Patent GB-349722-A (GB)
Abstract: 349,722. Cables and cable joints. SOC. ITALIANA PIRELLI, 21, Via Fabio Filzi, Milan, Italy.-(Assignees of Puritz, M. ; 43, Albemarle Street, Piccadilly, London.) April 14, 1930, No. 11795. Convention date, April 25, 1929. [Classes 36 and 38 (i).] In order to replace a damaged cable length without draining the oil from a cable, means are provided to maintain the undamaged lengths continuously under oil pressure while the cable is repaired. In the high-tension 3-phase underground cable system illustrated in Fig. 1, feeding reservoirs 1<1>, 1<11>, 1<111> of the type described in Specifications 255,034, 267,059, [both in Class 36, Electricity, Conducting &c.], are connected to the cable ends by pipes. Joints 21, 211, 2<111>, 31, 311, 3<111> .. 6<1>, 6<11>, 6<111> electrically connect the cable lengths and allow passage of the oil. The joint casings are formed with pig-tails which permit communication between the casing interior and external devices. The cable line is divided into sections, each composed of one or more lengths of cable, adjacent sections being separated by stop joints. Stop joints 7<1>, 7<11>, 7<111> limit the first section of the line, and may be of the construction described in Specifications 255,033 and 268,271, [both in Class 38 (i), Electric couplings &c.]. Pig-tails on each side of the stop-joints are adapted to receive the suction pipes of vacuum pumps used in evacuating the cable, and, later, to receive the pipes for admitting degasified oil to the cable. The stop-joints of the different phases are placed close to each other so that oil from one phase may be conveyed through the pig-tails to the other phases. The pig-tails 11<1>, 11<11>, 11<111> of the stop joints 7<1>, 7<11>, 7<111> are shown interconnected by pipes. Pressure reservoirs 8<1>, 8<11>, 8<111> of the type described in Specification 267,059, [Class 36, Electricity, Conducting &c.], are also installed and connected as shown. To compensate for leakage, a closed reservoir 9 is connected to the feed reservoir 1<1>. In the case of a fault in the first section of the cable between the joints 3<1>, 4<1> an auxiliary reservoir is placed on the joint 4<1>, or connection is made between the pig-tails 11<1>, 11<11>, 111<111>, and since oil will be supplied from the other end of the section by the reservoirs 1<1>, 1<11>, 1<111>, the damaged length may be cut out, the cut cable ends being closed by caps. The joint casing at each end of the gap made by cutting out the length is opened and the joint insulation is cut transversely on the line 14-14 shown in Fig. 2, leaving exposed the centre of the connector 15. A transverse bore 16 is then drilled in the connector 15, and is closed by a plug, Fig. 4, which has an axial passage 18 and a radial part 17. The plug is inserted so that the part 17 opens towards the new length of cable. The conductor of the damaged length is then disconnected by heating the exposed connector part and the new length is substituted. The joints 3<1>, 4<1> are connected to vacuum pumps 19, 20 which exhaust the new length, a reservoir 21 being then applied to the joint 3<1> to fill the new length with oil. When the new length is fully filled with oil, the casing of the joint 4<1> is opened and the plug replaced by a plug with a transverse bore. New insulation is applied to the joints which are enclosed in metal casings soldered to the cable sheath. Vacuum is then formed in the casings which are filled with oil and closed.