Study On The Whole Line Quick-Trip Protection Of Distribution Line Based On Beidou Navigation Satellite System And Real-Time Ethernet EPA

The medium and low-voltage distribution systems in our country, commonly use overcurrent protection as the primary protection of the distribution line. The instantaneous overcurrent protection can only protect a part of the line, the other internal fault can only be protected by the time delay instantaneous overcurrent protection and definite time overcurrent protection. A long fault clearing time may cause a lot of problems, such as the electrical equipment may be deformed or even destroyed, the bus load may be rejected, a long time voltage drop, the transient fault develops into a permanent fault, et al. The network structures of distribution systems are always complex. The distribution line may be long or short, and also there are a lot of tapped branches. So the setting of the relay protection is very complex, or even can not be set correctly. With the economic and social development, the requirements of electricity supply reliability and power quality are increasing. The users request less blackout times and shorter blackout time. The overcurrent protection can not adapt the distribution system development. So it is necessary to propose a new distribution line protection scheme.This paper proposed a new distribution line protection scheme based on longitudinal differential protection, considering the distribution line features, such as there are a lot of tapped branches and the neutral point is ungrounded or small current grounded. The longitudinal differential protection must be supported by high-precision synchronous sampling and large-capacity real-time communication. So this paper designed the high-precision BeiDou synchronous clock based on the timing function of BeiDou Navigation Satellite System, and the communication interface based on real-time Ethernet EPA. Then studied the optical fiber communication. That is to say, this paper can be divided into three parts:the determination of protection scheme, the designing of BeiDou synchronous clock, and the study on EPA communication system.The first part, proposed the protection criterion of fault component sampled value longitudinal differential protection of distribution line, by comparing the performance of the three candidate criterions on different types fault. And then did several simulation of the three candidate criterions and the protection criterions using PSCAD. The simulation proved that the theoretical proof was correct and the protection criterion was feasible. Then proposed the protection criterion of phasor longitudinal differential protection, zero sequence longitudinal differential protection and tapped branches protection, and also the phase selection criterion of single phase-to-ground fault. And then did the detailed arguments and the PSCAD simulation. At last, introduced the comprehensive protection scheme, include the coordination relationship of the protection criterions, action process of fault isolation and power supply restoration. Thus, when there is two or three phase fault on the distribution line, the protection will act quickly and accurately, cutoff the fault and then isolate the fault and restore the power supply, when there is single phase-to-ground fault on the distribution line, the protection will send the alarm information.The second part, briefly introduced the synchronization methods commonly used in power system, and also the composition, function, operation principle and advantages of BeiDou Navigation Satellite System. Deeply studied the outbound signal format and timing mode of BeiDou Navigation Satellite System, include superframe format, subframe format and broadcast message format of the outbound signal, and also the basic principle, comparison and error analysis of two timing modes. At last, designed BeiDou receiver, BeiDou synchronous clock and BeiDou/GPS each prepared synchronous clock, and described the function of each schematic module. Thus, supplied the high-precision synchronous clock to distribution line protection.The third part, briefly introduced the communication technologies commonly used in power system, and also the overview, network topology, devices and features of EPA standard. Deeply studied the EPA communication mechanism, include EPA communication model, data link layer model, principle and realization of the deterministic scheduling. Proposed the "Microprocessor+EPA chip+network chip" design scheme, by comparing two communication interface schemes. And then, designed the hardware architecture and the communication program. At last, studied the features, basic principle, performance parameters and channel multiplexing technology of optical fiber communication. Thus, supplied the large-capacity real-time communication to distribution line protection.