Stage Protection Operational Risk Assessment Of The Transmission Line

As the “first line of defense” to ensure safe and stable operation of power system, quick and accurate respond to the accident of protection devices is critical for grid security and preventing large-scale blackouts. Therefore, the study is to establish a protection risk assessment system that can monitor and assess the operation of protection system.First of all, in view of the fact that the current calculation of failure probability models of distance protection is usually complicated and unable to accurately reflect the protection principle and impact of protection coordination on relay failure probability, a new method of calculating the failure probability of protections based on start intercept and measuring intercept is proposed according to the action characteristics of protection relays. In order to quantify the potential impact on the system due to the failure of the protection system, the protection failure index of load loss out-of-limit and flow betweeness index are established.And on this basis, the calculation method of protection failure risk evaluation index is established.Secondly, through the determined protection risk assessment indices, a protection risk assessment system is established. In formulating the risk assessment process, first using the measuring intercept to identify the fault line. Risk assessment program is triggered by start elements. Protection action probability is uploaded from protective relays to the main station located in the dispatch center through sub-stations located at each substation. Information integration and filter are completed in the main station. The operation evaluation and risk assessment is completed in the main station considering the time and the link between the failed protection and follow-up action of other protective relays.Then, a protection malfunction recognition method using protection operational data is proposed. The assessment of the current protection operating status is completed through the protection action probability information uploaded regularly. The process of identification of protection presenting malfunction risk is formulated. For protection presenting malfunction risk, establish emergency control measures to prevent malfunction tripping. The validity of the proposed method is verified through the simulation under different operation conditions.Finally, in order to make the protection risk assessment be used for actualsystem, a communication framework of the protection risk assessment system is established. The hierarchical communication framework is consist of protection devices, the sub-stations located in the substations and the main station located in the dispatching center. Communication between protection devices and sub-stations are completed by GOOSE. Each sub-station transmits information to the main station through MSTP Ethermet interface accessing to the power communication network. Via the communication system model in OPNET simulation software, data stream of the protection risk assessment system is simulated to verify the feasibility of the establishment of the online protection assessment system.