US2723366A

US2723366A - Starting and operating circuit for high pressure gaseous discharge device

Info

Publication number: US2723366A
Application number: US195172A
Authority: US
Inventors: Harold A Breeding
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1950-11-13
Filing date: 1950-11-13
Publication date: 1955-11-08
Anticipated expiration: 1972-11-08

Description

Nov. 8. 1955 H. A. BREEDING 2,723,366

STARTING AND OPERATING CIRCUIT FOR HIGH PRESSURE GASEOUS DISCHARGE DEVICE Filed NOV. 13, 1950 2 Sheets-Sheet l i Fi .l. x 2

i /3 g5 i 20 /5' i a a 1 22 I I 1 L Inventor: Harold ABreedi Hg. 9

yw y His Attorney.

Nov. 8, 1955 H. A. BREEDING 2,723,366

STARTING AND OPERATING CIRCUIT FOR HIGH PRESSURE GASEOUS DISCHARGE DEVICE Filed Nov. 15. 1950 2 Sheets-Sheet 2 Fig.2.

0 200 400 600 800 I000 I200 I400 I600 I800 2000 2200 2400 2600 2800 SURFACE TEMPERATURE-DEGREE5.F.

VOLTS AMPERES O I 2 3 4 S 8 7 8 TIME MINUTES.

Inventor": Harold ABreedi n52,

WWW/W His Attorn ey.

STARTING AND OPERATING CIRCUIT FOR HIGH PRESURE GASEOUS DISCHARGE DEVICE Harold A. Breeding, Marblehead, Mass., assignor to General Electric Company, a corporation of New York Application November 13, 1950, Serial No. 195,172 4 Claims. (Cl; 315309) My invention relates to starting and operating apparatus for high pressure gaseous electric discharge devices, and more particularly to starting and operating apparatus and circuits adapted for use in conjunction with high intensity, high pressure mercury vapor discharge lamps and the like. I

The high pressure, high intensity mercury vapor discharge lamps which have lately come into general use have the characteristic that, when an arc is first struck the arc voltage drop and lamp resistance are both quite low. After the lamp has been in operation for three to five minutes its temperature has risen to a point where the gaseous pressure therein is in the neighborhood of twenty atmospheres, and the arc voltage drop rises to a steady state value of several times the arc voltage at starting and remains at this value substantially independently of the magnitude of current flowing. The lamp resistance under operating conditions is also considerably higher than that at starting and demonstrates a negative resistance-current characteristic.

With such a lamp the usual ballasting resistor having a positive temperature coefiicient of resistance is operable to regulate the lamp current under operating conditions, but does not sufficiently limit the starting current. The usual positive temperature coeflicient ballasting resistor has a low starting resistance. When such a resistor is connected in series circuit relation with a direct current lamp of the foregoing type, the starting resistance of which is also low, the resultant excessive starting current produces plate sputtering and lamp blackening. This effect is aggravated when a high frequency, high voltage oscillatory potential is superposed upon the unidirectional opcrating potential to start the lamp discharge. It is therefore desirable to provide means for limiting lamp starting current, as well as means for regulating lamp operating current.

Accordingly, therefore, it is a principal object of my invention to provide new and improved starting and operating apparatus for high pressure vapor discharge lamps and the like, and particularly direct current discharge lamps.

It is still another object of my invention to provide new and improved ballasting means for high pressure gaseous electric discharge devices.

it is a still further object of myinvention to provide new and improved means for limiting the starting current and regulating the operating current in a high pressure mercury vapor electric discharge lamp or the like.

It is a specific object of my invention to provide a new and improved discharge lamp ballast resistor which serves both to limit starting current and regulate operating current.

In carrying out my invention in one form I connect in series circuit relation with the vapor discharge device a ballasting resistor formed of a material which possesses a negative temperature coefficient of resistance below a predetermined temperature and a positive temperature coefiicient of resistance above said temperature. Such a ited Sttes Patent of an oscillatory nature.

Patented Nov. 8, 1955 series resistor thus demonstrates a minimum resistance value at the predetermined, or critical, temperature and a high starting resistance. When the critical resistor temperature is selected to be less than its steady state temperature under normal conditions of operating current how, the resistor also serves as a ballasting resistor having a positive temperature coeflicicnt of resistance.

My invention will be better understood and its various objects and advantages further appreciated by referring now to the following detailed specification taken in conjunction with the accompanying drawing, in which Fig. l is a schematic circuit diagram of a lamp starting and operating apparatus embodying my invention; Fig. 2 is a graphical representation of a typical resistance-temperature characteristic for a lamp ballasting resistor utilized in conjunction with my invention; and Pig. 3 is a graphical representation of various electrical characteristics illustrating the time-load characteristic of an electric discharge lamp operated in accordance with my invention.

Referring now to the drawing, 1 have shown a high intensity mercury vapor discharge lamp 1 provided with a pair of

electrodes

2 and 3 and terminals therefor mounted 'for operation between a pair of

terminal conductors

4 and 5. For use on direct current the anode 2 has a relatively much larger mass than the cathode 3, thereby to enable it to dissipate the heat resulting from electron bombardment during operation. As a typical example of a lamp having the electrical characteristics heretofore described, the lamp 1 may be a 5 kilowatt lamp which, under normal operating conditions draws approximately 7 3 amperes and has a potential drop across its arc of approximately volts. When an arc is first struck in such a lamp, the arc voltage drop is quite low, for example, approximately 15 volts. After the lamp has been in operation for three to five minutes its temperature has risen to such a point that the gaseous pressure therein is in the neighborhood of 20 atmospheres, and the arc voltage drop rises to its steady state value of approximately 70 volts.

The lamp 1 is connected for operation to a suitable source of direct current supply through a control switch 6, and the lamp operating circuit includes in series circuit relation with the lamp a ballast resistor 7 and an inductor 8. it will be understood by those skilled in the art that, if desired, the electric current supply source may be an alternating current source, but for purposes of illustration only I have shown a" direct current source.

The inductor 8 is provided for starting purposes only, and is arranged, in conjunction with a starting circuit 9, to impress directly across the lamp terminals a high frequency, high intensity alternating current voltage during the starting interval. The starting circuit 9 is more fully described and claimed in a copending application Serial No. 151,616 filed by Howard 1. Becker on March 24, 1950, and assigned to the same assignee as the instant application. 7

Briefly the starting circuit 9 comprises a capacitor 10 connected in series circuit relation with a spark gap 11 across a portion 8a of the inductor 8. The inductor portion 8a and the spark gap 11 constitute a discharge circuit for the capacitor 10, and the electrical constants of this circuit are so chosen that the capacitor discharge is This oscillatory discharge sets up a high frequency voltage across the inductor portion 8a, and this high frequency voltage is amplified by autotransformer action in the inductor 8 and applied to the lamp terminals through a bypass capacitor 12. In order recurrently to charge the capacitor 16, a suitable source of alternating current control voltage is supplied across the capacitor from a secondary winding 13 of a control transformer 14. The transformer 14 is provided with a primary Winding 15 which may be connected to any suitable source of alternating current supply.

For purposes of illustration the control transformer primary winding is shown as energized through a vibrator 17, which is connected to the direct current supply source through the normally closed contacts 16:: and 16b of a control contactor 16. Specifically, one. side of the control transformer primary winding 15. is. connected. to an intermediate voltage point through a capacitive. volt.- age divider comprising a. pair of capacitors. 18 and 19 connected in series circuit relation across the direct current supply source. The other side of the control transformer primary winding 15 is connected to a transfer contact 20,. which is. a part of the vibrator 17 and is arranged alternately to be. connected first to one and then to the other side of the direct current supply line. The transfer contact 2! of the vibrator 17 is a contact of an electromagnetic relay 21 having an actuating winding 22. The relay actuating; winding 22 is connected across the direct current supply source through a normally closed interlock contact 23 on the relay 21 itself, and the normally closed contacts 16a and 16bv of the control contactor 16. It will be' understood that, in operation, the vibrator relay 21 alternately picks up and drops out due to: the action of its normally closed interlock contact 23, the relay contact thus applying an alternating potential to the control transformer primary winding 15.

To complete the starting circuit the control contactor 16 is provided with an actuating winding 24 connected in shunt circuit relation across the ballast resistor 7. The actuating winding 24 is arranged to pick up the contactor 16 when a predetermined voltage drop is attained across the ballast resistor 7. As will be more fully explained hereinafter, such pickup voltage drop across the ballast resistor is not attained until after the starting interval. When the contactor 16 picks up and opens its contacts 16a and- 16bthe lamp starting circuit 9 is deenergized, and current is supplied to the lamp 1 only from. the direct current source through the inductor 8 and the ballast resistor 7.. The inductor 8 has a very low resistance, so that under direct current operating conditions. its impedance is negligible.

As previously pointed out, the ballast resistor 7 is formed of a material demonstrating a negative temperature coefficient of resistance below a predetermined critical temperature and a positive temperature coefficient of resistance above such temperature. One. such material which I have found suitable issilicon carbide, a crystalline compound of silicon and carbon. Resistor units made of silicon carbide are available commercially under the name Globar. A typical resistance temperature characteristic of such a silicon carbide. resistor unit. is shown at Fig. 2.. It will be observed from this figure that the resistance: of the resistor reaches a minimum value at a surface temperature of about 750 F. Below this surface temperature the temperature coefficient of resistance is negative and above this surface temperature the temperature coefiicient of resistance is positive; The temperature 750 F. is less than the steady state temperature of the resistor 7 under lamp operating conditions.

The mode of operation of the starting circuit 9 in temporarily applying across the. lamp 1 a high intensity, high frequency alternating current starting voltage has already been described. This high frequency starting voltage establishes an are between the

electrodes

2 and 3, but the alternating current flow is small due to the high inductance of the inductor 8 at high frequency. This small high frequency current is by-passed through capacitor 12 and consequently will not establish across the ballast resistor 7 a voltage drop to actuate the contactor 16. It is however sutficient to ionize the gap between the lamp electrod'es. When this gap has become sufficiently ionized, the operating source of direct current supply takes over and supplies the much larger operating current through the ballast resistor 7. It is the initial value of this direct current which is high because of the low cold resistance of the lamp and the low direct current impedance of the inductor 8. The resistor '7, having an initially high resistance, aids in limiting the initial direct current, and then later, due to its positive resistance-temperature characteristic at operating temperature, serves to regulate, or ballast, the lamp operating current. As soon as: the direct current flows through the. resistor 7,, the contact-or 16. is picked up and opens its contacts 16::- and 16b to 'd'eenergize the starting circuit 9.

Thus the ballast resistor, having a resistance which initially decreases and then rises to a final operating value in a region of positiyetemperature coeflicient of resistance, is connected in series circuit relation with the lamp 1 which possesses aninitially low resistance and an appreciably higher operating resistance demonstrating a negative current coefficient of resistance. In general, then, the ballast resistor 7, due to its initially negative temperature coefficient of resistance and consequent decrease in resistance when first heated, demonstrates a higher initial resistance for any predetermined operating resistance value than would a ballast resistor having a continuous positive temperature coefiicient of resistance. Since the ballast resistor must be chosen primarily for its operating resistance value, the higher initial resistance characteristic of the resistor 7 heretofore described provides a more effective limitation of starting current. This is, especially valuable in a high pressure gaseous discharge lampof the type. described wherein the arc voltage is initially very low and rises to an appreciably higher value after gaseouspressure has builtv up in the lamp.

The foregoing operation will be clarified by referring now to Fig. 3. At Fig, 3 I have shown a curve A representing the direct current passing in series through the resistor 7 and the above referred to 5' kilowatt lamp 1, plotted against time. It will be observed that the direct current reaches a maximum value of about 185 amperes in approximately of a minute as resistor 7' heats to the minimum resistance point at 750 F. As resistor 7 continues to heat, its resistance increases rapidly and the current drops sharply to about amperes in approximately of. a minute. after starting. It remains relatively constant at about 130 amperes as the electrodes and lamp bulb warm up. After about 1% minutes the temperature of the lamps is such that the mercury begins to vaporize rapidly increasing the lamp resistance and reducing the current. After about 5' minutes complete vaporization in the lamp produces maximum resistance and. the current drops to about 73 amperes. Curve B at Fig. 3 shows the voltage drop across the resistor 7 over the same operating interval, and curve C represents power dissipated in the resistor. Finally, the curve D represents power dissipated in the lamp. It will be observed that the power curves C and D for the resistor and lamp, respectively, are aPPIoXimately complementary, the resistor power decreasing. sharply and the lamp power increasing sharply as the gaseous pressure in the lamp builds up. Thus the total power consumed in the circuit remains. substantially constant during the starting interval as well as in steady state operation.

While I have described only a preferred embodiment of my invention by way of illustration, many modifications will occur to those skilled in the art, and I, therefore, Wish to-have it understood that I intend in the appended claims to; cover all such modifications. as. fall within the true spirit and scope ofmy invention.

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

1. In an apparatus for starting and operating a high pressure mercury vapor discharge lamp including a pair of electrodes and terminals therefor, said lamp having at its operating temperature and pressure a negative resistance-current characteristic and an arc voltage drop and resistance which is several times its starting arc voltage drop and resistance, a pair of electric current supply conductors adapted to receive said electrode terminals therebetween, and means for connecting in series circuit relation with said supply conductors a ballast resistor which, in response to lamp current flow therethrough, is heated to a critical temperature subsequent to the initiation of current flow through said lamp and before its pressure attains its said operating value, said resistor having a negative temperature coefiicient of resistance below said critical temperature and a positive temperature coeflicient of resistance above said critical temperature whereby the starting current of said lamp is limited by the high initial resistance of said resistor and the operating current of said lamp is regulated by resistance values of said resistor which are within its positive temperature coefficent of resistance range.

2. In an apparatus for starting and operating a high pressure mercury vapor discharge lamp including a pair of electrodes and terminals therefor, said lamp having a starting resistance appreciably lower than its operating resistance and a negative resistance-current characteristic at its higher operating resistance, a pair of conductors adapted to receive said electrode terminals therebetween, and means for connecting in series circuit relation with said conductors a resistor having, in response to the flow of lamp current therethrough, a steady state operating temperature greater than a predetermined temperature which is attained upon the flow of lamp starting current and before said lamp current assumes its operating value, said resistor having a negative temperature coefficient of resistance below said predetermined temperature and a positive temperature coeflicierit of resistance above said predetermined temperature.

3. In an apparatus for starting and operating a high pressure mercury vapor discharge lamp including a pair of electrodes and terminals therefor, said lamp having at operating temperature and pressure a negative resistance-current characteristic and a resistance and voltage drop appreciably greater than its low pressure starting resistance and voltage drop, a pair of conductors adapted to receive therebetween said electrode terminals of said discharge lamp, and means for connecting said conductors to a source of electric current supply, said means including a ballast resistor of crystalline silicon carbide connected in series circuit relation with said conductors and having a surface operating temperature greater than about 750 F. when heated by lamp current flow therethrough when said lamp is at its said operating pressure and temperature.

4. In an apparatus for starting and operating a high pressure mercury vapor discharge lamp including a pair of electrodes and terminals therefor, said lamp being of the type having under operating pressure a resistance which is appreciably higher than its low pressure starting resistance and having a negative resistance-current characteristic at its said operating pressure, a pair of conductors adapted to receive therebetween said electrode terminals of said lamp, and a silicon carbide ballast resistor connected in series circuit relation with said conductors and having a negative temperature coeflicient of resistance below a predetermined critical surface temperature in the range of 750 F. and a positive temperature coefficient of resistance above said critical surface temperature, the steady state operating temperature of said resistor being appreciably greater than said critical temperature which is attained upon the flow of lamp starting current and before said lamp current assumes its operating value.

References Cited in the file of this patent UNITED STATES PATENTS 2,177,695 Elenbaas Oct. 31, 1939 2,200,951 Elenbaas May 14, 1940 2,247,198 Kretft June 24, 1941 2,278,079 Knouse Mar. 31, 1942