Patent GB-191413933-A (GB)
Title: Improvements in or relating to Electric Cables.
IPC: H02H7/22
Filed: 1914-06-09
Granted: 1915-07-09
Abstract: 13,933. Waters, E. G., and Callenders' Cable and Construction Co. June 9. [Cognate Application, 14,946/14.] Protective systems. - Relates to protective systems in which a faulty section is adapted to be cut out by the fault current from the main conductor operating the cut-out devices and in which each cable or cable section comprises a main core with the addition of protective conductors in the form of strips insulated from the core and from each other and wound round the core so as to form substantially one layer. According to the invention, the protective strips b, b<1>, Fig. 1, wound round one or more cores a, are bare and are insulated from each other by means of a thin layer d of insulating-material, such as rubber tape, extending under the edge of one strip b and over the edge of the adjacent strip b'. Each of the protective conductors b, b' has one end open and the other end earthed through a relay h, Fig. 4, operating a cut-out device. Each conductor may have a battery h<1> in series with it, in which case the relays h respond to a fault between the protective conductors without there being a core fault. When a branch section is to be teed on to a main cable section, three protective conductors b are conveniently employed in the main and branch cables. In this case, two of the branch protective conductors are teed on to two of the main protective conductors, which are earthed through relays at one end, the remaining branch protective conductor being earthed through a relay at one end and teed on to the remaining main protective conductor, which is open at both ends. In such an arrangement, batteries may be included in order that the relays may respond to faults between the protective conductors. When a branch cable section is connected across two main cable sections, four protective conductors are conveniently employed in each cable. In this case, two of the conductors of each main cable are left open a.t both ends and two are earthed through relays, and each branch protective conductor is teed on to one earthed and one open main protective conductor. A joint for connecting two lengths of the.cables is shown in Fig. 5. The protective conductors b, b<1> of each length are connected by means of ooupling-elements i, j insulated from each other and arranged either as concentric sleeves as shown or as helically-wound or straight strips forming a single cylindrical layer. Three or more coupling-elements may be used according to the number of protective conductors in the cable. Such a coupling could not be ruptured without causing a current to flow through the protective conductors b. When the protective conductors are earthed through relays and batteries as shown in Fig. 4, the coupling elements i, j may be arranged so as to slip off their support k and be brought into contact with each other should any relative movement occur between the jointed sections, owing, for instance, to the subsidence of the ground in which the cable is laid. According to the Provisional Specifications, a single protective conductor earthed through relays at each end may be employed in the cable. Specification 23,449/13 is referred to.