| Multi-circuit transmission lines on the same tower have been widely applied in the power system of our state, due to the advantages of low cost of investment, low occupancy of land and narrow transmission corridor. To meet the demand of different transmission corridors and power grid construction, except the common complete-journey double circuit lines on the same tower, a variety of complex line structures on the same tower, such as incomplete-journey and mixed-voltage lines on the same tower have also derived. Due to the multiple structure forms, variety fault types and complex fault features, it brings many unfavorable influences on the operating characteristic of relay protection. Distance protection is one of the most widely applied protections in transmission lines, but it's seriously affected by the complex features of multi-circuit lines on the same tower. Hitherto, many research works have been carried out on the protection for lines on the same tower, but it's mainly limited for the structure of complete-journey double circuit lines, the research on other complex structures is less relatively. Therefore, further research on distance protection for complex multi-circuit lines on the same tower is much significant to improve protection performance and application level. The research works also have a great theoretical significance and application value for ensuring the security and reliable operation of power system.Theoretical analysis on the fault features of multi-circuit lines on the same tower is extremely difficult and hard to apply in the study on protection characteristic directly, so digital simulation is an important means to research the performance of relay protection. According to the complex tower structure features and the analysis demand of protection, a line model construction method suitable for complex tower structure is proposed based on the core of PSCAD, the key technology of automatic switching of different fault conditions and PSCAD operation dispatch control are realized, as well as the simulation data preprocessing and protection function module are designed. On this basis, a relay protection operating characteristic simulation analysis platform is developed, and a simulation example is implemented to verify the correctness of the platform. The developed simulation platform provides a powerful analytical tool for the follow-up protection principle research and adaptability.Aiming at the complete-journey double circuit lines on the same tower, this paper makes a deep research on operating characteristics of measured impedance element and phase selector for distance protection. Separately from interline grounded and ungrounded fault, the fault features of double circuit lines and measured impedance under different zero-sequence compensating coefficient are analyzed. Based on the developed protection analysis platform, the operating characteristics of common polygon and positive sequence polarized voltage impedance are evaluated by simulation, and the main problems that may exist are classified and summarized. On this basis, this paper puts forward distance protection application suggestions suitable for complete-journey double circuit lines on the same tower. Moreover, the present phase selection schemes are not perfect and even select the wrong phase. To solve the above deficiency, a new phase selection scheme based on voltage and judgment of the real fault phase is proposed. It's verified by extensive simulation results in single line fault and interline fault.Considering the differences in the tower structures, this paper makes research on distance protection adaptation for incomplete-journey double circuit lines on the same tower. As the influences of different operating conditions of each side power system and interconnection impedance between split-side's buses are considered, this paper analyzes the fault features and measured impedance on unite-side's and split-side's bus when interline fault is happened, then zero sequence voltage feature in interline ungrounded fault is studied theoretically. Moreover, the operating characteristics of two measured impedance elements and phase selection scheme proposed by this paper for incomplete-journey double circuit lines are researched by simulation, and the existing problems are discussed.For the same-voltage quadruple circuit lines on the same tower, the error of measured impedance under single line zero-sequence compensating coefficient in different operating conditions is analyzed, and the distance protection setting calculation is recommended. In addition, considering interline fault between different groups and among multi-circuit as well as other fault conditions, the operating characteristics of distance protection for same-voltage quadruple circuit lines are researched separately from the structure of complete-journey and incomplete-journey. The main problems that may exist in practical application are pointed out. On this basis, this paper discusses the protection configuration schemes and distance protection application suggestions suitable for same-voltage quadruple circuit lines on the same tower.As the mutual influence by power grid between two voltage levels is different, the fault features are more complex in mixed-voltage interline fault for mixed-voltage quadruple circuit lines on the same tower, and so it has a greater impact on the operating characteristic of distance protection. Considering interline grounded and ungrounded fault, the fault features and measured impedance of two different voltage levels are analyzed, the adverse effects that may brought for the protection performance are discussed. On this basis, the operating characteristics of two measured impedance elements and phase selector are evaluated with the platform from complete-journey structure and incomplete-journey structure. The existing problems are summarized to provide reference for distance protection practical application.Finally, the research work and results are summarized and further word to be studied is pointed out. |
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