Transformer and Bus Backup Protection Based on Longitudinal Comparison Principle

A new transformer backup protection based on longitudinal comparison principle (LCP) is introduced in this paper. The fault can be located by comparing action of measurement elements on all sides of transformer simultaneously. If the transformer internal faults occur, backup protection trips the breakers of all sides with a short time delay to avoid nuisance tripping caused by inrush current. If an external fault occurs, the backup protection can determine the fault side and trip the corresponding breaker after a predetermined time coordinated with downstream relays. The coordination of operation time and reach among overcurrent relays on different side is not needed. The backup protection can provide good protection performance for transformer and adjacent buses. It can shorten the operation time and improve selectivity and sensitivity