Research On A Distributed Digital Bus Protection System

Bus fault is one of the most serious fault in electric power system.Because it's the hinge of transmission and distribution in electric power system, accident will be enlarged when dealling with fault not seemly or not immediately, that destroys safe and steady running of electric power system, so it is necessary to collocate fast and reliable bus protection in high-voltage electric power system. As computer and network technologies have been deeply developed, substation automation gradually popularized, distributed installation of the protections has became a trend. It's very important to investigate a new distributed bus protection with high reliability, selectivity and fast action to safe and steady running of electric power system.Based on the research on the bus protection theory and system structure, this paper presents the disadvantage of bus protection and the shortage of research currently. Based on the basic theory of mathematical morphology, this paper compares the application in the power system, advantages and disadvantages beween mathematical morphology and wavelet transform, indicates that the extraction of transient character by morphological gradient has fast speed advantage. So morphological gradient suits the ultra high-speed protection much more.Based on the conclusion above, this paper presents a new method of distributed bus protection based on the transient current traveling waves and mathematical morphology, and establishes protection action criterion. Through establishing the system simulation model by EMTP/ATP for single bus and double bus, carry through a lot of simulation and result analysis in all of the faults. Simulation result have proven the correctness of the principle and algorithm, which can avoid the disadvantage of wrong action of traditional bus protection caused by current transformer transient saturation, and has more fast action, achieves precise and rapid distinguish between internal and external faults of protected bus. Based on the new method above, protection flow chart in double bus system has been designed.Finally, based on the new method of distributed bus protection, this paper designs a suit of new distributed bus protection precept which is bay-oriented: data communication between the bay units adopts optic-fiber Ethernet based on exchanging-type network structure, and redundancy collocation., which guarantees the high reliability and speed of the data communication and withstands EMI of substation. Lastly, this paper analyses simply some problems about real-time of optic-fiber Ethernet, format of data frame and synchronized sampling of analog signals.