Development On A Novelty Distributed Numeric Busbar Protection System

As computer and network technologies have been widely applied in electric power system and substation automation gradually popularized, distributed installation of the protections has become a trend. In compasison with the traditional centralized busbar protection, distributed busbar protection can be locally installed and shorten CT secondary cable, which accord with layered and distributed structure of substation automation. Based on research and analysis of several existed busbar protections, the thesis has developed a new type distributed busbar protection which is bay-oriented and can be locally installed, i.e. the bay units of protection are monogamy with each electric element connected with busbar in protection zone. Software and hardware of each bay unit is identical. Completion of protection algorithm uses pipelining between bay units, which simplifies hardware of the protection, and easily attains redundancy. Asynchronous serial port of 375kbps is taken as communication interface between bay units. Optical fiber is adopted for guaranteeing reliability of communication and withstanding EMI of substation. The thesis studies the principles of fiber optic data communication and designs a system of fiber optic data communication that can transmit arbitrary duty factor signal. Availability of the system is verified by experiments. Main criterion of protection is current differential algorithm according to every sampled value, which can accelerate the protection's trip. The precision of synchronized sampling of different bay unit is less than 5 microsecond by means of special technology. In the thesis, several existed criterions to detect CT saturation are introduced. From the point of view of engineering, the thesis pays more attention to realization of the criterions. The new type distributed busbar protection has been tested in digital and analog experiments and will be put into informal operation in a 220kV substation.