RU2100888C1 - Power transmission line with lightning surge protective gear - Google Patents

Abstract

FIELD: power transmission. SUBSTANCE: power transmission line has at least one supporting structure, at least one insulated conductor, at least one insulator for insulating mentioned conductor from mentioned supporting structure, fastening member for holding power conductor on insulator, and insulator lightning surge protective gear in the form of at least one hole in conductor insulation spaced at certain distance from fastening member. EFFECT: simplified design. 2 cl, 2 dwg

Description

 The invention relates to high-voltage technology, and more particularly to power transmissions with devices for protection against lightning surges.

 Known high-voltage power lines (transmission lines), as a rule, include a power wire mounted on poles through insulators, as well as lightning protection devices, i.e. devices to limit overvoltages arising in the line when lightning enters it. A line may contain several power wires, for example, if the line is multi-phase. Supports are usually grounded, but there are also power lines with ungrounded supports. The power wire is usually connected to the power cable through a cable cut.

 A feature of the lightning protection of a power transmission line with insulated wires is that, if no special measures are taken, during a lightning overvoltage, the line insulator overlaps and then breaks down the solid insulation of the wire. It is very likely that a thunderstorm overlaps into an industrial frequency arc that burns at the point of insulation breakdown until the line is disconnected. This can lead to firing of wire insulation, line insulator, and in case of high short circuit currents (short circuit) to burn the wire.

 In Finland, NOKIA uses a system for lightning protection, consisting of a metal spiral wound on an insulated wire in the place of its attachment to the insulator and arc horns installed at the ends of the spiral and galvanically connected to the wire using biting clamps. Such a system is installed on each phase of a three-phase line in such a way as to provide a spark discharge gap between the arc horns of neighboring phases.

 During overvoltage, a single-phase overlap of the insulator to the ground occurs and an arc forms, which moves along a metal spiral wound over the insulation of the wire. Under the influence of electrodynamic forces, the arc passes to the arc horn and then spreads to the adjacent horn of the adjacent phase (located at a distance of about 30–40 cm). Thus, a single-phase fault is converted into two-phase. The arc of a two-phase short circuit burns between the arc horns until the line is disconnected, which leads to a significant burning of the horns. Therefore, their periodic replacement is necessary. In addition, two-phase short circuits create strong electrodynamic shocks on the transformer windings, which leads to accelerated wear of their insulation and the entire equipment as a whole. Frequent switching also increases the cost of routine revisions of the switching equipment.

 In Japan, non-linear surge arresters (SPDs) are widely used for lightning protection of overhead lines [1] The arrester is connected through the spark gap and is designed for a 2.5 kA lightning overvoltage current, since 95% of lightning currents measured in Japanese distribution lines are less than 1 kA. Arrester effectively limit the induced overvoltage, but in the case of a relatively rare event when the lightning overvoltage current exceeds the calculated level, they are damaged.

 It is highly desirable to install any lightning protection system for power lines with insulated wires, including arrester, in parallel with each insulator. With mass installation, the main problem of arresters is their high price. Approximately one 10 kV surge arrester costs $ 100,120.

 In the USA, for lightning protection of power lines with insulated wires, it was proposed to remove the solid insulation of the wire in the section of the line near the support, and install massive clamps at the insulation border [2] This device is the closest to the proposed one and is accepted as a prototype.

 In such a line, during overvoltage, a lightning shutdown of the insulator to an uninsulated section of the wire occurs. The overlap passes into a power arc, which, under the action of electrodynamic forces, moves along the wire until it reaches the insulation border on which the massive clamp is mounted. Further, the arc does not move and continues to burn, resting one of its ends on the clamp, until the line is disconnected. In the case of a system with a grounded neutral (as, for example, in the USA), short-circuit currents are very high and the automation responds relatively quickly to a short-circuit and disconnects the damaged line. However, significant burning of the clamps occurs, which determines the need for their periodic replacement. In addition, the formation of a power arc leads to the need to disconnect the line.

 All of the above determines the need to search for new technical solutions that increase the reliability and economic efficiency of lightning protection measures.

 The objective of the invention is to create a reliable and low cost in the construction and operation of the power line by increasing reliability and simplifying the design of means of protection against thunderstorms.

 The technical result is to increase reliability and simplify the design of means of protection against thunderstorms.

This object is achieved in that in a power line comprising at least one support, at least one insulated power wire, at least one insulator of the specified power wire from the specified support, a fastener fixing the specified power wire to the specified insulator, and means for protecting the insulator against lightning surges, according to the invention, the means of protection are made in the form of at least one hole in the insulation of the power wire, the hole being removed from the fastener at a distance determined from the expression
0.06 U ^0.75 h <l <0.5 U ^0.75 h, (1)
where l is the distance from the specified hole to the specified fastener, m;
h is the length of the overlapping path of the insulator being protected, m;
U rated line voltage, kV.

 Practically, the authors proposed a new method of lightning protection, based on the use of the sliding discharge effect on the surface of insulated wires. Lightning surge protection in the proposed power line is based on the following principle.

 After a lightning insulation overlap, the probability of establishing a power arc mainly depends on the average electric field created by the line operating voltage on the floor channel.

 The physical laws associated with the transition of pulsed overlap into a power arc have been studied in various laboratories around the world. Based on a generalization of the results of these studies and the operating experience of existing power lines in Russia, a normative ratio has been adopted that allows us to assess the likelihood of a power arc arising from lightning isolation ceilings (A.V. Korsuntsev. NIIPT, p. 21 22, 1975).

P _d (1,59 U _f / L 6) • 10 ^-2 (1,59E - 6) • 10 ^-2 , (2)
where EU _f / L is the average electric field along the overlapping path, kV / m;
U _f phase voltage of the line, kV;
L the length of the overlapping path, m

Formula (2) is valid at E≥10 kV / m. At E≅7 kV / m, the formation of a power arc is practically impossible
P _d 0 at E≅7 kV / m. (3)
As can be seen from (2), for a given rated voltage, the probability of an arc occurring is approximately inversely proportional to the length of the overlapping path. Therefore, by increasing L, it is possible to reduce P _d and, therefore, reduce the number of line outages.

On lines with wooden poles, which are additional insulators, the length of the overlap path is significantly longer than on lines with metal or concrete poles. As a result of this, the probability of arcing for wooden supports is significantly lower than for metal or concrete. Operational experience shows that for metal supports P _d 0.7 0.85, and for wooden P _d 0.3 0.5.

 The brief technical analysis of the phenomenon under consideration allows us to establish that the improvement of lightning protection of power lines is possible by lengthening the path of pulsed lightning overlap.

The minimum length of the overlap path L _forms , providing a sufficient increase in the reliability of protection, can be calculated by
L _form 0.06 U ^0.75 m
where U is the rated line voltage, kV.

The table shows the maximum published insulation lengths l _{out of the} published in the literature.

 As can be seen from the table, the length of the path of the sparkover, determined by the above formula, is at least 20 70% longer than the maximum lengths of conventional insulation.

 In FIG. 1 shows a diagram of a power line with a hole in the wire insulation; in FIG. 2 diagram of a power line with a piercing clip.

 The power line (Fig. 1) includes a wire 1 coated with insulation 2 and mounted on an insulator 3 using a metal strapping 4. The insulator 3 is mounted on a support 5. At a distance l from the end of the metal strapping 4, a hole 6 is made in the insulation 2 of the wire 1 . 7 indicates the discharge channel.

 In FIG. 2 shows another embodiment of a line in which piercing clamps 8 are installed at a distance l from the end of the metal strapping 4 in the insulation 2 of the wire 1.

 Lightning surge protection works as follows.

 During overvoltage, insulator 3 first shuts off, and then a sliding discharge 7 occurs on the surface of insulation 2. Due to the very long discharge length, a lightning flashover does not go into a power arc of industrial frequency and the line continues uninterrupted operation without shutting down.

The total lengths of lightning ceilings L l + h, at which the transition of a pulsed discharge into a power arc is excluded (E≅7 kV / m, formulas 2 and 3), are
for power lines 6 kV L 60 cm
for power lines 10 kV L 80 cm.

 The modifications of the power line shown in the invention are given only to explain their device and operating principles. Specialists in the art should understand that there may be deviations from the above examples, which are also covered by the claims.

Claims (2)

1. A power line comprising at least one support, at least one insulated wire, at least one insulator of the specified wire from the specified support, a fastener fixing the specified power wire to the specified insulator, and also means for protecting the specified insulator against lightning overvoltages characterized in that the said means of protection are made in the form of at least one hole in the insulation of the wire, and this hole is removed from the specified fastener by a distance determined from expressions
0.06 U ^{0 , 7 5} h <l <0.5 U ^{0 , 7 5} h,
where l is the distance from the specified hole to the specified fastener, m;
h is the length of the overlapping path of the insulator being protected, m;
U rated line voltage, kV.  2. The power line according to claim 1, characterized in that in the at least one hole in the insulation of the wire has a piercing clip.

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