The Research On Over-Voltage And Protection & Control System For UHV Transmission Line

With the rapid development of our state electrical industry, the interconnection of electrical networks has been an inevitable trend. In states of the super-large-capacity remote transmission and the super-large-scale interconnected network, security safeguard and defense system are the new challenges for engineering and technical personnel of electrical industry in the coming period. The grid structures of our state power system are comparatively weak, and the ability for bearing accidents is rather weak. Even though relay protections can trip faults rapidly in time, it is also hard to avoid the spread of the accident. Accordingly, strengthening the construction of skeleton grid is the ultimate resolvent to ensure secure-and-reliable operation of power system. However, an economic and valid approach to strengthen the skeleton grid is to construct the ultra high voltage (UHV) transmission lines. As far as UHV transmission line is concerned, besides to satisfy the demand of system reliability, its configuration and action cooperation for protection and reclosure must take the occurrence of high-risk over-voltage into consideration. The allowable voltage peak value of UHV transmission line is directly associated with the factors such as voltage duration and so on. Therefore, the over-voltage restraint must be concerned especially in the action of protection and its relevant controlling devices of UHV transmission line. Aiming at the over-voltage and protection & control system of UHV transmission line, the main contributions of the paper are as follows: (1) The paper proposes that the tripping and closing operation of the two terminal breakers of UHV line must comply with certain operation orders. The difference of tipping time between two terminal breakers should be limited within 0.04~0.05s so as to avoid equipment insulation damages caused by the over-voltage. (2) The paper proposes that the reclosure of UHV transmission line must take limiting over-voltage into consideration. The research indicates that the reclosing time difference between two terminal breakers should be greater than 0.2~0.3s. Single-phase-reclosure is more favorable to improve secure and stable operation of power system. The paper proposes a novel scheme of single-phase adaptive reclosure to limit single-phase-reclosure over-voltage. (3) The paper proposes the novel single-phase adaptive reclosure techniques, which include phase criterion that is applicable to transmission line without shunt reactors, and adaptive reclosure criterion based on beat-frequency characteristics that are applicable to transmission line with shunt reactors. The proposed techniques develop more wide application scopes for single-phase adaptive reclosure. (4) The paper proposes a novel shunt reactors turn-to-turn fault protection that is based on negative-sequence power direction theory. The proper range of neural reactor is presented in the cases of different compensation degrees of shunt reactors. So it is valid to limit the resonance over-voltage when the single-phase is seperated after a single-phase-fault occurs, and to accelerate the arc extinguishment and ensure the success appliancation of single-phase-reclosure in the UHV transmission line. (5) The paper proposes the action cooperating relation of the line protection and the shunt reactor. The whole scheme of over-voltage restraint, protection and control of UHV transmission line is proposed, including action characteristics and cooperation relations among protective relays, reclosor and shunt reactors and etc. The scheme does not only benefit to ensure the reliable operation of the UHV transmission line, but also be able to restrain the over-voltage economically and effectively. (6) The paper presents a novel fast filtering algorithm, which can be applied to relay protection of EHV and UHV power system. The algorithm is based on the combination of constrictive band-pass filter and half-cycle discrete Fourier transform (HCDFT), and it only requires 11ms data window. Analyses and simulation verify that the filtering performance of the presented algorithm is very valid to meet the fast tripping demand of UHV transmission line.