The continental development of single-anode mercury-arc-rectifier valves of high power

Mercury-arc rectifiers for the conversion of power from alternating to direct current became familiar just after the First World War. Favourable results in operation led to rapidly increased numbers of mercury-arc-rectifier plants in service, especially when a.c. power distribution replaced individual local d.c. generating systems. By 1935 several well-known types of multi-anode mercury-arc rectifiers were being made by Continental manufacturers, each equipment consisting, in general, of a transformer and one, or several, multianode valves with appropriate auxiliary, controls and switchgear. This paper deals only with the valves commonly called rectifiers. About this time a critical point occurred in Continental mercury-arcrectifier technique in so far as definite limits for the multi-anode system, then exclusively used, appeared to have been reached. Attention was directed to the possibilities of building rectifiers using excited single anodes, as distinct from the American development of the ignitron, in which the anodes were similarly separated in individual selfcontained units. A brief review of the development and characteristics of glass-bulb and steel-tank multi-anode rectifiers is followed by a survey of the main theoretical and practical considerations affecting rectifier design, from which some general design rules are evolved. A description is given of experimental single-anode rectifiers which were designed and built in accordance with these principles, and the further development of the single-anode rectifier for low and high voltages is also outlined. A comparison is made of the characteristics of this type of rectifier and typical multi-anode steel-tank rectifiers. The problems of ionization and plasma-current relations are treated theoretically in appendices.