A new multiple high-speed air circuit breaker for mercury-arc-rectifier anode circuits and its relation to the arc-back problem

Mercury-arc power rectifiers have been used increasingly to supply power to d-c utilization systems in the United States since the early twenties. War requirements, because they have multiplied the demand for aluminum, magnesium, chlorine, zinc, and copper, all of which utilize d-c current in their reduction, have tremendously increased d-c power consumption. It is estimated that 12 1/2 per cent of the kilowatt-hours generated in 1941 were consumed in such electrochemical processes. Since the mercury-arc rectifier is now the almost universally accepted form of conversion apparatus for this purpose, the attention of many more engineers has recently been focused on it. Many advantages of the modern rectifier have led to its wide acceptance, but it is not within the scope of this paper to deal with these. One persistent factor in connection with the application of rectifiers which has claimed much attention is the phenomenon of arc-back. Various methods of attack have been employed successfully. High-speed anode switching appears to be the most satisfactory way to handle this problem. Such a solution is widely used in the aluminum industry.¹ Part I of this paper includes an analysis of the arc-back problem and various means of protection from its effects. Reasons why high-speed anode switching is an improved type of arc-back protection are set forth. Part II of this paper describes this multi-pole high-speed air circuit breaker. The requirements which the breaker must meet are discussed, and the electrical and mechanical features described. Performance of the breaker was checked in field tests. Oscillographic data are presented and prove that the performance is acceptable.