Capacitive Voltage Transformer (cvt) Super (special) High Voltage Transmission Line Protection

UHV transmission line acts an important role to the security, stabilization and the economic profit of the whole power system operation. As the important influence of UHV line to the whole system, the requirements for their protective relaying are stricter than other protection. With the micro-computer based protection equipments for UHV line are used in power system by degrees, the effects are good as a whole, but some limitations are also found through the long-term field operation. In order to solve these problems, comprehensive research is done in this thesis.Respectively from the aspects of time and frequency domains, in this thesis, the transient noise of Capacitor Voltage Transformer(CVT) is focused on and its main components, influence factors and evolving characteristics are analyzed by using theory deduction and simulation analysis as the basic research methods, and thereby the foundation to further research on its influence to relay protection is established.CVT's transient may cause the overreach of distance relay. A proposed real-time CVT transient error estimation approach based on the chosen fundamental wave algorithm and the rated CVT parameters consists of two stages. The first stage obtains the error coefficient. The second stage estimates the measure error of the voltage amplitude according to the secondary side voltage of CVT. A novel adaptive distance relay approach which can adjust action thresholds according to the error is proposed. The approach hardly affects the action performance for normal lines and acts rapidly for short lines with close-in faults, which is verified by the results of simulations. The whole performance is improved greatly compared with common distance relay approach.Expanded Prony algorithm is brought into the field of CVT transient research in this thesis. The result indicates that Prony algorithm is very effective, rapid and precise for estimation of CVT's transient fundamental wave which should be paid attention by protection experts.For the impact of CVT transient to direction protection, careful research is done, and a new method on the zero-sequence and negative-sequence direction relay is proposed which improved the security of direction protection greatly.The 1000 kV extra-high voltage project has only got start in our country. Based on Jindongnan-Nanyang-Jingmen model project, its over-voltage is discussed. However, for extra-high voltage transmission protection researches so far mostly concentrate on phase-separated differential protection, the ordinary protection (distance relay and direction relay) are used in this thesis. In the end, for precise frequency measure, the information of the sine signal filtered by Fourier algorithm is carefully studied and the conclusion is achieved that the real part and imaginary part of the phasor gained by Fourier algorithm satisfy an identical equation with the shifting of the data window. Hence, a new algorithm of frequency measurement comes into being. Simulations proved this algorithm's high precision under different conditions.