US3883774A - Lightning arrester spark gap - Google Patents

Abstract

A lightning arrester spark gap comprising an arc interrupting chamber with at least two electrodes the working surfaces whereof extend in the direction of stretching the arc. The gap also comprises two additional electrodes one of which is shaped as a split ring encompassing the chamber over most of its perimeter. This additional electrode is an extension of one of the electrodes of the chamber and is electrically connected thereto. The other additional electrode is in the form of a solid ring and is arranged coaxially with the first additional ring forming an annular gap therewith which has a portion, in direct proximity to the free end of the first additional electrode, wherein a flashover occurs. The second additional electrode is electrically connected to the second electrode of the arc interrupting chamber so that the arc periodically appearing therebetween determines the moment at which active quenching of the arc starts at currents below a preset values.

Description

United States Patent Volkenau et al.

[451 May 13, 1975 LIGHTNING ARRESTER SPARK CAP [76] Inventors: Vladimir Andreevich Volkenau, I 1 Parkovaya ulitsa 48, korpus 2, kv. 61; Gennady Georgievich Lavrentiev, Ketcherskaya ulitsa 6, korpus 2, kv. 125; Vitaly Vladislavovichs Shmatovich, Meierovsky prospekt, 28, korpus l, kv. 50, all of Moscow, USSR.

[22] Filed: Apr. 24, 1974 [21] App]. No.: 463,789

[52] US. Cl. 315/58; 315/35; 315/36; 313/23 1 .1 [51] Int. Cl. HOlj 19/78 [58] Field of Search 3l3/23l.l', 315/58, 35, 315/36 56] References Cited UNITED STATES PATENTS 3,576,470 4/1971 Tomura et a]. 3l3/23l.l X

Primary Examiner-Nathan Kaufman [57] ABSTRACT A lightning arrester spark gap comprising an are interrupting chamber with at least two electrodes the working surfaces whereof extend in the direction of stretching the arc. The gap also comprises two additional electrodes one of which is shaped as a split ring encompassing the chamber over most of its perimeter. This additional electrode is an extension of one of the electrodes of the chamber and is electrically connected thereto. The other additional electrode is in the form of a solid ring and is arranged coaxially with the first additional ring forming an annular gap therewith which has a portion, in direct proximity to the free end of the first additional electrode, wherein a flashover occurs. The second additional electrode is electrically connected to the second electrode of the arc interrupting chamber so that the arc periodically appearing therebetween determines the moment at which active quenching of the arc starts at currents below a preset values.

4 Claims, 5 Drawing Figures FIE 4 F155 LIGHTNING ARRESTER SPARK GAP The present invention relates to nonlinear resistor type arresters, and more particularly to spark gap of a lightning arrester employed for the surge protection of extrahigh voltage d-c as well as a-c installations.

A lightning arrester spark gap is known comprising two plates of arc-resisting insulating material, forming .1 narrow arc interrupting chamber with at least two electrodes the working surfaces whereof extend in the direction of stretching the arc and a blow-out coil whereto the current through the spark gap is transferred.

Although the above spark gap exhibits currentlimiting ability and, therefore, can be used in lightning arresters for surge protection of high-voltage d c installations, its field of application for this purpose is rather limited.

The difficulty is designing lightning arresters for surge protection of high and extrahigh voltage d-c installations resides in that they must be capable of interrupting the power follow current through conductors of a network having a substantially high inductance, following high-amplitude currents of long duration which occur after a flashover in the arrester as a result of voltage surges. For example, non-linear resistor-type arresters designed to protect the major insulation of substations of i 750 kV DC power lines 2,500 km long are rated at currents of 2 to 3 kA having a duration of up to 40 msec. In addition, the low insulation level of such power lines results in extremely low values of the ratio between the breakdown voltage U, and the arcquenching voltage U which makes the designing of such arresters still more difficult.

The above-mentioned current-limiting spark gap is not fit at all for use in long high-voltage d-c power lines, for active arc quenching, i.e. stretching the arc in the narrow arc interrupting chamber, starts almost immediately after a flashover in the spark gap, with a delay of 0.5 msecv Being subjected to the action of long current waves depending on the voltage surges in networks having a high inductance, conventional lightning arresters provided with such spark gaps suffer from intolerably high voltage increases as the arc is being quenched, which results in the spark gap's failure. In order to adapt such spark gaps for use in shorter power lines designed for lower voltage (1,000 km; i400 kV), they should be arranged in a substantially complicated pattern including two or three parallel-connected arresters operating in turn.

It is most expedient to use spark gaps in high and extrahigh voltage d-c lightning arrcstors, wherein active quenching of the arc starts only after the voltage surge has discontinued, when its energy is dissipated in the nonlinear resistor of the arrester. and the voltage at the point of its installation is close to the rated value.

A number of technical solutions of this problem are known in the art. In the simplest case, the initial moment of the blow-out, when the are is moved through the spark gap into the arc interrupting chamber, is delayed so that the duration of the initial delay increases from 0.5 to 23 msec. In more interesting solutions, the onset of active quenching of the arc is controlled by the intensity of the current through the arrester. Such a control may be effected, for example, by repeating several times the flashover in the spark gap which can be achieved by blowing. to the flashover area the ionized fill gases appearing therein prior to stretching the arc, at substantially high currents; are quenching in such a spark gap is only over when the current reaches a values corresponding to the moment when the voltage U; is set up across the arrester (so called quenching current In another embodiment of the spark gap in which provision is made to control the initial moment of active arc quenching by the current through the arrester, the are interrupting chamber is divided into two: are prestretching chamber and narrow arc quenching chamber, both chambers communicating through a narrow channel. Penetration of the are into the narrow arc quenching chamber (i.e. active arc quenching) is only possible, in this case, at currents equal to or lower than since at higher currents the arc cannot be moved thereinto from the are prestretching chamber through the narrow channel.

However, none of the above-mentioned improvements of the first described prior art current-limiting spark gap can solve the problem, since such spark gaps are only effective at insignificantly low arc quenching currents to 400 A), which does not permit of providing an arrester with a sufficiently low protective level U /U not do they possess sufficiently high carry ing capacity, i.e. current waves having a duration of no more than 10 to 15 msec can only pass therethrough, since an arc with higher current circulates, in all of the above-mentioned spark gaps, inside the are interrupting chamber.

It is, therefore, an object of the present invention to provide a lightning arrester spark gap enabling the initial moment of active arc quenching to be selected at currents below a preset level independently of the moment when this current level is reached or of its magnitude.

This object is attained by that a lightning arrester spark gap comprising two plates of arc-resisting insulating material forming a narrow are interrupting chamber with at least two electrodes the working surfaces whereof extend in the direction of stretching the arc and a blow-out coil whereto the current through the spark gap is transferred, is provided, according to the invention, with two additional electrodes, the first of these electrodes being electrically connected to the first electrode of the arc interrupting chamber and shaped as a split ring which is an extension of said first electrode of the are interrupting chamber, said first additional electrode encompassing the arc interrupting chamber over most of its perimeter, and the second additional electrode being made in the form ofa solid ring arranged coaxially with the first additional electrode, forming an annular gap therewith which has a portion, in direct proximity to the free end of the first additional electrode, wherein a flashover occurs, the second additional electrode being electrically connected to the second electrode of the are interrupting chamber so that the are periodically appearing therebetween determined the moment at which active arc quenching starts at currents below a preset value.

It is expedient that the second electrode of the arc interrupting chamber be electrically connected to the second additional electrode via an additional coil so arranged and wound that it sets up, in the gap between these electrodes, a magnetic field equal and directed opposite to the field of the blowout coil at a preset current level.

It is also expedient that the electrical connection between the second electrode of the arc interruption chamber and the second additional electrode be effected via a resistor having a resistance such as would ensure arc quenching between these electrodes at currents equal to or lower than the preset level.

Extra high voltage d-c lightning arresters employing the proposed spark gap offer surge protection to elec trical equipment used at i 750 kV DC power transmis sion lines at least 3,000 km long. Such lightning arrest ers possess very low protective level (Li /U in the order of [.75. since the spark gap used therein operates equally well at current waves of any duration and quenching currents of any magnitude, requiring no additional arresters connected in parallel at a converter substation.

A fuller understanding of the nature and objects of the invention will be had from the following detailed description of preferred embodiments thereof, taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a general view of a lightning arrester spark gap with the upper plate removed, according to the present invention;

FIG. 2 is a transverse section through the assembled spark gap of the invention;

FIG. 3 is a section view taken along line lIl-lll of the spark gap of FIG. 1;

FIG. 4 is an electric circuit diagram of a first embodiment of the spark gap, according to the invention;

FIG. 5 is an electric circuit diagram of a second embodiment of the spark gap, according to the invention.

Referring now to FIG. I, the lightning arrester spark gap comprises a narrow arc interrupting chamber 1 in corporating two electrodes 2 and 3 the working surfaces whereof extend in the direction of stretching the are into the chamber as it is being quenched. The chamber 1 is formed by two plates 4 and 5 (FIG. 2) of arc-resisting insulating material, such as porous ceramics based on M The plate 4 is provided with a shoulder 6 defining the periphery of the chamber 1, and the plate has a matching groove 6'. The shoulder 6 is shaped as a split ring the ends whereof define an entrance 7 (FIG. I) to the chamber 1.

Such structural features of the chamber as the width thereof, the material of which the plates 4 and 5 are made, and the exact shape of the electrodes 2 and 3 which can only be two in number, have been selected so as to ensure optimum arc quenching conditions.

The spark gap is further provided with two additional electrodes 8 and 9 arranged externally of the arc interrupting chamber 1. The electrode 8 is shaped as a split ring and is an extension of the electrode 2 which, in the embodiment under consideration, is brought out of the chamber 1. Therewith, the electrode 8 encompasses the chamber 1 over most of its perimeter and is electrically connected to the electrode 2 of this chamber. The electrode 9 is made in the form of a solid ring arranged coaxially with the electrode 8 and lies in the same plane therewith. Its size is such that an annular gap I0 2 to 3 mm wide is formed between the electrodes 8 and 9. The gap 10 has a portion 1] in direct proximity to the free end of the electrode 8, in which a spark gap flashover occurs. At the point where such sparkover occurs, the gap 10 is narrowed from 2 3 mm to 1 mm.

It should be noted at this point, that the electrodes 8 and 9 form, together with the end of the electrode 3 brought out from the chamber 1, a second spark gap wherein the are appearing at the flashover point rotates under the effect of a magnetic blow-out. In other words, these electrodes form what may be termed as the arc rotation chamber. The walls defining this cham ber from above and below may be made integral with the plates 4 and S (as is shown in FIG. 1). or separate, from another material.

The electrode 9 (FIG. 1) is electrically connected to the electrode 3 of the chamber 1 via an inductor 12 (FIG. 3) which is attached to the plate 5 directly over that portion of the gap 10 (FIG. 1) which is formed by the electrodes 3 and 9, and is wound so that it sets up in the gap between these electrodes, under the effect of the voltage across the are 13 therebetween, a magnetic field equal and directed oppositely to the field of a blow-out coil 14 (FIG. 4) at a given current level or at current 1 The appearance of the arc I3 (FIG. 1) between the electrodes 3 and 9 is accompanied by an are 15 struck between the electrodes 2 and 3, which ensures a current loop in the spark gap.

The coil 14 (FIG. 4) connects the spark gap of the lightning arrester to an external lead-in l6, and a leadin 17 is connected to the electrode 9.

The coil [4 may be of any appropriate design ensuring the required magnetic field both in the are interrupting chamber 1 (FIG. 1) and in the arc rotating chamber between the electrodes 8 and 9. It should have a means for protection thereof against insulation damage due to large voltage surges, such as a protective spark gap (not shown).

Another embodiment of the lightning arrester spark gap, similar to the one described above, is possible.

It differs from the above-described one in that the electrodes 3 and 9 are interconnected via a resistor I8 (FIG. 5). The resistance of the resistor 18 should be such as to ensure the equality of the current flowing therethrough under the action of the voltage across the are 13 between the electrodes 3 and 9 to the arc quenching current I The resistor 18 may be arranged in any convenient manner with respect to the electrodes 3 and 9, an does not exert any influence on the operation of the spark gap.

The lightning arrester incorporating the abovedescribed spark gap naturally includes a plurality of series-connected gaps the number whereof is deter mined by the are quenching voltage V The spark gap of the present invention operates as follows.

After a flashover in the portion 11 (FIG. I) of the spark gap, the are appearing between the electrodes 8 and 9 starts moving, under the action of the magnetic field set up by the coil 14 (FIG. 4), anticlockwise in the annular gap 10 (FIG. 1) of the arc rotating chamber. During the period of time which it takes the are to reach the entrance 7 to the arc interrupting chamber 1, which may be referred to as the initial delay. the current determined by the voltage surge attains a substantial value exceeding the selected value of the arc quenching current 1 At the entrance 7 to the chamber 1, the arc is split into two series arcs l3 and IS. The arc l5 struck between the electrodes 2 and 3 starts to move towards the chamber 1, while the arc l3 struck between the electrodes 3 and 9 continues to move in the arc rotation chamber and enters the zone of action of the coil 12 (FIG. 4). Since the gap between the electrodes 3 and 9 is about 2 mm wide, the voltage across the arc l3 (FIG. 1) equals 40 to 50 V and is independent of the current I through the spark gap. As a result, the field set up by the coil 12 (FIG. 4) in the gap between the electrodes 3 and 9 is independent of this current too.

Since, as has been mentioned above, I 1 the field of the blow-out coil 14 in the gap between the electrodes 3 and 9 is greater than that of the coil 12, and the total field causes the are 13 (FIG. I) to move in the same direction. This are passes the portion in which deceleration takes place and closes the gap 10 between the electrodes 8 and 9 in proximity to the sparkover portion 11.

The are struck between the electrodes 2 and 3, which has no time to penetrate deep into the chamber 1 and gain in voltage, is interrupted and the cycle of rotation of the are 13 is repeated.

As the energy of the voltage surge is being dissipated, the current through the spark gap drops, during consecutive arc rotation cycle, to the value of which is determined by the rated working voltage U When the arc l3 passes, in turn, through the decelerating portion, it lingers there because the field therein is zero at l I At the same time, the arc 15 between the electrodes 2 and 3 is stretched and enters the arc interrupting chamber 1, and the process of active quenching of the arc goes on in the usual manner, i.e. by stretching the arc 15 followed by intensive cooling and de-ionization thereof on the walls of the narrow chamber 1. It should be added that as the are 15 is being stretched and the voltage therein is increasing, the current through the spark gap and the field of the coil 14 (FIG. 4) diminish, hence, the the decelerating field in the gap between the electrodes 3 and 9 increases since the field of the coil 12 is independent of the current and remains inveriable.

When selecting the parameters R and L of the coil 12, it should be borne in mind that at a voltage of 40 to 40 V the ampere-turns thereof should be ofa preset value. Therewith, the current through the coil 12 should be substantially lower than l and the time constant R/L should be as low as possible.

The principle of operation of the spark gap embodied in accordance with FIG. 5 resides in that at l 1 as in the above case, there appear two arcs 13 (FIG. 1) and 15, the current through the arc l3 struck between the electrodes 3 and 9 being equal to the following difference:

40 50 n I rotation of the arc in the spark gap is, in this case, similar to that in the first embodiment.

When the current I becomes equal to the arc 13 is not struck, since the current I is completely transferred to R (40 5U)/l The rotation cycle in the spark gap is, in this case, similar to that in the first embodiment.

When the current I becomes equal to I the are 13 is not struck, since the current 1 is completely transferred to The rotation cycle is over and the are 15 between the electrodes 2 and 3 enters the chamber 1 in which it is interrupted in a manner described above.

It should be noted that at R 0, are quenching after the first rotation cycle starts at any current values, which makes it possible to substantially simplify the design of the spark gap.

The herein disclosed spark gap with the initial delay and affording control of the moment at which active arc quenching starts at currents of particular value, features, high current-carrying capacity, which is peculiar of rotating-arc spark gaps, as well as high currentlimiting and arc-quenching capacities, which is peculiar of narrow current-limiting spark gaps, thus combining the advantages of both types of spark gaps in one. The proposed spark gap may be advantageously employed in extrahigh voltage d-c lightning arrestors, as well as in a-c lightning arresters, when similar conditions arise. Therewith, the proposed spark gap is free of the limitations as far as current amplitudes and durations are concerned, i.e. it can be used in installations of any power and in power transmission lines of any length.

What is claimed is:

1. A lightning arrester spark gap comprising: two plates of arc-resisting insulating material, forming a narrow arc interrupting chamber; at least two, first and second, electrodes the working surfaces whereof extend in the direction of stretching the arc, which electrodes are disposed in said are interrupting chamber; a series blow-cut coil; a third electrode electrically connected to said first electrode of said interrupting chamber, made in the form of a split ring, said third elect ode being an extension of said first electrode of said arc interrupting chamber and encompassing the latter over most of its perimeter; a fourth electrode made in the form of a solid ring, arranged coaxially with said third electrode; an annular gap formed by said third and fourth electrode; a portion of said gap in direct proximity to the free end of said third electrode, wherein a flashover occurs; said fourth electrode being electrically connected to said second electrode of said are interrupting chamber so that the are periodically appearing between said electrodes determines the moment at which active quenching of the arc starts at currents below a preset value.

2. A spark gap as claimed in claim 1, comprising a second coil through which said second electrode of said are interrupting chamber is electrically connected to said fourth electrode, and which sets up, in the gap between these electrodes, a magnetic field equal to opposed to that of said series blow-out coil at a preset current value.

3. A spark gap as claimed in claim 1, comprising a resistor through which said second electrode of said are interrupting chamber is electrically connected to said fourth electrode, the resistance whereof ensures arc quenching between these electrodes at currents equal to a preset value.

4. A spark gap as claimed in claim l, comprising a resistor through which said second electrode of said are interrupting chamber is electrically connected to said fourth electrode, the resistance whereof ensures arc quenching between these electrodes at currents below a preset value.

Claims (4)

1. A lightning arrester spark gap comprising: two plates of arcresisting insulating material, forming a narrow arc interrupting chamber; at least two, first and second, electrodes the working surfaces whereof extend in the direction of stretching the arc, which electrodes are disposed in said arc interrupting chamber; a series blow-cut coil; a third electrode electrically connected to said first electrode of said interrupting chamber, made in the form of a split ring, said third electrode being an extension of said first electrode of said arc interrupting chamber and encompassing the latter over most of its perimeter; a fourth electrode made in the form of a solid ring, arranged coaxially with said third electrode; an annular gap formed by said third and fourth electrode; a portion of said gap in direct proximity to the free end of said third electrode, wherein a flashover occurs; said fourth electrode being electrically connected to said second electrode of said arc interrupting chamber so that the arc periodically appearing between said electrodes determines the moment at which active quenching of the arc starts at currents below a preset value.

2. A spark gap as claimed in claim 1, comprising a second coil through which said second electrode of said arc interrupting chamber is electrically connected to said fourth electrode, and which sets up, in the gap between these electrodes, a magnetic field equal to opposed to that of said series blow-out coil at a preset current value.

3. A spark gap as claimed in claim 1, comprising a resistor through which said second electrode of said arc interrupting chamber is electrically connected to said fourth electrode, the resistance whereof ensures arc quenching between these electrodes at currents equal to a preset value.

4. A spark gap as claimed in claim 1, comprising a resistor through which said second electrode of said arc interrupting chamber is electrically connected to said fourth electrode, the resistance whereof ensures arc quenching between these electrodes at currents below a preset value.

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