Gompre$$Bd Gn$Gtpaultor$

M ICAFIL LTD"

ZU RI CH

G 3428 E

The insulalion of lhe eleclrical equipmenl is an arl requiring shrewd seleclion of malerials and pro-

cessing. Lack of uniformify o{ lhe insulalion slrenglh of malerials, when used in lhe praclical Jormsand lhicknesses which are required by the dif{erenl equipmenfs, has impelled lhe developmenl of

various lesls and tesfing devices, amongsl which lhe Shering Bridge plays a very imporlanl parf.

The Compressed Gas Capacilors belong, as inlegraling parl lo lhese bridges and allow {or lhe

conneclion of lhe laller lo very high vollage sources, The Air Capacilors, which were inil ially used,

are now rapidly being discarded due lo lhe unconslancy of fheir ca.pacilance and lo their loo

large sizes. Micali l manufaclures lhree lypes of Compressed Gas Capacilors. All of lhem have a

capaci lance of 100 pF and have proved lheir re l iabi l i fy on many occasions.

Appl icat ions

Compressed Gas Capaci lors are pr imari ly used

as reference capaci lance for measur ing the di-

eleclr ic losses of lhe insu la l ion maier ia ls, o{power facfor capaci lors, c€rbles, bushings andstack insulalors. They can also be used {or f ie ld

corona losses measurernenfs and, used in con*necl ion wi th secondary capaci fors, can serve

as part of pofenl ia l devices for lhe measuremenl

of the t ransformaf ion rat io of potent ia l andpower t ransformers. Peak vol tage measurementscan also be ef fecfed.

Advantages

The ski l fu l design al lows for smal l s ize uni ls

which can be placed at a l l desired spols of ahigh vol tage f est ing laboralory. The absolute

slabi l i ty of the capaci tance which remains in-sensi t ive to changes of a i r pressure, of a i rdampness and of ambient lemperalure can bement ioned as a special advanfage, The accur-ate values are given in the fo l lowing table,

Raled vol tage Un (50 c/s)

Max. service vol lage Ub

Rated capaci lance Cn

Accuracy ofcapdci tance value (Cn)

(Bo -= 20oCi po:pbif i l l ing gas Nz

ACnChange of capaci lance -G

({ i l l ing gas N:) :

1. As f uncl ion of pressure(r9o : : - 20 o C, po: pbr Ap-+lafm.gauge

2. As funct ion o{ femperalure(r9o == 20 o C,

Po:Pb,Ar9o:+1oC)

3. As funcl ion of temperalure,wi lh consta nl f i l l ing(,9o-_ 20oC,

po:=pbo Ar9.-+1oC)

Change of pressure wi fhconstanl f i l l ing

273 * BxPX: Po 2n + sa

Loss angle fand (Cn)

Max, service pt" tsr t . pb

Slray capaci tances (given asa guide) Ca

C,CoCr",

lnsu la l ion resis lance: ( a, t s1 to

Fi l l ing volume:

CompressedOi l jackef

Residual f i l l ingcyl inder when

Acf ing vol lagecoarse {useglow fuse

9as

Nz in pressured ispatched

of

Admissible lemperalure range

Weighf, net

Tesf valueslesf pressure of pressurecyl i nder(50 c/s, I min,76A/20/11)a) belween eleclrodes

H-(M,A,5,E)b) befween electro.des

M-A-(S,E)

H High vol fage

M Measur ing eleclrode

A Inner screening

S Ouler screening

E Service ground

Cn Slandard capaci lance

Cun Cr, Cn, Cn Slray capaci iances

KVKVpF

o/os

x l0-a

x10-

x10-

alm.

9au9

pFpFpFpF

MQ

li l resl i t res

alm.

gduge

Vd.c.Vd.c.

oc

lbs

af m.gaug

KV

KV

Descpipt ion for circuit of principle, equivalent circuit and dimension

drawing on page 4

t,

5,3

Typ PGI

150

150

100+7

t 0,3

- (0,1

< 10-s12

165

c.., 130cr, 200

560r:, 0

> 2AO

,:

0,2

I 40070

0<E<40

315

22

1,5

300

300

100 + 5

t 0,3

5,6

- (0,5 0,9)

< 10-s16

n, 400c.., 1 000

550Ca.-, 0

> 200

'?o0,2

1 4007A

l}<40

840

26

330

2

I High vol lage eleclrode

2 Measur ing eleclrode

3 Screen eleclrode

4 Glow fuse

5 Coarse fuse

6 Plug

7 Pressure gauge

I Gas oul let f i l t ing

9 Gas in le l f i t t ing

I

Typ PG3 | tru PGs

s00500+3100

t 0,3

- (1 ,3 " ." 1,7)

< 10-5

18

\r 430N, 1000

:60*;0

> 200

13s9s

0,2

I 4007A

0 <" ql 1qA

1060 + 90

30

550

2

The execul ion is represenled in fhe pic lures on page 2 and 3, The acl ive par l consis ls ol two concenlr ic

and carelul ly pol ished melal e leclrodes which are assembled in lhe in ler ior o l a special varnished paper

wqund and gast ight cyl inder. This insulal ing cyl inder is l i l led wi lh sui table lop and bol fom armalures

which increase lhe mechanical s labi l i ly and ensure lhe necessary l ighfness. In lhe lool f i l l ing are localed

lhe gas- in le l bal l valve, lhe pressure gauge, lhe c i rcui l prolecl ion fuses as wel l as lhe screened plug.

The ouler eleclrode is faslened lo lhe lop { i l l , ing and is normal ly connecfed lo lhe source of h igh

vol lage. The inner eleclrode is connecled by means o{ a rugged cont l ruct ion lo lhe fool f i f l ing, lhus

render ing special precaul ions for ra i lways tronspor la l ion unnecessary. This. secondary eleclrode is con-

necled by means of a screened cable lo lhe lerminal M whereby lhe screen i lsel f is connecled lo lhe

lerminal A, These lwo lerminals are insulaled from each olher and l rom fhe fool l i f i ing ' A special screen

eleclrode is provided for avoiding corona ef lecls al lhe infer ior edge of the high vol lage eleclrode. This

eleclrode is galvanical ly connecled lo lhe base l i l l ing and lhus lo ground. The lwo separale lerminals M

and A permi l measuremenls in connecl ion wi lh lhe Wagner Auxi l iary Circui l or wi fh Polenl ia l Adiusl-

menf, The ferminal M is connected lo lhe c i r -

cui t of ihe galvanometer * f f i 'ereas

the term-

inal A should be connected fo the screen

circui t of the br idge, receiv ing al the same

l ime the auxi l iary polenl ia l f or the galvano-

mefer" The background circui l on the f ronl

page i l luslrales the required connect ions wi ih

accuracy. The layoul of the PG-Type Com-

pressed Gas Capaci lors renders impossible any

inf luence of the high vol fage on the br idge

by means of s l ray currents" When working

wi lhoul auxi l iary c i rcui f , both ferminals A and E

are lo be grounded.

Glow'fuses are provided for prolect ing the

instrumenfs connected fo lhe Compressed Gas

Capaci tor againsf overvol lages" These f uses

are inser led in the c i rcui f between ferminals

M and A and ground.

A special Si l icagel f i l ter is del ivered with each

capaci lor for c leaning and drying lhe f i l l ing

gds. The capaci fors are always del ivered wif h-

out gas and musf be f i l ted on the spof wi th

ni l rogen (Nr) 99,5 olo pure or wi th carbonic

acid (COz). The guaranteed lechnical data in

the table refer lo ni t rogen, which shows fhe

fewest anomal ies. l f lhese gasses are nof avai l -

able, a i r can also be used. Each uni t under-

goes severe lesl ing be{ore leaving lhe factory

and owing to i ts care{ul seal ing, f ur lher f i l -

l ing is rarely necessary.

9 4,5

Dese r ipt ion of d imension drawing: v ide page 3

(Sizes given in mi l l imeters)