| With the continuous development of interconnection and UHV construction of China power system, the grid structure becomes increasingly strong. However, it is getting more and more serious that large short circuit current in power systems excesses the regulation standard. Apparently, it has become a critical problem to limit the short circuit current levels economically and effectively, which is yet to be solved in the planning, operation and maintenance of power systems. Fault current Iimiters, namely FCLs, representing a novel fault current limiting technology with great application prospect, have been a popular topic in recent years. Among numerous types of FCLs, fault current limiter based on permanent-magnet-biased saturation, namely PMFCL, possesses outstanding performance with promising practicality in the high-voltage and large-capacity situations.Three crucial issues of straight-line type PMFCLs were investigated in this dissertation for the sake of engineering application in high-voltage power grids, including economical optimization and design, optimal allocation in large-scale power grids, and influence on the transient stability of power systems.The application value of FCLs ought to be mainly dominated by economy, rather than technical performance in high-voltage and large-capacity circumstances. Based on three independent electromagnetic variables of inductance ratio, inductance sum and saturation depth ratio, the economical evaluation and optimization models were built as to convert the economical optimization and design of PMFCLs into the issue of optimal combination of the aforementioned three electromagnetic variables. By virtue of a 500kV case for economical analysis, optimal cost and the corresponding structure parameters of the PMFCL was calculated. Finite element simulation proved the validity of the proposed models.Optimal allocation of PMFCLs in large-scale power grids is a vital problem to be solved before engineering application. Bus self-impedance was regarded as the measurement index of short circuit level, and an optimal allocation model of PMFCLs with consideration to. the overall current-limiting effect and economy was built on account of the increment of bus self-impedance. It was proposed that the starting condition of PMFCLs and the sensitivity index of bus self-impedance with respect to the branch impedance could be utilized to greatly decrease the searching space. Simulation of IEEE 39-bus system by the presented optimal allocation model verified the effectiveness of the optimal number, installation site and current-limiting reactance of PMFCLs.Transient stability of the system must be ensured when PMFCLs are applied in power grids. Taking single-machine infinite bus system as example, a transient analysis model containing one PMFCL was built in view of positive sequence augmented network. Based on power-angle curves of the generator and the equal area criterion, the influence of PMFCLs on the transient stability of the system was analyzed in detail when various types of short circuit faults occurred at different locations of the transmission line considering variation of the current-limiting reactance and fault-clearing time. Time-domain simulation agreed well with the theoretical analysis.In this dissertation, all the research contents are around the key issues related to the engineering application of PMFCLs. Research achievements which has important theoretical reference value and practical guiding significance will contribute immensely to the implement of high-voltage large-capacity PMFCLs and their application in power grids. |
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