articulo modelo torre

8/18/2019 Articulo Modelo Torre

1/9

IEEE

Transactionson Power Delivery ,Vol. 6 No. 3 July 1991

MULTISTORY TRANSMISSION'TOWER MODEL FOR LIGHTNING SURGE ANALYSIS

M a sa ru I s h i i , S e n i o r

Member,

IEEE Ta ts uo Kawamura, Member,

I E E E

Teruya Kouno,

Member,

IEEE

Uni ver s i t y o f T okyo

Tokyo, Japan

Uni ver s i t y o f T okyo Uni ver s i t y o f T okyo

Tokyo, Japan

Tokyo, Japan

Ei ic hi Ohsaki Kazuyuki Shiokawa Kaneyoshi Murotani , Member,

I E E E

Takemitsu Higuchi

The Tokyo Electr ic Power C o . , I n c . N i s s i n E l e c t r i c Co. , L td . T he Kans a i E l ec t r i c Power Co . , I nc .

Tokyo, Japan

Kyoto, Japan

A b s t r a c t

-

T r ans mis s ion tower s have been mode led

f o r l i g h t n i n g s u r g e a n a l y s i s b a s e d o n t h e m e as ur em e nt s

o n t h e t o w e rs a l o n e . For a n a c t u a l h i g h v o l t a g e

t r an s mi s s i on tower , however , g r ound

w i r e s

a r e e q u i p p e d

i n many c a s e s . I n v i ew o f t h i s , pr o p o se d h e r e

i s

a

m u l t i s t o r y t r a n s m i s s i o n t o we r m od el t o be u s e d i n t h e

mul t i - con duc to r an a l ys i s by EMTP. T he c i r cu i t pa rame-

t e r s

of t he model a r e de t e r mined bas ed on th e meas ure -

m en t o f v o l t a g e s a c r o s s t h e i n s u l a t o r s t r i n g s o n a n

a c t u a l 500kV t r a n s m i s s i o n t o w e r . T he f l a s h o v e r p h a s e

a n d c u r r e n t i n r e s p on s e t o a l i g h t n i n g s t r o k e t o a

UHV

t r a n s m i s s i o n t o w e r a r e a l s o a n a l y z e d b y u s i n g b o t h c on -

ve n t i on a l and new tower mode l s f o r compar is on .

Keywords: Li gh tni ng su rg e, Back f l as ho ve r , EMTP,

UHV.

INTRODUCTION

I n t h e c l a s s i c a l m ethod f o r p r e d i c t i n g b a c k fl a s h

r a t e s o f o v er h ea d p ow er t r a n s m i s s i o n l i n e s , t r a v e l i n g

w ave a n a l y s i s o f l i g h t n i n g s u r g e s i s a n e s s e n t i a l p a r t .

A

t r a n s m i s s i o n t o w e r

i s

o f t e n r e p r e s e n t e d b y a u n i fo r m

t r a n s m i s s i o n l i n e o f f i n i t e l e n g t h 1 11 , an d t h e s e n-

s i t i v i t y of t h e p a r a m e te r s o f t h e m od el ed t r a n s m i s s i o n

tower i s l a r g e w h en t h e t o w e r

i s

h i g h

[ 2 1 .

T hos e par a -

meters h a v e b ee n c h o s en b a s e d on t h e r e s e a r c h o f t h e

s u r g e r e s p o n s e o f t h e t o w e r a l o n e ; h o w e ve r, f o r po we r

t r a n s m i s s i o n l i n e s e q u i pp e d w i t h g r ou n d

w i r e s ,

t h e

p a r a m e t e r s may n e e d t o b e r e v i e w ed b a s e d o n t h e s u r g e

r e s p on s e i n s u c h c o n f i g u r a t i o n .

A s

m o st o f t h e t r a n s m i s s i o n l i n e s o f 5 00 kV an d

a b ov e v o l t a g e s i n J a p a n a r e d e s i g n e d do u bl e c i r c u i t a n d

e q u i p p e d w i t h g r ou n d w i r e s , a r e s e a r c h h a s b e e n mad e t o

d e v e l o p a new to w e r m od el f o r l i g h t n i n g s u r g e a n a l y s i s

c o p i n g w i t h s u c h a t r a n s m i s s i o n l i n e .

I t i s

a l s o

r e q u e s t e d t h a t t h e n ew t o w e r mo de l c a n b e c o u p le d w i t h

t h e m u l ti - c on d u c to r a n a l y s i s of l i g h t n i n g s u r g e s 131

u s i n g t h e E l e c t r o m a g n e t i c T r a n s i e n t s P ro gr am (EMTP) [ 4 ]

.

BasGd on t h e low-current measurement of vol t ag e

w av ef or ms a c r o s s t h e i n s u l a t o r s t r i n g s o n a n a c t u a l

5 00 kV d o u bl e c i r c u i t t r a n s m i s s i o n t o w e r e q u i p pe d w i t h

ground w ires , a new tower model

i s

developed. The

meas ur emen t was per f o r med under ve r t i ca l cu r r en t

i n j e c t i o n t o t h e t o w e r. W h et he r g r ou n d

w i r e s

ar e con-

n e c t ed t o t h e t ow e r o r n o t a f f e c t s t h e c i r c u i t p ara me -

t e r s

of t h e tower mode l .

T ho s e c i r c u i t p a r a m e t e rs u s e d i n a t r a v e l i n g w ave

a n a l y s i s a r e c o n c e p t s u n de r TEE1 f i e l d s w h e re a s t h e

f i e l d s a s s o c i a t e d w i t h a c u r r e n t w ave o n a t r a n s m i s s i o n

t o w e r u s u a l l y d i f f e r f r om

TEM.

T h e r ef o r e, e s s e n t i a l l y ,

t h e r e p r e s e n t a t i o n o f a t r a n s m i s s i o n t o w er w i th t h e

53 IJ?.I

193-3 PWRRD

by the

I EEE

T r ans mis s ion and Di s t r i bu t i on Commi tt ee

of

t h e

I E E E

P ow er E n g i n e e ri n g S o c i e t y € o r p r e s e n t a t i o n

a t t h e I E E E / P E S 1989 Win ter M eeti ng, New York, N e w

York, Jan uary 29 - Febr uar y 3, 1989. Manuscr ipt

s u b m i t t e d F e b r u a r y 1 , 1 9 88 ; made a v a i l a b l e f o r

p r i n t i n g J a n u a r y 9 , 1 9 8 9.

A

paper recommended and approved

Osaka, Japan

I327

combina t ion

of

l um pe d c i r c u i t p a r a m e t e r s a n d t r a n s m i s -

s i o n l i n e s

i s

o n l y a n a p pr o xi m at io n e x c e p t f o r t h e c a s e

of a c on ica l t ower . T he newly deve loped tower model

a p p ro x i m a te l y i n c o r p o r a t e s t h e i n f l u e n c e o f t h e r e f l e c t -

e d c u r r e n t wa ve f r o m t h e t o w e r b a s e , a n d

i s

recommended

t o b e u s e d i n a m u l ti - c on d u c to r s u r g e a n a l y s i s o f a

d o u b le c i r c u i t t r a n s m i s s i o n l i n e e q ui p pe d w i t h g r ou n d

w i r e s .

PREVIOUS STUDIES ON TOWER MODEL

T h e o r e t i c a l s t u d i e s [ 5 ]- [ 9] a r e v e r y Us e fu l i n

und er s t and ing th e phenomena . On th e o th er hand , it i s

i n d i s p e n s a b l e t o c o n du c t e x p e ri m e n ta l s t u d i e s t o e v a-

l u a t e t h e s u r g e r e s po n se

of

a complex- s haped ac tu a l

t r an s mi s s io n tower . On th e measur emen t

of

s u r g e

r e s p o n s e s o f a c t u a l a n d m od el t o w er s , t h e r e

i s

a good

r ev iew [ 21 .

The method of t h e measurement i s c l a s s i f ie d i n t o

two ty pe s . One i s t h e r e f l e c t i o n m et ho d r e p r e s e n t e d by

th e meas ur emen t by Br euer

e t

a l .

[ l o ] .

I n t h i s m e th od ,

a l e a d t o t r a n s m i t a

s t e ep

f r o n t t r a v e l i n g w ave i s con-

n e ct e d t o t h e t o p o f

a t ower under meas ur ement , and th e

r e f l e c t e d w av e o n t h e m e as u r in g l e a d

i s

o b se r ve d t o

e s t i m a t e t h e t r a n s i e n t i m pe da nc e a t t h e t o we r t o p . I n

t h i s c a s e , t h e w h ol e t o we r

i s

i l l u m i n a t e d b y t h e

TEM

f i e l d a s s o c i a t e d w it h t h e t r a v e l i n g w ave o n t h e

m e as u ri n g l e a d a s t h e w ave f r o n t a r r i v e s a t t h e t o we r

t o p . T he t r a n s i e n t i mp ed an ce a t t h e t o w e r t o p s ho ws

i n i t i a l l y a h i gh v a l u e , a n d d e c r e a s e s w i t h t i m e [21.

This method

i s

c o ns i de r ed v a l i d i n e v a l u a t i n g r e f l e c -

t i o n a n d r e f r a c t i o n o f s u r g e wa ve s a t t h e c o nn e c t in g

p o i n t o f t h e t ow e r a n d t h e g r ou n d

w i r e s .

T he o ther method

i s

t h e d i r e c t me th od r e p r e s e n t e d

by the meas urement o f Kawai [ l l ] . I n t h i s m e th od , a

p u l s e g e n e r a t o r

i s

p l a c e d o n t h e t o p o f a t o w e r , a n d

t h e v o l ta g e a c r o s s a n in s u l a t o r s t r i n g

i s

d i r e c t l y

m ea su re d. I n t h i s c a s e, n o e x t e r n a l f i e l d e x i s t b e fo r e

t h e a p p l i c a ti o n

of

t h e t e s t i n g c u r r e n t t o t h e t ow e r

t o p , a nd t h e e x t e r n a l f i e l d e xp an ds s p h e r i c a l l y f ro m

t h e to w e r t o p . T h e r ef o r e, n o TEM f i e l d e x i s t s u n t i l

s e v e r a l r e f l e c t i o n s i n t h e t o we r t a k e p l a c e . On a

tower wi tho u t g r ound w i r e s , t h e v o l t a g e a c r o s s a n i n su -

l a t o r s t r i n g g r ad u al l y r i s es u n t i l t h e r e f l e c t e d wave

f ro m t h e t o w er f o o t i n f l u e n c e s , a n d i s c o nt r ar y t o t h e

c h a r a c t e r i s t i c s m e as u re d b y t h e r e f l e c t i o n me th od . T he

s i t u a t i o n s i m u l a t e s t h e i n c i d e n t of a l i g h t n i n g s t r o k e

h i t t i n g t h e t ow e r t o p . I n t h i s m ea su re me nt a l s o , a

l e a d c o nn e ct e d t o t h e p u l s e g e n e ra t o r

i s

n e c e s s a r y

t o

p r o v i d e a p a t h f o r t h e r e t u r n c u r r e n t . I n m e a su r in g a n

a c t u a l t o w e r , it i s d i f f i c u l t t o p l a c e a v e r t i c a l l e a d

f ro m t h e t o p of t h e to w e r, t h e r e f o r e , t h e s i t u a t i o n i n

th e measur emen t

i s

s om ew ha t d i f f e r e n t f r om t h e i n c i d e n t

o f l i g h t n i n g s t r i k i n g t h e t o we r.

The

t e r m s

o f h o r i z o n t a l c u r r e n t i n j e c t i o n a n d v e r -

t i c a l c u r re n t i n j e c ti o n [ 9] i n pl a c e s of t h e r e f l e c t i o n

m et ho d a n d t h e d i r e c t m eth od a r e m i s l e a d i n g s i n c e t h e

l e a d f o r t h e r e t u r n c u r r e n t was h o r i z o n t a l l y c o n ne c t e d

t o t h e t o w e r t o p i n t h e K a w a i' s d i r e c t m e as ur em en t.

T h e r e f o r e , t h e

t e r m s

o f t h e r e f l e c t i o n me th od a nd t h e

d i r e c t me th od a r e u s ed i n t h i s p a pe r . T he d i f f e r e n c e

o f t h e s e m e a s u ri n g me th o ds a r e a l s o c l e a r l y s t a t e d by

Chisholm

e t

a l . [ 9 ] , a n d t h e y d e v e l o p e d a to w e r mo d el

b a s e d o n t h e r e f l e c t i o n m et ho d t o c o p e w i th t h e m i d sp an

l i g h t n i n g s t r o k e .

0885-8977/91/0700-1327$01.0001991IEEE


2/9

1328

T he n ew t o w e r m od el p r e s e n t e d i n t h i s p a p e r a i m s

a t p r e d i c t i n g t h e b ac k f l a s h o v e r a t i n d i v i d u a l i n s u l a t o r

s t r i n g when a d o u b l e c i r c u i t t o w er w i t h g r o un d

wires i s

h i t b y a l i g h t n i n g s t r o k e . T h e re f or e , t h e r e s u l t o f

th e new tower mode l s hou ld be compar ed wi th t he

r e s e a r c h e s b a s e d o n t h e d i r e c t m e as ur em e nt [ 7 1 [ 8 ] [ 1 1 1

.

SURGE R E S P O N S E CHARACTERISTICS OF ACTUAL TOWER

M eas ur ement Cond i t i ons

F i g u r e 1 sh ow s t h e m e as u re m en t c o n d i t i o n s a n d t h e

ar r angement o f meas ur ing equ ipment . T he tower under

measurement ( N o . 7 ) i s a 5 00 kV d o u b l e c i r c u i t s u s p e n -

s i o n s t e e l t ower o f 62.8m i n ov er a l l he ig h t and 10 .8m

i n b a s e w i d t h . T he g r o un d

wires

were i n s u l a t e d f r o m

N o . 6 t ow er b y i n s u l a t o r s t o a v o i d t h e r e f l e c t i o n a t

t h i s p o s i t i o n , s i n c e t h e s p a n be tw e en N o .

6

and

N o . 7

t o w e r s

i s

s h o r t . All t h e p h a s e c o n d u c t o rs were d i r e c t l y

c o n ne c te d t o N o s . 5 and 8 t o w er s t o r e du c e t h e r a d i o

n o i s e a f f e c t i n g t h e m ea su re me nt ( F i g . 1 ( a ) a nd ( b ) ) .

A 5 0 Q c o a x i a l c a b l e o f 300m i n l e n g t h wa s u s e d t o

i n j e c t c u r re n t i n t o

N o . 7

t o w e r fr o m a p u l s e g e n e r a t o r

PG) o n t h e g r o un d a s i s s e en i n F i g . 1 b) and ( c ) .

T h e c o r e o f t h e c a b l e w a s c o n n e c te d t o a g r o un d - w ir e

c r o s s a rm of t h e t o w er t h r o u gh a r e s i s t o r o f l kn f o r

wave s hap ing and 'a cu r r e n t s hu n t o f 0 . 5f i. T he s he a th

o f t h e c a b l e w as l e f t o p en a t t h e t ow e r en d . T h i s co n-

f i g u r a t i o n

i s

e q u iv a le n t t o se t t h e PG o n t h e g ro un d-

w i r e c ro ss a rm , a s n o e x t e r n a l f i e l d e x i s t s b e f o re t h e

t r a v e l i n g wave w i t h i n t h e c o a x i a l c a b l e f r om t h e P G

r e a c h e s t h e t o w e r t o p [ a ] . T h e r e f o r e , t h i s m et ho d o f

c u r r e n t i n j e c t i o n i s s i m i l a r t o t h a t o f K aw ai [ l l ] and

i s c l a s s i f i e d a d i r e c t me th od . N o o t h e r l i n e s f o r

measurement w e r e i n s t a l l e d .

4 4 9 ,

m e a s u r e m e n t

(a) Layout

of

t h e t r a n s m i s s i o n l in e

1 2 . 7 r n

6 2 . 8 m

3 2 2m

c) Layour of t h e t o w e r a n d

t h e p u ls e g e n e r a t o r

O p t i c a l c o a x i a l c a b l e

b)

Na

7 Tow e r

F i g . 1 . S e t u p f o r l i g h t n i n g s u r g e r e s p o n s e m ea su re -

men t s .

T he i n j e c t e d c u r r e n t wa s m ea s ur ed b y t h e c u r r e n t

s h u n t , a n d v o l t a g e s a c r o s s t h e i n s u l a t o r s t r i n g s were

m e a s u re d b y a lOkR r e s i s t i v e v o l t a g e d i v i d e r . T h e s e

s i g n a l s were c o n ve r te d i n t o l i g h t s i g n a l s a n d were

t r a n s m i t t e d t o w av efo rm r e c o r d i n g d e v i c e s o n t h e g r o un d

t h r o u g h o p t i c a l w a ve g ui de s . B u nd l e f i b e r s were u s e d

f o r t h e o p t i c a l w av eg ui de s w h ic h r e s u l t e d i n t h e c h a ng e

o f s e n s i t i v i t y a f t e r t h e w a ve g ui de w as d i s c o n n ec t e d a n d

r e co n n ec t ed t o t h e

E/O

t r a n s du c e r . T h e r e f or e , t h e

s e n s i t i v i t y w as c a l i b r a t e d b e f o r e a n d a f t e r ea c h

m ea su re me nt b y a c a l i b r a t o r i n c o rp o r a t e d i n t h e o p t i c a l

s i g n a l t r a n s m i s s i o n s y s t e m , a n d t h e a c c u r a c y w as ma in -

t a i n e d w i t h i n 2% o f e r r o r . I n m e a s u re m e n ts w i t h o u t

c o n n e c t i n g t h e g r ou n d wires t o t h e t o w er , t h e v o l t a g e

b e tw e en a n i s o l a t e d g r ou n d w i r e a n d t h e c r o s s a r m w as

a l s o m e a s u re d . T h e f r e q u e n c y ra n g e o f t h e m e a s u r in g

sys tem was

DC

t o

1 2

MHz, which was l im it ed by t h e

e l e c t r o - o p t i c a l s i g n a l c o n v e rt e r .

Recorded Waveforms

T he PG g e n e r a te d a r e c t a n g u l a r p u l s e w i t h a r i s e

t i m e o f 2 0 n s a n d d u r a t i o n of

4 p s .

It a l s o g e n e r a t e d

a s low - f r on t wave wi t h a

r i s e t i m e

o f 3 p s . F i g u r e

2

s hows th e wavef or ms of t h e i n j e c t e d c u r r e n t m e as ur ed

a t t h e t ow e r t o p . I n t h e c a s e o f s t e e p - f r o n t wa ve ,

a l th o u gh t h e PG s e n t o u t a n e a t r e c t a n g u la r p u l s e i n t o

t h e 50R c o n n e c t i n g c a b l e , t h e w av ef or m m ea s ur ed a t t h e

t o w e r t o p wa s d e f or m e d a s

i s

s e e n i n F ig . 2 ( a ) . Th e

d e f o r m at i o n a t t h e w av e f r o n t w as n o t c a u s e d b y t h e

p r o p a g a t i o n w i t h i n t h e 300m c o n n e c t i n g c a b l e , b u t b y

t h e t r a n s i e n t i m p ed an ce o f t h e c o n n e c t i n g c a b l e

o b s er v ed a t t h e t o w e r t o p , d e te r m in e d b y t h e e x t e r n a l

f i e l d

[81.

c u r r e n t w ave a s s o c i a t e d w i t h t h i s e x t e r -

n a l f i e l d p r o p a g a t e d o n t h e s h e a t h o f t h e 300m c a b l e

w i t h t h e s p e ed o f l i g h t , a n d w as r e f l e c t e d a t t h e PG

e nd r e s u l t i n g i n t h e s m a ll d i s c o n t in u i t y o b se rv ed a t

2 p s o n t h e c u r r e n t wa ve fo rm o f F i g . 2 ( a ) . F i g u r e 3

s hows th e wavefo r m of vo l t ag e be tween a g r ound- wi r e

c r os s a r m and a g r ound w i r e when ground w i r e s

were

i s o -

l a t e d f r om t h e t o w e r .

( a ) S t e e p - f r o n t c u r r e n t . ( b ) S l ow - fr o nt c u r r e n t ,

3 . 0 ~ s ave f r o n t .

F i g .

2 .

W av efo rm s o f c u r r e n t b e i n g i n j e c t e d i n t o t o w e r

to p , 1 . 13A/d iv . Sweep: 0 . 5ps / d iv .

Fig . 3 . Waveform of v ol t ag e between a grou nd-wire

c r os s a r m and a g r ound w i r e . Ground w i r e s

i s o l a t e d fr om to w e r, s t e e p - f r o n t c u r r e n t

i n j e c t i o n .

I n F i g u r e s 7 and 8 a r e s hown th e meas ur ed wave-

f o r ms when th e g r ound w i r e s a r e c o n n e ct e d t o t h e t o w er .

I n t h e s e c a s e s , i t w as i m p o s s i b l e t o m e a su re t h e t o w er

t o p v o l t ag e s i n c e t h e r e were n o p o t e n t i a l w i r e s t o b e

r e f e r r e d t o . T he d i f f e r e n c e of t h e v e r t ic a l s c a l e s i n

t h e o s c i l l o g r am s r e s u l t e d f ro m t h e p ro bl em i n t h e o p t i -

c a l t r a n s m is s i o n s y s t em a s s t a t e d b e f o r e , w hi ch d i d n o t

a f f e c t t h e a c c u r a c y o f t h e m e a s ur em e nt .


3/9

1329

I n F i g u r e 7

i s

a ls o shown a waveform of t he

c u r r e n t f l o w i n g i n t o a g ou nd

w i r e .

T h e d i s c o n t i n u i t y

a t

3 p s i s

t h e r e f l e c t i o n o f t h e t r a v e l i n g wav e o n

t h e g r o u n d

wires

f ro m t h e a d j a c e n t N o . 8 tower 449m

away.

A t 3 . 8 p s

t h e r e f l ec t i on F rom No. 5 t ower 566m

away

i s

a l s o s e e n .

Decrease

o f t h e c u r re n t a f t e r

4 p s

r e s u l t s f ro m t h e p u l s e d u r a t i o n of t h e i n j e c t e d c u r r e n t .

T he v o l t a g e w av ef or ms a c r o s s i n s u l a t o r s t r i n g s f o r

t h e s t e e p - f r o n t c u r r e n t

were

a l s o u se d t o r e pr o du c e t h e

r e s u l t f o r t h e s l o w - fr o n t c u r r e n t b y u s i n g a c o nv ol u-

t i o n t e c h n i q u e . T he c om pu te d r e s u l t a gr e e d q u i t e

w e l l

t o t h e m e a su re d wa ve fo rm s, t h u s v e r i f y i n g b o th t h e

l i n e a r i t y o f t h e s ys te m a nd t h e r e l i a b i l i t y of t h e

measurement .

MO D E L I N G OF THE SYSTEM

E q u i v a l e n t C i r c u i t of t h e Sys tem under Measurement

I n a n a l y s i s o f l i g h t n i n g s u r g e s o n a n a c t u a l

s y s t em , t h e c o u p l i n g b et w e en t h e g r o un d

w i r e s

a nd t h e

p h a s e c o n d u c t or s s h o u ld a l s o b e t a k e n i n t o c o n-

s i d e r a t i o n , a nd

it

i s e s s e n t i a l t o e xa mi ne a n d s e l e c t a

t ow e r mod el t h a t f i t s i n a m u lt i- c on d uc t or c i r c u i t a s

s hown i n F i g . 4 .

Nu 7 No

8

I’liase

conducl ors

F i g . 4 . E q u i v a l e n t c i r c u i t o f e i g h t - c o n d u c t o r s y s t e m

f o r EMTP an al ys is .

1 3 2 m ( N u 5 - 6 a

Gro u n d

w i r e

1

75 cm d i a m e t e r

Phase conductor

B’

4

X 3 84 cm

diameter

at

50 cm

spacing

A’ v?

400rn(No.5-6

)

2 6 0 m ( N o . 6 - 7 )

36.0m

No 7

-

8

)

b d

50cm

l-4

F i g . 5 . C o n d uc t or g e o m e tr y a t a v e r a g e h e i g h t .

I n F i g u r e 4 , EMTP Semlyen models a r e used t o

r e p r e s e n t t h e m u tu a l c o nd u ct o r c o u p l i n g i n e a c h s p a n ,

f o r m i n g a n e i g h t - c o n d u c t o r s y s t em i n v o l v i n g t w o g r ou n d

w i r e s

a nd s i x p h as e c o n d uc t or s f o r d ou bl e c i r c u i t t o

r e p r e s e n t t h e s y s t e m u n d e r m e as ur em e nt . F o r t h e p o s i -

t i o n a l r e l a t i o n s h i p o f t h e g ro un d

wires

and phas e con-

d u c t o r s , t h e c o n d uc t o r g eo m et ry a t t h e a v e r a g e h e i g h t s

a s s ho wn i n F i g . 5

i s

us ed .

I n m u l t i - c o n d u c t or c i r c u i t a n a l y s i s b y EMTP, t h e

m u t u a l c o u p l i n g o f t h e g r o un d

wires

and phase conduc-

t o r s

i s

s i mu l at e d, b u t t h e e f f e c t of t h e f i e l d r e t a r -

d a t i o n am on g t h e g r o u n d

w i r e s

a n d p h a s e c o n d u c t o r s a r e

n o t c o n s i d e r e d a t a l l . T he wa ve fo rm

of

t h e i n j e c t e d

c u r r e n t i n EMTP c a l c u l a t i o n

i s

a polygonal approxima-

t i o n o f t h e a c t u a l l y i n j e c t e d w av ef or m. T he gr o u n di n g

r e s i s t a n c e o f t h e t o w e r u n d e r m e as ur em e nt i s assumed

t o h av e a f l a t r e si s t an c e - ti m e c h a r a c t e r i s t i c an d

re-

p r e s e n t e d by a p u r e r e s i s t a n c e

of

170, which i s t h e

meas ur ed va lue .

T he f r e q u e n c y c h a r a c t e r i s t i c o f t h e g r ou n d w as

a l s o i n c o r p o r a t e d i n t h e c o m pu t at io n , b u t

i t s

e f f e c t

t u r ne d o u t t o b e n o t s i g n i f i c a n t .

Convent ional Tower Models

T he s u r ge impedance expr es s io n p r opos ed by Sar ge n t

e t . a l .

[ 7 ]

h a s b e e n w i d e l y u s e d a s a t o w e r m od e l f o r

t r a v e l i n g w ave c a l c u l a t i o n ( c o n v e n t i o n a l mo de l

( 1 ) ) .

A c c o rd i n g t o t h i s e x p r e s s i o n , t h e t o w e r un d e r m ea s ur e-

ment i s approxim ated by a cone, a nd

w e

have a s u r ge

i mp e da n ce o f 1 70R f o r t h i s s h a p e. I n t h i s c a s e , it i s

t r e a t e d t h a t t h e v e l o c i t y

of

s u r g e p ro p a g a ti o n i n t h e

t o w e r i s e q ua l t o t h e v e l o c i t y of l i g h t

( 3 0 0

m / p s ) a n d

t h e r e i s n o s u r g e a t t e n u a t i o n .

On th e o th er hand , a s u r ge impedance o f

100

t o 11 5

R,

a s u r g e p r o p a g a t i o n v e l o c i t y o f 2 10 t o 240

m / p s

( 7 0

t o 80 o f t h e v e l o c i t y of l i g h t )

a n d a s u r g e a t t e n u a t i o n

c o e f f i c i e n t o f

0 .8

t o

0 . 9

ob ta ined by Kawai e t a l . [ l l ]

t h r ou g h e x p e ri m e n ts on a n a c t u a l t o w e r a r e a l s o u se d i n

J a p a n e s e d e s i g n s ( c o n v e n t i o n a l mo de l

( 2 ) ) .

Chisholm

e t

a l . a l s o recommend a model wi th r educed s u r ge p r opaga-

t i o n v e l o c i t y [ 2 ] , w h ic h

w i l l

r e s u l t i n h ig h er i n s u l a t o r

v o l t a g e s t h a n t h e c o n v e n t i o n a l m od el ( 1 ) .

I n o r d e r t o a n a ly z e ea ch i n s u l a t o r v o l t a g e du e t o

a l i g h t n i n g s t r o k e t o a gr o un d -w i re d t o w e r , c o n v e n t i o n a l

t ow e r m od el s a r e d i v i de d a t t h e c r o s sa r m p o s i t i o n s i n t o

f o u r s e c t i o n s .

N e w Tower Model

When ground

w i r e s

a r e i s o l a t e d fr om a t o we r , t h e

t r a n s f e r i m pe da nc e o f t h e to w er p o t e n t i a l

r i s e

measured

b y t h e d i r e c t m e th od

i s

i n i t i a l l y

low

[ l l ] a s i s s e e n

a l s o i n F ig . 3 When ground wires a r e c o n n e c t e d ,

h ow ev er , t h e t r a n s f e r im p ed a nc e o f t h e v o l t a g e a c r o s s

a n i n s u l a t o r s t r i n g a b r u p t l y

r i s e s

a nd f a l l s t o a r e la -

t i v e l y c o n s t a n t v al u e u n t i l t h e r e f l e c t i o n f r om t h e

b a s e of t h e t o we r a r r i v e s , a s

i s

known f rom t h e

o s c i l l o g r a m s o f F i g u r e s 2 ( a ) a n d

7 .

T h i s i s b e c a u s e

t h e i n s u l a t o r v o l t a g e

i s

i n f l u e n c e d b y t h e c h a r a c -

t e r i s t i c s

o f t h e p o t e n t i a l

r i s e

o f b o t h t h e t o w e r a r m

and th e conduc to r . T he tower impedance es t i mat ed From

t h e i ’ n s u la t o r v o l t a g e o f u pp e r p h a s e a t

0 . 5 ~ ~

n F i g .

7 , t a k i n g i n t o a c c o u n t t h e c o u p l i n g b e tw e en t h e g ro u nd

w i r e s

a n d t h e p h a s e

w i r e s , i s

1 25 0, p o s t u l a t i n g t h e

combined surge impedance

of

ground

w i r e s

a s 3 4 20 . T h i s

v a l u e i s c l o s e t o t h e m e a su r e d t ow e r i m p ed a nc e

of

1190,

i n d i c a t e d i n F i g .

3 ,

f o r a t ower when th e g r ound

w i r e s

a r e i s o l a t e d .

T he s u r g e p r o p a g a t i o n v e l o c i t y

i s

c l e a r l y k n o w n

f r om t h e o s c i l l o g r a m s o f F i g . 7 , and i s v er y c l o s e t o

t h e s p e e d

of

l i g h t . T h e r e f o r e , i n t h e new t o w e r m o d e l,

t h e s u r g e pr o p a ga t i o n v e l o c i t y

i s s e t

e q u al t o t h a t o f

l i g h t .

When t h e r e f l e c t e d s u r g e w av e fr o m t h e b a s e o f t h e

t ow e r a r r i v e s , t h e p o t e n t i a l o f t h e t o we r b e gi n s t o

d e c r e a s e . T he d e c r e a s e i s r a t h e r s lo w a s s e e n i n t h e

o s c i ll o g ra m s i n F i g u r e s

3

and 7 , and

i s

c o n s i d e r a b l y

d i f f e r e n t f ro m t h e r e s p o n s e o f a u n i fo r m tr a n s m i s s i o n

l i n e s h u n te d w i t h a

l o w

i m pe d an ce a t

i t s

e n d . T h i s

c h a r a c t e r i s t i c o r i g i n a t e s f ro m t h e non-TEM f i e l d

181,


4/9

1330

model

(

1) model ( 2) model

Tower su rg e Zt1 170 n 115 C 220 n

impedance *1 Zt2 1 7 0 R 115 R 150 R

and i s d i f f i c u l t t o a c c u r a t e l y e x p re s s w it h a s i m pl e

e q u i v a l e n t c i r c u i t . K aw ai ap p ro x im a te d t h i s c h a ra c -

t e r i s t i c b y i n t r o d u c i n g a s u r g e a t t e n u a t i o n c o e f f i c i e n t

i n h i s t o w er mod el [ l l ] , wh ic h p h y s i c a l l y i s v e r y c l o s e

t o u n i t y . T he i n t r o d u c t i o n o f s u r g e a t t e n u a t i o n c oe f -

f i c i e n t may r e s u l t i n a h ig h r e s i d u a l t o we r v o l ta g e a s

t i m e e l a p s e s , a nd K awai h ad t o c ha ng e t h e c o e f f i c i e n t

a c c o rd i n g t o t h e s t e e p n e s s o f t h e i n j e c t e d c u r r e n t . I n

t h e new tower mode l , an induc tance i s c o n ne c t ed i n

p a r a l l e l w i t h t h e r e s i s t a n c e d e te r mi n in g t h e a t t e -

n u a t i o n c o e f f i c i e n t , e n a b l i n g a more a c c u r a t e a p p r o xi -

m at io n of t h e c h a r a c t e r i s t i c o f t h e wave t a i l . T h i s

i n d u c t a n c e

i s

a p a r a me t e r t o d e t er m i n e t h e s h a p e o f t h e

w av e t a i l , a nd h a s n o t h i n g t o d o w i t h t h e l u mp ed i n d u c-

t a n c e o f t e n u s ed t o r e p r e s e n t t h e t o we r i t s e l f .

T o e n a b l e c a l c u l a t i o n of e a c h i n s u l a t o r v o l t a g e ,

t h e new t o w er m od el c o n s i s t s o f f o u r s e c t i o n s d i v i d e d

a t t h e u pp er ,

m i d d le a n d l o w e r p h a s e c r o s s a r m p o s i t i o n s .

E ach s e c t i o n c o n s i s t s of a l o s s - f r e e t r a n s m i s s i o n l i n e

a n d lu mp ed c o n s t a n t s c o n s i s t i n g o f a d a m pi ng r e s i s t a n c e

shun ted by an induc tance . Thus , th e new tower mode l i s

m u l t i s t o r i e d a s s how n i n F ig .

6 .

T he d am p in g r e s i s t a n c e

i n e ac h s e c t i o n i s d e te r mi n ed f ro m t h e r e s i s t a n c e p e r

u n i t l e n g t h o f a t r a n s m i s s i o n l i n e c a l c u l a t e d fr om t h e

p o s t u l a t e d s u r g e a t t e n u a t i o n c o e f f i c i e n t o f a t ow e r.

F i g . 6 . N e w m u l t i s t o r y t r a n s m i s s i o n t o we re w m u l t i s t o r y t r a n s m i s s i o n t o we r

model.

S e le c t i on o f Tower Mode l P a rame t e rs

The c i rc u i t pa rame t e rs o f th e new tower model

w e r e

b a s i c a l l y d e t er m i n ed f r om t h e m e as ur em e nt w i t h t h e

s t e e p - f r o n t c u r r e n t , a s t h e l i n e a r i t y o f t h e s y st em was

con f i rmed . Highe r va lu e o f th e su rg e impedance i s

a ss um ed f o r t h e u p p er p a r t o f t h e t o w e r t o c o pe w i t h

t h e i n i t i a l l y h i g h t r a n s f e r i mp ed an ce o f t h e i n s u l a t o r

vo l ta ges when g round w i r e s a r e c o n ne c t ed . B e c au s e t h e

r e s u l t o f t h e m u l t i - c o n d u c t o r a n a l y s i s b y EMTP w as d i f -

f i c u l t t o p r e d i c t b y c a l c u l a t i o n by h an d, t h e optim um

v a l u e s o f t h e t ow e r s u r g e i m pe d an c es an d t h e a t t e -

n u a t i o n c o e f f i c i e n t h a d t o be d e te r mi n ed b y a t r i a l -

a n d - e r r o r p r o c e s s . T he d e t er m i n ed p a r a m e t e r s f o r t h e

new tower model i s l i s t e d i n T a bl e

I.

I n F i g u r e s and E, v a r i o u s w a v e f o r m s c a l c u l a t e d

f o r c o n v e n t i o n a l a nd new t o w e r m o de ls a r e s ho wn f o r

compar i son . The employed pa rame te rs fo r con ven t ion a l

m od el s a r e l i s t e d a l s o i n T a bl e

I.

The measured

r e s u l t s

w e r e

c o n v er t e d i n t o t h e i mp ed an ce e q u i v a l e n t s

a s fo l lows : fo r F ig . 7 , t he maximum vo l t age va l ue was

d i v i d e d b y t h e i n ~ e c t e d u r r e n t a t t h e moment w hen t h e

vo l ta ge reache d maximum; f o r F ig . 8 t h e maximum

v o l t a g e v a l u e s were d i v i d e d by t h e p e ak c u r r e n t v a l u e

i r r e s p e c t i v e o f t h e i r t i m e . T he i n s u l a t o r v o l t a g e s o f

u p p e r p ha s e , w hi ch a r e t h e h i g h e s t i n t h e m e as ur em e nt s,

a r e b e s t s i m u l a t e d b y t h e new to w e r m od el i r r e s p e c t i v e

o f t he c u r re n t waveform.

T a b l e

I.

Est ima ted Values of Tower Model Consta nts

f o r Tra nsm issi on Tower Under Measurement.

I ConventionallConventionallNew tower1

* I - Z t l

=

ZT1 = Z T 2 = Z T 3 , and Z t 2 = ZT4.

*2- D i s t o r t i o n l e s s t ra n s m is s i o n l i n e s e c t i o n s .

3 - L o s s -f r e e t r a n s m i s s i o n l i n e a n d d am pi ng r e s i s t o r .

*4-

T = H/VT: T o w e r t r a v e l t i m e .

DISCUSSION

I n d e v e lo p i n g a s i m p l e c u i c u i t m o de l t o r e p r e s e n t

a t r a n s m i s s i o n to w er f o r l i g h t n i n g s u r g e a n a l y s i s , it

u s u a l l y i s o n ly a n a pp r ox i ma t io n , s i n c e t h e i n i t i a l

e l e c t r o m a g n e t i c f i e l d a r o un d a t o w e r

i s

no t TEM whereas

s i m p l e c i r c u i t e l e m e n t s c a n b e s t s i m u l a t e p he no me na

a s s o c i a t e d w i t h TEM f i e l d .

A

c o n i c a l t o w e r i s a n

e x c e p t i o n , b u t t h e e f f e c t o f t h e r e f l e c t e d wave fr om

t h e t o w e r b a s e c a n no l o n g e r b e s i m u l a t e d b y a s i m p l e

l o s s - f r e e t r a n sm i s s i o n l i n e . M o re ov er , t h e s u r g e

r e s p on s e o f a t y p i c a l d o ub le c i r c u i t t o we r l i k e i n F i g .

l ( b )

i s

m ore l i k e t h a t o f a c y l i n d e r t h a n a c on e a s i s

known from F i g . 3 .

T he a u t h o r s ' a p pr o ac h t o t h i s p r o bl e m

i s

based on

t h e m ea su re m en t o n a n a c t u a l d ou b l e c i r c u i t t o w e r , a n d

t h e r e c e r t a i n l y i s l i m i t a t i o n i n e x te n di n g t h e r e s u l t s

d ra wn h e r e t o o t h e r t y p e s of t r a n s m i s s i o n t o w e r s .

H ow eve r, f ro m a s e n s i t i v i t y s t u d y of b a c k f l a s h r a t e s ,

t h e c i r c u i t r e p r e s e n t a t i o n o f a t ow e r be co me mo re

s i g n i f i c a n t when t h e t o w e r h e i g h t e x c e e d s a b o u t 40m

1 2 1 . Most o f such h ig h towers more o r l e s s re semble

t h e o ne i n F ig . l ( b ) , t he r e fo r e , t h e r e s u l t s i n t h i s

p a p e r a r e s t i l l c o n s i d e r e d v a l u a b l e .

F o r a tower h i gh e r tha n abou t 40m, it i s p h y s i -

c a l l y m ore a p p r o p r i a t e t o s i m u l a t e it b y a t r a n s m i s s i o n

l i n e t h a n b y a l um ped i n d u c t a n c e . W it h t h i s s e l e c t i o n ,

t h r e e p a r a m e t e r s n e e d t o be d e t e r m i n e d , na m el y, t h e

su rge impedance Z T , t h e s u r g e v e l o c i t y

VT

a n d t h e s u r g e

a t t e n u a t i o n c o e f f i c i e n t

y .

When t h e i n j e c t e d l i g h t n i n g

c u r r e n t h a s a l o n g f r o n t d u r a t i o n r e l a t i v e t o t h e t ow er

t r a v e l t i m e T , t h e v a l u e o f

Z T /V T ,

p r o p or t i o na l t o t h e

e q u i v a l e n t t o we r i n d u c t a n c e , w i l l a f f e c t t h e p ea k v a l ue

o f t h e to we r p o t e n t i a l r i s e [ 2 ] . T h e r e f o r e , t h e s e t w o

p a r a me t e r s i n a t o w e r mo de l a r e c l o s e l y r e l a t e d ea c h

o t h e r .

O b se rv e d v a l u es o f t h e s u r g e v e l o c i t y a r e s u s c ep -

t i b l e t o m ea su ri ng c o n d i t i o n s . I n t h e r e f l e c t i o n

m e th od , t h e m om ent o f t h e a r r i v a l o f t h e s u r g e wa ve

r e f l e c t e d f r om t h e t o w er b a s e i s us ua ll y more ambiguous

i n t h e v o l t a g e w av ef orm t h a n i n t h e d i r e c t m et ho d.

I n t h e d i r e c t m et ho d, o n t h e o t h e r ha n d, t h e i n s u l a t o r

v o l t a g e i s s i g n i f i c a n t l y a f f e c t e d by a n a d d i t i o n a l

a d m i t ta n c e i n p a r a l l e l t o t h e i n s u l a t o r when g ro un d

wires a r e n o t c o nn e ct e d t o t h e to we r [ l l ] . P h y s i c a l l y ,

t h e s u r g e v e l o c it y

w i l l

n e v e r e x c e e d t h e s p e e d o f

l i g h t . I n t h e o sc i l lo g r a m s i n F i g .

7 ,

th e moments of

t h e a r r i v a l o f t h e s u r g e wav e f ro m t h e to w er b a s e a r e

c l e a r , a n d t h e s p ee d o f t h e s u r g e

i s

v er y c l o s e t o t h e

s p e ed o f l i g h t . T h e r e f o r e ,

it i s

c o nc l ud e d t h a t t h e

a c t u a l v e l o c i t y of t h e s u r g e

i s

n e a r l y t h e s p e e d o f


5/9

1331

I

Tower

t o p

vo 1 a ge

Upper phase

i n s u l a t o r

v o l t a g e

Middle phase

i n s u l a t o r

v o l a q e

Lower phase

i n s u l a t o r

v o l t a g e

C u r r e n t

f l o w i n g

i n t o g ro un d

w i r e

.

I,. _L

.,

-

o n v e n t i o n a l m od el ( 1 )

171 V 8 5 Q

N e w

tower model

'onven t ion a l mode l 2 ) 1

143 V 69n 184 V 9 6 8

97 V 48 .Q (108%)

2IX)\

IM

r

I

-.

_ _ _ ----

2 3 2 6

2 8

' "&

111 V 5 6 8 ( 1 0 0 % )

k3 15

F i g . 7 .

Compar ison be tween ca l cu la t ed and measu red wave fo rms , g round

wires

c o n n e c t e d t o t ow e r t o p , S t e e P - f r o n t

c u r r e n t i n j e c t e d .

Calculated Waveforms ( F i g s . 7 and

8 :

Tower

t

O P

v o l t a g e

Upper phase

i n s u l a t o r

v o l t age

Middle phase

i n s u l a t o r

vo I t ge

Lower phase

i n s u l a t o r

vo

I t

a ge

l e a s u r e d ( Sweep

:

. 5 P

s / d i v )

__ T ower t o p o r i n s u l a t o r v o l t a g e

-

V o l t ag e a t t o w er c r o s sa r m p o s i t i o n

Vo l tage induced on phase conduc to r

__ -

:onven t iona l model (1 )

79

V

2 3 . 2 Q

j w,

i

zonven t io na l mode l 2

98 V

28.8R

F i g .

8 .

Compar ison be tween ca lc u l a te d and measu red wave fo rms, g round wire s connec te d to tower t op , s low-f ron t

c u r r e n t i n l e c t e d .


6/9

1332

t

l i ght , and t he crossanns of a doubl e ci rcui t t ower

do not much aff ect t he actual surge vel oci t y.

Because t he t r ansf er i mpedance of t he t ower i s

t i me dependent, t he val ue of ZT cannot be det erm ned

f r om an i nst ant aneous val ue of t he i mpedance. Because

of t he r eason di scussed before, i f t he equi val ent surge

vel oci t y i s chosen as t he speed of l i ght , opt i mum

ZT w l l be hi gher than t he case of sl ower VT f or l i ght n-

i ng curr ent of a sl ow f ront . To cope wi t h the case of

steep- f ront curr ent t o a hi gh tower, i t i s desi rabl e

f or t he tower model capabl e of handl i ng t he t i me-

varyi ng nat ure of t he t r ansf er i mpedance t o some extent.

Thi s i s t he reason why t he taper ed surge i mpedance and

a sophi st i cated t r eat ment of t he surge att enuat i on

coef f i ci ent was i ntr oduced i n t he new t ower model .

The obser ved t r ansf er i mpedance of t he i nsul ator

vol t age i s i ni t i al l y hi gh and decreases i n a short t i me

f or a ground- w r ed t ower. But even t aki ng i nto account

t he precedi ng di scussi ons, t he sel ected surge i mpedan-

ces of t he new t ower model i s consi der abl y hi gher t han

t he measurement w t h ground w r es i sol ated f r om t he

t ower. I t i s known f r omt he aurt hors' exper i ment usi ng

a geometr i cal model , t hat t he i nf l uence of hor i zont al l y

i ns ta l l ed cur r ent - i nj ect i on cabl e, i ns tead

of

ver t i cal

i nstal l ati on, cannot be di sr egarded i n the measurement

of t ower al one, but t hi s i nf l uence i s much smal l er i n

t he measurement of a ground- w r ed t ower.

So

er r ors i n

t he measurement i s consi der ed not si gni f i cant .

The reason of t he consi der abl y hi gh val ues of t he

sur ge i mpedance i n t he new t ower model m ght be at t r i -

but ed to t he Semyen model used i n t he mul t i - conduct or

ana lysi s of EMTP. I n th i s cal cul at i on, the ef f ect

of

t he f i el d ret ardat i on cannot be si mul ated, and the

vol t age on the ground w r es i s i nstantaneousl y i nduced

on t he phase w res. Thi s w l l l ead t o an over-

est i mat i on of t he eff ect of t he coupl i ng bet ween t he

ground w r es and a phase conductor dur i ng t he t i me as

l ong as about the t ower tr avel t i me. I f c ompensati ng

t hi s eff ect by t he val ue of equi val ent surge i mpedance

of t he t ower, i t must be hi gher t han a val ue t o be cho-

sen i n a s i ngl e-conductor ana lysi s .

The hi gh t ower s urge i mpedance w l l af f ect t he

i ni t i al port i on of the curr ent f l owi ng i nt o gound w res,

t hough t he eff ect doesn' t l ast for a l ong ti me. As i s

seen i n Fi g. 7 , t he cal cul ated curr ent f l owi ng i nt o a

ground w r e f or t he case of t he new t ower model i s 1.3

t i mes of t he measurement . But t he corona eff ect wi l l

cert a i nl y i ncrease t he i ni t i al curr ent i n to the ground

wi r es f r omt he case of l ow- vol t age measurement . Furt her

st udi es to i ncl ude the corona ef f ect ar e desi rabl e i n

t he next st ep.

Convent i onal Convent i onal New t ower

model

(

1

model

2 )

model

FO

I

MLSC FO MLSC FO MLSC

APPLI CATI ON TO U W TRANSM SSI ON LI NE

phase kA

Back fl ashover condi t i ons of a UHV t r ansm ssi on

l i ne were anal yzed usi ng t he convent i onal t ower model s

( 1) , ( 2 ) and t he new t ower model . Fi gur e 9 shows t he

phase kA

I

phase

I

kA

10

1 1

12

Z o = 4000

Grouritl

wires

M ddl e 200kA M ddl e 200kA M ddl e 18OkA

M ddl e 200kA M ddl e 190kA

M ddl e 180kA

M ddl e

200kA M ddl e 200kA M ddl e 180kA

anal yzed equi val ent c i rcu i t f or t he UHV l i ne.

Each phase l i ne has an ac vol t age source of 1100 x

n T

os (wt + e ) kV on bot h ends t o account f or t he

superposi t i onof t he phase vol t age on the surge vol t age.

Tower hei ght i s 107m Li ght ni ng cur r ent was i nj ected

i nto No. 3 t ower and the i mpedance of t he l i ght ni ng

di schar ge path was assumed t o be 400n. Whether or not

a f l ashover occur r ed on an ar ci ng horn of each i nsul a-

t or st r i ng was j udged based on t he l eader model [121

f or a l ong ai r gap. Cal cul ati on was made f or gap

l engt h of 5m whi ch was r educed f r omt he act ual l ength

of 5. 9m t aki ng i nto account a safet y f act or. Corona

eff ects were not consi der ed.

Tabl e I 1 l i st s m ni mumpeak curr ent s causi ng back

f l ashover on a UHV l i ne. The wave f r ont of t he curr ent

i s l ps. The m ni mumpeak cur r ent i s af f ected by the

phase of t he AC vol t age, and i s 150 t o 180 kA f or t he

new t ower model , whereas i t i s 180 t o 210 kA f or bot h

t he convent i onal model s. The use of t he new t ower

model i s r ecommended f or s af ety- si de l i ght ni ng protec-

t i on desi gn when t he mul t i - conduct or l i ght ni ng surge

anal ysi s i s perf ormed by EMTP.

Tabl e 11. M ni mum Li ght ni ng St roke Curr ent Causi ng

Back Fl ashover On a UHV Transm ssi on Tower.

1

( Cur r ent of l i near l y r i s i ng f ront. Wave f ront : l ps)

1 p. u. = 1100 x

n n=

98 kV.

' l ' ower

Fi g.

9

Equi val ent c i r cui t f or a U W t r ansm ss i on l i ne.


7/9

1333

CONCLUSIONS

A r e l i a b l e l o w -c u r r en t m e as u re m en t o f i n s u l a t o r

v o l t a g e s o n a n a c t u a l d o u b l e c i r c u i t 500kV t ra n s m i s -

s i on tower was per f o r med us ing a d i r ec t method . T he

t r a n s f e r i m pe d an ce of t h e to w e r c o n s i d e r a b l y v a r i e s

d e p e n di n g o n w h e t h er o r n o t t h e g r o u n d w i r e s a r e c o n-

n e c t e d t o t h e t o w e r .

Bas ed on the above meas ur emen t, a new mu l t i s t o r y

tower mode l f o r a dou b le - c i r cu i t t ower wi th g r ound

wires i s

d e ve l op e d t o b e u s ed i n t h e m u l t i- c o n d uc t o r

l i g h t n i n g s u r g e a n a l y s i s b y

EMTP.

T h i s a n a l y s i s

e n a b l e s t o p r e d i c t t h e w a ve fo rm o f e a c h i n s u l a t o r

v o l t a g e , w h i c h

i s

u s e f u l i n d e t e r m in i n g t h e p h a se a n d

t he ins t a n t o f a back f l as hov er . T he new tower mode l

i s r ecommended i n J apan t o be us ed i n t he mul t i -

c o n d u c to r a n a l y s i s o f EHV- and UHV- clas s doub le c i r c u i t

t r a n sm i s s i o n l i n e s .

The new tower model and conve nt io nal tow er models

a r e compar ed i n t he a na ly s i s of min imum back- f l as hov er

l i g h t n i n g c u r re n t s a t a

UHV

t r a n s m i s s i o n l i n e . T he new

model gives about

2 0 %

s m a l l e r c u r r e n t ,

a

m ore c r i t i c a l

e s t i m a t i o n .

I t

i s know n f r om t h e m e a su re m en t t h a t t h e a c t u a l

s u r g e v e l o c i t y i n t h e t ow e r i s c l o s e t o t h e v e l o c i t y of

l i g h t , a nd i s n o t much i n f l u e n c e d b y t h e e x i s t e n c e

of

c r o s s a r m s

of

a do u b l e c i r c u i t t o w e r . B u t w hen t h e

e q u i v a l e n t s u r g e v e l o c i t y i n t h e t o w e r m od el

i s

s e l e c t e d a s t h e s p e e d of l i g h t , t h e e q u i v a l e n t t ow e r

s u r g e i m pe d an c e may n e e d t o b e a h i g h e r v a l u e t h a n i n

t h e c a s e of a s l o w er e q u i v a l e n t s u r g e v e l o c i t y .

A

cons id er ab ly h igh er t ower s u r ge impedance i s

s e l e c t e d i n t h e new t ow e r m od el t h a n t h e v a l u e p r e d i c t e d

f r om th e meas ur emen t of a t o w e r w i t h i s o l a t e d g r o u n d

w i r e s . T he d i f f e r e n c e i s i n h e r e n t , h ow e ve r, t h e u s e

of

t h e S e m ly en m o de l i n t h e EMTP i s a m p l i fy i n g t h e d i f -

f e r e n c e .

T he h igh e qu i va l e n t s u r ge impedance o f t h e new

t o we r m od el r e s u l t s i n a h i g h e r i n i t i a l c u r r e n t f l o w in g

i n t o a g r ound wi r e t han a meas ur ed va lue . Corona

e f f e c t s , w h i c h i s n o t c o n s i d e re d i n t h i s p a p e r , w i l l

a l s o a f f e c t on t h i s a s p e c t . T h es e p ro b le m s s h o u l d b e

i n c o r p o r a t e d i n t h e f u t u r e w or k.

REFERENCES

T r ans mis s ion =Ref e r ence Book - 345 kV and

Above/Second Ed i t io n, publ is hed by E P R I , P a l o

A l t o , C a l i f o r n i a , 1 9 8 2 .

W A .

Chisholm e t a l . , " T r a v e l Tim e o f

T r ans mis s ion T ower s , " I E E E Trans . , vol . PAS-104,

N O .

1 0 ,

1985, pp. 2922-2928.

J . Ozawa e t a l . , " L i g h tn i n g Su rg e A n al y s i s i n a

M u l t ic o n d u ct o r S y st em f o r S u b s t a t i o n I n s u l a t i o n

Des ign , " I E E E Trans . , vol . PAS-104,

N o .

8 , 1985 ,

E le c t r o M agne t i c T r a ns i en t s P r ogr am (E MTP) Ru le

Book Mode 31, p ub li sh ed by

B . P . A . ,

P o r t l a n d

Oregon, Apr i l 1982.

R . Lundholm e t a l . , " C a l c u l a t i o n o f T r a n sm i s s i on

L ine L igh tn in g Vol t age by F ie ld Concep t s , "

Tra ns . , vo l . 77, 1958, pp. 1271-1283.

C .

F . Wagner and A . R. Hileman, A

N e w

Approach

t o t h e C a l c u l a t io n

of

t h e L i g h t n i n g P e r fo r m an c e

of T r ans mis s ion L ines

1 1 1 - A

Simpl i f i ed M ethod :

S t r o k e t o T ow er ,"

A I E E

T r an s . , vo l . 79 , 1960 , pp .

589-603.

M A .

Sar gen t and

M

Darve niza, "Tower Surge

Impedance,"

IEEE

Tra ns . , v ol . PAS-88, No. 5,

pp. 2244-2254.

__ __

__

~~

1969, pp. 680-687.

[ E ] A .

Br a uns t e in , "T he Induced Over vo l tages Acr os s

t h e I n s u l a t o r S t r i n g s of P o we r T r a n sm i s s i on

S y st em s d u e t o D i r e c t L i g h t n i n g S t r o k e s, I E E E

PES Sunmer Meeting , Pa per C72 559-3, 1972.

[91 W A . C h is h ol m e t a l . , " L i g h t n i n g S u rg e R e sp o ns e

of

T r ans mis s ion T ower s , "

I E E E

T r a n s . ,

v o l .

[ l o

G .

D .

B r eu e r e t a l . , " F i e l d S t u d i e s o f t h e Su r ge

Response

o

a 345-kV Transmission Tower and

Ground Wire,"

A I E E

T r a ns . , vo l . 77 , 1958 , pp .

1392- 1396.

i l l ] M Kawai, "S t ud ie s o f t h e Sur ge Response on a

T r a n s m i s s i o n

L i n e

Tower,"

~ _ _ _E E E

T r a n s . , v o l .

PAS-83, 1964 , pp . 30-34.

[12: T . Sh indo and T. S u z u k i , A N e w C a l c u l a t i o n

Method of Breakdown Voltage-Time C ha ra ct er is t i c

o Long A i r Gaps," IEEE Tra ns . , v ol . PAS-104,

No. 6, 1985, pp . 1556-1563.

PAS-102, N O . 9, 1983, pp. 3232-3242.

ACKNObILEDGEMENT

Th e a u t h o r s a r e g r a t e f u l t o t h e m em be rs o f t h e

C o mm i tt ee f o r S u r g e S t u d i e s i n E l e c t r i c P ow er S y s te m s

o f t h e I E E o f J a p a n f o r many u s e f u l d i s c u s s i o n s .

M asaru I s h i i ( SM '87) i s a n a s s o c i a t e p r o f e s s o r o f

I n s t i t u t e of I n d u s t r i a l S c i e n c e , U n i v e r s i t y of T ok yo ,

Tokyo, Japa n. He re ce iv ed B.S., M.S. and

D r .

Eng.

d e g r e e i n 1 9 71 , 1 9 73 a n d 1 9 76 a l l f r om U n i v e r s i t y o f

Tokyo.

H i s

s p e c i a l t y i s h i g h v o l t a g e e n g i n e e r i n g .

Tatsuo Kawamura (5 '5 6

-

M'59) i s a p r o f e s s o r o f

I n s t i t u t e of I n d u s t r i a l S c i e n c e , U n i v e r s it y of T ok yo ,

Tokyo, Japan. H e rec ei ve d B.S. , M.S. and

D r .

Eng.

d e g r e e i n 1 9 5 4, 1 95 6 a n d 1 9 59 , r e s p e c t i v e l y a l l f ro m

U n i v e r s i t y of Tokyo. H i s s p e c i a l t y i s HV and power

e n g i n e e r i n g .

Teruy a Kouno (M'78 )

i s

a p r o f e s s o r

of

t h e D e p a rt m e nt

of

E l e c t r i c a l E n g i ne e r i ng , U n i v e r s i t y of Tokyo, Tokyo,

Jap an. He re ce iv ed B.S. , M.S. and

D r .

E ng . d e g r e e i n

1957, 1959 and 1962, each f rom Univ er s i t y

of

Tokyo.

H i s

s p e c i a l t y

i s

h i g h v o l t a g e e n g i n e e r i n g .

E i i c h i O h s a k i i s a manager of UHV T r ans mis s ion L ine

P r e p a r a t i o n O f f i c e , T o ky o E l e c t r i c Po we r

C o . ,

I n c . ,

Tokyo, Japan.

H e

r e c e i v e d

B . S .

d e g r e e i n 1 97 3 fr o m

M e i j i

Univer s i t y , T okyo , J apan .

H e

has been engaged

m a in l y i n i n s u l a t i o n d e s i g n a n d s u r g e a n a l y s i s o f

UHV

t r a n s m i s s i o n s y s t e m .

Kazuyuki Shiokawa

i s

a member of

U H V

New Tec hno log y

Pr o je c t T eam, E ng inee r ing Depar tmen t , Tokyo E l ec t r i c

Power Co. , In c. , Tokyo, Japan. He rec ei ve d B.S. de gree

i n 1982 f r om Keio Uni ver s i t y , T okyo , J apan . He has

b e e n e ng a g ed m ai n l y i n i n s u l a t i o n d e s i g n a n d s u r g e a n a-

l y s i s o f

UHV

t r a n s m i s s i o n s y s t e m .

Kaneyos h i M ur o tan i ( M '69)

i s

t h e depu ty manager

of

Power Equipment Div. 11 N i s s i n E l e c t r i c C o ., L t d . ,

Kyo to , J apan . He r ece i ved B.S . deg r ee i n 1960 f r om

Uni ver s i t y o f T okyo , T okyo, J apa n . H e has been engaged

main ly i n r es e ar ch and deve lopment wor ks

on

power capa-

c i t o r a nd

G I S .

~ _ _

___

_____

T akemi t s u Higuch i i s t h e d i r e c t o r o f K o y ag u ch i C o n t r o l

C e n t e r , K a n s a i

E l e c t r i c

Power Co., In c. , Wakayama,

J apan . He g r adua ted Os aka T echn ica l J un io r Co l l eg e ,

O s a k a, J a p a n i n 1 96 6 a n d c o m pl e t e d a s p e c i a l c o u r s e o f

Osaka Un iv ers i ty , Osaka i n 1968. He ha s been engaged

m a in l y i n t h e r e s e a r c h on l i g h t n i n g p r o t e c t i o n .


8/9

1334

Discussion

W.A. CHISHOLM (Ontario Hydro Research Division. Toronto,

Ontario, Canada):

I

would first compliment the authors

on

com-

pleting a full-scale test of surge response on a com plete tower

-

skywire

-

phase condu ctor system. Scale measurements are

instructive, but do not allow modeling of magnetic permeability

and soil resistivity in a realistic way. Other full-scale measure-

ments, including those reported in reference 191,were performed

on isolated towers or partially-complete systems. Wh ile we

obtained good agreement between model and full-scale tests using

both direct and reflected techniques, we had an advantage of

very low soil resistivity

p =

4-6 0-m). The authors' test geometry

is more representative of a real

EHV

transmission line.

The authors state that Chisholm, Chow and Snvastava

recommend a model with reduced surge propagation velocity 121.

This is not quite correct. W e assume that all propagation along

tower elements takes place at the speed of light.

There are no

dielectric materials near the tower, and we ignore corona effects.

The additional travel time contributed by tower cross-arms is

caused by extra path length. A part of the surge current splits at

each juncti on between the tower and the cross-arms. Som e small

part of the surge current will travel from top to base at light velo-

city. The bulk of the current will, however, be reflected and

refracted several times. It is this additional path length that

increases the time needed to see a complete reflection from

ground.

I

believe that the authors'

Figure 7 shows a return

reflection mo re than 500 ns after the initial rise. Th e two-way

travel tim e expected from a 63-m tower would be only 420

ns.

An

expanded figure would clarify this point.

The experimental technique is exciting the impedance

between the tower and the outer sheath of the co-axial feed line.

This structure can be treated as a biconical antenna, with the cone

angle changing as the wave radiates out from tower top. The angle

associated with the coaxial cable sheath will be small, and the

resulting source impedance will be about 500-600 0 his will be

dominated by the 1-k n source resistor.

In the first 25 ns, the

cross-arm

supporting the skywire

is a cone with an impedance of 146 R . After encountering the

tower body, the angle decreases somewhat, and the tower

impedance increases to about

190

R . At ground level, the cone

angle increases, leading to a surge response for the ground plane

that falls to

15

fi at some distance /Al l.

100

o introdu ce a model fo r the travel-time delay. With this tower and

skywire model, vo ltages at several points were calculated for a unit

9

step current. Figures

A1

to A4 show the calculated transfer

-

impe danc es at tower top and each tower crossarm position.

3

80

Th e tower-top voltage indicates the current injected

'

nto the skywire. It can also

be

compared with the Tower Top

Voltage predictions for the three tower models.

It is closest to

Conventional Mo del 1. Dividing the 80-n transfer impedance by

the 266-n skywire impedance gives a ratio of 0.30. Thus, 30% of

the injected current will initially go down the skywires and 70%

will proceed do wn the tower. The measured value for the initial

current split appears to be 2x 0.21 or 0.42

if

the current flowing

ns, the reflection from tower base decreases slowly. After several

' 40

4

2 0

5

nto ground wire of Figure 7 is for

a

single groundwire. After 500

0

Surge Response

of

Ishii Tower

' '

1 1 , I

I , , , ,

,

{ /

lri\\;\

\4\ $v\

,

p7\?WkdrM&

' .

8

0

1

2

Time (microseconds)

Figure A l : Calculated Tower-Top Transfer Impedance

Surge Responseof Ishii Tower

0 1 2

Time (microseconds)

Figure A2: Calculated Transfer Impedance at Top Crossarm

Time (microseconds)

Figures A2 to A4 show transfer impedance waveshapes

at tower crossarm po sitions.

In

all cases, peak transfer impedances

Figure

A3:

Calculated Transfer Impedance at Middle Crossarm


9/9

Surge Responseof Ishi Tower

0 1 I

0

1 2

Ti me (mcroseconds)

Figure A4: Calculated

Transfer

Impedance at Bottom Crossarm

of nearl y

100

Q are seen. Thes e val ues are almost doubl e the

observed i nsul ator vol tages, whi ch highl i ghts t he i mport ance of

coupl ed vol tages to the phase wr e in the overal l probl em

Some

detai l s of predi cted waveshapes are seen i n the osci l l oscope

records. Th e top cr ossarm shows consi derable osci l l ati on and

other cr ossar ms

show

two

in tia steps. The refl ection f r omground

is a slowdecrease rather than a sharp drop in potenti al .

I amsomewhat t roubl ed by the coupl i ng model . I

woul d expect thephase conductor s to act as antennas, r ather than

surge i mpedances over ground, during the peri od before a

refl ecti on has r eturned from t ower top. 1 woul d appreci ate the

authors' vi ews on

ths

poi nt.

REFERENCE

/AI/

Li ght ni ng Surge Response

of

Gr ound El ect rodes , W.A.

Chi shol m and

W.

J ani schewskyj , I EEE

88

SM

562-1,

Presented at

I EEE-PES

Summer Meeti ng, Port l and,

Ore

gon, ul y 1988.

Manuscri pt r ecei ved Febr uar y 27, 1989

M

ISH11

and

K.

MUROTANI :

We appreci at e

Dr.

Chi sholm s

val uabl e comments and t he detai l ed anal ysi s

of

the f i ne

st r uctur e of t he t r ansf er i mpedance of t he t ower.

Dr. Chi shol m s r emark on actual and equi val ent

surge vel oci t i es i s an i mport ant poi nt, and we bel i eve

that o u r i nterpretat i on i s essenti al l y t he same. There

i s no doubt t hat t he surge propagat es al ong a t ower

el ement i n the ai r wi t h t he speed of l i ght . When t he

t ower i s modeled by a s i mpl e t ransm ss i on l i ne, i ts

equi val ent su rge vel oc i t y i s cl ose l y re l ated to i t s

surge i mpedance. And i t i s di f f i cul t to i ndependentl y

determ ne the equi val ent surge vel oci ty f rom an osci l -

1335

l ogr amof t he st ep response of t he t ower, whi ch usual l y

does not c l ear l y show the arr i val of the ref l ected

sur ge wave f r om t he ground.

I n

F i g.

7,

however, t he

i ndi cat i on of the arr i val

o f

t h e r e f l e ct i o n f r o m t h e

ground i s rather c l ear , y i e l d i ng the apparent surge

vel ocit y bei ng cl ose t o the speed of l i gh t . Thus. i n

t hi s st udy, t he equi val ent surge vel oci ty was chosen to

be the speed of l i ght. t hen t he surge i mpedance best

f i t f or t hi s vel oc i t y was determ ned.

l l t he wavef orms obtai ned in the f ul l - scal e test

were al so di gi t i zed every l Ons w t h 8- b i t r e s ol ut i on,

and t he appar ent t wo- way t r avel t i mes of t he sur ge

coul d be deter m ned

f ros

t he di gi t i zed records

wi t h

t h e

t i me resol uti on of 10ns. For t he wavef or ms of F ig.

7.

t he i nsul ator vol t age of t he upper phase yi el ds the

t wo- way t r avel t i me of 440ns, and skywi re cur rent

yi el ds 450 t o 46011s. Taki ng i nto account t he l ength of

t he tower arm of 7m and the skyw r e support of

1 Om

t he

appar ent vel oci t y for t he vol t age wavef orm

o f

t he upper

phase i s 98% and that f or t he skyw r e curr ent wavef orm

i s

98- 100%of the speed of l i ght . Therefor e, f rom

t hese f i gur es. t he i nf l uence of t he crossarms on t he

apparent vel oci t y i s not obvi ous.

On t he ot her hand,

i f

the apparent vel oc i t y i s

det erm ned based on t he hei ght of t he measur i ng poi nt ,

i t i s 87

of

t he speed of l i ght f rom t he vol tage wave-

f orm of t he upper phase. and i s 91- 93%f romt he skyw re

curr ent wavefor m The appar ent vel oci t y

so

det erm ned

i s s l ower f or the i nsul ator vol t ages of l ower pos i -

t i ons, because t he proport i on of t he

ar m

l ength

i n

the

Propagat i on path i ncreases.

As

t he t r avel t i me in each

sect i on of t he mul t i st ory tower model i s deter m ned

i n

t he way shown in Fi g. 6 i t m ght have been more ap-

propri ate to choose t he equi val ent surge vel oci t y as

about 90% of the speed of l i ght . For t hat choi ce,

l ower t ower sur ge i mpedance t han that f or t he new t ower

model i n Tabl e

1 wi l l

be

sel ected.

Dr .

Chi shol m s detai l ed anal ysis on the tr ansf er

i mpedance of t he t ower succeeds i n qual i t at i vel y e x-

pl ai ni ng t he fi ne st r uctur e of t he measured wavefor ms.

I t i ndeed demonst r ates t hat st eps and osci l l ati ons seen

i n

t he osc i l l ograms of Fi g. 7 are not noi ses. The

reason

why

h i g h f r equency components are not seen i n

the osci l l ograms i s not

f o r

the l i mt at i on of the f r e-

quency response of t he measur i ng sys t em

b u t

f or the

r esponse charact eri st i cs of t he i mpedance of a cyl i n-

dri cal st ructur e as seen i n Fi g. 3. The val ues of i m

pedance of vari ous part s adopt ed in Dr Chi sho l m s

analysi s may need some adj ust ment s to expl ai n t he i n i -

t i al cur rent sp l i t of

42%

to skyw res.

We agree t hat t he phase conduct ors act as antennas

i n

t he begi nni ng. As we used EMTP i n the surge anal y-

si s of t he mul t i phase syst em we had to si mpl i f y the

r epr esent ati on of t he phase conduct ors . B u t we suppose

t hat t h i s s i mpl i f i cat i on resul ted in the sel ect i on of

the rather h i g h i ni t i al surge i mpedance of 2 2 0 R f o r

t he new model , whi ch i s nearl y t w ce as

h i g h

as the

max i mum t ransi ent i mpedance of t he tower wi t hout sky-

w res, as seen in Fi g. 3.

Manuscr i pt r ecei ved August 20. 1990.

articulo modelo torre

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