Research On Wide Area Backup Protection Algorithm Based On Wide Area Measurement Information

With the increasing complexity of power grid structure and operation mode, the defect of traditional backup protection based on local measurement information is becoming more and more obvious. In recent years, with the development of wide area measurement technology, wide area protection has attracted wide attention of researchers. Generally pilot protection is used as the main protection of high voltage power network. Since the whole set is simple, the correct rate of action is high, fast and not affected by the load transfer. However, wide area information is required for sampling synchronization, and due to sampling device or transmission channel fault, information protection is easy to be wrong or missing, so research on wide area protection is mainly for backup protection, and committed to improve the performance of backup protection.In the process of information collection and transmission, the information is easy missing or wrong. Therefore, wide area backup protection is required to have the fault tolerance. In addition, the action performance of the wide area backup protection algorithm which uses protection action information in the complex operation condition may not meet the requirements of the relay protection. Therefore, the paper analyzes and studies the fault tolerance of the wide area backup protection and the motion performance under complex operating conditions. The main work of this paper include the following aspects:1、This paper introduces the structure and partition of the wide area backup protection system, and expounds the three basic structure of the existing wide area backup protection system and the limited partition theory of wide area backup protection. On the basis of this, a fault zone detection method based on incidence matrix is proposed, which identify the fault zone by identifying the faulty line. As a result of only information of the fault area uploaded to the decision center, which can be effective to reduce the transmission of the wide area information and improve the speed of fault identification.2、In order to improve the fault-tolerance of wide area backup protection and make it has satisfactory performance in complexity operating condition, a wide area protection algorithm combining fault voltage comparison and wide area protection information is proposed. The algorithm makes use of the information of protection action and voltage, current and other electrical quantity information to identify the fault components. Measured voltage and current by phasor measurement unit from one terminal of transmission line are provided to estimate the voltage fault components of the other terminal. Then the corresponding probability of failure is obtained by the ratio of measured and estimated value. Because of the fault voltage comparison algorithm in the case of non full phase operation may be mistaken, this paper has made the improvement to this problem to ensure fault components can be reliably identified under the non full phase operation, high resistance grounding and other complex operating conditions. At the same time, protection information of the line and the adjacent line are weighed to get the comprehensive value, then the corresponding probability of failure is calculated by the ratio of comprehensive and threshold value. These two probabilities are weighted comprehensive to find the fault component.3、This paper makes a specific analysis about possible misoperation or maloperation situation of traditional protection (main protection, distance protection, directional element) under the high impedance earth fault, non full phase operation and voltage transformer secondary circuit disconnection. Based on the above analysis, the performance of the proposed wide area backup protection algorithm in the complicated working conditions can be analyzed accurately.4、This paper uses PSCAD/EMTDC as a tool to build IEEE4-generator 8-bus system to test the fault tolerance of the wide area backup protection and the motion performance under complex operating conditions. The simulation tests based on IEEE 4 generator 8-bus system illustrate the validity under various complex conditions, such as high impedance earth fault, open-phase running of fault again, and voltage transformer secondary circuit disconnection.And shows the effectiveness and high fault-tolerance capability of the algorithm with the mis-operation and refuse-operation of multiple protections. In addition, the algorithm can accurately identify the fault components in the case of double faults.