Research On Distributed Wide-area Back-Up Protection System For High-voltage Transmission System

In recent years,with the development of the power grid,the level of intelligent power grid is constantly improving.The new generation of energy such as wind energy,solar energy and other clean energy power generation accounted for has been significantly increased,and large number of distributed units have been accessed to the main grid.As a result,the future development of the power grid will form into the third generation of intelligent power grid which is combined with main grid,local network and micro power grid.The grid topology will be more loosely as a whole,the average path of the new connection point will be larger,which both cause imperative upgrades and replacements for the relay protection system.Wide-area protection technology provides a new opportunity.Through the establishment of wide-area communication platform,the protection system is able to access to multi-point information within the system to achieve rapid fault location and isolation,which is especially applicable for the backup protection system whose decision-making response time requirements are not too high.However,a wide range of related research on wide area backup protection systems fail to jump out of the perspective that the protection device configuration is component oriented,and can not fundamentally solve the problem of complexity of protection coordination and the difficulty of standardized protection configuration.Distributed systems,as an important part of the study of wide-area protection,have not yet formed a unified discussion paradigm in many research directions.As a result,this paper puts forward the idea of using the wide-area means to design the protection scheme,and establishes a distributed system architecture whose basic structure and functional unit is circuit breaker centered IED(Intelligent Electronic Device),and defines its basic working mode and fault protection strategy.In this system,the object of the protection configuration changes from the original system component to the fault in the system and the cooperation object of the protection device is also changed from the original component protection device to the IEDs within the protection range.In this way,the circuit breaker IED can know the exact fault location,thus simplifying the protection coordination procedures and improving the rapidity and selectivity of the protection action,but also redefines the system backup protection function achieving the real realization of the distributed measurement,decision and the implementation of the distributed backup protection function.The principle of division of protection range based on IED is proposed.The principle specifies the coordination rules of the IED,realizing new near back-up protection and remote back-up protection based on IED objective.Thus,IEDs in different location of the system are able to identify there coordination objectives under various fault situations.In view of the overlapping situation of different protection ranges,the principle has been formulated and explained accordingly,and the principle has taken the certain IED failure into account.In different system operation mode,and the different connection state between the system components,the principle's adaptation is analyzed and the conclusion of high reliability,strong selectivity is gained.The division process is simple,compared with the traditional division method has certain advantages.A protection scheme based on three protection structures is proposed.Firstly,the wide-area protection principle based on the comparison of fault direction is proposed.This principle assigns the direction judgment result by stipulating the positive direction of the IED in different structures,and realizes the purpose of fault location between the IEDs through information exchange.Judgment information is simple,easy to obtain,the pressure on the communication system is small,ensuring accurate positioning of the fault.Based on this principle combined with the principle of protection range division,the IED types in the system are classified into three kinds of protection structures:"line-bus","line-transformer" and "bus-transformer".The fault handling process in the three protection structures is analyzed and explained.This method simplifies the cooperation of the protection unit,overcomes the inherent defects of the setting value based back-up protection,realizes the standardization of the protection device,and provides the more comprehensive backup protection for the system components.Finally,through the analysis of the system simulation example,it confirms the validity and accuracy of the implementation scheme.