GB475459A - Improvements in and relating to devices for protecting rectifiers containing an ionised gas - Google Patents

Abstract

475,459. Converting. SOC. ANON. HEWITTIC, and DEMONTVIGNIER, M. Jan. 15, 1937, No. 1222. Convention date, Jan. 25, 1936. [Class 38 (ii)] In a mercury-vapour rectifier installation, grids associated with the main anodes 5 are normally maintained positive by a D.C. source 10 opposed to the voltage drop across a resistance 12 which is normally maintained smaller than the voltage of the source 10 by reason of a series resistance 11 associated with the negative biassing source 9. Under fault conditions producing excess current on the A.C. side 1, an auxiliary anode 16 in the rectifier is rendered conductive, thus short-circuiting the resistance 11 and thereby increasing the drop across the resistance 12 to a value which exceeds the voltage of the source 10 and thus renders the main grids negative to effect suppression of the discharge. Control of the auxiliary anode 16 is effected by a grid energized by the difference between a D.C. voltage proportional to the load current derived from current transformers 2 through rectifiers 13 and the voltage drop across a part of the resistance 12. In a modification, Fig. 2 (not shown), the rectifier to be protected has its grids continuously subjected to a negative bias potential upon which positive ignition impulses of adjustable phase are normally superposed. These impulses are generated under the control of an auxiliary rectifier to the grids of which blocking potentials are applied under fault conditions producing excess current in the main rectifier by means of an auxiliary anode and resistance arrangement similar to that described with reference to Fig. 1.