US3015058A

US3015058A - Starting and operating circuit for arc discharge device

Info

Publication number: US3015058A
Application number: US718799A
Authority: US
Inventors: Popa John
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1958-03-03
Filing date: 1958-03-03
Publication date: 1961-12-26
Anticipated expiration: 1978-12-26

Description

Dec. 26, 1961 J POPA 3,015,058 STARTING AND OPERATING CIRCUIT FOR ARC DISCHARGE DEVICE Filed March 3, 1958 l/MMP .7- [ZAHP V l I fin/e1? tor: JO/Zl? papa,

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United States Patent 3,015,058 STARTING AND OPERATING CIRCUIT FOR ARC DISCHARGE DEVICE John Popa, Fort Wayne, Ind., assignor to General Electric Company, a corporation of New York Filed Mar. 3, 1958, Ser. No. 718,799 7 Claims. (Cl. 323-60) This invention relates to circuits for starting and operating arc discharge devices, such as mercury vapor lamps, and more particularly to a starting and operating circuit for such devices with provision for selectively varying the wattage and in turn the light output of the device.

All are discharge devices, such as mercury vapor and fluorescent lamps, possess an inherent negative resistance characteristic, i.e., their resistance decreases as the current flow therethrough increases. It is thus necessary to provide a high initial or open circuit voltage in order to strike the arc, i.e., to start the device, however, if this open circuit voltage were thereafter maintained, the device would rapidly destroy itself by virtue of the increasing current flow due to its negative resistance characteristic. It is thus additionally necessary to provide means for limiting the current flow to the arc discharge device after the device has started, such current limitation conventionally being referred to as ball-asting. A loose coupled or high reactance transformer has been commonly employed for performing both starting and ballasting functions for are discharge devices operating on alternating current, such transformers being admirably suited for the purpose since they provide a high secondary open circuit voltage which immediately falls to a much lower level after the arc discharge device has started and load current begins to flow. Such circuits are commonly referred to as lagging current circuits since the system is highly inductive; these circuits have had the recognized disadvantage of providing low line power factor and also relatively poor regulation of lamp current, and thus in turn wattage and light, output responsive to line voltage variations.

The low line power factor and poor regulation characteristics of the high reactance lagging current ballast circuit have been overcome by the common use in recent years of the so-called high reactance-lead circuit in which a capacitor proportioned to draw leading current is serially connected between the secondary winding of the high reactance transformer and the arc discharge device. In such a circuit and with a transformer designed for normal flux densities, the leading current drawn by the capacitor causes an increase in the secondary voltage of the transformer thus in turn tending to cause saturation of the transformer core in the region of the secondary winding; operation of the secondary portion of the core about the knee of its saturation curve causes the transformer to function in the manner of a non-linear reactor thus providing greatly improved regulation of lamp current responsive to line voltage changes, such a circuit further providing much higher line power factor than is provided by conventional high reactance-lag circuits. In such high reactance-lead ballast circuits after the are discharge device has operated long enough to develop full voltage across itself, it can be safely assumed that the transformer secondary terminal voltage is the vector sum of the voltage across the device and the voltage across the capacitor. Since, by virtue of its negative resistance characteristic, the voltage across the device is essentially constant regardless of the current flow therethrough, and since the secondary terminal voltage under load is dependent upon the load current, it is seen that the only variable remaining is the capacitor voltage. Thus, in such circuits, ti is customary to adjust the arc discharge 3,015,058 Patented Dec. 26, 1961 device current to its desired or rated value by suitable selection of the value of the capacitor.

In the particular case of arc discharge lamps, such as mercury vapor lamps, while a fixed value of lamp current and thus lamp wattage and light output, is generally desired, there are instances in which it is desired to operate a given lamp at more than one level of light output or to provide selectively variable light output, i.e., generally referred to as dimming action. While operation of the lamp at two different light output levels may be secured by the provision of two capacitors having respectively different values of capacitance with a selector switch for selecting one or the other capacitor, the capacitors employed in such circuits are expensive and further, such an arrangement provides only two light output levels; provision of a plurality of capacitors to provide corresponding plurality of light output levels is prohibitively expensive and still does not provide continuously variable dirnming action. Energization of the primary winding of the high reactance lagging current transformer through a variable voltage autotransformer has also been proposed, however, such an arrangement has a deleterious effect on the line power factor and further, the adjustment of the autotransformer to provide a low primary voltage may in turn reduce the secondary open circuit voltage to a point where the lamp will not fire. It is therefore desirable to provide a high reactance lead ballast circuit with means for varying the current of the arc discharge device operated thereby which does not require the use of more than one capacitor nor have the disadvantages of a variable voltage autotransformer connected between the source of alternating current and the primary winding.

It is therefore an object of my invention to provide an improved circuit for starting and operating arc discharge devices having provision for varyng the current of the device after it has started.

Another object of my invention is to provide a ballast circuit of the high reactance-lead type for are discharge devices with improved means for varying the current of the device after it has started.

A further object of my invention is to provide a ballast circuit of the high reactance-lead type for are discharge devices with means for selectively varying the current of the device after it has started and which does not possess the disadvantages of the applicant.

My invention in its broader aspects provides a high reactance transformer having its primary winding adapted to be connected to a source of alternatng current and having a capacitor and a source of selectively variable voltage serially connecting the secondary winding of the transformer across the arc discharge device. In the preferred embodiment of my invention, I provide an additional low reactance transformer having its secondary winding connected in series with the capacitor and having its primary winding energized from a variable voltage autotransformer. In this manner, a voltage which may be either bucking or boosting with respect to the capacitor voltage is provided thereby effectively to vary the capacitor voltage and thus in turn the current of the arc discharge device.

Further objects and advantages of my' invention will become apparent by reference to the following description and the accompanying drawing, and the features of novelty which characterize this invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

In the drawing,

FIG. 1 is a schematic diagram showing a starting and operating circuit incorporating my invention for an arc discharge lamp, and

prior circuits known to acispss FIG. 2 is a vector diagram useful in explaining the mode of operation of the circuit of FIG. 1.

Referring now to FIG. 1, my improved circuit, generally identified as 1, is shown here connected for starting and operation of an arc discharge lamp 2, as for example a 400 watt mercury vapor lamp. A conventional high reactance transformer T is provided having a core, schematically shown at 3, with a primary winding 4 connected across line terminals 5, which in turn are adapted to be connected to a suitable source of alternating current (not shown), such as 115 volts, 60 cycles. A secondary winding 6 is provided on the core 3 loosely coupled to the primary winding 4, for example by being spaced from the primary winding by means of magnetic shunts, shown schematically at 7, as is well known in the art; it will be understood that the specific high reactance transformer T does not form a part of my invention and that any conventional high reactance transformer construction may be utilized in my improved circuit.

A pair of output terminals 8 and 9 are provided adapted to have the arc discharge lamp 2 connected thereacross. One end 10 of the secondary winding 6 of high reactance transformer T is directly connected to output terminal 9 while the other end 11 is serially connected to the other output terminal 8 by a suitable capacitor 12 and secondary winding 13 of low reactance transformer T The primary winding 14 of transformer T has one side 15 connected to one side 16 of Winding 17 of a suitable variable autotransformer 18, the other side 19 of primary winding 14 of low reactance transformer T being connected to the selectively adjustable tap 20 of the variable voltage autotransformer 18. The

input terminals

16 and 21 of variable voltage autotransformer 18 are shown here as being connected across input terminals 5, however, it will be readily understood that they may be separately connected for energization from another suitable source of alternating current.

It will now be seen that by means of the variable voltage autotransformer 18 and the low reactance transformer T having its secondary winding 13 connected in series with capacitor 12, an inductive element has been added in series with the capacitor 12 in such a manner that the inductive element provides a continuously variable voltage which may be made either to buck or boost the capacitor voltage. Referring now to FIG. 2, there is shown a vector diagram which closely approximates the conditions in the circuit of FIG. 1 after lamp 2 has fired and come up to voltage, and with the voltage induced in secondary winding 13 of low reactance transformer T bucking the capacitor voltage. Since the arc discharge lamp 2 is essentially a resistive device, its current flow after starting, identified as L is in phase with the voltage developed thereacross, i.e., across output terminals 8 and 9, identified as V The capacitor voltage, identified as V naturally lags the lamp voltage and current by 90", as shown, with the voltage induced in the secondary winding 13 of low reactance transformer T identified as V leading the lamp voltage and current by 90, as shown. It will now be seen that since the voltage VTzsw opposed or bucks the capacitor voltage V the resulting voltage between end 11 of the secondary winding 6 of high reactance transformer T and output terminal 8 is the numerical difference of the two, i.e., V -V this voltage being vectorially resolved with the lamp voltage V to provide the secondary winding terminal voltage under load, identified as V which in turn vectorially equals V -j(V -t-V j. It will now be readily seen that adjustment of the adjustable tap 20 on the variable voltage autotransformer 18 will in turn vary the voltage V and thus in turn vary the terminal voltage of secondary winding 6 of transformer T and thus the lamp current. It will also be readily understood, however, that the connections of the low reactance transformer T may be reversed so that the voltage induced in the secondary winding 13 boosts rather than bucks the voltage across capacitor 12.

A circuit has been constructed in accordance with FIG. 1 for operation of a 400 watt mercury vapor lamp. In this system, primary winding 4 of transformer T had 196 turns of .07 63 inch diameter wire, secondary winding 6 had 4 62 turns of .0605 inch diameter wire, and thus provided an open circuit voltage of 253 volts with primary winding 4 connected to a source of volts, 60 cycles. Capacitor 12 had a capacitance of 20.9 rnicrofarads, transformer T had its primary winding 14 having 4-40 turns of .0302 inch diameter wire and secondary winding 13 having 227 turns of .0453 inch diameter wire. Variable voltage autotransformer with its

input terminals

16 and 21 connected across the input terminals 5 provided a selectively variable voltagebetween 0 and 214- volts. With this arrangement and the variable voltage autotransformer 18 adjusted to provide full wattage operation of lamp 2, i.e., 400 watts, the measured voltage appearing across the secondary winding 6 of transformer T was 420 volts and the voltage appearing across capacitor 12 was 400 volts, the voltage appearing across secondary winding 13 of transformer T was zero, the lamp voltage was 134 volts, and the lamp current 3.24 amps, When the lamp wattage of the circuit was reduced 50% in a continuously variable fashion to 200 watts, it was found that the measured secondary voltage of transformer T was 320 volts, the capacitor voltage was 213 volts, the voltage appearing across the secondary winding 13 of transformer T was 115 volts, the lamp voltage was 112.5 volts, the lamp current was 1.97 amps.

It will now be seen that I have provided an improved starting and operating circuit for arc discharge devices,- particularly arc discharge lamps, in which the lamp current and thus in turn lamp wattage and light output may be continuously varied, either upwards or downwards from a reference level, without requiring the use of capacitor banks, or the disadvantages of the energization of the primary winding of the high reactancc transformer through a variable voltage autotransformer.

While I have illustrated and described a specific em bodiment of this invention, further modifications and im provements will occur to those skilled in the art and I desire that it be understood therefore that this invention is not limited to the specific form shown and I intend in the appended claims to cover all modifications which do not depart from the spirit and scope of this invention.

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

1. A starting and operating circuit for an arc discharge device comprising: a high reactance transformer having a primary windin adapted to be connected to a source of alternating current and having a secondary winding; a pair of output terminals adapted to be connected to said arc discharge device; and a capacitor and a source of selectively variable voltage serially connected with said secondary winding across sadi output terminals, said voltage of said selectively variable source being in bucking relationship with the voltage of said capacitor.

2. A starting and operating circuit for an arc discharge device comprising: a high reactance transformer having a primary winding adapted to be connected to a source of alternating current and having a secondary winding; a pair of output terminals adapted to be connected to said are discharge device; a capacitor; and inductive means providing a selectively variable voltage serially connected with said capacitor and said secondary winding across said output terminals, said selectively variable voltage being in opposing relationship with the voltage of said capacitor.

3. A starting and operating circuit for an arc discharge device comprising: a high reactance transformer having a primary winding adapted to be connected to a source of alternating current and having a secondary winding; a pair of output terminals adapted to be connected to said arc discharge device; a capacitor; and a second transformer having its secondary winding serially connected with said capacitor and said high reactance transformer secondary winding across said output terminals and having .its primary winding adapted to be connected to a selectively variable source of alternating current voltage for varying the secondary voltage thereof thereby to vary the voltage of said are discharge device, said secondary voltage of said second transformer being in bucking relationship with the voltage of said capacitor.

4. A starting and operating circuit for an arc discharge device comprising: a high reactance transformer having a primary winding adapted to be connected to a source of alternating current and having a secondary winding; a pair of output terminals adapted to be connected to said are discharge device; a capacitor; 'a second transformer having a primary winding and a secondary Winding serially connected with said capacitor and said high reactance transformer secondary winding across said output terminals, said capacitor being proportioned to draw leading current through said high reactance transformer secondary Winding; and means connected to said other transformer primary winding for selectively varying the secondary voltage thereof thereby to vary the voltage of said arc discharge device.

5. A starting and operating circuit for an arc discharge device comprising: a high reactance transformer having a primary winding adapted to be connected to a source of alternating current and having a secondary winding; a pair of output terminals adapted to be connected to said are discharge device; a capacitor; a low reactance transformer having a primary winding and a secondary winding serially connected with said capacitor and said high reactance transformer secondary winding across said output terminals, said capacitor being proportioned to draw leading current through said high reactance transformer secondary winding; and means connected to said low reactance transformer primary winding for selectively varying the secondary voltage thereof thereby to vary the voltage of said are discharge device, said secondary voltage of said low reactance transformer being in bucking relationship with the voltage of said capacitor.

6. A starting and operating circuit for an are discharge device comprising: a high reactance transformer having a primary winding adapted to be connected to a source of alternating current and having a secondary winding; a pair of output terminals adapted to be connected to said are discharge device; a capacitor; a low reactance transformer having a primary winding and a secondary winding serially connected with said capacitor and said high reactance transformer secondary winding across said output terminals, said capacitor being proportioned to draw leading current through said high reactance transformer secondary winding; and a variable voltage 'autotransformer connected to said low reactance transformer primary winding and adapted to be connected to a source of alternating current for selectively varying the secondary voltage of said low reactance transformer thereby to vary the voltage of said are discharge device.

7. A starting and operating circuit for an arc discharge device comprising: a high reactance transformer having a primary winding adapted to be connected to a source of alternating current and having a secondary Winding; a pair of output terminals adapted to be connected to said arc discharge device; a capacitor; a low reactance transformer having a primary winding and a secondary winding serially connected with said capacitor and said high reactance transformer secondary winding across said output terminals, said capacitor being proportioned to draw leading current through said high reactance transformer secondary Winding; and a variable voltage autotransformer connected between said low reactance transformer primary winding and said high reactance transformer primary winding for selectively varying the secondary voltage of said low reactance transformer thereby to vary the voltage of said arc discharge device.

References Cited in the file of this patent UNITED STATES PATENTS 687,147 Fleming Nov. 19, 1901 2,683,240 Strange July 6, 1954 2,774,917 Passrnore Dec. 18, 1956 2,849,656 Karash Aug. 26, 1958 2,870,398 Sola Jan. 20, 1959