Current- and potential-transformer standardization

This report has been written to summarize the work of the AIEE current transformer subcommittee and to discuss the considerations which led to the adoption of the material in the revision of section 4, “Instrument Transformers,” of the Proposed American Standard for Transformers, C-57. Special attention is given to the principles underlying the establishment of the over-current requirements of current transformers for relaying service and the revision of the method of specifying the accuracy of instrument transformers for metering service. Mention is also made of the reasons for making other changes, such as in the preferred primary current ratings, potential-transformer ratios, and so forth.