US2819429A - Electric protective equipment - Google Patents

Description

Jan. 7, 1958 W. F. SKEATS ELECTRIC PROTECTIVE EQUIPMENT Inventor: VVilf`r')ed F. Skeats,

United States Patent O ELECTRIC PROTECTIVE EQUIPMENT Wilfred F. Skeats, Lansdowne, Pa., assignor to General Electric Company, a corporation of New York Application May 24, 1954, Serial No. 431,828

Claims. (Cl. 317-12) This invention relates to equipment for protecting electrical apparatus against overvoltages and, more particularly, to a spark gap device for safely by-passing excessive currents around the protected apparatus.

To provide overvoltage protection for the insulation of a wide variety of types of electrical apparatus, it is common to provide the apparatus with a by-pass circuit containing a spark gap device. The spark gap device is set to arc over at a safe voltage thereby to safely by-pass any excessive currents around the apparatus. To insure reliable `operation of such a gap device, it is important that the breakdown voltage, or dielectric strength, of the gap remain substantially constant. For many applications, the only significant factor tending to vary this dielectric strength isa varying ambient temperature.

Accordingly, i-t is a primary object `of the present invention to provide a new and improved spark gap device which includes a gap having a dielectric strength which remains substantially constant in spite of variations in ambient temperature.

The arcing which occurs in a spark gap device generates an appreciable volume of hot gases which are capable of subjecting the parts of the device to very high temperatures and forces which, unless properly controlled, may seriously damage these parts. This problem is especially critical when the parts of the gap device include relatively movable elements, such as are present in a temperaturecompensating mechanism.

Accordingly, it is a further object of my invention to provide, in a spark gap device having temperaturecompensating mechanism for rendering the device insensitive to ambient temperature variations, means which protect the mechanism from the high temperatures and forces which are present during arcing.

In accordance with one form of my invention, there is provided in a protective device, the combination of a pair of relatively-movable electrodes biased into spacedapart relationship to define a spark gap therebetween, compensating means responsive to variations in ambient temperature for effecting movement of one of said electrodes in a direction to vary the length of said gap as a direct function of said temperature variations and by an amount suicient to maintain a substantially constant dielectric strength of said gap, and current responsive means operative to move said electrodes together in response to current ow between said electrodes in excess of a predetermined value, whereby to relieve the compensating means of the stresses produced by the ancing which accompanies said current flow.

For a better understanding of my invention, reference may be had to the accompanying dnawing wherein Fig. l is an elevational view partially in section of ya spark gap device constructed in accordance with my invention; Fig. 2 is a cross-sectional view taken along the line 2-2 of Fig. 1, and Fig. 3 schematically illustrates the spark gap device of my invention as being utilized in protective equipment for a series capacitor.

Referring now to Fig. l, there is shown a spark gap 2,819,429 Patented Jan.` 7, 1958 device 10 comprising an insulating base 11 upon which are mounted a pair of spaced electrodes 12 and 13, preferably -formed `of graphite. The electrode 12 is a stationary electrode adjustably mounted on a threaded conductive stud 14 which, in turn, is carried by an adapter 15 having a rst terminal 16 secured thereto. The adapter 15 and the stationary electrode 12 are supported trom the base 11 by means of a suitable insulator, such as a porcelain column 17.

The other electrode 13 is mounted for movement with respect to the stationary electrode 12 by means of fa pivotally-mounted, L-shaped bracket 20. This L-shaped bracket is mounted on a pivot pin 21 which extends transversely between a pair yof spaced-apart stationary side walls 22. For mounting the electrode 13 at the upper end of the bracket 20, there is provided a suitable clamping screw 25 which is arranged to clamp a conductive strip 26 in electrically-connected relationship to the electrode 13. For reasons which will soon appear more clearly, this conductive strip 26 is Wound into a flattened multi-turn coil 2S extending laround spaced-apart mounting pins 27 and is suitably connected at the inner end of the coil to a second terminal structure 30. The turns of the coil 28 are insulated from each other by a suitable coating of insulation covering the strip 26.

The relatively-movable electrodes 12 and 13 are urged apart by biasing means including a compression spring 32 acting through a connecting rod 33. This connecting rod 33 is pivotally joined by ia pin 34 to the electrode-supporting bracket 20 and extends loosely through an opening formed 1n a stationary abutment plate 35. The compression spring 32, which has one end bearing against abutment plate 35, bears at its other end against a tension adjusting unit 36 suitably threaded on connecting rod 33.

Inorder to insure reliable operation of a spark gap device, it is important that the arc-over voltage, or dielectric strength, of the gap between the electrodes of the device remain substantially constant. Should this dielectric strength be appreciably diminished from its preset value, then false operation of the device is likely to occur, Whereas if the dielectric strength is appreciably increased from its preset value, then the protected apparatus may be damaged by overvoltage before the gap arcs over. In many applications, the only signicant factors tending to vary this dielectric strength are variations in ambient temperature. To insure that the dielectric strength of the gap between electrodes 12 and 13 of my device will remain constant in spite `of such temperature variations, I have provided, in accordance with my invention, ternperature compensating mechanism 40. This mechanism 40 comprises an elongated actuating rod 41 formed of a material having a low thermal expansion coeicient, e. g., stainless steel. At its outer end this rod 41 is adjustably attached to a tube 42 formed of material having a relatively high thermal expansion coelicient, e. g., an aluminum alloy. This expansible ltube 42 surrounds the actuating rod 41 in generally concentric relationship and contains suitable annular guides 9 slidably receiving the rod 41 so as to insure rectilinear motion of the rod within the tube 42. The tube 42 is rigidly connected at its inner axial end to the base 11 by means of an outer shielding tube 43 which is rigidly supported from the base 11 and is rigidly attached at 44 to the expansible tube 42. The supporting means for the outer shielding tube 43 comprises a pair of opposed nuts 45 and 46 threaded on the inner axial end of the shielding tube 43 and rrnly clamping the stationary abutment plate 35 therebetween. The abutment plate 35 is suitably secured to lthe stationary side walls 22, as by screws 47. The shielding tube 43 is supported intermediate its length by means yof a supporting plate 48 having an apertured portion snugly receiving the shielding tube 43. This supporting plate 48 is, in

turn, suitably secured to a rigid sub-base 49. At its outer end. the shielding tube 43 is provided with a closure member Sti slidably receiving the expansible tube 42. Secured to the outer end of expansible tube 42 is a socket 51 having a threaded bore which receives the threaded outer end of the elongated actuating rod 41. A suitable lock nut 52 maintains the rod 41 and socket 51 in a predetermined position of adjustment.

From this detailed description of the structure of temperature compensating mechanism 40, it will be apparent that expansion and contraction of the temperature sensitive tube 42 in response to ambient temperature variations will axially shift the central actuating rod 41 thereby varying the position of the inner end lof the rod 41 in accordance with these temperature variations. Since this inner end of rod 41 forms ya stop against which the movable electrode-supporting bracket is biased by means of compression spring 32, it will be apparent that the position. of movable electrode 13 will be varied in accordance with such temperature variations. Since. as seen in Fig. l, the movable electrode 13 will be shifted to the left in response to temperature decreases and to the right in response to temperature increases, it will be apparent that the length of the gap between electrodes 12 and 13 will be varied as a direct function of the temperature variations. The length of the expansible tube 42 and the moment arm between pivot pin 24 and the forcer-transmitting rod 41 are selected in such a manner that this variation of the gap length will be of such a value as to maintain the dielectric strength of the gap substantially constant in spite of said temperature variations.

Now when the gap between electrodes 12 and 13 breaks down to permit current to flow through the gap, the resulting arc will generate an appreciable volume of hot exhaust gases. These exhaust gases are capable of subjecting the parts of the gap device to very high temperatures and forces which, unless properly controlled, may seriously damage these parts. This problem is especially acute where, as in the present device, the parts include a relatively sensitive mechanism such as my temperature compensating mechanism 40. For example, the hot exhaust gases generated by arcing, in addition to creating high temperature conditions, also tend to force the electrodes 12, 13 apart with a relatively high, force which, if uncontrolled, might seriously impair the operation of temperature-compensating mechanism 40,

To protect the adjacent parts and, especially, the temperature-compensating mechanism 40, against the harmful effects of the hot gases generated by arcing, I utilize the multi-turn coil 28 to force the electrodes together as soon as arcing between the electrodes is initiated. More particularly, the coil 28 is of a lattened configuration, shaped in such a manner that it has two physically opposed sides and 61 disposed in close proximity to each other. As a result of this proximity, the two sides 60 and 61, when energized by current flowing through the coil, have a strong mutual repulsion. The lower side 61 of the coil is backed up by an insulated channel-shaped metal support 62 so as to be held firmly in place, but the upper side 60 is free to move upwardly in response to the repulsive force between the sides. For transmitting this upward movement to the movable electrode 13, there is provided a convex shoe 63, which rests on the concave upper surface of the coil and carries a force-transmitting pin 64 extending upwardly through a guide opening in the base 11 into a position adjacent the L-shaped, electrode-supporting bracket 20. A suitable compression spring 66 encircling the pin 64 tends to urge the coil into the conguration of Fig. l. Thus, when the upper side 60 of the coil moves upwardly against the bias of spring 66 in response to current ow through the coil, this upward movement is transmitted through pin 64 to a transversely-extending portion of L-shaped bracket 20, whereby to effect rotation of the bracket 20 counterclock- 4 wise about its pivot pin 21. This, of course, forces the movable electrode 13 toward the fixed electrode 12.

ln order to prevent the electrodes from being damaged by impact resulting from the movement of electrode 13 into engagement with the other electrode 12, there is provided a stop 76 which is arranged to prevent the electrode 13 from moving beyond a limit point immediately adjacent to but spaced from the fixed electrode 12. This stop 70 takes the form of a conical nut adjustably threaded on the shielding tube 43. By properly positioning the conical nut 70 on this tube, the minimum separation of the electrodes can be adjusted to any desired value. A jam nut 71 is utilized to prevent accidental loosening of the stop nut 70 from its preselected position of adjustment. This conical nut 70 is arranged to engage a crossbar 72 carried by the bracket 20 so that the travel of bracket 20, as it moves counterclockwise under the influence of coil 28, will be halted just prior to the point at which electrodes 12 and 13 would engage.

To further protect the temperature-cornpensating mechanism 40 against the hot exhaust gases produced by arcing, l have provided a barrier 73 constructed of a suitable insulating material` This barrier 73 is supported between spaced-apart side plates 74 and physically isolates the arcing gap between the electrodes 12 and 13 from the temperature-compensating mechanism 40. Because the barrier is generally disposed in a plane which is at an acute angle to a vertical plane, the hot arcing products will be deccted upwardly and away from the temperature compensating mechanism 40. The movable electrode 13 extends through a suitable opening 75 formed in the barrier 73` To illustrate an application of my invention, I have, in Fig. 3, schematically shown the device as utilized in series capacitor protective equipment. More particularly, there is shown connected in power line a bank of series capacitors represented schematically by the reference character S1. In shunting relationship to the series capacitor bank. 81 is a by-pass circuit 82 containing a self-clearing main spark gap 83. This main spark gap 83 is preferably constructed as described and claimed in application Serial No. 274,694, now Patent No. 2,760,121 filed by A. W. Roth and assigned to the assignee of this invention. As more fully described in this Roth application, when this main gap 83 arcs over in response to overvoltage across the series capacitor 81, the resulting current llowing through the by-pass circuit 32 immediately induces in current transformer S4 a current which is eiective to cause a blast valve 85 to open. Opening of this blast valve 85 permits a blast of high pressure iiuid to ow from a iluid pressure source 86 into the main spark gap device 83 thereby to extinguish the arc which had been established therein. In accordance with the aforesaid Roth application, the arc-over voltage of the main gap 83 has been rendered insensitive to ambient temperature variations by means of a trigger electrode 87 controlled by a hermetically-sealed pilot gap 8S. The pilot gap, being hermetically-sealed, has a dielectric strength which remains constant in spite of ambient temperature variations. When the pilot gap arcs over at its preset voltag, it immediately triggers, or ignites, the main spark gap 83, so that as a result, the main spark gap will almost always arc over at the voltage for which the pilot gap is preset.

Now, if for some unusual reason, the opening of the blast valve 85 should result in an excessive arc extinguishing effort in the main gap 83, it will be apparent that the main gap will not be effective to by-pass current around the series capacitor bank 81 in the desired manner. To protect the capacitor bank under such unusual circumstances, I have utilized the temperature-compensated gap device of my invention to function as a so-called backup gap. This back-up gap, which 1s schematically shown at 10 in Fig. 3, is connected in shunt to the capacitor bank 81 and in shunt with the main spark gap 83. The back-up gap is preset to arc over at a slightly higher voltage than the main gap 83. Thus, if for some unusual reason the main gap should fail to arc-over at its preset value of voltage, then the back-up gap immediately becomes effective to relieve the capacitor bank 81 of overvoltage. It will be apparent that optimum coordination between the operation of the back-up gap and operation of the main spark gap will be obtained if the preset difference between the arc-over voltages of these respective gaps remain constant in spite of variations in ambient temperature. More specifically, if this difference remains constant under all temperature conditions, then the backup gap may be set to arc over at any desired voltage larger than the arc over voltage of the main gap without the hazard of the back-up gap incorrectly arcing over first if the temperature should increase or without the hazard of the back-up gap arcing over at too high a voltage should the temperature decrease. This preset difference is maintained constant in my protective arrangement by reason of the fact that both of these gaps are insensitive to ambient temperature variationsthe main spark gap 83 by virtue of its pilot-controlled trigger electrode 87 and the back-up gap 10 by virtue of temperaturecompensating mechanism 40, described hereinabove. Thus, by utilizing the back-up gap of my invention in combination with a main spark gap such as 83, I am able to obtain between these gaps, an optimum degree of coordination, which coordination remains unchanged in spite of ambient temperature variations.

When the back-up gap 10 does arc over, the resulting are is extinguished after a predetermined number of cycles by a shoiting switch such as schematically shown at 90 in Fig. 3. More particularly, a current transformer 91, which is arranged to be energized by current flow through gap 10, is utilized to operate a latch 92 which, in turn, is released to permit the switch 90 to close under the influence of spring 93, thereby to completely short out the capacitor bank 81 as well as each of the gaps 10 and 83.

Although I have shown my temperature-compensated gap device utilized as a back-up gap in series capacitor protective equipment, it is to be understood that it is not limited to such uses and may be used as a protective device for any suitable electrical apparatus, even Without requiring the main spark gap device 83.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects and l, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

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

1. A protective device comprising a pair of relativelymovable electrodes spaced-apart in an unsealed atmosphere to define a spark gap therebetween, and compensating means operable in response to ambient temperature variations to vary the length of said gap directly in accordance with said temperature variations and by an amount suicient to maintain a substantially constant dielectric strength of said gap in spite of said temperature variations.

2. A protectective device comprising a pair of relatively-movable electrodes spaced-apart in an unsealed atmosphere to define a spark gap therebetween, compensating means operable to response to ambient temperature variations to vary the length of said gap directly in accordance with said temperature variations and by an amount sufficient to maintain a substantially constant dielectric strength of said gap in spite of said temperature variations, and current responsive means operative to move one of said electrodes toward the other in response to current flow between said electrodes, whereby to relieve said temperature-compensating means of the stresses produced by the arcing which accompanies said current ow.

3. A protective device comprising a pair of relativelymovable electrodes spaced-apart in an unsealed atmosphere to define a spark gap therebetween, compensating means operable in response to ambient temperature variations to vary the length of said gap directly in accordance with said temperature variations and by an amount suicient to maintain a substantially constant dielectric strength of said gap in spite of said temperature variations, current responsive means operative to move said electrodes relatively toward each other in response to current flow between said electrodes, whereby to relieve said temperature-compensating means of the stresses produced by the arcing which accompanies said current flow, and stop means for limiting the relative movement of said electrodes toward each other to a position wherein the electrodes are slightly spaced apart.

4. A protective device comprising a pair of relativelymovable electrodes spaced-apart in yan unsealed atmosphere to define a spark gap therebetween, compensating means operable in response to ambient temperature variations to vary the length of said gap directly in accordance with said temperature variations and by an amount sufficient to maintain a substantially constant dielectric strength of said gap in spite of said temperature variations, and an insulating barrier disposed between said spark gap and said compensating means whereby to shield said mechanism from the hot gases produced by arc-over of said gap.

5. A temperature-compensated spark gap device comprising a first electrode, a second electrode mounted for movement with respect to the first electrode, said electrodes being located in an lunsealed atmosphere, means for biasing said second electrode into a position spaced from said first electrode whereby to provide a gap between said electrodes, compensating means opposing said biasing means and operable in response to ambient temperature variations to effect movement of said second electrode into positions wherein the dielectric strength of said gap remains substantially constant in spite of said temperature variations, and current responsive means for moving said second electrodes toward said first electrode in response to current flow between said electrodes in excess of a predetermined value.

6. A temperatureacompensated spark gap device comprising a first electrode, a second electrode mounted for movement with respect to the first electrode, said electrodes being located in an unsealed atmosphere, means for biasing said second electrode into a position spaced from said first electrode whereby to provide a gap between said electrodes, compensating means opposing said biasing means and operable in response to ambient temperature variations to effect movement of said second electrode into positions wherein the dielectric strength of said gap remains substantially constant in spite of said temperature variations.

7. A temperature-compensated spark gap device cornprising a first electrode, a second electrode mounted for movement with respect to the first electrode, said electrodes being located in an unsealed atmosphere, means for biasing said second electrode into a position spaced from said first electrode whereby to provide a gap between electrodes, compensating means opposing said biasing means and operable in response to ambient temperature variations to effect movement of said second electrode into positions wherein the dielectric strength of said gap remains substantially constant in spite of said temperature variations, current responsive means for moving said second electrode toward said first electrode in response to current flow between said electrodes in excess of a predetermined value, and stop means for limiting the movement of said second electrode toward said first electrode to a position wherein the electrodes are slightly spaced apart.

8. A temperature-compensated spark gap device comprising a first electrode, a second electrode mounted for movement with respect to the first electrode, said electrodes being located in an unsealed atmosphere, means for 7 biasing said second electrode into a position spaced from said first electrode whereby to provide a gap between said electrodes, compensating means opposing said biasing means and operable in response to ambient temperature variations to eifect movement of said second electrode into positions wherein the dielectric strength of said gap remains substantially constant in spite of said temperature variations, a current responsive coil having a generallyflattened configuration and connected in series circuit relationship with said gap, said coil having a pair of closcly-spaced sides one of which is movable in response to the mutual repulsion produced between said sides by energization of said coil, and means operable in response to movement of said one side for forcing said second electrode toward said first electrode.

9. A protective device comprising a pair of relativelymovable electrodes spaced-apart in an unealed atmosphere to define a spark gap therebetween, compensating means operable in response to ambient temperature variations to vary the length of said gap directly in accordance with said temperature variations and by an amount suflicient to maintain a substantially constant dielectric strength of said gap in spite of said temperature variations, a current responsive coil having a generally-flattened configuration and connected in series circuit relationship with said spark gap, said coil having a pair of closely-spaced sides one of which is movable in response to the mutual repulsion which occurs between said sides when the coil is energized by currents through said gap in excess of a predetermined value, and means operable in response to movement of said one side for forcing one of said electrodes toward the other.

l0. A teniperature-compensated spark gap device comprising first and second electrodes located in an unsealed atmosphere, electrode-supporting struct-ure mounting said econd electrode for movement with respect to said first electrode, means for biasing said electrodes into spacedapart relationship whereby to provide a gap therebetween, an actuating member having a portion bearing against said electrode-supporting structure to provide a stop for limiting the length of said gap, and compensating means responsive to ambient temperature variations for adjusting the position of said stop portion in a direction to vary the length of said gap directly in accordance with said temperature variations and by an amount sufficient to maintain a substantial constant dielectric strength for said gap in spite of said temperature variations.

l l. The device of claim 10 in combination with current responsive means operable to move said second electrode toward said lirst electrode in response to current flow between said electrodes.

12. The device of claim l0 in combination with a eurrent responsive coil having a generally-flattened configuration and connected in series circuit relationship with said spark gap, said coil having a pair of closely-spaced sides one of which is movable in response to the mutual repulsion which occurs between said sides when the coil is energized by currents through said gap, and means operable in response to movement ot said one side for forcing said second electrode toward said first electrode.

13. in a by-pass circuit for protecting electrical apparatus from overvoltages, a main spark gap device having a gap which is set to arc-over in response t-o `overvoltage across said apparatus equaling at least a predetermined rst value, uid blast means associated with said main gap device for extinguishing said arc, temperature-compensating means for maintaining the arcover voltage of said main gap device substantially constant in spite of variations in ambient temperature, said fluid blast means being occasionally subject to the type of operation that acts to increase the arc-over voltage of said gap to a value considerably in excess of said first value, a back-up gap device connected in shunt relationship to said main gap device and having a gap located in an unsealed atmosphere, said gap being set to arc-over at a predetermined second value yof `overvoltage which is of a greater magnitude than said first value but of low enough magnitude to protect said apparatus, tempmature-compensating means for maintaining the arc-over voltage of said backup gap substantially constant in spite of variations in ambient temperature, and means for establishing a short circuit about said bacloup gap in response to arc-over thereof.

14. In a by-pass circuit for protecting electrical appara.- tus from overvoltages, a main spark gap device having a gap which is set to arc-over in response to overvoltage across said apparatus exceeding a predetermined first value, means associated with said main gap device for eX- tinguishing said arc, temperature-compensating means for maintaining the arc-over voltage of said main gap device subsantially constant in spite of variations in ambient temperature, a bacloup gap device connected in shunt relationship to said main gap device, said back-up gap device comprising a pair of relatively-movable electrodes spaced-apart in an unsealed atmosphere to deine therebetween a spark gap which is set to arc-over at a predetermined second value of overvoltage, said second value being of a greater magnitude than said first value, and compensating means operable in response to ambeint temperature variations to vary the length of said spark gap directly in accordance with said temperature variations and by an amount sutiicient to maintain the `arc-over voltage of said spark gap substantially constant at said second value in spite of temperature variations.

15. The gap device of claim 10 in which said compensating means comprises an eXpansible member having a positive thermal expansion coefficient, means for tixedly supporting one end of said expansible member 'adjacent said electrode-supporting structure with the other end thereof located remote from said structure, and means for coupling said other end of the expansible member to said actuating member.

References Cited in the file of this patent UNITED STATES PATENTS 1,024,555 Chapman Apr. 30, 1912 1,034,584 Chapman Aug. 6, 1912 1,197,099 Bliss Sept. 5, 1916 1,212,146 Nielsen Ian. 9, 1917 1,260,649 Conrad Mar. 26, 1918 1,735,820 Ward Nov. 12, 1929 2,172,666 Michel Sept. 12, 1939 2,323,702 Berkey July 6, 1943 2,571,910 Marbury et al Oct. 16, 1951 2,584,710 Johnson Feb. 5, 1952 FOREIGN PATENTS 581,621 France Sept. 30, 1924

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