CN218216103U - Double-safety lightning arrester - Google Patents

Abstract

The utility model discloses a double insurance arrester, its characterized in that includes: the fuse tube comprises an arc extinguishing tube and a fuse, the fuse is preset with fusing capacity, penetrates through an electrode part and a joint part of the arc extinguishing tube and is electrically connected with a pole tower; a parallel gap formed by a difference gap in which a distance between the electrode part and the lead is adjustable; after lightning breaks through the parallel gap, if the fault current is smaller than the fusing capacity, the fuse is not fused, and the gap arc is automatically extinguished; and after lightning breaks through the parallel gap, if the fault current is larger than the fusing capacity, the fuse is fused, and the arc in the tube is extinguished by the arc extinguishing tube. The utility model relates to a double insurance arrester can realize higher security and reliability, long service life, and the maintenance volume reduces by a wide margin, and the economic nature is showing, is fit for the lightning protection technical device who popularizes and applies comprehensively to eliminate thunderbolt tripping operation broken string basically.

Description

Double-safety lightning arrester

Technical Field

The utility model relates to a high-tension overhead distribution lines lightning protection technical field especially relates to a dual fail-safe arrester.

Background

The high-voltage distribution line in China is mainly based on 10kV alternating-current voltage, most of the high-voltage distribution line is an overhead line, single-loop or multi-loop erection is adopted, the span is about 50 meters, and the total amount exceeds 400 ten thousand kilometers. The overhead insulated conductor is very easily broken wire accident when suffering the thunderbolt, and repair time is long, and the power failure loss is big, and the person is electrocuted the risk height, needs to solve urgently.

High-voltage overhead distribution lines have been used for more than a hundred years so far, and the problems of lightning strike tripping, disconnection and the like always trouble relevant professional technicians in all countries in the world. Although a plurality of lightning protection technologies are applied, the lightning trip still generally accounts for 70% -80% of the total trip event of power distribution until now. The fundamental reason is that a product technology which fundamentally solves the problem of lightning trip-out and has the advantages of large-area popularization and application in the aspects of safety, reliability and economy is lacked.

The zinc oxide arrester can avoid the tripping operation of thunderbolt, and is used comparatively generally on transformer substation and transmission line, but is applied to overhead distribution lines, has the fault rate height, equipment and fortune dimension with high costs not enough. The probability of explosion and permanent faults of the equipment body is higher than the probability of tripping of a lightning line, periodic prevention tests are difficult to develop, the reliability of the line is difficult to improve in fact, in addition, a tower is required to lay a good grounding grid, the construction cost of the good grounding grid is up to thousands of yuan per base, land disputes are often involved, and the further popularization and application of the zinc oxide arrester are restricted.

The existing arrester with gaps is adopted, the gap margin is small, such as a multi-chamber arrester, the outer gap distance requires 50 mm, each tower is installed in one phase, the front and rear tower phase change dislocation installation is kept, when lightning occurs, the probability of interphase short circuit is increased, although arc can be extinguished when the short circuit current amplitude is not too large, voltage fluctuation is caused by the interphase short circuit, the electric energy quality is influenced, and the advantage that the influence of single-phase grounding on power supply in a neutral point ungrounded and arc suppression coil grounding system is small is lost.

The parallel gap is a lightning protection facility which is arranged on an overhead line insulator in parallel to prevent an insulator string (also called as an insulator, the same below) from being damaged by lightning stroke. The gap distance is less than the structural height of the insulator. When the overhead line is struck by lightning, high lightning overvoltage is generated on the insulator string, however, the lightning impulse discharge voltage of the parallel gap is lower than the discharge voltage of the insulator string, the volt-second characteristic of the parallel gap is expressed to be below the volt-second characteristic of the insulator (the same applies below), and the parallel gap is firstly discharged to protect the insulator from arc ablation. The parallel gap attached to the existing insulator is mainly used for protecting the insulator and an insulated wire from arc ablation, the lightning resistance level is reduced to a certain degree, the interphase short-circuit current cannot be extinguished, and the trip probability of a line is increased.

Due to the fact that the lightning-resistant level of the overhead distribution line is low, lightning falls in the range of 400 meters on each of the two sides of the line, and line faults can be caused due to lightning induced overvoltage. Induced overvoltage induced failures account for about 80% of the total number of lightning faults. Meanwhile, multiple lightning strokes exist in lightning, and for a lightning arrester which can only act for one time, the lightning arrester has higher probability of losing protection in the multiple lightning strokes, so that line faults are caused.

The 10kV overhead distribution line lightning strike failure rate is typically less than 5 times/hundred kilometers per year. According to the statistics of double-loop construction with the average span of 50 meters, the lightning stroke fault rate is usually less than 0.005 times/base year, which is equivalent to 200 years of one-touch. For lightning protection equipment installed on a distribution line with a plurality of millions of kilometers and a plurality of points, if the safety and reliability of an equipment body are not high enough, most of the lightning protection equipment cannot be repaired by self when a lightning stroke happens, the lightning protection equipment needs to be maintained by power failure, the self failure of part of the lightning protection equipment also causes the line to be tripped and powered off, and the recovered power transmission time is longer than that of the lightning stroke.

In order to ensure the safe and reliable power supply of a power distribution network, a lightning protection technical device which has higher safety and reliability, long service life, greatly reduced maintenance amount and remarkable economical efficiency needs to be researched and developed urgently so as to realize the basic elimination of lightning trip and disconnection.

SUMMERY OF THE UTILITY MODEL

The utility model aims at providing a double insurance arrester realizes higher security and reliability, long service life, and the maintenance volume reduces by a wide margin, has and is showing economic nature advantage to solve above-mentioned distribution overhead line lightning protection problem.

In order to achieve the above object, the utility model relates to a double insurance arrester installs in distribution overhead line, a serial communication port, include: the fuse tube comprises an arc extinguishing tube and a fuse, the fuse is preset with fusing capacity, penetrates through an electrode part and a joint part of the arc extinguishing tube and is electrically connected with a pole tower; a parallel gap formed by a difference gap with adjustable distance between the electrode part and the lead; if lightning breaks through the parallel gap, the fault current is smaller than the fusing capacity, the fuse is not fused, and the gap arc is automatically extinguished; if the lightning breaks through the parallel gap, the fault current is larger than the fusing capacity, the fuse is fused, and the electric arc in the tube is extinguished by the arc extinguishing tube.

Compared with the prior art, the utility model relates to a double insurance lightning arrester has following beneficial effect: 1. the parallel gap with the alternate difference and the matching of volt-second characteristics is formed between the electrode part and the lead, when the power distribution overhead line is subjected to lightning induced overvoltage, the probability of two-phase and three-phase grounding short circuit is greatly reduced, when a neutral point is not grounded or passes through an arc suppression coil grounding system, and only single-phase grounding occurs, the fault current is smaller than the preset fusing capacity of a fuse (the 10kV line is preset to be 10 amperes), the fuse is not fused, electric arcs on the parallel gap are automatically extinguished, the line cannot trip, the insulator is also protected, when the induced overvoltage caused by multiple lightning strikes is met, the parallel gap of the double-insurance lightning arrester can be repeatedly discharged for multiple times without damage failure, and the line trip fault caused by multiple lightning is avoided. 2. About 20% of distribution overhead line's thunder and lightning trouble is that the direct lightning caused, can make the three-phase simultaneous occurrence ground short circuit basically, punctures when the thunder and lightning behind the parallel gap, fault current (last kilo ampere) is greater than and predetermines fusing capacity, and the fuse fuses, and the electric arc of production is extinguished by the arc extinguishing pipe, can avoid distribution overhead line tripping operation. 3. The tower provided with the double-insurance arrester adopts natural grounding, and a grounding network is not required to be additionally built, so that thousands of elements are saved for each base tower. 4. The double-insurance lightning arrester is simple in structure, safe and reliable, greatly reduces maintenance amount, reduces lightning protection cost, and is suitable for comprehensive popularization and application.

Preferably, the arc-extinguishing tube comprises an insulating tube and a gas-generating material layer lined in the insulating tube, the gas-generating material layer is burned by the high temperature of the electric arc in the tube to decompose gas and is ejected from the electrode part to form longitudinal arc-extinguishing, or a pressure-releasing cover is arranged on the joint part, and the pressure of the gas is higher than the preset bearing force of the pressure-releasing cover and is ejected by being rushed out, so that the explosion of the arc-extinguishing tube is avoided.

Preferably, the arc extinguishing tube comprises an insulating tube and quartz sand filled in the insulating tube, or the fuse is wound and fixed on an internal insulating support.

Preferably, the electrode part is sleeved with an indication cover, the appearance color of the indication cover is different from that of the arc extinguishing tube, and when the fuse is fused, the indication cover is pushed away by high-pressure gas or a compression spring so as to be discovered by inspection.

Preferably, the gap distance of the parallel gap is adjusted by at least one arc starting electrode or the joint part, so that the volt-second characteristic of the parallel gap is lower than that of the insulator, the arc starting electrode is composed of a conductor and comprises a clamping part and a discharge electrode, and the clamping part is clamped on the electrode part or the lead.

Preferably, the lead is an insulated lead, the discharge electrode includes a first discharge electrode extending to the load side of the insulated lead and a second discharge electrode extending to the power supply side of the insulated lead, the first discharge electrode and the electrode portion form a parallel gap, the second discharge electrode and the joint portion form a backup gap, the volt-second characteristic of the parallel gap is lower than the volt-second characteristic of the backup gap, the volt-second characteristic of the backup gap is lower than the volt-second characteristic of the insulator, and after the fuse is fused, the backup gap provides a breakdown discharge channel to prevent the insulated lead and the insulator from being ablated by an arc.

Preferably, the distance of the parallel gaps is adjusted, so that the volt-second characteristic of one and only one phase of the parallel gaps is lower than the volt-second characteristics of the rest phases of the parallel gaps and the insulators, and the interphase short circuit fault caused by lightning is reduced.

Preferably, the parallel gap is adjusted in distance, so that the volt-second characteristic of the parallel gap is lower than the volt-second characteristic of the fused state of the fuse of at least one adjacent tower, the protection range of the double-safety lightning arrester extends to at least one adjacent tower, and the double-safety lightning arrester is continuously installed adjacent to each other to prevent multiple lightning strikes.

Preferably, the fusing capacity is preset to pass a 10 ampere single-phase earth fault capacitor current or a lightning induced overcurrent having an amplitude of 3000 amperes.

Preferably, the fuse comprises a copper wire with the diameter of 0.2-0.4 mm, an aluminum wire with the diameter of 0.3-0.5 mm or a stainless steel wire with the diameter of 0.6-0.8 mm, and the surface of the fuse is subjected to anti-corrosion treatment.

Drawings

Fig. 1 is a schematic view of a first embodiment of the present invention.

Fig. 2 is a schematic view of a second embodiment of the present invention.

Fig. 3 is a schematic view of a third embodiment of the present invention.

Detailed Description

In order to explain technical contents, structural features, and objects and effects of the present invention in detail, the following description is given in conjunction with the embodiments and the accompanying drawings.

As shown in fig. 1 to fig. 3, the utility model discloses a double insurance arrester is installed in distribution overhead line, include: the fuse tube 7 comprises an arc extinguishing tube (which is marked as the same as the fuse tube 7) and a fuse 17, the fuse 17 is preset with fusing capacity and penetrates through an electrode part 6 and a joint part 8 of the arc extinguishing tube 7 to be electrically connected, and the joint part 8 is electrically connected with a tower 9; the parallel gap 5 is formed by a difference gap with adjustable distance between the electrode part 6 and the insulated conductor 12 (bare conductor 14); if the lightning breaks through the parallel gap 5, the fault current is smaller than the fusing capacity, the fuse 17 is not fused, and the gap arc is automatically extinguished; if the lightning breaks through the parallel gap 17, the fault current is larger than the fusing capacity, the fuse 17 is fused, and the electric arc in the tube is extinguished by the arc extinguishing tube 7, so that the insulator 10 is protected from being ablated by the electric arc, and the lightning stroke tripping of the power distribution overhead line is avoided.

The parallel gap 5 is additionally arranged on the insulator 10 in parallel through a protective tube 7, so that the insulator 10 is prevented from being damaged by lightning. It consists of two electrodes, an insulated conductor 12 (bare conductor 14) is on the high voltage side, and the electrode portion 6 is at ground potential. The gap distance is smaller than the lightning discharge distance (insulation structure length) of the insulator 10. When the overhead line is struck by lightning, a high lightning overvoltage is generated on the insulator 10, but the parallel gap 5 is discharged first because the lightning impulse discharge voltage of the parallel gap 5 is lower than the discharge voltage of the insulator string. Because the overhead line of distribution generally adopts neutral point ungrounded mode or through arc suppression coil ground connection, allow to continue to operate for a period of time (can set for, for example 2 hours) when single-phase ground connection, after lightning induction overvoltage punctures parallel gap 5, single-phase ground fault current is less than 10 amperes, fuse 17 predetermined fusing capacity 10 amperes, fuse 17 does not melt, the electric arc on the parallel gap 5 because of the energy is less, can extinguish by oneself, insulator 10 receives the protection. When induction overvoltage caused by multiple lightning strokes occurs, the parallel gap 5 of the double-insurance lightning arrester can be repeatedly discharged for multiple times without damage and failure, and the insulator can be repeatedly protected for multiple times. Lightning induced faults in distribution overhead lines are caused by lightning induced overvoltages in about 80%. The technical characteristics that the distance between an electrode part 6 and an insulated conductor 12 (a bare conductor 14) of a parallel gap 5 is adjustable are utilized, so that the parallel gap 5 of the same base tower is distributed according to difference, the distance between the parallel gap 5 is minimum, single-phase grounding can be only caused with higher probability, an electric arc of continuous power frequency capacitance current is led to the end part of a metal electrode through a discharge channel formed by the parallel gap 5 under the action of electric power and thermal stress, and is fixed between the two end parts of the metal electrode for combustion, thereby protecting an insulator from arc ignition, greatly reducing the probability of circuit tripping and providing a first safety for an overhead line.

About 20% of distribution overhead line's thunder and lightning trouble is direct lightning and causes, can make the three-phase simultaneous occurrence ground short circuit basically, punctures parallel gap 5 back when the thunder and lightning, and fault current is greater than predetermineeing fusing capacity, and fuse 17 fuses, and the electric arc of production is extinguished by arc extinguishing pipe 7, can avoid the tripping operation of distribution overhead line. The protection radius of the lightning arrester is about 100 meters, the lightning arrester with double insurance is installed on a 5-base-rod tower in total before and after the first breakdown point, at most 5 heavy lightning strikes can be prevented, and a second insurance is provided for the overhead line.

The double-insurance lightning arrester has the advantages of double insurance, simple structure, safety and reliability, longer service life, great reduction of maintenance amount and remarkable economical efficiency compared with the prior art, and can basically eliminate lightning trip and disconnection by comprehensive popularization and application.

As shown in fig. 1, which is a first embodiment of the present invention, a gas-generating arc-extinguishing method is applied to a bare conductor. The arc-extinguishing tube 7 comprises a glass fiber insulating tube and a gas-generating material layer 16 lined in the glass fiber insulating tube, the gas-generating material layer 16 is made of high polymer materials such as vulcanized fiber paper, nylon and the like, and gas decomposed by high-temperature burning of electric arcs in the tube is sprayed out from the electrode part 6 or the joint part 8 to form longitudinal arc-extinguishing. The sprayed gas contains a large amount of charged ions, and the arc extinguishing tube 7 is parallel to the conducting wire, so that the phenomenon that the insulation performance of the interphase is reduced to cause the interphase short circuit can be avoided.

The electrode part 6 is sleeved with an indicating cover (which is marked with the electrode part 6), the appearance color of the indicating cover 6 is different from that of the arc-extinguishing tube 7, in the embodiment, the indicating cover 6 is in an aluminum alloy primary color, the arc-extinguishing tube 7 is orange, and after the indicating cover 6 is flushed away by gas, the electrode part 6 is exposed out of the orange arc-extinguishing tube 7 and can be discovered by patrol. The joint part 8 is provided with a pressure release cover 18, and the gas pressure exceeds the preset bearing force of the pressure release cover 18 to burst the pressure release cover 18 for spraying, so that the arc extinguishing tube 7 is prevented from bursting. The cross arm structure and the insulator 10 of the pole tower 9 are staggered at the joint part 8, so that the problem that the pressure relief of high-pressure gas is blocked, the flowing direction of the gas is changed, and the interphase insulation performance is reduced is avoided.

The clamping part 1 of the arc striking electrode 2 is clamped on the electrode part 6 and is electrically connected, the discharge electrode 4 and the bare conductor 14 form a parallel gap 5 with different volt-second characteristics, and the distance of the parallel gap 5 can be adjusted by rotating the clamping part 1. The volt-second characteristic matching is set to have a difference of 10% -30%, optimization can also be obtained through experiments, and when the gap matching with a small difference is carried out, the reduction range of the lightning resistance level of a line caused by the addition of a parallel gap can be reduced. For the overhead power distribution line erected by a single loop, when three-phase insulators are of the same type, the parallel gap 5 of the upper conductor of one phase can be selected to be 70% of the minimum arc distance of the insulator 10, and the parallel gap 5 of the other conductor of the two phases can be selected to be 85% of the minimum arc distance of the insulator 10. For the distribution overhead line erected by the double loops, when three-phase insulators are of the same type, the parallel gap 5 of the upper conductor of one phase can be selected to be 70% of the minimum arc distance of the insulator 10, and the parallel gap 5 of the other two conductors and the other three-phase conductor of the other loop is 85% of the minimum arc distance of the insulator 10. For one or more circuits erected on the same tower, the setting value of the parallel gap 5 of one circuit is smaller than that of other phases, and the parallel gap 5 has volt-second characteristic matching, when the lightning nearby the circuit induces induced overvoltage or the tower potential rises to form counterattack voltage, the parallel gap 5 with a small setting value has the chance of being punctured first, single-phase grounding is formed, the coupling effect is further formed on the other phase wires, the probability of two-phase or three-phase simultaneous grounding short circuit is reduced, the fault current of the two-phase or three-phase simultaneous grounding short circuit usually reaches the kiloampere level, the fuse 17 is fused, and the arc extinguishing tube 7 starts arc extinguishing.

As shown in fig. 2, the second embodiment of the present invention is that a gas-generating arc-extinguishing mode is applied to an insulated wire, and the difference from the first embodiment is that an insulating layer is added to the wire. When the insulating layer is punctured, the electric arc is fixed in the punching hole to burn, so that the wire breakage accident is easily caused, and the insulated wire must be prevented from being broken by lightning.

The arc starting electrode 3 is mounted on the insulated wire 12, the discharge electrode comprises a first discharge electrode 19 extending towards the load side (right side in the figure) of the insulated wire 12 and a second discharge electrode 18 extending towards the power supply side (left side in the figure) of the insulated wire 12, the first discharge electrode 19 and the discharge electrode 4 form a parallel gap 5, the second discharge electrode 18 and the joint part 8 form a backup gap 11, the volt-second characteristic of the parallel gap 5 is lower than that of the backup gap 11, the volt-second characteristic of the backup gap 11 is lower than that of the insulator 10, and after the fuse 17 (not shown) is fused, the backup gap 11 provides a breakdown discharge channel to prevent the insulated wire 12 and the insulator 10 from being ablated by an arc. The clamping part adopted by the arc striking electrode 3 is electrically connected with the conductor of the lead 12 in a puncturing mode, and the insulating sleeve 13 is covered outside the arc striking electrode, so that the exposure of the conductor is reduced. The ends of the first discharge electrode 19 and the second discharge electrode 18 are provided with spherical discharge metal structures which can be used for hanging grounding wires during maintenance. The arc striking electrode 3 is clamped on the insulated conducting wire 12, and the discharge current of the parallel gap 5 can directly flow to the conductor of the insulated conducting wire 12 through the arc striking electrode 3, so that the arc breakdown of the insulating layer is avoided to cause wire breakage.

The clamping part 1 of the arc striking electrode 2 is clamped on the electrode part 6 and is electrically connected, the discharge electrode 4 and the first discharge electrode 19 form a parallel gap 5 with different volt-second characteristics, and the distance of the parallel gap 5 can be adjusted by rotating the clamping part 1.

The electrode part 6 is sleeved with an indicating cover (which is marked with the electrode part 6), the appearance color of the indicating cover 6 is different from that of the arc extinguishing tube 7, in the embodiment, the indicating cover 6 is made of aluminum alloy with primary color, the arc extinguishing tube 7 is orange, and after the indicating cover 6 is flushed by gas, the orange arc extinguishing tube 7 is exposed out of the electrode part 6 and can be found by inspection. The joint part 8 is provided with a pressure release cover 18, and the gas pressure exceeds the preset bearing force of the pressure release cover 18 to burst the pressure release cover 18 for spraying, so that the arc extinguishing tube 7 is prevented from bursting. The cross arm structure and the insulator 10 of the pole tower 9 are staggered at the joint part 8, so that the phenomenon that the pressure relief of high-pressure gas is blocked, the flowing direction of the gas is changed, and the reduction of the interphase insulation performance is caused is avoided.

As shown in fig. 3, a third embodiment of the present invention is to apply a quartz sand arc extinguishing method to a bare conductor, and the difference from the first embodiment is that the arc extinguishing tube 7 made of ceramic or glass fiber is filled with quartz sand 21, and the built-in insulating holder 20 is used to wind the fixed fuse 17. The indicating cover 6 is internally provided with a striking device 22, and when the fuse 17 is fused, the striking device 22 triggers the ejecting indicating cover 6 to be discovered by patrol. The impact energy of the striking device 22 may compress a spring, arc hot air expansion or high temperature gas generating materials, etc. The joint part 8 is connected with a pole tower 9 through a bolt, and the distance of the parallel gap 5 can be adjusted by adjusting the elevation angle of the arc extinguishing tube 7. Similarly, when the conductor is an insulated conductor, the arc starting electrode held by the insulated conductor may be added, as in the second embodiment. As the arc extinguishing tube 7 is filled with the quartz sand 21, the arc extinguishing tube has high breaking arc extinguishing capability, and can cut off short-circuit current more than 50kA, thereby meeting the maximum short-circuit current requirement of a distribution line. The arc extinguishing tube 7 can not eject air outwards, and is different from gas-generating arc-extinguishing modes, the installation angle is not limited, and the adjustment mode of the parallel gap 5 is simpler and more flexible.

In the three embodiments shown in fig. 1-3, the blowing capacity of the fuse 17 is preset to pass 10 amps of single-phase ground fault capacitor current. The fuse 17 comprises copper wires with the diameter of 0.2-0.4 mm, aluminum wires with the diameter of 0.3-0.5 mm or stainless steel wires with the diameter of 0.6-0.8 mm, and the surface of the fuse 17 is subjected to anticorrosion treatment, such as silver or gold electroplating. The material of the fuse 17 is not limited to the above, and may be other metals or non-metals.

When the length of the insulator 10 is increased, it is possible to use two versions of the ignition electrode 2 simultaneously, one clamped on the conductor and the other clamped on the electrode part 6, with the parallel gap 5 between the discharge electrodes 4 of the two ignition electrodes 2 (see fig. 2).

The parallel gaps 5 are arranged on a multi-phase insulated wire 12 (or a bare wire 14) of a tower 9, the clamping position of the arc striking electrode 2 is adjusted through rotation, the distance of each parallel gap 5 is preset, and the volt-second characteristic inter-phase difference matching is realized, so that the volt-second characteristic of only one parallel gap 5 is positioned below the volt-second characteristics of the rest parallel gaps 5 and the insulator 10, and the inter-phase short circuit fault caused by thunder is reduced.

The distance of the parallel gap 5 is adjusted, so that the volt-second characteristic of the parallel gap 5 is lower than the volt-second characteristic of the fusing state of the same phase fuse 17 of at least one adjacent base tower 9, the protection range of the double-safety lightning arrester extends to at least one adjacent base tower, and the double-safety lightning arrester is continuously installed adjacently to defend multiple lightning strokes. When the power distribution overhead line is subjected to multiple lightning strikes, the tower 9 with the fused fuse 5 is protected by a double-safety lightning arrester on the adjacent tower.

The above embodiments have the advantages of simple structure, ageing resistance of materials, high stability and long expected service life, and can greatly reduce the operation and maintenance workload and reduce the time of power failure of the overhead distribution line caused by self-failure and defect treatment of equipment.

The above disclosure is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the scope of the invention, therefore, the invention is not limited thereto.

Claims (10)

1. The utility model provides a double insurance arrester installs in distribution overhead line, its characterized in that includes:

the fuse tube comprises an arc extinguishing tube and a fuse, the fuse is preset with fusing capacity, penetrates through an electrode part and a joint part of the arc extinguishing tube and is electrically connected with a pole tower;

a parallel gap formed by a difference gap with adjustable distance between the electrode part and the lead;

if lightning breaks down the parallel gap, the fault current is smaller than the fusing capacity, the fuse is not fused, and the gap arc is automatically extinguished;

if the lightning breaks through the parallel gap, the fault current is larger than the fusing capacity, the fuse is fused, and the electric arc in the tube is extinguished by the arc extinguishing tube.

2. A double-insurance arrester as claimed in claim 1, wherein the arc-extinguishing tube includes an insulating tube and a gas-generating material layer lined inside the insulating tube, the gas-generating material layer is burned by the high temperature of the arc inside the tube to decompose gas and eject from the electrode portion to form a longitudinal blow arc, or the joint portion is provided with a pressure-releasing cover, and the gas pressure exceeds the preset bearing force of the pressure-releasing cover to eject the gas through the pressure-releasing cover, so as to prevent the arc-extinguishing tube from bursting.

3. A double-insurance arrester as claimed in claim 1, wherein the arc-extinguishing tube comprises an insulating tube and quartz sand filled therein, or an internal insulating support is wound around and fixes the fuse.

4. A double-safety arrester according to claim 2 or 3 wherein the electrode unit encloses an indicator cap, the indicator cap having a different appearance colour from the arc-extinguishing tube, the indicator cap being pushed away by high-pressure gas or a compression spring when the fuse is blown, so as to be detected by inspection.

5. A double-safety arrester as claimed in any one of claims 1-3, characterized in that the parallel gap is adjusted in gap distance via at least one starting pole or the terminal part so that the volt-second characteristic of the parallel gap lies below the insulator volt-second characteristic, the starting pole being formed by a conductor and comprising a clamping part and a discharge pole, the clamping part being clamped on the electrode part or the conductor.

6. A double-insurance lightning arrester according to claim 5 wherein the conductor is an insulated conductor, the discharge electrodes include a first discharge electrode extending toward the load side of the insulated conductor and a second discharge electrode extending toward the power side of the insulated conductor, the first discharge electrode and the electrode portion form a parallel gap, the second discharge electrode and the joint portion form a backup gap, the parallel gap has a volt-second characteristic below that of the backup gap, the backup gap has a volt-second characteristic below that of the insulator, and the backup gap provides a breakdown discharge path after the fuse is blown, thereby preventing the insulated conductor and the insulator from being arc ablated.

7. A double-safety arrester as claimed in claim 5 wherein the parallel gaps are adjusted in distance such that the volt-second characteristic of one and only one of the phases of the parallel gap is below the volt-second characteristic of the remaining phases of the parallel gap and the insulator, thereby reducing lightning induced phase-to-phase short circuit faults.

8. A double-insurance lightning arrester as claimed in claim 5 wherein the parallel gap is adjusted in distance so that the volt-second characteristic of the parallel gap is below the volt-second characteristic of the same fuse in the adjacent at least one tower, the double-insurance lightning arrester extending over the adjacent at least one tower, the double-insurance lightning arresters being mounted in series adjacent to each other to protect against multiple lightning strikes.

9. A double-safety arrester as claimed in claim 1, wherein the fuse capacity is predetermined to pass a 10 amp single-phase earth fault capacitor current or a lightning induced overcurrent of 3000 amps magnitude.

10. A double-fuse arrester as claimed in claim 1, wherein the fuse comprises copper wires with diameters of 0.2-0.4 mm, aluminum wires with diameters of 0.3-0.5 mm or stainless steel wires with diameters of 0.6-0.8 mm, and the surface of the fuse is subjected to corrosion protection treatment.

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