Adaptive three-phase symmetric fault phase selecting method for ultra high voltage transmission line

Abstract

The invention provides an adaptive three-phase symmetric fault phase selecting method for an ultra high voltage (UHV) transmission line. The method comprises the following steps: adopting three-phase current on a fault circuit; calculating a zero-sequence current component, determining whether the zero-sequence current component exists or not, and respectively determining a threshold value Iset and a margin ratio Kset in three-phase symmetric fault phase selecting element criterion according to existence or not of the zero-sequence current component; calculating three-phase current break-variables delta IA, delta IB and delta IC; determining whether the amplitudes of the three-phase current break-variables are more than the set threshold value; and determining whether a ratio K between the maximum break-variable and the minimum break-variable in the calculated three-phase current is less than the definite value Kset of the set margin ratio or not. The method has reliable phase selection result and high action speed, can accurately and quickly select three-phase faults when convertible three-phase faults occur; and the provided three-phase symmetric fault phase selecting element is not affected by a transition resistor, and the transition resistor accelerates decay rate of a transient state component and ensures the break-variable to be reduced in asymmetric fault, thus being in favor of selection of three-phase fault.

Description

A phase selection method for self-adaptive three-phase symmetrical faults in UHV transmission lines technical field The invention relates to the field of relay protection for power system transmission lines, in particular to a phase selection method suitable for self-adaptive three-phase symmetrical faults of UHV transmission lines. Background technique Negative sequence direction longitudinal protection has a long history and rich operating experience. The UHV transmission line is long, the distributed capacitance is large, and the action range of the directional element is half a plane. After a lot of analysis, it is concluded that the negative sequence directional longitudinal protection can be used as the main protection scheme of the UHV line. The phase-to-phase distance of UHV transmission lines is generally more than 15 meters, and the possibility of completely simultaneous three-phase faults is very small. Most of the three-phase faults have short-term asymmetry at...

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Problems solved by technology

Therefore, none of the existing phase selection schemes can reliably determine the three-phase short circuit, and it is necessary to propose a new three-phase symmetrical fault phase selection element

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