Low-current-secondary current transformers

APPLICATION REQUIREMENTS for current transformers sometimes indicate the use of secondary currents lower than the generally accepted standard 5-ampere rating. Very little published information is available on this subject, other than a description of a few specific installations where such transformers have been applied. The natural question arises as to the advantages and disadvantages resulting from the use of current transformers with secondary ratings below five amperes, and under what circumstances their use should be considered. Because many of the applications of low-current secondaries involved relay protection, the AIEE relay subcommittee appointed a working group in October 1943 to study the problem, and from that study, gives recommended practice for their use.