Method with phase selection function for protecting composite-sequence component voltages of power transmission line

Abstract

The invention discloses a method with a phase selection function for protecting composite-sequence component voltages of a power transmission line. The method includes computing a real portion of a ratio of each fault-phase negative-sequence current to a zero-sequence current; dividing the real portion of the ratio of each fault-phase negative-sequence current to the zero-sequence current by an absolute value of the ratio to obtain a direction coefficient; computing a zero-sequence voltage at a protection setting range for the transmission line; computing an equivalent negative-sequence voltage at the protection setting range for the power transmission line; forming a composite-sequence component voltage protection criterion by the zero-sequence voltage at the protection setting range for the power transmission line, the equivalent negative-sequence voltage and the direction coefficients. The method has the advantages that relay protection for single-phase earth faults of the power transmission line is implemented owing to distribution characteristics of zero-sequence voltages and negative-sequence voltages along the power transmission line, influence of transition resistance on the performance of protection actions is eliminated in principle, and the performance of the actions is unaffected by load currents or fault positions.

Description

technical field [0001] The invention relates to the technical field of electric power system relay protection, in particular to a method for protecting the composite sequence component voltage of a transmission line with a phase selection function. Background technique [0002] The power frequency variation distance protection constitutes the distance protection by reflecting the sudden change of the working voltage amplitude. This method has the advantages of being less affected by the operation mode of the power system and having a strong ability to resist transition resistance. However, since the sudden change in the working voltage amplitude used in this method only exists in the initial fault stage, it cannot be used as a backup protection for EHV / UHV AC transmission lines. [0003] Impedance distance protection reflects the fault distance according to the measured impedance to distinguish whether the fault point is inside the protection zone or outside the protection z...

AI Technical Summary

Problems solved by technology

However, the action performance of impedance distance protection is seriously affected by the transition resistance. The main performance is that if the additional impedance generated by the transition resistance is resistive and inductive, it is easy to cause the impedance distance protection to refuse to operate when there is a fault in the protection zone of the transmission line; if the additional impedance generated by the transition resistance is resistive Capacitance is easy to cause the impedance distance protection action to exceed when there is a fault outside the protection zone of the transmission line

[0004] Over / extreme voltage AC transmission lines are often also heavy-duty transmission lines. Heavy-load currents will cause impedance distance protection to malfunction or refuse to operate. The impact of heavy-load current on the performance of impedance distance protection cannot be ignored.

Under the condition of overload transmission, the transmission line has no faults. The measured impedance of the traditional distance protection will seriously deviate from the actual measured impedance due to the influence of the overload current, which will easily lead to the misoperation of the traditional distance protection, which will cause the power grid to expand the scope of power outages, and even cause large load transfers to threaten other transmissions. The normal operation of the line has brought huge potential safety hazards to the safety of the power grid

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