Title:
SPARK GAP SYSTEM FOR MAGNETICALLY QUENCHED SURGE VOLTAGE ARRESTER
United States Patent 3670204
Abstract:
A spark gap system for a surge voltage arrester of the magnetically quenched type is composed of a stack of superposed plates each of which is provided with a recess which defines an arc chamber and a pair of spaced electrodes therein and between which an arc can be struck and lengthened by the magnetic field. The pairs of electrodes in adjacent arc chambers are electrically connected in parallel, and an arrangement of ducts which provide an inter-communication between adjacent chambers permit the ionized gas formed by an arc in either chamber after being lengthened to pass to the other chamber to assist in striking an arc in the latter chamber as the arc in the first-mentioned chamber is extinguished. The arc is thus enabled to be transferred back and forth between adjacent arc chambers until the current has been reduced to such an extent that no further arc can be sustained.
US Patent References:
Lightning arrester spark gap having arc-confining chamber walls of graded porosity
Stetson - November 1967 - 3354345
INCLINED ARC CHAMBER FOR A SPARK GAP
Stetson - June 1970 - 3515947
DIRECT CURRENT LIGHTNING ARRESTER WITH AUTOMATIC ARC QUENCHING MEANS
Smith - November 1970 - 3543097
DISCHARGE ARC CONTROL MEANS FOR A LIGHTNING ARRESTER
Sakshaug - February 1971 - 3566201
Lightning arrester spark gap having arc-confining chamber walls of graded porosity
Stetson - November 1967 - 3354345
INCLINED ARC CHAMBER FOR A SPARK GAP
Stetson - June 1970 - 3515947
DIRECT CURRENT LIGHTNING ARRESTER WITH AUTOMATIC ARC QUENCHING MEANS
Smith - November 1970 - 3543097
DISCHARGE ARC CONTROL MEANS FOR A LIGHTNING ARRESTER
Sakshaug - February 1971 - 3566201
Application Number:
05/159688
Publication Date:
06/13/1972
Filing Date:
07/06/1971
View Patent Images:
Export Citation:
Assignee:
Aktiengesellschaft Brown, Boveri & Cie (Baden, CH)
Primary Class:
Other Classes:
361/134
International Classes:
H01T1/04; H01T4/16; H01T1/00; H01T4/00; H02H9/06
Field of Search:
317/61.5,70,74,77 315/36
Primary Examiner:
Trammell, James D.
Claims:
I claim
1. A spark gap system for a surge voltage arrester of the magnetically quenched type which comprises a stack of superposed plates each of which is provided with a recess defining an arc chamber, a pair of spaced electrodes located in each such chamber and between which an arc can be struck and lengthened under the influence of the magnetic field, duct means formed in adjacent plates and which serve to interconnect the respective arc chambers of said plates whereby ionized gas formed by an arc struck in a first one of said chambers is passed to the other chamber for assistance in striking the arc in said other chamber accompanied by extinction of the arc in said first chamber, and means connecting the pairs of spaced electrodes in said chambers electrically in parallel.
2. A spark gap system as defined in claim 1 for a surge voltage arrester of the magnetically quenched type wherein each plate is circular, wherein the recess in each said circular plate is configured as a sector extending from substantially the center of the plate to the periphery thereof, wherein the electrodes in each recess are located such as to establish a strike point for the arc drawn therebetween at substantially the center of the plate, and wherein said duct means includes a duct extending radially outward from the recess at the center of each plate and through which the ionized gas flows in returning from one recess to the other.
1. A spark gap system for a surge voltage arrester of the magnetically quenched type which comprises a stack of superposed plates each of which is provided with a recess defining an arc chamber, a pair of spaced electrodes located in each such chamber and between which an arc can be struck and lengthened under the influence of the magnetic field, duct means formed in adjacent plates and which serve to interconnect the respective arc chambers of said plates whereby ionized gas formed by an arc struck in a first one of said chambers is passed to the other chamber for assistance in striking the arc in said other chamber accompanied by extinction of the arc in said first chamber, and means connecting the pairs of spaced electrodes in said chambers electrically in parallel.
2. A spark gap system as defined in claim 1 for a surge voltage arrester of the magnetically quenched type wherein each plate is circular, wherein the recess in each said circular plate is configured as a sector extending from substantially the center of the plate to the periphery thereof, wherein the electrodes in each recess are located such as to establish a strike point for the arc drawn therebetween at substantially the center of the plate, and wherein said duct means includes a duct extending radially outward from the recess at the center of each plate and through which the ionized gas flows in returning from one recess to the other.
Description:
The present invention relates to an improved spark gap system for a surge voltage arrester of the magnetically quenched type comprising a plurality of spark gap chambers formed by individual plates and being provided with preferably sector-shaped recesses within which the spark gap electrodes are located and the chambers being preferably disposed superjacently.
If the discharge in a spark gap which takes place within a chamber is not completed when the arc has acquired its maximum dimension, the arc will continue to burn. However, the cooling effect of the material of which the chamber wall is constructed diminishes as the time for which the arc burns increases and there is a risk of overheating of the spark gaps. The quenching capacity of the spark gaps is thus substantially reduced and the burn-up of the electrodes is greatly increased.
These disadvantages may be avoided in known manner by quenching the arc by renewed ignition at the contact position of the same arc gap after the said arc has reached its maximum dimension, current being conducted by the restruck arc and the cycle of restriking and extinction being repeated until the current has been reduced to a value at which no further striking can take place. In this known system, and after the arc has reached a defined size, gases ionized by the arc may be conducted through a duct past the electrodes or below thereof to the contact position of the arc gap, the threshold voltage of the arc gap being reduced to an extent which would allow restriking. Accordingly, the arc will not be prolonged at one position of the electrodes yet it will burn in only one chamber.
The prior art also discloses systems in which the arc, after having reached its maximum length in a first chamber, is drawn into a second chamber by virtue of ionized gases being conducted through the arc of the first chamber and through an ionization duct to the operating or answering position of the second chamber where the ionized gases reduce the threshold voltage to such an extent that it becomes smaller than the voltage of the arc portion in the first chamber, said arc portion being then transferred to the electrodes of the second chamber. The spark gap of the second chamber will then be struck but the arc in the first chamber continues to burn with the exception of the part diverted by the electrodes of the second chamber. This relates to a series connection of spark gaps, the arc being elongated into the second chamber by restriking after it has reached its maximum length in the first chamber. However, the fact that the first chamber is under stress during the entire discharge period and is intensively heated, particularly in the event of very large discharges is a disadvantage, more particularly since under these conditions, the electrode burn-off in the first chamber is greatly increased.
It is the object of the invention to provide an improved arc gap system which is free of the disadvantages disclosed by the prior art.
According to the invention the problem is solved in that spark gaps in successive chambers are connected electrically in parallel and means are provided for the alternate striking and elongation of the arc in the individual chambers namely by a separate ionization duct and a separate inter-communication aperture being disposed in the chambers which are formed by superposed plates.
The advantage of the invention is due in particular to the fact that the extinction capacity of the spark gap is retained in the event of substantial discharges since, after the arc has reached a defined length, a second spark gap, connected in parallel to the first spark gap, is struck in a second chamber, and the said spark gap conducts current while at the same time the arc is extinguished in the first chamber. Since the arc never burns for any prolonged period at the same position, it follows that the cooling and regeneration period of the spark gap is increased while the burn-off of the electrode is reduced. The electrically parallel connection of two identical spark gaps moreover improves the operating, i.e., its answering characteristics, that is to say, the dispersion zone of the answering voltage relative to that of an individual spark gap is reduced.
A preferred embodiment of the invention is illustrated in the accompanying drawing, the single FIGURE of which is an exploded view illustrating two pairs of spark gap chambers formed by a stack of four plates.
With reference now to the drawing, it will be seen that the spark gap system for the arrestor is comprised of a stack of circular plates in which recesses are provided for receiving spaced electrodes between which the arc is struck. In order to simplify illustration, only four such plates have been shown. As previously explained, in accordance with the invention, the spark gaps of successive chambers are connected electrically in parallel. Two pairs of such chambers appear in the drawing, and each pair of chambers is formed from two adjacent circular plates 1 and 1a made from a suitable insulating material such as a ceramic. Plate 1 of each pair is provided with a suitably configured e.g., sector-shaped recess 2 whose inner arcuate boundary reaches to substantially the center of the plate and whose outer arcuate boundary reaches to nearly the periphery of the plate and extends over an angle of about 120°. Located within the recess 2 are two spaced electrodes 3 and 4 forming a gap therebetween and across which the arc is struck. An ionization duct 5 extends in a radial direction from an intermediate point along the inner boundary of recess 2 to an intercommunication aperture 6 located near the rim of the plate which leads through the plate to the recess 2a of the next plate 1a below. Located diametrically opposite the inter-communication aperture 6 is another such aperture 7 which leads to the outer end of the ionization duct 5a of plate 1a which extends radially inward to recess 2a. As seen from the drawing, the recesses 2 and 2a are located at mutually opposite sides of the plates 1 and 1a so that a portion of the under surface of plate 1 forms the top wall of recess 2a in plate 1a. The electrical connections are such that the spark gap formed between electrodes 3-4 of plate 1 is connected in parallel with the spark gap formed between electrodes 3a - 4a of plate 1a. More particularly an electrical connection illustrated schematically by a conductor C1 extends from conductor C to electrode 3 in plate 1, a conductor C2 leads from conductor C to electrode 4a in plate 1a, and a conductor C3 leads from electrode 4 in plate 1 to electrode 3a in plate 1a. These two parallel-connected arc gaps are then connected by conductor C4 in series with the next two parallel-connected arc gaps formed in the next two plates 1' and 1a' in the stack which are structured in the same manner as plates 1 and 1a, respectively.
OPERATION
The improved spark gap system as described operates in the following manner.
In the event of a surge voltage being applied to the spark gap system, one of the two electrically paralleled spark gaps formed respectively by parallel connected electrodes 3-4 and 3a-4a will strike to form the first arc which, under the effect of the magnetic field produced by a blow-out coil, not illustrated, is progressively lengthened from the initial striking point 8, for example, into the arc chamber formed by the recess 2 in plate 1. The arc will continue to burn and expand in the direction of aperture 7 through which ionized gas produced by the arc passes into the ionization duct 5a in plate 1a. The ionized gas advances through duct 5a to the striking point 8a of the gap formed between electrodes 3a-4a in plate 1a and causes an arc to strike between these electrodes as the arc voltage is applied, while the arc in the first chamber between electrodes 3-4 is extinguished. The arc struck between electrodes 3a-4a then expands in the direction of the inter-communication aperture 6 through which ionized gas produced by the arc then passes through the ionization duct 5 back to the striking point 8 of the gap between electrodes 3-4 causing this arc to be restruck while the arc between electrodes 3a-4a becomes extinguished thus completing one cycle of arc transfer from electrodes 3-4 to 3a-4a and thence back to 3-4. This cyclic process of arc transfer between the two sets of electrodes 3-4 and 3a-4a is then repeated until the current has been reduced to such an extent that no further arc can be sustained.
In conclusion, it is desired to point out that the invention, as defined in the appended claims is not to be considered as restricted to the specific embodiment which has been illustrated. More particularly, while the illustrated embodiment provides two spark gaps connected in parallel, it is, of course, entirely practical to have three or more of such spark gaps connected electrically in parallel.
If the discharge in a spark gap which takes place within a chamber is not completed when the arc has acquired its maximum dimension, the arc will continue to burn. However, the cooling effect of the material of which the chamber wall is constructed diminishes as the time for which the arc burns increases and there is a risk of overheating of the spark gaps. The quenching capacity of the spark gaps is thus substantially reduced and the burn-up of the electrodes is greatly increased.
These disadvantages may be avoided in known manner by quenching the arc by renewed ignition at the contact position of the same arc gap after the said arc has reached its maximum dimension, current being conducted by the restruck arc and the cycle of restriking and extinction being repeated until the current has been reduced to a value at which no further striking can take place. In this known system, and after the arc has reached a defined size, gases ionized by the arc may be conducted through a duct past the electrodes or below thereof to the contact position of the arc gap, the threshold voltage of the arc gap being reduced to an extent which would allow restriking. Accordingly, the arc will not be prolonged at one position of the electrodes yet it will burn in only one chamber.
The prior art also discloses systems in which the arc, after having reached its maximum length in a first chamber, is drawn into a second chamber by virtue of ionized gases being conducted through the arc of the first chamber and through an ionization duct to the operating or answering position of the second chamber where the ionized gases reduce the threshold voltage to such an extent that it becomes smaller than the voltage of the arc portion in the first chamber, said arc portion being then transferred to the electrodes of the second chamber. The spark gap of the second chamber will then be struck but the arc in the first chamber continues to burn with the exception of the part diverted by the electrodes of the second chamber. This relates to a series connection of spark gaps, the arc being elongated into the second chamber by restriking after it has reached its maximum length in the first chamber. However, the fact that the first chamber is under stress during the entire discharge period and is intensively heated, particularly in the event of very large discharges is a disadvantage, more particularly since under these conditions, the electrode burn-off in the first chamber is greatly increased.
It is the object of the invention to provide an improved arc gap system which is free of the disadvantages disclosed by the prior art.
According to the invention the problem is solved in that spark gaps in successive chambers are connected electrically in parallel and means are provided for the alternate striking and elongation of the arc in the individual chambers namely by a separate ionization duct and a separate inter-communication aperture being disposed in the chambers which are formed by superposed plates.
The advantage of the invention is due in particular to the fact that the extinction capacity of the spark gap is retained in the event of substantial discharges since, after the arc has reached a defined length, a second spark gap, connected in parallel to the first spark gap, is struck in a second chamber, and the said spark gap conducts current while at the same time the arc is extinguished in the first chamber. Since the arc never burns for any prolonged period at the same position, it follows that the cooling and regeneration period of the spark gap is increased while the burn-off of the electrode is reduced. The electrically parallel connection of two identical spark gaps moreover improves the operating, i.e., its answering characteristics, that is to say, the dispersion zone of the answering voltage relative to that of an individual spark gap is reduced.
A preferred embodiment of the invention is illustrated in the accompanying drawing, the single FIGURE of which is an exploded view illustrating two pairs of spark gap chambers formed by a stack of four plates.
With reference now to the drawing, it will be seen that the spark gap system for the arrestor is comprised of a stack of circular plates in which recesses are provided for receiving spaced electrodes between which the arc is struck. In order to simplify illustration, only four such plates have been shown. As previously explained, in accordance with the invention, the spark gaps of successive chambers are connected electrically in parallel. Two pairs of such chambers appear in the drawing, and each pair of chambers is formed from two adjacent circular plates 1 and 1a made from a suitable insulating material such as a ceramic. Plate 1 of each pair is provided with a suitably configured e.g., sector-shaped recess 2 whose inner arcuate boundary reaches to substantially the center of the plate and whose outer arcuate boundary reaches to nearly the periphery of the plate and extends over an angle of about 120°. Located within the recess 2 are two spaced electrodes 3 and 4 forming a gap therebetween and across which the arc is struck. An ionization duct 5 extends in a radial direction from an intermediate point along the inner boundary of recess 2 to an intercommunication aperture 6 located near the rim of the plate which leads through the plate to the recess 2a of the next plate 1a below. Located diametrically opposite the inter-communication aperture 6 is another such aperture 7 which leads to the outer end of the ionization duct 5a of plate 1a which extends radially inward to recess 2a. As seen from the drawing, the recesses 2 and 2a are located at mutually opposite sides of the plates 1 and 1a so that a portion of the under surface of plate 1 forms the top wall of recess 2a in plate 1a. The electrical connections are such that the spark gap formed between electrodes 3-4 of plate 1 is connected in parallel with the spark gap formed between electrodes 3a - 4a of plate 1a. More particularly an electrical connection illustrated schematically by a conductor C1 extends from conductor C to electrode 3 in plate 1, a conductor C2 leads from conductor C to electrode 4a in plate 1a, and a conductor C3 leads from electrode 4 in plate 1 to electrode 3a in plate 1a. These two parallel-connected arc gaps are then connected by conductor C4 in series with the next two parallel-connected arc gaps formed in the next two plates 1' and 1a' in the stack which are structured in the same manner as plates 1 and 1a, respectively.
OPERATION
The improved spark gap system as described operates in the following manner.
In the event of a surge voltage being applied to the spark gap system, one of the two electrically paralleled spark gaps formed respectively by parallel connected electrodes 3-4 and 3a-4a will strike to form the first arc which, under the effect of the magnetic field produced by a blow-out coil, not illustrated, is progressively lengthened from the initial striking point 8, for example, into the arc chamber formed by the recess 2 in plate 1. The arc will continue to burn and expand in the direction of aperture 7 through which ionized gas produced by the arc passes into the ionization duct 5a in plate 1a. The ionized gas advances through duct 5a to the striking point 8a of the gap formed between electrodes 3a-4a in plate 1a and causes an arc to strike between these electrodes as the arc voltage is applied, while the arc in the first chamber between electrodes 3-4 is extinguished. The arc struck between electrodes 3a-4a then expands in the direction of the inter-communication aperture 6 through which ionized gas produced by the arc then passes through the ionization duct 5 back to the striking point 8 of the gap between electrodes 3-4 causing this arc to be restruck while the arc between electrodes 3a-4a becomes extinguished thus completing one cycle of arc transfer from electrodes 3-4 to 3a-4a and thence back to 3-4. This cyclic process of arc transfer between the two sets of electrodes 3-4 and 3a-4a is then repeated until the current has been reduced to such an extent that no further arc can be sustained.
In conclusion, it is desired to point out that the invention, as defined in the appended claims is not to be considered as restricted to the specific embodiment which has been illustrated. More particularly, while the illustrated embodiment provides two spark gaps connected in parallel, it is, of course, entirely practical to have three or more of such spark gaps connected electrically in parallel.