US3467936A - Lightning arrestor and method of using the same - Google Patents

Description

E. NASSER Sept. 16, 1969 2 Sheets-Sheet 1 Filed March 28, 1966 5 7w R w 0 a e n 0 a 3 a N Z 5 5 6 4 V Z 2 W E 4 VC--\HI-=V== W. 5 6 v. 3 0/ .7 6 a l I 0 3 a 40 0 4 9 Z I 1 2 w 1 IL l U! 1 I. a mu" 2 i l ESSA/W #452551? BY w E. NASSER Sept. 16, 1969 LIGHTNING ARRESTOR AND METHOD OF USING THE SAME 2 Sheets-Sheet Filed March 28. 1966 INVENTOR. ESSA/VI A ASSEE BY KQ ,%,W H%x United States Patent 3,467,936 LIGHTNING ARRESTOR AND METHOD OF USING THE SAME Essam Nasser, Ames, Iowa, assignor to Iowa State University Research Foundation, Ames, Iowa, a corporation of Iowa Filed Mar. 28, 1966, Ser. No. 537,892 Int. Cl. H01c 7/12 US. Cl. 33821 14 Claims ABSTRACT OF THE DISCLOSURE A lighting arrestor for use with high potential lines having an insulative housing, a top terminal adapted to be connected to a source of high potential, a bottom terminal adapted to be connected to ground, a plurality of spaced apart electrodes located between said terminals, and a shield means of high electrical resistance and low electrical conductivity located in spaced relation around said electrodes and electrically connected to said terminals. The method of maintaining constant equipotential planes between electrodes in a lightning arrestor by passing a current of constant value through a high resistance element located in the area surrounding the space between such electrodes.

Lightning arrestors are used in transmission systems as protective devices against high-voltage surges caused by lightning. They are designed to be nonconductive below a certain maximum allowable voltage. As soon as the voltage exceeds this value, a sparkover will take place across accurately designed spark gaps making the arrestor conductive, and the excessive charge is conductedito ground. This voltage is known as the sparkover voltage and should never change in service. It is a function of a spark gap configuration and the electric field intensity at the electrodes.

However, conductive films or contaminants of different materials often are deposited on the outside of the porcelain housing of such arrestors. Such a conductive' film is created when, for instance, fertilizer dust is deposited on the arrestor housing, and the dust becomes highly conductive when dew or the like causes it to become moist. Coal dust, residue from chemical manufacturing plants, and ocean salt are other kinds of contaminant that have a detrimental effect on lightning arrestors. The lightning arrestors consist of a number of air gaps connected in series with non-linear resistors, and such an arrestor is placed in a porcelain or glass housing or housings. The complete electric breakdown of air between electrodes which are separated by the air gaps depends only on the electric field intensity and its variation along the gap, provided all other factors such as gas pressure, external radiation and impurities remain unchanged. The sparkover voltage of an arrestor will therefore, only be affected if the electric field intensity within the gap is changed. The conductive contaminant on the surface of the arrestor can lower its sparkover voltage only by changing the field intensity at one or more locations of the air gaps. The conductive contaminant on the outside of the housing changes the shape and location of equal potential surfaces between the electrodes. For instance, if the contaminant is electrically connected to the potential of the line, it tends to move this equal potential plane downward as the equipotential surface seeks points of the same potential as the contaminant on the outside. The bending of this equipotential surface by the contaminant creates areas of higher field intensity between the electrodes in the air gaps, and sparks may take place within these areas of high field intensity.

The conductive contaminant not only reduces the sparking voltage by deformation of the electric field between the gap electrodes, but the sparking voltage can also be reduced through the contaminant creating a nonuniform voltage distribution between units. Either cause may lead to the breakdown of one single gap or more, at service voltages, and this can persist for hours. This is accompanied :by corona discharges within the arrestor which may lead to the complete deterioration of the unit insulation and to failure of the arrestor.

It is therefore a principal object of this invention to provide a lightning arrestor which can resist the adverse affects of a conductive contaminant on the outside sur face thereof, and which can maintain the predetermined and desired configuration of the equipotential surfaces and electric field lines between electrodes even when such contaminant is present.

A further object of this invention is to provide a lightning arrestor which is economical of manufacture, durable in use, and versatile in application.

These and other objects will be apparent to those skilled in the art.

This invention consists in the construction, arrangements, and combination of the various parts of the device, whereby the objects contemplated are attained as hereinafter more fully set forth, specifically pointed out in the claims, and illustrated in the accompanying drawings, in which:

FIG. 1 is a side elevational view of the lightning arrestor of this invention;

FIG. 2 is a partial sectional view at an enlarged scale of the simplified device shown in FIG. 1;

FIG. 3 is a partial sectional view through a conventional simplified lightning arrestor which has no contaminant on the outer surface thereof. This figure illustrates the electric field lines and equipotential surfaces which should exist between the electrodes of a lightning arrestor;

FIG. 4 is a partial sectional view of a conventional arrestor of the type shown in FIG. 3, but with a contaminant film on the outer surface thereof. This figure illustrates the deformation in the equipotential surface which is caused by the contaminant and which leads to a reduction of the sparkover voltage;

FIG. 5 is a partial sectional view of the device of this invention and is identical to the upper portion of FIG. 2, but this figure illustrates the condition of the equipotential lines of the arrestor of this invention when a contaminant film does exist on the outer surface of the arrestor housing;

FIG. 6 is a sectional view of the device of this invention taken on lines 6-6 of FIG. 2;

FIG. 7 is a perspective view of an alternate form of shield used within the housing of the arrestor of this invention;

FIG. 8 is a perspective view of a second alternate form of shield which is also used within the housing of the arrestor of this invention;

FIG. 9 is a perspective view of even a third alternate form of shield which is used within the arrestor housing as an alternate to the shields shown in FIGS. 2, 7 and 8; and

FIG. 10 illustrates a fourth alternate form of shield similar to that of FIGURE 2 but being comprised of a plurality of sections.

The numeral 10 generally designates the arrestor of this invention and the numeral 12 designates a conventional arrestor. The arrestor 10 includes a conventional housing 14 of porcelain, glass or the like with a plurality of spaced apart ribs 15 which extend laterally outwardly from the body of the housing. The housing 14 is generally hollow to create an inner compartment 16. A terminal means 18 is positioned on the upper end of housing 14 and includes a terminal cap 20 which can be positioned on a suitable shoulder (not shown) on the upper end of the housing. Terminal connecting element 22 is secured to the upper end of threaded shaft 24 which extends through terminal cap 20. Nut 25 on the upper end of shaft 24 serves to interconnect the cap 20, the connecting element 22, and the shaft 24. The lower end of shaft 24 extends downwardly through a suitable opening in the top of housing 14 and terminates in a conventional cupshaped electrode 26. An electro-conducting cap 28 is mounted on shaft 24 intermediate its length by the two nuts 26. Rods 30 of nonelectro-conducting material have their upper ends secured to the upper electro-conducting cap 28. A plurality of spaced apart pairs of Washers 32, 32A and 32B are secured in any convenient fashion between the rods 30. An electro-conducting cap 34 identical to the upper cap 28 is secured to the lower ends of rods 30.

A base 36 of housing 14 is also comprised of glass or porcelain material and serves to close the lower end of compartment 16. A ground terminal means 38 is secured to base 14 and includes a ground terminal element 40 which is secured to terminal bracket 42 by means of nut and bolt assembly 41. An L-shaped threaded shaft 44 is imbedded in base 36, and the upper threaded end of shaft 44 extends through the lower cap 34. Nuts 46 serve to connect the threaded shaft to the cap 34. The upper end of shaft 44 terminates in a conventional cup-shaped electrode 48.

Non-linear resistors 50, 52 and 54 are supported in pairs of washers 32, 32A and 32B, respectively. Cupshaped electrodes 48A and 26A are supported by and interconnected through resistor 50; electrodes 48B and 26B are similarly connected through resistor 52; and electrodes 48C and 26C are similarly connected through resistor 54.

A cylindrical shield 56 of adequately high electrical resistance covers the entire side wall area of the compartment 16 so as to surround all of the aforementioned electrodes. Shield 56 can be comprised of carbon or similar materials of high electrical resistance, and it can be either prefabricated and inserted into compartment 16 in the fabrication of the arrestor, or it can be coated or painted on the walls of compartment 16 without being prefabricated. Carbon has the further characteristic of having low electrical conductivity.

An alternate shield 56A is shown in FIG. 7. Shield 56A is comprised of a helical wire 58 of high electrical resistance. Wire 58 is electrically connected to the upper cap 28 and the lower cap 34. The helical turns of wire 58 should be as close as possible to each other, or at least much smaller than the distance between opposing pairs of electrodes, such as the electrodes 26 and 48A, for example.

A further shield 56B is shown in FIG. 9 and is comprised of a chain of helically disposed resistors 60 which are disposed upon a helical electrode 62. Again, the helical coils of electrode 62 should be as close as possible to each other, or at least much smaller than the distance between opposing electrodes. The opposite ends of the electrode 62 are electrically secured to the caps 28 and 34.

A further shield 56C is illustrated in FIG. 8. Shield 56C utilizes a plurality of vertically disposed electrodes 66 which have their opposite ends electrically connected to caps 28 and 34. A plurality of resistors 64 are electrically connected to each of the electrodes 66. The resistors 60 and 64 in shields 56B and 56C, respectively, should be of equal value in each arrestor so as to form a uniform resistance gradient from cap 28 to cap 34.

It should be understood that the shields 56, 56A, 56B and 560 would assume the precise position of shield 56 as illustrated in FIG. 2 so as to completely surround the electrodes within the compartment 16. They can also be subdivided into partial shields with each one surrounding a spark gap. The electrically connected partial shields 56D are shown in FIG. 10.

The essential difference between the arrestor 10 of this invention and the conventional arrestor 12 of FIGS. 3 and 4 is that the conventional arrestor does not utilize any type of shield within the compartment 16 to surround the electrodes, nor does the conventional arrestor utilize the electro-conducting caps 28 and 34 to electrically connect the upper and lower ends of the shield to the upper and lower terminal means, respectively. The components of the conventional arrestor 12 in FIGS. 3 and 4 which are common to the components of the arrestor of this invention as previously described have been given the same reference numerals as those numerals assigned to the same components in the arrestor 10, except that the letter A has been added thereto.

The numeral 68 has been used in FIGS. 3, 4 and 5 to designate the electric field lines between opposing elec trodes in both the conventional arrestor 12 and the arrestor 10 of this invention. Under ideal conditions with no contaminant on the outside of the arrestor housing, the equipotential line between opposing electrodes should assume the straight position shown by the equipotential lines 70 in the noncontaminated conventional arrestor shown in FIG. 3. Thus, under these circumstances, the equipotential surfaces are horizontal planes when no conductive contamination is present at the surface of the arrestor since the surface does not have any specific potentials. However, when a contaminant of adequate conductivity is present, such as the contaminants 72 shown in FIG. 4, various points of the outer surface of the arrestor assume different potentials. Since the contaminant 72 is in electrical contact with the upper terminal means 18 of high electrical potential, the equipotential surfaces between electrodes are bent downwardly as these planes of equipotential seek points of the same potential on the contaminant on the outside of the arrestor. The bending of the equipotential surfaces by the contaminant create areas of high electrical field intensity between the electrodes, as illustrated by the curved equipotential line 74 in FIG. 4, and sparkover at lower voltage values take place in these are-as of high field intensity.

When the shields 56, 56A, 56B, or 56C are used to surround the electrodes of the arrestor, as shown in FIGS. 2 and 5, the contaminant is prevented from having an adverse affect on the equipotential surfaces. A current of constant value flows through the shield being used at all times, and this circuit is completed from the upper terminal means to the upper cap 28, thence through the shield being used, thence the lower cap 34, and thence to an electrical ground through the lower terminal means 38. The equipotential surfaces within the spark gaps between opposing electrodes will retain their configuration regardless of all potential distortions created by a contaminant on the outer surface of the arrestor housing. Similarly, the field lines between opposing electrodes will also retain their configuration without interference. The sparkover voltage will therefore remain constant and will allow for the designed protection to take place only when a voltage surge of adequate value appears on the arrestor terminals.

Therefore, from the foregoing, it is seen that by placing a shield of high electrical resistivity around the electrodes of a lightning arrestor, distortion of the equipotential surfaces between electrodes by an electroconductive contaminant on the outside of the arrestor is prevented. This in turn eliminates the creation of areas of high field intensity between the electrodes, which in turn prevents sparkover between the electrodes at lower and undesirable voltages. The device of this invention is therefore seen to accomplish at least all of its stated objectives.

Some changes may be made in the construction and arrangement of my lightning arrestor without departing from the real spirit and purpose of my invention, and it is my intention to cover by my claims, any modified forms of structure or use of mechanical equivalents which may be reasonably included within their scope.

I claim:

1. In a lightning arrestor,

an elongated housing of insulative material and having a hollow interior,

a first conductive means in one end of said housing and being adapted for electrical connection to a high potential source,

a second conductive means in the other end of said housing and adapted to be connected to an electrical ground,

at least a pair of spaced electrodes mounted within said housing between said first and second conductive means and defining a space therebetween,

and an electro-conductive shield means of high electrical resistance and low electrical conductivity within said housing extending completely around the space between said electrodes in spaced condition with said electrodes, said electro-conductive means being in electrical contact with said first and second conductive means so that when an electrical current is passed through said cylindrical electro-conductive means when said first conductive means is connected to a high potential source, the equipotential planes in between said electrodes will remain constant and will avoid distortion by an accumulation ofany electroconductive material on the outside of said housing.

2. The device of claim 1 wherein said electro-conductive shield means is disposed adjacent the inner walls of the interior of said housing. l

3. The device of claim -1 wherein said electro-conductive shield means is comprised of carbon material of high resistivity.

4. The device of claim 1 wherein said electro-conductive shield means is a coating material on the inner walls of the interior of said housing.

5. The device of claim 1 wherein said electro-conductive shield means is a prefabricated hollow cylinder.

6. The device of claim 1 wherein said electro-conducting shield means is an elongated resistance wire disposed in a helix in spaced relation around said electrodes, said helix comprised of a plurality of convolutions tightly and closely wound on each other to present a continuous cylindrical shield comprised of helically wound wire.

7. The device of claim 1 wherein said electro-conducting shield means is an elongated wire disposed in a helix in spaced relation around said electrodes, with a plurality of resistors on said wire.

8. The device of claim 1 wherein said electro-conducting shield means is an elongated wire disposed in a helix in spaced relation around said electrodes, with a plurality of resistors of equal electrical resistance on said wire.

9. The device of claim 1 wherein said electro-conducting shield means includes a plurality of substantially parallel spaced apart electro-conducting elements with a plurality of resistors electrically connected to each of said electro-conducting elements.

10. The device of claim 1 wherein said electro conducting shield means includes a plurality of substantially parallel spaced apart electro-conducting elements with a plurality of resistors of equal electrical resistance electrically connected to each of said electro-conducting elements.

11. The device of claim 6 wherein the distance between the adjacent convolutions of said helically disposed wire is less than the distance between said electrodes.

12. The device of claim 7 wherein the distance between the adjacent convolutions of said helically disposed wire is less than the distance between said electrodes.

13. The device of claim 1 wherein a plurality of pairs of spaced electrodes are mounted within said housing, and said shield means includes separate shield elements extending around each pair of electrodes.

14. The method of stabilizing the sparkover potential of a lightning arrestor in contact with a source of high potential and having an elongated arrestor housing of insulative material and having a hollow interior, a first conductive means on one end of said housing and in electr'ical connection with a high potential source, and a second conductive means on the other end of said housing and in connection with an electrical ground, and at least two spaced apart electrodes mounted within said housing between said first and second conductive means and defining a space therebetween; comprising, placing an electro-conductive shield means of high electrical resistance within said housing completely around the space between said electrodes and in spaced condition with respect to said electrodes, passing a constant current through said cylindrical electro-conductive means to stabilize the intensity of the electric field between said spaced electrodes to prevent deviations in said electric fields that might be created by the presence of an electro-conductive contaminant on the outside of said arrestor housing.

References Cited UNITED STATES PATENTS 857,849 6/1907 Titus 33821 XR 1,569,154 9/1951 Donath 31541 X 2,888,608 5/1959 Kalb 31'7-70 X 2,916,667 12/1959 Person 31559 3,019,367 1/1962 Kalb. 3,099,770 7/1963 Sorrow et al 315-59 X 3,259,781 7/1966 Person 33821 X REUBEN EPSTEIN, Primary Examiner U8. 0!. X.R. 313 333; 317-2, 61

Images