| The extreme imbalance of distribution of power generation and load leads to the long-distance, large-capacity ‘power transmission from west to east' aiming to achieve the optimal allocation of electricity across the whole country. The energy used for electricity generation excessively relies on fossil fuels mainly coals which causes problems including the lack of resources, environmental pollution and climate changes. As a result, energy revolution needs to be promoted to increase the utilization of clean resources to ensure the safety and sustainability of resources in the country. DC transmission has advantages including large transmission capacity, long supplying distance and flexibility in power adjustment which are significant to the realization of large-scale long distance power transmission, asynchronous interconnection of grids, utilization of new resources and improving the stability of AC interconnected grids. DC transmission can do great advantage to new energy resource revolution and Smart Grid. In such a situation, the grids in the country sees the formation of large AC/DC hybrid grid whose parameters and structures are complicated and operations are flexible which gives rise to the new problem of the coordination of AC and DC protection. This is critical in the protection of the grids. If the single fault in the grid can not be stopped, it will cause complex accidents in AC/DC hybrid grid. So far in the central and eastern part of China, there has been electricity feeding to into the grid in a large scale, the emergency stop in DC will cause severe damage to the stability of the receiving end. To ensure the stable and safe operation of AC/DC hybrid grid, it is urgent to conduct research on the mechanisms of interaction ACDC systems and DC control and protection technology.The technology of control and protection of HVDC systems has been owned by few large international companies, resulting in a lack of resources for technical staff to be referred to that dramatically affect the operation and research of HVDC systems. This thesis, based on the DC transmission project from XX to XX of the sending end of Hubei, systematically and thoroughly analyses ABB's DC control and protection program on the Hidraw platform and categorizes important information including configuration scheme, principles, criterions, positions of measuring points and action strategy, thus forms a detailed complete file for DC protection technology for operation and research staff.DC harmonics is one of the typical protections relating to ACDC systems. In recent years, it often happens that inrush current and short circuit faults in AC system cause maloperations of DC harmonic protection. It threatens the safe operation of ACDC systems. This thesis by using switching function theory, analyses the transfer and interaction of harmonics in ACDC systems and the correctness of the results are verified via digital simulation underpinning the reasons of fault action of DC harmonics protection when excitation inrush current and short circuit fault and other transient fault happen.After illustrating the transfer mechanism between ACDC systems, focusing on the DC50 Hz harmonic fault action in the excitation inrush current period of AC systems, the thesis proposes an improvement plan based on the second harmonic voltage on the AC bus which identify the 50 Hz harmonics generated by the excitation inrush current precisely by judging the relativity between the AC side harmonic voltage and the DC side harmonic current. Simulation is employed to verify the feasibility of the proposal. |
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