Compositive Study On Protection Of Extra High Voltage Shunt Reactor And Transmission Line

With the fast development of electric power industry in china, the electric power grid's scale is bigger and bigger, the voltage grade gets higher and higher. It will be the inevitable trend that electric power grids interconnect. The safety and stability of Extra High Voltage (EHV) and Ultra High Voltage (UHV) transmission lines are a question faced by electric power grid in our country. Shunt reactors are used to provide inductive reactance to compensate for the effects of high charging current of long transmission lines. For light load conditions, this charging current can produce more leading reactive kVA than the system can absorb with risk of instability or excessively high voltages at the transmission lines, especially at the transmission lines terminals. Shunt reactors are usually equipped at one end or two ends of transmission lines. When shunt reactors are faulted, the typical relaying practice for line-connected reactors is to trip the local line breaker and transfer trip the remote line breaker. So the safe operation and stability of shunt reactors play an important role in the safety and stability of the whole electric power system. Especially the recent power cut in America and Europe produces severe results, it shows that safe and reliable control measures are one of the key problems of electric power system. Based on the analysis of EHV long transmission lines'power frequency overvoltage, the paper presents the application of shunt reactors in EHV transmission lines, and studies the protection of EHV shunt reactors, the development of shunt reactor equipment, the protection of EHV lines longitudinal differential and the fault location on double ends of EHV transmission lines. Turn-to-turn faults in shunt reactors present a formidable challenge to the protection engineer. The current and voltage changes encountered during a turn-to-turn fault can not be of the same order of magnitude as variations expected in normal service, and therefore, sensitive and reliable protection using the conventional relaying schemes are not possible. The paper analyzes the shortcomings of conventional zero-sequence power direction protection, and proposes a new protection scheme which uses zero-sequence and negative-sequence power direction protection at the same time. A novel energy protection principle is presented to solve the question that the sensitivity of zero sequence direction protection is low when the shorted-turns percentage of turn-to-turn fault is small.Based on zero-sequence and negative sequence components, the corresponding energy function is built, it can judge the fault type sensitivily and reliably when shunt reactor faults. Because the voltage grade is higher and the transmission distance is longer in EHV lines, the transient course after faults is complicated. When shunt reactors are adopted, the transient course is worsened. In order to keep the stability of whole electric power system, it should clear faults as soon as quickly, so novel protection principle which can meet the new demands is needed. The paper proposes two different kinds of discrete long line equation, on the basis of discrete equations, a novel protection principle based on power balance which uses voltage and current data on two ends of lines is proposed, the protection principle can make fast protection for the transmission lines with shunt reactors. On the fact that a fault location principle on double ends may produce fake roots, an improved fault location method on double ends is presented. The improved fault location method is based on discrete long line equation, and can make accurate fault locations under different faults. At last, the paper summarizes the whole paper and lists the work which will be finished in the future.