00037180
TRANSCRIPT
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CRI TERI A AND DESI GNS FOR
SURGE COUPLERS AND BACK- FI LTERS
SESSION
4C
Pet er Ri chman
KeyTek I nst r ument Corp.
260 For dhamRoad
W l m ngt on, MA 01887
Abstract
Surge coupl ers and back- f i l t ers ar e necessary
f o r per f or m ng sur ge t est s on el ect roni c
equi pment , i n order t o s i mul ate t he ef f ects
of
l i ghtn i ng and swi t chi ng t r ans i ent s on both
power and dat a l i nes. Such coupl er s and
f i l t ers are poor l y underst ood and i nadequate-
l y s t andardi zed, yet t hei r per f ormance can
s i gni f i c ant l y af f ec t t he r es ul t s of sur ge
t est s on both component s and equi pment.
Nomencl at ur e, desi gn and perf or mance
of
opt i mum conf i gur at i ons are i ncl uded,
f ol l owi ng a r e ci t a t i on
of
common exi st i ng
pi t f al l s and m sconcept i ons .
I nt r oduc t i on
f f enerators
of
shor t - dur at i on pul ses , t ermed
surges, have l ong been used t o t est t he
capabi l i t y of power t r ansm ssi on and
di s t r i but i on equi pment t o wi t hst and
hi gh-vo l t age peaks. Such t r ans i ent s occur
due both t o l i ght n i ng event s and t o var i ous
normal power systemoperat i ons , i ncl udi ng
swi t chi ng and f aul t - c l ear i ng. The dura t i ons
of such t r ans i ent s are t ypi ca l l y measur ed i n
t ens
of
m cr oseconds, hence t hey ar e of t en
t rans f ormed, wi t h onl y m nor al t er at i ons ,
down t o the l ower vol t age l evel s used t o
suppl y power wi t h i n i ndust r i a l and
r e si dent i al l oc at i ons . I n addi t i on,
t r ans i ent s due both t o l i ght ni ng and t o
swi t chi ng can be i nt r oduced di r ect l y i nt o l ow
vol t a ge c i r c ui t s . Thus , vi r t ual l y al l
e l ect r i ca l and e l ect r oni c equi pment used on
convent i ona l i ndoor power l i nes i s subj ected
t o what can be su rp r i s i ngl y hi gh, shor t - t erm
surge vol t ages and curr ent s. Ampl i t udes
of
such surges can reach l evel s
of
k i l ovol t s and
ki l oamper es at some l ocat i ons. Cl 1
I n or der t o i ns ur e compat i bi l i t y of
el ect r oni c equi pment wi t h t hi s sur ge
envi r onment , such equi pment i s subj ect ed t o
t est surges, bot h on power and si gnal
i nput / out put l i nes , dur i ng both des i gn and
manuf actur e. The obj ect
of
such t est i ng i s
t o ver i f y t hat equi pment des i gn f or sur ge
i mmuni t y i s successf u l , and that i t
i s
corr ect l y i mpl ement ed on a cont i nui ng basi s
as pr oduct s are shi pped. Al l of t hi s
ac t i vi t y r e s ul t s f r o m a bas i c mot i vat i on t o
shi p comput ers, t el ecommuni cat i ons equi pment ,
consumer el ec t roni cs , i ndus t r i al cont r ol
equi pment and
s o
on, t hat wi l l be robus t i n
t he f ace
of
such sur ges , s o t hat t hese
product s wi l l be perce i ved as r e l i abl e i n an
i ncreas i ngl y compet i t i ve market pl ace.
Sur ge t est i ng i s hamper ed, however, by l ack
CH2736-718910000-0202
1
OOU989 EEE
202
of adequate agr eement and s t andar di zat i on on
t he means f or coupl i ng t est surges t o t he EUT
( Equi pment Under Test) . I nt i matel y
associ ated wi t h such coupl i ng i s s i mul t aneous
back- f i l t er i ng on t he l i nes bei ng surged.
Such back f i l t er i ng has t wo pur poses. The
f i r s t i s t o pr e vent t e s t s u r ges f r o m r e achi ng
other equi pment t hat i s not bei ng t est ed, but
whi ch i s nonet hel ess bei ng oper ated on t he
same l i nes. The second i s t o provi de an
i mpedance f or t he sur ge gener ator t o dr i ve,
t hat i s bot h s i gni f i cant l y hi gher t han t hat
of t h e unf i l t e r ed l i ne, and yet s uf f i c i ent l y
l ow t o al l ow no rmal l i ne cur r ent t o f l ow,
wi t hout undue vol t age dr op, t o t he EUT.
Many sur ge coupl i ng conf i gur at i ons are
i ndependent
of
t he back- f i l t er s wi t h whi ch
t hey are necessar i l y associ ated. However ,
some back- f i l t ers c an i nf l uence and even
dom nat e the ef f ect i ve sur ge coupl i ng mode.
For t h i s r eason, surge coupl ers and back-
f i l t er s ar e cons i dered t oget her , as su rge
coupl er / f i l t er s ( o r coupl er / decoupl er s ) ,
s o
t hat such i ssues are i ncl uded i n t he s tudy.
What f o l l ows cover s the pr i nc i pal areas i n
whi ch surge coupl i ng and f i l t er i ng pr obl ems
exi s t . Rul es are devel oped f or speci f y i ng
and des i gn i ng surge coupl i ng conf i gur at i ons ,
so
t hat di f f erent sur ge t est equi pment s can
yi el d the same t est r esul t s on a gi ven EUT.
Surge Coupl i ng Modes
Nomencl at ur e
The most cont r overs i a l t erms i n sur ge test i ng
are t hose descr i bi ng coupl i ng modes, whi ch
def i ne t he l i nes between or among whi ch
sur ges ar e appl i ed. Many such t er ms have
never been pr eci sel y def i ned f or use i n sur ge
t est i ng, as t hey have been borr owed f r om
ot h er di s ci pl i nes , t y pi c al l y f r o m t e l e-
communi cat i ons or measurement i nst r ument at i on
pract i ce. I n addi t i on, some
of
t hese
meani ngs have changed over t i me, as el ect r i -
cal and e l ect r oni c t echnol ogi es have evol ved.
J us t beneath th i s i s sue of nomencl ature l i es
t he ever - pr esent need t o se l ect surge t est
coupl i ng modes whi ch wi l l best s i mul ate the
sur ge envi r onment i n t he equi pment ' s
i nt e nded appl i cat i on. Or d i nar i l y , a l l a r e
requi red f o r s i ngl e -phase appl i cat i ons , whi l e
a f ew of t he many possi bi l i t i es must be
sel ected i n t hree- phase appl i cat i ons.[ 2] I n
any case, l ack
of
preci se nomencl atur e onl y
makes the se l ect i on t ask more di f f i cul t .
r ecent s t andar d, ANSI / I EEE C62. 45-1987,
recogni zes t hese di f f i cul t i es by purposel y
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SESSION 4C
descr i b i ng surge test modes wi t hout r ef erence
t o t er ms l i ke nor mal and common mode. [2] I t
wi l l be shown t hat t h i s i s necessar y but not
s uf r i c i e nt f o r des c r i bi ng r e al i s t i c c oupl i ng
c onf i gur at i ons f o r sur ge t es t i ng. I n t he
cour se of demonst r at i ng t h i s , t he i nadequate
yet commonl y- used t erms wI l l cont i nue t o be
us ed i n what f ol l ows , t o f ac i l i t at e
present ati on. Once t he mat t er has been f ul l y
expl or ed, however, and s uch t er ms have been
shown t o be more conf usi ng t han usef ul , i t
wi l l be r ecommended t hat t hey be abandoned i n
surge t es t appl i cat i ons .
Normal Mode Many f am l i ar t er ms wer e si mpl y
not def i ned wi t h sur ge t es t i ng i n m nd;
" nor mal modeTr s an exampl e. Shoul d t wo
non-gr ounded l i nes bei ng surged i n so- cal l ed
normal mode move equal l y i n opposi t e
di r e ct i ons ? I f , i ns t e ad, t he ent i r e sur g e
appears on j ust one of t h e l i nes , i s t he
surge i n f act coupl ed i n nor mal mode? I s i t
nor mal mode when t wo phases ar e s ur ged wi t h
respect t o a th i r d i n a three- phase syst em?
Whet her
o r
not i t i s , what shoul d be the
r a t i o of t he surge vol t age appl i ed t o the
s i ngl e l i ne, t o t hat appl i ed t o t he ot her
t wo? I s i t al ways normal mode i ndependent of
t hat r at i o? What of t wo l i nes sur ged wi t h
respec t t o neut r a l i n a U.S. r es i dent i a l
power conf ' i gurati on, o r t hr ee l i nes versus
neutr a l i n t hree phase? Ar e these a l l nor mal
mode? There are many such i ssues. I f al l of
t hese exampl es are cal l ed nor mal mode, t he
connot at i on becomes s br oad t hat t he name
l os es al l ut i l i t y i n s ur g e appl i cat i ons .
Anot her cons i dera t i on i s that di f f e rent
hardwar e i mpl ementat i ons have generat ed
c ons t i t uenc i es par t i al t o o ne
o r
anot her
i nt e r pr e t a t i on. For exampl e, shunt and
s er i e s s ur ge i nj ec t i on gi v e r i s e t o di f f er ent
i nt e r p r et a t i ons of nor mal mode. [2] For shunt
coupl i ng, i t m ght r epr esent surg i ng t he hi gh
l i ne ver sus the l ow one; f o r s er i e s c oupl i ng,
i t m ght r epr esent surg i ng the hi gh one
ver sus t he l ow one and gr ound,
s i mu l t aneous l y . ( But t hi s l a t t e r case woul d
r eal l y appear t o be mor e l i ke a common mode
c oupl i ng, i n whi c h t h e hi gh l i ne, al one, i s
surged wl t h r espect t o gr ound )
I n di f f e rent f i e l ds , a var i e ty o f names may
be used f o r what i s general l y thought of as
nor mal mode. For i nst r ument at i on
appl i c at € ons i t i s of t e n c al l ed " di f f er e nt i al
modeT1,
r
s omet i mes l l l i ne- t o- l i nel l .Ne i t her
name woul d be r eadi l y ext endabl e t o
mul t i - l i ne systems. I n t e l ecommuni cat i ons
t he compar a bl e t e r m I s " me t a l l i c l ~,
r ef erence, no doubt , t o t he t i me when gr ound
may i n f act have been the eart h, s o tha t a
si gnal bet ween two non- grounded l i nes
i nvol ved onl y metal conduct ors .
I nt e rnat i ona l l y , norma l mode i s re f er r ed t o
as l t symmetr i c " , no t - i l l ogi cal name i n
s i ngl e -phase appl i cat i ons . I n a t hr ee- phase
syst em however , can a sur ge appl i ed to t wo
l i nes ver sus a t hi r d real l y be consi dered
s ymmet i c?
Common Mode Common mode
i s
a t e r m wi t h
di f f e rent hi s t o r i cal meani ngs . As wi th
normal mode, each was def i ned f or use i n a
di sc i pl i ne r emote f rom sur ge t es t i ng. One
meani ng connot es any s i gnal wi t h r espect t o
ground, s i nce gr ound was or i g i nal l y cal l ed
f t common11. [ 3] The ot her meani ng i s t he mor e
pr esentl y- accept ed one: a si gnal on t wo o r
mor e l i nes, i n common, wi t h r espect t o
ground. What, t hen, shoul d be t he name f or
t he mode i n whi ch onl y one l i ne i s sur ged
wi t h r espect t o gr ound?
Common mode i s t er med " l ongi t udi nal model 1 i n
t e l ecommuni cat i ons. However, i t i s unl i kel y
t hat t hi s name coul d be conveni ent l y
broadened t o be used i n connect i on wi t h
mul t i - phase power l i nes,
o r
wi t h genera l i zed,
mul t i - l i ne dat a c abl es .
I nt er n at i onal l y , a s i gnal appl i ed t o
o r
exi s t i ng on bot h l i nes wi t h r espect t o
ground i n a s i ngl e -phase sys tem i s ca l l ed
asymmetr i c . s i gnal on j ust one l i ne ver sus
ground i s cal l ed unsymmetr i c . Put t i ng as i de
t he ongoi ng conf us i on i nvol ved i n us i ng such
s i m l ar t e r ms ( t her e i s of t e n di f f i c ul t y i n
r emember i ng whi ch i s whi ch) , i t i s uncl ear
whi ch name, i f e i t her , appl i es
f o r
t wo l i nes
bei ng sur ged ver sus ground i n a t hr ee phase
s ys t e m o r one l i ne pl us neutr a l bei ng surged
ver sus ground al so i n t hree phase, and so on.
Br oadeni ng t he name l l unsymmet r i ct fo i nc l ude
t h em al l woul d r e nder i t , l i k e t he t e r m
"nor ma l model 1, i nsu f f i c i ent l y speci f i c t o be
useful i n sur ge work.
Coupl i ng Ci rcu i t s
Saf ety
I n s ome ci r c ui t s t hat f ol l ow, f i l t e r c apac i -
t ors ar e shown connect ed bet ween an act i ve
power l i ne and ground. These may suppl y t oo
a hi gh l eve l o f l eakage cur r ent shoul d the
gr ound connect i on become open. Not e t hat a
gr o und f a ul t i nt er r u pt er ( GF CI ) wi l l not
so l ve t he probl em So l ut i ons i nc l ude use of
an i so l at i on t r ansf ormer wi t h ground r e-
establ i shed on i t s secondar y, or a gr ound-
s ens e ci r c ui t wi t h i n t h e coupl er / f i l t e r .
Coupl i ng Ci r c u i t s
f or Nor mal Mode
Fi gs. 1, 2 and 3 show t hree schemat i c r epr e-
sent a t i ons sel ect ed f r omt hose t hat have at
one t i me o r anot her been present ed i n publ i -
cat i ons o r by manuf act ur er s as nor mal mode
c oupl i ngs . Al l t hr e e i nc l ude bac k- f i l t er s ,
f or t he r easons al r eady di scussed.
The test surge gener ator i t se l f i s assumed t o
be ungr ounded; t hus i t I s t aken t o be
" f l oat i ng" wi t h r espec t t o gr ound, except f o r
st r ay capac i t ances t o gr ound i n t he range of
hundreds
o r ,
at most , a f ew t housand pF.
When a c i r cui t under d i scuss i on uses a
grounded sur ge gener at or , t he ground i s added
ext ernal t o the generator .
Fi g. 1 woul d seemt o be sat i s f actor y f o r a
nor mal - mode coupl i ng; one non- grounded l i ne
appears t o be symmet r i cal l y sur ged wi t h
r espect to the ot her . Thus t he open- c i r cui t
out put sur ge wi l l be bal anced, i .e. , wi t hout
t he EUT t he t wo l i nes move equal l y, i n
oppos i t e di rec t i ons .
F i g. 2 al s o connect s t he sur ge gener at or
out p ut f r o m l i ne t o l i ne, b ut s i nc e i t
m st akenl y t r i es to use a gr ounded r a ther
203
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t han an ungr ounded
( des i gnated i n t he
T
LINE
I
sur ge gener at or
f i gur e by t he ground
I
I
==c3 I cc2 ==
symboi on one surge gener at or out put ) , i t
a l so connect s l i ne
i
t o gr ound t hr ough what
i s
presumabl y a l arge- val ue sur ge coupl i ng
capac i t or , CC1. I n t h i s conl i gur a t i on, l i ne
i t h er e fo r e i s n' t s ur g ed at al l , and
f ur t hermore capac i t or CCi res t r i c t s l i ne 1' s
abi l i t y t o move f r eel y shoul d ther e be a
sur ge coupl ed t o i t v i a a pr otector o r
f l ashover wi t hi n t he EUT. For these r easons ,
i t i s doubt f ul t hat measured EUT sur ge
i mmuni t y wi l l al ways be t he same usi ng t he
coupl i ng method of F i g.
2
as i t wi l l f or t he
ci r c ui t of F i g. 1. Pi g.
2
t hus can' t
possi bl y be consi der ed t o be a reasonabl e
i mpl ement at i on
o f
nor mal mode.
Fi g. 3 shows a ser i es surge i n j ect i on
t echni que, usi ng t r ansf ormer T1 t o coupl e the
surge t o t he hi gh l i ne. Thus , t he sur ge
i s
appl i ed t o l i ne
2
wi t h respect t o l i ne 1 AND
ground, r ather t han bet ween l i ne
2
and l i ne
i . . J ust as wi t h Fi g. 2, F i g. 3 doesn' t seem
t o meet a reasonabl e def i ni t i on of normal
mode, s i nce onl y l i ne
2
i s su rged, and l i ne
1
T1
INPUT I
=
-
LINE 2
I I
I ==c3
I
I I
I
I
cl
c 2 • ==
I
I
INPUT I
LINE
1
Fi g. i
Sur ge Generator Sat i s f act or i l y
Coupl ed t o EUT i n Nor mal Mode.
The surge
i s
appl i ed f r o m l i ne 2
t o l i ne 1, i n a ba l anced way;
i .e. , bot h l i nes move, equal l y and
i n oppos i t e di rec t i ons , wi t h
r espect t o gr ound.
EUT
F i g.
2
Sur ge Generat or I mproper l y Coupl ed
t o
ElJT
i n t l No rma lMode" .
Onl y one l i ne
i s
surged, i . e. l i ne
2, s i nce l i ne 1
i s
ef f ec t i vel y
grounded vi a coupl i ng capaci t or
Cci . Sur ge gener ator s bei ng used
t o sur ge act i ve l i nes shoul d be
ungr ounded.
Sur ge Generat or I mproperl y Coupl ed
t o EUT i n " Nor mal Mode".
Act ua l coupl i ng
I s
f r om l i ne 2
t o bot h l i ne i and ground
s i mul t aneous l y ; onl y l i ne
2 i s
surged, as i n Fi g.
2.
Thus ser i es
coupl i ng resul t s i n an unsym netr i c
surge, i . e. a s i ngl e- l i ne surge
ver sus common, o r ground.
INPUT
LINE 2
INPUT
LINE 1
SESSION 4C
i s
not . I t
i s
t here f ore unl i kel y t hat t es t
r esul t s wi l l cons i s t ent l y be the same wi t h
t hi s coupl i ng method as f or t hat o f F i g. 1.
Af t er cons i der i ng these th ree di f f erent
at t empt s at i mpl ementi ng normal mode sur ge
coupl i ng, i t appears t hat nor mal mode shoul d
per haps be def i ned as a coupl i ng
conf i gur at i on t hat appl i es a sur ge f r omone
l i ne wi t h r espect t o t he ot her , wi t h BOTH
l i nes sur ged
o r
movi ng dur i ng the sur ge, i n
equal amounts i n opposi t e di r ect i ons, bef ore
t he EUT
i s
connect ed. The i nt ernat i ona l
desi gnati on, symmetr i c, woul d seem t o i mpl y
somet hi ng of t hi s sor t . Expandi ng t hi s
def i ni t i on t o mul t i - l i ne s i t u at i ons s uch as
t hree- phase power l i nes, however, onl y l eads
t o new ambi gui t i es.
Coupl i ng Ci r cu i t s
f o r
Common Mode
There ar e var i ous conf i gur at i ons t hat are
t er med, by one
o r
another publ i cat i on
o r
manuf actur er, t o be appl yi ng t he t est s urge
i n common mode. Thr ee t ypi cal common- mode
SURGE
GENERATOR
EUT
I I
I
L
_ _ _ _ _ _ _
1
l l
1
URGE
BACK-FILTER
GROUND
r
SURGE
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SESSION
4C
conf i gura t i ons a re shown i n F i gs . 4 ,
5
and
6
Al l i nc l ude s ur g e/ bac k- f i l t e r s , and i n al l
of
t hem t he sur ge / genera to r i s t aken t o be
ungr ounded.
The c i r cui t o f F i g. 4 appl i es t he surge
gener ator output , v i a sur ge coupl i ng
capac i t ors CCi and CC2, s i mul t aneousl y t o
l i nes i and 2 r espect i vel y . I t seems t o meet
r easonabl e r equi r ement s
f o r
common mode
surg i ng , i . e. i t app l i es t he same t es t sur ge
t o al l ungr ounded l i nes , wi t h respec t t o
gr ound. The c i r cui t
of
Fi g.
5
uses an
I s ol at i on t r a ns f or mer , T 1, t o f ac i l i t a t e
coupl i ng t he sur ge gener ator out put t o both
EUT i nput l i nes at t he same t i me. Thus, i t
does appear t o be what we expect t o f i nd
f o r
a " common mode" coupl i ng. Unf or t unat el y,
wi t h t h e c i r c ui t
of
Fi g.
5
a f l ashover
bet ween ei t her l i ne and gr ound wi t hi n t he EUT
won' t a l l ow what i s cal l ed power f o l l ow,
o r
ac l i ne cur r ent f l ow t hrough t he f l ashover
pat h. Power f o l l ow capabi l i t y i s needed i n
sur ge t es t i ng, i n o rder accur a te l y t o
r epr esent t he e l ect r i cal env i r onment i n whi ch
t he EUT wi l l event ua l l y be i ns ta l l ed at t he
user' s slte.[2] Thus Fi g.
5,
a sur ge
coupl i ng method t hat d i sconnect s l i ne i
o hm c al l y f r o m gr ound and l ea ve s i t f l o at i ng,
i s c l e ar l y not a suf f i c i ent l y r eal i s t i c t e st
mode. I t i s al so unl i kel y t o g i ve EUT surge
i mmuni t y t est r esul t s a l ways consi st ent wi t h
t hose obt ai ned us i ng t he c i r cui t o f Fi g. 4.
v ar i a nt of t h e c i r c ui t of Fi g.
5,
wi t h a i
ki l ohm
o r
o t he r r el at i v el y hi gh- v al ue
r es i s t o r connec ted f r omone s i de o f t he
i so l a t i on t r ans f o rmer secondary t o ground,
has been descr i bed i n some dr af t spec i f i ca-
t i ons as pr ovi di ng "power fo l l ow- t hr u" ( s i c ) .
However power f o l l ow, t he corr ect t erm can
har dl y be sai d to be avai l abl e i f power l i ne
cur r ent f o l l owi ng f l ashover to gr ound i s
l i m t ed t o 0. 1-0.2 v i a t he 1K res i s to r .
The ci r c ui t o f Fi g. 6 uses t r ansf ormer
coupl i ng t o appl y t he surge v i a thr ee- wi ndi ng
t r ans f o rmer T1, t o bo th i nput l i nes of t he
EUT. I t woul d theref ore appear j ust as
s at i s f ac t o r y f o r common- mode coupl i ng as t he
c i r c ui t of Fi g.
4
Unf o r t unat el y , i t has
pr a ct i c al l i m t a t i ons : s pec i f i c al l y, a
pr a c t i c al 1: l : i t r ans f or me r r e qui r e d t o
coup l e a t ypi cal , 1. 2 x 5 0 u s powe r - l i ne t e s t
s ur ge wi t h f i del i t y i s s i mpl y unf eas i bl e.
T hi s f a ct doe s no t p r e ve nt t he c i r c u i t f r o m
f i ndi ng i t s way i nto some t est st andar ds.
There ar e two other , r e l ated coupl i ng
c onf i gur at i ons of gr e at p r ac t i c al i nt e r e s t ;
ei t her can be obt ai ned by di sconnect i ng one
o f t he t wo coupl i ng capac i t ors , CCi
o r
CC2,
i n t h e c i r c ui t of Fi g. 4. The r esul t i ng
c i r c ui t s s ur g e ei t her l i ne 2 o r l i ne i ver s u s
ground, r espec t i vel y . I n t he genera l case,
r e s ul t s
of
t es t s us i ng ei t her
o f
t hese t wo
c i r c ui t s wi l l c l e ar l y be di f f er e nt f r o m t hos e
of
F i g. 4 , a l t hough bot h appl y tes t surges
wi t h r espect t o ground, o r common ( t he ol d
def i ni t i on) . I nt er e s t i ngl y , when onl y l i ne 2
i s surged v i a CC2, t he resu l t i ng
c onf i gur a t i on wi l l be l i k e t h e c i r c ui t of
Fi g. 3 nom na l l y "nor ma l modeTv , r evi ous l y
di scussed as havi ng the pr opert y of sur gi ng
onl y l i ne 2 and not i nvo l v i ng l i ne i .
Both coupl i ng c i r cui t s obt ai ned by om t t i ng
one
of
t he capac i t ors i n F i g. 4 and sur gi ng
onl y one l i ne ver sus ground, are t he coupl i ng
modes t hat ar e i nter nat i onal l y t ermed
unsymmetr i c . These are per f ect l y l egi t i mate
t est modes, and ar e i n f act f avor ed by many
as bot h qui t e r e al i s t i c , and of t en di f f i c ul t
f o r
EUTs t o pass, wi t hout upset
o r
damage.
Ho we ver , t h ey a r e c l ea r l y di f f er ent f r o m t he
ci r cui t
of
F i g. 4.
Coupl i ng Ci r c u i t s f or Hi gh-
I mpedance Sur ge Gener at or s
Rel at i vel y h i gh l i ne i mpedances ar e t hought
t o r epr esent t he s i t uat i on i n some Eur opean
i nsta l l at i ons when gr ound and neut r a l are
bonded out s i de, and f a r f r om t he poi nt at
whi ch power ent ers a bui l di ng. I t
i s
not
cl ear t hat such remot e ground bondi ng i s
al ways t he si t uat i on; bondi ng may occur near
o r
even at t he bui l di ng i n some cases,
f o r
var i ous reasons. These i nc l ude pr oxi m t y of
t he bui l di ng to a power sub- s t a t i on, un-
pl anned l oca l shor t c i r cui t s bet ween neut r a l
and gr ound, and l ocal f l ashover dur i ng a
sur ge, bet ween neut r al and ground. Any such
s i t uat i on wi l l make f o r a wors t - case scenar i o
s i m l ar t o the convent i ona l one i n t he U. S. ,
i n whi ch common mode and no r mal mode s ur ge
source i mpedances ar e essent i al l y the same.
The ci r c ui t
of
Fi g. 7 i s somet i mes used t o
prov i de a h i gh back - f i l t e r i mpedance, t o
avoi d i mpose excessi ve l oad on a
hi gh- i mpedance sur ge gener at or, up t o per haps
5 0 ohms, whi l e at t he same t i me al l owi ng
es s ent i a l l y nor mal f l o w of ac power l i ne
curr ent t o t he EUT. To do t hi s , i n addi t i on
t o t he f i l t er i nduc t o r s Li and L2 f am l i ar
f r o m pr e vi ous f i gur e s , F i g. 7 al so uses a
t r ansf ormer, T1. I t pr ovi des a h i gh mutual
i nduct ance bet ween wi ndi ngs, wi t h one wi ndi ng
i n ser i es wi t h each o f t he two ac i nput l i nes
as shown. Ty pi c al l y , T i i s a i : i t r a ns f or mer
wi t h equal pri mary and secondar y i nduct ances,
each on t he or der
of
tens of mH. I t o f f e rs
m ni mal i mpedance t o t he f l ow of ac cur r ent
s i nce i t s t wo wi nd i ngs a re i n oppos i t i on; but
i t const i t utes a hi gh I mpedance
f o r
surges
appl i ed t o both l i nes i n common wi t h respect
t o gr ound.
Pour sur ge gener at or s and associ at ed
c oupl i ngs t o t h i s f i l t e r ar e s hown i n Fi g.
7,
each wi t h dot t ed connec t i ons to t he c i r cui t
t o i ndi cat e t hat onl y one i s connect ed at a
t i me. SGi surges l i ne 2 v er s u s l i ne 1, SG2
surges both l i nes wi t h respect t o ground, SG3
sur ges l i ne 2 wi t h r espect t o gr ound, and SG4
sur ges l i ne i wi t h r espect t o ground.
Ti present s SGi wi t h a l ow, i n fac t
t heoret i cal l y zero i mpedance, as i t does t o
t he f l ow of ac power cur r ent ; s t hat i n
l i ne- t o- l i ne s ur g i ng i t has no i nf l uenc e. Ti
does however pr esent SG2 wi t h a hi gh
i mpeda nc e, and t he r e f o r e I t f ac i l i t at es
surgi ng wi t h hi gh sur ge gener ator sour ce
i mpedances i n t wo- l i nes- t o-gr ound coupl i ng
modes. T1 pr esent s SG3 and SG4 wi t h a hi gh
i mpedance as wel l ; however, i t ef f ect i vel y
subver t s t he at t empt t o surge one l i ne t o
ground, s i nce i t coupl es t he surge to t he
other l i ne at t he same t i me. Thus wi t h the
back- f i l t e r o f Fi g. 7, i t i s i mpos s i bl e
to surge one l i ne at a t i me wi t h respect t o
ground. At t empts t o i mprove t h i s s i t uat i on
by addi ng f i l t er capac i t ances t o ground f r om
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t h e j unc t i on
of
T i and L1, and f r omt he
j unc t i on
of
Ti and L2, ar e s omet i mes made i n
order t o t r y s i mul t aneousl y t o achi eve a hi gh
f i l t er i mpedance t o the sur ge, and f r eedom
f r om t he unwant ed coupl i ng
of
t he sur ge f r om
one l i ne t o t he ot h er . f ul l y s uc c es s f ul
compr om se has el uded such at t empt s, and t he
conf i gur a t i on remai ns usef ul onl y f o r surg i ng
bot h l i nes s i mu l t aneous l y t o ground f r oma
hi gh i mpedance sur ge, no smal l advant age
nonet hel ess. However, i t shoul d be at l east
as i mpor t ant t o sur ge a s i ng l e l i ne ver sus
gr ound
i f
t he hi gh i mpedance assumpt i on
i s
LINE
I
I
I
I
I
INPUT
I
LINE 1
I
cz •
Fi g. 4
- -
ry
I
==c3
I
I
EUT
l I
=
Sur ge Gener a t o r Sat i s f ac t o r i l y
Coupl ed t o EUT i n Common Mode.
The sur ge is appl i ed f r ombot h
l i ne s, equal l y , t o gr o und.
Fi g.
5
Sur ge Gener at or I mproperl y Coupl ed
t o GUT i n Common Mode.
No po wer f ol l ow i s a vai l a bl e
f o l -
l owi ng f l ashover to gr ound i n t he
EUT. Thus t h i s t est
i s
unr eal i s t i c, s i nce i t f a i l s t o
r e pl i c at e t he s i t u at i on i n whi ch
t he EUT wi l l event ual l y be used.
F r om t hi s s t a ndpoi nt i t al mo st
amount s t o an unpower ed s ur ge
t e s t .
Fi g.
6
Sur ge Ge ne r at or Sa t i s f a ct or i l y
Coupl ed t o EUT i n Common Mode.
Howev er , no pr a c t i c al i : i : l
t r ansf ormer, T1, can be des i gned
f or a i 2/50 vol t age surge to
4- 6
kV. The c i r cui t never t he l ess
f i nds i t s way i nto standards and
s pec i f i c at i ons .
Fi g. 7
Sur ge Gener a t o r Sa t i s f a ct or i l y
Coupl ed t o ETJT
i n
Nor mal Mode and
Common Mode. I t I s I nef f ect i vel y
Coupl ed
i n
Li ne 2-t o- Gr ound and
Li ne i - t o-Gr ound Modes.
I n l i ne 2- t o- ground o r l i ne i - t o-
gr ound, T i ' s t r ans f o rmer ac t i on
provi des t he same sur ge t o the
"unsur gedl l i ne. Thus a surge t o
one l i ne aut omat i cal l y becomes a
s ur ge t o bot h. T he ba ck - f i l t e r ,
i n th i s s i t ua t i on, has become par t
of
t he coupl er .
INPUT
LINE
2
INPUT
LINE 1
SESSION 4C
val i d, as i t i s t o sur ge bot h of t hem
s i mul t aneous l y . The c i r cui t
of
Fi g.
7
when
appl i ed to t he probl em of surg i ng one l i ne a t
a t i me ver sus ground,
i s
t hus per haps t he
best exampl e of a c i r cui t i n whi ch one sur ge
mode i s i ntended, but i n whi ch anot her
occur s , as a resul t of t he desi gn
of
t he
back- f i l t er .
Vi abl e al t er n at i ves t o F i g. 7 i nc l ude
el i m nat i ng T1 and e i t her us i ng a 10- 12 ohm
generato r ,
o r
compr om si ng on a vol t age wave
dur at i on t hat
i s
much short er t han
5 0
us .
I
-I
I L.,
I
I
1 1 -
I
I
GROUND
U
SURGE
i
GENERATOR
I
I
I c2
C , l
e
I
I
@
GROUND
I I
I
1
EUT
SURGE I
L
_ _ _ _ _ _ _ _ _
ACK-FILTER
I
206
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6/6
R u l e s f o r S u r g e C o up l i ng
Most s u r g e c o up l in g c i r c u i t s i n c u r r e n t u s e
d o i n f a c t a p p l y t e s t s u rg e s t o a t l e a s t some
o f t h e l i n e s t h e y
are
supposed to . However ,
o n l y a f ew s u c h c ou p l i n g c i r c u i t s a p p l y
s i g n a l s t o
a l l
o f t h e l i n e s t h e y s ho u l d,
whi le l e a v i n g un -s ur ge d t h e l i n e s t h a t a r e
n o t i n t e n de d t o
b e
su rge d . Some o f t h e
c o n f i g ur a t i o n s t h a t d o a p p ly s i g n a l s t o a l l
of t h e r i g h t l i n e s , n e v e r t he l e s s r e d uc e t e s t
realism
by r e s t r i c t i n g t h e f r ee do m o f
u n- su rg ed l i n e s t o move, i f c i r c u i t s
o r
f l as ho ve r wi th i n t he EUT conne ct un-surged
l i n e s t o p o i n t s t h a t a r e s ur ge d . O t he r
c on f i gu ra ti on s a p p l y s u r g e s t o t h e c o r r e c t
l i n e s , b u t o n l y by c h an g i ng t h e n or ma l i n p u t
g r o un d in g s i t u a t i o n , a g a i n r e d u ci n g
t e s t
realism. F i n a l l y , s o m e o f t h e me t ho d s c o r -
r e c t l y a l l o w a t l e a s t some r e a s o n a b l e l e v e l
o f p ow er f o l l o w t o o c c u r when f l a s h o v e r t o
g r ou nd t a k e s p l a c e w i t h i n t h e GUT; o t h e r s
a g a i n
l i m i t t e s t
r e a l i s m b y n o t d o i n g
s o .
R e g a rd i n g c o u p l i n g mode n o m e n c l a t u re , t h e
o n l y r e a s o n a b l e c o u r s e
seems
c l e a r : a v o i d
te rm s l i k e norma l mode, common mode,
symmetr ic , unsymmetr ic , asymmetr i c , and
s o
o n. I n a d d i t i o n ,
i t
i s n o t s u f f i c i e n t t o
d e f i n e t h e s u r ge c o u p li n g c o n f i g ur a t i o n i n
terms o f t h e l i n e s b e i n g s u r ge d w it h r e s p e c t
t o o ne
o r
mor e r e f e r e n c e l i n e s .
A
comDlete
~
d e s c r i p t i o n o f s u r g e c o u p l i ng r e q ui r e s
d e f i n i t i o n
o f
t h e d i s p l a c e m e n t
of
e v er y l i n e
i n t h e s y s te m w i t h r e s p e c t t o g ro un d.
A ny th in g s h o r t o f t h i s l e v e l o f r i n o r c a n
l e a d to - th e p o s s i b i l i t y o f d i f f e r e n t t e s t
r e s u l t s w i t h d i f f e r e n t s u r g e
t e s t
equipment.
Here
a r e some examples:
S i n g l e p ha s e , t h r e e - w i r e s y s te m s :
L i ne t o l i n e , b a l an c ed ( i . e . , w i t h e q u a l
a nd o p po s i t e p o l a r i t y s u r g e s a p p l i e d t o
t h e two l i n e s w i t h r e s p e c t t o g r ou nd ).
B ot h l i n e s t o g r ou nd .
High
( o r
l i n e
2)
t o g r ou n d.
Low
o r
l i n e
i
t o g r ou nd .
F i v e -wi re , t h r e e -p h a s e s y s t e m s :
Xach o f t h e t h r e e p h a s e l i n e s , o n e
a t a
t ime,
t o e v e ry o t h e r p h a s e l i n e ; b a l an c e d
( i . e . ,
w i t h e q u a l a nd o p p o s i t e s u r g e s
a p p l i e d t o t h e t wo l i n e s i n t h e s u r ge d
p a i r , w i t h r e s p e c t t o g ro un d) .
Each
of
t h e t h r e e p ha s e l i n e s , o ne a t a
t ime,
t o n e u t r a l ; b a la n ce d ( i . e . , w i t h
e q u a l a n d o p p o s i t e s u r g e s o n l i n e a n d
n e u t r a l , w i t h r e s p e c t t o g r o un d ) .
Two of t h e t h r e e ph a se l i n e s
a t
a
t ime,
t o g r ou n d.
A l l
t h r e e p ha s e l i n e s , s i m ul t a ne o u sl y , t o
n e u t r a l ; w i t h t h r e e
t imes
t h e s u r g e
v o l t a g e o n n e u t r a l
as
on e a c h o f t h e
t h r e e p ha se l i n e s . ( No te : e q u al f i l t e r
i n d uc t a n ce s i n e a ch l i n e a nd n e u t r a l
i m pl y t h i s v o l t a g e a p p o r ti o n m e n t .)
E ac h o f t h e t h r e e
p h as e l i n e s a n d
n e u t r a l , o n e
a t a
time,
t o g r ou nd .
SESSION 46
l l
t h r e e p h as e s an d n e u t r a l ,
s i m u l t a n e o u s l y , t o g r o un d .
The above exemplary coup l in g mode de scr ip -
t i o n s
a r e
c l e a r , p r e c i s e a n d u na mb ig uo us .
U s in g th em p e r m i t s a d v a n c i n g t o t h r e e d e s i g n
r u l e s
f o r
s u r g e c o u p l i ng . T h e i r p u r po s e i s
t o p r o vi d e r e a so n ab l e c r i t e r i a f o r d e s i g n i n g
a nd e v a l u a t i n g c o u p l i n g me t ho ds f o r s u r g e
t e s t i n g .
Ru le
i :
Rule
2:
Rule
3 :
S u rg e t h e i n t e n d e d l i n e s ; d o n t
s u r g e t h e o t h e r s .
D on t r e s t r i c t t h e f re ed om of l i n e s
t h a t a r e n t b e i ng s u r g e d, a nd d o n t
p r o vi d e f re ed om f o r l i n e s t h a t d o n t
o r d i n a r i l y h av e i t n a l t e r n a t e
f o r mu l a ti o n o f t h i s r u l e
i s :
d o n t
m a t e r l a l l y a l t e r t h e ohmic or
c a p a c i t i v e i m pe da nc e t o g r o un d
o f
ETJT
i n p u t
o r
o u t p u t , l i n e s .
A l l o w a t l e a s t some power fol low, if
t h e r e
i s
f l a s h o v e r f r om an y l .i ne t o
g r o u n d w i t h i n t h e
EUT.
C o n c l u s i o n s
S u rg e c o u p l i n g c o n f i g u ra t i o n s h a v e b ec om e
mor e i m p o r t a n t i n q u a l i f y i n g mo de rn
e l e c t r o n i c e q ui p me n t f o r s u r g e i mm un it y.
However,
t h e
e x i s t i n g
s t a t e
o f n o m e n c l a t u re
a nd c i r c u i t d e s i g n s f o r s u c h c o u p l i n gs an d
t h e f i l t e r s t he y d r i v e
i s
q u i t e
uns
at i s
a c o y
.
I n r e g a r d t o n om e n c la t u r e, i t
i s
p ro p o s e d
t h a t e a c h c o u p l i n g mode b e d e s c r i b e d i n terms
o f t h e d i s p l a c e me n t O P e ve ry l i n e i n t h e
s y s te m w i t h r e s p e c t t o gr o u nd .
R eg ar di ng d e s ig n , t h r e e c r i t e r i a a r e p ro p o s e d
i n t h e f o rm
of
r u l e s ,
as
t h e
b a s i s
f o r
i m -
p r ov e d a n d b e t t e r - s t a n d a r d i z e d s u r g e c o u p l e r /
f i l t e r s :
i )
s u r g e
t h e
i n t e n d e d l i n e s a n d no
o t h e r s ;
2 )
d o n t m a t e r i a l l y c h an ge t h e
i m pe d an c es d r i v i n g EUT i n p u t l i n e s ; a n d ( 3 )
a l l o w
a t l e a s t
some power fol low.
T he r e v i s e d n om e n c la t u r e a nd t h e t h r e e
s u gg e s te d c o u p l i n g r u l e s p r o v i d e t o o l s f o r
d e s i g n a nd a n a l y s i s o f s u r g e c o u p l i n g
m e th od s , w i t h t h e o v e r a l l p u r p o s e of
a c h i e v i n g b e t t e r - s p e c i f i e d a nd t h e r e f o r e mor e
r e p r o d u c i b l e s u r g e t e s t i n g .
Acknowledgments
Gregory G . S en ko f i r s t r e c og n iz e d t h a t p ow er
f o l l o w l i m i t a t i o n s c a n r e s u l t f ro m i m pr o pe r
u s e o f l i n e i s o l a t i o n t r a n s f or m e r s, l e a d i n g
t o t h e f o r m u l a t i o n o f R u le 3 .
R e fe re n c e s
[l]
ANSI/IEEE C62.4i-1980 ( fo rm er ly I EEE
S t d . 5 8 7 ) , I E E E G ui de f o r S u r ge V ol t a g e s i n
Low-Voltage A C P o w e r C i r c u i t s .
[2]
ANSI/IEEE 052.45-1987,
I E E E
Guide on
S u rg e T e s t i n g f o r E q u i pm e nt C o n ne c te d t o
Low-Voltage
AC
P o w e r C i r c u i t s .
C31
ANSI/IEEE Std. 100-i984,
I E E E
S t a n d a rd
D i c t io n a ry o f E l e c t r i c a l a nd E l e c t r o n ic s
Te rm s .
207