I E C TR 62 0 -3 ® Edition 201 6-09 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 -3:201 6-09(en) Part 3: M od el l i n g I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n 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variety of criteria (reference number, text, technical committee,…) It also gives information on projects, replaced and withdrawn publications 65 000 electrotechnical terminology entries in English and French extracted from the Terms and Definitions clause of IEC publications issued since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 I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n 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 -3 ® Edition 201 6-09 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 – P art 3: M od el l i n g INTERNATIONAL ELECTROTECHNICAL COMMISSION ICS 29.200 ISBN 978-2-8322-3655-0 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 I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n –2– I EC TR 62001 -3: 201 © I EC 201 CONTENTS FOREWORD I NTRODUCTI ON Scope Normative references Harmonic interaction across converters General Practical experience of problems 1 3 I ndicators of where harmonic interaction is significant 3 I nteraction phenomena I mpact on AC filter design 5.1 General 5.2 AC side third harmonic 5.3 Direct current on the AC side 5.4 Characteristic harmonics 6 General overview of modelling techniques 6.1 General 6.2 Time domain AC-DC-AC interaction model 6.3 Frequency domain AC-DC-AC interaction model 6.4 Frequency domain AC-DC interaction model 6.5 Frequency domain current source model I nteraction modelling 20 7.1 General 20 7.2 Coupling between networks 20 7.3 Driving forces 21 7.4 System harmonic impedances 22 Study methods 22 8.1 Frequency domain 22 8.2 Time domain 22 Composite resonance 23 Core saturation instability 23 1 Particular considerations for back-to-back converters 23 I ssues to be considered in the design process 24 2.1 General 24 2.2 Fundamental frequency and load issues 24 2.3 Negative phase sequence 25 2.4 Pre-existing harmonic distortion 26 2.5 AC network impedance 27 2.6 Converter control system 28 2.7 Combination with "classic" harmonic generation 29 2.8 Relative magnitude of pairs of low-order harmonics 29 2.9 Superposition of contributions 30 3 Parallel AC lines and converter transformer saturation 30 Possible countermeasures 32 4.1 AC (and/or DC) filters 32 4.2 DC control design 32 4.3 Operating restrictions and design protections 33 I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n I EC TR 62001 -3: 201 © I EC 201 –3– Recommendations for technical specifications 33 5.1 General 33 5.2 Specified design data 33 5.3 Requirements regarding calculation techniques 34 AC network impedance modelling 35 General 35 I mplications of inaccurate definition of network impedance 36 Considerations for network modelling 37 3.1 General 37 3.2 Project life expectancy and robustness of data 37 3.3 Network operating conditions 37 3.4 Network impedances for performance and rating calculations 38 3.5 Modelling of network components 39 3.6 Representation of loads at harmonic frequencies 40 4 Network harmonic impedance envelopes 40 Methods of determining envelope characteristics 43 5.1 General 43 5.2 Low order harmonics 43 5.3 Mid-range and higher order harmonics 44 5.4 Balancing of risk and benefit 45 5.5 Consideration of tolerances on harmonic bands 46 5.6 Two separate envelopes for one harmonic band 48 5.7 Critical envelope parameters 49 5.8 I mpedance envelopes for performance and rating conditions 49 Examples of the impact of different network impedance representations 50 6.1 Effect of network envelope parameters on resultant distortion 50 6.2 Effect of network minimum resistance on filter rating 53 I nterharmonic impedance assessment 54 Measurement of network harmonic impedance 56 Conclusions 57 Pre-existing harmonics 57 General 57 Modelling and measurement of pre-existing harmonic levels 58 Harmonic performance evaluation, methods and discussion 60 3.1 General 60 3.2 "I ncremental" harmonic performance evaluation 60 3.3 "Aggregate" harmonic performance evaluation 61 3.4 Both "incremental" and "aggregate" performance evaluation 62 3.5 "I ncremental" and "maximum magnification factor" harmonic performance evaluation 63 Calculation of total harmonic performance indices 63 5 Harmonic rating evaluation 64 Difficulties with the voltage source/worst network model for rating 65 6.1 Background 65 6.2 I llustration of the voltage source/worst network method 66 Further possible calculation procedures for rating evaluation 68 7.1 Using measured levels of pre-existing distortion 68 7.2 Applying compatibility level voltage source at the filter busbar 70 I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n –4– I EC TR 62001 -3: 201 © I EC 201 Limiting the filter bus harmonic voltage to a maximum level for filter rating (MLFR) 72 7.4 Limiting total source distortion to the defined THD 73 7.5 Limiting harmonic order of pre-existing distortion 75 Conclusions 75 Annex A (informative) Location of worst-case network impedance 76 Annex B (informative) Accuracy of network component modelling at harmonic frequencies 79 B General 79 B Loads 79 B Transformers 82 B 3.1 Transformer reactance 82 B 3.2 Transformer resistance 82 B Transmission lines 85 B Synchronous machines 87 B Modelling of resistance in harmonic analysis software 88 Annex C (informative) Further guidance for the measurement of harmonic voltage distortion 91 Annex D (informative) Project experience of pre-existing harmonic issues 93 D.1 General 93 D.2 Third harmonic overload of filters in a back-to-back system 93 D.3 Third and fifth harmonic overload of filters in a line transmission 94 D.4 Overload of a DC side th harmonic filter 94 Annex E (informative) Worked examples showing impact of pre-existing distortion 96 E General 96 E Pre-existing distortions 97 E 2.1 Example – I llustration of magnification 97 E 2.2 I mpact of network impedance parameters 01 Annex F (informative) Comparison of calculation methods 03 F General 03 F Reference case – Converter generated harmonics only 06 F Method – Source voltages behind impedance sector 06 F Method – Source voltages at filter bus (see 5.7 2) 06 F Method – Limiting the filter bus harmonic voltage to a maximum level for filter rating (MLFR) (see 7.3) 07 F Method – Limiting total source distortion to the TH D level (see 5.7 4) 07 F Method – Pre-existing harmonics considered only up to the th , with % margin on converter generation for remainder (see 7.5) 1 Bibliography 1 7.3 Figure – Key elements of a complete AC-DC-AC harmonic interaction model Figure – Equivalent circuit for evaluation of harmonic interaction with DC side interaction frequency greater than AC side fundamental frequency 21 Figure – DC side th harmonic voltage due to AC side th harmonic (fixed angle) and th harmonic (varying angle) 27 Figure – Simple circuit used to represent AC network impedance at th and th harmonics 28 Figure – Example of a single impedance locus for harmonic orders to 49 41 I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n I EC TR 62001 -3: 201 © I EC 201 –5– Figure – Example of simple circle envelope encompassing all scatter points for harmonic orders to 49 42 Figure – Example of an impedance envelope for th to th harmonic with associated scatter plots 44 Figure – Example of an impedance envelope for th to th harmonic with associated scatter plots 45 Figure – Example of an impedance envelope for th to 25 th harmonic with associated scatter plots 45 Figure – Example of the need to extend the band of harmonics to allow for resonance effects 47 Figure 1 – Application of tolerance range in percentage of the harmonic number 48 Figure – Application of tolerance range in percentage of the harmonic number, zoomed to show 1 th and th harmonics 48 Figure – Example showing two impedance envelopes for a particular band 49 Figure – Example of impedance envelopes under "performance" and "rating" conditions for harmonic orders th to th 50 Figure – Example of impedance envelopes "performance" and "rating" conditions for harmonic orders 25 th to 31 st 50 Figure – Discrete envelopes for different groups of harmonics 51 Figure – Example showing a distributed generation causing about % attenuation of ripple control signal at the PCC 55 Figure – Generic circuit model for calculation of harmonic performance or rating 59 Figure – I llustration of basic voltage quality concepts with time/location statistics covering the whole system 60 Figure 20 – Circuit model for calculation of incremental performance 61 Figure 21 – Equivalent circuit of a network for the h th harmonic 66 Figure 22 – Typical voltage magnification factor 67 Figure 23 – Pre-existing distortion set to measured levels (plus margin) 68 Figure 24 – Pre-existing distortion applied directly at the filter bus 70 Figure 25 – Harmonic voltage stress on a shunt capacitor with I EC planning levels applied 72 Figure A.1 – Equivalent circuit model for demonstration of worst-case resonance between AC filters and the network 76 Figure A.2 – Diagram indicating vectors ZF , ZN and ZH 77 Figure B.1 – Typical equivalent load network 80 Figure B.2 – Relative error of equivalent load loss resistance R n of using [28] compared with Electra 67 [27] model 83 Figure B.3 – Effect of temperature on transformer load loss 84 Figure B.4 – Ratio between harmonic and fundamental frequency resistance as calculated for balanced mode components and calculated from averages of reduced Z matrix resistance values 86 Figure B.5 – Ratio between harmonic and fundamental frequency resistance as calculated for balanced mode components and calculated from averages of reduced Z matrix resistance values, for varying earth resistivity 87 Figure B.6 – Comparison of synchronous machine reactance between [4-1 ] recommendation and test measurements for a salient pole hydro generator of 370 MVA 87 Figure B.7 – Comparison of synchronous machine resistance between [1 7] recommendation and test measurements for a salient pole hydro generator of 370 MVA 88 Figure B.8 – Comparison of different approximations for resistance variations 89 I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n –6– I EC TR 62001 -3: 201 © I EC 201 Figure B.9 – Network impedance for Araraquara substation 90 Figure E.1 – Harmonic models for converter and for pre-existing distortion 97 Figure E.2 – Geometrical visualisation of selecting worst-case impedance for converter harmonics 97 Figure E.3 – Simple filter scheme to illustrate magnification 98 Figure E.4 – Plots illustrating magnification of various pre-existing harmonics 01 Figure F.1 – Network impedance sector used in example 03 Figure F.2 – Assumed filter scheme for examples of different methods of calculation 04 Figure F.3 – I EC planning levels used for source voltages in the study 05 Table – Dominant frequencies in AC–DC harmonic interaction Table – Comparison of calculated harmonic voltage distortion between two methods of representing network harmonic impedance 52 Table – Comparison of calculated harmonic voltage distortion considering the variation of network impedance angle 53 Table – Comparison of calculated filter harmonic current considering the variation of network minimum resistance and filter detuning 54 Table – Amplification factor tan Φ at different network impedance angles 66 Table – Variation of calculated filter harmonic current as a function of detuning 71 Table B.1 – Constants for resistance adjustment – five parameter equations 89 Table E.1 – Parameters of elements of a simplified filter scheme shown in Figure E.3 98 Table E.2 – Voltage and current distortion for Zmin = Ω and varying Φ 01 Table E.3 – Voltage and current distortion for Φ = ± 85 ° and varying Zmin 02 Table F.1 – Table F – Parameters of components of filters shown in Figure F 04 Table F.2 – Component rating calculated using different calculation methods 06 Table F.3 – Rating calculations using Method – for BP1 1 C1 07 Table F.4 – Rating calculations using Method – for H P24 R1 09 Table F.5 – Rating calculations using Method – for BP1 1 C1 1 I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n I EC TR 62001 -3: 201 © I EC 201 –7– I NTERNATIONAL 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 D E S I G N E VAL U AT I O N P a rt : AN D O F AC F I L T E RS – M od el l i n g FOREWORD ) The I ntern ati onal El ectrotech nical Commi ssi on (I EC) is a worl d wi d e org anization for stan dard izati on comprisi ng all nati onal electrotech nical committees (I EC N ational Comm i ttees) The object of I EC is to promote i nternati on al co-operati on on al l q u esti ons cernin g standard izati on i n the el ectrical and el ectronic fi el ds To this end an d in ad di ti on to other acti vi ti es, I EC pu bli sh es I nternati onal Stand ards, Technical Speci fi cati ons, Technical Reports, Pu blicl y Availabl e Specificati ons (PAS) an d Gu id es (hereafter referred to as “I EC Pu blicati on(s)”) Their preparati on is entru sted to technical committees; any I EC N ati onal Committee interested i n the subj ect d eal t with may parti ci pate i n thi s preparatory work I nternati on al , governmen tal and non governm ental organizations l iaisi ng wi th the I EC al so participate in this preparation I EC coll aborates cl osel y wi th th e I n ternational Organizati on for Stand ard izati on (I SO) i n accordance wi th cond i ti ons d etermined by agreement between th e two org anizati ons 2) Th e form al d ecision s or ag reements of I EC on technical matters express, as nearl y as possibl e, an i nternati onal consensus of opi ni on on the rel evan t su bjects si nce each technical com mittee has representati on from all i nterested I EC N ati onal Commi ttees 3) I EC Pu blications have th e form of recommend ati ons for intern ati onal u se and are accepted by I EC N ati onal Comm ittees i n th at sense Whi le all reasonabl e efforts are mad e to ensu re that the technical conten t of I EC Pu blicati ons is accu rate, I EC cann ot be hel d responsi bl e for th e way i n wh i ch they are used or for an y misin terpretati on by any end u ser 4) I n ord er to promote i n ternational u ni formi ty, I EC N ati onal Commi ttees u nd ertake to appl y I EC Pu blicati on s transparen tl y to the maxi mum extent possibl e i n thei r nati onal and regi onal pu blicati ons An y d i verg ence between an y I EC Pu bl icati on and the correspond i ng nati onal or region al publi cation shal l be cl earl y i nd icated i n the l atter 5) I EC i tsel f does not provi d e any attestation of conformity I nd epen d ent certi ficati on bodies provi d e conformity assessment services and , i n some areas, access to I EC marks of formi ty I EC i s not responsi bl e for an y services carried ou t by i n d epend en t certi fication bodi es 6) All users sh ould ensu re that they h ave the l atest edi ti on of this pu blicati on 7) N o li abili ty shal l attach to I EC or i ts di rectors, empl oyees, servants or agents i nclu di ng ind ivi du al experts and members of its tech ni cal comm ittees and I EC N ati onal Com mittees for any personal inju ry, property d amage or other d amage of any n atu re whatsoever, whether di rect or i nd i rect, or for costs (i ncl ud i ng l eg al fees) and expenses arising ou t of the pu blication, use of, or reli ance u pon, thi s I EC Pu bl ication or any other I EC Pu blicati ons 8) Attention is d rawn to the N orm ative references ci ted i n this pu bl icati on U se of the referenced pu blicati ons is i ndi spensabl e for the correct appli cation of th is publicati on 9) Attention is d rawn to th e possibili ty that some of the elements of thi s I EC Pu bl icati on may be the su bj ect of patent ri gh ts I EC shal l not be held responsi bl e for i d enti fyi ng any or all such patent ri ghts The main task of I EC technical committees is to prepare International Standards However, 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 -3, 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 -3, together with I EC TR 62001 -1 , I EC TR 62001 -2 and I EC TR 62001 -4, cancels and replaces I EC TR 62001 published in 2009 This edition constitutes a technical revision This edition includes the following significant technical changes with respect to I EC TR 62001 : I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n –8– a) b) c) d) e) f) g) h) i) I EC TR 62001 -3: 201 © I EC 201 expanded and supplemented Clause 6; new Clause 4; new Clause 5; new annexes on the location of worst case network impedance; accuracy of network component modelling at harmonic frequencies; further guidance for the measurement of harmonic voltage distortion; project experience of pre-existing harmonic issues; worked examples showing impact of pre-existing distortion; comparison of calculation methods The text of this Technical Report is based on the following documents: En q ui ry d raft Report on voti ng 22F/41 /DTR 22F/41 5/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 ISO/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 IEC website The committee has decided that the contents of this publication will remain unchanged until the stability dateindicated on the IEC 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 R T AN T th a t it – u n d e rs t a n d i n g c o l o u r p ri n t e r I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n Th e c o n ta i n s of 'col ou r c o l o u rs i ts i n si d e' wh i ch te n ts l og o a re U s e rs on th e c o ve r c o n s i d e re d sh ou l d pag e to t h e re fo re o f th i s be p ri n t pu b l i cati o n u s e fu l th i s fo r i n d i c a te s th e d ocu m en t c o rre c t using a – 02 – I EC TR 62001 -3: 201 © I EC 201 T a b l e E – V o l t a g e a n d c u rre n t d i s t o rt i o n fo r Z U PCC h \T H D 8, % Ω I LI NE 428, % U PCC 7,9 % Ω I LI N E 332, % U PCC 7,8 % Φ ± ° 85 = Ω I LI N E 20,1 % U PCC 7,8 % Z a n d va ryi n g Ω 32 I LI NE 75, % U PCC 7, % Ω I LI N E 66, % 1 ,8 % 29, % 1 ,8 % 31 , % 1 ,8 % 31 , % 1 ,8 % 31 , % 1 ,8 % 29, % 1 ,5 % 48, % 1 ,5 % 52, % 1 ,5 % 52, % 1 ,5 % 52, % 1 ,5 % 48, % 11 3, % 422, % ,9 % 324, % 0, % 95, % 0, % 32, % 0, % 3, % 13 6, % 23, % 6, % 1 ,6 % 6, % 1 ,6 % 6, % 1 ,6 % 6, % 24, % 23 ,4 % 28, % ,4 % 29, % ,4 % 27, % ,3 % 20, % 0, % 5, % 25 ,0 % 27, % ,0 % 26, % 0, % 26, % 0, % 21 , % 0, % 0, % I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n I EC TR 62001 -3: 201 © I EC 201 – 03 – Annex F (informative) Comparison of calculation methods F.1 General The aim of this annex is to illustrate numerically the impact of the different methods for taking into account pre-existing distortion when rating equipment The methods considered are as follows, applying pre-existing distortion: Method Method Method Method Method as source voltages behind a worst network impedance; as source voltages directly on the filter bus as in 5.7.2; limiting the filter bus harmonic voltage to a maximum level for filter rating (MLFR) as in 3; limiting total source distortion to the TH D level, as in 7.4; limiting explicit representation of pre-existing distortion to below the th harmonic, and adding % to converter harmonics for all the remaining harmonics above th , as in I n addition, a reference set of converter generated harmonic stresses is calculated for comparison The preconditions are identical for all cases I t is assumed that the scheme has a rated power of about 600 MW connected to a 50 Hz, 400 kV system with a short circuit level of between 500 MVA and 000 MVA The AC network harmonic impedance envelope is defined by the sector shown in Figure F.1 where: ã n ì Zmin 50 Zn n × Zma 50 where n is the harmonic order and Zmax50 and Zmin 50 are the maximum and minimum network impedances at fundamental frequency, evaluated from minimum and maximum short circuit power respectively 0° 80° −70° 70° for n jX • the phase angles are: −75° ≤ ϕ n ≤ 75° 4 = 51 1 50 Zm in Φ + Φ Zm ax R – IEC Figure F.1 – Network impedance sector used in example I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n – 04 – I EC TR 62001 -3: 201 © I EC 201 For the example, it is assumed that the complete filter design consists of two identical filter banks, but in the calculations only a single filter bank is considered to be connected, consisting of a double-tuned 1 /1 th bandpass branch and a high-pass 24 th harmonic branch No low-order filter, such as an H P3, is provided The filter is detailed in Figure F.2 In the calculations, the following is further assumed • Fundamental frequency 50 Hz ± 0,1 Hz • System voltage 400 kV ± 20 kV • Detuning is modelled through explicit frequency variations and component tolerances – The BP1 1 branch is tuneable, and a capacitance variation between -2, % and , % is considered (dielectric temperature variation and element failures) The reactor is assumed to have taps with a maximum tap step of 0, %, and a tuning error of 0, % (i.e half a tap step) – The H P24 branch is non-tuneable, and a capacitance variation of -4,1 % and 3, % is considered (manufacturing tolerances added) For the reactor, a manufacturing tolerance of ± % is considered The pre-existing harmonic distortion is arbitrarily taken as the I EC planning levels, see Figure F.3 C1 C1 T1 T1 F1 L1 L2 R1 L1 R1 F1 C2 T3 T2 T2 BP1 1 H P24 IEC Figure F.2 – Assumed filter scheme for examples of different methods of calculation Table F.1 – Parameters of components of filters shown in Figure F.2 Bran ch BP1 1 H P24 43 47 1 and 24 C1 , u F 0, 85 0, 94 L1 , mH 84, 8, C2 , u F 30, L2, mH 2, 250 250 Q , M var 3ph h , R1 , I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n Ω I EC TR 62001 -3: 201 © I EC 201 – 05 – IEC F i g u re F – I E C p l a n n i n g l e v e l s u s e d fo r s o u rc e vo l t a g e s i n t h e s t u d y I n assessing equipment stresses for the different methods, calculated stresses are determined as indicated in the tables for each method as RSS, qRSS or SU M, which are defined as: • root-sum-square values (RSS), for example I = ∑ Ih2 ; • quasi-root-sum square values (qRSS), for example U = Uk + ∑ Uh2 h ≠k • where Uk is the maximum individual harmonic; arithmetic sum values (SUM), for example U = ∑ Uh Table F.2 summarises the results The converter generated stresses are given both excluding and including fundamental frequency stresses, whereas the pre-existing distortion cases (Methods to 5) only contain harmonic stresses As the table demonstrates, the harmonic stresses due to pre-existing distortion for most methods exceed or are comparable to the converter generated stresses That is, for the assumptions made here, the impact of preexisting distortion would be dominant for component stresses That would not be expected nor representative for the general experience of H VDC plants in service These examples therefore emphasise that preconditions should be selected with care The example also demonstrates that the selected method used in determining stresses will be critical and directly decisive From Table F 2, it can be seen that the impact of the various methods on the separate components is significantly different, depending on the dominant harmonics responsible for the particular component stresses, and how these are affected by the applicable rating method No low order (3 rd or th /7 th ) filters have been included here, but if they had been, then the impact of low order stresses on these would be dominant and a different pattern of stress reduction by the various methods would be seen I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n – 06 – F.2 I EC TR 62001 -3: 201 © I EC 201 Reference case – Converter generated harmonics only This calculation is provided as a reference case to show the stresses calculated for the converter operating at 600 MW transfer with a single filter bank in service The calculated TH D is about ,9 % The fundamental frequency components are excluded Equipment stresses are summarised in Table F.2 Table F.2 – Component rating calculated using different calculation methods Method Method Method Method Method kV 74 57 63 64 50 36 246 √Σ U h kV 223 269 70 20 34 61 299 ΣU h I C1 and L1 A 94 487 80 82 96 06 20 I C2 A 000 780 999 000 29 573 573 I L2 A 030 890 020 030 21 606 609 I R1 A 35 98 35 35 21 21 kV 36 16 24 28 35 243 kV 40 82 04 62 90 20 261 I C1 A 96 80 80 72 64 25 77 I L1 A 89 70 71 69 63 22 76 I R1 A 36 39 35 23 11 12 12 Converter Converter harmonics including only fundamental BP1 1 U C1 √ Σ Ih HP24 U C1 √ Σ Uh Σ Uh √ Σ Ih M ethod : as sou rce vol tag es beh ind a worst n etwork i mpedance M eth od 2: as sou rce vol tages d i rectl y on th e fi lter bu s as in M eth od 3: li mi ting the fi lter bu s harmoni c voltage to a maximu m level for fil ter rati ng (MLFR) as i n M ethod 4: li mi ting total sou rce d istorti on to the TH D level, as i n M ethod 5: l im iting explicit representati on of pre-exi sti ng di storti on to bel ow the th harmonic, and ad di ng % to verter harmonics for al l the remai ni ng harm onics above th , as in F.3 Method – Source voltages behind impedance sector With the source voltages located behind the sector impedances, Method gives a THD at the converter bus of about 4, % (dominated by th and th harmonic) Equipment stresses are summarised in Table F F.4 Method – Source voltages at filter bus (see 5.7.2) With the source voltages located directly on the filter bus, Method gives a THD at the converter bus of about 5, % Equipment stresses are summarised in Table F I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n I EC TR 62001 -3: 201 © I EC 201 F.5 – 07 – M e t h o d – L i m i t i n g t h e fi l t e r b u s h a rm o n i c v o l t a g e t o a m a x i m u m l e v e l fo r fi l t e r t i n g ( M L F R) ( s e e ) The maximum levels of distortion at the filter bus to be considered as realistic for filter rating (the MLFR) are here selected as times I EC planning levels for all harmonics except characteristic harmonics where a maximum level of ,2 times is used, based on the concept that effective filtering is present at these frequencies These are arbitrary levels selected for illustration – they may be chosen as higher or lower as appropriate to a given project Table F illustrates the methodology, using the current as calculated for BP1 1 filter H V capacitor The second column gives the calculated filter bus distortion for the worst-case impedance and the third the MLFR harmonic distortion limits The fourth gives the calculated current corresponding to the raw calculated distortion and the fifth gives the current as corrected by MLFR T a b l e F – R a t i n g c a l c u l a t i o n s u s i n g M e t h o d – fo r B P 1 C BP1 1 I D h Calc D h limit I h Cal c I h C o rre c t e d C1 √ Σ Ih 93, 62 79, 23 , 82 % 2, 80 % 2, 37 2, 37 4, 21 % 4, 00 % 8, 53 8, 11 4, 57 % , 60 % 3, 06 4, 57 7, 66 % 4, 00 % 29, 45 15, 38 , 52 % 0, 80 % 7, 77 4, 08 7, 55 % 4, 00 % 51 , 47 27, 26 , 50 % 0, 80 % 4, 03 7, 51 3, 68 % 2, 00 % 51 , 08 27, 73 10 , 24 % 0, 70 % 30, 50 17, 25 11 ,1 % , 80 % 39, 44 39, 44 12 0, 30 % 0, 64 % 4, 4, 13 , 00 % , 80 % 96, 82 96, 82 14 0, 60 % 0, 59 % 22, 99 22, 62 15 0, 41 % 0, 60 % 8, 51 8, 51 … … … … … Clearly, the impact of the MLFR method in reducing stresses (see Table F.2) is greatest where the dominant harmonics for a particular component are not the sharply-filtered 1 th and th harmonics, where the calculated voltage level was anyway not high enough to be limited by the application of this method F.6 M e th o d – L i m i ti n g to ta l s o u rc e d i s t o rt i o n to th e TH D l e ve l ( s e e ) This recognizes that if, for example, I EC planning levels are taken as the pre-existing source voltage, the quadratic sum of the individual harmonics exceeds the allowable maximum THD I n this method, the individual harmonic contributions are therefore limited such that the specified THD is not exceeded This is done such that a different set of individual harmonics may be selected for each filter component, depending on which harmonics give the highest stresses for that particular component I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n – 08 – I EC TR 62001 -3: 201 © I EC 201 As an example to illustrate the method, Table F and Table F show this calculation procedure for the current in the BP1 1 C2 capacitor and the H P24 R1 resistor respectively Two components are shown to illustrate that a different set of harmonics is chosen for each component, depending on the sensitivity of the loading of that component to each harmonic As a first step, the raw calculated harmonic stresses for the given component (C2 or R1 ) are sorted in descending order, as shown in column ICalc Then, using this order, harmonics stresses are added up starting with the largest harmonic contribution and adding successively smaller harmonic contributions, also adding the individual source voltages until the chosen TH D limit for the harmonic source is reached The other (arbitrarily) selected limits on maximum limits for individual groups of harmonics are also respected while performing these additions, as follows: • • • TH D of the corresponding source voltage is limited to ≤ 3,0 % (THD Total ); contribution of rd , th and th harmonic is max 70 % of THD, i e ≤ 2, % (THD 3, 5, ); contribution of harmonics ≥ is max 50 % of THD, i.e ≤ , % (THD ≥ ) The resulting harmonic stresses are given by ICorrected For information, the voltage levels at the filter bus are also given ( D Fi lter Bus Corrected ) For the H P24 R1 resistor, this method has a significant impact on the rating Table F.4 shows that the rating current is not dominated by just a few large harmonics, but is composed of many fairly equal harmonics A large proportion of the more dominant ones are higher frequency non-characteristics, which are probably not realistic, and these are limited by the h ≥ criterion The limitation on h 3,5,7 contributions is also enforced, and finally the TH D = % limit cuts off remaining harmonic contributions Harmonics 25, 5, and being reduced proportionally at each of these limits respectively to maintain the contributions from those groups within their respective limits The total current is reduced from 35,27 to 23,25 A, a reduction in power rating of 56 % However, Table F shows that the mitigating influence of this method on the calculated current rating of the BP1 1 C2 capacitor is negligible The current in this component is mainly composed of 1 th and th harmonics, which are not limited by this algorithm as their total does not exceed THD and as they are not covered by the other arbitrary limits The only limitation which is applied here is when the total reached %, when the th harmonic is reduced accordingly to limit the total to % All subsequent harmonic contributions are then neglected, but this makes an almost insignificant difference to the total I n both these cases, the resulting voltage distortion on the converter bus is still unrealistically high, both for some individual harmonics and for TH D, which implies that Method could be applied in addition to Method to derive an overall more realistic rating for these components Tables showing the calculated stresses for all components are shown further below, and these are summarized in Table F I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n I EC TR 62001 -3: 201 © I EC 201 – 09 – T a b l e F – R a t i n g c a l c u l a t i o n s u s i n g M e t h o d – fo r H P R H P24 D D S o u rc e h =3, 5,7 D D h ³1 O t h e rs THD To tal I cal c I c o rre c t e d D F i l te r B u s C o rre c t e d I A R1 19 23 25 17 29 31 35 37 41 43 47 49 22 20 24 26 18 21 30 28 32 34 36 38 14 33 40 27 39 42 44 10 45 46 48 50 16 15 13 12 11 , 07 0, 89 0, 82 , 20 0, 70 0, 66 0, 58 0, 55 2, 00 0, 50 , 00 0, 47 0, 43 0, 42 0, 25 0, 26 0, 24 2, 00 0, 23 0, 27 0, 20 0, 22 0, 23 0, 22 0, 22 0, 21 0, 21 0, 30 0, 20 0, 21 0, 20 0, 20 0, 21 0, 20 0, 35 0, 20 0, 20 0, 20 0, 20 0, 28 0, 40 0, 30 , 50 0, 80 0, 32 0, 40 , 50 2, 00 , 40 % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % TH D √Σ I h I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n , 07 % 0, 89 % 0, 56 % , 07 % , 39 % , 50 % 2, 00 % 2, 50 % , 00 % 0, 64 % 2,1 % 2, 69 % 2, 77 % , 50 % 0, 30 % 2, 78 % 0, 35 % 2, 81 % 0, 40 % 2, 83 % 0, 98 % 3, 00 % , 53 3, 00 % 3, 33 3, 02 1 ,1 1 ,1 8, 87 8, 40 7, 37 6, 87 6, 68 6, 00 5, 64 5, 62 4, 97 4, 69 3, 66 3, 48 3, 40 3, 34 3, 05 2, 92 2, 91 2, 84 2, 84 2, 80 2, 74 2, 67 2, 60 2, 59 2, 55 2, 52 2, 51 2, 45 2, 45 2, 39 2, 38 2, 33 2, 32 2, 27 2, 21 , 92 , 77 , 77 , 58 , 26 , 03 0, 97 0, 94 0, 67 0, A 3, 33 3, 02 7, 62 , 28 % 0, 80 % 0, 43 % 6, 68 7, 53 % 5, 64 3, 67 % , 07 2, 45 % 2, 59 0, 58 % 2, 38 , 22 % , 77 , 49 % , 04 0, 28 % % 9,1 35, 27 22, 35 % – 110 – I EC TR 62001 -3: 201 © I EC 201 T a b l e F – R a t i n g c a l c u l a t i o n s u s i n g M e t h o d – fo r B P 1 C BP1 1 I D S o u rc e D h =3, 5,7 D D h ³1 O t h e rs THD I Tota l I cal c c o rre c t e d A C2 D F i l te r B u s C o r re c t e d A 13 , 50 % , 50 % , 50 % 790, 790, , 00 % 11 , 50 % , 50 % 2, % 593, 03 593, 03 ,1 % 14 0, 30 % 0, 30 % 2, % 95, 23 95, 23 0, 60 % 12 0, 32 % 0, 32 % 2, % 83, 08 83, 08 0, 30 % 10 0, 35 % 0, 35 % 2, % 61 , 93 61 , 93 , 24 % , 00 % , 00 % 2, 41 % 60, 70 60, 70 3, 68 % 17 , 20 % 2, 69 % 34, 48 34, 48 , 44 % 2, 00 % 3, 00 % 25, 6, 66 4, 99 % 15 0, 30 % 25, 19 , 07 % 8, 82 , 20 % , 32 % … TH D , 32 % ,20 % , 41 % 3, 00 % 6, 69 % √Σ I h F.7 001 ,38 00 0, 51 M e t h o d – P re -e x i s t i n g h a rm o n i c s c o n s i d e re d o n l y u p t o t h e 1 % m a rg i n o n c o n v e rt e r g e n e t i o n th , wi th fo r re m a i n d e r ( s e e ) Stresses were calculated considering explicitly the pre-existing harmonics up to the th harmonic using the voltage source/worst network approach, and then adding % of converter generated harmonic stresses for all higher harmonics (as in 5) The results are listed in Table F The impact on the characteristic harmonics is clearly much lower than with any of the methods involving a voltage source/worst network approach at these harmonics I t is arguable whether this is sufficiently conservative at these harmonics No limitation on pre-existing harmonics is applied even though the corresponding calculated TH D level at the filter bus is unrealistically high at % (compare to Method ) I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n I EC TR 62001 -3: 201 © I EC 201 – 111 – Bibliography [1 ] CIGRE WG 25, "Cross-modulation of harmonics 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Distortion Monitoring Devices in Transmission Systems", IPST05, paper 031 , 2005 [35] F Ghassemi, P.F Gale, "Method to Measure CVT Transfer Function", I EEE Transaction on Power Delivery, Vol 7, No 4, October 2002 [36] R A.deA Goncalves, "The I nfluence of the rd /5 th Harmonic Filters in the I taipu H VDC Performance with the Presence of th Harmonic in the I nterconnected System", Decimo Encuentro Regional Latinoamericano de la CIGRE, 2003 [37] R A Goncalves, E M Brandi, G S Luz, J R Medeiros, A R Saavedra, "Projeto dos Novos Filtros 3/5 H armonica de I biuna Desempenho e Dimensionamento dos Componentes", XIX SN PTEE, 2007 (in Portuguese) [38] I EC 61 803, [39] I EC TR 61 869-1 03, Instrument transformers – The use of instrument transformers for power quality measurement [40] 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 [41 ] I EC TR 62001 -1 , [42] I EC TR 62001 -4, Determination of power losses in high-voltage direct current (HVDC) converter stations I EC 61 000-4-7, High-voltage direct current (HVDC) systems – Guidebook to the specification and design evaluation of AC filters – Part 1: Overview High-voltage direct current (HVDC) systems – Guidebook to the specification and design evaluation of AC filters – Part 4: Equipment I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n 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 I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n