Extensive field measurements support new approach to protection of arc furnace transformers against switching transients

Recent investigations of systems involving vacuum switching have forced a reappraisal of the traditional protection methods necessitating major changes in protection philosophy. The new philosophy has been developed on industrial systems supplying are furnace transformers where the exceedingly large number of switchings makes such systems particularly sensitive. This paper discusses a new transient voltage protection system which has been developed in response to these recent investigations. In support of the development of the new protection system, transient voltage measurements have been made on 14 are furnace systems at various locations within the United States and abroad. This paper also documents the instrumentation used to monitor transients on these systems and describes its application. Typical oscillographic records are presented as indications of the performance of the system with and without the new transient voltage protection system.