Operation Characteristic of Inter-phase Distance Protection When Cross-line Faults Happen on the Common-terminal Lines

Lines with common-terminal is an economic and practical erection form in the multi-circuit transmission system, which also presents extra challenges to the protection. The feature of cross-line fault on common-terminal lines and its impact on the protection principle are discussed in this paper. Theoretical analysis shows that sound phase can also exhibit fault feature, under the effect of fault phase in the neighboring line. Furthermore, combined with inter-phase measured impedance (IPMI) expression derived in this paper, the operation characteristic of different distance relays are discussed by their setting range. For the loop only has one fault phase, the risk of maloperation is extremely high when fault is nearing the protection installation. The accuracy of theoretical analysis is verified by the validation tests in PSCAD.