US3064164A - Excess voltage protective device - Google Patents

Description

Nov. 13, 1962 N. K. OSMUNDSEN ETAL 3,

EXCESS VOLTAGE PROTECTIVE DEVICE Filed July 6, 1960 WITNESSES 67 z zy INVENTORS Norman K. Osmundsen 8- Philip W. Bogner ATTORNEY Unite rates 3,064,164 EXCESS VGLTAGE PROTECTEVE DEVHCE Norman K. Osmundsen and Philip W. Bogner, Elnoraington, Ind, assignors to Westinghouse Electric t'lorporation, East Pittsburgh, Pa., a corporation of Pennsyl- Vania Filed July 6, 1960, Ser. No. 41,069 3 Claims. (Cl. 317-66) The present invention relates to excess voltage protective devices, and more particularly to a drop-out device for an excess voltage protective device which operates to relieve excessive pressure within a faulted excess voltage protective device.

Certain excess voltage protective devices such as lightning arresters consist of one or more spark gaps which isolate the arrester from the line under normal conditions, but which sparkover to permit the passage of surge currents when a high surge voltage occurs on the line. In addition, lightning arresters of the valve type usually include one or more blocks of resistance material having valve characteristics; that is, blocks of material which are substantially non-conducting under normal voltage, but which become capable of carrying large surge currents when a sufiiciently high voltage is applied across them. These elements are assembled in series relation in a housing usually of porcelain. A sufiicient number of gaps and blocks are employed to obtain the desired voltage rating.

Such a device is designed to be connected between a power line and ground and carries no current except when subjected to a potential surge of predetermined magnitude, in excess of the normal line voltage. When the gap sparks over in response to abnormal voltage, current flows from the line, across the gap and then through the valve material to ground. It is a function of the valve material to interpose high resistance in the ground path to the flow of current therein at normal line voltages, thereby causing the arc to be extinguished immediately following each high voltage surge, thus promptly restoring the ordinarily non-conducting ground path to normal. It sometimes occurs that excess voltage devices of this type and character become inoperative to interrupt the flow of current to ground because of the valve material or gap having become damaged. If the lightning arrester is unable to revert to its insulating condition after being discharged by a surge, it puts a ground on the system and causes the operation of a circuit breaker unless the lightning arrester is cleared from the circuit. If the arrester stays on the system, in its non-insulating condition, it becomes impossible to reclose the breaker and hence the line is locked out of service until the failed lightning arrester has been found and removed.

When an arrester carries a fault current because of the failure of the arrester to interrupt the power current, gases are sometimes generated within the arrester. These gases or vapors result from vaporization of certain materials in the faulted block which becomes heated due to the continued flow of fault current and therefore vaporizes. A lightning arrester is usually enclosed in a sealed housing to prevent the entrance of moisture and other undesirable materials. Thus, the vapor and gas produced in a faulted arrester accumulate very high pressures creating a hazardous condition. The vapors and gases within the fauted arrester under pressure may cause the porcelain housing to explode throwing sharp particles throughout the area. This may be a hazard to persons and property in the area.

One method to release the pressure in these faulted arresters which has been utilized is to release the pressure by drilling a small hole in the housing. This method requires the person venting the arrester to be very careful not to ignite the gas. Another means employed is to Patented Nov. 13, 1962 use a long stick and smash the housing. Again this creates a hazardous situation because the flying porcelain will be thrown about the area. This flying porcelain is extremely dangerous. It could also happen that the arrester, might itself blow apart during fault conditions. These previous methods make it necessary for a considerable lapse of time to occur before the faulted arrester is found and the pressure is relieved. In the interim it is quite possible that the arrester might blow itself apart.

Various expedients have been resorted to for clearing lightning arresters and other excess voltage protective devices from the line upon failure of the device to interrupt the follow current upon the return of the line voltage to normal. These previous expedients have included the use of a ceramic ring having a center portion adapted to crack upon the application of heat. It has also been proposed to incorporate in an excess voltage device of this kind a relatively large mass of fusible material which is intended to melt in response to continued current flow for a sufficient period of time.

The above-mentioned methods of removing the faulted arrester from the line would, of course, open the housing and relieve the gas pressure. However, in this case the entire arrester would be destroyed. It would be desirable, of course, to provide a means for disconnecting the arrester from the line without destroying the arrester and making it possible to replace only the elements which have been damaged. Furthermore, the type of drop-out de vi e described above would result in the falling of arrester elements from the casing when the units are cleared from the line. In many locations Where these arresters are placed it is not permissible or desirable to allow this. It has been proposed in copending application Serial No. 41,081, by Norman K. Osmundsen and Philip W. Bogner, filed on July 6', 1960, and assigned to the assignee of the present invention, to provide a separate drop-out device which disconnects the ground lead from the arrester but retains the arrester housing intact. Thus, the problem of pressure venting the arrester, as described above, arises with this type of a drop-out device. The present invention proposes an improvement on the device of the said copending application Serial No. 41,081, above cited, which would automatically vent the arrester when the ground lead is separated.

Therefore, the principal object of the present invention is to provide a drop-out device in combination with an excess voltage protective device which will automatically vent the housing of the excess voltage protective device upon operation when the protective device is damaged.

Another object of this invention is to provide a drop out device for an excess voltage protective device which will disconnect the excess voltage protective device from the line upon failure of the excess voltage protective device and which will vent the excess pressure accumulated in the housing of the excess voltage protective device.

Other objects and advantages of the invention will be apparent from the following detailed description, taken in connection with the accompanying drawing, the single figure of which illustrates the drop-out device of this invention embodied in a valve type lightning arrester.

Referring to the drawing, a lightning arrester 10 is shown having a housing 12 which may be made of porcelain or any other suitable insulating material. The housing 12 is substantially cylindrical and contains an axially disposed chamber 14 in which is contained a plurality of spark gap electrodes 16 and 18. The housing 12 is closed at its end by an upper end closure member 217 and a lower end closure member 22. The upper end closure member maybe of any suitable type and may be cemented or otherwise secured to the housing 12. The

lower end closure member is shown as an essentially discshaped circular closure plate 22 and bears against a suitable spring ring 24. The arrester consists of a spark gap assembly 17 and a plurality of valve type resistor blocks Zitdisposed in series in the housing 12. The valve blocks 21 may be of any suitable type having nonlinear resistance characteristics and are preferably'made of granular silicon carbide molded with a suitable binder such as sodium silicate, and baked. The valve blocks 21 are disposed in a column in the housing 12. Any

suitable number of blocks may be used depending on the desired voltage rating of the arrester.

The spark gap assembly 17 is disposed in the housing 12. The gap assembly consists of a plurality of spark gap devices disposed in a series column. Any suitable number of gaps may be employed depending on the voltage rating of the device. Each of the gap assemblies 17 consist of a pair of formed electrodes 16 which cooperate with flat electrode plates 18 on each side. The electrodes 16 and 18 are preferably made of brass but may be made of any suitable conducting material. Each of the formed electrodes 16 is shown as having an annular ridge 26 formed on its surface and the electrodes 16 are placed together with their ridges 26 extending oppositely towards the electrodes 18 to form annular gap spaces or spark gaps 17 extending continuously around the electrodes 16. Spacers 28 are provided centrally between the electrode 16 and its adjacent electrode 18 to provide the proper gap space.

The housing 12 has a line terminal 30 entering at the top .and a terminal stud 32 at the bottom. The terminal stud 32 extends through the bottom closure plate 22 and has a central opening 34 therethrough for a purpose which will be explained hereinafter. A conducting spacer 36 and a bottom contact plate 38 disposed on top of the cylindrical conducting spacer 36 are provided to position the blocks 20 within the housing. The gap as sembly 17 is surmounted by a spring 40 which holds the various parts together under pressure. The spring bears against a conducting spring (not shown) which makes contact with the line terminal 30 at the top of the housing. The terminal stud 32 is provided with an enlarged threaded portion 44 at its lower end for the purpose of securing it to the drop-out assembly as will be hereinafter described. 8

In accordance with the present invention, there is an opening 34 through the bottom closure plate 22 which extends into the inside of the arrester. This opening 34 extends through the stud 32. The purpose of this opening is to vent pressure which has built up within the arrester when an arrester fails. When fault current flows through a faulted block 21 for a substantial period of time, the material in the blocks 21 vaporizes and builds up considerable gas pressure. This leaves the arrester in a hazardous condition even after the arrester is disconnected from the line in that the pressure built up may cause the housing to blow apart when the arrester is disturbed or moved. In order to disconnect the arrester from the line when fault current flows due to a damaged arrester block, a drop-out device 46 is provided.

It is essential to provide a tightly sealed enclosure for the arrester elements to prevent entry of moisture. Moisture in the housing would tend to corrode the gaps and change their sparkover voltage.

The drop-out device of this invention serves a dual function. In addition to disconnecting the arrester from the line upon failure, it also serves the function of sealing the opening in the closure plate 22 and of venting the opening upon failure ofthe arrester. In the particular embodiment illustrated, a drop-out device of the type disclosed in copending application Serial No. 41,081, by N. K. Osmundsen and Philip W. Bogner and assigned to the assignees of the present invention is utilized. Although this is the preferred type of drop-out device to be utilized with'this invention, it will of course be under- 4 stood that other and different modifications of this dropout device may be employed so long as a sealing means is provided to seal the vent opening 34 and means are provided for opening of the sealing means upon operation of the drop-out device.

The drop-out device of this invention includes a cup shaped housing 48 having straight interior walls 50 and tapered exterior walls 52 which result in a housing hav ing a bottom with a thin wall annular section 54. The thin wall annular section 54 is coextensive with the diam eter of the inside wall. Upon operation of the drop-out device the bottom portion 56 of the drop-out device 46 is designed to separate itself from the housing. The bottom portion 56 includes a ground terminal stud 58 to which the ground lead is secured when the arrester is connected for operation. Thisstud drops out along with the bottom portion 56. The housing 48 is a molded housing and the stud 58 is molded therewith. The housing is preferably of translucent plastic material such as, for example, Lucite 'or other acrylic resin material; Other suitable insulating materials may be employed.

The stud 58 enters the bottom portion and has an en larged head 60 which extends to the inside of the housing 48. A contact member 62 surmounts the enlarged head portion 60 and has a plurality of fingers 64 extending ra dially therefrom and upward.v Resting on the spring fin: ger 64 is a contact pressure plate 66 having an annular flange 67 extending downward and engaging the weakened wall portion 54 of the drop-out device. An outer fiber cylindrical tube 70 having a diameter substantially equivalent to the inside diameter of the housing but having slight clearance therewith rests on the contact pressure plate 66. A smaller cylinder 72 having an outer diameter substantially equal to the inner diameter of the tube 70 but also having slight clearance therewith rests on the pressure plate 66. The cylinder 72 is of substantially the same length as the cylindrical tube 70. The cylinder 72 receives a coil of a fine wire or other suitable conductor 74 which may be of copper or any other suitable conducting materiaL The tube 74 and cylinder 72 may be of any insulating material which evolves gas when exposed to suflicient heat, but is preferably made of fiber. Concentric with the tube 70 and the cylinder 72 is a spacing cylinder 76 which may be of brass or other suitable conducting material. This spacing cylinder 76 is disposed centrally and concentrically with the tube 70 and cylinder 74 and is provided to space the gap assembly 78 from the pressure plate 66. The gap assembly 78 includes a cylindrical spacing element 80 which may be of fiber or other suitable insulating material. The spacing element 80 has an annular flange 82 disposed centrally between its ends and extending inwardly. Disposed on each side of the flange 82 are electrodes 84 which may be of brass or any suitable conducting material. The flange 82 serves to space the electrodes apart to form a spark gap 86 therebetween. The electrode 84 is supported on the spacer 76 and in turn supports the cylindrical spacing cylinder 80 by its flanges 82. The upper electrode 84 rests on the'upperside of the flange 82.

A sealing plate 88 of conducting material is surmounted on the tube 70 and is of a diameter substantially equal to the outside diameter of the tube 70. When in position on the arrester and connected thereto, the sealing plate 88 bears against the enlarged portion 44 of the bottom terminal stud 32 of the arrester and covers the opening 34 therethrough. A coil spring 77 is disposed longitudinally between the plate 88 and the upper electrode 84 of the drop-out device. The coil spring 77 serves to urge the sealing plate 88 into sealing engagement with the enlarged portion 44 of the terminal stud 32 to form a tight sealing engagement which closes the vent opening 34.

At its open end the housing 48 of the drop-out device 46 has an enlarged internally threaded diameter. Received in this internally threaded diameter is'a closure ring 90 having its external and internal peripheries threaded.

The ring 90 is threadedly received in the enlarged diameter portion of the housing 48 and the internal threads of the ring 90 threadedly receive the enlarged portion 44 of the arrester ground terminal stud 32. An annular washer 91 is disposed between the opposing faces 93 and 95 of the drop-out device housing 48 and the housing 12 of the arrester respectively. This seals the housing against moisture and other detrimental external material. The pressure of the head 44 against the sealing plate 88 compresses the coil spring 70. Thus, the coil spring urges the plate 88 against the opening 34 in the terminal stud 32. The coil spring 77 includes a short circuiting strip 79- to eliminate the inductance effect of the spring. The coil 74 wound on the cylinder 72 has its upper end engaging the sealing plate 88 and its lower end engaging the contact pressure plate 66 to connect the coil in series with the arrester. The spacer 76 and the coil spring 77 also engage the pressure plate 66 and the sealing plate 88 respectively to correct the spark gap in parallel with the coil. It can be seen that the spring 77 provides a spring biased spark gap 86 in which the electrodes can move and return to normal position when subjected to high surge voltage.

In normal operation, the excess voltage device or lightning arrester will permit high potential surges to pass freely to ground while operating instantly to obstruct the flow of fault current to ground thus serving to prevent short circuits and consequent outages. The coil 74 is so designed that it will present high impedance to any ordinary surge current thereby causing the gap 86 to arc over and permitting the high potential surges to pass freely to ground. However, if subjected to fault current or a substantial normal frequency current of extended duration, the coil will vaporize and the vapor of the coil, together with the vapor generated by the fiber tube 70 and the cylinder 72 from the heat of the vaporized coil, will build up pressure within the drop-out device suflicient to blow out the bottom portion 56 and its associated terminal stud 58. The concentrated pressure plate 66 with its annular flange 68, it can be seen, will distribute the pressure uniformly about the annular thin wall portion 54 so as to cause a clean break at that point. When this happens the interior portions of the drop-out device 46 will fall out through the open bottom of the housing 48. All of these parts have suificient clearance, including the sealing plate 88, so they will not hang up within the housing 48. When the pressure plate 88 drops, the opening 34 is vented to the outside relieving the gas pressure which has built up Within the arrester. The bottom part of the drop-out is broken and the internal parts of the drop-out are expelled. This automatically and quickly removes the seal plate 88 from the bottom of the arrester and vents it. There is then no danger of flying particles of porcelain from a damaged arrester With high pressure built up inside the housing. The pressure venting prevents any hazardous condition from remaining in the arrester housing after the fault is cleared.

It should now be apparent that a lightning arrester has been provided which has many advantages. The drop-out device of the new arrester is very compact and simple in construction. It is a completely self-contained device. The action is in no way tied in with the arrester except that drop-out action is initiated by arrester failure. The new drop-out device permits the arrester to be positively and rapidly vented upon failure of the arrester. It is so designed that there is no danger of failure of operation of the venting device. It prevents any hazardous condition from remaining in the arrester housing after the fault current is cleared.

A particular embodiment of the invention has been shown and described for the purpose of illustration, but it will be apparent that various other embodiments are possible within the scope of the invention. Thus, for

example, the thin wall portion 54 of the housing 46 may consist of a material that fractures upon application of heat thus dropping out the bottom portion permitting the seal plate 88 and the terminal connection 58 to drop out. The bottom portion 56, may also, for example, be secured to the arrester by a fusible solder which may fuse upon heat from the operation of the drop-out device thereby falling out and letting the internal parts including the sealing plate 88 drop out of the dropout device. Similarly, numerous other modifications and embodiments will be apparent to those skilled in the art and all such modifications and embodiments are within the scope of the invention.

We claim as our invention:

1. In combination, an excess voltage protective device including a housing having an axially disposed chamber, discharging means disposed within said chamber, a separate drop-out device comprising a cup-shaped closed housing independent of the housing for said protective device having a bottom portion carrying a connecting terminal, means for discharging surge current disposed within said cup-shaped housing, means within said cupshaped housing for evolving gas to effect separation of said bottom portion and terminal, an imperforate closure plate disposed adjacent the upper end of said housing, said plate being free to drop out upon separation of said bottom portion, an annular ring having a threaded inner diameter disposed above and abutting said closure element for closing said chamber, said closure member having a threaded connecting stud extending therethrough, an axial opening in said stud, said stud being received in said threaded inner diameter of said annular ring and having its end abutting said closure plate, whereby said closure plate serves to close said axial opening.

2. In combination, an excess voltage protective device including a housing having an axially disposed chamber, discharging means disposed within said chamber, closure means at an end of said chamber, a separate drop-out device comprising an enclosed housing independent of said protective device having an end portion carrying a connecting terminal and means within said enclosed housing to eflect separation of said end portion and terminal from said housing upon passage of continued current flow through said protective device, means connecting said drop-out device to said closure means, said closure means including an opening communicating with said drop-out device, separable closure means in said drop-out device for closing said opening, said separable closure means adapted to drop out upon separation of said end portion and said terminal.

3. In combination, an excess voltage protective device including a housing having an axially disposed chamber, discharging means disposed within said chamber, closure means at an end of said chamber, a separate dropout device comprising an independent enclosed housing having an end portion carrying a connecting terminal, first and second parallel paths through said drop-out de vice, said first path effective to conduct surge current through said drop-out device, said second path including means to effect separation of said end portion and terminal from said housing upon passage of continued current flow therethrough, means connecting said drop-out device to said closure means, said closure means including an opening communicating with said drop-out device, separable closure means in said drop-out device for closing said opening, said separable closure means adapted to drop out upon separation of said end portion and said terminal.

References Cited in the file of this patent UNITED STATES PATENTS 2,777,095 Stoelting Ian. 8, 1957

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