Importance

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Abstract

A high voltage d.c. power transmission system utilizes a metallic return conductor for carrying return current between converters at opposite ends of the system. The return conductor is connected to earth ground at one end of the system and is otherwise insulated from earth ground so that its opposite end is floating with respect to d.c. The return conductor has no capacitor connected from earth ground thereto of a size capable of limiting the voltage thereon. But connected between said opposite end of the return conductor and earth ground is a valve-type surge arrestor having a primarily zinc-oxide valve element and no gap in series therewith. This surge arrestor has a protective level that is reached by the overvoltages produced by the normal operating transients of the system, such as those produced by system start-up and commutation failures.

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First Claim