Study On Transmission Lines And Transformer Transient Protection Based On Rogowski ECT

Current differential protection is widely used in line protection and power transformer protection for its simple principle, high reliability and high speed. At present, it is one of the most important protective relaying to ensure the safety and stabilization of power system. However, it has several problems in applying as follows:the first is that the electromagnetism TA saturation may easily result in its mal-operation. The second is that distributed capacitive currents of transmission line make the currents at the two sides not satisfy the Kerchief's current law (KCL), which may also result in its mal-operation, especially in EHV long lines. This will badly threaten the safety and stabilization of power systems. Aiming at the first problem, microprocessor-based protective relaying adopts lots of methods to distinguish TA saturation moment and eliminate effects of TA saturation, which make its arithmetic and criterion more complex, and also lower its rapidity, sensitivity and reliability. The Rogowski ECT has advantages of no saturation and high ability of being free of the electromagnetism interfering, which could solve this problem radically. Aiming at other problems, though it adopts kinds of compensating methods, it could not solve radically the problem of the differential frequency content of non-periodic components affect the protection of the problems due to the line distributed capacitive current to ground. Thus studying new principles or new ways of realizing current differential protection is the leading way.Using PSCAD/EMTDC for simulation by the method of the least square to extract decaying component, the analysis and researches show that the lines on both sides of non-periodic components of the initial value and direction is relation of the time the failure occurs, and fault lines in the region is in the performance of the fault current, fault in line outside is of the pass through of current. It can be accurately determined the nature of failure after calculation and comparison Rogowski ECT, which can accurately measure non-periodic components and is based on the ratio of non-periodic components and direction of differential protection principle of differential protection is given to protect the principle of two algorithms and operating criteria. This new principle will be applied in line differential protection and transformer differential protection without the impacts of the distribution of capacitance and transformer inrush current, which can resolve the frequency content differential protection problems. Based on Non-periodic components differential protection, it is simulated and analyzed on lines and power transformers under different operating conditions. As a result, it is proved the accuracy and reliability of this new principle of protection.