嵌入式同塔三回直流系统多重相模变换及其在故障选线中的应用OA

Embedded high voltage direct current system is an effective solution to enhance the regional power grid's power transfer and dissipation capacity.To effectively utilize the transmission corridor,some projects have transformed the double-circuit AC transmission line on the same tower into three bipolar DC transmission systems.The formed embedded co-tower three-circuit DC system has more complex coupling characteristics and richer fault types.Faults on any line can lead to voltage and current fluctuations on non-faulted lines,which can seriously impact the fault localization of DC lines.However,the existing decoupling schemes cannot realize the effective decoupling of this system,and cannot ensure the regularity and easy recognition of the fault characteristics after decoupling.To address these issues,this paper proposes a faulty line identification scheme based on multiple phase-mode transformation. The coupling characteristics of the embedded co-tower three-circuit DC system are analyzed.The impedance matrix is constructed by considering the effects of layer height and symmetrical line arrangement.A decoupling method based on multiple phase-mode transformation is proposed,which combines the accurate identification of faulty circuits and the effective decoupling of faulty lines;Aiming at the fault voltage mutation features,the polarity features that are more clear,easy to recognize and have significant differences are extracted,and then a fault line identification scheme based on the modulus polarity combination is proposed.Finally,the performance of the proposed protection scheme is verified by constructing a model of the embedded co-tower three-circuit DC system in PSCAD,and the simulation results show that the proposed scheme is able to identify all fault types accurately,and still has excellent results even under high-resistance fault conditions. The following conclusions can be drawn from the simulation analysis:(1)The proposed incomplete decoupling method for the embedded co-tower three-circuit DC system is adaptable and has a simple decoupling matrix structure,which significantly reduces the computational difficulty compared to the traditional decoupling scheme.(2)Applying the proposed decoupling scheme,a faulty line identification scheme based on modulus polarity combination is proposed.The fault characteristics of the system are significant during failure,which significantly reduces the complexity and workload of faulty line identification compared with the traditional analysis methods.(3)The proposed fault type prediction method based on multiple phase-mode transformation of fault components can effectively address the problem of overlapping polarity combinations,and has strong capacity of withstanding transition resistance and anti-interference performance.