The Research On Over-voltage Extinction And Protection & Control Strategy For UHV Transmission Line

With the persistent development of our state economy, the demand of electric power is increasing rapidly. In order to satisfy the need of large-capacity remote transmission and national interconnected network while ensuring secure-and-reliable operation of power system, we must strengthen the construction of skeleton grid. An economic and valid approach to strengthen the skeleton grid is to construct the ultra high voltage transmission lines. So it is imperative to study the new classification of voltage in advance. Over-voltage is the premise and basis of other research subjects, even is the one of critical factors which decides whether the UHV is adopted. It not only affects the insulated intension designs of power equipments, such as transformer, switch and transmission line, but also is concerned with whether the power system can operate safely and reliably.Due to the lower over-voltage tolerance of UHV insulators, the economic losses is quite enormous for the breakdown and renewal of insulators, and it's not worth raising the level of insulation purely. The allowable voltage peak value of UHV transmission line is directly associated with the factors such as voltage duration and so on. So it's feasible to restrain the over-voltage by the action of protection,reclosing configuration and its relevant controlling devices of UHV transmission line.At first, the over-voltage based power frequency and it's restraint by using the shunt reactors has been discussed. Then the mechanism of over-voltage production has been analyzed including the conditions of single or double sources connected with long line without shunt reactors. The distributing voltage along the line with different mode of reactor connection has been analyzed at the meantime.Subsequently, the transient over-voltage in different operational conditions have been studied through building the simplified transmission line model based on lumped parameter with T orπmodel. The approximate expression of various transient over-voltage have been obtained by analysis and deduction according to the simplified transmission line model.Finally, after theoretical analysis and carrying on a great deal of EMTDC simulations, the general rule of over-voltage for UHV transmission line has been generalized. Based on the results, the feasibility and practicability of over-voltage restraint and protection controlling strategy has been testified. Also, the chief method and suggestion has been given here. Based on the discussion of secondary arc extinction methods, the proper value of the neutral reactor is also put forward to ensure the successful reclosure of single pole autoreclosor.