RU2576017C2 - Single phase earth fault current limitation method for overhead transmission lines in networks with insulated neutral - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: method consists in single phase earth fault current limitation by the variable active resistance with the nonlinear volt-ampere characteristic which has sufficient value for current limitation at the phase voltage of high voltage power transmission line and low value at the atmospheric overvoltage. The resistance is series connected to the grounding device circuit on each support.

EFFECT: improvement of reliability and safety of operation of overhead power transmission lines.

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Description

The invention relates to electrical networks and is intended to improve the safety of the operation of overhead power lines (VLEP) in distribution networks with insulated neutral.

A known method of limiting the current of a single-phase earth fault (OZZ), according to which the limitation is achieved due to the occurrence of resonance between the capacitance of the electrical network and the inductance included in the ground circuit of the neutral transformer. According to the method, a coil is connected to the neutral circuit of the transformer, the inductive conductivity of which at the industrial frequency is equal to the total capacity of the electrical network. When an SCR occurs, the capacitive current at the location of the insulation damage is summed with the inductive current equal to it and the opposite in phase. Thus, by compensating inductive capacitive current, the development of an electric arc is prevented and contact voltage is limited at the point of insulation damage. (“The extinguishing reactor”, material from Wikipedia, the free encyclopedia [Electronic resource] URLL: http://m.wikipedia.org/wild/%C4%F3%E3%EE%E3%E0%F1%FF%F9%E8 % E9_% F0% E5% E0% EA% F2% EE% F0 (accessed 12/2/13).

The disadvantages of this method are: the difficulty of fine-tuning the inductance for the capacitance of a branched electric network with uneven parameters, the likelihood of intermittent arc faults to earth, accompanied by overvoltages in other phases.

The objectives of the invention are to increase the reliability and safety of high-voltage lines, by eliminating the risk of overvoltage between the ground and the phases with intact insulation, as well as eliminating contact voltage in the place of damage to the insulation of the support.

This problem is achieved due to the fact that in the known method of limiting the currents of a single-phase earth fault instead of inductive grounding, included in the neutral of the transformer, elements with a variable active resistance having a non-linear current-voltage characteristic (CVC) are included in the grounding device circuit at each support.

The operation of the invention is illustrated by drawings, where in FIG. 1 shows a diagram of the operation of the method during breakdown of the VLEP insulation, and 2 - scheme of the method during lightning overvoltage.

The scheme of the method during breakdown of insulation contains: insulation 1 of the VLEP support, metal structure 2, variable resistance 3 with a non-linear I – V characteristic, the path of current flow OZZ marked with a wavy line.

The scheme of the operation of the method during lightning overvoltage contains: insulation 1 of the VLEP support, metal structure 2, variable resistance 3 with non-linear I – V characteristic, lightning discharge 4, the path of the lightning discharge current marked with a wavy line.

The proposed method works as follows.

When the breakdown of insulation 1 of the support on the metal 2 appears, a potential equal to the potential of the phase with damaged insulation. The characteristic of the variable resistance 3 is selected in such a way that if there is a phase potential on the metal structure 2, its value is so large that the current through the grounding device is practically absent. In this case, the voltage between the metal structure 2 and the phases with the whole insulation increases to the linear voltage of the VLEP on only one support, which leads to an increase in the reliability of the operation of the VLEP by reducing the wear of the insulation on the remaining supports.

Since there is no voltage relative to the ground on the grounding conductor of the support below the set alternating resistance, it will also be absent in the zone of possible contact with the grounded metal structures of the high-voltage line. Thus, the goal is to increase the safety of VLEP operation.

The method allows you to save the functional properties of grounding devices designed to protect the VLEP supports from lightning overvoltages. In case of lightning discharge 4 on the metal structure 2 of the support, the voltage reaches a breakdown value of variable resistance 3. In this case, excess voltage is discharged to the ground. Thus, overlapping of the insulation between the metal structure and the phase is prevented.

The application of this method will significantly improve the reliability and safety of operation of high-voltage power lines with isolated neutral. The method can be found especially widely in the operation of VLEP in populated areas, where the issue of the safety of the population and animals is most categorical.

Claims (1)

A method of limiting the current of a single-phase earth fault for an overhead power transmission line (VLEP) in an isolated neutral network, which consists in limiting the current of the OZZ resistance, characterized in that the resistance has an active alternating character with a non-linear current-voltage characteristic and is connected in series to the grounding device circuit on each VLEP support.

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