Research On Station Protection Key Technologies Of AC And DC Hybrid Power Network

With the rapid development of power system,the scale of power grid is expanding and the structure is increasingly complex,especially the large-scale application of HVDC transmission technology.The traditional AC power grid has evolved to the AC-DC deeply integrated hybrid network.Its complex fault characteristics and variable operation modes bring a large number of problems and challenges to traditional relay protection based on single interval information.In recent years,with the continuous development of smart-grid construction,especially the engineering application of smart substation,it provides favorable technical support for improving the performance of traditional relay protection.As an opportunity,the relay protection system is gradually developing from a decentralized and independent configuration to a hierarchical protection with interval protection,station protection and wide-area protection as the main body.As an intermediated layer of hierarchical protection,station area protection plays an important role.At the same time,due to the advantages of no inter-station communication and realization convenience,its research and application have been paid close attention to.As a new protection form,its construction mode and implementation principle are quite different from traditional protection system.How to scientifically and rationally plan the construction scheme of the station protection system and study the new protection principles based on station domain information is of great theoretical and practical significance for promoting the engineering application of station protection and ensuring the operation safety of the power grid.Based on the research needs of national major projects,this paper focuses on the research of station protection construction mode and protection principle of AC-DC hybrid power system.In AC-DC hybrid power grid,there are a large number of AC substations,occucpying the leading position.At present,many researches have been carried out on the station protection of AC substation.However,the design principle,functional configuration,construction methods and other basic procedures have not yet formed a unified understanding.It restricts the development and application of station protection.Based on the characteristics of station protection,considering the different technology and economy application needs,this paper puts forward the basic principles that should be followed in the design of station protection.On the basis of analysis and summary of the technical requirements and main problems of different-level station relay protecion,for the 220 kV and above high voltage substations and 110 kV and the following voltage level substations,the function configuration and construction scheme of the station area protection are put forward respectively.The conclusion can provide important guidance and reference for the standardized design and application of station protection.DC converter station is responsible for AC and DC conversion and interconnection.Its structure form,protection configuration and so on are far more complex than that of AC substation.The research on DC station protection is still in the preliminary discussion stage.This paper makes a comprehensive analysis of the technical characteristics and functional configuration of the DC coverter station relay protecion.Meanwhile,it also considers the interaction of the fault characteristics in AC-DC power grid and the influence on the relay protection.It put forwards the basic ways to improve the protection performance.On the basis of this,it put forward the station protection construction mode which respectively design the AC field and DC field.Also,the function configuration and netwrok scheme of station protection communication system are put forward.The above research work will hepl promoting the engineering application of station protection in DC converter station.Station protection has the technical advantage of information sharing.How to use its characteristcs to improve protection performance is one of the key points in the field of station protection research.The DC line longitudinal current differential protection and 50 Hz harmonic protection are the important backup protection in the DC system.In the practical application,the traditional differential protection has a long action time and the 50 Hz harmonic protection is affected by the excitation inrush current.Based on station protection,a new principle of differential protection based on station area information is put forward in this paper.By using the information of AC side bus-line voltage and the harmonic current of the DC side,it can distinguish the fault of AC power grid and the DC system,so that the action speed of the differential protection can be greatly improved.For 50 Hz protection,a new method of identification of inrush current is proposed by using the correlation between the twice-harmonic of AC bus voltage and the 50 Hz harmonics of DC side,which can effectively prevent the incorrect operation of 50 Hz harmonic protection during inrush current duration.The simulation results show that the overall performance of the proposed principles of station protection is obviously better than that of traditional protection,so it has good prospects for engineering application.At the end of this paper,it sums up the main works and achievements.Meanwhile,it makes a prospect for the furture research priorities.