| China's power resources and power demand presents a reverse distribution, so the construction of large-scale transmission channels seems to be imperative. Due to the large population and deficiency of land resources in China, the parallel lines on same tower technology has been widely used in the construction of transmission lines, because of its less land occupation, large transmission capacity and low construction cost. To meet the requirements of different applications, besides the double lines on same tower, there are a variety of complex parallel transmission lines in engineering practice, such as unwhole paralles lines on same tower, four parallel lines on same tower and mixed-voltage parallel lines on same tower, etc. The complex of parallel lines on same tower structure brings a lot of adverse effects to the planning and designing of the grid, operational controlling and relay protection action. On the one hand, with the complex structure of parallel lines on same tower, the calculation method of line parameters is starved for meeting the requirements of line design, power flow calculation and relay protection setting calculation. On the other hand, subject to technical constraints, it's hard for parallel lines on same tower to transpose, so if the lines arrangement is unreasonable, it's easy to cause the asymmetry of line parameters which could affect the normal operation of the grid. In addition, with the increasing of parallel lines on same tower parameters asymmetry and complex cross country faults, the associated protection performance may become worse, so there are many issues needed to be further research and discussion. This article will do the research work about parameter calculation method, phase sequence arrangement, the effect of parameter symmetry on distance protection and applicability of power directional element of complex parallel lines on same tower.The calculation of complex parallel lines on same tower parameters is the important foundation of power flow computation, short-circuit current calculation and relay protection setting calculation. Based on the "single line-earth" circuit as the foundation, starting from the basic parameter matrix of parallel lines on same tower, this paper proposes a calculation method of parallel lines on same tower which has good adaptability. On this basis, develop the parameter calculation and analysis software of parallel lines on same tower. Through comparing the calculated results with measured line parameters and PSCAD simulation parameters, validate the correctness of the software. This paper introduces the basic principle of parallel lines on same tower parameter calculation method, the basic structural and functional features of the software, and explains the processing methods of special problems in parallel lines on same tower.Due to the transposition difficulties of parallel lines on same tower, optimizing design of lines phase sequence arrangement is the most effective and economical mean to improve the parameters symmetry. This paper analyzes the effect of different tower structures and lines arrangement on line parameters symmetry, defines multiple factors measuring the line parameter unbalanced degree, which including: single-sequence component unbalanced degree and composite-sequence component unbalanced degree. In order to measure the size of imbalance objectively, assign weight to each unbalance factor with(0, 2) scale method, and then form the comprehensive evaluation. On this basis, study the optimization of line phase sequence arrangement concerning the several common tower structures for four-circuits on same tower with the calculation software and the comprehensive evaluation. This paper introduces the calculation method of the defined unbalanced degree for parallel lines on same tower, through comparing the comprehensive evaluation of different phase sequence arrangements, propose the optimal phase sequence arrangements of different tower constructions.Comparing with common lines, the complex parallel lines on same tower have more outstanding asymmetric problems limited by transposition technology which could bring adversely affect on relay protection action performance, especially the distance protection which is sensitive to line parameters. Through theoretical derivation and numerical simulation, derive the the error of parallel lines on same tower measured impedance and analyze the effect of line parameters asymmetry on distance protection. According to the error of measured impedance, put forward the improvement suggestions for distance protection.Directional element is an important part of line protections, it is widely used in distance protection, zero-sequence current protection and pilot protection. The various fault types and complex electromagnetic coupling of parallel lines on same tower put forward higher requirements to directional elements. Analyze the applicability problem when the typical directional elements which include: positive sequence break variable directional element, negative sequence directional element and zero sequence directional element are used in the complex parallel lines on same tower systematically through theoretical and simulation analysis. Summarize the main problems that might exist and provide a reference for the rational use of directional elements.Finally, summarize the full text and prospect the follow-up research direction. |
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