A 400-Ampere Sealed Ignitron

As rectifier capacity is increased, it becomes desirable to use larger capacity rectifying elements. The choice of rectifying element size requires careful consideration in order to provide a complete range with a minimum number of units. The sizes of industrial ignitron tubes for welding control and for rectifier service have been chosen on a preferred number scale providing a proportionate increase at each increment. The development of a 400-ampere ignitron for rectifier service was undertaken to provide the next larger size tube in the series. Development work on the 400-ampere ignitron disclosed that design problems become more complex as the physical size of the tube is increased. The ability of a tube to rectify a given current with a minimum number of arc-backs is affected by circuit duty and by control of ionization, particularly at the end of the current commutating period. None of the factors involved have indicated an upper limit in size, but rather a need for a more exact understanding of the phenomena involved.