CT polarity testing verifies the correct directional relationship between the primary and secondary windings of a current transformer (CT). In substations, engineers rely on accurate polarity to ensure protection relays, metering systems, and differential schemes operate correctly. They compare current from CTs with voltage from PTs to determine the fault direction. Ensure protection systems operate correctly. Abstract: The issues concerning testing and verification of the correctness of differential and polarizing circuits are described and discussed in this guide.