US3704388A

US3704388A - Spark gap for surge diverters

Info

Publication number: US3704388A
Application number: US77218A
Authority: US
Inventors: Bengt Johansson; Erland Nilsson
Original assignee: ASEA AB
Current assignee: ABB Norden Holding AB
Priority date: 1970-07-06
Filing date: 1970-10-01
Publication date: 1972-11-28
Anticipated expiration: 1989-11-28

Abstract

A spark gap for surge diverters is composed of a plurality of plates of insulating material stacked one on the other with spaces there between. Electrodes are carried on each face of the plates. The electrodes have parts connected to each other by attachment members passing through the plates. The electrodes at each space have vertically aligned parts forming a spark gap and the parts deviating from vertical alignment and forming a running-out path which becomes substantially parallel to the plane of the plates.

Description

United States Patent J ohansson et a].

[54] SPARK GAP FOR SURGE DIVERTERS [72] inventors: Bengt Johansson; Erland Nilsson both of Ludvika, Sweden I73] Assignee: Allmanna Svenska Elektriska Aktlebolaget, Vasteras, Sweden [22] Filed: Oct. 1, 1970 [2]] Appl. No.: 77,218

[30] Foreign Application Priority Data July 6, 1970 Switzerland ..9315/70 52] U.S.CI. ..315/36,3l7/74,317/77 51 Int.Cl. ..H02h 1/00 [58] FieldofSearch ..315/36;3l7/74,77

[56]v References Cited UNITED STATES PATENTS Lee et al ..3l5/36 NOV. 28, 1972 3,515,947 6/1970 Stetson ..3l5/36 Primary Examiner-Roy Lake Assistant'Examiner--Darwin R. Hostetter Attorney-Jennings Bailey, Jr.

[ ABSTRACT A spark gap for surge diverters is composed of a plurality of plates of insulating material stacked one on the other with spaces there between. Electrodes are carried on each face of the plates. The electrodes have parts connected to each other by attachment members passing throughthe plates; The electrodes at each space have vertically aligned parts forming a spark gap and the parts deviating from vertical alignment and forming a running-out path which becomes substantially parallel to the plane'of the plates.

8 Chain, 7 Drawing Figures INVENTOR. BEN a r CJOHAN s so! BY ER rwo m L saw Wwx PATENTEBNnv 28 m2 3. 704 388 SHEET 2 BF 3 INVENTOR.

@ENGT ATOIIAMSSOA/ SPARK GAP. FOR SURGE DIVERTERS BACKGROUND or THE INVENTION I 1. Field of the Invention ters.

2. The Prior Art A surge diverter havingmagnetic blowing of the arcs comprises a number of stacks in .which there is a number of spark gaps, one or more blowing coils, and

blocks of non-linear resistance elements. The spark gaps are built up of circular plates of insulating material and arranged so that the are always lies ina plane parallel to that of the plates and perpendicular to the axial magnetic flux generated by the blowing coils. This axial l5 SUMMARY OF THE INVENTION The presentinvention relates to a surge diverter having magnetic blowing of the arcs, but where the electrodes are designed and arranged 'sothat the spark-over distance, that is, the distance between the two surfaces on the electrodes which form the spark-over gap, is axial. The extension of the are immediately after thearc has sparked over in the spark-over gap is effectedby placing the spark-over gap eccentrically on the plate,

and preferably near the edge of the plate, where the arc will come under the influence of the horizontal component of the magneticflux so that it is blown out in a tangential direction. Since the surfaces of the spark-. over gap are parallel with the plane of the plate, they can be made large without affecting the height of the stack axially, and this means that much larger currents 5 can be permitted in the spark-over gap without risk of erosion and alteration of the spark-over distance.

According to the invention the electrodes are curved in the plane of the plate and the two electrodes forming a spark gap have difierent radii of curvature so that the distance between them increases from the spark-over point outwardly. The axial distance between the electrodes, however, remainssubstantially unaltered. This arrangement of the electrodes means that, as the arc is blown out from the spark-over point and is moved from the spark-over distance out into the running-out path, the arc is deflected from a substantially vertical to a substantially horizontal direction and at the same time it comes under the influence of the vertical component of the magnetic flux. The running-out path in this case means the distance between the electrodes which the arc follows when, under the influence of the magnetic flux and the arc force it moves from the spark-over point out towards the free ends of the electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings.

The invention relates to spark gaps for surge diver- 5 FIG. 1 shows a vertical section through a stack in a surge diverter according to the invention.

FIG. 2 is a horizontal section along the line Il-II in FIG. 1.. v

FIG. 3 shows a single plate with electrodes.

FIG.'4 is a vertical section along the line IV-IV in rlasanu FIG. 5 is a section along the line v v in FIG. 3. FIG. 6 is a view from above of a plate and FIG. 7 is a section along the line VII VII in FIG. 6;

DESCRIPTION OF THE PREFERRED EMBODIMENTS arranged one on top of the other. Above the blowing coil is an annular metal plate 4 which is connected at 5 to the coil winding. On its lower side the coil is connected to another metal plate 6. The

plates

2 and 2a which carry the electrodes are made of arc-resistant insulating material. The upper plate 2a which is in contact with the metal plate 6 has an electrode 7 on its lower side. The electrode is attached to the plate by a rivet 9 which goes through the plate 2 and is in contact with the metal plate 6. The upper plate 2a is flat whereas the other plates 2 have a peripheral, upwardly directed flange 10 so that a space 11 is formed between two plates. The two intermediate plates are provided with an electrode 8 on the upper side and an electrode 7 on the lower side. The electrodes are connected to each other and attached to the plate 2a by the rivet 9. Successive rivets9 are arranged substantially in vertical alignment to provide vertical spark-over gaps.

The two

electrodes

7 and 8 which are in the same space 11 when the plates are stacked on top of each other form a spark gap in which an arc arises when the surge diverter sparks over. In order to define the spot on the electrode at which the spark-over between the two electrodes should occur, at least one of the electrodes is provided with a somewhat raised sparking surface 12. Preferably both electrodes are provided with said sparking surfaces. As can be seen from FIG. 1, the sparking surface is in a plane parallel to that of the plate 2 and this means that the sparking surface can be made large, which is an advantage when large surge currents occur. The current density will therefore be less and also it is certain that the arc will not always start from exactly the same point on the sparking surface each time an arc arises. Both these facts contribute to decreasing the erosion on the sparking surface. This makes the spark gap last longer and counteracts the alteration in the spark-over distance of the gap which is a result of erosion of the spark-over surfaces.

As is clear from FIG. 2 the electrodes are curved and of different lengths and deviate from vertical alignment with each other. The electrode 8 is longest and its outer edge is substantially concentric with the periphery of the plate 2 and is in close contact with the inner surface of the flange 10. The electrode 7 is more curved and its outer edge extends in towards the central part of the plate 2. The electrodes are preferably shaped so that the distance between the two electrodes arranged in the same space increases successively from the sparkover point out towards the free ends of the electrodes.

Since the blowing coil 1 is at one end of the spark gap stack and the spark-over gap is placed at the periphery of the plates, a nonhomogeneous magnetic flux will flow through the spark-over gap, which is shown by the dotted lines in the left-hand part of FIG. 1. The flux flowing through a spark-over gap may thus be imagined to consist of a horizontal and a vertical component. At the moment of spark-over, the arc is vertical and is then influenced by the horizontal component of the flux so that it moves clockwise in FIG. 2. When the arc has run so far that its base points on the electrodes are no longer above one another, the main extension of the arc will start to change from a direction substantially perpendicular to the plane of the plates to a direction which becomes more and more parallel with said plane as the arc runs out and its running-out path increases. As the arc changes direction it comes more and more under the influence of the vertical component of the magnetic flux and the arc will therefore be forced out and extended.

In the region outside the free ends of the electrodes, the space 11 is shaped to form an extinguishing chamber 13 which is lower than the space. The extinguishing chamber starts approximately at the dotted line 14 in FIG. 2. The length of the arc increases in the extinguishing chamber and, because of the decreasing distance between the limiting surfaces, the arc. is cooled. This is a well-known expedient in surge diverters and in and of itself forms no part of the invention.

Between the extinguishing chamber 13 and the attachment point of the electrodes a barrier 15 of insulating material is inserted so that a space 16 is formed which is separated from the extinguishing chamber. In this space the ionizing meansnecessary for the sparkover gap and control impedance elements, if desired, are placed.

In the embodiment of the invention shown in FIG. 1 the electrodes are completely flat at the attachment point and connected by the rivet 9. In a diverter for high currents the rivet must be made thick so that it can handle the current load. This causes certain complications in the attachment of the electrodes. FIGS. 3, 4 and 5 show another alternative which is particularly suitable for use with high currents. The electrodes are provided with a depressed part 17 directed towards the plate 2 and fitting into a hole 18 through the plate. This part of the electrode is depressed to a depth of approximately half the thickness of the plate. The electrodes are connected to each other by means of a rivet 19.

- When the rivet is in place, the depressed parts of the starts to run substantially horizontally, its base point I will be on the edge surfaces of the electrodes which are relatively narrow, thus causing great current density in the base point itself. On way of increasing the contact surface between the electrodes and the arc is to turn the electrode a quarter turn and initiate the turning where the arc starts to turn itself. The turning be carried out continually along a certain distance, or more abruptly, the electrodes being bent rather sharply. Since the running-out speed is greater at the base point of the arc running on the outer electrode 8, it is often sufificient to turn this electrode. FIGS. 6 and 7 show how the electrode 8 is turned a quarter turn. At the attachment and at the spark-over point the electrode is completely parallel with the plate but at a point 20, where the arc starts to turn from the purely vertical position, the electrode also starts to turn about its longitudinal direction and the turn is preferably chosen so that the arc is substantially perpendicular to the surface of the electrode. The turn may be made quickly or not so quickly and a limit may be considered to be a sharp bend in the electrode. It is also possible to turn the inner electrode, although this does not usually give such pronounced advantages as turning the outer electrode.

In order to prevent reignition of the arc straight across the running-out distance between the free ends of the

electrodes

7, 8 when the arc has been extended so that it is far into the extinguishing chamber and has high arc voltage drop, it may be necessary in certain cases to arrange a spark-over block 21 between the electrode ends. The spark-over block may consist of a ridge of ceramic material projecting from the plate or a metal plate attached in the plate. The spark-over block prevents the strong ionization which occurs at the base points of the are on the electrodes from going over to the opposite electrode. The phenomenon is more pronounced with high currents and arcs of long duration. The spark-over blocking device is shown in FIGS. 1 and 2.

We claim:

1. Spark gap for surge diverters having magnetic blowing of the arc comprising at least two plates of insulating material stacked on top of each other with a space between the plates, metallic electrodes one secured to each of the plates within said space, said electrodes forming a spark gap and having substantially vertically aligned parts to provide an arc gap with a predetermined spark-over distance situated near the periphery of the plates and with a pre-determined spark-over distance in a plane perpendicular to the planes of the plates, other elongated parts of the electrodes deviating from the area of said arc gap with respect to each other to provide a running-out path for the arc generated in the arc gap, whereby said arc gap is directed substantially perpendicular to the plane of the plates whereas the running-out path lies substantially in a plane parallel with that of the plates.

2. Spark gap according to claim 1 in which at least some of the plates carry electrodes on opposite sides, an attachment device electrically and mechanically connecting the electrodes on opposite sides of a plate to each other, said attachment device running through the plate in the vicinity of its periphery.

3. Spark gap according to claim 1, at least one of the electrodes having a spark-over surface for the arc gap,

said spark-over surface being parallel with the plane of the plate.

4. Spark gap according to claim 1, in which the electrodes are elongated and attachment devices located near one end of each of the electrodes secure the electrodes to the plates, the other ends of the electrodes being free:

5. Spark gap according to claim 1, in which the arc gap is located closely adjacent point of securement of the electrode to the plate.

6. Spark gap according to claim 1, in which the electrodes are each provided with a depressed part directed towards the plate which fits into a hole through the plate, said part being depressed to a depth of approximately half the thickness of the plate, the attachment device. comprising .a member extending through said electrode at said gap lying substantially in the plane of the plate.

Claims

3. Spark gap according to claim 1, at least one of the electrodes having a spark-over surface for the arc gap, said spark-over surface being parallel with the plane of the plate.

4. Spark gap according to claim 1, in which the electrodes are elongated and attachment devices located near one end of each of the electrodes secure the electrodes to the plates, the other ends of the electrodes being free.

6. Spark gap according to claim 1, in which the electrodes are each provided with a depressed part directed towards the plate which fits into a hole through the plate, said part being depressed to a depth of approximately half the thickness of the plate, the attachment device comprising a member extending through said depressed part holding the electrodes in direct metallic contact with each other.

7. Spark gap according to claim 1, in which the electrodes are curved, one electrode being substantially concentric with the periphery of the plate and the other electrode extending from the gap in an arc towards the central part of the plate.

8. Spark gap according to claim 1, in which at least one of the two electrodes is turned substantially a quarter turn about its longitudinal axis, the part of the electrode at said gap lying substantially in the plane of the plate.