GB515839A - Improvements in and relating to electric control systems - Google Patents

Abstract

515,839. Switching control of electricity supply. BRITISH THOMSON - HOUSTON CO., Ltd. June 10, 1938, No. 17303. Convention date, June 10, 1937. [Class 38 (iv)] An electric control system adapted more particularly for electric welding comprises a transformer 12 with a magnetic shunt 14 mounted adjustably adjacent thereto, the secondary winding 11 of the transformer being connected in the welding circuit, and the primary 10 being in series with an impedance 15 across the line 16, so that when the secondary circuit is closed by contacting the electrode 18 with the work 17 the resultant rise in voltage across the impedance 15 operates a relay 26 which closes pairs of contacts 23 and 33, thereby energizing an electromagnetic switch 19 with contacts 20 which short-circuit the impedance 15. Simultaneously, the voltage generated in a winding 29<1> upon the magnetic shunt 14 operates a relay 25 which closes pairs of contacts 22, 32 in parallel with the pairs 23, 33 whereby the energization of the winding 21 of the 'switch 19 is maintained after the short circuiting of relay 26 by contacts 20. The closure of contacts 33 of relay 26, and the subsequent closure of contacts 32 of relay 25, complete the circuit of a rectifier 31 in series with the winding 30 of a relay 27, this relay being of the time-delay type controlled by means such as a dashpot 34 so that its contacts 24 are closed instantaneously but open with a predetermined time interval. If, during welding, the arc is momentarily interrupted, the contacts 22 of relay 25 may be opened without de-energizing the winding of switch 19, which is maintained through the contacts 24 of relay 27.