GB808328A - Improvements in or relating to the manufacture of oil-filled electric cables - Google Patents

Abstract

808,328. Making cables. BRITISH INSULATED CALLENDER'S CABLES Ltd. Oct. 30, 1957 [Oct. 31, 1956], No. 33303/56. Class 36. An aluminium-sheathed oil-filled cable is made by drying and evacuating a cable core and the interior of a length of aluminium tubing, drawing the core into the tubing and reducing the cross-section of the tubing while maintaining the vacuum and then admitting oil to the interior of the tubing. The cable core is wound on a drum in a drying vessel which has an outlet for evacuation and a vertical slot closed by a tapered hood 23 (Fig. 8) closed by wall 27 having an outlet 26. An insulated towline 28 is connected to each end of the core so that the core may be heated by passing current therethrough. The free end of each of the towline conductors 30 is held in an hydraulicallyoperated clamp, one clamp 31 being mounted near the outlet 26 and the other (not shown) close to the drum. An extension 47 on wall 27 has a tapered bore fitted with a tapered plug 49 to make a vacuum-tight seal, the small end of the plug being attached to the free end of towline conductor 30 and the large end carrying an eyebolt 64. Extension 47 is joined to an hydraulically-operated valve 54 having slide 55 which may be closed to form a vacuum-tight seal across passage 53. The outer end of the passage 53 carries a pipe coupling 63 for making a vacuum-tight connection with aluminium tube 51. A track 66 (Fig. 10) extends away from the drying vessel and carries a die 69 and a vacuum-tight winch housing 73 for a tow-line winch 74 and its hydraulic motor 75. A towline 76 is led from the housing through an hydraulically-operated valve 77, which is similar to valve 54 and carries a pipe coupling 78 for securing the leading end of tube 51. The housing 73 may be drawn along the track by a winch (not shown) having a hawser which is secured to eye-bolt 88. In operation the cable core is vacuum-dried with the valve 54 closed. Die 69 and housing 73 are positioned close to the drying vessel, with valve 77 open. Pipe 51 is drawn from a drum and a messenger attached to the end of tow-line 76 inserted in the pipe, the end of which is passed through die 69 and secured to coupling 78. Housing 73 is drawn away from the drying vessel to draw out the required length of pipe, the die 69 being carried along by the pipe. The messenger is blown through the pipe and removed from the end of tow-line 76, which is secured to eye-bolt 64, valve 54 being opened and clamps 31 released. The trailing end of tube 51 is drawn back and secured to coupling 63. Pipe 51 is evacuated through housing 73 and winch 74 operated to pull plug 48 from its seating and the cable core through the pipe until its leading end is nar diee 69. The winch 74 is stopped and a die 69 is drawn towards the drying vessel by a further winch (not shown). The chamber 73 is drawn forwards to accommodate the resulting increase in length of the pipe, and the trailing end of the core is thus drawn into the pipe from the drying vessel. When the whole of the core is in the reduced pipe 51 the valves 54 and 77 are closed, severing the insulated tow-lines 28 and isolating the interior of the pipe in a vacuum-tight manner. Impregnating fluid is then supplied through port 72 on valve 54 and allowed to escape through port 72 on valve 77 until impregnation is complete. The cable is disconnected from the valves and the ends plugged. In an alternative arrangement the plug 48 is omitted and the tow-line conductor 30 and the tow-line 76 are secured to connectors. After drying the core, dry air or gas is admitted to the drying vessel, the valve 54 is opened and the connectors joined. The pipe 51, previously filled with dry air or gas, is secured to coupling 63 and the vacuum re-applied before the process continues as described above.