| As the first defense to protect the safety and reliability of power system, the relay protection is an important component of power system, and its operational reliability plays an important role to the overall power supply reliability. In recent years, with the advance of national economy, power grid construction is in a high-speed development period. Power system scale expands day by day, and the voltage class and transmission capacity increase continuously, and the electrical link among subsystems of power grid gets more and more closely. On the one hand, it improves the efficiency of power supply, on the other hand, it also increases the uncertainty of power grid operation and the damage to community. Any fault will leads to the cascading failure of power grid if the relay protection can not cut off the failure quickly and selectively. As a result, to build the reliability evaluation model in order to evaluate the operational reliability of relay protection and find the weakness of operation has a good application value and realistic guiding significance.This paper relates the research status and research history of reliability evaluation of relay protection, and points out some problems existed at present, and analyze the main factors on the reliability of the reliability of relay protection, based on failure mechanism of protection, and operational reliability of stepped current protection and distance protection installed on transmission lines is evaluated in this paper. The main jobs are as follows:(1)This paper introduces the composition and working characteristics of protection, and analyzes the factors on the reliability operation of relay protection. It elaborates the failure mechanism of relay protection and points out that reliability evaluation results resulted from the failure models of hardware, software, breakers, secondary circuits and the other related units can only reflect the long-term average of reliability of protection, which will not reflect the reliability of relay in the actual operating conditions of power grid. So it is necessary to study the reliability of relay protection in the actual operating conditions of power grid, including the configurations and setting schemes of protection, and operating modes of grids and so on.(2)Based on the reliability evaluation indicators including operational fail-operation probability and operational false-operation probability put forward by previous references, this paper puts forward a more reasonable evaluation indicator, that is the percentage of operation of protection, which can reflect the influence of real-time changes of operating conditions of power grid has on the fail-operation and false-operation of protection from different angles such as clearing time and the accuracy of fault removing.(3)To stepped current protection, this paper analyzes the operation probability distribution of protection with the changes of length of lines, and builds the probability distribution of stepped current protection.(4)To distance protection, this paper studies the resistance circular characteristic of distance protection, and analyzes the operation probability distribution of distance protection on total impedance circular.(5)This paper gives the algorithm of the percentage of operational operation of stepped current protection and distance protection.At last, this paper shows the calculation steps of the percentage of operational operation of protection, and elaborates how to evaluate the operational reliability of protection based on results of percentage of operational operation of protection. |
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