Surge protection devices for a high-voltage power line

Abstract

A surge protection device comprising: a surge arrester (9) and a spark gap (11) with a first electrode (13) which is connected to one end of the surge arrester (9), wherein the spark gap (11) and a central axis of the surge arrester (9) enclose an angle of less than 180°, characterized by the fact that a torsional moment compensation element (15) is provided which is dimensioned to counteract a torsional moment of the first electrode (13) about the central axis of the surge arrester (9) caused by wind.

Description

[0001] High-voltage power lines, i.e., power distribution or transmission lines, are typically suspended from power poles by insulators, which serve to electrically isolate a line voltage from ground and additionally prevent electric current from flowing from the power distribution or transmission lines to the power pole.

[0002] Temporary or transient overvoltages can lead to an insulator flashover, which can cause a system failure and potential damage to the insulator and high-voltage lines. This can result in a follow current in the network, leading to an unintended shutdown of the line. Damage to the insulator, pylon, and line is also likely.

[0003] To reduce insulator flashover or to decrease the probability of an insulator flashover, a surge arrester, also known as a line arrester, is typically used in parallel with the insulator.

[0004] Surge arresters are connected to the power distribution or transmission lines to divert electrical surge currents to earth and thus prevent damage to the high-voltage lines and the devices connected to them.

[0005] Surge arresters offer high resistance to normal operating voltage on high-voltage lines and very low resistance to surge currents caused by sudden high-voltage events, such as those caused by lightning strikes. They thus reduce the risk of insulator flashover during overvoltage events.

[0006] After the surge currents are dissipated, the voltage drops and the surge arrester returns to its high-resistance state. However, sometimes the surge arrester is overloaded and fails, so the high-resistance state is not reliably restored. In this case, the surge arrester continues to provide an electrical path from the high-voltage line to ground.

[0007] One possible approach to addressing this problem is the use of so-called non-gapped line arresters (NGLAs), which are surge arresters without an external spark gap. These are combined with a disconnect device, usually an explosive charge, that physically disconnects the surge arrester from the power line when needed. However, in many areas, especially those prone to forest fires, the use of such explosive devices is problematic.

[0008] Even cutting devices without explosive charges tend to produce strong sparks during the cutting process, which can cause hot particles to fall.

[0009] Furthermore, the constant phase-to-earth voltage acting on the NGLA usually requires a high rated voltage, and installation sites at altitudes above 1000m necessitate long jump distances. This increases the length of the required surge arrester, which usually results in the specified phase-to-earth distances on the power pole being undercut.

[0010] Another approach is to use so-called EGLA arresters (Externally Gapped Line Arresters), which are electrically connected in parallel to the line insulators on the transmission line masts and in which a spark gap is provided in series with the surge arrester.

[0011] Examples of this are also shown in US 7 292 424 B2, US 5 283 709 A, US 5 172 297 A, DE 692 19 935 T2 or DE 10 2017 215 127 A1.

[0012] DE 10 2017 215 127 A1 discloses an arrangement for power transmission with a high-voltage pylon having several cross arms, each supporting at least one high-voltage line, wherein an insulator keeps each cross arm at an insulation distance from a high-voltage line, and wherein a surge arrester is connected in parallel to each insulator. The insulation distance is at least 15% smaller than in a design of the arrangement without a surge arrester.

[0013] DE 692 19 935 T2 discloses an improved line arrester device comprising a nonlinear resistor. The arrester device includes a pair of arc horns, one on the grounding side and one on the line side of the arrester device, with an air discharge gap between them. The air discharge gap is electrically connected in parallel with the resistor. The length of the air discharge gap is selected such that no flashover occurs in response to currents less than the rated discharge current of the resistor, but a flashover occurs in response to a current greater than the rated discharge current but less than a critical discharge current of the resistor.

[0014] With this arrangement, the resistor is protected against lightning impulse currents that are greater than the critical discharge current.

[0015] US 5,172,297 A shows a surge arrester with a surge arrester unit that is arranged between the line and earth sides of transmission lines and parallel to an insulator across an air discharge gap. Surge arrester elements incorporated in the surge arrester unit are activated by a reference voltage that is greater than the rated line-to-earth voltage of the lines but less than the sonic phase surge resulting from a single earth fault.

[0016] US 5,283,709 A discloses a surge arrester designed for a power transmission line to prevent damage to a line-supporting insulator string from a lightning strike. An arrester unit is rigidly mounted on a fixture attached to an arm structure of a tower, such that its grounded side is electrically isolated from the fixture, and an operational sensing device is connected between the grounded side of the arrester unit and the fixture. The operational sensing device is configured as an operational indicator, a flashover indicator, and / or an operational recording device. In the event of a lightning strike, the operational sensing device detects lightning current flowing from the grounded side of the arrester unit to the fixture.

[0017] US Patent 7,292,424 B2 discloses an arc horn system with a dynamic current-breaking capability, which includes, for example, a dynamic current-breaking capability sufficient for short-circuit faults and other purposes. The arc horn system is capable of repeatedly maintaining the dynamic current-breaking capability.

[0018] In other words, the EGLA, in addition to a classic surge arrester, also called an SVU (Series Varistor Unit), usually consisting of a stack of metal oxide varistor blocks in a porcelain or plastic housing, features an external air gap or spark gap in series with the surge arrester. When lightning strikes the high-voltage line or pylon, which can lead to a reverse flashover if the pylon is poorly grounded, the spark gap is dimensioned so that the surge arrester becomes conductive and the lightning impulse current can be safely discharged to ground without the insulator itself flashing over.

[0019] The surge arrester or surge protection device is dimensioned so that the varistors interrupt the mains follow current generated after the flashover at the zero crossing, thereby immediately interrupting the arc at the spark gap and directly eliminating the resulting earth fault.

[0020] The gap between the spark gap must be sufficiently large to prevent flashovers during switching-induced impulses, i.e., the energy-rich switching overvoltages on the conductor, and to ensure safe electrical separation of the line from ground even with overloaded surge arresters after the overvoltage has subsided.

[0021] The air gap of the spark gap must still be sufficiently small to prevent flashover at the insulator itself in the event of lightning overvoltage, and to ensure that flashover occurs exclusively at the spark gap of the EGLA.

[0022] For details of these two techniques, please refer to ISBN: 978-2-85873-560-0 “TECHNICAL BROCHURE Effectiveness of line surge arresters for lightning protection of overhead transmission lines” Copyright 2021.

[0023] Especially at very high voltages, for example in the range of 500 or 800 kV or more, the air gaps of the spark gaps of an EGLA (Electrostatic Discharge Arrester) become considerably long, for example 2 m or more. Furthermore, the pylons supporting such high-voltage lines are very tall. This results in the surge arresters and the electrodes of the spark gaps connected in series with the surge arresters being highly exposed to wind.

[0024] In other words, conductor arresters are exposed to strong wind loads and are subjected to continuous winds with static bending moments and wind gusts with cyclic bending moments and torsional moments due to resonant self-vibration.

[0025] While modern surge arresters, thanks to their fiberglass-reinforced plastic housings, can withstand bending loads well, they have significant weaknesses under torsional loads. Furthermore, since surge arresters are in operation for many years, it is crucial to ensure that even frequent mechanical stresses do not cause damage that could impair the reliable function of the surge arrester, such as fatigue fractures and similar defects.

[0026] Surge arresters are typically cylindrically symmetrical, so no torsional forces act on them around their central or longitudinal axis. Therefore, torsional or torque loads are not known to occur in arresters without an external spark gap (NGLA), as they are generally rotationally symmetrical and held at both ends, while the other end is only electrically, but not mechanically, connected.

[0027] Torques from wind loads on electrical connecting lines can be ignored due to the small wind attack surface of connecting lines.

[0028] The situation is different, however, with external spark gap arresters (EGLAs). In surge arresters with an external spark gap, an electrode of a spark gap is typically connected to one of the arrester terminals. These electrodes can reach considerable sizes and weights, for example, up to 2 meters in length and weighing more than 5 kg. The wind-exposed surface area, its length, and the associated leverage of this electrode increase when used at higher system voltages, as phase-to-ground distances also increase and longer electrodes are required. This, in turn, increases the applied static and cyclic moments.

[0029] A surge protection device with an insulator and an EGLA (electromagnetic field-locked electrode) is often constructed in a triangular configuration. The insulator forms the longest side, while the other two sides are formed by the surge arrester on one side and the spark gap on the other. The conductor is held in place by two V-shaped insulators. This design, also known as a V-string insulator arrangement, offers several advantages, particularly regarding the height of the conductor. However, it also results in the spark gap electrode being connected to the surge arrester at an angle of 90° or more and less than 180° to its longitudinal or central axis. This angle can cause a torsional moment to occur due to wind loads acting on the spark gap electrode.

[0030] It is also known that in this V-string insulator arrangement, the connection between the electrode of a spark gap and a surge arrester is designed in such a way that the length of the spark gap can be adjusted by a few centimeters. This allows for length tolerances in the actual application on the power pole, so that part of the electrode is located on the side of the surge arrester opposite the spark gap. This adjustment of a few centimeters has no significant influence on the bending moment or the torsional moment that the electrode exerts on the surge arrester.

[0031] To avoid this problem, the electrode of the spark gap attached to the surge arrester has previously been dimensioned small, or the problem was circumvented by placing the spark gap on the extension of the central axis or axis of symmetry of the surge arrester. However, this design, which is mostly used in so-called I-string configurations where the high-voltage line is connected vertically to the pylon via a single insulator, is disadvantageous for a number of reasons. In particular, the distance between the planes of the high-voltage lines increases, and thus the height of the pylons increases.

[0032] It is also known that symmetrical electrodes are used in these I-string insulators when it can be assumed that the conductor cable changes the insulator's inclination due to wind influence. The shape of the electrode serves to maintain a constant electrode spacing within the spark gap. Such arrangements require considerable space between the support arms of the power pole because the surge arresters must be aligned with the spark gap. This necessitates significantly longer insulators and increases the height of the poles.

[0033] Therefore, greater flexibility is desired in the design of both the electrodes of the spark gap and the geometry of the arrangement of the individual components of an EGLA.

[0034] The object of the present invention is therefore to provide an overvoltage protection device for a high-voltage line which is improved in terms of its mechanical stability and allows greater flexibility in its design.

[0035] The problem is solved by an overvoltage protection device according to claim 1. The dependent claims relate to further advantageous aspects of the invention.

[0036] The invention is described below with reference to a preferred embodiment and the accompanying figures. These figures show: Fig. 1: the overall structure of a surge protection device according to the invention; Fig. 2: a detailed view from Fig. 1, and Fig. 3: a power pole with surge protection devices according to the invention attached to it.

[0037] Fig. Figure 3 shows a pylon 1 of a typical high-voltage power line 3. Lines for the three phases of the high-voltage current are arranged on three levels. A shielding conductor 5 may be provided on a fourth level above.

[0038] The high-voltage lines 3 themselves are connected to the power pylon 1 via insulators 7. The length of the insulators 7 is chosen such that a flashover between the respective high-voltage line 3 and the power pylon 1 can be prevented with sufficient safety.

[0039] In addition, a series connection consisting of at least one surge arrester 9 and a spark gap 11 is provided in parallel to each of the insulators 7.

[0040] The surge arrester 9 can be relatively small in this EGLA configuration. Furthermore, surge arresters with plastic housings can be used. The surge arrester 9 is rigidly connected to the power pole 1 at one end, while the other end is free. It is therefore advantageous to arrange the surge arrester(s) 9 vertically to avoid gravity-induced bending moments on the surge arrester.

[0041] The other end of the surge arrester 9 is connected to a first electrode 13 of the spark gap 11. The second electrode, or counter electrode 17, of the spark gap 11 is connected to the insulator 7 on the side where it connects to the high-voltage line 3. In this way, the surge arrester 9, the spark gap 11, and the insulator 7 form a triangle, with the insulator 7 forming the longest side of the triangle.

[0042] This second electrode 17, which helps to reliably determine the length of the air gap of the spark gap 11, can optionally be omitted, in which case the line-side insulator connection, a control ring, a spark horn, a clamp, or the high-voltage line itself constitutes the "second electrode". An insulator control ring is typically used.

[0043] The appropriate dimensions for the surge arrester 9 and the length of the spark gap 11 are described in detail in the aforementioned prior art, so that reference can be made here to the disclosure listed therein.

[0044] Due to the first electrode 13, which is attached to the free end of the surge arrester 9 and forms an angle of less than 180° with it to the longitudinal axis, the rotational symmetry about the symmetry or central axis of the surge arrester 9 is broken. The angle between the central axis of the surge arrester 9 and the spark gap 11 is preferably 90°, as this allows for the most compact design in the vertical direction and thus the smallest possible distance between the planes of the high-voltage lines 3 on the pylon 1. However, angles between 90° and 120° or between 90° and 150° are also conceivable, to name just a few examples.

[0045] Since the surge arrester 9 hangs on the power pole 1 at a considerable height, often between 30 and 100 m, the surge protection arrangement is exposed to a potentially large and changing wind load, which leads to both a permanent load in constant wind conditions and to fluctuating loads during wind gusts.

[0046] Suitable surge arresters 9 are known, for example, from EP 4 016 555 A2 or from DE 10 2015 007 707 A1. With such surge arresters, the resistance to bending moments is many times greater than the resistance to torsional moments about the central axis. Typical values ​​for a permissible load in the direction of the central axis are in the range of 2000 Nm to 4000 Nm, while the torsional strength is in the range of 100 Nm.

[0047] To prevent damage to the surge arrester 9 over time due to torsional loads, an additional torsional moment compensating element 15 is provided according to the invention, which compensates for the torsional moment. An example of this torsional moment compensating element 15 is a wind fin, which is installed as a counter-lever on the side facing away from the electrodes at the same attachment point on the surge arrester 9, and which, through its lever and its wind-exposed surface, produces approximately the same torsional moment – ​​but in the opposite direction of rotation – and thus compensates the electrode torque or torsional moment about the central axis of the surge arrester 9.

[0048] Care must be taken to ensure that the wind fin 15 does not widen the mast geometry. In power line construction projects, widening the mast geometry is not permitted or even undesirable due to prescribed corridors and safety distances. Furthermore, the lightning protection concept of the power mast 1 would be significantly affected if the wind fin extended laterally far beyond the power mast.

[0049] This is a fundamental difference from an asymmetrical electrode arrangement, as occasionally used in I-string configurations, where the effective electrode portion is simply mirrored on the opposite side of the connection to the surge arrester 9. While such a design would compensate for the wind torsional moment, the long projection of 2 m or more that this design would require in a V-string configuration is impractical due to the pylon geometry.

[0050] According to the invention, a short wind fin with a larger wind attack area is therefore used as a torsional moment compensation element 15.

[0051] Preferably, the torsional moment compensating element 15 is attached to the same end of the surge arrester (9) as the first electrode (9). However, this is not mandatory. The torsional moment compensating element 15 can also be attached to the first electrode 13 itself. It is also possible to attach the torsional moment compensating element 15 to a different location on the surge arrester.

[0052] Preferably, this wind fin 15 should have sufficient weight to compensate for any bending or tilting moment exerted by the first electrode 13 on the surge arrester 9 in a direction perpendicular to the central axis of the surge arrester 9. This also compensates for the permanent bending moment, contributing to an advantageous distribution of forces within the arrangement.

[0053] Furthermore, in a further advantageous embodiment of the invention, it is possible to provide a damping element 19 within the structure of the wind fin 15, so that a certain elasticity is provided which can dampen the resonant natural oscillation of the surge arrester 9.

[0054] Preferably, the first electrode 13 on the side exposed to the wind should have a round surface, since this results in a lower coefficient of air resistance and therefore a lower moment.

[0055] Furthermore, the wind fin 15 itself should preferably have a flat and large surface area, as this results in a high drag coefficient and thus a large bending moment acting on a smaller area. This reduces the additional bending moment load perpendicular to the central axis of the surge arrester 9 at the arrester connection.

[0056] Furthermore, the connection between wind fin 15 and the discharge terminal should preferably have the smallest possible cross-sectional area in order to further reduce the additional bending moment load at the discharge terminal.

[0057] The calculation of the wind bending moment can be carried out according to IEC 60099-4 ed. 3.0 Annex G.4.

[0058] A guideline for the dimensioning of the wind fin 15 can be obtained by the expert from the following equation 1, which is based on corresponding calculations from the aforementioned standard. M=0=AEL×LF1×C1×P−AWF×LF2×C2×P where P is the dynamic wind pressure P1 / 2 × v 2 , ρ the density of air at 1.013 bar and 0°C = 1.29 kg / m³ 3 , v the wind speed, A EL the cross-sectional area of ​​electrode 13, A WF the cross-sectional area of ​​the wind fin 15, LF1 is the distance between the conductor's central axis and the electrode's centroid. LF2 the distance between the central axis of the surge arrester 9 and the centroid of the wind fin 15, C1 is the air resistance coefficient of electrode 13 (1.2 for a flat surface to 0.8 for a round surface), C2 is the drag coefficient of the wind fin 15 (1.2 for a flat surface to 0.8 for a round surface).

[0059] Since the air density and wind speed can be assumed to be the same at all positions, i.e., both at the first electrode 13 and at the wind fin 15, the equation can be simplified to: 0=AEL×LM1×C1−AWF×LM2×C2

[0060] To also compensate for the bending moment exerted on the surge arrester 9 by the first electrode 13, equation 2 must also be taken into account: 0=m1×LM1−m2×LM2 where m1 the mass of electrode 13, m2 the mass of the wind fin 15, L M1 the distance between the central axis of the surge arrester 9 and the center of mass of the electrode 13, L M2 the distance between the central axis of the surge arrester 9 and the center of mass of the wind fin 15.

[0061] To simplify the presentation, in Fig. 2. Assume that L F1 and L M1in turn, as well as L M2 and LF2, on the other hand, are each the same, meaning that the centroid and center of mass coincide. Therefore, these distances are only labeled L1 and L2 in the figure.

[0062] The shape of the wind fin 15 is not particularly restricted. However, care must be taken to ensure that the wind fin 15 maintains a sufficient distance from all components of the power pylon 1 connected to the mass, so that no arcing can occur between the wind fin 15 and the power pylon 1.

[0063] More precisely, the distance between the wind fin 15 and earth should always meet at least the insulation resistance criteria according to IEC 60099-4, cl. 8.2 (Insulation withstand tests) with regard to the protection level of the surge arresters 9 or SVU.

[0064] Furthermore, for the reasons mentioned above, the wind fin 15 must not protrude significantly beyond the power pole 1 and the dimensions of the corridor must not be increased.

[0065] The material of the wind fin 15 is also not further restricted. For manufacturing reasons, it is advantageous to manufacture the wind fin 15 and the first electrode 13 as a single piece, and therefore to use the same metal as for the first electrode 13.

[0066] Alternatively, since the electrode 13 should be made as light as possible, the wind fin 15 can be made of a heavier material. For example, the electrode 13 could be made of aluminum and the wind fin 15 of galvanized steel or V2A steel.

[0067] It is further preferred to design the tip of the electrode 13 and, if applicable, the counter electrode 17 in such a way that they can better withstand the high stresses of an air penetration, e.g. by choosing a material with higher heat capacity, higher melting point and greater strength, for example V2A steel.

[0068] On the other hand, it may be advantageous to design the wind fin 15 in an insulating manner, for example made of ceramic or glass, as this reduces the risk of an arc flash from the wind fin 15 to the power pole 1 or other objects nearby.

[0069] The shape of the wind fin 15 is also not further restricted, although care must be taken to ensure that the wind fin 15 is not impaired in its function or soiled by birds.

[0070] The invention has been described above with reference to a preferred embodiment. The invention is not limited to this embodiment. For example, it is possible to additionally provide a second wind fin on the side of the counter electrode 17 of the spark gap 11 in order to compensate for corresponding torsional moments on the insulator 7. However, this is not of the same importance, since the insulator 7 is held at both ends.

[0071] More recently, a trend has emerged to mechanically stabilize the spark gap 11 by connecting an additional insulator parallel to the spark gap between the two electrodes of the spark gap 11. This has the advantage that the distance between the two electrodes and their orientation relative to each other are fixed, so that mechanical deformations, whether on the side of the surge arrester 9 or on the side of the insulator 7, do not lead to a change in the distance between the two electrodes. An example of this is disclosed in EP 3 629 430 A1.

[0072] However, here too the problem arises that the rotational symmetry of the surge arrester 9 is broken by the first electrode 13 adjacent to the surge arrester 9, so that a torsional load can occur. The invention is therefore also applicable to such surge protection devices.

[0073] In the construction method made of Fig. In section 3, the surge arrester 9 is divided into two separate surge arrester units connected in series. This is also only a preferred embodiment. It is also possible to provide a single surge arrester unit or three or more surge arrester units.

[0074] The aforementioned preferred configurations can of course also be combined with each other, without this having been explicitly stated here. 1 power pole 3 High-voltage line 5 Shielding conductor 7 Insulator 9 surge arresters 11 Spark gap 13 first electrode 15 Torsional moment compensation element 17 second electrode or counter electrode 19 Damping element

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