Research On The Principle Of Adaptive Reclosure For Double-circuit Transmission Lines

Because of the economic efficiency, double-circuit transmission lines on thesame tower are being more widely used in China's EHV transmission system. As theauto-recloser installed on the double-circuit lines operates in the conventional scheme,the possibility that the tripped phases may be reclosed to permanent faults does exists,which may cause the double-circuit lines both be tripped when reclosed topermanent cross-line faults, which is a quite severe threat to the stability of powersystem.To avoid the disadvantages mentioned above, a new technique called"adaptiveauto-reclosure"is proposed byChinese scholars, which first makes a distinction of thefault characteristic, and then would reclose the tripped phase on condition that thefault is transient. It is no doubt that the contribution to improve the power systemreliability and stability will be significant if the adaptive technique could be applied tothe auto-reclsoers of double-circuit transmission lines.When double-circuit lines are parallel connected at both ends, it is possiblethat more than two healthy different phases may exist after a multi-phase fault. In thispaper, an optimal trip scheme for double-circuit lines is proposed, compared toconventional trip scheme, the proposed scheme has advantages on trying to maintainthe system transmission capability, restraining the unbalanced components injectedinto system. It is available to improve the system stability, and creates better operationconditions for auto-devices like auto-recloser. Dynamic simulation and BPAsimulation have proved the conclusions.The precondition that double-circuit lines can be reclosed is that: after the faulthas been tripped, there are at least two different healthy phases still running.Consequently, there is probably going to be a multi-phase reclosure after amulti-phase fault. In this paper, it is proved that the electrical quantity at the faultpoint reflects the fault characteristic more clearly, and is less affected by the loadcondition. Based on this conclusion, an adaptive auto-reclosure criterion and reclosingstrategy for double-circuit lines are proposed, which can adaptively distinguish thefault characteristic under most fault types, and declining periodic component has lessaffect on the validity. For transmission lines of long distance or large distributed capacitance, usinglump parameter models for calculation can result in great error. Thus a more precisemethod for the calculation of voltages at fault point and power frequency voltages oftransient faulted phases is proposed based on the uniform transmission line model,which is not affected by the distribution parameter effects and helps to improve thereliabilityand sensitivityof the criterion.