Electric cable

“ As the earth is used for completing the electric circuit, the signals received on such sensitive instruments as these are liable to be disturbed by the return currents of other systems in their immediate neighbourhood, which also use the earth as return, when such are of the magnitude generated by the working of electric tramways or similar undertakings, and to obviate this it is necessary to form the “earth” for the cable a few miles out at sea and make connexion thereto by an insulated return wire, which is enclosed in the same sheathing as the core of the main cable. ”

“ If an underground or submarine cable connects two portions of an overhead line, as in the Portsmouth and Dover transmission above mentioned, lightning arresters should be provided at each end of the cable, as was done in that case. One advantage of a high rather than a low voltage on underground cables, where power is to be transmitted at any given rate, lies in the fact that the amperes flowing at a fault in the cable determine the destructive effect there, rather than the voltage of the transmission. ”

“ If single-phase or two-phase current is transmitted, each cable should contain the two conductors that go to make up a circuit. In work with alternating currents the use of only one conductor per cable should be avoided because of the loss of energy that results from the currents induced in the metallic sheath of such a cable. ”

“ Cables employed between the generating and sub-stations of the Manhattan Elevated Railway, to distribute three-phase current at 11,000 volts, are of the three-conductor type, rubber insulated, lead covered, and laid in tile conduits. Each cable contains three No. 000 stranded conductors, and each conductor has its own insulation of rubber. Jute is laid on to give the group of conductors an outer circular form, and outside of the group a layer of insulation and then a lead sheath is placed. Outside diameter of this cable is nearly three inches, and the weight nine pounds per linear foot. ”

“ He described 'high tension cables for 3,000 volts' having paper insulation impregnated 'with a rather thin liquid, oily and not too resinous mass' with cable joints bound with linen tape first boiled in oil so that it is completely saturated, with the wrapped joint inclosed in a lead sleeve, soldered to the lead sheath of the cable. Through a hole cut in the top of the sleeve or socket 'hot insulating mass is poured into the socket. ”

“ The design of the cable was a subject of experiment by Professor Morse and others. It was known that the conductor should be of copper, possessing a high conductivity for the electric current, and that its insulating jacket of gutta-percha should offer a great resistance to the leakage of the current. Moreover, experience had shown that the protecting sheath or armour of the core should be light and flexible as well as strong, in order to resist external violence and allow it to be lifted for repair. ”

“ If a plain lead-covered cable is employed the acids of the soil attack it, and if stray electric currents from an electric railway find the lead a convenient conductor it is rapidly eaten away where they flow out of it. To avoid both of these results the underground cable should have a lead sheath, and this sheath may be protected by an outside layer of hemp or jute treated with asphaltum. ”

“ Also high-tension currents, ranging upwards from 15,000 volts, develop heat in the conductors and adjacent material, with consequent expansion and corresponding contraction when cooling, known as 'breathing.' This causes migration of the in sulating compound within the cable and to some extent its extrusion, and produces cracks and voids in it, with resulting ionization of the interstitial air at high tensions, and the lowering of the dielectric strength or resistance of the cable at the joint. ”

“ With a well-manufactured cable, improved paying-out machinery and an experienced staff of mechanical engineers, not to mention the foremost electricians of the day, the immersion of the cable was successfully effected, after which the American end of the cable of 1865 was raised, a new length spliced on, and the shore-end safely landed in Trinity Bay. Europe and America were thus united together by two electric bonds. ”

“ The insulated wires being drawn into them, any short circuit or heating of the wire cannot give rise to a fire, as it can only take place in the interior of a non-inflammable tube. A third system of electric light wiring is the safety concentric system, in which concentric conductors are used. The inner one, which is well insulated, consists of a copper-stranded cable. The outer may be a galvanized iron strand, a copper tape or braid, or a brass tube, and is therefore necessarily connected with the earth. ”

“ The cable was coiled in a dry pit in the yard, with its two ends accessible. The ends of the different wires could be united, so as to make of all these wires merely one wire six hundred and sixty miles in length, through which the electric current could circulate in the same direction. This current was itself furnished by an insulated battery formed of one hundred and forty-four Wheatstone's pairs, equal to fifty of Grove's. ”

“ They shall not move the machine while the cutter chain is in motion. When connecting the power cable to the electric wires, they shall make the negative or grounded connections before connecting to the positive, and when disconnecting the power cable, shall disconnect from the positive line before disconnecting the negative or grounded. When positive feed wires extend into rooms, they shall connect such wires to the positive wire on the entry before connecting the power cable, and as soon as the power cable is disconnected shall disconnect such wire from the wire on the entry. ”

“ The prime advantage of an overhead line at high voltage is its comparatively small first cost, which is only a fraction of that of an underground or submarine cable in the great majority of instances. At very high voltages, like 40,000 to 50,000 or more, the overhead line must also be given first place on the score of reliability, since the lasting qualities of underground and submarine cables at such pressures is as yet an unknown quantity. ”

“ On the other hand, at voltages in which cable insulation has been shown by experience to be thoroughly effective, underground or submarine cables may be more reliable than overhead lines because of the greater freedom from mechanical disturbances which these cables enjoy. ”

“ Alterations in the Electrical Apparatus.—Since the manufacture of the cable in 1857, Professor Thomson had become impressed with the conviction that the electric conductivity of copper varied greatly with its degree of purity. As a result of the professor’s further investigations, the extra length of cable made for the coming expedition was subjected to systematic and searching tests for the purity and conductivity of the copper. Every hank of wire was tested, and all whose conducting power fell below a certain value rejected. ”

“ When they pass along a damp wall, it is best to fix a board and loosely staple them. In no case allow more than one wire to lie under the same staple, and do not let the staples touch one another. In many cases, electric bells have been an incessant annoyance and complete failure, through driving the staples tight up to the wires, and several wires to the same staple,—this must not be done on any account. A number of wires may be twisted into a cable, and run through a short piece of gutta-percha tube, and fastened with ordinary gas hooks where it is an advantage to do so. ”

“ To produce the effects by which the messages are expressed at the end of a telegraphic wire or cable, it is necessary that the electric current should have a certain intensity or strength. Now the intensity of the current transmitted by a given voltaic battery along a given line of wire will decrease, other things being the same, in the same proportion as the length of the wire increases. Thus, if the wire be continued for ten miles, the current will have twice the intensity which it would have, if the wire had been extended to a distance of twenty miles. ”

“ It is of consequence, therefore, to ascertain the inductive capacity of a cable; as the less it is, the greater will the speed of signalling be.
The resistances and capacity of a cable are usually tested, according to the standards of resistance and capacity—that is, with the ohm, meg-ohm, and micro-farad—by measuring the strength of an electric current passing through the cable, by means of an instrument called the galvanometer, or current measurer. ”

“ Edward Orange Wildman Whitehouse (formerly a medical practitioner) , who became electrician to the first Atlantic cable. Mr. Whitehouse was a man of very high intellectual and scientific attainments, and a most ingenious and painstaking experimenter.
The retardation of the electric current through an insulated wire due to induction—a phenomenon practically unknown with bare, aerial wires suspended on posts, and of no consequence with quite short cables—was overcome by using a succession of opposite currents. ”

“ Where poles have heavy circuits and several cross-arms each it is sometimes desirable to attach a guy or strut beneath the lowest arm and also a guy close to the pole top. Galvanized iron or steel wire is the material best suited for guys, and the cable form has greater strength and is more flexible than solid wire. ”

“ The guard wire at the tops of the poles is about thirty-three inches from each of the power wires on the upper cross-arm. In this three-phase line there is about 1,440 feet of three-conductor underground cable, and this cable lies between the end of the overhead line and the sub-station in Montreal. At the juncture of the overhead line and the cables there is a terminal house containing lightning arresters, and there are also arresters at the Chambly plant and the Montreal sub-station. ”

“ For high-voltage work underground the lead covering is generally preferred without iron wire, but in submarine work coverings of both sorts are employed. The lead sheath of a cable being continuous completely protects the insulation from contact with gases or liquids. As ducts of either tile, wood, or iron form a good mechanical protection for a cable, the rather small strength of a lead sheath is not a serious objection in conduit work. ”

“ So we have only to send down earth-wires at the two ends—one into the earth of Ireland, the other into the earth of Newfoundland, and straightway the circuit is closed, and the electricity generated in our batteries passes through the cable from earth to earth. ”

“ The expansion of the interior cable parts and insulating material, accompanying the rise in temperature, forces the oil from the joints along the cable and also causes it to exude at the joints. As the cable cools, the fluid insulation, particularly at the joint, may not be sufficient to fill it and voids result. This occurs the more readily if the insulating compound tends to solidify at cooling temperatures. These consequences are avoided by the use, in conjunction with the reservoir, of oil which is sufficiently fluid to flow freely at ordinary cable temperatures. ”

“ I feel that the toast which I have the honour to propose deserves a foremost place in the toasts of the day, and that you will heartily respond to it, namely, Success to the Telegraph Construction and Maintenance Company, for that Company has laid scores of cables since its formation, and has now successfully commenced, and will doubtless triumphantly complete, the laying of the cable which we have met to celebrate to-day—the fourth great enterprise, I may remark, which the Company has undertaken—the cable that is soon to connect India with England. ”

“ It has been proved beyond a doubt that no obstacle exists to prevent our ultimate success; and I see clearly how every difficulty which has presented itself in this voyage can be effectually dealt with in the next.
The cable has been laid at the expected rate in the great depths; its electric working through the entire length has been satisfactorily accomplished, while the portion laid, actually improved in efficiency by being submerged—from the low temperature of the water and the increased close texture of gutta-percha thereby effected. ”

“ Such a cable may work at the regular line voltage, or a transformer station may be established on one side or on each side of the body of water. Even where it is possible to span a body of water with a transmission line, the cost of the span and of its supports may be so great that a submarine cable is more desirable. A moderate increase in the length of a transmission line in order to avoid the use of a submarine cable is almost always advisable, but where rivers are in the path of the line it is generally impossible to avoid crossing them either overhead or underneath. ”

“ Engineering Demonstration.—Still the engineer of this great undertaking had the satisfaction of knowing that he had demonstrated (1) the possibility of laying over 2,000 miles of cable in one continuous length across a by no means calm ocean at depths of two to three miles; and (2) that, by the agency of an electric current, distinct and regular signals could be transmitted and received throughout an insulated conductor, even when at such a depth beneath the sea, across this{153} vast distance. The feasibility of either of these had been scouted at on all sides. ”

“ Since practically all disturbances on lighting circuits are of low frequency, the series resistance can be used with good results; it aids the horn in extinguishing the arc, limits the size of the arc and prevents short circuits occurring during the period of discharge.
Fig. 2,382.—General Electric horn arrester for pole installation. Quite frequently series circuits are run underground in cables for some distance from the generating station. In order to protect the cables it is advisable to place horn arresters at the points where the cable joins the overhead wires. ”