Analysis of the operation characteristics of zero sequence current differential protection for non-transposition lines on the same tower

With the rapid development of the economy, Non-transposition Lines on the Same Tower (NTLST) are widely used in power systems. The significant asymmetry in electrical parameters impacts the sensitivity and accuracy of zero sequence current differential protection (ZSCDT). An electromagnetic transient model of the NTLST is built to simulate the characteristics of zero sequence current in NTLST under different operation modes in this paper. The parameters of the NTLST, such as line length, power flow magnitude, and fault location, which affect the operation characteristic of ZSCDT are studied. The adaptability of ZSCDT under different operating conditions, such as normal operation and out-of-zone short circuits, inner cross-line faults within the same phase zone, cross-line faults within non-identical phase zones, and single-line faults, are simulated and analyzed. When faults out of NTLST occur, no matter what type it is, the ZSCDT will not maloperate. When cross-line faults of non-identical phase zones in NTLST occur, the ZSCDT will maloperate. The research results not only improve the performance of ZSCDT for non-transposition lines on the same tower, but also provide theoretical guidance for the design, construction, and operation of power grid engineering.