Section 7 Differential protection7.1 Transformer differential protection T2WPDIF andT3WPDIF7.1.1 IdentificationFunction description IEC 61850identificationIEC 60617identificationANSI/IEEE C37.2device numberTransformer differential protection, two-windingT2WPDIF3Id/ISYMBOL-BB V1 EN87TTransformer differential protection,three-windingT3WPDIF3Id/ISYMBOL-BB V1 EN87T7.1.2 ApplicationThe 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 cables betweenthe current transformers and the power transformer. When bushing currenttransformers are used for the differential IED, the protective zone does not include thebus-work or cables between the circuit breaker and the power transformer.In some substations there is a current differential protection relay for the busbar. Sucha busbar protection will include the bus-work or cables between the circuit breaker andthe power transformer. Internal electrical faults are very serious and will causeimmediate damage. Short circuits and earth faults in windings and terminals willnormally be detected by the differential protection. Interturn faults are flashoversbetween conductors within the same physical winding. It is possible to detect interturnfaults if sufficient number of turns are short-circuited. Interturn faults are the mostdifficult transformer winding fault to detect with electrical protections. A smallinterturn fault including just a few turns will result in an undetectable amount ofcurrent until it develops into an earth or phase fault. For this reason it is important thatthe differential protection has a high level of sensitivity and that it is possible to use asensitive setting without causing unwanted operations during external faults.1MRK 502 071-UEN - Section 7Differential protectionGenerator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 127Application manual
