| Power system relay protection composed a very important part of the whole Power System and is as the first line of defense to ensure safe and stable operation of power grid. Its reliability is also the important guarantee to prevent the accidents in power grid from expanding and chain reaction. Relay protection should meet the requirements of speed and mobility, reliability, selectivity and sensitivity, so how to improve the reliability of protection system is becoming an important subject on people’s increasing attention. With the development of computers and techniques of communications and the requirements of security and stability of large-scale interconnected power grid, Wide-area protection is proposed and paid much attention. Wide-area communication system is the foundation and key to the wide-area protection system, therefore, it has guiding significance on operation level of wide-area protection to do research on reliability of wide-area protection communication system.This thesis has done models and conducted analysis to microcomputer relay protection system and wide-area protection communication system, the main research and details of this thesis is as follow:1) By analyzing the specificity of microcomputer relay protection system and considering the influence of secondary circuit and other components on the reliability of microcomputer relay protection devices, establish the hardware reliability model of microcomputer protection system. Network method has been used to analyze the reliability. The conclusion is conductive to designing, updating and maintaining protection system.2) Comprehensively considering the influence factors on the reliability of microcomputer relay protection system:software, hardware and people factor, divide status of microcomputer protection system and use Markov state-space method to assess the comprehensive reliability of microcomputer protection system. The availability of this model is more close to the statistical data of failure rate of the national220kV and above from2006to2008.3) Combining the operation status of the primary equipment and considering failure action and malfunction of protection system, establish Markov models of dual protection configuration, get the reliability indicators of relay protection system under three kinds of protection configuration. What this thesis has done is conductive to calculating reliability of system composed of protection devices made by different configurations or manufacturers.4) Combining with the structure of three-level wide-area protection system, modeling and analyzing reliability of substation, system/regional protection system and backbone/regional network by Markov. Take IEEE14Bus bar system for example, divide wide-area protection communication system into System Protection Center, backbone network and regional communication system, regional communication system can be divided into LAN Protection Center, regional network and sub-station system. Each subsystem is logically composed of series system, calculate availability of each unit and finally obtain the availability of the whole wide-area protection communication system. This method can provide a certain basis for reliability design and safe operation of wide-area protection communication system. |
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