Study On Optics Differential Current Protection For EHV Transmission Lines

With the rapid development of the power system,the power grid changes day to day such as:the number of parallel lines increases greatly,the transmission lines become much longer and the load is much more heavy. Furthermore, T lines and the multi-terminal lines are commouly used. The traditional protections,including the Phase Differential Protection Based on High Frequency, the Diroctional Protection Based on High Frequency and the Distance Protection cannot meet the demand of these developments.The performance of transmission line protection relay is influenced by the distributed capacitance along the line,the shunt reactor,the serial compensation capacitor,two phases operation status after tripping one phase,complex faules and the transient process of the CVT and CT when faule accurs.The differential current protection has been widely used in the transmission line in virtue of its simple principle,high sensitivity and inherent phase selection ability.The thesis is focus on the research of the optical-fiber differential current protection that can adapt to the rapidly changing power grid.It mainly contains the following four parts:(l)Theoretical analysis of some operation criterions and some factors that influence the operation of the differential protection,(2) Analysis and comparison of some synchronization methods used by domestic and abroad companies.(3) Introduce hardware design scheme about DF3320EA line different relay in detial (4)Briefly illustrates actual practise operation.The devices have many merits.They can sensitively and reliably cut off all the faults occurring in the power system.Even under the critical situation faulting on the long heavy load transmission lines through high ground resistances,the criterion based on fault components still has considerable sensibility.The devices has past the static test in EPRI, and the dynamic analog test in NCQTR, and which has been widely used.