GB512672A - Improvements in or relating to alternating current switching devices - Google Patents

Abstract

512,672. Supply systems for consumption apparatus; rectifying alternating current. SIEMENS-SCHUCKERTWERKE AKT.-GES. March 3, 1938, No. 6731. Convention date, March 3, 1937. Addition to 490,509, [Group XXXVII]. [Class 38 (iv)] An alternating current switching arrangement as set forth in the parent Specification comprising a switching choke 13, which produces flattening of the current wave form in the neighbourhood of zero current passage, connected in series with switch contacts 15 which are shunted by an impedance arrangement 16, 17 is provided with a control arrangement which automatically effects switching on at a predetermined voltage condition following closure of switch 10a and automatically effects switching off during the period of zero current passage following closure of a switch 10b. On closure of switch 10a the transformer 4, the core of which is only unsaturated in the neighbourhood of zero current passage and the current in which lags nearly 90 degrees behind the voltage, charges the condenser 7 through the rectifier 8 and removes the blocking voltage from the grid of valve 2 at the instant when the voltage of mains 11 reaches its maximum value. The valve 2 conducts and coil 3 closes the switch 15 condenser 9 being charged. The condenser 7 is arranged to discharge through a variable resistance 5 and switch 10a is opened to prevent further charge of 7 during succeeding alternate half cycles. On closure of switch 10b a current is passed through the resistance 26 at the instant of the succeeding zero current passage from transformer 14 which is desaturated only in the neighbourhood of the zero current passage. The condenser 9 then discharges through the valve 12 and energises coil 3 to open the switch 15. The switching arrangement may be arranged to control energisation of a welding transformer 13 as shown and the switch 15 may be operated by compressed air controlled by valves operated by the means described. The switches 10a, 10b may be arranged on an adjustable rotating contact carrier so that an adjustable regular switching sequence is produced. The invention is stated to be suitable for controlling polyphase systems the switching contacts being preferably so driven that a direct current is obtained. Specifications 492,369, 492,807, 492,887, 493,436 and 506,015 are referred to.