US2985795A

US2985795A - Starting and operating circuit for high pressure arc lamps

Info

Publication number: US2985795A
Application number: US690305A
Authority: US
Inventors: Lester F Bird
Original assignee: Engelhard Hanovia Inc
Current assignee: Engelhard Hanovia Inc
Priority date: 1957-10-15
Filing date: 1957-10-15
Publication date: 1961-05-23
Anticipated expiration: 1978-05-23

Description

L. F. BIRD May 23, 1961 STARTING AND OPERATING CIRCUIT FOR HIGH PRESSURE ARC LAMPS Filed Oct. 15, 1957 INVENTOR. 55727? 45/517 ATTORNEYS United States Patent Ofilice 2,985,795 Patented May 23, 1961 STARTING AND OPERATING CIRCUIT FOR HIGH PRESSURE ARC LAMPS Lester F. Bird, Newark, N.J., assignor to Engelhard Hanovia, Inc., a corporation of New Jersey Filed Oct. 15, 1957, Ser. No. 690,305

2 Claims. (Cl. 315-174) The present invention deals with a starting and operating circuit for high pressure vapor arc lamps and more particularly with a starting and operating circuit for high pressure compact arc type lamps.

High pressure compact arc lamps comprise either a substantially spherical or elliptical envelope of light transmissive fused quartz or high temperature glass which contain an ionizable gas at pressures above atmospheric, when the lamp temperature is about 25 centigrade, and a pair of electrodes spaced apart about one centimeter and less.

In the ignition of such lamps, the time between the application of high starting voltages and the establishment of a stable arc should be kept at a minimum to preserve the life of the lamp and to retard deterioration of light output. Ordinarily, the lamps are provided with pulse starting voltages by means of radio frequency impulses impressed upon the lamp electrodes, in addition to the normal voltages of an operating source of voltage, and the pulse voltages continue to operate until an ionized path is established between the electrodes.

Continued operation of the pulse voltages produces a rapid deterioration of the light output because of the sputtering of the electrode metal. Usually, the pulse system. in order to ignite a cold lamp, operates from about five to ten seconds to ionize a path through the high pressure gas.

Since the final operating wattage of the lamp is fixed by its construction, it is necessary that the impedance of the lamp ballast be adjusted to a definite value in accordance with the operating wattage. Such an adjustment can be made by providing a low and high impedance ballast. whereby the lamp is started through the low impedance ballast and after ignition the high impedance is switched into the lamp circuit. Such ballast impedance adjustment is subject to substantial delay before optimum operating impedance in accordance with lamp operating wattage is provided.

In the absence of a switch means for adjusting the im pedance, the impedance, e.g. a resistance, is provided with a resistance value in accordance with the lamp operating wattage. With this type of ballast, the impedance is a function of the resistance metal, and since the prime consideration is the ballast impedance for operating the lamp after ignition the impedance must be sufficiently high to ballast the lamp. However, this presents the disadvantage that the resistance is too high to provide the optimum high starting currents for lamp ignition. For this reason. the adjustment of impedance has heretofore been provided by use of the switch means hereinabove mentioned.

It is an object of the present invention to provide an ignition and operating circuit including an automatically adjustable means for providing both low ignition impedance and higher operating impedance in accordance with the lamp wattage. It is another object of the present invention to provide an impedance means which is automatically adjustable for providing both starting and operating impedance for a high pressure compact are type lamp. Other objects and advantages will become apparent from the description hereinafter following and the drawings forming a part hereof, in which:

Figure 1 is a schematic view of a lamp operating cir cuit according to the invention,

Figure 2 is a perspective view of a modified component of the circuit of Figure 1,

Figure 3 illustrates a perspective view of another modified component of Figure 1,

Figure 4 is a longitudinal sectional view of an improved ballast structure according to this invention, and

Figure 5 is a cross-sectional view along lines 5-5 of Figure 4.

The present invention deals with an ignition and operating circuit, especially for high pressure compact arc type lamps, and includes a lamp ballast means which is automatically adjustable from optimum high current carrying capacity and low impedance to the higher impedance necessary to ballast the lamp during operation at high temperatures, and which ballast has a controlled impedance change.

Regarding Figure 1, the circuit comprises supply lines 1 and 2 leading from a source of alternating current voltage for operating the compact arc lamp 3. A resistance means or ballast 4 is connected in one of said supply lines in series with the lamp 3. A shunt capacitor 5 is shunted across the leads 1 and 2 between the resistance 4 and lamp 3. Since the normal operating voltages are insufficient to ignite the lamp 3, which contains an ionizable gas at a pressure above atmospheric pressure when the lamp is cold, e.g. at a temperature of about 25 centigrade, a pulse system is connected into the circuit to assist in igniting the lamp by establishing an ionized path in the gas between the electrodes. The pulse system comprises a secondary coil 6 of a radio frequency transformer connected in series with the lamp 3 between the lamp and the capacitor 5. A primary coil 7 of the radio frequency transformer is operatively associated with the secondary coil 6. A radio frequency capacitor 8 is connected in one of the leads 9 and 10 leading to the primary coil 7, and a spark gap 11 is connected across the leads 9 and 10 between the primary coil 7 and the secondary coil 12 of a high voltage transformer 13. The primary coil 14 of the high voltage transformer 13 is connected across the leads 1 and 2 between the resistance 4 and capacitor 5.

Having provided the circuit above described, the invention is particularly concerned with the ballast 4 in combination with the circuit.

The resistance or ballast 4 comprises a winding, coil, strip, or other equivalent structure composed of nickel or nickel compounds wherein nickel is the major component of the compound, e.g. nickel alloyed with a minor proportion of iron or cobalt.

According to the invention, it has been found that nickel wire, as a ballast resistance, provides automatically variable resistance with varying temperature, and in the circuit described above, it provides an automatically adjustable impedance for the high pressure lamp. Be-

tween the temperature range of from 20 centigrade to 400 centigradc the resistance of the nickel wire increases from about 7.8 to about 60.2 ohms/cm. which permits high currents of the order of 4050 amps. to pass through the resistance at the lower temperatures and, as.

rate of temperature rise and automatic increase from low to higher resistance values.

assures With a resistance composed of metal such as a nickelchromium alloy, the resistance does not change materially with increase in temperature, and as such, the ballast is substantially incapable of automatic ballast adjustment and in such cases switch means are resorted to for providing initial low ignition impedance and high ballast impedance for the lamp. With such systems, the lamp would require from about five to about ten seconds of ignition pulse, which is detrimental to the lamp electrodes.

With a nickel resistance and its attendant high current capacity when at the lower temperatures, such initial high currents assist the pulse system in the ignition of the lamp, whereby the joint function of the high currents and pulse voltage establish an ionized ignition path through the gas in from about one to about five seconds, thereby having less detrimental effect on the electrodes of the lamp.

In operation, when the leads 1 and 2 are connected to a source of current, the current flows simultaneously through the resistance 4 and the secondary coil 6 of the radio frequency transformer. Since the lamp is cold and filled with high pressure gas, its impedance is higher than that of the pulse system, which continues to send pulses through the capacitor and the lamp 3 until an arc is struck. As soon as the arc is struck, the lamp I impedance is lower than that of the pulse system which then ceases to function. During the functioning of the pulse system, the resistance 4 is rapidly heated and the resistance rapidly increases from about 7.8 ohms/cm. to higher resistance. The attendant current carrying capacity of the resistance 4 is rapidly decreased from a high value to approximately the optimum operating impedance in accordance with the lamp operating wattage. However, since the initial current through the resistance 4 is high, this high current assists the pulse system, whereby the time of ignition of the lamp is considerably shortened. The cooperation of the nickel resistance with the pulse system automatically provides low impedance to assist the pulse system and continues to operate the lamp under ballast impedance when the pulse system ceases to function.

While Figure 1 illustrates the resistance 4 schemati cally, the resistance is provided with a ceramic support 15 as shown by Figures 2 and 3, and the

nickel wires

16 and 17 are wound on the support 15 either as a helical coil or a coiled-coil as illustrated.

However, enclosed arc lamps, especially compact arc lamps, have a warming up time after they are lighted and before their light output is at the maximum value. It is desirable in many instances that this time be made as short as possible. The cause lies in the nature of the lamp because its voltage of operation is low at starting and increases as the warm-up time increases to a final value. During this time the input is usually low in wattage and the light below normal for the lamp.

Ballasts as shown by Figures 2 and 3, while satisfactory for ordinary high pressure lamp operation, do not assure maximum current to the lamp and sufiicient light intensity during the warm-up period because the nickel heats up at a rate faster than that of the lamp.

It is not possible to increase the starting currents instantaneously after lighting to compensate for the low voltage as this would impose undesirable strains upon the lamp structure. However, it is possible with a resistor type of ballast for the lamp to have the resistor automatically correct for some of the loss and so provide two desirable features. One feature being increased light during the warm-up period and the other a shortened warm-up time.

Both of these effects can be secured by having the nickel and the lamp warm-up at the same rate so that the wattage in the lamp during warm-up will at all times remain a maximum. This maximum is assumed to be about the normal wattage for the lamp when hot.

For a lamp which consumes 1000 watts when hot and at about 60 volts, the current when hot is about 17 amperes. Since these lamps are started at voltages of 25 or less, it would be necessary to have the lamp current increased almost by a factor of three, if the starting wattage were the same as the running one. The starting current would be in the order of 48 amperes.

When the lamp voltage had increased to 30 volts, the current would be about 33 amperes, and at 40 volts the lamp current would be 25 amperes, etc. With a simple structure for the resistance windings, as shown by Figures 2 and 3, the nickel warms up faster than the lamp and these currents in practice are all too low to provide the lamp with the optimum wattage during the warmup period.

The resistance wire can be slowed up in heating by placing it in the equivalent of an oven where it 'is warmed up by heat furnished from another source than itself.

The invention, therefore, is concerned with a lamp circuit, for example the circuit of Figure 1, including a ballast of the type illustrated by Figures 4 and 5, wherein a refractory support 18, e.g. a tubular ceramic support, has a ballast winding 19 of nickel, or a nickel-rich compound, on its outer surface. The winding 19 is preferably positioned in a helical groove 20 formed along the sup port 18. The nickel ballast winding is particularly associated with the rate of warm-up of the lamp, i.e. it is dimensioned so that it has substantial mass whereby it heats at a rate slower than that of the lamp. A plurality of windings in parallel connection and on independent supports may be employed to provide such mass. However, since the substantially massive winding 19 now heats up too slowly, it becomes necessary to provide an external source of heat therefor to increase the rate of impedance change to more nearly approach the rate of lamp warm-up. For this purpose, the support 18 and the winding 19 are positioned inside an outer coaxial tubular ceramic support 21 having a resistance winding 22, e.g. of nickel-chromium wire, positioned thereon, preferably in helical grooves 23 formed along the support 22. The winding 22 is proportioned to heat up rapidly with the application of current thereto, i.e. it heats up faster than the winding 19 and heats up the support 21 which, in turn heats up the winding 19 by either conduction or radiation depending on the spacing of the tubes 18 and 21. The rate of heat transferred to the winding 19 through the support 21 can be regulated by the thickness or mass of the support 21. Consequently, heat is transferred to the winding 19 by transmission through support 21 and the rate of heat transfer can be regulated to be as slow as desired to cause the change in resistance to occur at a rate which will properly adjust the lamp current during the warm-up period for increased light output during the warm-up period.

In application, the windings 119 and 22 are connected in parallel between the line voltage lead it and the lamp lead 24. However, the ballast of Figures 4 and 5 may be also employed in lamp circuits'which do not necessitate pulse type ignition.

While the foregoing description is directed to the invention as illustrated, the invention is intended to include various modifications within the scope of the appended claims.

What is claimed is:

l. A starting and operating circuit for high pressure are lamps comprising in combination an arc lamp, electrical leads connected to the lamp, a ballast in one of the leads in series with the lamp, the ballast comprising a parallel arrangement of first and second resistances, the first resistance being composed of a metal selected from the group consisting of nickel, nickel-rich nickel-cobalt alloys and nickel-rich nickel-iron alloys, the resistance of said group being capable of increasing resistance with increasing temperature, the second resistance being composed of metal which maintains a substantially constant the second resistance is composed of a nickel-chromium resistance with increasing temperatures, a capacitor connected across the leads between the ballast and the lamp, a radio frequency transformer having a secondary coil. References Cited m the file of this patent the secondary coil of the radio frequency transformer 5 UNITED STATES PATENTS connected in one of the leads between the lamp and ca- 2 043 023 westendorp u 2, 9 pacitor, whereby the ballast and coil are in electrical 2,160,323 Bl k June 6, 1939 series and initial low impedance of the ballast assists the 2,231,999 Gustin Feb. 18, 1941 coil in the ignition of the lamp. 10 2,291,926 Sperti Aug. 4, 1942 2. A starting and operating circuit according to claim 2,377,506 McWhirter June 5, 1945 1, wherein the first resistance is composed of nickel and 2,815,423 Polye Dec. 5, 1957