Patent GB-371471-A (GB)
Title: Improvements in high voltage systems
IPC: H01B17/46
Filed: 1931-01-28
Abstract: 371,471. Protective arrangements. TRIGGS, W. W., 57, Lincoln's Inn Fields, London.-(Ohio Brass Co.; Mansfield, Ohio, U.S.A.) Jan. 28, 1931, No. 2756. [Class 38 iv]. In order to avoid flashover or arcing to ground in a high-tension transmission line, means are provided to reduce the difference in voltage between the conductors and the supports under operating conditions so that an arc will not form. In the construction of Fig. 1, a supporting tower is formed with an upper metallic section 10 insulated by a central wood section 16 from a lower metallic section 17. The section 16 has conducting horns 18 which screen the wood, a shunting resistance 19 and a shunting condenser 20. Arms 11 on the sections 10 carry insulators 12 on which are mounted conductors 13. A sectionalized protective wire 14 is mounted on the peak of the section 10. In operation the release of a bound charge such as a stroke of lightning in the vicinity of the line will raise the voltage both of the line 13 and the metal section 10. Should the electrostatic capacity between the section 10 and the ground be large, the wire 14 will tend to raise the potential of the section 10 to that of the condenser 13. Where very heavy conductors 13 are used, electrostatic condensers may be provided on the section 16 by fitting plates or wire screens 23 at the sides of the section 16, or by mounting conductors 24, 25 to extend from tower to tower. The conductor 24 may be sectionalized, and the conductors 25 may be used as a guy across a tower. The screening horns 18 may be increased in length so as to increase the capacity of the section 16, or overlapped cylindrical conducting members may be connected to the opposite sides of the section 16. The upper screening horn 18 may be in the form of a weather shield. The resistance 19 mav be a high resistance wire immersed in electrolyte or in an insulating medium or may be an insulating tube filled with water to which alcohol has been added to prevent freezing. Where there is no danger of freezing, water without alcohol may be used, the resistance being regulated by the addition of sodium or calcium chloride. Where a high resistance is required, e.g. to deal with shorting of the insulator strings by birds, a small tube filled with water and alcohol or glycerine may be used as the resistance. Figs. 6 and 7 show means for directing the arc so that it will not strike into the wood support. A wood pole 30 carries wood cross-arms 31, 32. An earth wire 33 on the arm 32 is grounded through a lead 34. Conductors are carried by insulators 35, 36, 37, and the cross-arms are provided with high resistance leakage paths 38 to prevent charring of the wood cross-arms. Arcing horns 39 on the arms 31, 32 are fitted with sleeves 40 of insulating material to direct the discharge from one horn to the other and to prevent the arc striking into the wood. In Fig. 8 a strain insulator 41 is fitted with arcing horns 42, 43, the ends of which are screened by insulator sleeves 44, or an arc insulating member 45 mounted on an insulating sleeve 46 may be supported between the ends of the horns as shown. Fig. 9 shows a suspension string 47 which has insulating members 44 attached to arcing horns 48. Flux control members 49 are mounted at intermediate points in the string. The member 49 may be formed with an electrode member 55 in the centre of the tube or with electrodes 56, 57 at one or both ends. Fig. 10 shows an insulator string with grading shields 50 preferably equipped with projecting electrodes 51 to initiate discharge. The electrodes 51 are provided with insulating coverings 52 so that a discharge initiated between the electrodes 51 will pass through the centre of the members 52. In order that the stream of gases from adjacent open ends of control members may be out of alignment so tending to break up an arc, the construction of Fig. 11 may be used. The control members 44 are inclined relatively to the vertical plane of the conductor, and a central member 58 is curved so that the opening in its central passage will be at an angle to the line of the opening of adjacent members 44. The upper end of the opening in the member 58 and the lower end of the opening in the member 44 are directed to the same side of the plane of the conductor while the lower end in the opening in the member 58 and the upper end of the opening in the member 44 are directed to opposite sides. The control member may be provided with an enlarged recess in the bore in which hot gases may expand to produce a blast through the narrower throat, thereby tending to clear the arc. In other constructions of control members, the tubes may be curved outwardly at the ends to provide an overhanging lip which directs the arc outwardly away from the insulator string. A perforation for draining the tube and allowing the escape of gases, may be provided. An explosive cartridge may be inserted in the control tube to ignite and blow out the arc. Fig. 17 shows a discharge device used as a voltage limiting and arc clearing device or lightning arrester. A lead 66 attached to a high-voltage conductor ends in an arcing horn 67 supported on an insulator 68 which may be rotatable so as to change the width of the gap between the horn 67 and a complementary horn 69 carried on an insulator 70. In operation, excess voltage will cause discharge between the horns 67, 69, and, if there is sufficient capacity between the horns 67, 69, a discharge may take place in a tube 71 carried on the horn 69. Capacities 74, 75 may be mounted on the tube 71 so as to initiate discharge between terminal members 72, 73 in the tube 71. In a string of insulators 47 shown in Fig. 20, the arcing horns carry insulating balls 86, each of which may have an arc-directing spur 87. Control members 88 are mounted on pins 89 between the insulator ends. Each member 88 comprises a conducting core 90 enclosed in insulation which is thicker on the inside of the core than on the outside. Fig. 21 shows an arc extinguisher 91 mounted on the horn 48 of Fig. 20. The extinguisher 91 is formed with an expansion chamber 92 and a long narrow discharge opening 93 for creating a rapidly moving blast for extinguishing the arc. In Fig. 22, the horn 48 is formed with a tubular insulating member 94 having an expansion chamber 95 filled with liquid and held in place by a cork 96. On formation of an arc in the chamber 95, the liquid will vaporize, blow out the cork 96, the escaping vapour tending to extinguish the arc.