Research On On-Line Verification For Relay Protection Considering Risk

With the rapid development of electric power construction, China’s power networkgradually forms a modern interconnected power network of cross-regional, large-scale andmulti-ring network. The characteristics of the flexible and changeable operation mode forthis modern interconnected power network make the drawbacks of the traditional offlinesetting calculation model more obvious, and one of effective means to compensate for theshortcomings of the program is on-line verification. However, with the actual operation ofon-line verification system, we found that, it is often difficult for users to judge the weakdegree of relay settings when applied to the large-scale, complex-structure andflexible-mode grid, limiting the further generalization of on-line verification system. Forthe weak degree of relay settings, the probability of relays operating incorrectly and thecaused severity is the users’ primary concern. As the risk usually means the probability andconsequences of the accident, the risk of relays operating incorrectly reflects the weakdegree of relay settings to a large extent.Therefore, this paper introduces the risk to the on-line verification system, and carriesout a deep research on on-line verification for relay protection considering risk. The maincontents are as follows:Firstly, in view of the problem that it is difficult for users to determine the weak degreeof relay settings, risk based on-line identification of weak region with relay settings ispresented. And this paper tries to analyze the probability of the relays operatingincorrectly(refuse operation and miss operation included) on distance protection in thesituation that the standards given by verification are not met and, using relative load loss toquantify the results, defining the risk indices for the operation of relays, to identify theweak region with relay settings based on risk under current operation mode on-line.Secondly, to the relay settings that do not meet the verification requirements, the risk-based optimization target of inverse-time overcurrent protection is proposed by meansof optimization theory. With the reliability of protection being taken into account, theincorrect action probability model of inverse-time overcurrent protection is built andseveral risk indices of incorrect action are also given. On this basis, this paper takes the riskminimization as the optimization target, builds the optimization model, and finally gives thecorresponding recommended relay settings.Last, for the lack of generally applicable verification procedures at the present stage,and the current inadequate method of protection range verification, an on-line verificationmethod based on the inverse process of protection setting is presented and the universalformulae and principles of on-line verification on distance protection are given. The style ofthe method presented is consistent with the protection setting calculation, making it easy toachieve in computer, as well as to quickly divert from setting calculation to verificationcalculation for users.