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In this paper, a reliability evaluation model and a bilevel unreliability allocation model for the ±500-kV HVdc transmission system with the double-circuit lines on the same tower (DCLST) are proposed. The reliability evaluation indices associated with this DCLST HVdc system are also defined. The reliability model is based on the characteristics of common starting point and terminal point structure and double-circuit HVdc coordination operation. And it is developed by integrating HVdc subsystem reliability models together. A multistate Markov model for the dc line (DCL) subsystem is built by considering the common-cause outage of four DCLs on the same tower. The reliability evaluation model of the ac filter (ACF) subsystem is constructed by considering the derated capacity operation state caused by ACF failures. On the other hand, a bilevel unreliability allocation model is constructed based on the proportion-allocation criterion. The allocation model is embedded into the reliability evaluation model so that all reliability indices can be allocated to each component after only one reliability evaluation calculation. As a result, the impact of each component on the system reliability and weak components of the system can be explicitly and unambiguously identified. An actual ±500-kV HVdc transmission project with the DCLST is used for case study to validate the effectiveness of the proposed models and indices. [ABSTRACT FROM PUBLISHER]

In this paper, an optimal reliability allocation (ORA) model of ±800 kV ultra-high voltage direct current (HVDC) transmission system is proposed. The model intends to provide the means to determine the availability requirements of components in the bidding process of ±800 kV ultra HVDC transmission projects. In this model, the component availability is optimized based on the prespecified system reliability. The objective function is composed of the component investment cost and the operation and maintenance cost. The ORA is formulated as a constrained nonlinear programming problem, and the genetic algorithm (GA) is used to find its solution. An improved dagger sampling (IDS) method is proposed to evaluate the reliability of ultra HVDC systems, and a bisection method is used to generate the initial population of the GA. An actual ultra HVDC project is used to conduct the case study. Results show that the proposed ORA model can minimize the component investment, operation, and maintenance costs, while achieving optimal allocation of the system reliability index to obtain the availability of components. In addition, the impact of the component spare on the ORA result is investigated. Performance comparison on the sampling efficiency of the IDS method and the direct Monte Carlo sampling method is also presented. [ABSTRACT FROM AUTHOR]

Double 12-pulse ultra HVDC transmission systems of \pm 800 kV and \pm 660 kV have larger transmission capacities, more complicated configurations, more complex operation modes, and more components, in comparison to \pm 500 kV or less HVDC transmission systems. Hence, the reliability evaluation of the ultra HVDC transmission system is more complicated than that of the HVDC system. To thoroughly describe different operating modes, this paper presents two new reliability measures for ultra HVDC transmission systems, that is, partial monopole forced outage times and partial bipole-forced outage times. Reliability evaluation models for individual subsystems, including converter transformers (CT), ac filters, converter valve groups, and smoothing reactors have been built considering operation modes and configuration characteristics. In particular, the reliability model of the CT subsystem was built by considering the type and the number of standby CTs, and that of the ac filter subsystem was built by considering the capacity state table of filters. A reliability evaluation model for ultra HVDC transmission systems was proposed by combining reliability logic relationships among subsystems and using the state enumeration method. Case studies of practical ultra HVDC transmission systems illustrate the correctness of indices and the proposed models. In addition, sensitivity analysis and standby analysis of major components were also conducted. [ABSTRACT FROM PUBLISHER]