Iec tr 62001 4 2016

Part 4 – Eq ipment This p rt con ern ste d -state an tran ient ratin s of AC fi ters an their comp nents, p wer los es, au ible noise, desig is ues an sp cial a pl cation , fi ter protec

IEC TR 62001 -4

Editio 1.0 2 16-0

High-voltage direct cur ent (HVDC) sy stems – Guidance to the specification and

design evaluation of AC fi ters –

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IEC T R 62001 -4

Editio 1.0 2 16-0

design evaluation of AC fi ters –

CONTENTS

FOREWORD 6

INTRODUCTION 8

1 Sco e 9

2 Ste d state ratin 9

2.1 General 9

2.2 Calc lation method 9

2.2.1 General 9

2.2.2 AC s stem pre-existin harmonic 1

2.2.3 Combination of con erter an pre-existin harmonic 11 2.2.4 Eq ipment ratin calc lation 12 2.2.5 Ap l cation of voltage ratin s 15 2.3 AC network con ition 16 2.4 De- u in ef ects 16 2.5 Network imp dan e for ratin calc lation 16 2.6 Outages 17 3 Tran ient stres es an ratin 17 3.1 General 17 3.2 Switc in impulse stu ies 18 3.2.1 Energization an switc in 18 3.2.2 Faults external to the fi ter 19 3.2.3 Faults internal to the fi ter 21

3.2.4 Tran former inru h c r ents 21

3.3 Fast fronted waveform stu ies 21

3.3.1 General 21

3.3.2 Lig tnin strik s 21

3.3.3 Bu b r flas over stu ies 2

3.4 In ulation co-ordination 22 4 L s es 2

4.1 Backgrou d 23 4.2 AC fi ter comp nent los es 2

4.2.1 General 24 4.2.2 Fi ter/s u t ca acitor los es 2

4.3 Re ctor an resistor los es 2

4.3.1 General 25 4.3.2 Fi ter resistor los es 2

4.3.3 Sh nt re ctor los es 2

4.4 Criteria for los evaluation 2

4.4.1 General 27 4.4.2 Fu damental freq en y AC fi ter bu b r voltage 27 4.4.3 Fu damental freq en y an ambient temp rature 2

4.4.4 AC s stem harmonic imp dan e 2

4.4.5 Harmonic c r ents generated by the con erter 2

4.4.6 Pre-existin harmonic distortion 2

4.4.7 The anticip ted lo d profi e of the con erter station 2

5 Desig is ues an sp cial a pl cation 2

5.2 Performan e asp cts 3

5.2.1 L w order harmonic fi terin an resonan e con ition with AC s stem 30 5.2.2 Definition of interferen e factors to in lu e harmonic up to 5 kHz 31

5.2.3 Triple- u ed fi ter circ its 31

5.2.4 Harmonic AC fiters on tertiary win in of con erter tran formers 3

5.3 Ratin asp cts 3

5.3.1 Limitin hig harmonic c r ents in p ral el-resonant fi ter circ its 3

5.3.2 Tran ient ratin s of p ral el circ its in multiple tu ed fi ters 3

5.3.3 Overlo d protection of hig -p s harmonic fi ter resistors 3

5.3.4 Back- o-b ck switc in of fiters or s u t ca acitors 3

5.3.5 Short time overlo d – re sona le sp cification of req irements 3

5.3.6 L w voltage fi ter ca acitors without fu es 3

5.4 Fiters for sp cial purp ses 3

5.4.1 Harmonic fi ters for dampin tran ient overvoltages 3

5.4.2 Non-l ne r fi ters for low order harmonic /ran ient overvoltages 3

5.4.3 Series fi ters for HVDC con erter station 3

5.4.4 Re- u a le AC fi ters 4

5.5 Imp ct of new HVDC station in vicinity of an existin station 41

5.6 Red n an y is ues an sp res 4

5.6.1 Red n an y of fiters – savin s in ratin s an los es 4

5.6.2 Internal fi ter red n an y 4

5.6.3 Sp re p rts 4

6 Protection 4

6.1 Overview 44 6.2 General 4

6.3 Bank an s b-b nk overal protection 4

6.3.1 General 4

6.3.2 Short circ it protection 4

6.3.3 Overc r ent protection 4

6.3.4 Thermal overlo d protection 4

6.3.5 Dif erential protection 4

6.3.6 Earth fault protection 4

6.3.7 Overvoltage an u dervoltage protection 4

6.3.8 Sp cial protection fu ction an harmonic me s rements 4

6.3.9 Bu b r an bre k r fai ure protection 4

6.4 Protection of in ivid al fiter comp nents 4

6.4.1 Unb lan e protection for fi ter an s u t ca acitors 4

6.4.2 Protection of low voltage tu in ca acitors 5

6.4.3 Overlo d protection an detection of fi ter detu in 5

6.4.4 Temp rature me s rement for protection 5

6.4.5 Me s rement of fu damental freq en y comp nents 5

6.4.6 Ca acitor fu es 51

6.4.7 Protection an ratin of in trument tran formers 51

6.4.8 Examples of protection ar an ements 5

6.5 Person el protection 5

7 Au ible noise 55 7.1 General 5

7.2 Sou d active comp nents of AC fi ters 5

7.4 Noise red ction 5

8 Seismic req irements 5

8.1 General 5

8.2 L ad sp cification 5

8.2.1 Seismic lo d 5

8.2.2 Ad itional lo d 5

8.2.3 Soi q al ty 60 8.3 Method of q al fication 6

8.3.1 General 60 8.3.2 Qual fication by analytical method 6

8.3.3 Desig criteria 61

8.3.4 Doc mentation for q al fication by analytical method 6

8.4 Examples of improvements in the mec anical desig 62 9 Eq ipment desig an test p rameters 6

9.1 General 6

9.1.1 Tec nical information an req irements 62 9.1.2 Tec nical information to b provided by the c stomer 6

9.1.3 Cu tomer req irements 6

9.1.4 Tec nical information to b presented by the bid er 6

9.1.5 Ratin s 6

9.2 Ca acitors 6

9.2.1 General 66 9.2.2 Desig asp cts 6

9.2.3 Electrical data 6

9.2.4 Tests 68 9.3 Re ctors 6

9.3.1 General 68 9.3.2 Desig asp cts 6

9.3.3 Electrical data 7

9.3.4 Tests 71 9.4 Resistors 7

9.4.1 General 72 9.4.2 Desig asp cts 7

9.4.3 Electrical data 7

9.4.4 Tests 7

9.5 Ar esters 7

9.5.1 General 75 9.5.2 Desig asp cts 7

9.5.3 Electrical data 7

9.5.4 Ar esters: Tests 7

9.6 In trument tran formers 7

9.6.1 Voltage tran formers 7

9.6.2 Cur ent tran formers 7

9.7 Fiter switc in eq ipment 8

9.7.1 Fi ter switc in eq ipment: Introd ction 8

9.7.2 Desig asp cts 8

9.7.3 Electrical data 8

9.7.4 Test req irements 84

An ex B (informative) Example of resp n e sp ctra ( rom IEEE Std 6 3-2 0 ) 8

Bibl ogra h 8

Fig re 1 – Circ it for ratin evaluation 10 Fig re 2 – Inru h c r ent into a 12/2 th double- u ed fi ter 19 Fig re 3 – Voltage acros the low voltage ca acitor of a 12/2 th double- u ed fi ter at switc -on 19 Fig re 4 – Voltage acros the HV ca acitor b nk of a 12/2 th double- u ed fi ter u der fault con ition 2

Fig re 5 – Typical ar an ements of s rge ar esters 2

Fig re 6 – Non-l ne r low order fi ter for Vienna Southe st HVDC station 3

Fig re 7 – Sin le- u ed series fi ter an imp dan e plot 3

Fig re 8 – Triple- u ed series fi ter an imp dan e plot 3

Fig re 9 – Mixed series an s u t AC fi ters at Uru uaiana HVDC station 3

Fig re 10 – Re- u a le AC fi ter bran h 41

Fig re 1 – Example of a protection s heme for an u e rthed s u t ca acitor 5

Fig re 12 – Example of a protection s heme for a C- yp fi ter 5

Fig re 13 – Electrical sp ctrum 56 Fig re 14 – Force sp ctrum 5

Fig re B.1 – Resp n e sp ctra 8

Ta le 1 – Typical los es in an al - i m ca acitor u it 2

Ta le 2 – Electrical data for ca acitors 6

Ta le 3 – Electrical data for re ctors 71

Ta le 4 – Electrical data for resistors 7

Ta le 5 – Electrical data for ar esters 7

Ta le 6 – Electrical data for c r ent tran formers 7

Ta le 7 – Electrical data for fi ter switc in eq ipment 8

Ta le A.1 – Ca ital zed costs of the future los es 8

INTERNATIONAL ELECTROTECHNICAL COMMISSION

HIGH-VOLTAGE DIRECT CURRENT (HVDC) SYSTEMS –

Part 4: Equipment

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data of a diferent kin from that whic is normal y publ s ed as an International Stan ard, for

example "state of the art"

IEC TR 6 0 1-4, whic is a Tec nical Re ort, has b en pre ared by s bcommit e 2 F:

Power electronic for electrical tran mis ion an distribution s stems, of IEC tec nical

commite 2 : Power electronic s stems an eq ipment

con titutes a tec nical revision.

This edition in lu es the fol owin sig ificant tec nical c an es with resp ct to

IEC TR 6 0 1:

a) Clau es 10 to 16, 18, An exes F an G have b en exp n ed an s p lemented

The text of this doc ment is b sed on the fol owin doc ments:

En uiry draf Re ort o v tin

Ful information on the votin for the a proval of this doc ment can b fou d in the re ort on

votin in icated in the a ove ta le

This publ cation has b en draf ed in ac ordan e with the ISO/IEC Directives, Part 2

A l st of al p rts in the IEC TR 6 0 1 series, publ s ed u der the general title High-v lage

direct cu rre t (HVD C) systems – G u ida ce to th sp ecificato a d design e alu ato ofAC

fi ers, can b fou d on the IEC we site

The commite has decided that the contents of this publ cation wi remain u c an ed u ti

the sta i ty date in icated on the IEC we site u der "ht p:/we store.iec.c " in the data

related to the sp cific publcation At this date, the publcation wi b

INTRODUCTION

IEC TR 6 0 1 is stru tured in four p rts:

Part 1 – Overview

This p rt con ern sp cification of AC fi ters for hig -voltage direct c r ent (HVDC) s stems

with l ne-commutated con erters, p rmis ible distortion l mits, harmonic generation, fi ter

ar angements, fi ter p rforman e calc lation, fi ter switc in an re ctive p wer management

an c stomer sp cified p rameters an req irements

Part 2 – Performan e

This p rt de ls with c r ent b sed interferen e criteria, desig is ues an sp cial

a pl cation , field me s rements an verification

Part 3 – Model n

This p rt ad res es the harmonic interaction acros con erters, pre-existin harmonic , AC

network imp dan e model n , simulation of AC fi ter p rforman e

Part 4 – Eq ipment

This p rt con ern ste d -state an tran ient ratin s of AC fi ters an their comp nents,

p wer los es, au ible noise, desig is ues an sp cial a pl cation , fi ter protection, seismic

req irements, eq ipment desig an test p rameters

HIGH-VOLTAGE DIRECT CURRENT (HVDC) SYSTEMS –

Part 4: Equipment

This part of IEC TR 6 0 1, whic is a Tec nical Re ort, provides g idan e on the b sic data

of AC side fiters for hig -voltage direct c r ent (HVDC) s stems an their comp nents s c

as rating , p wer los es, desig is ues an sp cial a pl cation , protection, seismic

req irements, eq ipment desig an test p rameters

This doc ment covers AC side fi terin for the freq en y ran e of interest in terms of

harmonic distortion an au ible freq en y disturb n es It ex lu es fi ters desig ed to b

ef ective in the p wer l ne car ier (PLC) an radio interferen e sp ctra

It con ern the "con entional" AC fi ter tec nolog an l ne-commutated HVDC con erters

2 Stea y state rating

2.1 Ge eral

The calc lation of the ste d state ratin s of the harmonic fi ter eq ipment is the

resp n ibi ty of the contractor Clau e 2 gives g idan e on the calc lation of eq ipment

ratin p rameters an the dif erent factors to b con idered in the stu ies It is the

resp n ibi ty of the c stomer to provide the a pro riate s stem an en ironmental data an

also to clarify the o erational con ition , s c as fi ter outages an network contin en ies,

whic ne d to b ta en into ac ou t

2.2 Calc lation method

2.2.1 Ge eral

Ste d state ratin of fi ter eq ipment is b sed on a solution of the fol owin circ it whic

re resents the HVDC con erter, the fi ter b nks and the AC s p ly s stem Se Fig re 1

NOT Th symb ls use in this fig re are e plain d afer Formula (1)

Figure 1 – Circ it for rating e alu tion

The harmonic c r ent flowin in the fiter is the s mmation of two comp nents, the

contribution from the HVDC con erter an the contribution from the AC s p ly network

Usin the prin iple of s p rp sition, Formula (1) an (2) can b u ed to evaluate the

contribution to the harmonic fi ter c r ent of order n from these two sources

is the existin s stem harmonic voltage

The definition of network imp dan e is des rib d in 2.5

To solve Formula (1) an (2), the fol owin in e en ent varia les ne d to b known

• The harmonic c r ent (I

n) prod ced by the rectifier or in erter of the HVDC station It is

calc lated for al harmonic (se IEC TR 6 0 1-1:2 16, Clau e 5) This evaluation s ould

con ider the worst case o eratin con ition whic can oc ur in ste d state con ition ,

example con erter tran former imp dan es or o eratin ran e of the ta c anger, ne d

to b ta en into ac ou t Harmonic interaction phenomena as dis u sed in IEC TR

6 0 1-3:—, Clau e 3, s ould also b ta en into ac ou t

• The pre-existin s stem harmonic voltage, as dis u sed in 2.2.2

• The harmonic imp dan e of AC network (Z

sn), as dis u sed in IEC TR 6 0 1-1:2 16, 7.3

Note that diferent values of Z

sncan b defined for the calc lation of I

de en in on how the pre-existin harmonic distortion is sp cified (se 2.2.3)

The harmonic imp dan e of the fi ter (Z

fn) ne d to ta e ac ou t of the de- u in an

toleran e factors dis u sed in 2.4

In the case of an HVDC l nk con ectin two AC s stems of diferent fu damental freq en ies,

an p rtic larly if the l nk is a b ck- o-b ck station, b th con erters may generate c r ents on

their AC sides at freq en ies other than harmonic of the fu damental The fu damental

freq en ies either may b nominal y diferent, for example 5 Hz an 6 Hz, or may b

nominal y identical but difer at times by up to 1 Hz or 2 Hz This ad itional generated

distortion (interharmonic ) wi b at freq en ies whic are harmonic of the fu damental

freq en y of the remote AC s stem, an wi b tran fer ed acros the l nk Interharmonic

may give rise to sp cific pro lems not fou d with true harmonic , s c as

a) interferen e with rip le control s stems, an

b) l g t fl ck r d e to the low freq en y ampltu e mod lation cau ed by the b atin of a

harmonic freq en y with an adjacent interharmonic

h rmo ic p n tratio from a 6 Hz system

The ef ect of interharmonic (se IEC TR 6 0 1-1:2 16, 4.2.7), althou h smal , s ould also

b ta en into ac ou t in the calc lation of fiter comp nent ratin

2.2.2 AC s stem pre-e isting h rmonic

It is imp rtant that the efects of pre-existin harmonic distortion on the AC s stem are

in lu ed in the fi ter ratin calc lation Con entional y, this has b en ac ommodated not by

direct calc lation as s own a ove, but by cre tin an arbitrary margin of a 10 % to 2 %

in re se in con erter harmonic c r ents (I

th

) whic exists on

man p wer s stems As modern con erter station prod ce only smal amou ts of s c low

order harmonic , a simple en an ement of the mag itu e may not adeq ately reflect their

p tential contribution to fi ter ratin s

To model a multipl city of harmonic c r ent sources in a detai ed network model is impractical

for the purp ses of fi ter desig Therefore, it is pro osed that a Thévenin eq ivalent voltage

source is model ed b hin the AC s stem imp dan e, as s own in Fig re 1, to cre te an

o en circ it voltage distortion at the fi ter bu b r, i.e the level of distortion prior to

connection of the fi ters The mag itu e of the in ivid al harmonic voltages can b b sed on

me s rements or on the p rforman e l mits, but l mited by a value of total harmonic

distortion This a pro c provides a more re l stic as es ment of the contribution to

eq ipment ratin cau ed by ambient distortion levels

2.2.3 Combination of con erter a d pre-e isting h rmonic

As there is no fixed vectorial relation hip b twe n I

in ivid al contribution to fi ter ratin are s mmated on ro t s m s uare (RSS) b sis at e c

harmonic:

i2 i 2

For pre-existin harmonic , of relatively low mag itu e, RSS s mmation is re sona le, as

some harmonic may b in phase an others not, an as these relation hips wi vary with

time an o eratin con ition

Alternatively, l ne r ad ition would provide gre ter sec rity again t the p s ibi ty of the

contribution at a sig ificant freq en y b in a proximately in phase, but would entai an

in re se in cost, p rtic larly if u ed for the voltage ratin of the hig voltage ca acitors

Line r ad ition s ould b con idered for an pre-existin in ivid al harmonic of s c

mag itu e that l ne r ad ition would sig ificantly afect the c r ent ratin of the comp nents

Otherwise, if in practice the two sources were in phase for a p riod of time, the fi ter could

trip on overc r ent protection If l ne r ad ition is to b u ed, care s ould b ta en to en ure

that the con ition u der whic the two c r ents are calc lated are con istent, i.e the

calc lated c r ents can oc ur simultane u ly in practice

in lu ive

It is imp rtant that this ran e is covered to en ure that an resonan e con ition b twe n the

fi ters an the AC network an b twe n diferent fi ters are in erently con idered Harmonic

e c bran h of the fi ter to b evaluated From this c r ent data, in ivid al element ratin s

can b calc lated

2.2.4.2 Capa itors

From the sp ctrum of c r ents in the ca acitor b nk (I

fc), the total RSS c r ent can b

The mag itu es of the sp ctrum of most sig ificant harmonic c r ents s ould b sp cified

As the voltage ratin of the hig -voltage ca acitors is the most sig ificant factor in

determinin the total cost of the AC fi ters, the q estion of whic formula is u ed to derive

this ratin s ould b careful y con idered There have b en man dis u sions amon uti ties,

con ultants an man facturers in the p st regardin this p int The most con ervative

as umption in derivin a total rated voltage would b to as ume that AC s stem resonan e

oc urs at al harmonic an that al harmonic are in phase However, the u e of this

as umption for an HVDC fi ter ca acitor would res lt in an exp n ive design with a large

margin b twe n rated voltage an what would b exp rien ed in re l ty In practice,

ampl fication d e to fi ter-AC s stem resonan e may ta e place at some harmonic

freq en ies, but not at most Simi arly, some harmonic may b in phase u der some

o eratin con ition , but in general the harmonic have an u predicta le phase relation hip

Other a pro c es have therefore b en formulated by HVDC u ers an man facturers in an

at empt to en ure an adeq ate desig at a re sona le cost

The is ue is therefore one of p rceived risk again t cost, an d e to the diversity of existin

o inion it is not p s ible to give a cle r recommen ation here Variou a pro c es are

dis u sed b low Al have b en u ed s c es ful y in practice on dif erent HVDC s hemes

In the most con ervative a pro c , the maximum voltage (U

m) can b calc lated as an

arithmetic s m of the in ivid al harmonic an the fu damental, that is

4

1n

is the harmonic impedan e of order n of the ca acitor b nk

However, s c an evaluation, esp cialy when b sed on simultane u resonan e b twe n

the fi ters an the AC s stem at al harmonic , is overly p s imistic, as it as umes that al

harmonic are in phase, an wi res lt in an exp n ive ca acitor desig

A more re l stic method is to u e Formula (5) but to as ume that only a l mited n mb r of

harmonic are con idered to b in resonan e (e.g the two largest contribution ) an al other

harmonic are evaluated again t an o en-circ it s stem or fixed imp dan e However, this

method sti as umes that al harmonic are in phase, whic wi not b the case in practice

In a further a pro c , al harmonic are as umed to b in resonance, but Formula (5) is

modified s c that only the fu damental an largest harmonic comp nent are s mmed

arithmetical y Al other harmonic comp nents of voltage are s mmed on an RSS b sis an

ad ed arithmetical y to the s m of fu damental an largest harmonic comp nents to evaluate

U

m

This "q asi-q adratic" s mmation th s ta es ac ou t of the natural phase an le diversity

b twe n in ivid al harmonic comp nents:

4

2

2n

is the in ivid al harmonic comp nents of order n ex lu in the largest comp nent

The a ove may b ta en a ste further by ad in only the fu damental comp nent to the

RSS s mmation of al harmonic comp nents, again as umin resonan e at al freq en ies

4

2

2n

This is les con ervative than the method u ed in Formula (5) or (6), but has b en

s bstantial y a pl ed in practice an has proved adeq ate The as umption of resonan e at

al harmonic , an the u e of worst case as umption regardin toleran es in the

calc lation , provide some margin in the ca acitor ratin , whic is as umed to cover the

eventual ty of phasor s mmation b in more severe than is impl ed by Formula (7)

As ca acitors man factured to certain international stan ard have up to a 10 % prolon ed

overvoltage ca a i ty, it is p rmis ible to as ig a rated voltage (U

N) for the ca acitor b nk

up to 10 % b low U , i.e

mNU

(8)

However, the value of U

Ncalc lated from Formula (8) s ould b at le st eq al to the

maximum fu damental freq en y voltage on the ca acitor b nk If this is not the case, then

When low voltage ca acitor b nks are in tal ed in fi ters, for example in double or triple

freq en y fi ters, the rated voltages calc lated as a ove may not b s ita le For s c b nks,

the rated voltage may have to b in re sed to en ure that the b nks can with tan the

tran ient stres es, as dis u sed in 3.4

From the sp ctrum of harmonic c r ents the eq ivalent "thermal" re ctive p wer ratin of the

ca acitor (sin le phase) can b calc lated as

4

2

1n

fu damental freq en y imp dan e (X

fc1

as

f2

Nc

by sp cifyin the mag itu es of the most sig ificant in ivid al harmonic c r ents

2.2.4.3 Re ctors

The harmonic c r ent (I

fln) sp ctrum an the total RSS harmonic c r ent ne d to b sp cified

to the man facturer to en ure adeq ate thermal desig is ac ieved an the b sis of thermal

typ tests is cor ectly evaluated The ratin of the re ctor is b sed on

4

2

1n

is the harmonic imp dan e of order n of the re ctor

To en ure that s rface stres acros the re ctor do s not ex e d the desig ca a i ty, the

rated voltage acros the re ctor s ould b sp cified as

4

2n

Durin routine switc in an when the fi ter is s bjected to fast fronted s rges, very hig

tran ient stres es can a p ar acros the re ctors As dis u sed in Clau e 3, these ne d to

b al owed for in the re ctor desig an hen e in lu ed in the eq ipment sp cification

2.2.4.4 Re istors

The thermal c r ent lo din can b expres ed from the harmonic c r ent (I

frn) sp ctrum as

4

2

1n

To en ure that the resistor elements an b nk in ulation do not s fer flas overs d e to the

a pl ed voltage, the rated voltage acros the resistor s ould b sp cified as

4

12n

resistor internal s p ort in ulation (se also 2.2.5) Althou h the c oice of an arithmetic

s mmation of fu damental an harmonic voltages a p ars to b u d ly p s imistic an in

confl ct with the general a pro c to in ulator cre p ge distan es, the internal in ulators are

s bjected to u u ual o eratin con ition The ef ects of atmospheric p lution can res lt in

sig ificant bui t up of de osits on in ulator s rfaces whic are not s bject to was in by

rainfal Durin normal o eration the in ulators exp rien e elevated temp ratures, typical y

10 °C to 3 0 °C, in re sin the risk of s rface flas overs Maintenan e has typical y b en

p rformed on an an ual b sis, but some c stomers are now exten in maintenan e intervals

to 3 ye rs Th s a con ervative a pro c on the a ove b sis for internal in ulation cre p ge

may b neces ary

Durin routine switc in of damp d fi ters an u der fast fronted s rge con ition as

dis u sed in Clau e 3, the resistors can exp rien e very hig stres es These predicted

stres levels ne d to b in lu ed in the eq ipment sp cification

2.2.5 Ap l c tion of volta e ratings

The voltage ratin s for the eq ipment as defined a ove can b u ed to define the minimum

level of the maximum contin ou o eratin voltage (MCOV) for s rge ar esters The ful d ty

on the s rge ar esters wi b determined from the stu ies des rib d in Clau e 3

The u e of arithmetic or q asi-arithmetic s mmation of fu damental an harmonic voltages

for in ivid al items of eq ipment is inten ed to provide sec rity again t lo din con ition

whic may oc ur only for s ort p riod of time

However, it would b u d ly p s imistic if these voltages b come the b sis for the

calc lation of external in ulation cre p ge distan es The voltage to b u ed for the

calc lation of total cre p ge distan e s ould b the q adratic s m of the ste d state

fu damental an harmonic voltages Th s dif erent external cre p ge distan es would b

evaluated at variou location within a fi ter with graded in ulation

2.3 AC network condition

Fi ter eq ipment s ould b rated for o eration at the ste d state voltage ran e of the AC

s stem, typical y 0,9 p.u to 1,0 p.u of nominal on an EHV s stem For voltage ex ursion

in ex es of this value, the time d ration of the overvoltage s ould b sp cified

2.4 De-tuning ef e ts

To en ure that fi ter eq ipment ratin is s ficient to with tan l fetime o eration, the

fol owin factors ne d to b con idered

• Eq ipment toleran es: The extreme g arante d ran e of toleran es s ould b u ed for

ratin stu ies Unl k other efects con idered here whic are s bject to c cl c variation,

an efects d e to man facturin toleran e wi p rsist for the eq ipment’s l fetime

• Freq en y variation: Where s normal anticip ted freq en y variation s ould b u ed for

p rforman e, extreme variation s ould b con idered for ratin These extreme

con ition may b sp cified as contin ou or for sp cific time p riod The former wi

define contin ou ratin s where s the lat er wi define s ort time overlo d

• Temp rature variation: Where s maximum an minimum average temp rature s ould b

con idered for p rforman e stu ies, a solute maximum an minimum temp ratures

s ould b con idered for eq ipment ratin As dis u sed previously, the temperature wi

afect the ca acitan e value an hen e wi de- u e the fi ter In ad ition, cold

temp rature con ition are of p rtic lar imp rtan e for ca acitor b nks, esp cial y for

energization con ition

• Ta p sition on re ctors: Adju ta le ta s are ofen provided on re ctors for tu ed fi ters

to of set ca acitor toleran e ef ects The ef ect of ta p sition on the tu in of the fi ter

an its s bseq ent ratin s ould b con idered

• Ca acitor u it fai ure detection s hemes normal y have three set levels: alarm only (1

• When multiple tu ed b nks of the same typ are in tal ed, it is imp rtant to con ider

p s ible circ latin c r ents b twe n the b nks d e to dif eren es in tu in Su h

c r ents wi ne d to b con idered for fi ter eq ipment ratin However, me s res to

control this efect, s c as the u e of p ralel n bu es, can b u ed if the fi ter layout is

s ita le

2.5 Network impe a c for ratin c lc lation

The representation of the AC network harmonic imp dan e (Z

sn) for the purp ses of

eq ipment ratin s ould b diferent from that u ed for predictin p rforman e As dis u sed

in IEC TR 6 0 1-1:2 16, 7.3, a n mb r of dif erent distin t ge metric s a es can b u ed to

define the harmonic imp dan e for p rforman e stu ies This data s ould cover al normal

an plau ible contin en y network o eratin con ition an lo d con ition anticip ted

throu hout the l fetime of the eq ipment For ratin stu ies, a wider ran e of network

con ition may b u ed to en ure that eq ipment ratin s are adeq ate for the anticip ted

l fetime This can b ac ieved by sp cifyin larger se rc are s an /or in re sed s stem

an les It is imp rtant to en ure that re l stic levels of minimum resistan e are con idered to

avoid u damp d resonan e con ition oc ur in

The detai ed sp cification of the network harmonic imp dan e by the c stomer has a direct

b arin on the ratin s, an hen e costs, of the fiter eq ipment

In some cases, the zero seq ence imp dan e of the s stem may b req ired to evaluate the

voltage u b lan e on the con erter bu fol owin u -s mmetrical faults, s c as a lne to

e rth fault The res ltant negative seq en e voltage comp nent is u ed for the purp se of

s ort time (0,1 s to 1,5 s, de en in on l ne protection phi oso h an auto-reclose fe tures)

2.6 Outa e

Fi ter eq ipment is rated to with tan the in re sed harmonic lo din whic wi oc ur when a

defined n mb r of fi ters are out of service The specific outage req irement wi vary from

project to project an wi de en up n the n mb r of fiters avaiable an the level of p wer

tran fer req ired Typical y, the outage of one switc ed fi ter or fi ter group s ould not res lt

in an overlo d of the remainin fiters or the ne d to red ce p wer tran fer In the event of

one fi ter or fi ter group b in out of service for maintenan e an a trip oc ur in on a secon

fi ter or fiter group, it is stron ly recommen ed that the c stomer red ces DC power to

prevent fiter overlo d an hen e cas ade fi ter trips The sp cification s ould cle rly define

the c stomer's sp cific outage req irement criteria to b fol owed by the contractors in the

pre aration of the pro osal

In order to avoid the costs as ociated with in tal n red n ant fi ters, or ratin fi ter

eq ipment for fi ter outages, the c stomer may c o se to al ow a red ction of tran mited DC

p wer to avoid fi ter overlo d Su h a strateg can have a sig ificant ef ect in red cin fi ter

costs, esp cial y in relatively low p wer s hemes where the n mb r of in tal ed fi ters is

smal

In cases where switc ed fi ters are u ed as p rt of the re ctive p wer control, the fi ter

eq ipment s ould b rated for al via le switc in strategies

3 Transient stresse and rating

3.1 Ge eral

In ad ition to the ste d state fu damental plu harmonic lo din , harmonic fi ters wi

exp rien e tran ient stres es d e to a wide variety of disturb n es These con ition wi

ne d to b in estigated to en ure that the ca a i ty of the eq ipment is s ficient to

ac ommodate the s p rimp sed tran ient d ty

Su h stu ies wi req ire a tran ient analy is computer program, s c as EMTP, AT ,

NETOMAC or EMTDC

2

, to model s stem p rameters, in lu ing non-l ne r asp cts s c as

tran former saturation an s rge ar ester c aracteristic The res lts of these stu ies wi

in icate whether the calc lated stres es ex e d the eq ipment’s ca a i ty In s c cases,

the eq ipment ratin wi ne d to b in re sed to ac ommodate the predicted d ty

Alternatively, s rge ar esters can b u ed to l mit the tran ient d ty on the eq ipment

Where neces ary, the res lts of s c stu ies may ne d to form p rt of the eq ipment

specification an may also b come the b sis for ac e tan e test levels

In the case of double tu ed fi ters, the res lts of tran ient stu ies u ual y in icate that the

pro osed ratin s of the low voltage fi ter comp nents, b sed on ste d state lo din , are

inadeq ate an en an ed eq ipment ratin s are req ired to me t the tran ient d ty

The res lts of the transient stu ies wi give imp rtant information for the sp cification of the

in ivid al items of fi ter eq ipment

The tran ient stu ies dis u sed in Clau e 3 are the resp n ibi ty of the contractor; however,

the c stomer s ould define in the sp cification an minimum req irements for contract stage

stu ies For example, the c stomer s ould define an sp cific network an s heme o eratin

con ition that are con idered Ad itional y, an fault s enarios to b stu ied s ould b

stated together with detai s of an auto-reclose s hemes that o erate on the s p ly network

_ _ _ _ _ _

2

EMT , AT , NE OMA a d EMTD are e amples of suita le pro u ts a aia le c mmercialy This

informatio is giv n for th c n e ie c of users of this d c me t a d d es n t c nstitute a e d rseme t b

Althou h the tran ient stu ies wi b p rformed an re orted at the contract stage, the

bid er wi ne d to p rform a few stu ies at the tender stage in order to cost the station

eq ipment These stu ies are req ired to esta l s eq ipment in ulation levels an s rge

ar ester ratin s The extent of an s c stu ies s ould b at the bid er’s dis retion

There are two main groups of stu ies that s ould b p rformed

• The first, as dis u sed in 3.2, comprises switc in impulse stu ies s c as routine fi ter

switc in , auto-reclose events, s stem faults an fault a pl cation/cle ran e in olvin DC

l nk lo d rejection

• The secon group, as dis u sed in 3.3, in lu es fast fronted waveform stu ies, s c as

l g tnin strik s an bu flas overs whic res lt in ra id dis harge of ca acitor b nks

3.2 Switc ing impuls studie

3.2.1 Energization a d switc ing

For e c typ of fi ter avai a le in the HVDC s heme, initial energization stu ies ne d to b

p rformed to esta l s maximum levels of overc r ent, overvoltage an energ Point on

-wave stu ies wi esta l s worst case con ition b sed on energization from the hig est

re l stic s stem voltage However, in more complex fi ter config ration , the same p int on

-wave may not esta l s worst case con ition for in ivid al items of eq ipment These

stu ies may also establs the ne d for switc in overvoltage control devices in the bre k rs

(pre-in ertion resistors, s n hronized closin , etc.) and the bre k r switc in ca a i ty

u der overvoltage con ition for overvoltage control

Routine switc in of fi ters, with other b nks alre d in service, wi b the most common

tran ient duty on the fi ter comp nents The n mb r of switc in op ration p r an um may

vary widely b twe n s hemes For example, a lon distan e HVDC s heme desig ed for bulk

p wer tran mis ion may req ire very infreq ent fi ter switc in , where s a b ck- o-b ck

HVDC s heme with a re ctive p wer control faci ty may switc fi ters freq ently An estimate

of the n mb r of switc in events wi b ne ded to ac omp n the tran ient res lts an

s ould b in lu ed by the contractor in the in ivid al eq ipment sp cification Freq ent

switc in of fi ters is of p rtic lar imp rtan e for the ca acitor b nks as the hig level of

dielectric stres imp sed d ring the tran ient event has an imp ct on the eq ipment l fetime

Stan ard on ca acitor b nks, s c as the IEC 6 8 1 series an IEEE Std 18, give g idan e

on the ac e ta le levels of tran ient voltage an c r ent an the n mb r of switc in events

p r an um

In a simi ar man er to initial energization stu ies, p int on-wave stu ies of routine switc in

wi b ne ded to esta l s worst case con ition The stu ies s ould con ider the case of

e c typ of fi ter in turn b in the last to b switc ed, for example al other fi ters are in

service at the maximum re l stic s stem voltage Where s u t ca acitor b nks are in tal ed

as p rt of the re ctive p wer control strateg , the p rtic lar case of p ralel switc in wi

ne d to b stu ied In this case, the hig levels of inru h c r ent into one b nk d e to the

dis harge from an energized ca acitor b nk may res lt in damage to the ca acitor

eq ipment Su h stu ies would in icate the ne d for c r ent l mitin re ctors to b in tal ed

as p rt of the b nk

The stu ies wi ne d to con ider the ran e of s ort circ it levels (SCL) a pl ca le at the

p int of con ection of the fi ters There is normal y no simple cor elation b twe n SCL an

the mag itu e of p a c r ents an voltages on the fi ter eq ipment

Typical examples of the tran ient waveforms whic oc ur d rin routine fi ter switc in are

s own in Fig res 2 an 3:

Figure 2 – Inrus c r e t into a 12/2

th

double-tun d fi ter

Figure 3 – Volta e a ros th low volta e c pa itor of a 12/2

R

G

B

109

87

65

43

R

G

B

109

87

65

43

2

100

phase faults Su h faults may in olve rejection of the DC lo d, for example blockin of the

con erters, le din to a large prosp ctive recovery voltage This voltage, exacerb ted by the

presen e of the fi ters, wi b l mited by s stem l ne- o-e rth s rge ar esters an is normal y

the b sis for their energ ratin When stu yin s c fault a pl cation an lo d rejection

s enarios, it is imp rtant to re resent ac urately the o eratin strateg of the HVDC s heme

in terms of bre k r fault cle ran e times, fi ter trip in strateg an de-blockin of the

con erters Normaly, harmonic fi ters are not switc ed d rin d namic overvoltage (DOV)

con ition to avoid an restriction of o eration fol owin the DOV However, if fiters do

switc out this wi imp se a sig ificant d ty on the circ it bre k r an also on an dis harge

voltage tran formers (DVT), if in tal ed

Where sin le phase auto-reclose s hemes are u ed on the circ it bre k rs of the in omin

tran mis ion l nes, the strateg in the event of re e ted fai ed re-clos re atempts wi ne d

to b stu ied In s c cases, s c es ive re-energization of the fi ters may res lt in sig ificant

overc r ents an overvoltages on the eq ipment an in p rtic lar may dictate the energ

levels of the fi ter s rge ar esters If thre phase auto-reclose s hemes are u ed, whic wi

res lt in isolation of the con erter station, this wi also ne d to b stu ied to determine the

ef ects on ar ester ratin s Where dis harge voltage tran formers are in tal ed on the fi ter

b nks, they can ra idly dis harge the DC voltage on the ca acitor b nks al owin

re-energizin of the fi ters

The d ration of s c tran ient stu ies would ne d to b c osen to cover al bre k r

o eration an to en ure that worst case overlo d con ition an ar ester energ a sorption

con ition had b en re c ed However, it is recog ized that it is impractical to re resent lon

bre k r cle rin times, for example several min tes, in digital stu ies an a red ced p riod

can b model ed as the cle rin time for stu k bre k r con ition

Fig re 4 i u trates a combination of fault con ition : at 2 ms, the HVDC con erter is

block d res ltin in a severe overvoltage on the main fi ter ca acitor b nk At 7 ms, a

3-phase bu fault is simulated whic is cle red at 10 ms, a red ced p riod to minimize

computation time, res ltin in a severe tran ient overvoltage on the ca acitor b nk

Figure 4 – Volta e a ros the HV c pa itor ba k of a 12/2

th

IEC Time (mi ise o ds)

64

3.2.3 Fa lts intern l to the fi ter

The efects of faults within the fi ter wi de en up n the typ of fi ter an the electrical

ar an ement of the fi ter Usin a sin le- u ed fi ter, as an example, a lne-e rth fault at the

HV terminal of the ca acitor b nk wi a ply the in tantane u DC voltage on the ca acitor

directly acros the low voltage re ctor an an s rge ar ester, as dis u sed further in 3.3.2

A l ne-e rth fault at the ca acitor LV terminal would simply byp s the re ctor an res lt in

very l tle c an e in c r ent in the ca acitor b nk whic is the predominant fiter imp dan e

If the fi ter config ration were in erted, for example the re ctor at the HV terminal an the

ca acitor con ected to the neutral, a l ne-e rth fault from the re ctor HV terminal would res lt

in a simi ar tran ient d ty on the re ctor as in the a ove case However, a l ne-e rth fault

from the re ctor LV terminal, for example the ca acitor HV terminal, would res lt in a

con idera le fault c r ent in the re ctor, d e to the low imp dan e of the re ctor comp red

with the ca acitor To en ure that re ctors would s rvive s c an internal fi ter fault, a s ort

circ it test of the re ctor would b req ired

Althou h the fault con ition con idered a ove are normal y worst case con ition for fi ter

tran ient d ty, for more complex fiter config ration , other credible internal fault con ition

would ne d to b stu ied

When stu yin the efects of s c faults on fi ter comp nent an ar ester ratin s, it is

imp rtant to con ider the protective level aforded by the bu ar ester an to co-ordinate the

desig of this ar ester with the fi ter ar esters to ac ieve an overal o timized desig

3.2.4 Tra sformer inrus c r e ts

Energization of the con erter tran former, or adjacent con entional tran formers, wi res lt in

sig ificant levels of inru h c r ent that can b s stained for considera le p riod of time As

the inru h c r ents are as mmetric an with a hig harmonic content, p rtic larly of low order

harmonic , they can res lt in harmonic c r ent flow in adjacent fi ters In a pl cation where

low order harmonic fi ters are in tal ed, s c ef ects wi ne d to b stu ied Althou h in

normal practice the con erter tran formers would b energized prior to fi ter switc in , d rin

fault recovery con ition , tran former switc in on adjacent con erter p les, or switc in of

adjacent grid tran formers, energization can oc ur with fi ters con ected Studies wi in icate

the ne d for overvoltage control devices in the bre k rs for the definition of economic

in ulation levels of the eq ipment an /or to decre se the oc ur en e of commutation fai ures

Stu ies in olvin tran former inru h c r ents ne d to model the tran former in some detai

in lu in b th l ne r an non-lne r, for example saturation, in u tan es The los es within

the tran former, whic wi dictate the decay of inru h c r ents, s ould b model ed

3.3 Fa t fronte wa eform studie

3.3.1 Ge eral

Becau e of the large rates of c an e of voltage an c r ent in olved in these stu ies, it is

imp rtant that stray in u tan es an ca acitan es within the fi ter circ its an eq ipment are

model ed Th s the ph sical location of the eq ipment, an p rtic larly of s rge ar esters,

s ould b con idered when model n the fi ter

3.3.2 Lig tning strik s

Althou h direct l g tnin strik s on fi ter eq ipment are u l k ly, esp cial y if overhe d e rth

-wire protection is provided, the ef ect of strik s on the remote AC s stem tran fer ed to the

fi ters s ould b con idered The maximum voltage on the fi ter terminal wi b l mited by the

main HV s rge ar ester These s rges wi b tran fer ed to the low voltage comp nents of

double- u ed fi ters an may have a sig ificant b arin on their in ulation levels Where

a pro riate, a pl ed l g tnin strik s s ould b simulated at variou p ints within the HV

3.3.3 Bu bar fla hov r studie

A flas over to e rth on the fi ter HV busb r wi cau e a ra id dis harge of the fi ter ca acitor

b nk throu h the fi ter comp nents Su h an event may oc ur d rin a hig s stem voltage,

however, the ca acitor fu es s ould not o erate for this con ition as they are tested to

with tan s ort circ it c r ents Due to the s ort time of these dis harges (a few

microsecon s), they fal into the same category as l g tnin impulses an this is not normal y

a decisive ratin case

3.4 Ins lation co-ordination

From the res lts of the studies des rib d in 3.2 an 3.3, the overal in ulation co-ordination

of the fi ter can b derived The ne d for s rge ar esters distributed within the fi ters wi b

determined In most cases the c oice b twe n the ar ester’s protective voltage level an

energ a sorption ca a i ty an the voltage with tan ca a i ty of the protected eq ipment

wi b b sed on relative costs Althou h low voltage station clas ar esters are relatively

inexp n ive, if sig ificant energ a sorption ca a i ty is req ired then p ral el hou in s are

ne ded an costs may b hig In s c cases in re sin eq ipment in ulation levels may b

the o timum solution

When model n s rge ar esters, it is important to con ider the maximum toleran e on the

ar ester c aracteristic when evaluating protective levels and the minimum toleran e when

evaluatin energ a sorption ca a i ty

There are a n mb r of p s ible con ection ar an ements for fi ters with emb d ed s rge

ar esters Typical examples for double- u ed fi ters are s own in Fig re 5

Figure 5 – Typic l ar a geme ts of s rge ar e ters

The res lts of the l g tnin an switc in impulse stu ies wi confirm that the req ired

margin b twe n the eq ipment with tan levels an the cor esp n in s rge ar ester

protective levels, ac ordin to IEC 6 0 9-4 or the c stomer’s sp cification, are ac ieved

Note that margin in ex es of those normal y sp cified by IEC 6 0 9-4 wi res lt in

in re sed fi ter costs The energ a sorption d ty imp sed on s rge ar esters by l g tnin

s rges wi normal y b les than the energ arisin from the fault con ition dis u sed in 3.2

In the case of the double- an triple- u ed fi ters, the res lts of the fault stu ies or switc in

stu ies u ual y in icate that the maximum tran ient voltages on the low voltage ca acitors

gre tly ex e d the ste d state ratin s as derived in 9.2.2 As the cost of s c b nks is

u ual y low, in re sin the rated voltage s c that overlo d ca a i ty compl es with

predicted maximum tran ient voltage can give an ac e ta le desig without in ur in the

IEC

By esta l s in a coherent in ulation co-ordination s heme throu hout the fi ter, it is p s ible

to define the fol owin p rameters for the fi ter eq ipment

• tran ient c r ent throu h ar esters an fi ter comp nents;

• protective levels of fi ter ar esters;

• fiter ar ester location an req irements

These p rameters can b defined at e c terminal of the eq ipment or in the case of large

HV ca acitor b nks at a n mb r of p ints where s p ort in ulators, c r ent tran formers or

voltage tran formers may b con ected The neutral p ints of e c phase of the

star-con ected fi ter are normal y in ivid al y isolated by a low, but con istent in ulation level, an

then brou ht together to form a sin le star p int whic is then con ected to e rth

It is imp rtant that an in ulation level is defined for the neutral of the fi ter to avoid spuriou

e rth faults d rin tran ient disturb n es

The cost of los es can b a sig ificant factor of dif eren e b twe n the desig s of diferent

bid ers for an HVDC s heme The c stomer ne d to en ure that los evaluation is made

ac ordin to cle rly defined proced res, an u der comp ra le con ition , for e c ofered

desig

An introd ction to HVDC con erter station los es is given in An ex A

Harmonic fi ters as ociated with the AC side of HVDC con erter station are typical y

resp n ible for up to arou d 10 % of the total con erter station los es Unl k man plant

items the los es for harmonic fi ters can only b determined by calc lation, esp cial y those

relatin to los es at harmonic freq en ies (althou h the los fig res for the in ivid al

comp nents of the fi ters may b avai a le as the res lt of works tests)

The widely ac e ted stan ard proced re for calc latin los es in HVDC station is defined in

IEC 618 3 This pro oses calc lation of los es u der es ential y nominal con ition , whic is

a fair b sis for most HVDC plant

However, for AC fi ters, the calc lated los es can vary over a wide ran e de en in on

factors s c as detu in , AC network resonan e, an level of negative seq en e comp nent

in the AC s p ly voltage Con eq ently, a calc lation made u der nominal con ition can

gre tly u derestimate the l k ly level of los es u der re l stic o eratin con ition

The c stomer s ould therefore b aware that by fol owin the g idan e of IEEE Std 1 9

(now with rawn), he may not o tain a re l stic estimate of pro a le AC fi ter los es

Furthermore, as the los es p rtainin to diferent AC fi ter design vary s bstantial y, he wi

also not b a le to ma e a fair comp rison of the desig s ofered by diferent bid ers

The fol owin items therefore ofer g idan e to the c stomer, where a pro riate, on how to

los es s ould b calc lated b th u der the nominal con ition of IEC 618 3, an u der the

s g ested alternative con ition des rib d in 4.4 b low, in order to provide al the

information ne ded by the c stomer

4.2 AC fi ter compone t los e

4.2.1 Ge eral

The AC fi ters comprise ca acitive, in u tive an ofen resistive elements, al of whic

contribute to the total los es of the con erter station As p rt of the fi ter design proces ,

ac ou t wi have b en ta en of the los ca ital zation in c o sin the n mb r an typ of

fi ters req ired Clau e 6 in IEC TR 6 0 1-1:2 16 hig l g ts the variou ad antages an

disad antages of tu ed fi ters, whic typical y prod ce low los es, again t damp d fi ters

whic general y prod ce hig er los es on a p r Mvar b sis

Further dis u sion with resp ct to overal fi ter comp nent costs, ta in into ac ou t their

los es, is provided in CIGRE WG 14.0

4.2.2 Fi ter/s unt c pa itor los e

For large hig voltage ca acitor b nks havin ratin s of man Mvars, the los an le b comes

imp rtant; the lower the los an le, the lower the los es are for the b nk

Ta le 1 detai s the s bdivision of los es within a typical al - im typ ca acitor unit

Table 1 – Typic l los e in a al -fi m c pa itor unit

The a ove los es are typical; g arante d values would b in the order of 2 % hig er

Fu eles ca acitors have simi ar dielectric, dis harge resistor and con ection los es to those

stated a ove In resp ct of external y fu ed u its, the los es d e to the external fu e are

ad itional to those q oted With improvements in the c oice an desig of dielectric, it is

noteworth that the los es in the ca acitor u it dis harge resistor now ten to dominate The

req irements an d ty for s c resistors are not within the direct control of the ca acitor

man facturer, but are dictated by dis harge time req irements imp sed by international

stan ard or the c stomer’s own req irements If an en an ed dis harge req irement is

sp cified then the los es as s own in Ta le 1 wi b hig er

The los es dis u sed a ove refer to new ca acitor u its Dielectric los es ten to red ce

with time, re c in their minimum fig re within a few h n red hours of o eration for al - i m

typ ca acitor u its However, the red ction is minimal, and b cau e the dielectric los is no

lon er the major contributor to los es, the ef ect of the red ction on the total fiter los es is

minimal Tests con u ted by ca acitor man facturers also confirm that the los es at low

order harmonic (in terms of W/kVAr) are simi ar to the values given a ove at fu damental

freq en y

The p wer los es of e c in ivid al ca acitor b nk, as umin that the los an le is the same

at harmonic freq en ies as at fu damental freq en y, can b determined by:

nnXIP

1

c2

cc

is the ca acitor re ctan e at harmonic order n;

tan(δ) is the tan ent of the ca acitor los an le

Sh nt ca acitor b nks are of en provided in ad ition to harmonic fi ters to provide p rt of the

total con erter station re ctive p wer req irements Their los es, at b th fu damental an

harmonic freq en y, can b as es ed in a simi ar man er to fi ter ca acitors as dis u sed

a ove However, b cau e the los es of the ca acitor u its themselves are low, the ef ects of

los es in other comp nents whic may then b come sig ificant s ould not b overlo k d In

this resp ct los es d e to the fol owin plant items can typical y in re se the los es d e to

the ca acitor u its alone by some 5 %:

• the intercon ectin ca les an bu b rs;

• the ca acitor b nk switc ge r;

• the ca acitor b nk (dis harge) p tential tran former (PT);

• the inru h reactor (when provided);

• the ca acitor fu es;

• the ca acitor b nk internal con ection

4.3 Re ctor a d re istor los e

4.3.1 Ge eral

In general, fi ter re ctors (an where provided, resistors) are the dominant source of total

fi ter los es This is p rtic larly so for a fi ter b nk that provides aten ation for low order

harmonic , either in the form of sin le freq en y tu ed fi ters or damp d typ s

For sin le frequen y tu ed fi ters, the fiter desig er is ofen req ired to ma e a compromise

b twe n the Q (q alty) factor for the re ctor at fu damental freq en y an at the tu ed

harmonic freq en y At fu damental freq en y, to minimize los es, the req irement is to

sp cify a Q factor as hig as p s ible, where s at harmonic freq en ies, in p rtic lar the

tu ed freq en y, it is desira le to sp cify a Q factor comp tible with the fi ter p rforman e

req irement The req ired Q factor at the harmonic freq en y may b low when the fi ter is

l k ly to b s bjected to wide detu in efects b cau e of large s stem freq en y variation

an /or ambient temp rature ran e The final b lan e can ofen b a compromise b twe n

these confl ctin req irements, esp cialy when a fi ter re ctor man facturer's lowest initial

cost desig is not o timal in resp ct of los es

Me n are however avai a le to the re ctor desig er (at le st for natural y air co led re ctors

of o en con tru tion) to control or o timize this b lan e of Q factor req irements at the

variou freq en ies by me n of ad itional de-Q’ n coi s in taled on the re ctor, or even by

the u e of self tu in fi ters

For damp d fi ters, the c oice of re ctor Q factor at harmonic freq en ies is general y

u imp rtant in terms of ac ievin the req ired p rforman e an o timal ratin , le vin the

fi ter desig er a relatively fre c oice in sp cifying Q factor at fu damental freq en y to

satisfy the b lan e b twe n re ctor cost an los es However, for double- u ed damp d

minimize the ef ects of circ latin harmonic c r ents within the fi ter itself In re sin the Q

factor may in certain circ mstan es in re se the harmonic los es in the re ctors

The re ctor Q factor at harmonic freq en ies is general y defined with a certain ran e of

toleran e arou d a nominal value For the calc lation of los es, the minimum Q (i.e the

hig est resistan e) rather than the nominal value s ould b u ed

The p wer los es in the re ctor can b determined by

n

n

nn

Q

XI

P

1

l2

In determinin the overal fi ter config ration, the desig er wi have evaluated the c oice

b tween tu ed an damp d typ fi ters an also b twe n the variou typ s of damp d fi ter in

terms of minimizin fi ter resistor los es In this context, con ideration s ould have b en

given to the red ction in resistor los that can b gained by the u e of third order an C- yp

fi ters rather than secon order typ , again t a general y p orer p rforman e Con ideration

wi also have b en given to whether it is neces ary for sin le freq en y tu ed fiters to b

provided with an external resistor to ac ieve the req ired fi ter Q factor at the tu ed harmonic

freq en y

In determinin the c oice b twe n the variou typ s of damp d fi ter, it s ould b

rememb red that esp cial y for AC fi ters con ected to a hig s stem voltage, the cost of the

resistor b nk itself is not directly pro ortional to the req ired los dis ip tion sin e the cost of

the in ulation req ired can b a sig ificant pro ortion of the total cost

The p wer los es in the resistor can b determined by

Sh nt re ctors may form p rt of an HVDC con erter station to provide in u tive

comp n ation for AC harmonic fi ters esp cial y u der l g t lo d con ition where a certain

req irements The derivation of their los es is simi ar to that in con entional tran mis ion

s stem a pl cation It s ould b noted that in general their los es at harmonic freq en ies

are almost neglgible in comp rison to those at fu damental freq en y

4.4 Criteria for los e aluation

4.4.1 Ge eral

L s evaluation is ofen given a hig profi e by c stomers purc asin HVDC con erter

station in their ten er analy is The criteria for their as es ment therefore ne d to b

con istent an u ambig ou an b cle rly defined in the tec nical sp cification, whic

s ould not b nefit or disad antage one bid er with resp ct to another

IEC 618 3 provides a set of criteria for as es in AC fi ter los es an is of en sp cified by

purc asers of HVDC con erter station /s hemes As s c it u eful y provides a me n of

as es in desig s from a variety of p tential bid ers on an eq al b sis However there are

in tan es where the criteria sp cified in this doc ment do not alway ful y reflect o eratin

con ition oc ur in in practice, whic may give rise to los es of a diferent mag itu e

These p rtic lar in tan es are dis u sed later

The variou asp cts that ne d to b con idered when as es in los es are

a) fu damental freq en y AC fi ter bu b r voltage,

b) fu damental freq en y an ambient temp rature,

c) AC s stem harmonic imp dan e,

d) harmonic c r ents generated by the con erter,

e) pre-existin harmonic distortion, an

f anticip ted lo d profi e of the con erter station

These are dis u sed in turn in 4.4.2 to 4.4.7

4.4.2 Fun ame tal fre ue c AC fi ter busbar volta e

Sin e the c oice of AC fi ter bu b r voltage is not a sen itive is ue, i.e it s ould not in

general favour one desig of AC fi ter config ration over another, los es s ould b

determined for nominal AC fi ter bu b r voltage

4.4.3 Fu dame tal fre ue c a d ambie t temperature

Initial y it mig t a p ar that in common with the c oice of fu damental freq en y AC s stem

voltage, los as es ment s ould also b b sed on the nominal value of fu damental

freq en y

Whi st this a pro c is general y satisfactory for the majority of other comp nents comprisin

the con erter station, it may b ina pro riate for AC harmonic fi ters, an the c oice of

fu damental freq en y an ambient temp rature variation may b a sen itive is ue

De en in on the typ of fi ter ar an ement, the fi ter harmonic los es u der the extremes of

freq en y variation (an of ambient temp rature where a pro riate) can vary sig ificantly

from those calc lated u in nominal freq en y an a "nominal" temp rature This is

esp cial y sig ificant for ar an ements whic comprise sin le or double- u ed fi ter bran hes

For damp d fi ters the efect of s c variation is however negl gible

Therefore, in order to provide the c stomer with a ful er knowled e of the los es p s ible

from e c fi ter desig , los as es ment for AC harmonic fi ters s ould b determined at the

extremes of fu damental freq en y an ambient temp ratures as sp cified for harmonic

p rforman e calc lation

This s ould b in ad ition to the calc lation method u in nominal freq en y an an ambient

temp rature of 2 °C (IEC 618 3), whic is of u e in comp rison of los es for the overal

con erter station

4.4.4 AC s stem harmonic impe a c

The c oice of an a pro riate s stem harmonic imp dan e for the calc lation of los es is also

a sen itive is ue HVDC project sp cification have ten ed to in icate (an

IEC 618 3:19 9/AMD1:2 10, 5.3.1, recommen s) that for los as es ment the AC s stem

s ould b as umed to b o en circ ited "so that al the con erter harmonic c r ents are

con idered to flow into the AC fi ters"

However, this criterion neglects the fact that resonan e b twe n the AC fiters an the s p ly

s stem harmonic imp dan e can oc ur, le din to mag ification of the harmonic c r ents

generated by the con erters (an an other sources)

A c oice of s stem harmonic imp dan e more re resentative of con ition actual y oc ur in

in practice is to u e the imp dan e employed for the determination of fi ter p rforman e ( he

alternative u e of the s stem harmonic imp dan e employed for fi ter ratin con ition may

b to p s imistic for los as es ment

As with 4.4.3 a ove, this calc lation could b done in te d of, or in ad ition to, the

calc lation with o en circ ited AC s stem

4.4.5 Harmonic c r e ts ge erate by the conv rter

IEEE Std 1 5 -19 1, 4.3.1, an several HVDC project sp cification recommen that the

determination of AC fi ter los es s ould b b sed only on the c aracteristic harmonic

c r ents generated by the con erter an imply that non-c aracteristic harmonic s ould b

neglected

However, for several HVDC s hemes it has b en neces ary to in lu e low order harmonic

fi terin sp cifical y to at en ate resid al non-c aracteristic harmonic c r ents to satisfy the

p rforman e criteria In s c cases, in order to o tain a re l stic as es ment of exp cted

los es, the fi ter los calc lation s ould ta e these non-c aracteristic harmonic into ac ou t,

as they may have a sig ificant imp ct on the mag itu e of fi ter los es De en in on the

a pro c ado ted by the c stomer, this may b req ested in te d of, or in ad ition to, an

as es ment whic ex lu es non-c aracteristic harmonic

In resp ct of con erter c aracteristic harmonic c r ents for los as es ment, values

calc lated for "p rforman e" con ition are a pro riate, i.e those b sed typical y on nominal

values of delay an le an commutation re ctan e

If non-c aracteristic harmonic are to b con idered, then values for re ctan e imb lan es

b twe n con erter tran formers comprisin a 12-pulse group, imb lan es b twe n in ivid al

con erter tran former phases, an imb lan es in delay an le b twe n valve groups in a

12-pulse p ir an within a 6-pulse valve group, s ould b b sed on "exp cted" levels rather

than "g arante d" levels, s bject to the agre ment of the c stomer

The ef ects of negative phase seq en e voltages on los es in con erter plant are of en

overlo k d in the as es ment of los es Su h voltages present at the con erter station AC

s p ly s stem res lt in p sitive seq en e third harmonic c r ents b in prod ced by e c

con erter an therefore influen e the los es in an as ociated low-order harmonic fi ters

These los es can b s bstantial, an the c stomer is ad ised to o tain a re l stic knowled e

of their l k ly level For s c a los calc lation, the level of negative phase seq en e voltage

u ed s ould b that defined for the as es ment of harmonic p rforman e

4.4.6 Pre-e isting harmonic distortion

Whether the efects of pre-existin harmonic distortion s ould b in lu ed in the los

as es ment or not largely dep n s on the req irements of the p rforman e sp cification If in

the as es ment of p rforman e the efects of pre-existin harmonic distortion are to b

neglected (se also IEC TR 6 0 1-1:2 16, 7.1.6) then it is also a pro riate to neglect them

in los as es ment On the other han , where the performan e req irements state that

pre-existin harmonic distortion s ould b in lu ed, los es s ould also b b sed on their

con ideration

Where the con erter station in lu es p wer electronic re ctive comp n ation, for example an

static var comp n ator (SVC), as p rt of the total p ck ge, s c plant may itself b a source

of harmonic c r ent generation an to comply with the p rforman e criteria may req ire

as ociated harmonic fi ters Nonetheles , a certain level of its harmonic c r ent wi flow into

the harmonic fi ters as ociated directly with the con erters an s c levels s ould also b

ta en into ac ou t in their total los as es ment

4.4.7 The a ticipate loa profi e of th conv rter station

The evaluation of the economic cost of los es from the AC fi ters wi b he vi y de en ent on

the exp cted lo d profi e for the con erter station, whic also ta es into ac ou t the amou t

of time that e c con erter o erates in rectifier an in erter mode ( or bi-directional

s hemes) an o eration u der " e d " (or "stan by") mode con ition

Re d mode is defined as the con ition when al the eq ipment neces ary for o eration of

the l nk is lve an tran mis ion may b esta l s ed by de lockin the valves It is also of en

termed standby mode L ad los es are those cor esp n in to the o eration of the l nk at an

p rtic lar o eratin con ition a ove re d mode, up to an in lu in ful lo d

For certain a pl cation , it may b a req irement that in re d mode a minimum n mb r of

fi ters s ould b con ected even thou h the th ristor valves are block d The n mb r of

fi ters con ected for s c con ition would b that whic satisfies the harmonic p rforman e

req irements for the minimum fe sible DC lo d con ition an also satisfies the re ctive

p wer b lan e req irement

For e c lo d con ition as es ed, the n mb r of AC fi ters in service s ould b con istent

with the p rforman e an re ctive p wer b lan e req irements an the total los es s ould

b determined for con istent o eratin p rameters (s c as delay an le)

The los es for e c of the in ivid al lo din con ition may then b weig ted with s ita le

factors re resentative of the anticip ted o eratin profi e to determine the total eq ivalent

los es It s ould however b noted that de en in on the a pro c ado ted by the c stomer

for evaluatin the cost of los es, los es at fu damental an harmonic freq en ies may b

weig ted dif erently, as may b those for re d mode an lo d los es

5 De ign issue and special a pl cations

5.1 Ge eral

Clau e 5 provides some g idan e regardin a selection of more ad an ed desig is ues an

some sp cial fi ter a pl cation , alway with referen e to con entional p s ive AC fi ters

Newer tec nologies, for example active fi terin , are des rib d in IEC TR 6 0 1-1:2 16,

Clau e 10

Exp rien e from n merou HVDC s hemes is con en ed in the fol owin The s bjects

dis u sed in lu e to ic whic have arisen in a n mb r of projects, as wel as some more

u u ual a pl cation

Some of these to ic may have an imp ct on the wordin of the c stomer’s tec nical

sp cification, but most are in lu ed in order to as ist the c stomer d rin the bid evaluation

stage an s bseq ent dis u sion with the bid ers an later the contractor

5.2 Performa c a pe ts

5.2.1 Low ord r h rmonic fi tering a d re ona c conditions with AC s stem

The mec anism of generatin non-c aracteristic low-order harmonic is wel known an

des rib d in IEC TR 6 0 1-1:2 16, Clau e 5 The p rtic lar influen e of negative seq en e

voltage on the generation of 3

rd

harmonic is tre ted in IEC TR 6 0 1-1:2 16, 5.4.6

Harmonic AC fi ters tu ed for the c aracteristic 12-pulse harmonic b have as a ca acitive

imp dan e at lower freq en ies By nature the AC s stem harmonic imp dan e, whic is in

p ral el with the fi ter imp dan e, cre tes p ral el resonan e phenomena at con erter

bu b rs In some HVDC s hemes, therefore, low-order harmonic fi ters have b en in tal ed to

damp s c resonan e (CIGRE WG 14.0 ) an to lmit the distortion generated by some non

-c aracteristic harmonic from the con erters

From exp rien e, s c typ s of fi ters are extremely exp n ive, an d e to the normal y low

Mvar ratin of the fi ter ca acitors (whic themselves are exp n ive) an the low tu in

freq en y of the circ its, the fi ter re ctors ne d to b desig ed with u u ual y hig

in u tan e values an fu damental freq en y ratin s Ad itional y, the los es, if dampin

resistors are provided, are relatively hig

This typ of fiter may ne d to b in service over the whole ran e of con erter lo d

Con iderin the re ctive p wer req irements, this would have an imp ct on the n mb r of

minimum fi ters p s ible at l g t lo d con ition an in re se the re ctive p wer ex han e

with the AC s stem In some s hemes this s rplu has b en comp n ated with ad itional

s u t re ctors, whi e some other s hemes o erate the converters with in re sed firin an les

an hig er re ctive p wer con umption

The ac urate model n of the harmonic AC s stem imp dan es at the secon an third

harmonic is imp rtant in order not to overdesig s c low order fi ters For harmonic b low

the 1

th

order, a detai ed an ac urate re resentation is recommen ed to en ure that

mag ification of harmonic is damp d out to the o timum If this is not p s ible d rin the

plan in stage some flexibi ty an al owan e for risk s ould b given to the contractor to

stu y this phenomenon d rin project exec tion an to mitigate an pro lem u der his own

resp n ibi ty at a later stage of the project In some cases, con erter control with sp cial

fe tures could b u ed as a solution for low order harmonic pro lems in te d of expen ive

harmonic fi ters (CIGRE WG14.0 /c 0 (JTF 01)

It is also vital to model ac urately the harmonic interaction b twe n AC an DC sides of the

con erter, an the influen e of the con erter control s stem, when determinin the ne d for,

or the desig of, s c low-order fiters (se IEC TR 6 0 1-3:—, Clau e 3) Ig orin these

factors can res lt in completely misle din con lu ion , an p s ibly the u neces ary

sp cification for a low-order fi ter to b in tal ed

A major disad antage of low order fi ters (3

rd

harmonic, or 3/5

th

for example), is that they are

lo ded not only by c r ents from the con erter, but also from other harmonic sources in the

AC s stem Ofen s c sources are not the resp n ibi ty of or u der the control of the

c stomer, may not b fi tered local y, an their mag itu e is not known They may also have

come on l ne d e to in u trial develo ment ta in place afer the desig of the HVDC station

The c r ents from s c sources may, furthermore, b mag ified by resonan es within the AC

network It is therefore dif ic lt to predict how mu h network harmonic c r ent may flow in the

low-order fi ters, an in the p st low-order fi ters have b en trip ed or damaged d e to s c

overlo d Over-ratin of the fi ters is the only solution, but it is dif ic lt to predict how mu h

over-ratin is ne ded to en ure sec rity, an the fi ters can b come very exp n ive

It is therefore ad isa le to exp n con idera le ef orts, if neces ary, in stu yin low-order

harmonic pro lems u in ac urate model n , in order to try to avoid the neces ity of

in tal n low-order fi ters The c stomer s ould b aware of the is ues an b pre ared to

dis u s with bid ers an asp cts of the tec nical sp cification, for example the pres rib d

AC s stem imp dan e en elo e, level of sp cified negative seq en e voltage or in ivid al

harmonic voltage l mits, whic may force the contractor to in lu e low-order fi ter bran hes

in the desig

5.2.2 Definition of interfere c fa tors to in lude h rmonic up to 5 kHz

In most tec nical sp cification , the maximum harmonic order to b con idered for AC fi ter

p rforman e is the 5 th However, a few sp cification have exten ed the ran e to b

con idered up to the 8

rd

harmonic at 6 Hz, i.e 5 kHz The imp ct on the fiter desig an

costs when con iderin harmonic hig er than the order of 5 can b sig ificant, an careful

con ideration s ould b given by the c stomer b fore ma in s c a req irement

Stan ard commu ication on analog e tele hone l nes s ould not b sig ificantly af ected in

this up er freq en y b n b twe n the 5

th

harmonic an 5 kHz by the level of harmonic

actual y generated by the HVDC con erters However, if the AC fi ter desig do s not in lu e

hig -p s damp d fi ters, then p tential resonan e con ition b twe n tu ed AC fi ters an

the AC s stem could b cre ted These would ne d to b stu ied in order to avoid ex es ive

interferen e in the ne rby commu ication s stems To o tain re l stic res lts of s c stu ies,

pro er model n of freq en y de en en e for the major comp nents s c as l nes,

tran formers an lo d is of gre t imp rtan e However, the freq en y de en en e is largely

u known in this up er freq en y ran e an so s c detai ed stu ies are general y not

fe sible

If hig -p s damp d fi ters are u ed in the con erter station , the hig er order harmonic

injected into the AC s stem wi b negl gible However, the u e of hig -p s fi ters large

enou h an with s f icient dampin to satisfy strin ent p rforman e criteria over this

exten ed freq en y ran e may in re se the fi ter costs an los es sig ificantly

The c stomer is therefore faced with a di emma – if the tec nical sp cification l mits the

p rformance req irements to the 5

harmonic Su h a desig would fulfi

the sp cified req irements, but could cre te a resonan e with the AC s stem at hig er

freq en ies, ampl fyin harmonic whic would otherwise b negl gible

If however the c stomer exten s the freq en y ran e to say the 8

rd

order at 6 Hz (or 100

th

order at 5 Hz), an if the levels of sp cified tele hone interferen e factor (TIF), etc are

those typical y u ed for s hemes with a maximum harmonic order of 5 , then rather large an

hig ly damp d fi ters may b ne ded, at a con idera le extra cost

The c stomer s ould therefore con ider the o tion careful y b fore exten in the sp cified

freq en y ran e for AC fi ter p rforman e a ove the 5

th

order Two p s ible alternative

a pro c es could b con idered:

• sp cify p rforman e req irements only up to the 5

th

harmonic, but sp cify in ad ition

that the AC fi ters s ould have a damp d c aracteristic a ove the 5 th (p s ibly also

definin the maximum p rmited fiter imp dan e phase an le p rmited at harmonic

for TIF, tele hone harmonic form factor (THFF) or the prod ct of RMS c r ent I an TIF

(IT produ t ac ordin ly, in order to avoid an u neces ari y exp nsive fi ter desig

5.2.3 Triple-tune fi ter circ its

Double- u ed fi ter circ its have b en esta l s ed in the p st as a stan ard desig for

ju tify a fi ter desig with more than one tu in freq en y In certain circ mstan es, further

o timization may b p s ible if more than two tu in freq en ies can b ac ieved In ten ers

for recent projects, man facturers have identified a cost savin ad antage if triple- u ed

fi ters could b provided (se also IEC TR 6 0 1-1:2 16, 6.4.3)

In the p st, the introd ction of triple- u ed AC fi ters has b en resisted, mainly on the

grou d that on site- u in would b dif ic lt However, the u e of modern in truments

el minates an seriou dif ic lties Tu in is sti more compl cated than for sin le- or doubl

e-tu ed fi ters, but is q ite fe sible More ver, if the fi ter is desig ed so that s arp tu in is

only req ired at one of the freq en ies, with bro d-b n damp d c aracteristic at the other

two freq en ies, then s f iciently ac urate tu in can b re di y ac ieved

A triple- u ed fi ter wi general y b at ractive if the alternative desig req ires smal fi ter

b nk sizes at an extremely hig AC s stem voltage In order to ac ieve an economical desig

of HV ca acitor, it is then desira le to fi ter several major con erter harmonic within one

fi ter b nk If neces ary, hig -p s c aracteristic can b implemented with ad itional

dampin resistors

The fol owin req irements can also le d to a triple- u ed fi ter b in con idered as a

solution:

• o erational req irements for re ctive p wer control within nar ow lmits;

• combination of strin ent THFF or TIF voltage distortion combined simultane u ly with low

IT prod ct lmits;

• minimizin fi ter re ctive p wer in tal ation close to generators;

• low order fi terin combined with a 12/2

harmonic circ it, th s red cin the ne d for s u t re ctors;

• hig er red n an y for al typ s of fi ter u ed

Pos ible disad antages to b con idered (se also IEC TR 6 0 1-1:2 16, 6.4.3), a art from

the more compl cated on-site tu in , are as fol ows:

• sen itivity of the tu in to blown ca acitor fu es;

• n mb r of c r ent tran formers (CTs) req ired to en ure protection of al comp nents, or

p s ible over atin of u protected low voltage comp nents

The c stomer an contractor s ould therefore ta e al these factors into ac ou t an give

seriou con ideration to whether the u e of triple- u ed fi ters would provide the most

economic solution

5.2.4 Harmonic AC fi ters on tertiary winding of conv rter tra sformers

Some HVDC con erters up to a rated p wer of a proximately 20 MW to 3 0 MW have b en

ar an ed with harmonic AC fi ters con ected to a tertiary win in of the con erter

tran formers, for example Blackwater, McNei an Vyb rg HVDC con erter station

Savin s can b exp cted in the sp ce an in estment costs of the fi ter circ its, in lu in the

AC fi ter bre k rs, b cau e the l mitation on economic minimum ca acitor b nk ratin are

red ced by employin a lower con ection voltage In ad ition, identical voltage an Mvar

desig of the comp nents for b th rectifier an in erter side can save costs in providin a

minimized n mb r of sp re items for the con erter station Further, with this solution the fi ter

re ctors can b con ected in the l ne side of the tertiary fi ter Then, the fi ter main ca acitor

can b made in a simple thre -phase ar an ement, simpl fyin the AC fi ter protection

comp red to a con entional HV fi ter desig

Con ideration s ould b given to fi ter outages An sp re or red n ant fi terin has to b

provided on a p r- ran former rather than a p r-station b sis, an this can sig ificantly

red ce an cost ad antage Fi ters may b s ared by the u e of of -lo d dis on ectors to

al ow s arin without in re sin fault levels

With this solution, the series con ected tran former imp dan e b twe n the fi ter an the HV

s stem side red ces the contribution of the hig er order harmonic an this can simpl fy the

fi ter ar an ement (hig -p s fi ters only b in ne ded for hig er freq en ies) If s u t

re ctors are req ired, the tertiary bu b r con ection ( ypical voltage ran e b twe n 3 kV

an 6 kV), al ows air core typ re ctors to b provided, whic are pro a ly more economical

comp red to oi immersed typ HV s u t re ctors

The tran former costs comp red to a con entional s heme wi sl g tly in re se an the

savin s in the fi ter are s have to b comp red again t this, to determine the o timum

solution The fol owin asp cts relatin to the con erter tran former s ould also b ta en into

ac ou t

• The ad itional tertiary win in has to b desig ed for the s ort circ it d ty an has a

relatively low le k ge imp dan e from tertiary to the HV bu win in

• The tran former rel a i ty wi b lower

• The four win in con erter tran former is not a stan ardized item of eq ipment an for

s stem stu ies a detai ed tran former model ne d to b develo ed by the contractor to

prove al the as umption an ratin s

• The con erter tran former imp dan e selection has to reflect the req irement to l mit the

s ort circ it c r ents to ac e ta le l mits; but on the other han the c oice of the

tran former imp dan es has an imp ct on the overal harmonic performan e of the AC

fi ters an ne d to b c osen in s c a way that resonan es b twe n the fi ter circ its

an the AC s stem are damp d out to a minimum

• The voltage profi e at the tertiary fi ter bu b rs has to b con idered when calc latin the

re ctive p wer comp n ation, an in general a larger re ctive comp n ation wi b

req ired than if fi ters were in tal ed on the hig voltage bu

5.3 Rating a pe ts

5.3.1 Limiting high harmonic cur e ts in paral el-re ona t fi ter circ its

Double- u ed or triple- u ed fi ters in lu e p ral el resonant circ its, whic cre te the anti

-resonan e p ints b twe n the tu ed freq en ies For the comp nent c r ent an voltage

ratin s of these circ its the dampin at harmonic freq en ies is an imp rtant factor Unles a

se arate dampin resistor is in lu ed in the circ it, the circ latin harmonic c r ent is l mited

mainly by the resistan e of the re ctor Optimization b twe n the fe sibi ty of providin L-C

comp nents with hig harmonic c r ent ratin s an the alternative of los inten ive resistive

dampin is one of the major tasks for the fi ter desig er

An iterative desig proced re is req ired, sin e if the re ctor q al ty factor c an es, the

c r ent an voltage ratin s in the p ralel resonan e circ it can vary sig ificantly Close

co-o eration b twe n the s stem desig er an the comp nent man facturer is ne ded to o tain

an economic comp nent desig

If in sp cial cases, the q al ty factor of the re ctors has to b red ced b yon what is

p s ible within the re ctor itself, an ad itional series dampin resistor can b con ected to

the fiter re ctor coi or to the fi ter ca acitor

5.3.2 Tra sie t ratings of paral el circ its in multiple tu e fi ters

For double- u ed an triple- u ed fi ters, exp rien e has s own that the tran ient ratin s of

the comp nents of the low voltage tu in circ its are of major imp rtan e in the fi ter desig

Therefore it is recommen ed to in lu e re resentative os i ograms for the worst case

In some cases with extreme low dampin in the circ it, voltage os i ation have to b

con idered for the decisive voltage- ime c rve for the ca acitor voltage ratin s, for example

NEMA c aracteristic The tran ient voltages acros ca acitors are u ed to desig for the

dielectric stres es in ide the ca acitor u its

For low order harmonic fi ters, extreme mag itu es of tran ient low order harmonic c r ents

an voltages can oc ur d e to the harmonic c r ent injection cau ed by tran former

saturation ef ects For s c fi ter comp nents, the tran ient ratin s in terms of c r ents,

voltages an energ dis ip tion may b the decisive cases It is the resp n ibi ty of the

contractor to define these ratin s an to prove that the fi ter desig is adeq ate The worst

case for the dif erent comp nents has to b selected out of variou stu y cases varyin fault

initiation, fault d ration an fault cle rin s enarios for diferent lo din an AC s stem

con ition

5.3.3 Ov rloa prote tion of high-pa s harmonic fi ter re istors

If resistors are provided in hig -p s fi ters, diferent cases of overlo d con ition can stres

the resistors d rin emergen y situation Su h cases ne d to b c eck d again t the

protective s heme an the s ort time overlo d ratin s of the resistors Typical examples are

• mismatc of fi ter config ration vers s lo d,

• internal faults or inter uption in the fi ter circ it,

• con erter malo eration,

• freq en y deviation d rin emergen y s stem con ition , an

• future modification of the AC s stem imp dan e, le din to fi ter-AC s stem resonan e

In some HVDC s hemes, the resistors are not directly protected by their own c r ent

tran former Some man facturers’ protective s hemes in lu e the a i ty to calc late the

resistor stres es from other values me s red within the fiter circ it, as input to the protective

relayin s heme However, if req ired, it is also pos ible to provide an ad itional resistor

c r ent tran former an the related protection fu ction It is recommen ed to in lu e in the

sp cification the req irement for sp cific resistor protection but req est the bid er to

pro ose, as an alternative, another solution in ac ordan e with his practical exp rien e an

desig phi oso h , to b dis u sed d rin the bid evaluation proces

5.3.4 Ba k-to-ba k switc ing of fi ters or s unt c pa itors

Back- o-b ck switc in refers to switc in one fi ter or s u t ca acitor b nk on a bu to

whic one or more other b nk(s) are con ected Su h switc in ten s to cau e hig inru h

c r ent in the fi ter or ca acitor b nk b in switc ed in

If tu ed fi ters are u ed, the tu in re ctors are s ficient to l mit these inru h c r ents If one

or more s u t ca acitors in p ral el are in lu ed in the desig , it is recommen ed to provide

ad itional c r ent l mitin re ctors in the s u t ca acitor b nks to damp the dis harge

b twe n the in ivid al bran hes For circ it brea er desig asp cts refer to 9.7

Another ad itional ad antage could b ac ieved, if the c r ent l mitin re ctors are c osen so

that the s u t ca acitor b nks are tu ed to some hig er order c aracteristic harmonic or

alternatively – in case only 12

th

/2th

fi ters are in taled – to a freq en y sl g tly lower than

the 3

th

By this me n , p ralel resonan es b twe n the fiters an the s u t ca acitor wi

avoid al c aracteristic 12-pulse harmonic hig er than the 2

th

an can b s if ed to non

-critical freq en ies

5.3.5 Short time ov rloa – re sonable spe ific tion of re uireme ts

Subclau e 5.3.5 dis u ses how far in erent s ort time overlo din of the fi ters d e to

s stem emergen ies s ould b re sona ly sp cified Short time overlo d for fi ter

• s ort time overvoltages in the AC s stem;

• s ort time AC s stem freq en y deviation ;

• s ort time overlo d of the HVDC con erters

Al combination of freq en y ex ursion , detu in of fi ter comp nents an AC bu voltage

levels ne d to b stu ied to determine the worst case lo din con ition

As an example, typical s ort time d ration to b con idered can b clas ified as:

Disturb d s stem con ition : 1 min to 10 min d ration

Also, when desig in fi ter comp nents for al these req irements with resp ct to l fetime an

risk, a re sona le d ty c cle s ould be clearly defined These definition s ould also reflect

the initial an fol ow-up s stem con ition for the s stem d ty c cles

Evidently, it would b desira le that the decisive ratin of fi ter comp nents s ould not b

determined by a normal situation of s ort time d ration Of en, fi ter comp nents pro erly

rated for ste d -state con ition wi also with tan s ort time con ition However, these

con ition s ould b calc lated an the s ort time ca a i ty of the fi ter comp nents

c eck d

In the event that the s ort time con ition proves to b decisive, the c stomer an contractor

together s ould con ider whether it is economical y re sonable to sp cify the fi ter for the

s ort time con ition in question, or whether in s c a pos ibly u l k ly event the fi ter s ould

b al owed to trip The pro a i ty of the combination of s ort time con ition with maximum

detu in con ition s ould also b q estioned

The efect of s ort time lo din on the variou fi ter comp nents is dis u sed b low

a) Fi ter ca acitors

Short time fu damental freq en y overvoltages may b decisive for the voltage ratin of

the ca acitors Due to their worst case harmonic voltage lo din , ca acitors in lu e some

in erent overvoltage ca a i ties as lon as b th maximum harmonic voltage ratin s an

s ort time overvoltage do not oc ur at the same moment If b th the ste d state

harmonic ratin s an the s ort time s stem overvoltages are s p rimp sed, the s m of

b th s ould b reflected within the voltage- ime c aracteristic of the ca acitor

The s ort time s stem freq en y ran e s ould b con idered when calc latin the

maximum fu damental freq en y voltages an c r ents acros an within the fi ter

ca acitors with the fi ter detu ed to the minimum/maximum extent This may in lu e

outages of ca acitor u its an the worst case toleran es as umed for the ratin

calc lation le din to the hig est voltage an c r ent stres es for the ca acitors

The voltage an c r ent ratin of the fi ter ca acitors has to b c eck d again t the s ort

time overlo d o eration of the HVDC con erters However, normal y, for con erter

overlo d con ition al fi ters/s u t ca acitors are energized, an so the lo din p r fi ter

is u ual y les onerou than d rin the emergen y cases as umin outages of fi ter

bran hes, oc ur in at p rtial lo din con ition , whic ten to determine the fi ter

ratin s

b) Fi ter re ctors

The c r ent stres es are of gre test interest for the fi ter re ctors The sp cified ste d

state ratin s ne d to b c eck d again t the s ort time overlo d stres es

c) Fi ter resistors

Fiter resistors are the comp nents most sen itive to overlo d, d e to the los dis ip tion

The overlo d stres es de en on al the imp cts dis u sed a ove In some recent

projects stu ies s owed that the ratin of the resistors is the critical p int when

con iderin s ort time overlo d

Detai ed calc lation are neces ary to determine the worst case s ort time overlo d of

the fi ter resistors

5.3.6 Low volta e fi ter c pa itors without fus s

For double- an triple- u ed fi ter ar an ements, the low voltage ca acitors are general y not

stres ed by fu damental freq en y c r ent an voltage Therefore the fu es of these

ca acitors ne d to b desig ed for the harmonic c r ent stres es, whic vary de en in on

the lo din con ition of the con erters an on the actual n mb r an typ of the AC fiters in

service From these varyin lo din con ition the fu e o eratin c r ents have to b

co-ordinated with the maximum worst case c r ent lo din con ition of the ca acitor u its

For o eratin c r ents lower than the rated values, the fu es wi not b a le to cle r fai ed

ca acitor u its d e to the mis in dominatin fu damental freq en y comp nent in the

c r ent Therefore in some HVDC projects, low-voltage fi ter ca acitors without fu es have

b en u ed for p ral el tu in circ its In some cases, these have b en desig ed for extremely

hig harmonic c r ent ratin s (d e to detunin an outages of fi ter b nks) For example, in

some fi ters, 1

th

an 13th

harmonic c r ent ratin s up to a proximately 1 0 0 A RMS for low

voltage comp nents of double- u ed fi ters have b en req ired

5.4 Fi ters for spe ial purpos s

5.4.1 Harmonic fi ters for damping tra sie t ov rvolta e

In some HVDC projects, harmonic fi ters of a low-order type are u ed for b th stead state

an tran ient fiterin Tran ient fi ters to l mit temp rary overvoltage (TOV) at the converter

station bu b r can b u ed for l mitin the saturation overvoltages of the con erter

tran formers af er AC bu faults or lo d rejection If the s ort circ it level at the AC bu b rs

is very low the overvoltages may b q ite hig

Durin tran former saturation the secon an third harmonic tran ient overvoltages cau ed

by the injected harmonic tran former c r ents can b hig , if the AC s stem imp dan e

resonates with the AC fi ters close to the secon or third harmonic In this case the fi ters

ne d to b desig ed to a sorb a hig energ level an to damp the saturation overvoltages

for the first time p a s b fore other cou terme s res s c as fiter trip in an SVC

o eration can b initiated It is desira le to hold the ste d state lo d rejection voltage to

b twe n 1,1 p.u an 1,2 p.u comp red to the bu voltage prior to the fault

As an example, for the 1 0 0 MW Chate u uay HVDC con erter station two fi ter b nks

(2 × 13 MVAr 2

n

harmonic hig -p s fi ters) have b en in tal ed Sp cial desig stu ies

were exec ted for determination of the amou t of energ to b dis ip ted in fi ter resistors

an fi ter ar esters

5.4.2 Non-l ne r fi ters for low order harmonic /tra sie t ov rvolta e

Non-l ne r fi ters can b req ired to b desig ed for two diferent fi terin p rforman e

req irements These two req irements are fi terin of harmonic in the ste d state ran e,

an tran ient fi terin of non-c aracteristic harmonic d rin fault recovery con ition in

order to damp/l mit tran ient an /or temp rary overvoltages The non-l ne r c aracteristic of

this fi ter are cre ted by con ectin non-l ne r metal-oxide ar esters in series with other fi ter

tu in devices

As an alternative a pro c to that dis u sed in 5.4.1 a ove, a sp cial fi ter was desig ed an

s c es ful y commis ioned in Au tria for the Dürnrohr an Vien a South-East HVDC

con erter station For one p rtic lar AC s stem config ration, variou stu ies were car ied

out to detect the worst case s enario for temp rary an tran ient overvoltages The dampin

in the AC s stem was relatively low, an therefore low order harmonic overvoltages,

saturation phenomena an ampl fied by the low dampin of the AC s stem d rin low s ort

circ it ratio (SCR) o eratin con ition of the AC s stem These overvoltages oc ur ed

almost u damp d an the AC bre k rs se med to b in uf icient to cle r again t these fault

overvoltages Stu ies recommen ed the in tal ation of a SVC combined with low order

harmonic fi ters, to l mit the tran ient an temp rary overvoltages in lu in tran former

saturation phenomena

The decision for the Vien a Southe st an Dürnrohr station was to in tal a non-l ne r fi ter

for the 2

n

rd

harmonic with the fi ter ar an ement as s own in Fig re 6 This fi ter

ar an ement has practical y no los es at fu damental freq en y an in erts its fi terin

ca abi ty from a certain trig er level (determined by the ar ester ar an ement A group of

p ral el con ected ar esters in ide the fiter config ration controls the ste d state an

tran ient imp dan e of the fi ter The ar esters have b en desig ed for the worst case energ

dis ip tion d rin fault con ition

Figure 6 – Non-l n ar low order fi ter for Vie na Southe st HVDC station

5.4.3 Serie fi ters for HVDC conv rter stations

Existin exp rien e in AC harmonic fi terin is b sed almost entirely on the u e of s u t typ

fi ters Some detai ed in estigation have b en car ied out in the u e of a mixed config ration

of series an s u t fi ters for Itaipu an one actual a pl cation, in the Uru uaiana b ck-

o-b ck station in Brazi , has given go d o erational exp rien e

A series fiter is fu ctional y simi ar to the wave tra u ed in p wer l ne car ier a plcation

an is bui t with an in uctor (in the ran e of 1 mH to 2 mH) in p ral el with a series-con ected

ca acitor plu resistor (Fig re 7), tu ed to a sin le resonan e freq en y If several

resonan e freq en ies are req ired, a n mb r of s c fi ter circ its can b cas aded in

series, e c of them tu ed to a p rtic lar harmonic freq en y Multiple- u ed series fi ters

(Fig re 8) can also b u ed, presentin two or more imp dan e p a s (imp dan e p a s for

car ier an /or for radio freq en y may also b in lu ed if neces ary) A damp d b n -sto

c aracteristic can also b ac ieved to fi ter a ran e of hig er order harmonic

The a ove mentioned in estigation have in icated that, con iderin the con erter as a

source of harmonic c r ent, the u e of a series fi ter is ef icient only if it is as ociated with a

s u t imp dan e of relatively low imp dan e, s c as can b o tained with a ca acitor b nk

an /or s u t fi ter Therefore the a pl cation of a series fi ter s ould b done in a mixed

config ration of series an s u t fi ters (Fig re 9)

De en in on the sp cific req irements of the project an on an economic evaluation, one

sin le series fi ter for the whole con erter station, in tal ed b twe n the s u t fi ter bu an

the AC l ne bu , or one fi ter for e c l ne con ected to the AC con erter station can b u ed

For the solution with a sin le fi ter for the whole station, the series fi ter s ould b formed by

Figure 7 – Single-tune s rie fi ter a d impe a c plot

Figure 8 – Triple-tune s rie fi ter a d impe a c plot

Ad antages of series fi ter circ its are:

• fewer ca acitor u its an smal er fi ter re ctor size than for s u t fi ters;

• les sp ce req irements;

• no ne d for circ it bre k rs an as ociated switc ge r, but only p ral el dis on ect

switc es (as umin that these can remove a faulted p ral el bran h on-lo d or if a n

o-red n an y a pro c is ac e ta le);

• minimum of protection eq ipment

Disad antages of series fi ter circ its are:

• the main re ctor has to car y the fu damental freq en y lne c r ent;

• ca acitor/overvoltage protection again t s ort circ it faults is exp n ive;

• no re ctive p wer s p ort comp ra le with con entional s u t fi ters;

• if hig -p s resistors are provided, the resistor los es are relatively hig ;

• comp nents ne d to b desig ed with a hig s ort circ it ca a i ty;

• protective devices s ould b rated for ful AC bu voltage;

• may introd ce fu damental freq en y or s b-harmonic resonan e an sta i ty pro lems;

• relatively compl cated protection s hemes

Cn Ln Rn

IEC C

Lin tra

R

Z

f