A Novel Current-Based Differential CT Supervision Function

This paper reviews some traditional supervision functions and presents a new advanced universal current based current transformer supervision (CTS) function, which has been developed for differential protection applications. Traditional CT supervision methods for instance rely on a voltage measurement in order to compare sequence components, and in the case of transformer differential protection may not be feasible if no voltage transformer is available, or the user preference is not to wire-in a VT. A novel technique is shown that evaluates the ratios of sequence components at CT ends for differential current transformer supervision. This technique is suitable for line, transformer and busbar differential protection schemes with no additional requirements placed on CT or VT inputs compared to existing relay hardware.