Study On Ethernet-based Distance Protection For 110kV Transmission Lines

Data of present distance protection device are generally obtained through its own data acquisition system for implementing the protection function, and serial communication and field bus communication mode are still used for communication between different protection devices. One problem is that a lot of redundancies exist in data acquisition and data can't be shared by different protection. Thus, the function of large-scale and regional protection can't be efficiently implement because of the difficulty in data synchronization. The other one is that conventional serial port and field bus mode used for protection can't meet the demand of communication along with the development of digital substation integrated automation system and further research on wide-area protection. The continuous development of optical fiber electric transformer and the widespread use of IEC61850 Protocol have put forward new demands to distance protection. This paper arranges its work around the central task of study on Ethernet-based distance protection for 110kV transmission lines.Based on the analysis and research upon the shortcomings of criterion for fault phase selector and power swing blocking element in practical application, this paper puts forward corresponding countermeasures and modified approach. The results of system simulation and test have shown the validity and reliability of the two modified criterions. Aiming at the characteristics of 110kV transmission lines, an integrated set of distance protection scheme is presented, and the development of prototype is implemented in existing hardware platform. Due to the requirement of protection test and the restriction of preliminary study, this article establishes models of unsymmetrical /symmetrical fault and power oscillation using electromagnetic transient simulation software EMTP whose simulation result provide a series of typical fault data and oscillation data for function testing. Also it develops a software-tool to realize the virtual information- merging unit in computer. Simplified four-layer network model is adopted in virtual information merging unit and distance protection, and the IEC61850 protocol is applied into application layer. As a result of Ethernet communication between virtual information merging unit and distance protection, data exchange is realized. Consequently, it is validated by the test that protection function has been maturity and the results have achieved the desired research objective.The issues to be considered in the future are presented in this paper, such as the adoption of more consummated adaptive distance protection approach; the utilization of dynamic test data to verify the protection function; the actual connection with information merging unit of optical fiber electric transformer and the adoption of more reliable network transmission protocol.