Load Pickup by a Group of Ignitron Rectifiers

One of the advantages of the application of mercury-arc rectifiers to large electrochemical loads, such as aluminum cell lines, is that, if all the rectifiers are excited simultaneously, they will pick up and share the load together. This eliminates need for large d-c cell-line circuit breakers. The conventional method of starting simultaneously several ignitron mercury-arc rectifiers, widely used in large electrochemical plants, has been to energize the individual ignitor firing circuits from a master starting switch. Differences in closing time of the control contactors were reflected in proportional irregularity of load pickup between the ignitron rectifiers. Recent tests, described in this paper, show that the grids usually employed in the ignitrons for anode shielding can be used as an alternative method to energize cell lines. If all the grids are biased negatively, they will prevent current flowing from the rectifiers while the firing circuits are all energized and the switches closed in the power circuits. Then, by operating one switch or a plurality of accurately timed switches, all grids can be made positive at the same instant with the result that all the rectifiers pick up load at the same instant and share it equally.