A Novel Distance Relaying Algorithm Of Parallel Transmission Lines For Single-Phase Ground Fault

Same tower paralleltransmission linesare widely used in the extra or ultra high voltage engineering. Currently, the distance protection algorithmsin the actual operation of parallel transmission linesare seriously influenced by zero-sequence mutual inductance, which hardly meet the needs of power system operation. It is of great significance in theoretical and practical field to research new protection algorithms and improve the performance of distance protection of parallel transmission lines.In this paper, a double-ended power supply system with parallel transmission lines is researched. The zero sequence network of the system when single-phase ground fault happed is established.Results proved that zero sequence current ratio K of parallel transmission lines is closely related with the system operation and fault point location. K varies with fault distance D as a monotonically increasing concave curve.The smaller zero sequence impedance ofthe system, the greater the curvature of the curve. When fault distance D changes, K is anapproximate real number. When the fault distance is shorter than 85% of the line, K is small and changes slightly as fault distance D changes; when the fault distance exceeds 85%of the line, K changes greatly. When faultoccurred atthe end of the line, K is 1.A new algorithm of first-zone distance relayingfor single phase to ground faults on parallel lines is presented.The main advantage of the new algorithm over thedistance relaying algorithm with cross-connected zero-sequence current is that only local data of protected line is required.The largest K whensingle phase groundedat 85% of protected line under different system operation states is used as Kset.The zero-sequence current of adjacent lines is equal to theproduct of Kset and the zero-sequence current line of protected line. A new algorithm of first-zone distance relayingfor single phase to ground faults on parallel lines is presented which only use single-ended electrical quantities of protected line. The simulation shows that when metallic ground faults occur, the new algorithm is reliable in the protection zone and will not tripwhen faults occur beyondthe protection zone. Traditional algorithm without cross-connection of zero-sequence current from adjacent line may under-reach. When the ground resistance is 15Ω, the new algorithm still has good reliability and accuracy, while two traditional algorithms may mistakenly trip in external faults eventhe export of next line fault.Finally, good applicability of new algorithm is proved through detailed simulation.When faults occur at adjacent line, the new algorithm is reliable, but the traditional algorithm will happen false tripping. The problemthat the in-close faults in protected line may lead false tripping of adjacent line where traditional algorithms are used are solved by thenew algorithm. When system operation states changes, protectionscope of first-zone distance protection of new algorithmis enlarged, but when the end of the line is grounded, malfunction doesn’t happen. The protection scope of traditional algorithms without compensationis shortened. When protected line is groundedthrough fault resistance, first-zone distance protection of new algorithmbehaveswell, while traditional algorithms in the external fault will mistakenly trip. The new algorithm is not affected by the load and shunt capacitance of lines.