Misoperations of line distance protection due to CT connection errors

These two case studies are about distance relay tripping in Forward Zones during reverse faults due to CT polarity reversal. They teach us the importance of having proper commissioning checks and checking the normal load current readings of various bays during annual relay testing and maintenance programs to understand existing CT/PT polarity and wiring issues. It also highlights the importance of analysing DR files of all started elements at various substations during tripping at other substations to find out hidden problems.