installed Mvar to be independent of the AC bus voltage But comparing the 240 kV and 500 kV designs with each other there is a significant difference The reason for this is that the I T criterion is an absolute measure, in terms of amperes, and not a measure relative to fundamental voltage, such as voltage distortion, TI F etc (see example at the end of this Annex E) For the 500 kV filters, the effect of an overhead line, of varying length, between filters and network is also taken into account I n brief, the outcome of this assessment is that more filters are required, but to what degree will depend on the line length A simplified explanation is that if the line is terminated by a sector impedance, the complete circuit (line + sector) represent a low impedance path, such that even if there is a low degree of residual voltage across the filter, it will cause a high current to flow into the line The following harmonic impedance models are used: ) worst case impedance for individual harmonic selected from a generalised sector impedance such as discussed in I EC TR 62001 -1 : 201 6, , and frequently used in design of AC filters for H VDC schemes, though typically with requirements of TI F rather than I T; 2) a resistance in parallel with an inductance, corresponding to the positive sequence surge impedance of the two incoming AC lines and the short circuit impedance of the network See discussion in I EC TR 62001 -1 : 201 6, ; 3) the worst case impedance from the sector for the two harmonics that gives the highest I T product and the RL-equivalent for remaining harmonics; 4) worst case impedance from sector impedance for the two harmonics that gives the highest I T-product, plus RL-equivalent for other harmonics, with an explicit modelled transmission line in between PCC and filter bus Copyright International Electrotechnical Commission I EC TR 62001 -2: 201 © I EC 201 – 61 – The results are summarized in Table D , and the calculations are described in detail in the following sections Tabl e E – R e q u i re d t o t a l a m o u n t o f i n s t a l l e d fi l t e r M va rs t o m e e t a I T l i m i t o f k A fo r 0 M W t n s m i s s i o n R e q u i re d as fi l t e r M va r % o f te d 40 kV R e m a rk power 50 kV 1) 73 % 42 % Worst case i mped ance 2) 28 % 24 % RL eq u i valent , sh u nt reactor n ot req u i red 3) 53 % 33 % Worst case i mped ance harmoni cs 4) 52 % Worst case im ped ance harmoni cs, km 4) 58 % Worst case im ped ance harmoni cs, 20 km 4) 45 % Worst case im ped ance harmoni cs, 40 km The assumptions and preconditions of the example are quite arbitrarily selected (though not unrealistic); however, no detailed optimisation of the designs are made I n other words, the purpose of the examples is not to give any firm absolute guidance in how to design filters nor on how preferred filter designs should look, it is simply to demonstrate that if I T requirements are given they are likely to be decisive and to emphasize that the AC network impedance should be very carefully modelled to avoid unduly costly/complex filter schemes E.2 As s u m p t i o n s a n d p re - c o n d i t i o n s The convertor is a 600 MW monopole, with dx of %, operating with firing angle ( α ) between ° and ° For simplicity, only characteristic harmonics are considered (1 th to 49 th ), that is effects of any unbalances, asymmetries, etc are not considered The convertor is assumed to be connected to a network with • • a short circuit ratio assumed to be between to 20, (1 800 MVA to 000 MVA), and AC system voltage of 240 kV or 500 kV ( ± %) and a fundamental frequency of 60 H z For simplicity, filter detuning is considered by applying an equivalent frequency deviation of ± % ( ± 0, H z), which is rather small and would correspond to a frequency excursion in the range of ± 0, H z or less, thus allowing approximately ± 0, H z equivalent to account for filter component tolerances The plots in Figure E give the converter harmonic current generation (in amperes) versus load (in pu), both unweighted and also with I T weighting applied, at system voltage of 240 kV For 500 kV, the currents will be decreased by 240 ÷ 500 Figure E shows a plot giving converter Mvar absorption versus load (in %) Assuming a zero deficit at nominal load, a total of about 300 Mvar in installed filters and shunt banks is a reasonable assumption Copyright International Electrotechnical Commission – 62 – I EC TR 62001 -2: 201 © I EC 201 240 kV 20 11 13 23 25 35 37 47 49 00 80 I h' A 60 40 20 0 0, 0, 0, 0, 1 ,2 P D' pu 300 × I h ' kA 50 240 kV 11 13 23 25 35 37 47 49 00 × f1 × 200 h C m essag e 250 IEC 50 0 0, 0, 0, P D' pu F i g u re E Copyright International Electrotechnical Commission – C o n v e rt e r h a rm o n i c s u n - w e i g h t e d 0, 1 ,2 IEC ( A) a n d I T w e i g h te d ( kA) o n 40 kV b a s e I EC TR 62001 -2: 201 © I EC 201 – 63 – 400 M var 300 α = 12 α = 18 200 00 0 10 20 30 40 50 60 70 80 90 00 110 20 DC power (%) IEC Figure E.2 – Converter Mvar absorption versus load E.3 Harmonic impedance of AC network The different assumptions regarding harmonic impedance are briefly discussed below The impedance sector in Figure E defines the network impedance as having the following × n ≤ Zn ≤ Z1 × n , where Z1 is the fundamental frequency short circuit impedance H ere, Z1 varies between 4, Ω to 32, Ω and 20, Ω to 38, Ω • Magnitude within Z1 • mi n max for 240 kV and 500 kV respectively Phase angle of ± 70 ° (as only characteristic harmonics are studied) I n I EC TR 62001 -1 : 201 6, 6, it is proposed that I T could be calculated with a phase equivalent impedance modelled by a parallel connection of a resistance and a reactance The reactance can be calculated from the fault level produced by the lines being modelled by this equivalent, and the parallel resistance can be produced by the positive sequence surge impedances of these lines H ere this RL-equivalent is selected to have an inductance of 2, mH and 55, mH for 240 kV and 500 kV respectively The feeding line is assumed to be a double circuit, with a surge impedance of 276/2 Ω and 260/2 Ω for 240 kV and 500 kV respectively Copyright International Electrotechnical Commission – 64 – I EC TR 62001 -2: 201 © I EC 201 jX Zm i n Φ + R Φ − IEC Z m ax IEC I mpedance sector RL-equivalent F i g u re E – I m p e d a n c e s e c t o r d i a g m a n d R L - e q u i va l e n t c i rc u i t For the typical topology of a line commutated converter (see Figure E 4), the worst case impedance of a sector is determined from IN = IC ZF ZF + ZN impedance ( ZN ) of a sector will be that which minimises ZN That is the worst case network Z F + ZN ZF IEC F i g u re E – S i m p l i fi e d c o n ve rt e r/s ys t e m t o p o l o g y To select the worst case impedance for each individual harmonic is usually considered to be too pessimistic an assumption As a compromise between this and an RL-equivalent for all harmonics, design requirements can be limited to use the worst case impedance for the one or two harmonic(s) that give the highest value of I T and using an RL-equivalent for the remaining harmonics Which harmonics to select is best demonstrated by an example Let x h and y h be the weighted harmonic components as calculated for the RL-equivalent and for the worst case impedance respectively Though not necessarily the case, it is reasonable to assume that x h ≤ y h , then the maximum I T product is given by IT = ∑ xh2 + Copyright International Electrotechnical Commission ( i2 − i2 ) + ( 2j − 2j ) y x y x (E ) I EC TR 62001 -2: 201 © I EC 201 – 65 – where harmonic i and j are those which give the maximum difference between the squares of individual harmonic components I f, as in Figure E 5, there is an impedance between the network sector and the filter/converter bus, the network impedance sector, in theory, would need to be mapped across the impedance, in order to maximise the current into the mapped network impedance H owever, for practical reasons, the worst case impedance of ZN is selected instead such that the current into the sector impedance is maximised, i e the sum of ZN and Z´ is minimised, Z´ being the impedance as seen from the network impedance node towards the converter and filter (by a positive or negative sequence harmonic voltage/current) Z´ OHTL ZN ZF IEC Figure E.5 – Simplified circuit including overhead transmission line E.4 Filter design Filter designs for the 500 kV and 240 kV systems are now described under the four different assumptions regarding network representation: 1) Worst case sector impedance for each individual harmonic The total need for installed filtering Mvar can be assessed by assuming that no individual harmonic should contribute with more than about 25 ≈ kA to the I T product over the complete load range, the underlying assumption being that the eight characteristic harmonics (up to h48 ) will be the dominant contributors to I T To achieve harmonic performance on a 500 kV system will require about 250 Mvar of filters realised as sharply tuned band pass filters at 1 th , th , 23 rd and 25 th harmonic and also tuned high pass filters at 36 th and 48 th harmonic Given that the converter-generated individual harmonic current maxima will occur at different load levels, the filters can be optimised and the total Mvar can be brought down to about 21 Mvar About two thirds of the total is required to manage 1 th and th harmonic and the rest for the 23 rd and higher order harmonics I n other words, the filter scheme would become complex when realised, with either many small different banks or fewer, larger banks plus shunt reactors to restrict Mvar surplus For the 240 kV alternative, the harmonic currents will increase with the decrease in voltage and almost 2, times more of Mvar would be required, i e 440 Mvar, which would be unrealistic for most 600 MW schemes, and a series filter, self-tuned filters or an active filter would most probably be required Copyright International Electrotechnical Commission – 66 – 2) I EC TR 62001 -2: 201 © I EC 201 RL-Equivalent for each individual harmonic For the 500 kV system, a design with fewer tuned branches is possible, for example band pass branches at 1 th and th and high pass branches at 24 th and 36 th harmonics, but it would still require about 21 Mvar and most likely shunt reactors to limit Mvar surplus at low loads H owever, if a design with branches tuned to 1 th , th , 23 rd , 25 th , 36 th and 48 th harmonic is used, a total of about 45 Mvar is sufficient About 00 Mvar, or two thirds, are required for 1 th and th harmonic and if a bank size of about 00 Mvar would be acceptable, a design without a shunt reactor should be possible For the 240 kV system, a total of about 65 Mvar is required, divided into sharply tuned band pass branches tuned to 1 th , th , 23 rd and 25 th harmonic and a high pass branch tuned to 36 th harmonic The 1 th and th harmonics require about 75 Mvar of the total and, as above, a design without a shunt reactor should be possible 3) Worst case sector impedance for two harmonics and remaining from RL-equivalent As discussed previously, to assume that worst case impedance would occur simultaneously for each and every individual harmonic is a pessimistic assumption To assume a given (fixed) impedance for each and every individual harmonic can be considered to give little room for erroneous assumptions Measures such as used for TI F and TH D consider the worst case impedance for the two harmonic(s) that give the highest value of I T and use an RLequivalent for remaining harmonics At first sight, such a requirement is difficult for a filter designer, given that when the first pair th of "worst case" harmonic is filtered out, for example 1 th and , the next pair becomes dominant and with that filtered out the following next pair dominant, etc H owever, as a first assumption, the limit of each harmonic "worst-case-impedance-value" of about 25 kA +κ can be used, where the additional harmonic(s) ( κ) is added to give a design margin for the additional values With κ between and 2, the individual harmonic "worst-case-impedancevalue" should be below kA to kA For the 500 kV system, the required amount of filters is about 200 Mvar, and band pass branches tuned to 1 th , th , 23 rd and 25 th harmonic and high-pass branches tuned to 36th and 48 th will be required This relaxation in the requirement for network representation therefore did not give a significant simplification of the design One advantage is that the design would probably not require a shunt reactor For the 240 kV system, the required amount of filters is about 320 Mvar, and branches tuned as for the 500 kV design To restrict Mvar surplus would require shunt reactors 4) Worst case sector impedance for two harmonics and remaining from RL-circuit, with intermediate transmission line For the 500 kV system, the configuration with the H VDC station feeding a transmission line of km, 20 km and 40 km length is evaluated The line is terminated with worst case sector and RL-equivalent as above km line: 20 km line: 40 km line: Copyright International Electrotechnical Commission About 31 Mvar will be required with the same topology as (3) above About two thirds are allocated to 1 th and th harmonic With the same filter but with a line length of 20 km, the increase in I T is about 30 % due to 1 th and th harmonics About 348 Mvar would be required, of which 78 % is allocated to 1 th and th harmonics With increasing line length, the sensitivity to 1 th and th harmonic moves and instead will occur at 35 th harmonic About 270 Mvar in total is required, of which about 58 % is allocated to 1 th and th harmonic I EC TR 62001 -2: 201 © I EC 201 – 67 – For all three cases, a shunt reactor would be required to limit Mvar surplus E.5 Explanation of the difference in impact of relative and absolute performance criteria on required filter Mvar H ere the term "absolute" means based on a physical quantity (amps or volts) whereas "relative" means as a fraction or percentage of the fundamental frequency quantity The above examples show a significant difference between the 240 kV and the 500 kV systems in terms of the filtering Mvar required to be installed in order to satisfy an absolute limit such as I T This is in contrast to what would be expected for a filter design made to satisfy a limit of TI F or other relative measure The following equations are included to explain why this should be the case With reference to Figure D 5, the voltage at, and the current into the AC network can be written as: ZF ZN Un = IC In = IC For a different voltage level, U´ , and ZF + ZN (E 2) ZF (E 3) ZF + ZN instead of U, U , • the converter (source) current will be: IC′ • the filter impedance, with the same Mvar, will be: • the network impedance will be • at each frequency as determined by the network-frequency resonance and the voltage distortion will remain identical: Un′ U′ • = U′ IC ′ = IC U′ ′ = ZN ZN U U′ U′ ZF′ = ZF U , , where this is the critical network impedance ′ ′ U ZF ZN U′ ZF ZN Un U′ = = Un = IC U ′ Z ′ ′ ′ ′ U Z U U U U + F N ZF + ZN but the current (in amps) into the network will change with the ratio of U to ′ ′ In = IC ′ ZF U ZF U = IC = In ′ ′ ′ U Z + Z U′ N ZF + ZN F U´ (E 4) as: (E 5) That is, for two identical converters under identical conditions but connected to system voltages of 240 kV and 500 kV, filters of the same Mvar (and tuning frequencies, q-factors) will give the same performance in terms of voltage distortion, TI F, THFF; but in order to give the same performance for requirements such as I T and Ipe , the filter at 240 kV would need to be approximately twice the size of the filter at 500 kV Copyright International Electrotechnical Commission – 68 – I EC TR 62001 -2: 201 © I EC 201 Bibliography Special aspects of AC filter design for HVDC systems , CI GRÉ TB [1 ] CI GRE WG B4 47, N o 553, 201 [2] CI GRE WG1 03/CC 02 (J TF 02), Connection of Harmonic Producing Installations in AC High-Voltage Networks with Particular Reference to HVDC Guide for Limiting Interference Caused by Harmonic Currents with Special Attention for Telecommunication Systems , Electra N o 59, April 995 [3] I EEE Std 368-1 977, IEEE Recommended Practice for Measurement of Electrical Noise and Harmonic Filter Performance of High-Voltage Direct-Current Systems [4] I EEE Std 51 9-1 992, IEEE Recommended Practice and Requirements for Harmonic Control in Electrical Power Systems [5] CAN /CSA-C22 N o 3-98, [6] A Deri, G Tevan, A Semlyen and A Castanheira, Electrical Coordination , August 998 The Complex Ground Return Plane: A Simplified Model for Homogeneous and Multi-Layer Earth Return , I EEE Transactions on Power Apparatus and Systems, Vol PAS-1 00, N o 8, August 981 , p 3686-3693 [7] Mutual Coupling between Finite Lengths Parallel or Angled Horizontal Earth Return Conductors , vol 4, E J Rogers, J F White, I EEE Transaction on Power Delivery, no , J an 989, p 03-1 [8] I TU , Calculating induced voltages and currents in practical cases , Directives concerning the protection of telecommunication lines against harmful effects from electric power and electrified railway lines, Volume I I , 999 [9] I EEE Std 1 24-2003, I EEC [1 0] I TU -T K 68, Operator responsibilities in the management of electromagnetic interference by power systems on telecommunication systems [1 ] I TU , I TU -T EMC-1 6, Danger, damage and disturbance , Directives concerning the protection of telecommunication lines against harmful effects from electric power and electrified railway lines Volume VI , 2008 [1 2] I EEE Std 820-2005, 2005 [1 3] Electrical Coordination Guide, Canadian Electrical Association, May 989 [1 4] N A Patterson, D E Fletcher, I EEE Proceedings of the I nternational Conference on DC Power Transmission, The Equivalent Disturbing Current Method for DC Guide for Analysis and Definition of DC Side Harmonic Performance of HVDC Transmission Systems IEEE Standard Telephone Loop Performance Characteristics , Transmission Line Inductive Coordination Studies and DC Filter Performance Specification , Montréal, Quebec, Canada, J une 4-8, 984, p 98-204 [1 5] M Kuussaari, Statistical Evaluation of Telephone Noise Interference Caused by AC Power Line Harmonic Currents , I EEE Transaction on Power Delivery, Vol 8, N o 2, April 993 [1 6] E W Kimbark, 971 Copyright International Electrotechnical Commission Direct Current Transmission , Volume , Wiley-I nterscience, N ew-York, I EC TR 62001 -2: 201 © I EC 201 – 69 – Electromagnetic compatibility (EMC) – Part 3-6: Limits – Assessment of emission limits for the connection of distorting installations to MV, HV and EHV power systems [1 7] I EC TR 61 000-3-6: 2008, [1 8] I EC TR 62001 -3: 201 6, [1 9] I EC TR 62544, [20] CI GRE Technical Brochure, Survey of Schemes, Working Group 4-02, 994 [21 ] CI GRE WG 03, AC Harmonic Filter and Reactive General Survey, Electra N o 63, p 65-1 02, 979 [22] CI GRE WG 03, High-voltage direct current (HVDC) systems – Guidebook to the specification and design evaluation of AC filters – Part 3: Modelling filters High-voltage direct current (HVDC) systems – Application of active Controls and Control Performance in HVDC Compensation for HVDC, A AC Harmonic Filter and Reactive Compensation for HVDC with Particular Reference to Non-Characteristic Harmonics , Complement to the paper published in Electra N o 63(1 979), CI GRE Technical Brochure N o 65, J une 990 High-voltage direct current (HVDC) installations – System tests [23] I EC 61 975, [24] I EC 61 000-4-7: 2002, Electromagnetic compatibility (EMC) – Part 4-7: Testing and measurement techniques – General guide on harmonics and interharmonics measurements and instrumentation, for power supply systems and equipment connected thereto I EC 61 000-4-7: 2002/AMD1 : 2008 [25] CCI TT, Danger And Disturbance, Directives Volume VI , Geneva, 989 [26] I EEE Std 776-1 992, IEEE Recommended Practice for Inductive Coordination of Electric Supply and Communication Lines [27] CI GRE WG 05, I nteraction between Converter and N earby Generator, CI GRE Brochure 1 9, October 997 _ Copyright International Electrotechnical Commission Copyright International Electrotechnical Commission Copyright International Electrotechnical Commission INTERNATIONAL ELECTROTECHNICAL COMMISSI ON 3, rue de Varembé PO Box 31 CH-1 21 Geneva 20 Switzerland Tel: + 41 22 91 02 1 Fax: + 41 22 91 03 00 info@iec.ch www.iec.ch Copyright International Electrotechnical Commission