Abstract :
WE HAVE BEEN hearing much about the “sonic wall.” Electrical science, too, has had its barriers, not so spectacular perhaps, but none the less real. About 1920 it became evident that if lightning protection were to keep pace with the rapidly expanding power systems, some new principle would have to be employed. The limit to the abilities of the electrolytic arrester about had been reached. Then, as power systems continued to grow, the ability of circuit breakers to interrupt the enormous potential short circuits seemed faced with a stalemate. Again, as engineers in the early ´30´s were struggling to convert the attractive mercury-arc-rectifier principle into economical, reliable, heavy-power devices, their efforts appeared hopelessly blocked by the phenomenon of arc-backs that had defied explanation.
