US2018672A - Surge diverter - Google Patents

Description

0a. 29, 1935 L. H. HILL 2,018,672

SURGE DIVER'I'ER Filed March 13, 1933 Patented Oct. 29, 1935 UNITED STATES PATENT OFFICE SURGE DIVERTEB Leland H. Hill, Wlllwatm, Wll.,

uslgnor to Allis- Application March 13, 1933, Serial No. 660,487

9Clalms.

This invention relates in general to devices for preventing the flow of high voltage surge currents into electrical apparatus such as transformers, reactors, circuit breakers, and the like; and relates more particularly to surge diverters which may be mechanically attached to apparatus of the above type in such a manner as to form a spark gap in air with long creapage paths.

The utility of applicants invention may best be understood by reference to the-power distribution art wherein this invention has its widest application. For example, it is common practice to protect distribution transformers from lightnine by connecting lightning arresters between the conductors of the transmission line and ground at points adjacent the transformers. These lightning arresters are usually mounted on across-arm on a pole or on a bracket attached to the transformer casing, but in either event the lightning arrester must be provided with adequate insulation to prevent a flashover from line to ground. This requires bulky and expensive parts of insulating material and also requires numerous connecting leads which naturally are not only a hazard to the lineman who must work in close proximity to these leads, but are also a potential source of trouble caused by short circuits and grounds. The lightning arresters of the prior art usually comprise a resistance element and one or more series spark gaps all enclosed in an insulating housing. In such enclosed arresters there is a tendency for the spark discharges to cause a deposit of metallic powder on the inner walls of the insulating housing adjacent the gaps and this action combined with the tendency for moisture-to collect on these walls tends to permit leakage discharges which cause radio interference or static.

It-is an object of the present invention to minimize the above hazards by so mounting a surge diverter of novel construction directly on the apparatus to be protected and adjacent the bushings thereof in such a manner that these bushings insulate the surge diverter.

Another object of this invention is to provide a surge diverter which has a resistance element so mounted adjacent an insulating bushing of the apparatus to be protected that an unlnclosed spark gap is formed whereby leakage discharges 50 which cause radio interference are minimized.

Another object of the invention is to provide a surge diverter which is mounted directly on the casing or hangers of the. apparatus to be protected and is provided with an arcing element arranged in close proximity with a line conductor or terminal of the apparatus so as to form a spark gap for the discharge of surge currents. A further object of the invention is to provide a surge diverter having a novel form of container for a body of material having a negative resistance coeflicient with respect to voltage.

A still further object of the invention is to provide a surge diverter which is easily manufactured, is rugged in its construction, and may be readily installed or replaced without the necessil0 ty of making connections to high voltage conductors.

These and other objects and advantages are attained by this invention, various novel features of which will be apparent from the descrip- 15 tion and drawing herein, and will be more particularly pointed out in the claims.

Various illustrative examples of the application of this invention are shown in the accompanying drawing in which: 20 Fig. 1 is a side view of a surge diverter embodying the invention as applied to electrical apparatus having a terminal supporting bushing, the housing of the surge diverter being shown in section;

Fig. 2 is a top in Fig. 1;

Fig. 3 is a side view of a transformer installation showing a different way of connecting and mounting a surge diverter embodying the invention;

Fig. 4 is a side view of a surge diverter embodying the invention as applied to an electrical apparatus having a cable extending through an insulating bushin 35 Fig, 5 is a side view of a surge diverter embodying the invention as applied to electrical apparatus having a mounting hanger;

Fig. 6 is a top view of Fig. 5 with a portion of the apparatus housing in section; 40

Fig. 7 is a side view of a surge diverter embodying the invention connected and secured to the bushing supportedterminal of electrical apparatus; and

Fig. 8 is a modified surge diverter embodving 45 the invention as applied to electrical apparatus having an insulating bushing.

Referring now more particularly to the drawing, Ill isthe metal casing of electrical apparatus such as a transformer,.reactor, circuit breaker or the like which is either directly connected to ground or connected thereto through a grounding gap ll. Casing I0 is provided with a hole through which the shank portion of an insulating bushing'll projects, noting that a gasket I1 25 view of the surge diverter shown with a lug portion is adapted to cover the exposed parts of terminal device l8 and is provided with a slot in one lip through which surge currents may discharge as will be more fully described hereinafter.

The preferred form of surge diverter embodying the present invention comprises a cup-shaped receptacle 2| of insulating material, such as porcelain, which has a hole in the end thereof for the passage of bolt 22, noting that a gasket of material, such as cork, is interposed between the head portion of bolt 22 and the body of the receptacle. An arcing contact finger 24 is secured to receptacle 2| by means of nuts 25, noting that this finger is provided with lip portions 26 which cooperate with raised shoulders on receptacle 2| so as to permit contact finger 24 to be adjusted to a plurality of positions. Receptacle 2| containsa resistance material 21 which has the characteristic of reducing its resistance when the voltage impressed thereon is increased. This material is preferably in the form of one or more cylindrical blocks which contain silicon carbide and graphite. A suitable form of this material is known commercially as Globar. However it is to be understood that other resistance materials known to the art having a valve characteristic may be-used, such as granular silicon carbide compounds and oxide pellets for example. When resistance material in the form of blocks is used, the faces of these blocks are preferably provided with metallic coatings produced by electroplating or by the Schoopgun process. Resistance material 21 isheld in place in receptacle 2| in electrical contact with bolt 22 by means of any suitable semiplastic compound 28. A conducting base member 29 is held in electrical contact with one end of resistance material 21 by means of bushing cement 3|, noting that it is preferable to provide the lip portions of receptacle 2| with sanded surfaces in order that base member 29 may be firmly secured to receptacle 2|.

In Fig. 2 base member 29 is shown as provided 32 which has a plurality of mounting holes 33. therein. Mounting holes 33 are utilized to bolt the surge diverter to casing It in such a manner that arcing contact finger 24 extends a predetermined distance away from terminal member It so as to thereby form a spark gap which is substantially surrounded by Inasmuch as arcing contact finger 24 is not connected to line conductor H, the possibility of leakage currents creeping along solid insulating material and flowing through resistance material 21 to ground is In' Fig. 3 a transformergis shown connected to transmission line conductors 34 by means of fuse cutouts 35 and lead conductors II which are insulated from casing It by means of insulating bushings |2. Two surge diverters similar to those shown in Figs. 1 and 2 are mounted on insulating pillars 36 in such a manner that arcing contact fingers 24 form spark gaps with the line terminals as hereinabove described. Base members 3| of the surge diverters are connected to ground by part ring l4 and a plurality of means of insulated conductors 31. This manner of connecting surge diverters to electrical apparatus is of utility where it is not desired to ground the casing III. Obviously a grounding gap I may be inserted in the ground circuit if desired.

Fig. 4 shows-how a surge diverter such as disclosed in connection with Figs. 1- and 2 may be used to protect electrical apparatus oi the type having bushings such as shown by 38 through which a flexible insulating cable 39 extends. Rather than remove a portion-of the insulation on cable 39, it is preferable to use a pointed screw I 4| which pierces the insulation of cable 39 and is held in place by any suitable means, such as threaded member 42 which is mounted in an insulating collar 43 which may be readily slipped over cable 39.

In Figs. 5 and 6 a surge diverter such as disclosed in connection with Figs. 1 and 2 is mounted in close proximity to the terminal member of a transformer by means of a bracket 46 which is bolted to the usual hanger strap 44 which in turn is'bolted to a hanger bracket 45 which is preferably welded to casing member l0.

Fig. 7 shows how a surge diverter similar to that disclosed in Figs. 1 and'2 may be supported from the terminal member of an insulating bushing l2. This method of mounting a surge diverter may be accomplished by extending the length of lug portion 32, noting that large hole 33 (Fig. 2) enables this portion to be clamped between the base portion of terminal l8 and bushing H with a suitable gasket 30 i. :rposed therebetween. A contact button 48 may be welded or otherwise secured to casing ||l so as to form a spark gap with nut 25 which may be adjusted to vary the length of this gap, may be varied to adjust the length of the spark gap.

In Fig. 8 bushing member I2 is provided with an extra long shaft in order that an annular ring of resistance material 21 may be mounted between casing l0 and the shoulder of said bushing. An arcing contact 5| having one or more arcing points and gasket l3 are interposed between resistance material 21 and the shoulder of bushing l2. In order to exclude moisture from resistance material 21 an insulating tube 2| surrounds material 21 and is sealed by means of compound. A conductive gasket 49 is interposed between the other end of resistance ring 21 and grounded to casing Although Figs. 3, 4, 5, 7 and 8 show casing member connected directly to ground, it is to be understood that this member may be connected to ground through a grounding gap as shown at H in Fig. 1, it being understood that the term grounded casing embraces both of these arrangements.

As to the operation of the surge diverter; upon rise of voltage on conductor lead l1 due to lightning or other surge disturbances the spark gap formed by arcing finger member 24 (or its equivalent) will break down permitting a discharge oi surge current through resistance material 21. Inasmuch as this material has a resistance coefiicient inversely proportional to the voltage impressed thereon, the surge current will be quickly conducted to ground, however upon oessation of flow of surge current the voltage will drop again to normal and the resistance of element 21 will automatically rise to such a value as to prevent the fiow at line current through the surge diverter. Inasmuch as the spark gap in or the thickness of gasket 30- supported by said housing the housing member ii and is unenclosed. there will be substantially no opportunity for leakage currents to flow through the surge diverter in such a manner as to cause radio interference. It is also to be noted that surge diverters em the present invention may be applied to electrical apparatus as shown in Figs. 1, 8, 4, and 6 withthe necessity of using leads to connect the surge diverter with the line conductor. Certain features of the invention herein disclosed are claimed in my copending application Serial No.

628,876, filed August 15, 1932 for apparatus.

' Although but a few embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims;

It is claimed and desired to secure by Letters Patent:

l. A surge diverter for protecting electrical apparatus which has current conducting means extending through an opening in the housing of said apparatus and is insulated from said housing by an insulating bushing which extends through said opening, said surge diverter comprising in combination, a body of material having a negative resistance coeincient with respect to voltage, means for mounting said body on the exterior of said housing and adjacent said bush ing, and means forming a path for conducting currents induced by surge voltages on said current conducting means through said body and said housing, said last mentioned means comprising conductive members having electrical connection with said conducting means and said body respectively forming an unenclosed spark gap in series with said body.

2. A surge diverter for protecting electrical apparatus which has current conducting means extending through an opening in the housing of said apparatus and is insulated from said housing by an insulating bushing which extends through said opening, said surge diverter comprising in combination, abody of material having an inverse resistance characteristic with respect to the voltage impressed thereon, means for mounting said body exteriorly of said housing adjacent said bushing, and means forming a path for conducting currents on said conducting means through said body and through said housing to ground, said last mentioned means comprising metallic members associated with said body forming a spark gap in series with said body and external thereto.

3. A surge diverter for protecting electrical apparatus which has current conducting means extending through the housing of said apparatus and is insulated from said housing by means of an insulating bushing, comprising in combinaticn, a resistance element having an. inverse resistance characteristic with respect to voltage adjacent said bushing, and means for establishing a circuit for the flow of surge currents from said current conducting means through said resistance element to said housing upon occurrence of high potential on said conducting means, said circuit establishing means comprising conductive members in electrical connection with said conducting means and said resistance element respectively arranged in spaced relation so as to form a spark gap in series with said resistance element and external thereto.

4. A surge diverter for protecting electrical apparatus which has current conducting means extending through an opening in the grounded 5 casing of said apparatus and is insulated from said grounded casing by an insulating bushing projecting through said opening, said surge diverter comprising in combination a body of material having an inverse resistance coemcient 10 with respect to the voltage impressed thereon, means for attaching said body to said grounded casing adjacent said bushing so that one end of said body is conductively connected with said grounded casing, a metallicmember electrically connected with said current conducting means adjacent said insulating bushing, another metallic member electrically connected with the other end of said body and arranged in spaced relaticn'with said first mentioned metallic member so as to form a spark gap in air between said body and said current conducting means.

5. A surge diverter for protecting a transformer which has a bushing supported terminal connected to a transmission line and has a grounded casing. comprising in combination, a resistance element containing carborundum and having two contact faces, an insulating shell member surrounding said resistance element, a metallic base member attached to said shell member and in electrical contact with one of said contact faces, a contact member mounted on said insulating shell and in electrical connection with the other of said contact faces, and means for attaching said-base member to said grounded casing in such position adjacent said bushing that said contact member forms a spark gap with said' bushing supported terminal.

6. A surge diverter for protecting electrical apparatus having aterminal supported by an 40 insulator bushing mounted on a grounded housing, comprising in combination, an open ended shell of insulating material, a body of resistance material within said shell having an inverse voltage resistance characteristic, a base member secured to said shell and in electrical contact with one end of said body of resistance material, a contact member secured to said shell and in electrical connection with the other end of said body of resistance material, and means for so securing said base member to said grounded housing adjacent said bushing that a spark gap between said contact member and said terminal is established, said spark gap being of such a length across said spark gap through said body of resistance material and through said grounded casing.

'1. In combination, a grounded casing, an insulating bushing extending through said casing and having a high voltageterminal, a container of insulating material, a pair of electrodes carried by said container, a body of resistance material within said container and electrically eonnectedacross said pair of electrodes. and means for attaching said container to said terminal so that one of said electrodes is electrically, connected tosaid terminal and so that the other electrode is spaced a predetermined distance from said grounded casing thereby forming a spark gap for the discharge of surge currents.

8. In combination, a grounded casing, a high voltage conductor extending through said casing, an insulating bushing arranged to insulate said conductor from said grounded casing, an

that excessive voltages are discharged 55 v terminal carried bysaid bushing, an annular ring of resistance material surrounding said bushing and having electrical connection with said casing and an annular ring of metal surrounding said bushing and in contact with said 5 resistance material, the said ring of metal being so arranged relative to said high voltage terminal as to provide therewith a spark gap path for the discharge of surge voltages from said terminal through said resistance material to said 10 grounded casing.

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