US3222556A - Electric discharge device - Google Patents

Description

Dec. 7, 1965 D. s. GUSTIN 3,222,556

ELECTRIC DISCHARGE DEVICE Filed April 17, 1962 DANIEL S. GUSTIN INVENTOR.

ATTORNEY United States Patent 3,222,556 ELECTRHC DTSQHARGE DEVHCE Daniel S. Gustin, ilondonderry, N.H., assiguor to Sylvania Electric Products line, a corporation of Delaware Filed Apr. 17, 1962, Ser. No. li8,091 5 Claims. (Cl. 313-25) This invention relates to high pressure, electric discharge devices for use in constant current series circuits.

High pressure electric discharge devices, commonly known as mercury vapor lamps or merely mercury lamps, are Well known to the art and such devices have previously been used in constant current series circuits. These devices include an inner arc tube which encloses a mercury discharge during lamp operation. The are tube is generally supported within an outer bulbous envelope by a metallic frame or harness. At one end of the arc tube a starting probe is located in close proximity to a main discharge electrode and another electrode is located at the opposite end. A filling of argon gas and a drop of mercury are enclosed within the tube.

When the lamp is turned on, full starting voltage is applied between the starting probe and electrode near it. The voltage causes a glow discharge of argon gas between these members and gradually, the heat of the discharge vaporizes some of the liquid mercury in the tube. As the vaporization continues, pressure builds up and mercury ions are formed under the influence of the electrode discharge. When sufiicient ionization occurs, an arc will then strike between the two main discharge electrodes.

Although the arc in the tube is usually quite stable during a continuing application of line voltage, it may fail if an interruption in the current occurs. When such interruptions occur in a constant current series circuit, and the arc tube is still warm, often the arc does not restrike between the electrodes but rather may randomly form between various elements on the arc tube harness. Formation of an arc upon the harness will cause its destruction.

Even a momentary interruption of a few cycles may cause failure of the arc in the tube. The ionization of the mercury in the tube then ceases almost immediately and will not reoccur even with the application of excessive voltages if the mercury vapor pressure remains high. However, ionized mercury is essential for the formation of an arc. Only cooling of the tube together with reduction of mercury vapor pressure will allow arc reformation and such cooling can take up to a half hour.

Yet, a constant current transformer which is included in the circuit will keep attempting to strike an are between the electrodes by delivering higher and higher voltages irrespective of whether the mercury vapor pressure is high or not. Excecdingly high voltages, possibly as high as 6,000 volts, can be built up in the circuit. With voltages this high, an arc may randomly stroke on the arc tube harness since an arc is not forming in the arc tube. When such random arcs occur, the heat generated will gradually melt the harness at the point of discharge and may eventually destroy the lamp.

Not withstanding the fact that this problem occurs in a constant current series circuit, such circuitry is quite commonly used in street lighting with mercury lamps. Probably the main reason for the prevalency of such circuitry is that before the advent of mercury vapor lamps for street lighting, and possibly even before the customary use of incandescent lamps, carbon arcs were frequently used. The industry had found that it was easy to combine carbon arcs into series circuits and wiring costs were materially reduced. Rather than doubling wiring costs by using parallel circuitry, it was substantially more economical to extend a single wire loop from a power station out to the carbon arcs and back again to the station. Then when mercury vapor lamps were introduced for street lighting, they were incorporated into the existing series circuits.

Accordingly to my invention, to control random arcing in a constant current series circuit, I place a pair of higl1- melting conductive annuli within the bulbous envelope upon conductors of different potentials. These annuli are placed fairly close to each other so that any random arcing will preferentially form between them rather then between portions of the harness. Since these conductive annuli are made of highdnelting materials, even great heat produced by the random arcing will not melt them and if such arcing occurs, the harness will remain intact. Once the random arc is established, it will continue between these conductors so long as current is maintained in the circuit. When the current is turned off again the random arcing will stop and if the arc tube is then cool, subsequent application of current will produce the formation of a normal are within the tube. Thus, if the current momentarily fails during the evening, and the arc in the arc tube fails, a controlled arc can then strike between the conductors and continue until the current is turned off, possibly the next morning. The following evening when the current is again turned on in the circuit, an arc will reform properly within the arc tube.

Accordingly, the primary object of my invention is the prevention of uncontrolled random arcing on an arc tube harness.

A feature of any invention is the positioning of a pair of high-melting conductors within the bulbous envelope so that an arc will preferentially strike between these con ductors when it cannot form in the tube.

An advantage of any invention is that outage of mercury lamps caused by random arcing and destruction of the arc tube harness is reduced.

The many other objects, features and advantages of the instant invention will become manifest with those versed in the art upon reading the following specification when taken in conjunction with the accompanying drawings, wherein a specific embodiment of this invention is shown and described by way of an illustrative example.

Referring to the figure an elevational view of a mercury vapor lamp is shown. For clarity of presentation, the outer bulbous envelope and the base for the lamp are shown in phantom lines surrounding the arc tube harness and the arc tube.

A high pressure mercury vapor lamp such as shown in the drawing, comprises an outer vitreous envelope or acket 2 of generally tubular form having a central bulbous portion 3. The jacket is provided at its lower end with a re-entrant stem it having a press through which extends relatively stiff lead-in wires 6 and 7 connected at their outer ends to the electrical contacts of a usual screwtype base 8 and at their inner ends to the arc tube and the harness.

The are tube 12 is made of quartz and has sealed therein at opposite ends, the main discharge electrodes 13 and 14, which are supported on lead-in wires 4 and 5 respectively. Each main electrode comprises a core portion which may be a prolongation of the lead-in wires 4 and 5 and may be prepared of a suitable refractory metal such as tungsten or molybdenum. The prolongations of the lead-in wires 4 and 5 are surrounded by tungsten wire helixes. A small elongated piece or sliver of thorium metal (not shown) is inserted between the core and the helix to reduce the cathode drop during operation. An auxiliary starting probe or electrode 18 is provided at the base end of the arc tube 12 adjacent main electrode 14 and comprises an inwardly projecting end of another lead-in wire.

Each of the current lead-in wires described above have their ends welded to intermediate foil sections of molybdenum which are hermetically sealed within pinch seal portions of the quartz arc tube. The foil sections are very thin, for example, approximately 0.0008 thick and go into tension without rupturing or scaling off when the quartz cools. Relatively short molybdenum wires 23, 24- and 35 are welded to the outer ends of the foil and serve to convey current to the various electrodes inside the arc tube 123.

Metal foil strips 45 and 46 are welded to the outer ends of the lead-in wires 23 and 24 respectively. A resistor 26 is welded to foil strip 45 which in turn, is welded to the arc tube harness. The resistor may have a value of, for example, 40,000 ohms and serves to limit current to auxiliary electrode 18 during normal starting of the lamp. Metal foil strip 4-6 is Welded directly to stiff lead-in Wire 7. Lead-in wire 35 is welded at one end to a piece of molybdenum foil sealed in the arc tube 12 which in turn is welded to main electrode 13. Metal foil strip 4-7 is welded at one end to lead-in wire 35 and at the other end to the harness. The pinched or flattened end portions of the arc tube 12 form a wide seal using substantially the full diameter of the tub-e 12 and are made by flattening or compressing the ends of the arc tube 12 While it is heated. The are tube 12 is provided with a filling of an ionizable media such as mercury in sufficient quantity to be completely vaporized when pressure is developed in the order of A2 to several atmospheres during operation of the lamp. In addition, a small quantity of a rare gas such as argon, at a normal pressure of 25 mm. of mercury is introduced to facilitate starting.

The U-shaped wire, internal supporting assembly or arc tube harness serves to maintain the position of the are tube 12 substantially coaxial within the envelope 2. To support the arc tube 12 within the envelope 2, the stiff lead-in wire 6 is welded to the base 53 of the harness. Because stiff lead-in wires 6 and '7 are maintained at different electrical potentials, they must be insulated from each other, together with all members electrically associated with each of them. Clamps 56 and 57 which hold the arc tube 12 at the pinched end portions are fixedly attached to legs 54 of the harness and thus support the arc tube 12 within the outer envelope 2. A rod 59 bridges the free ends of the U-shaped support wire 54- and is fixedly attached thereto to impart stability to the structure. The free ends of the U-shaped support wire 54 are also provided with a pair of resilient metal leaf springs 60, frictionally engaging the upper tubular portion of the lamp envelope 2. A heat shield 61 is positioned beneath the arc tube 12 and above the resistor 26 so as to protect the resistor from excessive heat generated during lamp operation.

Conductive annuli 30 and 31 are preferably disposed upon stiff lead-in wire 6 and '7 respectively. Each of these conductive annuli 6 and '7 are spaced from each other so as to form a gap across which an arc can form if it can not form in the arc tube 12. Ordinarily the random arcs would form between the sharpest points available in a device and in mercury lamps this would be between the end 27 of the wire leading to the resistor 26 and stiff lead-in line '7. Of course, the conductive annuli 30 and 31 must be in a conductive relationship with the members on which they are disposed.

In normal operation of the lamp, the stiff lead-in wire 6 serves as one source of potential and the lead-in wire '7 serves for the other. Since base 53 of the U-shaped harness is welded to stiff lead-in wire 6, the harness, together with members electrically connected with it, become part of the circuit. Thus, starter probe 18 and main electrode 3 are connected to one side of a power line in the circuit and main electrode 14 is connected to the other side of the line. Lead-in wire 7 thus not only must be electrically insulated from lead-in wire 6, it must be insulated from the rest of the harness to prevent shortcircuiting. Insulating tubes, 33 and 34 surrounding foil strips 45 and 46, respectively, insure insulation of the 4 strips from each other and also of strip 45 from the harness and heat shield 61.

Many materials may be used for the conductive annuli and although I prefer to use compacted graphite because: of its economy, tantalum, zirconium, tungsten, vanadium or molybdenum and the carbides of each of these several metals may also be used. I prefer to use a conductiveannulus with a round peripheral shape, however other shapes such as squares or triangles are also very readily adapted to the structure. Round is preferred however, because even if the annulus moves upon its support a constant gap distance is maintained.

The gap between the conductive annuli 30 and 31 is quite important and these members must be spaced sufficiently apart so that an arc will not form during nor mal starting or operation of the lamp but will only strike upon malfunction of the circuit. However the gap distance will vary depending upon the normal starting voltage of the lamp and the metal or metal compound used for the conductive annulus. These distances can be readily determined by routine experimentation and for a graphite annulus I prefer to have a gap of about The diameter of the conductive annuli together with the thickness is not critical so long as the requisite arc gap is maintained. Although, of course, the thickness must be sufficient so that each annulus is self-supporting and the diameter should not be so large that fitting into the outer bulbous envelope is difficult.

Although we have shown the conductive annuli disposed upon the stiff leadin wires 6 and 7, it is apparent that they may be placed elsewhere on the lamp harness so long as they are on members connected to opposite sides of a power line and if the arc gap is maintained. For example, a conductive annulus may be fitted upon the support frame 53 and another upon the stiff leadin wire 7 or the metal strip 46 which is welded thereto. It is apparent that other modifications may be made in the instant invention without departing from the spirit and scope thereof. Thus, it is my intention only to be limited by the scope of the appended claims.

As my invention I claim:

l. A high pressure electric discharge device comprising: an outer bulbous envelope; a first and a second stiff lead-in wire disposed at the base of said envelope, each of said lead-in wires being adapted to conduct current from opposite sides of a power line; a metallic harness disposed in said envelope and supported upon said first stiff lead-in wire; an arc tube supported upon said metallic harness; electrodes disposed at either end of said arc tube, one of said electrodes being electrically connected to said harness and the other of said electrodes electrically connected to said second stiff lead-in wire; conductive means disposed within said envelope and upon each of said lead-in wires for preferentially forming an arc therebetween when an arc cannot strike between said electrodes in said are tube.

2. In a high pressure electric discharge device comprising an outer bulbous envelope; a first and a second stiff lead-in wire disposed at the base of said envelope, each of said stiff lead-in wires being adapted to conduct current from opposite sides of a power line; a metallic harness disposed within said envelope and supported upon said first stiff lead-in wire; an arc tube supported u on said metallic harness; electrodes disposed at either end of said are tube, one of said electrodes being electrically connected to said harness and the other of said electrodes being electrically connected to said second stiff lead-in wire; conductive means disposed upon each of said first and second stiff lead-in wires for preferentially forming an are when an arc cannot strike between said electrodes in said are tube.

3. In a high pressure electric discharge device comprising an outer bulbous envelope; a first and a second stiff lead-in wire disposed at the base of said envelope, each of said lead-in wires being adapted to conduct current from opposite sides of a power line; a metallic harness disposed within said envelope and supported upon said first stiff lead-in wire; an arc tube supported upon said metallic harness; electrodes disposed at either end of said arc tube, one of said electrodes being electrically connected to said harness and the other of said electrodes being electrically connected to said second stitf lead in wire; a pair of conductive annuli disposed within said envelope and upon each of the conductors from opposite sides of said power line for preferentially forming an arc therebetween when an arc cannot strike between said electrodes in said arc tube.

4. In a high-pressure electric discharge device comprising; an outer bulbous envelope, a first and a second stiif lead-in wire disposed at the base of said envelope, said lead-in wires being adapted to conduct current from opposite sides of a power line; a metallic harness disposed within said envelope and supported upon said first stiff lead-in wire; an arc tube supported upon said metallic harness; electrodes disposed at either end of said are tube, one of said electrodes being electrically connected to said harness and the other of said electrodes being electrically connected to said second stiff lead-in wire; a first conductive annulus disposed upon said first stiff leadin Wire and a second conductive annulus disposed upon said second stifr lead-in Wire, the conductive annuli being spaced from each other for preferentially forming an arc therebetween when an arc cannot strike between said electrodes in said arc tube.

5. The device according to claim 4 wherein the conductive annuli are formed of graphite.

References Cited by the Examiner UNITED STATES PATENTS 2,677,068 4/1954 Martt a- 313-25 DAVID J. GALVIN, Primary Examiner.

Claims (1)

1. A HIGH PRESSURE ELECTRIC DISCHARGE DEVICE COMPRISING: AN OUTER BULBOUS ENVELOPE; A FIRST AND A SECOND STIFF LEAD-IN WIRE DISPOSED AT THE BASE OF SAID ENVELOPE, EACH OF SAID LEAD-IN WIRES BEING ADAPTED TO CONDUCT CURRENT FROM OPPOSITE SIDES OF A POWER LINE; A METALLIC HARNESS DISPOSED IN SAID ENVELOPE AND SUPPORTED UPON SAID FIRST STIFF LEAD-IN WIRE; AN ARC TUBE SUPPORTED UPON SAID METALLIC HARNESS; ELECTRODES DISPOSED AT EITHER END OF SAID ARC TUBE, ONE OF SAID ELECTRODES BEING ELECTRICALLY CONNECXTED TO SAID HARNESS AND THE OTHER OF SAID ELECTRODES ELECTRICALLY CONNECTED TO SAID SECOND STIFF LEAD-IN WIRE; CONDUC-

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