US3144582A

US3144582A - Lightining arrester

Info

Publication number: US3144582A
Application number: US69087A
Authority: US
Inventors: Billy B Sorrow; Robert T Innis; Ned T Kunkle
Original assignee: Westinghouse Electric Corp
Current assignee: Westinghouse Electric Corp
Priority date: 1960-11-14
Filing date: 1960-11-14
Publication date: 1964-08-11
Anticipated expiration: 1981-08-11
Also published as: CH391859A; DE1438235A1

Description

Aug. 11, 1964 Filed Nov. 14, 1960 Fig.3.,

B. B. SORROW ETAL 3,144,582

LIGHTNING ARRESTEZR 3 Sheets-Sheet 2 1964 B. B. SORROW ETAL 3,144,582 LIGHTNING ARRESTER Filed Nov. 14, 1960 3 Sheets-Sheet 3 United States Patent 3,144,582 LIGHTNING ASTER Billy B. Sorrow, Robert T. Innis, and Ned T. Kunkle,

Ellettsville, Ind, assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Nov. 14, 1960, Ser. No. 69,087 8 Claims. (Cl. 31536) This invention relates to lightning arresters and, more particularly, to a high voltage lightning arrester having an improved arc transfer device.

Lightning arresters of the valve type consist essentially of a plurality of spark gap devices and a plurality of valve type resistance elements or blocks, disposed in series relation in a housing. The are transfer device of the present invention is especially adapted for use in high voltage, station-type lightning arresters, although it may be used in other types of lightning arresters as, for example, distribution arresters. The are transfer device of this invention is illustrated as embodied in a lightning arrester of the type disclosed and claimed in Patent No. 2,858,476, issued October 28, 1958, by Edward F. W. Beck and Otto Ackermann, and assigned to the assignee of the present invention. This is a compact, high voltage lightning arrester having columns of arrester elements disposed side by side in an insulating housing and in which the columns of arrester elements are connected in series. I

Lightning arresters of the valve type consist essentially of a plurality of spark gap devices and a plurality of valve-type resistance elements or blocks, disposed in series relation in the housing. The spark gaps normally isolate thearrester from the line to which it is connected but break down under excess voltage conditions, such as lightning surges, to permit the surge to be discharged to ground through the non-linear resistance blocks, which have low resistance under surge voltage conditions. After discharge of the surge, the blocks because of the valve characteristics, reduce the power-follow current to a small value which can readily be interrupted by the series gap.

Lightning arresters of this type are usually tightly sealed to exclude moisture, which may have a very detrimental effect on the electrical characteristics of the blocks and of the series gaps. On occasion, the arrester may fail to interrupt the power current. Then the full short-circuit current of the system to which the arrester is connected flows through it to ground. When a lightning arrester fails, the semiconductor non-linear resistance blocks are punctured creating a short circuit from the line to ground. The system fault current will flow through this short circuit, generating a large quantity of gas from the block material. Since thehousing is tightly sealed, in the conventional construction, very high gas pressures are rapidly built up in the housing in case of failure of the arrester, and these high pressures may cause rupture or shattering of the porcelain housing unless the pressure is promptly relieved and further gas generation is stopped or slowed. These ruptures may occur with explosive force, causing parts of the housing to be violently thrown around, endangering adjacent apparatus, or persons who may be in the vicinity. These explosions vary in severity with the amount of fault current available.

The arrester short circuit occurs when the resistance elements or blocks become damaged. A relatively low resistance path through the resistance blocks allows system fault current to flow almost unrestricted. The 'continued flow of fault current through the blocks causes the resistance material to sublimate. This sublimation generates most of the internal gas resulting in excessive pressure. In case of high system fault current, if the current is allowed to continue flowing through the damaged arrester blocks, the arrester will explode even though 3,144,582 Patented Aug. 11, 1964 ice pressure relief diaphragms are open. So great is the volume of gas generated by the block sublimation that if allowed to continue beyond the first half cycle of fault current flow, an arrester with completely open ends may explode.

The principal object of the present invention is to provide a valve-type lightning arrester in which the danger of shattering or explosion is minimized in case of failure of the arrester.

Another object of the invention is to provide a valvetype lightning arrester having an arc transfer device within its housing which will transfer fault current from the arrester elements and gas-generating material to another path where little or no gas is generated.

A further object of the invention is to provide a valvetype lightning arrester having an arc transfer device within its housing which will transfer fault current from the arrester elements and gas generating material to another path where little or no gas is generated and which will effect rapid opening of the sealed arrester housing without shattering the housing.

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

FIG. 1 is a side elevational view partly in section of a lightning arrester embodying the invention;

FIG. 2 is a perspective view of a lightning arrester embodying the invention with the outer housing omitted;

FIG. 3 is an enlarged partial sectional view of the arrester showing the arc transfer device of this invention in enlarged detail; and

FIG. 4 is a top plan view of a lower end cap of a lightning arrester unit.

In the preferred embodiment of the invention shown in the drawing, for the purpose of illustration, the arc transfer device is embodied in a lightning arrester of the type disclosed and claimed in Patent No. 2,858,476 by E. F. W. Beck and O. Ackermann, issued October 28, 1958, and assigned to the assignee of the present invention. As more fully disclosed in the above cited patent, the arrester comprises a generally cylindrical housing 1 which is preferably made of porcelain although any suitable weather-resistant insulating material might be used. The housing 1 is provided at each end with metal end fittings 2 of any suitable design which are secured to the housing 1 by cement as indicated at 3, or in any other desired manner. The ends of the housing 1 are closed by metal diaphragms 4 which are secured to the end fittings 2 in any desired manner, as by bolts (not shown), a gasket 5 being interposed between each of the diaphragms 4 and the housing to seal the interior of the housing. It will be understood that any suitable construction may be used for the end-fitting and closure means for the housing, the end fittings providing for electrical and mechanical connection of the unit in a column of similar units in the usual manner. Each end fitting is provided with a directional vent part 2' with the openings directed toward each other for a purpose hereinafter explained.

The arrester unit as disclosed includes an upper arrester assembly 6 and a lower arrester assembly 8 stacked thereon. The

arrester assemblies

6 and 8 are identical in construction and only one such assembly will be described, and similar reference numerals will be applied to like parts in the two

assemblies

6 and 8.

Each arrester assembly, which is contained in the housing 1, consists of three

columns

10, 12 and 14 of lightning arrester elements connected in series and disposed side by side in the housing in a triangular arrangement. The arrester elements comprise spark gap devices 16 and valve blocks or non-linear resistance elements 18, which may be of any usual or desired type. Each of the columns may consist of any combination of spark gaps and valve blocks arranged in a series stack in any desired manner. The gap assembly 16 may be of any suitable type, as, for example, the type disclosed in Patent No. 2,858,476 cited hereinabove. Any necessary number of spark gap assemblies may be provided, depending on the desired Voltage rating, and they are disposed in an insulating tube 20 in a vertical column. The ends of the tube 26 are closed by metal end caps 22 which are sealed to the tube 26 in any suitable manner as by soldering as at 19. The end plates 22 serve as contact means for the gap assembly 16.

The valve blocks 18 may be of any suitable type of valve element or non-linear resistor, and are preferably made of granular silicon carbide molded to the desired size and shape with a binder of sodium silicate and baked to provide valve elements of the usual type.

Each

column

10, 12 or 14 may, by way of example, consist of:a spark gap assembly 16, and valve blocks 18 disposed in a series column in a tube 24 of any suitable rigid insulating material. However, any suitable arrangement of blocks and gap assemblies may be employed, such as all gap assemblies or all valve blocks. A different arrangement may be employed in each column. The three

columns

10, 12 and 14 of arrester elements are disposed side by side in the housing 1 in a triangular arrangement as shown in FIGS. 1 and 4. They are supported in insulating end members 26 and 319. The end members 26 and 3d may be formed of any suitable insulating material, and, as shown in FIG. 2, each of the end members is generally clover-leaf-shaped with a flange portion 32. Ribs 34 are provided which, together with the flange 32, provide three relatively deep recesses 36 of circular outline equidistantly spaced from each other to receive the columns of arresterelements. Lugs 38 are formed on the end caps 26 and 36) having openings 40 which are provided for receiving tie rods 43 of insulating material.

Contact means are provided in the

end members

26 and 30 for making electrical connection to the columns of arrester. elements for connecting them in series. In the illustrated embodiment, the end member 36 has a copper strap connector 42 disposed on the bottom of two of the recesses 36, and having its ends disposed in position to engage the contact means of the arrester column received in the respective recesses 36 so as to connect these two columns together in series. The third recess 36 has a copper contact member 46 in the bottom of the recess in position to engage the contact means of the arrester column placed in that recess, and the contact member 46 has a strap portion 48 extending out of the end member through a slot 50.

The upper end member 26 may be identical to the lower end member, and when assembled, the upper end member is inverted in position with respect to the lower end member so that the three arrester columns received in the corresponding recesses 36 of the upper and lower end members are electrically connected in series. Thus, for example, in the arrangement shown, the circuit extends from the strap portion 43 and contact member 46 of the lower end member 30 through the arrester column to the connector 42 of the upper end member 26 and through this connector and the adjacent arrester column 12 to the connector 42 of the lower end member 36 which connects the arrester column 12 to the arrester column 14. The upper end of the column 14 is in contact with the contact member 46 of the upper end member 26 to complete the series circuit.

The

arrester assemblies

6 and 8 are stacked one above the other respectively with a spring ring 54 'therebetween. Lugs 38 on the end caps 26 and 30 serve to space the

assemblies

6 and 8 from each other.

In assembling the arrester, the arrester columns are placed in the proper recesses in the two

end members

26 and 30, and the tie rods 42, are inserted through openings 53 in the spring rings 54 and openings 40 in the lugs 38 to secure the assembly together.

The complete arrester is preferably supported in housing 1 by spring means to protect the assembly from mechanical shock to which the arrester may be subjected during shipment and'handling. For this purpose, the diaphragms 4 which close the ends of the housing 1 have a plurality of integral projections 60 extending inwardly and they are provided with reduced end portions 61 forming annular shoulders 63. An annular

metal spring ring

56a and 56b is supported on the shoulders 63 of the projections 60 on the upper and inner diaphragm 4, respectively. The spring rings 56a and 56b have openings 57 which fit over the reduced portion 61 of the projections 60. Conducting bushings 58 are threaded on the ends of the tie rods 42 to clamp the arrester assembly itself together into a unitary assembly and to make electrical contact between rings 54a and 56a, and between springs 54]) and 56b. The ends of the tie rods are received in openings of the spring ring 56 positioned between the openings 57 which receive the projections 61 so that the arrester assembly is re siliently supported on the spring rings 56. The conducting bushings 58 are held in tight engagement with and between the spring rings 54a and 56a, and 54b and 56b, respectively to effect electrical connection.

In order to prevent continued gas generation when the valve blocks are punctured in case of failure of the arrester, an assembly is provided to transfer the fault current away from the semiconductor blocks. This assembly is shown most clearly in FIGS. 2 and 3. A central opening is provided in each of the end covers 26 and 30 of the

arrester assemblies

6 and 8. These central openings are provided to receive current sensitive elements located on the central axis of the arrester unit. These openings are aligned on a longitudinal center line through the arrester units and external to any of the

columns

10, 12 and 14. Each arc transfer assembly includes a pair of upper and lower current

sensitive elements

62 and 64 and an intermediate current sensitive element 66. The upper and

lower elements

62 and 64 are identical, and only the upper element 62 will be described in detail herein.

The current sensitive element 62 comprises a hollow insulating cylinder 68 having a pair of substantially cylindrical electrodes 70 and 72 'at its ends. These

electrodes

70 and 72 have central openings therein. The electrodes are disposed within the hollow center portion of the insulating tube 68. The electrodes may be of brass or any other suitable conducting material. Connecting the

electrodes

70 and 72 is an electrical conductor wire 74 of relatively small diameter. The insulating tube 68 has a reduced diameter end portion 76 which receives a metal conducting bushing 78 having a central opening in alignment with the opening of the electrode 72. The electrode 70 extends outwardly from the hollow tube and is received in the opening in its associated

end cap

26 or 30. A shoulder is formed by the electrode 70 and insulating tube 68. This shoulder rests on the outer surface of the end cap 26. The current sensitive element 64 is identical to element 62 but is disposed at the opposite end of the arrester assembly. The spring rings 56a and 56b each have secured thereto across a diameter a conducting strap 84. The strap 84 may be secured to the spring ring 56a in any suitable manner as by the screws and nuts 86 as shown. The strap 84 has a central opening which re ceives the bushing 78 and is in electrical contact therewith. The current

sensitive elements

62 and 64 each have a connecting terminal 102 which extends outwardly from the electrode adjacent the arrester unit through the insulating tube 76. The contact 46 in the end cap 26 has a strap extending through an opening 50 in the cap. This strap 48 is connected to the connector 102 of the current sensitive element 62.

The intermediate current sensitive element 660cmprises a hollow cylindrical tube 94. At its ends the hollow tube 94 has an enlarged inner diameter to receive the upper and

lower electrodes

96 and 98, respectively. The

electrodes

96 and 98 are substantially hollow cylinders having enlarged diameter ends to fit closely within the hollow cylinder 94. The

electrodes

96 and 98 may be of brass or any desirable or suitable conducting material. The

electrodes

96 and 98 are electrically connected by a small electrical conductor or relatively small diameter wire 100. The projecting ends 96 of the

electrodes

96 and 98 are received in the openings of the

adjacent end caps

26 and 30 of adjacent arrester units. The intermediate current sensitive element 66 has a pair of

connectors

104 and 106 which extend from the upper and

lower electrodes

96 and 98, respectively, through the insulating tube 94 to the exterior of the current sensitive element. Each of the contacts 48 in the

adjacent end caps

26 and 30 of adjacent arrester units have projections 48 extending outwardly through the end caps 26 and 30 connected respectively to the

connectors

104 and 106 of the current sensitive element 66. Thus, it can be seen that these

elements

62, 64 and 66 are connected electrically in series with the arrester parts.

The upper and

lower assemblies

6 and 8 are connected in series through the intermediate current sensitive element 66. The straps 48 extending through slots 50 in

adjacent end caps

26 and 30 are connected to the elec trodes 96 and 98 which in turn are connected by conductor 100. The internal circuit of the arrester extends from upper end cap 2 through upper diaphragm 4, spring ring 56a, bushing 58 to spring ring 54a and then through strap 84 to the upper electrode 72 of current sensitive element 62. The circuit then extends through conductor 74 and electrode 70 to the strap 48 and then through the arrester elements and intermediate current sensitive element 66 to the lower current sensitive element 64. From electrode 74 of lower current sensitive element 64 the circuit follows a path similar to the path described through the upper end of the arrester to the lower end fitting 2.

When the arrester current starts to rise upon failure, the

electrical conductors

74 and 100, being in series with the arrester elements, will vaporize and sparkover will occur between the electrodes of the current sensitive elements thereby generating ionized gases which are blown through the center of the arrester from end to end. These ionized gases provide an easy path for the arc down the center of the arrester causing the current to be transferred away from the silicon carbideblocks. Usually enough gas is generated to cause the diaphragms 4 at the ends of the arrester torupture and allow the gas to pass to the outside of the arrester. When this gas flows to the outside, a second arc transfer may be accomplished from the inside to the outside. The directional vent ports 2' in the end fittings 2 will direct the escaping ionized gases toward each other axially along the outer housing external thereto, thereby effecting an external arc between the end fittings.

A unique and effective arc transfer system for lightning arresters which provides positive protection against explosion of damaged units, and which permits an increased fault current rating, has been provided. When an occasional failure of a lightning arrester occurs, the semiconductor blocks are punctured creating a short circuit from line to ground. The system fault current will flow through this short circuit, generating almost instantaneously tremendous volumes of gas. Unless the resulting pressure is properly relieved and further gas generation is stopped or slowed, the arrester may explode. In cases of high system fault current, if the current is allowed to continue flowing through the damaged arrester blocks, the arrester will explode even though pressure relief diaphragms are open. So great is the volume of gas generated by the blocks vaporization, that if allowed to continue past the first half cycle of fault current flow, an arrester with completely open ends may explode. Halting of continued gas generation is accomplished in the present invention by transferring the fault current away from the semiconductor blocks. The current-

sensitive elements

62, 64 and 66 fire expelled gases toward each other. Each gas jet travels toward the gas jet of the opposing current-sensitive device. The fault current transfers from the arrester blocks to this path where little additional gas is generated.

When the end pressure relief diaphragms are broken, the gases which are vented to the outside atmosphere are highly ionized. If these exhaust gases were allowed to flow in any direction, the possibility exists of causing fiashover of other arresters, poles or transformer bushings. For this reason, directional vent ports 2' are provided on the arrester end castings as shown clearly in FIG. 1. The arrester is designed so that these vent ports deflect the two streams of expelled gases from the damaged arresters toward each other to form an outside ionized path. If the duration of the fault current is long enough, the fault current will transfer a second time from the inside to the outside of the arrester.

It should now be apparent that a high voltage lightning arrester unit has been provided which has many advantages. The new arrester provides positive arc transfer and prevents explosion of damaged arresters. If required, the arc will transfer a second time from the inside to the outside of the arrester. Positive means are provided for rupturing the diaphragm by energy generated within the arrester housing. 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. All such modifications and embodiments are within the scope of the invention.

We claim as our invention:

1. In a lightning arrester including a plurality of lightning arrester elements connected in series with an insulating outer housing and an insulating inner housing, an arc transfer assembly comprising a plurality of current sensitive elements each including a conductor connected in series with the arrester elements and vaporizable when subjected to excess current for a predetermined length of time, said elements located within the outer housing, exteriorly of said inner housing of the arrester, means for directing gases longitudinally in the arrester housing in a path exteriorly of said inner housing and parallel to the current path through the arrester elements, said conductors being disposed within said gas directing means, whereby the gases resulting from the vaporization of said conductors are directed longitudinally of the arrester to form a current path parallel to and external to said arrester elements upon flow of excess current for a predetermined length of time.

2. In a lightning arrester, an arc transfer assembly comprising a plurality of current sensitive elements each including a conductor connected in series with the arrester elements and vaporizable when subject to excess currents, said elements located within the outer housing of the arrester remote from the arrester elements, open ended tubular means for directing gases longitudinally in the arrester housing in a path parallel to and insulated from the current path through the arrester elements, said conductors being disposed within said tubular means, whereby the gases resulting from the vaporization of said conductors are directed longitudinally of the arrester to form a current path parallel to and external to said arrester elements upon flow of excessive current for a predetermined time.

3. In a lightning arrester, an arc transfer assembly comprising a plurality of current sensitive elements each including a conductor connected in series with the arrester elements and vaporizable when subjected to excess current, said elements located within the outer housing of the arrester open ended tubular means of material capable of evolving gas when exposed to sufiiciently high temperature for directing gases longitudinally in the arrester housing in a path parallel to and insulated from the current path through the arrester elements, said conductors being disposed Within said tubular means, whereby the gases resulting from the vaporization of said conductors and evolved by said tubular means are directed longitudinally within the arrester housing to form a current path parallel to and external to said arrester elements upon flow of excess current for a predetermined length of time. g

4. In a lightning arrester including an insulating outer housing closed at each end by a rupturable diaphragm having a weakened portion and an inner housing for receiving arrested elements; an arc transfer device comprising a plurality of current sensitive assemblies each of said assemblies including a conductor connected in series with the arrester'elernents and vaporiza'ole when subjected to excessive current for a predetermined length of time, said elements locatedwithin the outer housing of the arrester exteriorly of the inner housing, open ended tubular means for directing gases longitudinally in the arrester housing in a path parallel to the current path through the arrester elements, said conductors being disposed within said tubular means and certain of said elements disposed in close proximity to said weakened portions of said diaphragm, whereby'upon flow of excessive current for a predetermined length of time, the gases resulting from the vaporization of said conductors are directed longitudinally of the arrester to form a current path parallel to and external to said arrester elements and to aid in rupturing said diaphragms.

. 5. In combination a lightning arrester including a closed, insulating outer housing and an insulating inner housing enclosing arrester elements, an arc transfer device comprising a plurality of'current sensitives assemblies each of said assemblies including means for initiating a current path Within said outer housing exteriorly of said inner housing, parallel to and external to said'arrester elements upon flow of excess current through said arrester elements for a predetermined length of time.

6. In combination a lightning arrester including a plurality of lightning arrester elements connected in series within an insulating outer housing closed at each end by a rupturable diaphragm, an arc transfer device comprising a plurality of current sensitive assemblies, each of said assemblies including means for initiating a current path Within said outer housing parallel to and external to said 'arrester elements upon flow of excess currentthrough said arrester elements for a predetermined length of time and said are transfer device including means adjacent at least one of said diaphragms for directing internal energy toward said diaphragm to aid in rupturing said diaphragm.

7. In combination a lightning arrester including a plurality of lightning arrester elements connected in series 'within an insulated inner housing and an outer housing closed at each end by a rupturable diaphragm, baffle means at each end of the arrester disposed exteriorly of the diaphragms for directing gases exterior to and longitudinally of the arrester housing, arc transfer means within the outer arrester housing and exteriorly of the inner housing comprising current sensitive means for initiating a current path within said outer housing, exteriorly of said outer housing, parallel to and external to said arrester elements upon flow of excessive current through said elements, said are transfer-means evolving gas when the v arrester is subjected to excessive current flow and including means for directing the gas evolved toward said diaphragm to aid in rupturingsaid diaphragm, whereby said 'baifie means directs said gas exterior to longitudinally of the arrester housing to initiate and transfer the current 'path exteriorly of said outer housing.

8. In a lightning arrester including a plurality of lightning arrester elements connected in series within an insulated inner housing and an outer housing closed at each end by a rupturable diaphragm and baffle means at each end of the arrester disposed exteriorly of the diaphragm for directing gases exterior to and longtudinally of the arrester housing; an arc transfer assembly within said outer housing, exteriorly of said inner housing including a plurality of current sensitive elements each including a conductor connected in series with the arrester elements and vaporizable when subjected to excessive current for a predetermined length of time, and open ended tubular means of material capable of evolving gas when subjected to sufiiciently high temperature for directing gases longitudinally within the outer arrester housing, exteriorly of the inner housing in a path parallel to and insulated from the current path through the arrester elements, said conductors being disposed within said tubular means and certain of said current sensitive elements being disposed in close proximity to said rupturable diaphragms, whereby upon flow of excessive current for a predetermined length of time the gases resulting from the vaporization of said conductors and evolved bysaid tubular means are directed longitudinally within the arrester housing to form a current path parallel toand external to said arrester elements, and 'to aid in rupturing said diaphragms, the gases being directed by said baflle means exterior to and longitudinally of the arrester housing to initiate and transfer the current path exteriorly of said arrester housing.

References Cited in the file of this patent UNITED STATES PATENTS