The Distance Protection Filtering Algorithm Studies Of Ultrahigh Voltage Electrical Network

With the rapid development of modern power grid, EHV and UHV transmission lines are builded large-scale, Because its effective resistance and inductance is small, distributed capacitance is large, the high-frequency component transmission line is rich, transient process duration is long after fault, Protection based on frequency content will be difficult to meet the requirements of rapid action, So reveal the characteristics of the transient process after fault, and use the appropriate power system simulation software to simulate and find the corresponding solving strategy is necessary. A series of corresponding researches at home and abroad were carried out. Then a new real-time micro-dynamic physical simulation means for power system is proposed, theoretical research and practical exploration was done about protection based on frequency content. The detailed research works include the following aspects:(1) Using Matlab/simulink, model of power system transmission line is established. Including the distributed transmission line parameter module, voltage and current measurement module, fault generated module, display module, packaged relay module and so on, they are used to realize the basic functions of the power system.(2) The distance protection model is established. Including operating voltage module, the reference voltage module, phase comparison module, filter module and the interface to work space module and so on, they are used to give the result of phase comparison. By observing the phase angle of the work space, we demonstrate the feasibility of the model.(3) The transient process of short-circuit are simulated. We classify the fault and measure the impact of short-circuit caused by location of fault, fault type, fault time, transition resistance and other factors on. And then, we analyze the spectrum of fault current and voltage, classify the transient component clear the influence to the relay. (4) The design of filter. We take the advantage of spline, using the Matlab m-file programming, design a band-pass filter which response time is 40ms, it can meet the operational requirements of the relay.(5) The design of filter system. For the non-frequency component in the transient current, we use the band-pass filter filter to reduce the impact of distance protection caused by the non-frequency component and the harmonic component. The results show that the designed scheme can meet the requirements of the distance protection.The researches and results above show that the transmission line and the distance protection model can basically reflect the situation of the actual power system, a number of experimental verificate the feasibility of the model; The simulation results about transient process show that the transient components impact distance protection seriously, by simulate the transient process on purpose, we discuss and classificate the mechanism of the factors, and then lay the foundation for analysising the action of protection deeply; The performance of the band-pass filter designed spline which time is short, computational performance is good. Simulation results show that the designed filter can reduce the impact of distance protection caused by the non-frequency component, so as to greatly reduce the probability of the distance protection refusing to move, the results show that the designed scheme can meet the requirements of the distance protection.