Research On Adaptive Reclosing Sequence Of Transmission Line

Automatic reclosure is widely used in transmission lines.If the reclosing onto a permanent fault,the short-circuit current will cause a secondary impact on the system and equipment in a short time.The concept of adaptive reclosure is of great significance for transmission line protection.The research content of adaptive reclosure mainly includes distinguishing between transient faults and permanent faults and optimization of reclosing sequence.At present,most of the methods for discriminating between permanent faults and transient faults focus on the single-phase reclosure and the three-phase reclosure with shunt reactor lines.In this paper,for the optimization method of adaptive reclosure sequence of transmission lines,the following research contents are carried out:First of all,for a line without a shunt reactor,the energy storage in the transmission line will rapidly decay after the three-phase circuit breakers on both sides of the transmission line are tripped because of a fault or reclosing failures.At this time,it is impossible to determine whether the fault is a transient or permanent fault.In response to this problem,this paper distinguishes between transient faults and permanent faults by the method of phase-by-phase reclosing sequence control,and proposes an adaptive reclosing sequence scheme based on this method.For an asymmetrical ground fault,the circuit breaker on the side of a non-faulted phase is first reclosed.Use the coupled voltage of the faulty phase to distinguish transient or permanent faults.For a short-circuit fault between two phases,first of all,the circuit breaker on the side of one of the faulted phases is reclosed.Distinguish between transient and permanent faults according to the terminal voltage of another faulty phase.For permanent faults,trip the circuit breakers that have been reclosing,and at the same time block the reclosing of this lines;for transient faults,the effect of overvoltage of reclosing is taken into account,and other circuit breakers are closed in sequence.This solution can reduce the impact of permanent faults on the system,quickly restore power supply,and improve the stability of the systemSecondly,in the UHV AC/DC transmission system,when the AC transmission line near the inverter side fails and then reclosing onto a permanent fault,it may cause continuous commutation failure,and in extreme cases may lead to pole-blocked.In order to avoid the commutation failure caused by reclosing of faults,this paper proposes an adaptive phase-by-phase reclosing sequence for the double-circuit transmission lines on the inverter side of the AC-DC hybrid system.After the double-circuit transmission lines fault,the protection action trips the fault phase circuit breakers.For the cross-country ground faults,firstly,the two different-name breakers containing the same-name fault phase(if any)on the far side of the commutation bus are reclosed.For the cross-country unground faults,first,the two differ-ent-name breakers containing the same-name fault phase(if any)on the far side of the commutation bus are reclosed.Then use the zero sequence current ratio or fault phase current to determine whether the reclosing is successful.The sequence scheme can reduce the number and duration of commutation failures on the inverter side when reclose with faults,and even avoid the commutation failureThe PSCAD/EMTDC simulation verifies the validity of the proposed sequence scheme.