The results of an IEEE working group's study of the gapped core current transformer (ct) are presented. The characteristics and performance of ct having small gaps are discussed. The effect of remanent flux in ct cores on ct performance, and of small gaps to control remanence for improved transient performance of ct are also discussed. Advantages and disadvantages of gapped core ct are enumerated. Proposed performance requirements for gapped core ct are presented and a method of specifying gapped core ct to produce the required performance for protective relaying application of such ct is proposed. A short description of terms are included for clarity of the discussion. © 1990 IEEE