A Research On The Wide Area Backup Protection Of The High Voltage Transmission Line And Its Communication

With power grid interconnecting widely, a higher demand for protection has been put forward according to the increasing load and more complicated power grid. It is required that not only faults can be isolated fast, accurately and dependably, but also system can remain steady operation while greater disturbances take place. Studies of significant power system incidents indicate that protection relays, especially the back-up protection relays, are involved in 75% of major disturbances. Because of their limited view of the interconnected network based on their locally measured inputs, conventional back-up protection relays generally take actions to protect a localized region of the network without considering the impact on the whole network. Wide area protection has been proposed in recent years to meet the requirement of the stability of the growing power system. As a result of the recent advances in communication, information and computer networks, and the significant development in inter- and intra-substation communication standards, such as IEC61850, the capability of broadening the scope of a protection system has been provided today. Wide area protection may locate the fault precisely to prevent unnecessary trips. This will significantly improve the reliability of power systems and prevent the occurrence of cascading outages.In this dissertation, the background and research situation of the wide area protection, communication networks of substation and communication standards are introduced. The characteristics, function and structures of the wide area protection system are discussed. A practical wide area transmission line backup protection scheme is proposed in this dissertation. The design of the system structure, the basic principle of protection and the algorithm of fault location is analyzed. A new algorithm using fractal techniques is presented for phase selection.The proposed wide area transmission line backup protection system can be divided into two parts: the protection master system and the protection slave system. These two parts can communicate with SDH device. The structure and function of master system and slave system are discussed. The APCI5000 industrial computer, used as the hardware of the protection equipment, is introduced. Because the wide area backup protection is based on the reliable communication, a detail design of the communication program is presented. The overall design of the protection software including the program flow is introduced. The dynamic simulations show practicability of the proposed scheme.