Section 6 Differential protection6.1 Transformer differential protection T2WPDIF andT3WPDIF IP14639-1 v36.1.1 IdentificationM15074-1 v5Function description IEC 61850identificationIEC 60617identificationANSI/IEEE C37.2device numberTransformer differential protection, two-windingT2WPDIF3Id/ISYMBOL-BB V1 EN-US87TTransformer differential protection,three-windingT3WPDIF3Id/ISYMBOL-BB V1 EN-US87T6.1.2 Application M16722-3 v9The transformer differential protection is a unit protection. It serves as the mainprotection of transformers in case of winding failure. The protective zone of adifferential protection includes the transformer itself, the bus-work or cablesbetween the current transformers and the power transformer. When bushing currenttransformers are used for the differential IED, the protective zone does not includethe bus-work or cables between the circuit breaker and the power transformer.In some substations there is a current differential protection relay for the busbar.Such a busbar protection will include the bus-work or cables between the circuitbreaker and the power transformer. Internal electrical faults are very serious andwill cause immediate damage. Short circuits and earth faults in windings andterminals will normally be detected by the differential protection. Interturn faultsare flashovers between conductors within the same physical winding. It is possibleto detect interturn faults if sufficient number of turns are short-circuited. Interturnfaults are the most difficult transformer winding fault to detect with electricalprotections. A small interturn fault including just a few turns will result in anundetectable amount of current until it develops into an earth or phase fault. Forthis reason it is important that the differential protection has a high level ofsensitivity and that it is possible to use a sensitive setting without causingunwanted operations during external faults.1MRK 504 169-UEN A Section 6Differential protectionTransformer protection RET650 2.2 IEC 75Application manual
