US1004530A - Protective device. - Google Patents

Description

E. E. F. CREIGHTOIII.

PROTECTIVE DEVICE.

APPLICATION IILED FEB. 23, 1907.

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E. E. 1". GREIGHTON.

PROTECTIVE DEVICE. APPLICATION FILED FEB. 23, 1907.

Patnted Sept. 26,1911.

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PROTECTIVE DEVICE- APPLICATION rum: 113.23, 1907.

1,004,530. Patented Sept. 26, 1911.

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E. B. F. CREIGHTON.

PROTECTIVE DEVICE.

APPLICATION IILED FEB. 23, 1907.

Patented Sept. 26, 1911.

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UNITED STATES PATENT OFFICE.

ELMER E. F. CREIGHTON, 0F SCHENECTADY, NEW YORK, ASSIGNOR T0 GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

PROTECTIVE DEVICE.

Specification of Letters Patent.

Patented Sept. 26, 1911.

To all whom it may concern:

Be it known that I, ELMER E. TON, a citizen of the United States, residing at Schenectady, county of Schenectady, State of New York, have invented certain new and useful Improvements in Protective Devices, of which the following is a specification.

My present invention relates to protective devices for electrical systems and apparatus.

Electrical transmission lines and systems are subject to high potential charges arising from atmospheric disturbances, static, resonance, switchboard manipulations, and various'other causes, and ordinarily must be provided with some means by which these abnormal and high potential charges can be conducted away. A simple spark gap connected between a line conductor and ground will serve to relieve the conductor of all charges having a sparking distance greater than the length to which the spark gap is adjusted. Unfortunately, however, such a spark gap, when once broken down by high potential charges, offers practically no resistance to the flow of line current and therefore may act as a short circuit on the system. If the terminals of the spark gap are of the so-called non-arcing metals, the potential across a short are carrying say ten amperes,

is in the neighborhood of 16 volts. With carbon electrodes it is in the neighborhood of 40 volts. These potentials are, of course,

too small to have any appreciable effect in holding back the line current at sparking potential. Various means have been re sorted to for extinguishing the line-current arc after the lightning or other high potential charge has been conducted away. Horn shaped gaps have-been used to increase the length of the arc, and air blasts and various other means have been used for blowing out the arc and establishing the original nonconductive'gap. 77

My present invention comprises a protective device differing radically from those above referred to. I make use of conductive elements between which a flow of high potential current may take place, but between which,.owing to the peculiar nature and relation of the conductive elements or electrodes, the normal voltage of the system will not maintain an arc. In general I utilize an electrolyte, such as an aqueous solution, for one' of the conductive elements above mentioned. By the use of an electrolyte I am F. OREIGH- ments of my invention in sufiicient detail to enable persons skilled in the art to apply my invention to practice. My invention is not, however, limited to a particular embodiment or embodiments and constitutes, I believe, a radical departure in the art of protecting electrical systems from lightning or other high-potential disturbances.

Figure l is a sectional elevation of a cell suitable for use according to my invention; Fig. 2 is a perspective view of the metal electrodes and cover of the cell; Figs. 3, 4 and 5 are diagrams illustrating relations between current and electromotive force; Fig. 6 is a perspective view of a group of cells arranged for use on a high-potential system; Fig. 7 is a modified form of cell in which the electrodes are heldin definite position with respect to the electrolyte by. a float; Fig. 8 is an exploded perspective view of a modified type of cell; Fig. 9 is a sectional elevation of the same; Figs. 10, 11 and 12 illustrate additional modifications, and Fig. 13 is a diagram illustratingthe use of cell-s on a high potential system.

The cell illustrated in Fig. 1 comprises a glass jar 1 having a porcelain cover 2 with a depending bafile plate 3. The baffle plate is long enough to extend well below the surface of the solution or electrolyte 4 with which the jar is partially filled. Two copwithin a short distance from the surface of and consequently of its copper wire, with respect to the level of the electrolyte. The bafile plate 3 serves to divide the cell into two compartments, each of which communi- I cates with the outer air through a small hole 11' normally closed by a spring pressed trap door 12, which opens to allow the es- .cape of vapors generated Within the cell by the electric discharges which take place in its normal operation.

A cell of the type above described may be used alone or in groups, the specific arrangement depending on the voltage of the system to be protected. For purposes of illustration, I have indicated in Fig. 1 one method of connecting the cell in circuit between :1- line conductor 13 and ground. The electrode 6 is connected direct-1y to the line conductor and electrode 5 is connected to ground through an adjustable spark gap 14.

When the apparatus is installed, I adjust the distances between electrodes and solution and the length of spark gap 14 so that the total sparking distance between line con ductor and ground is suflicient to hold back the line voltage. In case a high potential charge occurs on the line from lightning or any of those causes heretofore referred to, the high potential charge will jump the gap between electrode 6 and electrolyte 4 and the second gap between electrolyte 4 and electrode 5 and the third gap between the metallic conductors of spark gap 14. I find from experiment that the line current does not follow on the high-potential discharge unless the line voltage is higher than 1500 volts. I attribute the current rupturing feature of the cell to the difiiculty in producing or maintaining an arc between a solid electrode such as a copper wire and a liquid electrode such as an aqueous solution, or more generally to the difliculty in maintaining an arc to an electrolyte as cathode. I find it substantially impossible to maintain an arc to an electrolyte as cathode, provided the potential of the circuit is maintained lower than 1500 volts. At about 1500 volts an unsteady arc may be obtained and at higher voltages an arc may be produced without difficulty.

If the discharge is from line conductor to ground, in the arrangement shown in Fig. 1, the opposition to the flow of line current will reside principally between electrode 6 and electrolyte 4 and only in a minor degree at the other two gaps in series. If, however, the discharge of current takes place in the opposite direction, the opposition will exist near electrode 5 and the circuit will. be ruptured at this point. The metallic spark gap 14 has very little influence on the rupturing action, and as long as current is flowing the electrode'5 is connected to ground through. a connection which offers very little resistance to current flow, because the voltage between the sparking points of the gap 14 is not much above 15 or 20 volts while a discharge is passing. It does have atfunction, however, in preventing continuous leakage from line to ground through the cell.

Various electrolytes may be used in the cell, but I prefer to use an aqueous solution of pota sium carbonate and sodium carbonate having sufficient concentration to give high conductivity. The salts are preferably used in such proportion that the normal evaporation of the water is counteracted by the absorption of water by the solution. Such a solution is of good conductivity and otters a low resistance to the passage of current. If desired I may use a. solution of ammonium chlorid which I find gives an arc voltage approximately 100 volts higher than that obtained with a carbonate mixture. Asbestos may be added to the solution to prevent sloping of the electrolyte, or the solution may be rendered more solid by the addition of gelatinous substances. The use of electrolytes rendered solid by cold is not recluded when of proper conductivity. Various fused salts, as the nitrates, may also be used.

The electrolyte must. be maintained at low resistance to prevent a high voltage drop therethrough when the lightning discharge passes. The lightning is of high frequency and often of high quantity and any impedance in the discharge path, whether of resistance or reactance, may develop a voltage drop between line and ground materially higher than the safe voltage for the line in sulation. The are rupturing quality of the solution appears to be largely independent of its chemical composition or concentration. Possibly it depends on the difiiculty with which a spark gap can be ionized when the cathode of the gap is an electrolytic solution.

WVhile I do not wish to be limited to any particular theory for the operation of my improved protective device, I have indicated in Figs. 3, 4 and 5, certain interesting relations between current and voltage. These relations are deducible from oscillograms taken under conditions hereinafter set forth. Fig. 3 illustrates the relation between voltage and current when the normal voltage "of the system is less than 1500 volts and the electrodes 5 and 6 of the cell are not immersed in the electrolyte. Curve 15 is the normal pressure wave across the protective device and curve' 16 indicates the flow of current when a lightning discharge passes through the arresterat the instant indicated by the vertical line 17. The current flow is of exceedingly short duration. Practically no energy except the lightning,-

flows through the arrester. In case the electrodes are immersed in the electrolyte, the current flow is somewhat diflerent as shown in Fig. 4, in which 18 is the pressure wave, 19 the current wave, and 20 the line indicating the instant of lightning discharge. c In this case the flow of current persists for a substantial period of time and some line energy passes through the arrester. It should be noted, however, that the flow of line current ceases some time betective device is less than 1500 volts.

' discharge fore the pressure wave reaches its zero value. I find that the discharge never persists up to the zero value of the pressure wave and consequently never lasts for more than a fraction of a half cycle. As previously stated, the above-mentioned curves are obtainable in case the voltage across the p13- 7 however, the voltage is higher than this, the protective device will transmit a very considerable quantity of energy and in fact will act as a low resistance path for all that part of the energy having a voltage higher than 1500. This relation is indicated diagrammatically in Fig. 5, in which line 21 is a voltage curve having a maximum considerably above 1500 volts. Curve 22 shows the current flow following a lightning at the instant indicated by vertical line 23. It will be noted that the current rises almost instantly to a very high value and continues at a high value until the voltage across the device has lowered to 1500 volts, after which the current almost instantly drops to zero. The rapid liberation of energy at potentials higher than 1500 volts prevents a dangerous rise of voltage across the protective device. have indicated 1500 volts as approximately the value at which a cell fails to interrupt the circuit, but it should be understood that for working on high potential systems, I may use these cells in series and thereby obtain a total break down voltage of any desired value.

Fig. 6 illustrates a group of six cells assembled in a suitable receptacle 24'. I prefer to pour melted wax or paraflin around the cells to hold them in position and to prevent spilling of the electrolyte in case one of the jars or receptacles breaks from any cause.

Fig. 7 illustrates a modified form of cell in which the metal electrodes 25 and 26 are carried on an insulating bar 27 adjustablymounted on a fioat 28. The float maintains the electrodes at a definite and predetermined distance above or below the surface of the electrolyte, irrespective of changes in the level of the electrolyte due to evaporation or other cause. It will be understood that the electrodes may be adjusted to contact with the electrolyte and that the operation of the device is similar to that of Fig. 1 when similarly adjusted.

Figs. Sand 9 illustrate a different form of apparatus in which both arcing electrodes are electrolytes. This form has the advantage that an electrolyte is cathode irrespective of the'direction of current flow through the cell. The cell comprises a box 29 having a plurality of water- tight partitions 30, 31 and 32 and metal end electrodes 33 and 34. These end electrodes serve to conduct current to and from the electrolyte grooves or cuts is vaporized and establishes an are between the bodies of electrolyte on opposite sides of the partitions. These arcs, like those in the device of Fig. 1, do not persist at a voltage lower than 1500 volts per arc and therefore prevent line current from following the lightning discharge. Even though the levelof the electrolyte falls below the notches of the partitions, I find that the lightning will jump through the air from one electrolyte to the other and that the line current will not follow to any considerable extent. A cover 35 may be provided for the cell and may have longitudinal holes 36. therethrough for the escape of vapors generated within the device. Baflle plates 37 may be secured to the cover and may project downwardly below the surface of the electrolyte.

Fig. 10 illustrates a modified form in which the openings through the partitions consist of small holes 38 preferably arranged near the surface of the liquid. In all the above described devices, I have purposely arranged the arcing space near the surface of the liquid so that the vapors produced by the arc may be free to expand without destructive. explosive action. There is, of

course, some disturbance to the electrolyte nished a ready means of escape.

Figs. 11 and 12 show a modified form of cell in which each metal electrode and its 00-- operating liquid electrode are inclosed in a separate chamber. The walls of the chamber are of metal and are used to conduct current to and from the electrolyte. The two metal vessels 39 and 40 are electrically connected by a metal strip 41. The vessel 39 is lined at the bottom with felt or asbestos 42 and this lining extends upward possibly onethird the height of the vessel. A porcelain cylinder 43 fits loosely within the metal vessel' and rests on the felt or asbestos lining. The upper end of the porcelain cylinder is closed by a cover 44 through which extends a metalelectrode 45, similar in all respects to those illustrated in Fig. 1. The electrolyte 46 is in contact with the metal vessel and its surface may form a spark gap with the metal electrode 45, or may contact directly therewith. The other vessel 40 is similarly equipped with a metal electrode 47 and a liquid electrode 48. In case of a lightning discharge in the direction from electrode 47 to electrode 45, the principal opposition to its flow occurs between the electrode 47 and its cooperating liquid electrode 48. If the lightning discharge takes place in the opposite direction the principal opposition to its flow is between electrode 45 and its liquid electrode 46. In this modification, the metal ,vessel affords such a large surface area for conducting current to and from the electrolyte that the total resistance through the device, excluding the opposition at the arcing surfaces, is small. As previously stated, this quality is highly desirable in a protective device of the liquid electrode type.

As previously indicated, any of the cells above described may be regarded as a single unit, capable of use with other units in protecting a high voltage system. As illustrating the use of-a series of units, I have indicated in Fig. 13 an arrangement suitable for protecting a 14,000 volt transmission line. Each group of cells consists of seven units of the type shown in detail in Fig. 1, and the three groups, 49, 50 and 5-1 are connected to ground through spark gaps 52, 53 and 54. If the cells are adjusted with the electrodes out of contact with the electrolyte, the spark gaps in series may be relatively small, or may be omitted entirely, but if the electrodes are in contact with the solution, the spark gaps should be adjusted for the full sparking potential to which they may be subjected by the line current, allowing a certain percentage increase in Voltage before the arrester comes into operation.

What I claim as new and desire to secure by Letters Patent of the United States, is,

1. The combination with a line conductor, of a discharge path consisting of connections having a low resistance while current is flow-- ing and electrodes mounted in such relation that an arc forms between them-in response to a discharge from said conductor, at least one of said electrodes being formed by the surface of an electrolyte which is of good conductivity.-

2. The combination with an electrical sys-v tem, of a low resistance discharge path for said system consisting of connections having low resistance while current is flowing, an electrode connected to form part of said path, and an electrolyte, said electrode being mounted above the surface of said electrolyte to cooperate therewith and form a spark gap and proportioned to cause the formation of an arc to said electrolyte by a discharge from said system.

3, A protective device for electric transmission systems comprising a vessel containing an electrolyte and an electrode mounted above the surface of the electrolyte and cooperating therewith to form a spark gap containing an insulating gas .and across which a high potential discharge forms an are which has the surface of said electrolyte as a cathode, whereby the flow of line cur-.

across which an arc will not hold when the impressed voltage is materially lower than 1500 volts, at least one of said conductors being a body of electrolyte of good conductivity and of which the surface forms a terminal for the are.

5. The combination of a line conductor, a

discharge path for said conductor comprising a connection having low resistance while current is flowing, and an electrolytic interrupter in said discharge path comprising a vessel containing an electrolyte and means cooperating with the surface of said electrolyte, to cause a flow of current in either direction through said ground connection to produce an are which has the surface of said electrolyte as a cathode.

' 0. The combination with a line conductor, a ground connection through which abnormal potential may be discharged and an electrolytic interrupter in said ground connection comprising a vessel containing an electrolyte and two electrodes mounted above the surface of said electrolyte and cooperating therewith to form two spark gaps in series with said electrolyte, whereby each of said electrodes produces an arc to the surfaceof said electrolyte in response to flow of line current through said ground connection.

7. A protective device for electrical systems comprising connections to points between Which abnormal potential may arise, and a discharge path in said connections comprising-a vessel containing an electrolyte, said path being constricted at a plurality of points near the surface of said electrolyte to cause a flow of current through said connections to produce a plurality of arcs in series to the surface of said electrolyte, whereby each arc has an electrolytic cathode.

8. A protective device comprising a body i of electrolyte of good conductivity, a plurality of electrodes proportioned to produce an arc to the surface of said electrolyte in response to current discharge and mounted above the surface of said electrolyte to enable the surface of said electrolyte to act as cathode for the arc produced-by any of said electrodes in response to current discharge, whereby the flow of energy through said protective device is suppressed, and connections between said electrodes for causing said arcs to be in series.

' trode mounted above the surface of said electrolyte for 'conducting a discharge to and from said electrolyte, the electrode area available to said discharge being proportioned to produce an arc to said electrolyte, and low resistance connections to the system to be protected for rendering said electrolyte the cathode of the arc. I

10. A protective device for relieving electrical systems of abnormal potential comprising a vessel containing an electrolyte of good conductivity, and means cooperating with said electrolyte to form a discharge path having constricted portions adjacent the surface of the electrolyte proportioned to concentrate in said constricted portions the energy of the discharge and thereby produce an arc with the surface of said electrolyte as an electrolvtic cathode.

11. The combination of a body of electrolyte of good conductivity, a plurality of electrodes mounted above the surface of the electrolyte and cooperating therewithto eX- pose a limited surface area and produce an arc to the surface of the electrolyte, a line conductor subject to high potential strains connected with one of said electrodes, a ground connection for another electrode, and a spark gap in the path of a high potential discharge from line to ground.

12. A protective device comprising a vessel containing an electrolyte, two electrodes mounted above the surface of said electrolyte to coiiperate with the surface of said electrolyte and connected in series through said electrolyte, said electrodes being proportioned to cause an arc to form from either electrode to the surface of said electrolyte in response to flow of current.

13. A discharge path including an elec trolytic interrupter comprising a body of electrolyte of good conductivity, means whereby an arc may be established to the surface of said electrolyte as cathode at a point where the arc is free to expand away from the surface of the electrolyte and interrupt the current flow therein, and low resistance connections to said interrupter.

14. The combination of a vessel containing an electrolyte of good conductivity, conductors passing into said vessel and having their ends in proximity to the surface of said electrolyte, insulating means for limiting the area exposed to contact with said electrolyte, means for connecting one of said conductors to an electrical system subject to high potential disturbances, and means for connecting another of said conductors to ground.

15-. The method of protecting an electrical conductor from abnormal potentials, which consists in conducting charges of abnormal potential to ground through a predetermined path of low resistance and opposing the flow of line current with an arc I having the surface of an electrolyte as an electrolytic cathode.

' 16. The method of protecting an electrical system subject to abnormal potentials which consists in conducting away charges of abnormal potential through a low resistance path comprising a body of electrolyte, and developing an arc to the surface of said electrolyte as cathode at a potential in the neighborhood of 1500 volts.

17. The combination of a vessel containing an electrolyte, a lid for said vessel, conductors passing through said lid with their ends above the surface of -said electrolyte to form spark gaps having the surface of the electrolyte as one terminal, and a vent in said vessel to permit the escape of gases.

In Witness whereof, I have hereunto set my hand this 21st day of February, 1907.

ELMER E. F. CREIGHTON.

Witnesses:

' BENJAMIN B. HULL,

HELEN Onronn.

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