Patent GB-451963-A (GB)
Title: Improvements in and relating to electric vacuum switches
IPC: H01H33/66
Filed: 1935-02-22
Abstract: 451,963. Distortable-container switches. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London. Feb. 22, 1935, No. 5732. Convention date, Feb. 23, 1934. [Class 38 (v)] Magnetic blow-outs.-A H.T. vacuum switch comprises an evacuated casing containing relatively movable contacts adapted to be separated for effecting interruption of the circuit and for entirely or substantially counteracting the tendency of the cathode spot formed on the contacts during separation thereof to generate metallic vapour in a quantity which would result in hindering the interruption of the circuit, the switch has means arranged to produce a magnetic fixed adjacent the contacts to effect a rapid and predetermined shifting of the cathode spot on the contact surfaces. In Fig. 1, the polepieces 23 are located one on either side of a highly-evacuated casing 1, preferably of non-magnetic, high-resistance metal, and the coil 22 is connected through terminal 25 and lead 24 to the movable contact 3, which is operable by means of an arm 4 sealed to a flexible metal diaphragm 7 and carried in a yoke 9 pivoted at 10 to the case 1. Contact 2 is mounted on a stud 11 which is insulatingly mounted by collars 12, 13 and flanges 14, 15 and is sealed by means of a sleeve 16 and flexible metal diaphragms 17, 18, substantially as described in Specification 370,443. The magnetic field on opening circuit causes a rapid shifting of the electron discharge and cathode spot to the contact tips. In Fig. 3, all or the part 42 of casing 30 is of non-magnetic, highresistance metal, to a low-resistance part of which are secured an annular contact 32, with a gap 32<1> to minimize eddy-currents, and the inner turn of the spiral coil 37, the outer turn of which forms a terminal 38. A movable contact 33 with three wedge-shaped contact parts, as 33<1>, bridges contact 32 and a fixed disc-like contact 31 in the closed position. Split polepieces 43 are disposed adjacent the ends of the limbs of U-shaped magnetic plates 39, which abut on the part 42 of the casing and are maintained in radial arrangement by means of insulating spacers and a band 41. When the member 33 is lowered, the currents in 31 induced by the main field produces an opposing field, the resulting field traversing the gap between 31, 32 in a definite direction causing rotation of the electron stream and cathode spot about the contact surfaces. In Fig. 5 contacts 46, 47 are mounted on helical coils 46<1>, 47<1> which produce opposing fields, the resultant of which is a radial field in the annular gap set up when 47 is lowered to open circuit. Automatic circuit - breakers.-The repulsive force on the contact 47 due to the opposing fields of 46<1>, 47<1> is utilized to trip the switch on overload, a slight counter-clockwise rotation of 50 about its pivot 9 causing the arm 50<1> to impinge on 57<1> to break the toggle 57 and allow spring 61 to open the switch. The arm 50 is held closed by spring 56 which is held compressed by the overset toggle 57 and latch 59 acting on the end of lever 58. A trip solenoid 60 actuated automatically or by press-button, is arranged to move the latch 59. Toggle 57 is reset by releasing latch 59, whereupon the switch is reclosed by anticlockwise rotation of 58 by the closing solenoid 55.