Design Considerations in the Application of Current Transformers for Protective Relaying Purposes

A procedure is presented which enables one to design a current transformer (CT) to meet arbitrary specifications on the required number of cycles of accurate secondary current following a system short circuit which results in a fully offset short circuit current waveform. The procedure enables one to relate the resulting current transformer design to its physical characteristics and to its accuracy classification. The procedure also enables one to account for an arbitrary amount of remanent flux in the current transformer resulting from previous short circuit currents.