Excitation circuits for ignitron rectifiers

THE development of the ignitron type of mercury arc rectifier, with its outstanding advantage in efficiency, introduced the need of a new type of excitation circuit. For the theory of how the arc is initiated, the reader is referred to the previous papers on ignitrons.^1,2 Associated with each anode of an ignitron rectifier is an ignitor for initiating the arc. Each ignitor requires a positive impulse of current once each cycle to start the arc at the beginning of the conducting period of the main anode. In order to accomplish control of the output voltage of the rectifier, it must be possible to adjust the phase position of these impulses with respect to the supply voltage, either manually or by automatic provisions. Although the instantaneous current and power of the impulses are quite high, the impulse duration may be such that the average power is low and does not seriously affect the efficiency of rectifiers with the ratings usually encountered. If an excitation system such as “main anode” is used with which only enough energy is applied to the ignitor each cycle to ignite the arc, the average power is very small. However, with separate excitation systems, every impulse must have the same energy and this must be adequate to ignite the arc under the most adverse conditions encountered.