| With the development of High voltage direct current (HVDC) transmission system, it plays more and more important role in the power grid of China. How to improve its safety and reliability has become a problem needed to be solved urgently. Therefore it is necessary to pay more attention to the simulation and study towards the protection scheme and control characteristics of HVDC transmission system. It is known that the core of HVDC system is the protection system, in which the protection of direct current transmission line is the basic security of the safe and stable operation, thus further research and improvement towards the protection scheme of direct current transmission line is needed. This paper contains the relation study about HVDC system and its protection system which is researched by the author during her master degree period. Main results as follows:(1)The 12-pulse bipolar HVDC simulation model based on the electromagnetic simulation software PSCAD/EMTDC is presented in this paper, which is suitable to every operation model and can reflect different faults situation. The operation mode and typical faults in HVDC system are simulated and studied based on this model.(2)The travelling wave protection scheme of ABB and SIMMENS are studied and their performance are evaluated in this paper. The result is verified by the 12 pulse bipolar HVDC model mentioned above.(3)Through the compare of the currently travelling wave protection criterions in HVDC transmission line, a new type of single-ended travelling wave protection scheme of HVDC transmission line is presented in this paper. It can identify the direct current transmission line fault and other external faults effectively with high speed , meanwhile it can obtain the fault location. The correct operation of protection scheme has been verified with extensive simulation studies.(4) Finally, the results towards these research mentioned above are concluded and the direction of further work is pointed out.
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