Reliability Analysis Of Area Protection With Communication Constraints And Study On Improving Differential Protection

In recent years,the power industry has developed rapidly and the power network has become increasingly large.As a secondary system to protect the reliable operation of the power system,any fault in any link will bring great hidden dangers to the power industry.Traditional relay protection,especially backup protection,is prone to mismatching and long delay when the system has non-preset fault.Regional protection based on regional multi-source information has become one of the main research directions of secondary systems in recent years.With the help of wide-area communication network,regional protection integrates multi-source information and constructs a new protection principle,which solves the complex problem of protection cooperation and can improve the protection action speed.However,regional protection is oriented to regional large power grid,and its control object covers multiple circuit breakers.Once misoperation occurs,it will bring greater risks to power grid reliability.Therefore,the reliability analysis of regional protection system becomes an important problem to be solved under the increasingly complex regional power grid environment.However,in the field of reliability analysis of relay protection system,there is a problem of "unifying the correct action rate of the same element in the system",which leads to the inaccuracy of quantification of the existing reliability analysis model.In this paper,the reliability of regional protection system is analyzed by using the least path set method.Considering the constraint of communication on the reliability of protection system,an improved differential protection algorithm is proposed to reduce the traffic and improve the reliability of protection system.The regional protection system is further modeled by segments,and the reliability analysis model which takes into account the communication constraints is established.The specific work is as follows.A retrieval method of the minimal path set based on table filling method for topologies of regional protection secondary systems is proposed in the paper.To form a two-terminal network,a sub-station in the protection system of regional power network is set as the input endpoint,and the regional main station is set as the output endpoint.The topological initialization table,serial path storage table and path retrieval table were constructed by network topological connection matrix,and the minimal path set of the system was quickly retrieved by matching the parent branch number with branch branch numbers.In order to reduce the longitudinal current differential information communication,an improved current differential protection method based on "0-1" reconstruction of current sampling value is proposed in this paper.On the premise of ensuring the protection performance,the floating-point number in the traditional sampling method is transformed into an integer containing only "0,1,-1" by setting a reasonable threshold.Based on the converted waveform,a new differential protection action amount and braking amount are constructed by integrating the sampling value in the data window.At the same time,the encoding rules of "0,1,-1" are proposed for information transmission.This method can greatly reduce the amount of communication information and improve the reliability of the protection system.A reliability analysis method for regional protection system based on communication constraints is proposed.Firstly,the architecture and characteristics of the regional protection system are analyzed,and the protection system is divided into two relatively independent subsystems--"station node system" and "optical fiber communication system”.Based on the filling method,the subsystem reliability analysis model is established.The improved differential protection algorithm and the subsystem model in series are considered to realize the overall reliability analysis of regional protection.The improved differential protection and reliability analysis methods proposed in this paper are verified by dynamic simulation experiment and numerical simulation.