US2862132A

US2862132A - Spark gap device

Info

Publication number: US2862132A
Application number: US590137A
Authority: US
Inventors: Jr Tom L Dyer
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1956-06-08
Filing date: 1956-06-08
Publication date: 1958-11-25
Anticipated expiration: 1975-11-25

Description

Nov. 25, 1958 T. DYER, JR 2,862,132

SPARK GAP DEVICE Filed June 8, 1956 Magnet \Y\\\\ i "r 2' WITNESSES INVENTOR Tom L. Dyer, Jr.

ATTORN Y United States Patent SPARK GAP nnvrcn Tom L. Dyer, Jim, North Huntingdon Township, Westrrioreiand (Iounty, Fa assignor to Westinghouse Elec trio filorporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application June 3, 1956, Serial No. 590,137

4 Claims. (Cl. 313-156) The present invention relates to spark gap devices and, more particularly, to a spark gap for lightning arresters of the valve type.

Valve type lightning arresters consist essentially of a spark gap, or a series of spark gaps, of fixed lengths, connected in series with a resistance element having valve or nonlinear characteristics; that is, a resistor whose resistance decreases with increasing voltage, so that under normal voltage conditions it offers a very high resistance and at overvoltage conditions offers a low resistance, so as to permit a surge to be discharged to ground with low discharge voltage; and which is capable of thereafter increasing its resistance to reduce the power follow current at normal voltage to a small value. The series gap device normally insulates the arrester from the line to which it is connected, but sparks over under a predetermined overvoltage to connect the arrester between line and ground to allow the surge to be discharged to ground. After discharge of the surge, the valve element of the lightning arrester reduces the power follow current, which tends to flow due to the normal line voltage, to a small value which is interrupted by the gap to again insulate the arrester from the line.

Recent improvements in lightning arresters of this type have resulted in improved protective characteristics of the valve element and, in particular, in reduced discharge voltage. The effect of this lower discharge voltage characteristic is to increase the power follow current which flows through the arrester after a discharge, and which must be interrupted by the series gap. With moderate power follow currents, the Valve elements act as an appreciable resistance against the flow of follow currents. Thus the series gap of fixed length is well able to interrupt the current flow at the first current zero, and remain physically unchanged. However, with the higher power follow currents resulting from the improved protective characteristic mentioned above, the conventional .types of series gaps are inadequate to interrupt the current flow at the first current zero. The flow of power follow current for an appreciable time is highly undesirable because it raises the temperature of the gap electrode, which is usually made of brass, above its melting point and thus causes deformation or serious burning of the electrode. Such deformation is likely to cause a sufficient change in the shape of the electrode to reduce the effective spacing between the electrodes, thus lowering the sparkover voltage of the gap, so that interruption of the arc is made more diflicult.

The principal object of the present invention, therefore, is to provide an improved spark gap device which will facilitate interruption of the arc, and which is better able to resist the burning effects of the arc.

Another object of the invention is to provide in a spark gap device a magnetic field in the gap in a direction to cause outward movement of the arc until it is extinguished.

A further object of the invention is to provide a spark gap device wherein the initial arc is broken into a pluice rality of smaller arcs without permitting recombination of the plurality of arcs into a single arc.

A still further object of the invention is to provide a magnetic spark gap device in which the need for costly and bulky coils to produce a magnetic field is eliminated.

Other objects and advantages of the invention will be apparent from the following detailed description, taken in connection with the accompanying drawing, in which:

Figure 1 is a top plan view of a spark gap device showing a preferred embodiment of the invention;

Fig. 2 is a side elevation of the spark gap device;

Fig. 3 is a sectional view taken on the line III-III of Fig. 2; and

Fig. 4 is a sectional view taken on line IVIV of Fig. 1.

The present invention is particularly suitable for use in lightning arrester spark gaps, although it will be understood that its usefulness is not necessarily limited to this specific application. As can best be seen in Fig. 4, the spark gap assembly is enclosed by a pair of ceramic circular shaped housing members 1 which contain the remaining parts. The housing members 1 each consist of a flat disc-shaped base 2 and an annular flange 3 which encircles the perimeter of the base 2. Each flange 3 is provided with a pair of notches 4 on opposite ends of a diameter (Fig. 2) to receive and properly position a pair of wedge-shaped electrodes 5. The electrodes are preferably made of brass but may be made of any suitable conducting material. The flanges 3 are also provided with narrower notches 6 circumferentially spaced between the notches 4 to receive and space a series of radially arranged metallic arc splitters 9 (Fig. 3). The flanges of the housing 1 extend toward each other and they are spaced apart a small distance by the electrodes and are splitters. The corresponding notches 4 and 6 of each housing flange 3, as best shown in Fig. 2, are

dimensioned and aligned to receive and properly space electrodes 5 and arc splitters 9.

A pair of substantially disc-shaped permanent magnets 7, made of any suitable permanent magnet material but preferably an insulating material, are received in each housing member within the recess formed by the base 2 and flange 3.

In the preferred embodiment shown herein the magnets 7 are magnetized in an axial direction, each having a north pole on one face and a south pole on the opposite face. The magnets 7 are positioned in the housing in such a manner that the north pole of one magnet will face the south pole of the other or, in other words, the magnets are arranged in attraction.

However, any suitable arrangement of the magnets may be used which will producea magnetic field perpendicular to the path of the are and the magnets need not necessarily be arranged in attraction. Thus, by the disclosed arrangement there exists at all times a relatively strong magnetic field perpendicular to the magnet faces.

The permanent magnet 7 may be made of any suitable permanent magnet material. It is preferable, however, to use a ceramic material belonging to the ferrites and in particular barium ferrite (BaFe O Magnets made of this material have very advantageous properties. It has great resistance to demagnetization by transient external magnetic fields or other external forces such as heat or shock. Most permanent magnet materials are quite easily demagnetized by such influences and must be very carefully handled and protected to prevent demagnetization. The magnetic stability of the preferred material makes it very desirable for the purposes of the invention since it is not subject to any substantial loss of. magnetic strength even if any unusual conditions of handlingor use appear. Another advantageous property of this permanent magnet materialis its electrical insulating quality.

The preferred material is an excellent insulator. Thus the advantageous placement of the magnets of the present invention is made possible. The magnets can bridge the gap electrodes without danger of short circuiting them as any ordinary metallic magnet would do. The problem of insulating the magnet from the electrodes is thereby eliminated.

If desired, the thickness of the permanent magnet can be made slightly less than the height of the flange 3 between the base 2 and the closed edge of the notches to permit the positioning of a ring washer 3 made of arcresisting material within the recess adjacent each magnet and flush with the closed edge of the notches 4 and 6. The ring washer 8 serves to protect the magnet faces from are erosion. The washer 8 may be made of any insulat ing material having arc resisting properties. it is preferred, however, to use polytetrafluoroethylene because of its high order to resistance to are erosion. These washers 8 have been used in the preferred embodiment illustrated in the accompanying drawings. it will be appreciated, however, that the use of ceramic magnets eliminates the need for these washers for the purpose of insulation. The use of washers 3 is desirable, however, for the purpose of preventing arc erosion on the face of the permanent magnets 5, thereby prolonging the life of the gap device. Breakdown of the washers due to are erosion will not render the gap device useless inasmuch as short circuiting of the electrodes will not occur. Washers 8 further prevent possible breakage of the magnets 7 due to high thermal shock.

The wedge-shaped electrodes 5 and are splitters are sandwiched between the pair of housings 1, their associated magnets 7 and washers 8. Electrodes 5 and are splitters 9 are received in notches 4 and 6, respectively, and extend radially outwardly beyond the periphery of the housing as clearly shown in Figs. 1 and 3. The longitudinal center lines of the electrodes 5 are aligned along a diameter of the assembly. The apices of the electrodes extend toward each other and are spaced apart adjacent the center of the spark gap assembly to form an air gap it) between them. The arc splitters are arranged in radial spaced relationship between the outwardly diverging edges of the electrodes and converge adjacent the air gap It In actual use in a lightning arrester, one electrode is connected in series with a valve block 11, or non-linear resistance, which is, in turn, connected to ground. The other electrode is connected to a transmission or distribution line or other device to be protected.

A plurality of these gaps may be connected in series if desired in any suitable manner in accordance with the usual practice in lightning arresters.

The operation of the invention can be seen from the above detailed description. An arc is initiated in the gap 10 between the electrodes 5. There is at all times a relatively strong magnetic field perpendicular to the faces of the magnets 7. Since the arc is at right angles to the magnetic field, it will move parallel to the magnet faces toward one or the other groups of arc splitters. After the arc enters the splitters, it will divide into a series of smaller arcs and continue to move outwardly since it always moves at right angles to the magnetic field. At some point outwardly of the gap, the arc will be extinguished because of extension of the arc path, cooling of the gases, and failure to reignite after current zero has been passed.

It will now be apparent that a spark gap device has been provided which has very desirable characteristics since it has means for positively interrupting the arc. It has been been proposed to accomplish this result by means of coils through which the discharge current passes and which produce a magnetic field for the purpose of moving the arc. Such an arrangement has many disadvantages, however, and does not positively insure movement of the are because the strength of the magnetic field varies with the'magnitude of the current, so that a constant, strong ifield is not provided. The necessary coil is fairly bulky and requires a relatively large amount of space which is not readily available, and also requires an auxiliary gap to protect the coil itself from surges of steep wave front. Thus, the use of a magnetic coil to produce a field for moving the arc is not a satisfactory solution of the problem because of the numerous disadvantages involved. The present invention avoids these disadvantages in a simple and effective manner by using a permanent magnet in a manner which requires no additional space. The use of a permanent magnet makes possible the provision of a strong constant magnetic field which is independent of the magnitude of the discharge current, and no auxiliary gaps or other protective means are required. Thus, a very effective and desirable means is provided for positively producing movement of the arc in a gap device.

A particular embodiment of the invention has been shown and described for the purpose of illustration, but it will be apparent that various modifications and other embodiments are possible within the scope of the invention. Thus, the electrodes may be of any desired configuration, and the permanent magnet itself may be of any desired shape to conform to the electrode configuration and to the configuration of the housing, and may be magnetized in any desired direction to produce a magnetic field which extends throughout the gap space in a direction generally perpendicular to the path of a discharge. It is to be understood, therefore, that the invention is not limited to the specific embodiment shown for the purpose of illustration, but includes all equivalent embodiments and modifications.

I claim as my invention:

1. In a lightning arrester, the combination comprising a pair of substantially flat spark gap housing units each having an annular flange said flange having a first pair of notches in alignment and other notches circumferentially spaced, said housing units arranged with their flanges in face-to-face relation and positioned with corresponding notches in alignment, a permanent magnet of insulating material received in each of said housing units and enclosed by said flanges, said magnets arranged in attraction, a thin arc resisting ring Washer having one of its faces lying adjacent its corresponding magnet and its other face flush with the free end of a corresponding housin flange, a pair of stationary electrodes received in said first pair of notches, said electrodes spaced apart radially to form a spark gap between them and a series of radially extending arc splitters received in said other set of notches.

2. In a lightning arrester, the combination comprising a pair of substantially flat spark gap housing units each having an annular flange, said flange having a first pair of notches in alignment and other notches circumferentially spaced, said housing units arranged with their flanges in face-to-face relation and positioned with cor responding notches in alignment, a permanent magnet of insulating material and low permeability received in each of said housing units and enclosed by said flanges, said magnets arranged in attraction, a thin arc resisting ring washer having one of its faces lying adjacent its corresponding magnet and its other face flush with the free end of a corresponding housing flange, a pair of stationary electrodes received in said first pair of notches, said electrodes spaced apart radially to form a spark gap between them and a series of radially extending arc splitters received in said other notches.

3. In a lightning arrester, the combination comprising a pair of substantially flat spark gap housing units each having an annular flange, said flange having a first pair of notches in alignment and other notches circumferentially spaced, said housing units arranged with their flanges in face-to-face relation and positioned with corresponding notches in alignment, a permanent magnet of ferromagnetic ferrite ceramic material being an insulater and having low permeability received in each of said housing units, and enclosed by said flanges, said magnets arranged in attraction, a pair of stationary electrodes received in said first pair of notches intermediate and in close proximity to said permanent magnets, said electrodes spaced apart radially to form a spark gap between them and a series of radially extending are splitters received in said other notches.

4. In a lightning arrester, the combination comprising a pair of substantially flat spark gap housing units each having an annular flange, said flange having a first pair of notches in alignment and other notches circumferentially spaced, said housing units arranged with their flanges in face-to-face relation and positioned with corresponding notches in alignment, a permanent magnet of ferromagnetic ferrite ceramic material being an insulator and having low permeability received in each of said housing units, and enclosed by said flanges, said magnets arranged in attraction, a thin arc resisting ring washer having one of its faces lying adjacent its corresponding magnet and its other face flush with the free end of a corresponding housing flange, a pair of stationary electrodes received in said first pair of notches, said electrodes spaced apart radially to form a spark gap between them and a series of radially extending arc splitters received in said other notches.

References Cited in the file of this patent UNITED STATES PATENTS 2,566,895 Kalb Sept. 4, 1951 2,614,232 Kalb Oct. 14, 1952 2,644,116 Olsen et a1. June 30, 1953 2,677,032 Wells Apr. 27, 1954 2,759,989 'Anderson Aug. 21, 1956 2,762,777 Went et a1 Sept. 11, 1956