Document JYkg2DDdp3ERmxRDyKaZxw66

T LIA23866 "'i -* ' -*--' - LEAD INDUSTRIES ASSOCIATION, INC. aa MAOIHON AVINUf NCW VORK >7, K. V. October 10, 1963 SUBJECT: BROCHURE CM LEAD SiEATKsa f o r Kfeft c a b l ^T To Kacbers of tha Load Industries Association, Xno.: Wo aro pleasod to enclose a copy of our Just published brochure entitled 'load Sheathing for Power Cable." It describes ohe uses and advantages of lead sheathing and provides a sheathing guide for an engineer or administrator concerned with the installaticn of power cable ayatoca. The Itrochure will bo nailed to 16,000 engineers and supervisors in the poser transmission and equipment fields, and college engineer* lng libraries. Approxiaately 150 copies are being distributed to the electrical power and engineering press. Additional copies are available free of charge in qutntltlee up to 25 and at our cost of $15 for hundred for larger quantities. Sincerely yours, RBT/S Ena 1 Robert B. Travis Q O Loo* with L&+d r LIA23867 Sr.**---- ----- - --' - '- ' -* N 1941.01 LEAD SHEATHING FOR POWER CABLE Tabic of Contents Introduction Cable Sheathing Principles Power Cable Design Cable Manufacture Mechanical Stress and Creep Corrosion Resistance Lead as a Sheathing Material Types of Cable 5 7 8 9 II 14 17 21 Lead Industries Association. Inc. 29k Madison Avenue. Nov York.N. 1.10017 **r!S**Ai .W ..Jv.'fl'flar LI423869 / ^/ 'V<A: /: ' lit . *** . ym; ! irtxwrT 3870 \.\& ftVWrvnn - i i- ' i.n.ft **<!: i INTRODUCTION Lead sheathing for electric power ing is economical and has the added cable otters the optimum protection advantage of high scrap value. lor power cables that operate in all common voltage ranges and in every This booklet is intended as a general type of installation whether subma guide for prospective cable pur rine. conduit, aenal. or buried directly chasers to enable them to have a m the ground Lead provides the es broad *dea ol their sheathing require sential properties for durable cable ments m terms of the operating re sheathing; flexibility, moisture im quirements of their electrical installa permeability . corrosion resistance, tion. As cable des-gn and installation chemical stability, availability in very is a highly complex field, the specific 0 long lengths. an efficient return path examples and data given here are only lor fault currents and a return for the typical and not meant to be consid neutral teg of the circuit. Lead sheath ered definitive. t *< v<1* t*a 5 I mm - LI&23871 T Jh ' 1 : i s n, :.'3WtV*T* LIA23872 ) ' *' <V. ti4 c*nXct*. nan- LEAD SHEATHING PRINCIPLES Designing and specifying cable for electrical power systems is a complex and spcoaii2ed jot with many inter* rented problems. One of the most im portant of these is selecting the mate rial for the cable sheath The sheath most protect the cable wiring against mechanical and chemical damage while containing it both physically and electrically. Where cables are employed in power systems. the sheath must withstand almost every conceivable environ ment. ranging <rom harbor bottoms to deserts. And almost all installations impose many hazards on the sheath at the same time; consequently, a good sheathmg material must have a broad combination of properties to be gen erally useful. lead uniquely combines the proper ties most desirable in a cable sheath ing material. It provides mechanical protection during installatron and op erations: it is moisture proof, resist ant to sunlight and weather and to many corrosive elements that attack other sheathing materials. The sheath contains both the conductors and the insulation. In addition to providing highly effective protection against the environment, lead sheaths also play an active role in the electrical system itself by providing electrical shielding and a ground cturn path. Y'hcn used as a ground return, the lead sheath eliminates the need for the neutral conductors in the cable. Economically, lead offers other ad vantages as well. It is extremely dura ble and can. under proper conditions, crve for hundreds of years. On the other hand, its value as scrap metal significantly reduces the cost of re placing obsolete cable networks. 7 rwr UtJl a'l^l'Ti ^ Ll^23&73 i*u4& f* * tAwi<4 cab*. M|' (A(n1rtc t'tA44 (4A 0vCl*f. POWER CABLE DESIGN t An almost infinite variety of types and sues of cable are available commer cially. so ft will be possible ia tins brief report to discuss them only in general terms. Essentially, any power cable consists of one or more groups of wires, individually insulated and covered with a containing and protec tive sheath. The number, size and arrangement of the conductors is dictated by the elec tr.ca! and operating requirements of each installation. There are a number ol types of insulation used for cover ing conductors, the most important of which are Oil impregnated paper, var nished cloth, rubber and rubber like Synthetics and plastics. Selection de pends principally on the system's op erating voltage and installation condi tions. Certain cables are mechanically pro tected with round wires or flat armor tapes applied helically over a bedding on th* outside of the sheath. Such constructions are used m submarine and direct earth burta] runs where estra mechanical protection *nd strength is needed. The sheath that covers the cable core provides the pnys*:al and chemical protection of th.- cable during trans porting. installing and operating. Lead combines more of the mechani cal and physical properties than any other material required to meet the users* requirements. * t- : U* r,M * WM Wf cb' t* l*i C*A4<10'* l* LIA23874 |fci<d*4. *4 (k 4v <Im. FWG53H Q CABLE MANUFACTURE The first lead covered cables were made by drawing the cable core, con Sisting o* one or more insulated con ductors. through a cyhndrtctl ppe. A method was soon developed lor ex truding the sheath directly around Wfe core In this process, molten lead is fed into the chamber of a large by drauhe press where it is cooled under pressure to the extrusion tempera ture. The cable core is centered within the circular dx that forms the cuter surface of the sheath. When hydraulic pressure forces lead through the die. it carries the core along with it. Very long cable runs can be covered in this way; the limiting factors are the Sup ply of lead m the press reservoir, which can be rer'emshed. and the length of the cable core. In a typical press, the pressure on the lead is about 54,000 psi. /^The extrusion process forms a defect^"^Iree. homogeneous sheath with uni form wall thickness and practically unlimited length. Lead's low tempera ture during o*truson. about 400dSO'T docs rot injure the conductor insulating materials. Cable is coiled o* wound on reels as it comes from the extrusion press lead provides the flexibility for the addition of armoring or other protective coatings and other manufacturing steps. A recently developed method of mak ing lead cable sheathing is by con tinuous extrusion In this method, mc'ten lead or alloy is introduced at one end of the machine which has a screw type feeder. Under controlled cooling conditions the metaf is con veyed by the screw through the ma chine and emerges solid around the cable core through a die at the other end. This machine can now be used with commercially pure or alloyed lead. Paradoxically, the heavy metai lead, because of its unusual pliability, rfr7 A2367' Li V*, >^| k'<TM V uM * > KtK4 Vf fK p~t%\ I-V" |^4 f*'*fl.<** #* ifM| enables (he designer to minimize sheath thickness and weight while meeting the operating r3u<fements of the installation and without risking buckling or kinkmg when the cable is bent. Cable Shipment Vihen finished power cable is shipped from the manufacturer to the mstaMa tion site it is wound cn targe reels and the cable ends are firmly secured It is important that the reel be rolled in the right direction to insure that the cafe does not unwind or slacken If the latter should happen, the cable sheath must either have sufficient ten$;!c strength to carry the load or have sufficient ductility to stretch and relieve the stress Manufacturers guard against this slackening by Showing the wind direction of the cable and the direction in which the reel should be rolled The lead sheath mg on a properly designed power cable has sufficient tensile strength and clast.City to w.thstjnd vibrjtionsj or ofhor stresses that may occur dur mg shipment, installation or service. 10 LIA23876 !** l*fsO4 (^vd*^ ~3Z2~-toiial ... ________ @ MECHANICAL STRESS AND CREEP When a cable >s installed and in use, ill shealhmg is subjected to some combination of the following mecham cal stresses: Continuous tensile hoop stress from Steady mtcrn.it pressure Continuous compressive hoop stress from external pressure. longitudinal tensile stress Slo* bendmg m one direction that creates lon'ludinjl tensile and compressive stresses. Alternating tensile and compressive stresses which may be irregular and unpredictable and cause the lead to Lead sheathing offers sufficient re sistance to tensile and compressive stress and fatigue for most cable ap plications. In addition, alloying lead with arsenic or other metals and armoring the cable e*tenor with steel wire or tape enables the lead sheath to meet more severe operating cond t*ons j Wttdx'^Ml ItM (ib'l *< v1*r l $ **> #** v* /<** *1 **<* >* m.#****#*< 1i J v- - LIA23877 V>.; r- 5 -* *| A Hi .* /a '! << t >0'r lo rC-'* "**1I fl (t>< test could he weighted so that it would stretch and break in a specified time; he maximum load before failure would be ore value of tensile strength. However, because lead creeps, a smaller weght could break the speci men m a longer time with a conse quent change in nominal tensile strength. fluid filled types (oil or gas) of lead covered cable commonly operate at 15 p$< pressure. On oil filled types, however, higher in ternal pressures may develop at the low point of the run when the cable is la d on a slope or at the bot tom of a vertical riser. Reinforced, double walled sheaths may be used in these S'tuatrons. The most prevalent forces acting on a lead sheathed cable are: Changes in electrical load on cables during the day's operation cause them to heat and e*pand and cool and contract. Movement of the entire cable caused by mechanical forces m the envi ronment Jacketmg with neoprene or polyethylene provides additional protection agamst the deleterious effects of such vibration. It should be pointed Out Ihjt any ref crence to the ' tensile strength'* of lead requires application. Time is a far more important factor in deter mmmg the tensile properties of lead than it s vrith the hard metals Tor rramplc. a lead specimen m a tensile Creep Resistance The sheaths of most convention*1 solid type power cables are not nor mally subjected to conditions that cause creep; consequently lead with strengthening alloying elements is not 12 LIA23878 selected except for special mslalla tion requirements. The sheaths of oil filled cables and cables that operate at elevated tem peratures arc. however, subject to significant internal pressures during service and creep can occur m their sheaths. Alloy lead or metal tape remfo'ced sheath may be employed when creep is a factor. In this type of mstal laton it is not the lead's resistance to creep that matters, but is rather the sheath's ductility that permits slow expansion to the limits of the tape ithout rupturing. The desirable ability to deform uni formly and to a considerable extent without rupturing depends largely on the lead's composition and cleanli ness. that is its freedom from oxygen and sulphur films or inclusions. Oxides and sulphides form grain boundary films that are brittle and re duce ductility and fatigue resistance. These films between grains also make a sheath sensitive to stress-cracking when subjected to sustained toads at relatively low stresses with only slight elongation (creep). The presence or absence of certain trace elements in lead can decrease the tendency for dross formation, thus adding to its cleanliness. In addi tion. uniformity of grain structure is very important in aiding ductility. Ctcan, wett crystallised welds with uni form gram size are also highly de sirable. Considerable research is being con ducted on the effect ol grain structure on p-operties and also on the effect of extrusion conditions in varying the gramof sheathing lead. l-- ** l**4 l-oTM (k<* to *' l<en l*i*1 *w U-vKt U.lirti p*. C*b! M > tKlU4 !*' (AtftfCl** <*W*- CORROSION RESISTANCE There are two principal types of corro sion that attack power table sheaths: The first is natural corrosion in which the electrical current causing the damage1 is created by the interaction between the sheath metal and chemi cals m the immediate environment. This includes both direct chemical at tack (such as salt used in highway snow removal) on the sheath and the formation of a galvanic cell and an other motaJ. The second is stray current corrosion from buried or submerged power lines (dc. railroad, subway power or pipe lines that use one of the rails for the return leg of the system) As stray cur rent corros*on problems depend on the geometry of each specific installa tion there is little reason for a detailed d scussion here. In general, direct currents are lar more destructive than alternating Under some conditions Stray current corrosion can severely damage lead sheaths unless they are protected by iwan-conducting jackets. However, it should be pointed out that any metal cable sheath, and lead sheaths in particular, afford the con ductors an extra measure of protec tion by providing an excellent, low re sistance return path for str veurrents in the soil or fault currents arising from some breakdown in the power system itself. There are also a number of ways of designing the cable system that eliminate, or at least minimise, stray current damage. The most prevalent and expensive form of corrosion is not due to stray currents but is natural corrosion caused by the electrochemical inter action of the cable surface and the chemical it is exposed to m soils, in waters, or in the air. Corrosion in Soils -- lead cabled sheathing resists the corrosive action of soils because of the presence of M <i t*e*m n-- ~0>r- LIA23880 L0S5 OF WEIGHT AND MAXIMUM PENETRATION Of LEAD PIPE EXPOSED TWO AND FOUR YEARS* 4*4 N*. Trp C^nllCOt 1.4*4 (4> UiilnnHn Pf*o Toflvrtom l*4 (01 l* *t W*M W*ir*vwn CltlOA An(m*n4l ltf Id Ul ot VM*i**< Uhtmun TtM' ('POA 2 y*' 4 y*r% 2 riin 4 r** 2 r**% 4 rr 2 r**'> 4 r*<n 7 rtt 4 r**'* 7 y*n 4 SI Ck djr to* SI K(|*nlwn l4fli 44 l*h C4i*+* d*f 14 Mack 40 R>ft 4t Sh**r<**i *2 SwoovoHonno cUf 44 TMil mirth 44 Dmm cUr 4S Chloo tM loom 44 Uo*v* Roi I'M*/ !* l Ctn4 41 mwc* 70 Uff*4 i<lt n44 0 42 in 0M 4 St on 4 10 1.24 021 OM OH 0 4) IS2S 1 St 0 14 fr*44 0 44 0 42 0 44 SOS 0 so 4 42 1 04 eon 0 40 022 021 2SS 1 40 0 7S nMl u 24 >4 S4 14 It 12 14 24 40 44 n 21 44 mJH 12 24 SI 20 IS SO 20 10 14 24 >4 104 IS 14 m44 104 142 1 SO 701 041 S 04 IS! 0 21 0 71 164 14 0 004 040 **44 0 41 0 00 1 71 SOS 042 su 1 S4 oom 0 so OSS 02s IIS 224 0 31 m* 12 24 SO 3S 20 11 10 10 21 22 21 71 0 14 milt 20 24 41 S4 10 SO St I2f II 14 41 04 12 77 **44 1 04 0 DO l JUS 404 0 42 SOS MS 0 14 OSO 0.71 027 IS I 004 0 42 md4 0 44 0 11 1 04 4 4j 0 44 144 2 1* 0 02 0 40 0 44 0 71 4 0 7 JO 0 20 m4t 19 24 SO SO C SI 12 12 S 12 14 0 II w4* 10 IS S2 SO r 42 ) 12 IS IS so 7 12 *..rt H "S*<t C******** $t*#4**v IWI," 2 N1l s>* Vinl'4t. >1. 1<S lll4 *f 1407 * 1 *b* 4 <*) Cm. e*N. <. 0 007%; S4. 0 D011 %. J HH 2o*wt W.** 4 lor**. Ia c , H V*f%. 40 444. r%lC 007%. Tr 0 04J%. 44. 0 0011%. <c> Cm. OOHS. S..0 014* :S4. S SIV- R **4<a\** ~t.rsrtt bul no ** f (*) 0<ti l< *pon* th 4 nH. substances such as silicates, sulfates and carbonjtes that form protective films on the surface of the lead. Sili cates lorr. highly protective coatings; sulfates are less pronounced as lead sulfate *, soluble and forms a some what porous Mm, and although carbo rvates are generally protective they are soluble tn high concentrations of carbon donde--net a common con diton. Protective films may also be formed by cataphoretic action in which postively charged colloidal par ticles of Silt, clay or organic matter migrate to cathodic areas on ths sheath, discharge and deposit on the metal. Other factors of importance are the concentration of oxygen, ni trates, organic acids and alkalis. In general, the corrosion of lead in soils is not a single, clearly defined process, but is rather the ratio of the rate of formation o# reactive sub stances versus the rale of formation of soluble protective films. The National Bureau of Standards has intensively studied the corrosion re sistance of lead m soils. Typical find ings. Table I, indicate that lead sheathing is able to withstand soil cor rosion. except cinders, for many years withoi/t failure. Corrosion in Water -- lead is gener ally impervious to non potable water. Sett water, distilled water, and some acid water found in mines generally attack lead so that it would be neccs sary to protect the lead if it is exposed to them--again, an unusual circum stance. For example, tap water from metropolitan New York contains about 40 parts per million of dissolved chemicals and is not corrosive, where distilled water, lacking film forming substances, corrodes lead with com parative rapidity lead and lead alloys are universal'*used on submarine cable and other power lines exposed to salt water be cause lead shows only slight corrosion (4-5 mils per year when exposed to 1 N sodium chloride solution and practically no corrosion when exposed to salt spray). In a typical test, lead bars were exposed to the salt water cf the Bristol Channel off England The corrosion rate for soft lead and 1.6 percent antimomal lead were less than 0.3 mils per year. No localised pitting was found on bars submerged for 93 percent of the test period. Corrosion in Air -- lead is extremely durable in air. even in polluted city and industrial environments. Virtually nothing happens to lead sheaths ex posed to dry air. whereas, moist air containing carbon dioxide covers the lead surface with a protective film of lead carbonate. Sulfides tend to blacken or discolor lead but the sul fide coating is not particularly corro Sion resistant. Years of experience have shown lead cable sheaths to be resistant to atmospheric corrosives m installations ranging from the arctic to the equator. 16 Ll^38 82 T"* r*U4 (r. t^'v (a4<k ter. c*b*e LEAD AS A SHEATHING MATERIAL lead is particularly suited to use wth rubber, varnished-cambric and paper insulated cables because it <s the rrrst effective protection against mc-sturc. oxidation and weathering. It has the additional advantage of flcxifc My that permits the cable to be bent during handling and installation, and cf availability in long lengths essential for submarine and similar systems. Cables sheathed with lead can be in stalled aerially or in underground duct systems as well as directly buried or m submarine installations; any of these environments may be subject to varying degrees of corrosion. Lead sheathing can be protected against extremely severe corrosive elements or electrolysis caused by stray electric currents by applying a suitable ther mosetting or thcrn.upljstic jacket over the lead sheath of neoprene, poly ethylene Of polyvinylchloride. Lead sheaths are useful for oil or gasfilled cables operating at pressures about 15 psi The sheaths of cables operating up to 50 psi arc usually re inforced with two 0 005 in. thick hard copper or bronre tapes. Table III g*vcs the thickness of lead sheaths for rubber or varnished cam bric; Table IV tor vot*d type impreg nated paper insulated cables: Table V for smgle and double sheaths for lowpressure oil filled paper insulated ca bles; and Table VI for low pressure gas filled paper insulated cables. Lead Sheathing Alloys Alloying lead with cc-rtam other metals provides the stability and mechanical properties essential for cable sheath ing. The foremost alloys are the fol lowing: 17 \yrrrr LIA23883 substances such as silicates, sulfates and carbonates tnal form protective films on the surface of the lead. Sili cates form highly protective coatings; Sulfates are less pronounced as lead sullatc is soluble and forms a some what porous Mm, and although carbo nates are generally protective they are soluble m high concentrations of carbon dioxide--not a common con dition. Protective films may also be formed by cataphoretic action in which post-vely charged colloidal par ticles of Silt, clay o* organic matter migrate to cathodic areas on the sheath, discharge and dcposn on the metal. Other factors of importance are the concentration of oxygen. ni trates. organic aods and alkalis In general, the corro$*on of load m sols is not a single, clearly defined process, but 'S rather the ratio of the rate of formation of reactive sub stances versus the rate of formation of soluble protective films The National Bureau of Standards hjs ir.tens*vfly $!udu.-d the corrosion re S'Sfance cf lead m sols Typical f*nd mgs. Table I. indicate that lead ^lu-Jthing is jble to withstand soil cor rosion. except Cinders, for many years without failure. Corrosion in Water -- lead is gener ally impervious to non potable water. Soft water, d-st'ilod water, and some aod water found in mines generally attack lead so that ft would be neces sary to protect the lead if it is exposed to them--ogam, an unusual circumslance. For example, tap water from metropolitan New York contains about 40 parts per million of dissolved chemicals and is not corrosive, where distilled water, tacking film forming substances, corrodes lead with com parative rapidity. Lead and lead alloys are universally used on submarine cable and other power lines exposed to salt water be cause load shows only slight corrosion (4 5 mils per year when exposed to l N sodium chloride solut.on and practically no corros:on when exposed to salt spray). In a typical test, lead bars wore exposed to the salt water of the Bristol Channel off Cngland. The corrosion rale for soft lead and 1.6 percent antimomal lead were less than 0 3 mils per year. No localized pitting was found on bars submerged for 93 percent of the test period. Corrosion in Air -- Lead is extremely durable in air. even m polluted City and industrial environments. Virtually nothing happens to lead sheaths cx posed to dry a*r. whereas, moist air containing carbon dioxide covers the lead surface with a protective Mm of lead carbonate. Sulfides tend to blacken or discolor lead but the sul fde coatmg is not particularly corro Sion resistant. Years of experience have shown lead cable sheaths to be resistant to atmospheric corrosives m installations ranging from the arctic to the equator. 16 LIA23884 Vi BN4 trtM, (V# (a 4X` to>, vrni(h4 (mfcrl LEAD AS A SHEATHING MATERIAL Lead is parlicu'arly suited to use with rubber, varnished cambric and paper insulated cables because it is the most effective protection agamst moisture. oi'daton an^^eathenng It has the additional advantage of fle*i bility that permits the cable to be bent during handling and installation, and of availability m lo' `engths essential for submarine and s . i.lar systems Cables sheathed with lead can be in stalled aenaMy or m underground duct Systems as wt-li as directly huned Of m submarine installations, any of these environments may be subject to varying degrees of corrosion. Lead sheathing can be protected against e*tremely severe corrosive elements or electrolysis caused by stray clectrc currents by applying a suitable ther I ^^mosetlmg or thermoplastic jacket over the lead sheath of neoprene, pofy' ethylene or polyvinylchloride. Lead sheaths are useful for oil or gas filled cables operating at pressures about 15 ps. The sheaths of cables operating up to 50 psi are usually re inforced wdh two 0 005 n. thick hard copper or bronze tapes. Table HI gives the thickness of lead sheaths for rubber or varnished cam bric; Table IV lor solid type impreg nated paper insulated cables; Table V for single and double sheaths for low pressure oil filled paper insulated ca bles. and Table VI for low pressure gas filled paper insulated cables. Lead Sheathing Alloys Alloying lead with certarnother metals provides the stability and mechanical properties essential for cable sheath mg The foremost alloys arc the fof lowing; 17 LIA23885 ik 4 [M'M >n 1M m<I |K<t (ib*< !**" *a | 1) Copper bearing load--stable, um versatly used commercial lead, usually considered not an alloy. 2) Arsenical lead--for underground and aerial use where fatigue re sistance and lew creep rates are necessary for durability. C m tu '' f* l. t >**' 3) Antimony lead--not now generally used on power cables br-causc heat ccles induce age hardening that reduces cable fleibihty The chem-cal classif-cat-ons of lead grades suitable for sb.Hd*ng are given in A$TM 0 29 as shewn n Table II The alley selected for the particular r.ihV d*S'gn and operates cond-t oS must be assessed in terms of some of or a combination of the following characteristics: 1) Structural stability, particularly* avoiding the formation of coarse grained, weak crystals. 2) Resistance to cyclic stresses or strains at frequencies as low as one cycle per day. 3) The rate of age hardening. 4) Creep resistance of unrcmforced s'-v.iths on pressurized cables. 5) Cr*ip duct-hly under vrry Slew stra-r og rates (determines sheath e*panvon m pressurized sys terns). TABIC -- CHCMiCAl RCQUlRCMChTS v-*.#* r-> {*( CfH S >. . p*r wM Ct<>p Ctrl C*<4 < **-'< !i, /nji tc!*' | / * *. -> &< l-*v ri p< l diKulb. I>li p* < l*<4 bf p** "< L CCCIS -- c oo: -- o oo.'s C 00? 0 001 0 00? 0 2SO n S4 CO.'O c oc? o oso 0 0*3 -- o oo? 0 O0I 0 OC? C CCS tis) *<* ft11> i J o ac? c cm c o*o c ? 0 001 C OC? CO.-* tiw r **<*-* C*l 4d''1*4 a oc? o oc;s -- o oos 000? 000? 0ISO st s So< .jig fi t M#i*< h Si It* * 4 It*-'. *srw I ?S SS " 18 T '.'iv**" * j i w.ipwTWf>' i ij w j u j . 'i i,i nut**- / yf r--- LIA 2388 6 TABLE III* THICKNESS Of ICAO SHEATH fOR RUBBER OR VARNiSHEO-CAWBRlC INSULATED CA8LC OilmftH < C*# h 1 0 I* 0 471 0 424 to 0 200 0 701 I* 1.0)0 1 0)1 to 1 )O0 1 Ml lo 7 000 7 001 to 1 OOO ) 001 U'to* TKttMii W )N*rtN wwM 47 71 94 109 17) 141 In # mf t**d M l fUt 1* IM <** A*M H IM l (tM IK* (k-tl'ftt ** |K* %N*IN (h*n u Ml *<(*^l*<4 't* |N# ibtMl ltV' fK*t IN* Im IN* krtl l (*fl *N*'I t< 71 INfc * U*44|'*w a4 H m Te-'fc Ctf !*<( I*t. (!<( l*U4U, IM), TABLE fV* THICKNESS Of LEAO SHEATH fOK IWfflECNArCOfA^ER INSULATED CABLE "SOLIO TYRE** O.f c' <'t Tl'Kl'MU * li4 Sal'll m.* < Cv' ."<I < l4diN*/- "V'l oi0 4 0 441 ttt : Ml c 44 1 l0 III C914tol0>9 j c;io t 1 7M i* I 1 19) I* 1 1 )7)t I ;j > 194 VI 7*) I 740 to 1 1 94) to 7 7 l)<7( 7 7 11) I* 7 944 W) 714 499 n 7 VM t ; ui *0 7 194 l 970 99 7 9*1 1c 1 CM *o 1 CV* to I .*40 9) ).'4M)4.') 10) 1 4 74 ! 1 411 10) 1 4 i 7 to ] 794 no 1 79 7 to J 991 II) 1 997 to 4 144 170 4 147 to 4 |)1 IT) 1X3 m 140 14) 1)0 I)) |M 14) I 70 17) 1*0 U*4*>|'Ma 4 IpUmi Cook, li ke* t'fO'K Intt-iwto 19)7 N Vo^O C4f *n ollof <#d \KI r% t*d t*# >*4 * (-* >**' b pv'l *i -*.* in # <i ttlu 71 (*/ c> IN* trp < *1 H*4 f-4 tCPC*' U*4. *"d 0*1 il-#*l/#-d l#d H irct-*' 4*>'*~4 *K*#IN * w*4 IN* trp* *N bo 1K* (nAOl W<4 M *<-d(Ofp#' t**0 If * *"# *i>**in .4 w*#d in * t##i vkrd p**p*'( fN* #<0# \K#1 tN* o/ A)fM 79 19 L IA23887 TABU V* THICKNESS Of ICAO SHCATH FOR IMPRCGNATtD PAPCR INSULAUO CABU -tow pr c s s u r c oa-riuco nrpc- D.*m*t*r *4 Co' kh Ota 1 4*7 1 44) ta 1 4-1 I 44* la 1 an t 1)4 10 1011 2 01* la 2 203 ? 704 la I j *4 7 )I1 la 2 >M 2 9/9 la 2 799 7 740 t7 944 2 94) | 1 129 .* 110 la 111 3 3IS la J9* ) 100 talus 3 4*4 la 1 4/0 3 111 ta OSS |K.< k* *4 1**4 INoolV 110 IIS 120 in 110 in 140 149 ISO ISS ISO ) 41 170 179 ISO Ctowto* SN*1h| D`0'^*!*' 04 <.** >N<A Tfc.<fcn*t *4 l*4 mrtt 0l* 1 ill 1 411 le 1 9I| 1 917 f#/30S } 704 i*7<99 2 S00 la 2 794 2 799 la 2 044 ) 099 1* 1 )J 1 111 la 1 4/4 3 4/7 1* 1 970 2 9/| 1*47*4 99 (00 109 no its 170 129 Lrt 1>S 149 fo* |N* Un4*'{'a''d )jUw (*/' Ibcst >11*. wNa *n alto* totd N*at*> vu< IN* i**d H ly IN* Kjtfc |iin t>* ** toad n*l-n{ |H* >*Qv>*'*to*<t d A5TW S 79 ((y a*** a* IN* to *4 < (<4 t* l<h m* r* l tSitM iMMtit* HV, ik * (M*< tod I(CM*< r*4 Wll IMk OMM H *n t"tif itoiiA h v4*d Ito tod vwd in l*to , *U rv**t *# as t w a 7a TABU VI* THICKNCSS Of ICAO SHCATH FOR IM PR GNAT tO PAPtR WSUIATCO CABU -LOW PRCSSURC GAS-FILLCO TYPC* *4 C*'. "H* 0 la 2 141 2 344 la 7 447 2 4 1*2 952 2 993 1*2 4)4 2 43 7 ta 2 /*0 7 741 fa 7 4*4 7149 la 7 944 2 949 la 3 072 3 073 la 3 J 77 ) 171ta 9 211 1 747 la 1 34S 3 347 ta 3 419 l**d v-**. *** no ns 170 171 1)0 111 140 14S ISO 19S 140 149 Ca*a 4 3 4*3 ia ) 991 1 994 ta 3 49/ 3 491 to 3 *37 3 t3) le 3 tt 3 90/ ia 4 010 4 Oilta < 114 4 119 la 4 214 l**d 5r-*tft > * no >/5 140 119 190 199 700 ' Un4fi|'*w^4 Sftlimt lk, (Mn (toctrc lnl<t*t# l*y. N* Tort C*lf (<91 N*n *n #'too 10 U%*d. IN* to*< w-4 *9* tn N*lh **!! maat |h* i i^w ii'"HI pf A5tM 79 -|N* *< to*4 a' t<d to ad 20 LIA 2388 8 lw **<' gal P'N* (*n<vcl* ClM. \^aagB&mxgtu TYPES OF CABLE Service conditions and operating vol tages largely determine which type of cable construction s best suited to the system. In general, the types of insuiation employed are: plastics, rub ber like materials, varnished cloth and impregnated paper. Rubber-Insulated Cable--Low vol tage cables (120-600 v) jacketed in neoprene, polyethylene or vinyl are used for distribution at utilization vol tage lines. Lead sheaths are often used instead of nonmetatNc sheaths because of their supenor resistance to environmental factors. Varnished-Cloth Insulated Cable -- Varnished cloth insulated cables are not recommended for use in under ground installations subject to mois ture attack without the protection of _an impervious lead sheath. ^'armshod-clolh insulated cables are suitable for voltages up to 28,000 v. Lead clad cables are used in aerial runs, and for vertical risers, mineshafts and boreholes where they may be provided with an armored covering for additional support. Paper Insulated Power Cable -- Oil impregnated paper is the most widely used insulating material for power cables operating above 15 kv. Solid Cable -- consists of paper wrapped conductors enclosed in the sheath and impregnated with high grade oil. The design assumption is that the presence of loni/abte gaseous voids within the cable is inevitable. CA*r<4'u<l **-* **(I*N"<> lA <** ** LIA23889 Therefore, the insulation must be of sufficient thickness to permit stable operation despite the aging effects of electric discharge in voids. Adding an impermeable lead sheath prevents the penetration of air or moisture, precluding degradation by oxidation, and so enables the cable to operate dependably at the original de sign specifications. Solid type cable is available to 69 kv; however, its pre dominant use is at voltages below 35 kv. Low Pressure Oil-Filled Cables -- are used m 15 230 kv systems. This type of cable is filled with a high grade oil that flows both radially through the paper insulation and longitudinally in special channels made of strips of steel wound m an open hetu. Threeconductor cables have a channel m eich outer filler space: Single conduc tor cables have one in the center of the stranded conductor. In manufac ture of the cable the lead sheath is applied after which the cable is heat dried, gasses removed from the core by a vacuum pump, and the msulation impregnated. Reinforced sheaths or double sheaths arc used for higher oil pressures m the operating range. Higher pressures permit slopes or vertical risers to be successfully incorporated into the run. Cow Pressure Gas-Filled Cables -- both single conductor and three con ductor gas filled cables are used in low pressure (15 psi) power cables that arc lead sheathed. Gas filled cables have three advan tages that are unusual: Internal pressure provides a means of continuously checking the sheath for breaks (i.e. continuous sheath super vision). Low pressure alarms at cable terminals signal when any gas is cs capmg through a sheath break or the joints. Similarly, high pressure alarrn warn of excessive pressure buiidu; Damage from any normal sue leak can be prevented by maintaining in ternal gas pressure until the teak is repaired. This is an important safe guard against lost operating time. Gas can be used safely in risers and on slopes without pressure buildups at the low points of the run. Three conductor low pressure gas filled cable is generally similar n ap pearance to oil filled type except that one of the oil channels is replaced by a sold copper tube with no lateral openings to the insulation, but it is open a* the cable joints. The other channels arc open sided helixes carry ing gjs at about 15 psi 7 he solid wall tube ptovidcs the pressure between manhole sections at all times in the event that the helical channels be come slugged due to oil drainage. Single conductor cables do not have the gas tube at their axis but ra!h<F!j hove flutes in the lead sheath to server as gas channels. 22 | 11'TW' rr'** LIA23890 " *"** i t BIBLIOGRAPHY Corrosion Handbook: H. H. Uhlig, John Wiley & Sons, Inc , New York City. Lead and Lead Alloys for Cable Sheathing: S. A. Hiscock, Ernest Benn Ltd., London. Lead in Modern Industry: Lead Industries Association, Inc., New York City. Metallic Corrosion Passivity and Protection: U. R. Evans; Longmans, Green A Co., New York City. Underground Systems Reference Book: Edison Electric Institute, New York City. "Cable Engineering A Multidisoplme Technology,*' L. F. Hickernell; Electrical Engineering, Oct.. 1961. ^lead and Lead Alloy Cable Sheathing." S. A. Hiscock. Lead Development AssotJt'on. London. "Development of a Continuous Extrusion Machine for Sheathing Cable With Lead AJioyS." S. F. Radtke. C. J Snyder. C. C. Childress; American Institute of Electri cal Engineers Transactions 60-1219, 1960. "Mechanical Properties of Lead and Lead Alloys,** Abstracts of 6NF Research Reports, 1926-1960, The British Non Ferrous Metals Research Association. Association of Edison Illuminating Companies. New York Cty: "Specifications for Impregnated Paper-Insulated Lead Covered Cable OilFilled Type." "Specifications for Neoprene Protective Coverings on Impregnated-PaperInsulated lead Covered Cables." "Solid-Type impregnated Paper-Insulated Lead Covered Specifications." "Specifications for Impregnated-Paper lnsutated Lead Covered Cable `Low Pressure Cas Filled* Type." Insulated Power Cable Engineers Association. National Electrical Manufacturers Association, American Standards Association. Inc., Montclair. N. J.: "American Standard Requirements fer Varnished Cloth Insulated Cables." ``American Standard Requirements for Asbestos, Asbestos Varnished Cloth and Asbestos Thermoplastic Insulated Wires and Cables.** "IPCEA NEMA Standards Publication Rubber Insulated Wire and Cable for the Transmission and Distribution of Electrical Energy.** "IPCEA NEMA Standards Publication Thermoplastic Insulated Wire and Cable for the Transmission and Distribution of Electr<cal Energy." 23 1 y -i */ . ;! < LI A23891 i -* 1-- i--'*-- -----;------- TEN REASONS WHY LEAO SHEATHED CABLE PROVIDES THE IDEAL POWER PACKAGE; Adaptability lo Under or Above Ground Use Wide Operating Temperature Range Available in Extra long Lengths Good Bend life and Workability fault Current Return Path Complete Impermeability Corrosion Resistance High Scrap Value Fireproof Stability Lixx A**v*xF fTtspl cj.K^g L*-*c f ^ - wUU ": CH l20*Jl J/4J