Study On The Establishment Of Critical Failure Risk Assessment System For Distance Relay With Round Characteristic

Several major power outages occurs earlier during this century at home and abroad show that, the process of grid failure and failure mode is unforeseen for off-line analysis. And the lack of necessary means and methods to understand and analyze the system state after actual failure, resulting in the expansion of the accident. The risk of failure probability model of relay protection is an important part of the reliability evaluation for power transmission system operation, so correlative basic theories and application technologies are becoming indispensable key issues in order to ensure security and stability for the large-scale grid.Paper describes the all-embracing development process and the overall operation of the transmission system protection technology, describes two types of failure mechanism respectively, which takes into account the short-circuit fault type and fault transition resistance. Weighted forms are been used to expresses the unique characteristics of external environment which protect device suffered. Critical of the protection system failure risk assessment model is been put forward, and the specific implementations for failure factor and failure curve in the evaluation model is also been studied. The above-mentioned studies could solve the problem that traditionally only pursuant to a protection element statistics to estimate the failure probability, deal with the uncertainties of grid operation accurately, and provide a theoretical foundation and credibility indicators for the transmission system reliability assessment which taking into account the protection system.The circular features ohm distance relay and the partial transformation ohm relay are the most commonly used in transmission line protection devices. According to the principle and configuration of the protection program, a variety of second type relay failure risk algorithms under real-time short-circuit fault conditions are advised:1.Based on the practical ohm relay round action features in the impedance complex plane and the measured impedance equations, the relay measurements of critical relay failure resistance distribution maps and critical failure factors are derived;2.Based on the measured impedance equations under different fault types, the relay measurements of critical failure of the resistance distribution maps and critical failure factors under single-phase and inter phase faults are derived;3.Based on the deflection characteristics of practical ohm relay round action features in the impedance complex plane and the measured impedance equations, the relay measurements of largest action domain distribution maps and the largest action domain coefficient are derived, which calculated based on the domain of the failed state;4.Analyzes the measured impedance characteristics of non-fault phase components by the combined effects of the grid state change.Taking into account the advantages of negative sequence voltage at protection installation side can adaptive adjust action boundary with the transition resistance change, analyzes and founds that the changeable critical circle operating characteristics and other prerequisites when offset voltage turn into the "in-same-phase" region, and an adaptive distance protection scheme for transmission line is established. Calculates the measuring impedance changes in the scope when relays under the load operation, and extends critical failure model to the scope of the "in-same-phase", combining with changes in the power angle, voltage loss, network structure and some other real-time state variables, to build the critical of failure risk assessment model with changeable circle characteristics. To test the improved relay protection program, by using of EMTDC verify its performance of tolerance in the transition resistance changes, and forecasts the possibility of disoperation failure.The paper also proposes solutions for the lack of traditional oscillations anti mistake locking devices, which taken the electrical change-distance relay measurement of the impedance locus circle as the overall program of the correction criterion. Because of the line impedance ratio between forward and reverse relay installation, and the potential ratio at both ends are all depends on the actual operation situation, a total of eight cases were identified about the oscillation case measured impedance locus when relay installed on the sending and receiving side, the approach to obtain the required trend information from the resistance part of measured impedance change rate symbols is discussed. Finally, a simple four nodes reliability test system is been applied for assessing to demonstrating protection can adaptive adjust the blocking criterion function to the trend turned under continuous fault conditions, confirmed the safety of the relay device.