US2520624A - Leakage indicating device for gasfilled electric cables, pipe lines, or the like - Google Patents

Description

4 Sheets-Sheet l SEQ wm ww mb ug. 29, 1950 l LEAKAGE INDICATING DEVICE FOR GAS FILLED ELECTRIC CABLES, PIPE LINES, 0R THE LIKE Filed Jan. 4, 194'? y 8 N. m, .C A

Aug. 29, 1950 DAvEY 2,520,624

E. L. LEAKAGE INDICATING DEVICE FOR GAS FILLED ELECTRIC CABLES, PIPE LINES, 0R THE LIKE '4 Sheets-Sheet 2 Filed Jan. 4, 194'? /m/enor 5W @Arf-MM Atto/weg LIKE 4 Sheets-Sheet 5 Aug. 29, 1950 E. DAvEY LEAKA INDICAIING DEVICE FOR GAs FILLED c CABLES, PIPE LINES, 0R THE ELEC Filed Jan. 4, 194".

/venar y EZ ffm Attorney Aug. 29, 1950 E. DAVEY 2,520,624

LEAKACE INDICATING DEVICE -EoE CAS FILLED ELECTRIC CABLES, PIPE LINES, CR THE LIKE Filed Jan. 4, 194'? 4 Sheets-Sheet 4 E .4A phon-f Patented Aug. 29, 1950 LEAKAG minorenne, prlvres For; `slas- FILLED ELVEQTRIGWCABLES, PrPE LINES',

lOR' THE' LIKE Edward Leslie Davey, Hale",l England, assigner to' W.- T.-,Glover &l IComparisr Limited; Eraiord Bark, England, a British company ppucajtiqrr january 4, 1647, seria-1 Nq; rzozis tu Great-missin Jausry rr, 1ste f an elestrir.;v cas-ble system. whiolr is? intended to l remains il'led: with gas-i atv aipressure* different -lirom that ofi the? eaeterrfalv atmosphene, it,v is; im"- pprtant to` have: som'e mean'st et detecting a1 leak and ndingr t'hezpositionj ot itl. This meahs cans be provided if the` systemI is sectionalisedg; sir-idd an agreemen't cam then he set upf for obtai ngi an indication, of any pres-sure. difiererrce arising b'e- 'tween adjacent sections.. Permanent seetipmalisiing; however;r makes: diieult: the llihgi. ot the systeme either; initially.' or when; required arter ins-taIlatiorr.

'Fhe pnesexrt irri/entice resides ira the: incorpo*- ra'tionl in"` aa sectionaliz'edi gassfilleti eleetrie oalle system ofE as; deyicei which;Y while*4 capablef of-' formiimgL aiy out-oft Between yseetions and: indicati-hg sma'lh differences of pressure on opposite. sides oil the outsoff, also* permits ready fiow* or? gasy he?- tween: tl're: sections when aa substantially laiger pressure.'- dilterence existsi. such as established during llingf of thej system gas-a. Y

Ther-devlcsfisia pressure;reliermahometferwri' h oomprisesalargeboreflil-tiibeiwhibhlisihserte ih abr-.passieonnentedl across @barrier bets/sensatie sections of the system-randisiunderinerml operati f:

due? t'oai smallf diferendo" the pressure@ a'crbssv ,13%

4 claims; (or 73me)- eur.-

the process of filling the system. with gas under pressure'54 while it-serve'sasi a' complet-e2 seal and a sensitive! detecting devi-'ee for leakage condiiiiohs'i.- In the! latter state: the displacement of the mercury level' may' only be of the order' of f/Y irloli,` \r1l1e'reasv un'der` the' former conditions filiere is'imore or less violent bubbling through of IeJg'aSWililithe' throwing of the mercuryl up one In order to prevent carry-over of mercury out jef the? Uf-'tubaintoltheiterhal system when' gas isbubhling. through the mercury, a U-'tube with much elongated legs `soul-'dV be used. This', however; would. generally be ihcorivemlerit,v andi in general' Il prefer' toI provide a porous barrier at each side of the U-tube, which Will readily permit the passage of gas uhder the' pressures existing, lutfwillhotpermit the passage ofmeroiry'uhder the maximum pressure ciitheheriee which can o'cfli'a'ch barrier is preferably in' a chamber connected to`v a side.'` lorahch from' a' part-v of the lJ-tilbe leg-below the top thereof.r Thispermits the mercury which is thrown? upward bythepasisage? or the' airto fly past( the. opening. of: the branchlto theupper partofithef U-tub'e'legwhieh isfA closed ofi. The. hrahohl preferably slopes' up- Wards'# from the? Uitube so that any" globules of merery'which'zenterit Willpass back again tothe Elf-tube;- Th'e' porous barrier. is= preferablyA of'. a larger diameterithan the bore" of? the'A U`tube1 so a'st'ogive anextehded surf'aoefr the passage' o'f gars. Asuitable'loarrier isp'rovided byfa' plate of s'tled glass Whibhfhasj the? additional attiva-li'- taged tha-'ti it can: se fused integral with the: wsu of@ theehamber" it is olosed This" may h'ea short'eylirlder with` ai disc of? sihtere'dglass aoross the centre'pf itandiwith-ashort coiirieiet'- ihgtube at each eridi thattube which' is for cohnecti'on to the branch from the' U-tube, being at one" side ofr the-end' offthe cylinder, namely' the lw'e'r'si'lewh'eh iii position. This also facilitates the ruhninghac'k of ahym'e'rcury which is'parried over iito theihrariehand'iihto 'the chamber onfit rPhevv Uf-tilloe" withits branches' is also preferably madeof glass". K

'The indication of ah'unbalanc'e"offthemercury levels in thelegs oitheV U-tub'e dueto the'eii'stence ofr ai letaliL may he obtained by i direct observa? tio'ri ofthe tube; where that is convenient;V butit isusually preferable' and advahtageousto 'proL vide for ari'ihdieat'ion of a small" out' oi`r balance bythe' elo'siiig of f electric Contact'sby' meansof the risiiig'surface" of: mercury: Thiseah' readilybe providd'ifor' by arranging'jin each leg ofA theiU- short distance above the normal balanced position of the mercury surface. These wires may pass through and be fused into the glass Walls of the legs of the U-tube at a distance above the normal mercury level and project downwards to the required point, This arrangement may provide for local signalling at the barrier between sections. or may give an indication at a distance or produce an automatic record or control of the conditions.

By constructing the U-tube device in the manner indicated it can be made as a completely sealed enclosure consisting of the U-tube with its mercury and its contact wires and the two branches with their porous discs and the chambers enclosing them.

The understanding of the invention will be assisted by the following description of an example in which it is applied to an electric cable containing gas under pressure constructed in accordance with the specification of United States Patent No. 2,067,169.

In this specication reference will be made to the accompanying drawings,wherein,

Figure 1 is a longitudinal section of a complete joint between two length of the cable,

Figure 2 is a View, partly in elevation and partly in longitudinal section and on an enlarged scale as compared with Figure 1, of the leak indicating device with which the joint shown in Figure 1 is iitted,

Figure 3 is a view, which is partly an end elevation and partly a section on the line III- III of Figure 2, of the deviceshown therein,

Figure 4 is a plan of the device shown in Figures 3 and 4 with the dome in which it is housed re- 1 moved,

Figure 5 is a fragmental section taken on the line V-V of Figure 4 but drawn to a larger scale than Figures 2-4 and Figure 6 is a circuit diagram of the leak lndicating device tted with a signalling device.

The cable joint shown in Figure 1 is a joint between two lengths I, Ia of 33 kv,v three core, gas filled paper insulated cable of the kind in which thepaper tapes are pre-impregnated with a setting compound and the interstices between the tapes are filled with gas--for instance nitrogenunder super-atmospheric pressure. The cable is provided with a double lead sheath, the inner sheath of the lengths I and Ia being designated 2 and 2a, and the outer, 3 and 3a, respectively. In this joint, the three core conductors 4 of one length are connected by ferrules 5 to the corresponding conductors 4a of the other length and the conductor joints are individually insulated with hand applied insulation 6 which is covered with con-ducting tape and tin foil to form a screen which is a continuation of the core screens. The jointed and insulated cores are then enclosed in a copper tube 1 fitted with conical ends, 8 and 8a, 'by which it is jointed by wiped metal joints to the ends of the inner lead sheaths, 2 and 2a, respectively. This sleeve is enclosed in a twopart brass alloy sleeve 9 which is sealed at its ends to the inner and outer lead sheaths of the cable by cast metal joints, I0 and IM, and is iilled to the level indicated with liquid insulating compound, The anchored ends of the metal tape reinforcement, II and IIa, are respectively embedded in the cast metal of the joints In and Illa. To the outer ends of the conical moulds, I2 and I2a, for these joints are secured clamps, I3 and I3a, by which the wire armouring of the cable is anchored. The whole is enclosed in a protection box I4 of reinforced concrete. Normally a bypass' connection is provided between the interior of one cable length and the interior of the other cable length, consisting of pipes, I5 and I5a, sealed into the inner sheaths, 2 and 2a, respectively and respectivelyleading to domes, I6 and I 6a, on tonof the outersle'evef, 'and'. of .a pipe II leading from the interior of one dome to that of the other. This permits of a free iiow of gas between one jointedlength and the next.

To apply the invention to the joint described in the proceeding paragraph only minor structural modications are necessary: One of the two domes, which are normally similar and of the across the ends of the pressure equalising pipes I5 and l'I therein, and the resistance of the joint to flow of gas therethrough is increased by the application of a barrier I8 of insulating tape over the screening of each of the exposed parts of `the cores of one cablelength and of a barrier I9 of insulating tape overthe end of the inner lead sheath of that length and over and in between the barrier tape covered cores emerging therefrom.

The construction of the leak-indicating device housed in the larger dome I6, shown to the left in Figure 1, is .shown more clearly in Figures. 2, 3 and 4. It comprises a, U-tube 20 of glass secured in a clamp 2I mounted on a pillar 22 upstanding from a horizontal baille plate 23 which separates the interior of the dome .I6 from the underlying gas space in the-outer sleeve 9 which space is charged up by gas leaking. past the screws by which the baie plateis secured. This U-tube'may have a boreof 15mm. and an overall height of 60 mm. It contains mercury just sufficient to close'the bend in the U-tube with a small margin. The upper end of each leg is closed by a dome 'shaped end wall as is shown most clearly in Figures Band 5. A short distance below the upper end of each leg is a short branch tube, 24,V 24a., On each oithese branch tubes, 24,2441,- is acylindricalglass chamber 25, 25a, respectively, each: of about 30;mm. internal diameter andhaving'across the middle of its length a disc 26 of sinteredl glass about 2 mm. thick with4 pores of the .order of 50 microns diameter. Infthe Vend wall of :each chamber adjacentto the Urtube is a short connecting tube 21 adapted'to t in 'andbe sealed to the branch tube. This connecting rtube is atfthelowerside of the chamber sothat thef surface of its wall at thelowest part 'forms aclearcontinuation of the lowestpart of -the wall ofathej chamber; thus giving a clear run back for any globules of mercury that may enter thechamber. 1 The .branch tube, 24-and 2M,Y areinclined upwardsfrom the U-tube so as to facilitate this run back from the chambers 25 and 25a, respectively., In the other end walls of these. chambersy there.; are short centrally placed tubular pieces, 28 and 28a, rrespectively. To the tubular piece -ZB-issealed the neighboring end of the by-passpipe Il. The neighboring end oi theotherfby-pass pipe I5 is open to the interior vof the Vdome so that the enclosed space forms the connection between pipe I5 and the open end28a of the chamber 25a.

In each of thelegs ofY the U-tube is fusedv a pair of wires, 29 and 30 in one and 29a and 30a in the other. The lendsof, thesefwires insidevthe tube extend downwardtoabout one sixteenthof one inch above the ,level of the Amercury'.when in the balanced position.l The'hwi'res/S and 30a, their, me @feali Daitsrfglsid.externally fa-sagem to the dome I6, which is of metal, and'thl'ough it to the metal of the joint enclosure -9- and thereby to the external metal parts of the cable itself, thus providing a continuous earthed connection. The other wires, 29 and 29a, of the two pairs are, brought out and connected to the 'cores of a twin-core cable 3| passing through the top of the dome. This cable is preferably a cable having a metal sheath which can be soldered to the dome wall. A compound seal 32 is preferably provided for its lower end. The cable 3| together with the by-pass pipes 33 and .i3-,3a vfor the outer lead sheaths 3 and 3a, respectively, are led out through an opening in the lid of` the box I4', the cable terminating in varthree-pin socket outlet 34 in an inspection chamber 35 (Figure 6), the metal sheath of the cable being connected to the earth socket of the socket outlet. Into this socket outlet can be plugged a portable device 36 for electrically detectingjand indicating a displacement of the mercury in the U-tube. This comprises a battery 37,r one terminal of which is connected to the earth pin o f the plug 38 and the other of which is connected through a volt meter 30 or the like and a two-way switch 40 to one or other of the other two pins of the plug, depending on the setting of the switch. A displacement of the mercury in the U-tube suicient to short circuit one pair of wires is, if the switch is appropriately set, indicated by a reading on the instrument 39, the direction of displacement, and hence the direction of flow of gas due to the leak, being indicated by the position of the switch.

With such an arrangement ow of gas through the device at the rate of 0.01 cu. ft. per second can take place continuously for the lling of the cable without the risk of the passage of mercury through either of the porous discs. Under leak detecting conditions the contacts will be closed When there is across the U-tube a pressure difference of 1/8 inch of mercury which may correspond to a lgas leakage of 0.000001 cu. ft. per second.

It will be understood that although Figure l of the drawings Shows only the jointed end of two cable lengths the system of which these -from`each limb at a .point below the closed end thereof, a chamber on each branch,- a gas porous,

mercury-resistant barrier in each chamber dlviding iti'nto a lower part in communication with the branch carrying the chamber-and an upper `part,'-means for connectingr the upper part/Stof'sad'-ChaniberS t0 Said by-p'asS' Il'd YStifiicient mercury in said `Utube to closethe passagebetween the limbs thereof and prevent flow of gasVv through the Joy-epass when thepressure difference between the g'as inf'said sections' 'isf small, as when there is a gasv leak in one of said sections, and indicate the presence of said small pressure difference by its displacement but not so much as to'p'revent gas `from bubbling through said U-tube when the pressure differencebetween the gas in said sections is large, as when the iristallation is being-charged with'gas.

- 3. In an electric gas-lled-cable installation comprisingat- 'least two cablel lengths, a'joint between said lengths which comprises means for jointing each conductor of one `cable length to the corresponding conductor of the other cable length, means for insulating the jointed conductors, a tubular enclosure for the jointed and insulated conductors making joint at each end with a gas-impervious sheath of the adjacent cable length, means restricting the flow of gas from at least one of the two jointed cable lengths into said enclosure, a large bore U-tube disposed outside said enclosure, means for placing one limb of said U-tube in gas communication with the interior of one cable length at a point outside said enclosure, means for placing the other limb of said U-tube in gas communication with the interior of the other cable length, sufficient mercury contained in said U-tube to close under normal operating and under leak conditions the passage between the limbs of said U-tube but not so much as to prevent gas 'from bubbling through said U-tube when the installation is being charged with gas, means for prelengths form part will as a rule comprise many lengths and joints and that it will be advantageous to sectionalize the system at, and to apply the invention to, every joint.

What I claim as my invention is:

1. An electric gas-lled cable installation cornprising in combination at least two sections of cable containing gas under pressure, a joint between said sections constituting a barrier restricting ow of gas between said sections, a by-pass across said barrier and a pressure relief manometer in said by-pass consisting of a large bore U-tube containing suflicient mercury to close the passage between the limbs thereof and prevent flow' of gas through the by-pass when the pressure difference between the gas in said sections is small, as when there is a gas leak in one of said sections, and indicate the existence of said small pressure difference by its displacement and provided with means for preventing carry-over of mercury therefrom into the cable when said pressure difference is sufficiently large to cause the gas to bubble through the mercury as when the installation is being charged with gas.

2. An electric gas-filled cable installation comprising in combination at least two sections of cable containing gas under pressure, a joint between said sectons constituting a barrier reventing entry of mercury into the interior of the jointed cable lengths whenthere exists a pressure difference between the cable lengths suflicient to cause gas to bubble through the mercury, and means for indicating a displacement, and the direction of such displacement, from normal of the mercury level due to a small pressure difference between the cable lengths occasioned by a leakage of gas from one cable length.

4. In an electric gas-filled cable installation ycomprising at least two cable lengths, a joint between said lengths which comprises means for jointing each conductor of one cable length to the corresponding conductor of the other cable length, means for insulating the jointed conductors, a tubular inner enclosure for the jointed and insulated conductors making joint at each end with a gas-impervious sheath of the adjacent cable length, means restricting the flow of gas from at least one of the two cable lengths into said enclosure, an outer enclosure for the inner enclosure also making joint at each end with the said gas-impervious sheath of the adjacent cable length, an opening in the top of said outer enclosure, a baille plate covering said opening, a large bore U-tube mounted on said .baffle plate having limbs with closed ends, a

7 c'over nclosingfsaid U-tube andr making 'a gastight joint with the Wall of the outer enclosure, anupwardly extending tubular branch in one of the' limbs of said U-tube, a tubular connection between said branch and the interior of one cab-1e length, passing through said baille plate and between said inner and outer enclosures, said connection including a.- gasporous, mercury-resistant barrier, an upwardly extending tubular branch in the other ot the vlimbs of said U-tube in communication through a gas-porous mercury-resistant barrier with the interior of said cover, a tubular connection between the interior of said cover and the interior l of the other cable length, passing through said bale plate and between said inner and outer enclosure, sufficient mercury contained in said u-tube to close under normal operating and @leak lconditions the passage between the limbs thereof but not so much as to prevent gas from bubbling through said U-tube when the installation is being charged with gas, and means for indicating a displacement, and the direction of lsuch displacement, from normal of the mercury level due to a small pressure difference between the cable lengths occasionedby from one cable length.

EDWARD LESLIE DAVEY.-

a leakage of gas REFERENCES CITED UNITED STATES PATENTS Number Name Date `430,010 Flad June 10, 1890 557,534 Baker Apr. 7, 1896 1 882,141 Cope Mar. 17, 1908 1,642,615 Lommel Sept. 13, 1927 1,732,035 White Oct. 15, 1929 1,959,863 GriSS May 22, 1934 1,975,075 Bennett Oct. 2, 1934 2,043,227 Bennett June 9, 1936 2,079,856 Hoohstadter et al. May 11, 1937 2,430,034 Stern Nov. 4, 1947 2,449,271

Bennett et a1 Sept. 14,- 1948 OTHER REFERENCES Review of Scientific Instruments, Noir.r 1942 issue, p. 504, Figure 1. v

Certificate of Correction Patent No. 2,520,624 August 29, 1950 EDWARD LESLIE DAVEY It is hereby certied that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column l, line 7, for the Word agreement read arrangement; column 3, line 25, flo;- length read lengths; column 4, line 11, for proceeding read preceding; column 5,

' e 46, for end read ends;

and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Oce.

Signed and sealed this 14th day of November, A. D. 1950.

THOMAS F. MURPHY,

Assistant @omissioner of Patents.

Certificate of Correction Patent No. 2,520,624 August 29, 1950 EDWARD LESLIE DAVEY It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column l, line 7, for the Word agreement read arrangement; column 3, line 25, flor length read lengths; column 4, line 11, for proceeding read preceding; column 5,

'ne 46, for end read ends;

and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Oflce.

Signed and sealed this 14th day of November,l A. D. 1950.

THOMAS F. MURPHY,

Assistant @omissioner of Patents.

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