Abstract: Current Transformer is mainly used to convert high primary current in the power system to the level which can be handled by electromechanical or microprocessor based Relays and metering devices. The current transformer should be chosen correctly for a particular application considering the burden connected to the secondary, primary fault current and X/R ratio of the system. Over dimensioned or under dimensioned CT can cause mal-operation of relays. In this study, we have developed a windows application to check whether CT selected for particular application having certain burden is adequate or not. If in case the selected CT is not adequate then the application will suggest new CT design to avoid saturation. Proper Selection of CT is required for good protection scheme requirement.

Keywords: Current Transformer saturation, X/R ratio, Burden, AC and DC saturation.