Research On Relay Protection Of Active Distribution Network With Micro-source

With the depletion of traditional energy source and the deterioration of the environment,distributed generation technology has been developed rapidly,a large number of micro-sources has been connected to distribution network,making the traditional distribution network develop into the active distribution network gradually.Compared with the traditional distribution network,the structure of active distribution network with micro-source is more complex,and the system power flow will be changed with accessing situation of micro-source.When the fault has been taken place in the network,the fault current will be influenced by the situation of the micro-source connected and the size and direction of the fault current may be changed,resulting in the traditional over current relay protection can not work normally.In this paper,the relay protection of active distribution network with micro-source is researched.Firstly,the related concepts of active distribution network and the research status of relay protection of active distribution network with micro-source are introduced.The short circuit current characteristics of three kinds of micro-sources have been discussed based on the principles of common micro-source and the influence of micro-source on distribution network.The principles and application of traditional three-segment current protection,automatic reclosing and longitudinal current differential protection for traditional distribution network are introduced.Next,the influence of micro-source on active distribution network relay protection is studied.According to the connection position and capacity,the influences of micro-source on current protection and automatic reclosing of distribution network are researched emphatically and the simulation analysis is conducted.The analysis result shows that the variation of the connection position of micro-source can make the fault current level becoming great and small,and also has an influence on the direction of fault current.With the micro-source capacity increasing,the influence will be intensified continually,that will lead to the traditional relay protection sensitivity drop or rise,or even refuse to act normally,thereby the reliability of over-current protection will be reduced.Based on the traditional directional over-current protection,the longitudinal bi-directional over-current protection method is put forward,aiming at the fault characteristics of active distribution network with micro-source.In the proposed method,the dual setting over-current relays are configurated in the system and the two action value are set for forward and reverse fault current respectively.The forward set value act as main protection and the reverse set value act as backup protection.The longitudinal protection is also configurated in the system,and the blocking signal is transmitted through the communication channel,shutting the relays which do not meet the operating conditions and ensuring the protection can be acted according to the logical requirements.A simulation model of distribution network with micro-source is established in Matlab/Simulink based on IEEE 14 bus system.The traditional directional over-current protection and longitudinal bi-directional over-current protection are configurated and simulated respectively.By analyzing the protection action behavior,the conclusion can be obtained that compared with using traditional directional over-current protection,using longitudinal bi-directional over-current protection can short the protection distance,reduce the action time and simplify the protection logic,so that the action speed,sensitivity and reliability of the protection can be improved.