BSTJ 10: 3. July 1931: Bridge Methods for Locating Resistance Faults on Cable Wires. (Henneberger, T.C.; Edwards, P.G.)

11.2 MB·English

Bridge Methods for Locating Resistance
Faults on Cable Wires

ty 1. G HENNERERGER and PG. RDWARDS

In sone des ee gy ong itr
ene cie ther ae arte

LN the cll lepone plans, insstion Cate auch a gromnde” and
cose” ar asta eet ly the" Varey lop” methut wich
jnvolwee essentially the measurement of the dat. resistance of the
Feufly te beeween th pia of fault and one end of the cable, and
ie vomparizon of this restanee with the total conductor eesisance
of tie wire tu obs the" percent Fasaina” of tbe Fault ona re
fistance boss. Cievectione are then applied to aceonne for such
Tnvtors asthe resistance ott" als Tetween te cable vu te bre
the resstonces af Luediae chy ane non-unifermicy 0” wndueror
Fesitance cane by teuperaturedifeences beseeen underground and
NO Uections ofthe lin Aller al eormectame ame npplice the
feel nie distaace Kom one

formeted peccentage cation i conve
fale Io he fal

Tn general the mint Woublesome inelation faule wo late is @
“see spot" due to absnrction of mistre y the insulation through &
tierce ip the fea! covering of the eae, whieh seat in low insalation
edstance fetwers wives anit tv ground. Stancra sqysratt. now
Evailale Zor Inating gious aed errr is sufficiently senscive to
Droit accurate loatinte of wer pote up ts about Cue megolims ix
Feistaree, Tae Varey Kop metheds ordincriy empinyed in com
Devon with che spate il ve urate resus pried = wir

CT very ch higher insti reste than she fully ite is used

ta the ijeed" wire for tensinetents, "Thew are the conditions
‘hie uscally ace fons! wen wet spots oerue. Cazes wrt or
[Riatigy however, in which @ gun! wire having scent gh

inealaton resstanew nsenmpared the foul’ wie cannot be ola,
es cause all of I witem avaiable for measuremenes ne alerted
Ivy the faule or becase the Soult resistance is high. ‘The mete far
Tncating insulation faults discuss in thi paper ae especially aril
ae 1 sich cies

THesratance tnbulasces oa sable wires are of eelatvely infuayent
wcurvence red are sly cult to oe. A szcthod frequently
fpr for raring is Sates 4 to mraeare the inpedance un-
tance ut verious frequencion of ri-vul containing the fully wie
seul tr algae pesioe iperLinneequeney curves pots fom the
Treotireseate? The metIuaisor leeetng series resiatanee unbalttces
Giseused in this paper iavalve the ww of aedinary Wheatstone
Trslyes, ave simple to apps, and ave sesults which so believes to be
comperaie co those obesine by the mpedanee Feeney method.

Noman, Insuiation Resterasec or Cane Wanss

he alles of insulstion ssstanee ablained by measurements on
valle wives mich are not fall ate dependene on the circumstances
"vwhl the meceurements are made, I the cae af paper insulated

Telephore eable the suave hapovtane factors alerting sasuletion ce
Sslaaee are elecrifeatinn period ad temperature

“the following. éiscesion of nermsl insulation seistasce refers
rtvulary to messurenents between izes of pine in a typical
Feveater sti of tial all sie approximately 0 miles Hog, the
fives beng al geound potential ac the time of applestina of the
Teving ootental Insular neetanee to gd Fea 0 nee

That isdfcale to mensine arate i ong lengths of ae because
Clincesering potentials, Atanmugh apgsun mation, sorta! sult
ebunee betweer a wine re growad ean be conser ta be about
Tm this as great ae normal insulator resistnner between wires,

‘Leueve ilustrating the variation of imlaion reitanee Between
wwses of typed! cable pair ovrs a Slsinuteelectiicatinn period is
Thwowu ia Tig, 1. In general, the eleetniFeation pesiods necessary or
SSbuaining reasonully ronscaat yalues of solutes esistance der
Spprecably fo llesent pats, a or the sre pair ab dteren times
‘The usual period ranges (oun 15 ner to an aur fora par 0 mie
tng Routine mesaremens ave generally made, owever, using
devarikeation perie’s wf sme nite

Te parce tee for iaafating the wires wf celine cable Sas ar
appreciate negative ten peaiave cueticlewe of ination sesistanes.
Thins indicated by ie carve of Figs 2 which exows variations of
average Ino ntion sesetase with temportcune. The 22icts fe: the

"Tala ii Un
curve were obtained by nueraying, for euch fve-degree sange of tem
Deralure, the iailaton vesstnces obtained by measutemiea atade

eH 5

Vig. 1a of inaloe nance th detttoapsod pal SO ik

CIN ||

ruin, sarge

Sulit Tareratrt at Mascring Staton -CxgreesFarenht

epee epee

ily over che course of 8 year on rapraaentasive pare in a repeater
‘evinsingelecsfcnson nesodacre miautelong. Tehaseen found

hat the percentage changein insulation sesisane per cegteechaige a
lemperatate <ere willy fer difleene cable wotines wl even forthe
inividual pais in partivalay section, Toe aweraze change per
Aleyor Facer seit is yeaby alas! lor percent forthe ten:peraire

range eueguntensd on the part

ctl] ry
“TEER ih

“The cxeves of Vig #llnirase onmparaive vison of Sauietion
redanee between weve ni a sgpresnercie cxble pais, eominir
Jecotarce nf the pair, and onteile srmpera-use, dosing 24-rar
dei whith cludes 9 stnngesmeamar Cuvee evens wore plotter
Tren meastsemente wads evary hal vi, cme nina elec ati
Peviode se ral whan aieasuring ineelaion recatance. I: iy onl
Tneomiaon td ll he inauiaton resists of aati rire

(tng oy factors of thee to one Curing ve wurae of 2 day
‘Conpursnive varia one ef average ineulnion resiance between
snes of puis nd of rasan outside temperature over the course
Year ce illutated by the curves Figs TRE ports for the ine
Winn nevetonee carve here nhbdare by metaur'g he iauation
Sreistances of a sumber of pale each -werking day during tHe F8"
fotibeation pers, and aoecagicg the revere

vals for ee

In poner average ination vier aly to vary by fa
oC Te trie dung tie couree of yer Ta€heuah tes ar, of
fourse,evhiect iw much wider avait arialnaa ia inslaticr 7
otance. During winter it ie rat meommon to Bed partie pais
fins 36 nile repeater sesion wih lation reatances Let wer wir

of several chowsaad maggehras, while duviag aumaner, especialy im
fables which have been service fora suimber of yrs, the aati
Fesiscanves between wires 0 some pai in a SO.mile repeater section
Say bes ln as 25 angele (1250 megs.

Vans Looe Memon

‘The Vavley loop citeuite which are used ceinarly for locating
rounel and ersten om tee of tll cable ave ilustcated in Figs. § and
Behe Whectatone brie hus eval salto arms, The" good”

a

ig, 5 Vari he or se

ans fairy cable wins have equal conduccor resiaanoes, ¢ ard are
Gonatcete togeiln at che dstentend ofthe able. isthe resistance
Sf the ful and isthe conduetoeresicane ote fully wire between
the falta thw Cia end of the cae

rly fouty wire
WHUh the attery switch in “Varley” position, & Varley nioanures
sents ie by Telco the ridge to a rheostat value, P, a8 which
(here is no galvanemeter current, ‘Then

Aarts
ne

o

wll fe mete thae the fan resistance, isin series with the
Iattery and hae no effect om the menewreriens except to Hit the
sermitvity of the rig,

With the hueeery switch in "loop" pasion, a loop vesstance
reaearement is mare By balancing the bridge to eheostnt wale,
The

TFrom there Varley and loop mcgaurements the percentage loration
of the fulton wresstence sia, ean be aleulated a follows

_ ¥
From ce stant ert Ean per cet).

bv.

Fo he sacar et: {2 per von)

Corrections for russtanoes of ride eds oan els, ete ane then
made, the covrected percentage location i eoavevted into fet, a! the
Tesetion of che fant is detec hy refeenee cn eable vera
Teae Varley eictita and tocuilsa are well sepeed to the toll
cable plant where sires are rsually well balanced ia corduetor ee
nce, and the resistence of the leas between the bridge sud the
‘able small compared to the conductor resisance of the ene wies,
Inv exchange cable werk, mode orm of the Varley lop, which do
vt require that the "good" and faulty wines be uf equal canduczor
Sreitanre and ahich correct nuomatcally forthe msetacce oF bilge
le 8 Sree eh

“Torat, Cann Panucens

Tn the cate of total cable failure, due, for instance, to a wet pat
Were sce no wins i the cable which ave unatectad by che Fal, nd
the fault relates ofa lerge muse af the wire are ‘on, kof the
same order of magnitude as che eontducer resistances of the wires
yn mets by which ach Flt eat he Located are discussed belo
A" Cunrevted Varley” method which may be wei provide wn wires

ing Flt ressanrs to ground dieing by at least 25 per ent are
avalible for mecsuremests; aad a "'Staight Resistance” method
hich dovs not require that the two aires have fate of unequal

Correct Vorey Method
Consider a cable in which ali wis luave Low insulation resistance co
roe Hera ofa wet eb, and awn thac from among te faulty
bites two wites are selected for Vasley mosanrement. Aawuming ©
edge heving equal rate asa. the Vactey wet
Seated as chow fn Fig. 7, ule and Fore the elective resistanone
the feulte on the two wis rx the conductor resistance of either
trve, aad ig te restouce of that portion neither wize which fx
Tetween the distant end of the ele and te faults

nk cam be repre

‘The Varley cirewt af Fig. 7 ie equivalent to the Varley circuit of
Tig. whee the "type network formed by the thee resistances,
WF unl 2s, haw been ceplaced by 7" type network having reise
ance values ts infiaced, When the bridge is balanced by adustment
fhe sheoatet eo a resistance, V, at whieh there = no alvanometer

ee eR ns tn a esa oe eet

ad ee unin puto hse ef te ae
2M
roto
Solving or

@

Compurio of this formula with Tormals (1) indicates thet the
Facer 7/2, a8 determined hy Varley measurement, represents the

2

TF

soycent rater shan the true cesses Tesi he ligcant en of

ans Fi
wer=%)
ie a consction factor and expresses the vlation becween ¥/2 and
the tru resistance, x. Ifthe fan, My very seh higher i rit
farce than either the fault of che bslencing resistance, Vy the
correction factor becomes practically equal to one and 1/2 becomes
practically equal to In these circumstances the wire having the
Tht, a, car property oe elle! "soot" wine ane Formal (1) ll
tive aoaiate raul

Since the apparent reitance, 1/2, can be detremined by Varley
sncesurenent the fault be ied tle va of he ener
factor can be sleterminal, The eermetion factor car be evalnatd
by addons! seasuremests sada vm the ‘on Feulty wires From the
fend of the cable peste 19 at anal Gor the Wark meinem ae
deaeibed below

Refecing 20 Fig. 7, the vastence of either wire between the faults
and the exd of the cabis epposite to that used in suaking the Varley
Imeacuremens int. Il-¢ Voyp rnnane nmrenent senile From

ther wite aad the location of che saute, ‘Phe festor
is oppeeite er, usins a bridge heving cnuel rss anus with
iiton! ends a the tires ape, and the ess ance inthe bide rhe
ve lance i desgasted Le

MAPoty 2

a Vasley messiremet ie made Irom the same cad, using a bridge
svg esa tio crm, thule ddan! eds afte vies ape and te
resisane in he Unlye shila a! Tevance i decgaated Fy

WaPo %
Substituting those vas of (AFF) and (AE =F) in

vhs

ear

. 8

A pplication: To aumly Ure Cecverted Varley seth? a etiny
‘Varley meaetserscrt i mde from one and ofthe cable, cd ational
Tho seistance and Visley memurenente, ax describe sue, are
role Irma che oppsite end, Phe ales af ven resis tus
UDiained are svostinnted in Formula (4). The location of the trouble
fom resistor ss xr, can then he ealeulated, sad se lato eae
bbe convert te tin the usual mance

Taually ir wll be sacessery 20 determine she loop ceaduetor re
sisvamey 2, of ce Saale ese fom eable records rather han Iy
reeurement at he lime che vation is being ae. A. neaeurement
ff inop ronductor vesistance would be in error because of the low
‘este shunt (AF | en the portion of the loop beeween the faulte
fit tie slurtciveuited ends ofthe wires, The accuracy of loeatinn
ie depetvdens therefore, on the yccurtcy 20 which coneictr resistance
cen be estimated

In coate where it i desirable to we the

osreted Varley metho

rei esis wil he lee, wo hk waa Ue amg ree
ancy Fa wi un exceed 1000 cs WE et high meee
Using a bridge with ecual raio arms, unequal rato arms, and 3,

z
(8). Measurement of Vy Bowever, should be made wing a bridge
with equal ratio ems.

‘The Covtected Varley meted wi give accurate veeultsezly under
the following conditions

may be wed and the quantity 4 Zy aubsttuted for Zo ia Forms

LU) Borh Faults mast be ae the sime point along che eae
(2) The fale sesetances must rem conetame throuetae the test,