US3151276A

US3151276A - Plural lamp ballast

Info

Publication number: US3151276A
Application number: US42285A
Authority: US
Inventors: Victor W Olson
Original assignee: Jefferson Electric Co
Current assignee: Jefferson Electric Co
Priority date: 1960-07-12
Filing date: 1960-07-12
Publication date: 1964-09-29
Anticipated expiration: 1981-09-29

Description

Sept. 29, 1964 v. w. oLsoN PLURAL LAMP BALLAST Filed July 12. 1960 FII-5.5

NKJUX Jang United States Patent() 3,151,276 PLURAL LAMP BALLAST Victor W. lson, Chicago, lll., assigorto Jefferson Electric Company, Bellwood, lili., a corporation of Delaware Filed .luly 12, 1960, Ser. No. 42,285 7 Claims. (Cl. 315-231) This invention relates to a plural lamp ballast for are discharge devices.

The plural lamp ballasts heretofore used have been either a series type or a lead-lag type. In the series type, if one lamp is extinguished, the other lamp is necessarily extinguished. In the lead-lag type if one lamp is extinguished, the other will remain in operation, but the power factor of the ballast is very poor.

It is an object of the present invention to provide a plural lamp ballast in which the various lamps are connected in parallel across the ballast, and in which the arrangement is such that one or more of the lamps will operate satisfactorily even after one or more of the other lamps have been extinguished or removed.

Due to the unstable characteristics of gaseous discharge devices it has heretofore been though necessary to provide a separate inductance in each branch of a parallel lamp circuit, in order to provide for independent lamp operation.

According to the present invention, I have found that a common inductance can be provided for all branches, and still obtain independent lamp operation.

In general, if a separate capacitance is provided for each branch circuit, and if the common inductance is nonlinear, I have found that when one or more lamps are removed, the ballast will stabilize itself at a somewhat lesser secondary voltage, and provide regulated operation thereafter for the remaining lamps.

Thus it is possible to obtain considerable savings in the manufacture and installation of plural lamp lixtures because only on transformer is required for each group of two, three or four or more lamps.

Another object is to provide in a plural lamp ballast of the character described, an arrangement which deliverssubstantially constant wattage to each of the lamps irrespective of quite substantial variations in line voltage, andirrespective of variations in the voltage delivered to each branch circuit.

For instance when several ballasts are connected in parallel across a line, it frequently happens that the line yvoltage for the end ballast is considerably less than the line voltage for the iirst ballast, due to line loss. According to my invention this does not affect the wattage or light output of the lamps energized from the last ballast. Similarly, in instances where several lamps are energized from a common ballast and are located at varying distances therefrom, the voltage available for the last lamp may be somewhat less than that available for the others, but according to the present invention, the wattage of all lamps will be approximately the same.

The invention is described herein as applied to mercury vapor lamps such as those used for street lights, however, it will be understood that the invention is applicable to ballast for other types of gaseous discharge devices such as the ordinary lluorescent lamp.

Other objects, features and advantages will become apparent as the description proceeds.

With reference now to the drawings in which like reference numerals designate like parts:

FIG. l is an elevation of the core structure of a preferred embodiment of my invention, the windings being shown in dotted lines;

FIG. 2 is an electrical diagram of the ballast;

3,151, PatentedV Sept. 29, 1964 ICC FIG. 3 is a graph illustrating the operating range of my invention; and

FIG. 4 is a graph illustrating the constant wattage char acteristic of my improved ballast.

With reference now to FIG. 1, the ballast includes a high reactance transformer 10 having a primary winding 11 and a secondary winding 12. The

windings

11 and 12 are mounted in end to end relationship on a winding leg 13 so as to provide a linx leakage path therebetween.

In the embodiment shown, the leakage path is of comparatively low reluctance due to the provision of magnetic shunt portions 14 on the winding leg.

The core structure may be of any desired construction; as shown in FIG. l it is a shell type pressed lit core which includes the winding leg 13 and a yoke 15. The yoke is also provided with shunt portions 16 which are separated from the shunt portions 14 by an air gap 17.

The core structure is designed to operate at saturation which fact is indicated diagrammatically in FIG. 1 by showing the width of the winding leg as being somewhat less than the sum of the widths of the yoke portions. However, it will be understood that saturation is a function of core cross section with respect to ampere turns and that the core parts, if desired, may be of the customary proportions in which the width of each yoke leg is oneehalf the width of the winding leg.

As shown in FIG. 2, the primary winding 11 is connected to a line 20. Leads 21 and 22 extend from the secondary winding 12. The secondary circuit includes two or more branches. The first branch circuit comprises a condenser 23 and a lamp 24, such as a 400 watt mercury vapor lamp type H-l or H-33. The second branch circuit comprises a condenser 25 and a lamp 2.6. Cther branch circuits may be provided as indicated by the

condensers

27, 29 and lamps 28, 3l) shown in dotted lines, although the specific example described below applies only to the parts shown in solid lines.

The characteristic of my invention is that when the ballast is designed for two lamp operation, as indicated by the solid line circuit of FIG. 2, if one of the

lamps

24 or 26 is removed, the remaining lamp will continue in operation, at a somewhat reduced wattage. The same applies if one of the lamps is broken or becomes inopera- -tive for any reason.

When the ballast is designed to operate three lamps, if one lamp is removed the other two remain in operation. Similarly the circuit may be designed -to operate four or six or an` even greater number of lamps, and in general up to half of the lamps may be removed, and the remaining lamps will continue in stable operation.

In general, this result is obtained by designing the transformer 10 with a relatively small number of turns so that the secondary winding 12 will draw a magnetizing current which is high with respect to the load current. The cross section of the core structure, or at least of the winding leg 13, is relatively low with respect to the magnetizing current so that the transformer operates at saturation.

As a rough design parameter, the magnetizing current of the secondary winding at operating voltage should be substantially 50% to 75% of the full load current. This is determined by a primary open circuit test in which the voltage applied to the secondary is the same as the secondary voltage when operating under full load.

The curve of 31 of FIG. 3 represents the violtage-eurrent characteristic of the secondary winding as the line voltage is increased from zero up to and through the normal operating range. The flattened portion 31a of the curve which extends from I1 to I2 represents the desired range of operation. For instance, in the design of a four lamp ballast, the transformer would be wound so that the full load current would occur at about the point where the 33 curve 31 intersects the abscissa I2, and so that the current drawn by only two lamps would be that which would occur where the curve 31 intersects the abscissa I1. Thus it will be seen that even though the current is reduced by 50%, the voltage across the secondary leads 21 and 22 is maintained within the operating range of the lamps.

As a specific example, a transformer was constructed having a core as shown in FIG. 1. The winding leg 13 was 1.25 inches in width, and each of the yoke legs was .S75 inch in width. The overall dimensions of the yoke 15 were 5.75 inches square, and the other parts were dimensioned in the proportions shown in FIG. l. The

magnetic shunts

14 and 16 were .625 inch wide, and the gap 17 was .050 inch long.

The laminations were stamped from M19 grade (A.I.S.I. type) 26 gauge steel. The lamination stack was 3.75 inches high.

The primary winding 11 contained 98 turns of number 11 wire (A.W.G.) and the secondary winding 12 contained 200 turns of number ll wire. This turn ratio provided suiiicient o-pen circuit voltage to strike the lamps.

The condensersr23 and 25 were 31.0 mfd. each, or in the alternative, two 15.7 mfd. condensers were used in parallel. The lamps were 400 watt I-I-l mercury Vapor lamps.

When the two lamp system was energized by connecting the primary 11 to a 115 volt line; the primary ilux density was substantially 110,000 lines per square inch and the secondary Eux density was substantially 130,000 lines per square inch.

During operation, the crest factor of the lamp current was less than 1.7, and regulation was better than 1%, meaning that a plus or minus 13 change in line voltage resulted in a change of less than plus or minus 1% in the wattage across the lamp.

During both two lamp operation and single lamp operation at 115 line Voltage, the voltage drops across the various circuit elements, and the current traversing the same, are set forth below:

is to say, when all of the lamps are operating. In the above tabulation shown, it will be observed that under two lamp operation, the voltage drop across the condenser Xc is almost twice the voltage drop across the lamp. This relationship is believed to contribute materially tothe apparent constant impedance of the branch circuit above referred to. v

Variations in the condenser size may require slight variations in the length of the air gap 17. However, for the particular type of circuit shown, I have found that the air gap should be relatively small, of the order from .030 inch to .080 inch, the longer gap being associated with a small condenser size, and vice versa.

Furthermore, with respect to each of the several conditions of operation, such as all lamps in circuit, one lamp removed, two lamps removed, etc., the system provides relatively constant lamp wattage with respect to line voltage variation. This constant wattage characteristic is shown in the graph of FIG. 4, in which the vertical axis represents percentage variation in Watts delivered to a given lamp, and in which the horizontal represents line voltage, normal voltage being 115 volts. Curve 32 indicates lamp wattage under two lamp operation, and curve 33 represents lamp wattage under one lamp operation, in the circuit of FIG. 2.

Although only a preferred embodiment of my invention has been shown and described herein, it will be understood that various modifications and changes may be made therein without departing from the spirit of my invention as pointed out in the appended claims.

I claim:

1. A plural lamp ballast comprising a leakage reactance transformer having a core including a Winding leg, a primary winding and a secondary winding located on said winding leg in end to end relationship to provide a flux leakage path, the cross sectional area of a substantial portion of that part of said core which is linked by said secondary winding being suiciently small so that said transformer will operate at saturation, lead means Primary Secondary Branch I. Watts RF., V. 1. Y X., Lamp I. Lamp percent Watts 1 Two lamp operation. 3 Open circuit.

The foregoing tabulation shows that in the circuit 2 Single lamp operation.

for connecting said primary winding to a source of A.C.

shown, the impedance of the transformer 10, instead of causing an increase in the secondary voltage as the load is reduced, cooperates with the other circuit elements so that the voltage across the secondary terminals is reduced as the lamps are removed one by one.

Furthermore, with respect to each branch circuit, the combination of the condenser in the branch circuit and the inductance in the transformer not only provides stable ballasting for each lamp, but due to the saturation, a very desirable type of regulation is provided in which a decrease in the secondary voltage due to removal of a lamp results in a much smaller decrease in the voltage across the remaining lamp or lamps.

Actually, in the two lamp ballast shown, the decrease in the branch circuit current is roughly proportional to the decrease in the secondary Voltage which suggests that the impedance of the branch circuit remains substantially constant, although due to changes in wave shape, it is not possible to speak unequivocally.

However, I have found, especially with respect to the ballasting of mercury vapor lamps, that stable operation can be obtained, in spite of a change in the secondary voltage of as much as 10 to 15%, if the impedance of the condenser is considerably in excess of the impedance of the lamp under full load conditions of the ballast, which voltage and a plurality of branch circuits connected in Yparallel across said secondary, each of said branch circuits including a condenser and lead means for connection to a gaseous discharge device for energizing same, whereby removal of a gaseous discharge device from its branch circuit will render said branch circuit inoperative so that both the load current and the capacitive reactance of the load will be reduced, resulting in a decrease in the voltage across said secondary winding, the saturation of said core causing said resulting decrease in secondary voltage to be much smaller proportionately than said reduction in load current.

2. A plural lamp ballast as claimed in claim 1 in which the impedance of said condenser is approximately twice the impedance of said lamp when said ballast is operated at full load current.

3. A plural lamp ballast as claimed in claim 1 having a gapped magnetic shunt interposed between said primary and secondary windings to reduce the reluctance of said ux leakage path.

4. A plural lamp ballast as claimed in claim 3 in which the gap of said magnetic shunt is from .030 to .080 inch in length.

5. A plural lamp ballast as claimed in claim 1 in Which the inductance of said secondary winding is suiiiciently U small that when a voltage is applied to the terminals thereof of a magnitude equal to the normal operating voltage, the current drawn by said secondary winding when said primary winding is open circuited will be from substantially 50% to 75% of the full load current during normal operation.

6. A lighting system comprising a leakage reactance transformer having a core structure, a primary winding and a secondary Winding mounted on said core structure in spaced relationship to provide a flux leakage path therebetween, a source of A.C. voltage connected to said primary Winding and a plurality of branch circuits connected in parallel across said secondary, each of said branch circuits including a condenser and a gaseous discharge device, whereby removal of a gaseous discharge device from its branch circuit will render said branch circuit inoperative so that both the load current and the capacitive reactance of the load will be reduced, resulting in a decrease in the Voltage across said secondary winding, the impedance of said condensers being substantially greater than the impedance of said lamps under normal operating conditions, whereby a remaining branch circuit will stabilize itself for continued operation at said reduced secondary voltage.

7. In combination, a leakage reactance transformer adapted for energizing a plurality of gaseous discharge devices in parallel, said transformer having a core including a winding leg, a primary winding and a secondary winding mounted on said winding leg in end to end relationship, a magnetic shunt disposed between said Windings, a source of A.C. voltage connected to said primary winding, a plurality of gaseous discharge devices, and a plurality of condensers connected in parallel across said secondary, each condenser being connected in series to a gaseous discharge device, said secondary winding being constructed to draw a magnetizing current which is relatively high with respect to the normal load current of said secondary, and said normal load current being sufficiently high as to saturate the secondary portion of said winding leg.

Wiegand July 23, 1935 Feinberg June 22, 1954

Claims

1. A PLURAL LAMP BALLAST COMPRISING A LEAKAGE REACTANCE TRANSFORMER HAVING A CORE INCLUDING A WINDING LEG, A PRIMARY WINDING AND A SECONDARY WINDING LOCATED ON SAID WINDING LEG IN END TO END RELATIONSHIP TO PROVIDE A FLUX LEAKAGE PATH, THE CROSS SECTIONAL AREA OF A SUBSTANTIAL PORTION OF THAT PART OF SAID CORE WHICH IS LINKED BY SAID SECONDARY WINDING BEING SUFFICIENTLY SMALL SO THAT SAID TRANSFORMER WILL OPERATE AT SATURATION, LEAD MEANS FOR CONNECTING SAID PRIMARY WINDING TO A SOURCE OF A.C. VOLTAGE AND A PLURALITY OF BRANCH CIRCUITS CONNECTED IN PARALLEL ACROSS SAID SECONDARY, EACH OF SAID BRANCH CIRCUITS INCLUDING A CONDENSER AND LEAD MEANS FOR CONNECTION TO A GASEOUS DISCHARGE DEVICE FOR ENERGIZING SAME, WHEREBY REMOVAL OF A GASEOUS DISCHARGE DEVICE FROM ITS BRANCH CIRCUIT WILL RENDER SAID BRANCH CIRCUIT INOPERATIVE SO THAT BOTH THE LOAD CURRENT AND THE CAPACITIVE REACTANCE OF THE LOAD WILL BE REDUCED, RESULTING IN A DECREASE IN THE VOLTAGE ACROSS SAID SECONDARY WINDING, THE SATURATION OF SAID CORE CAUSING SAID RESULTING DECREASE IN SECONDARY VOLTAGE TO BE MUCH SMALLER PROPORTIONATELY THAN SAID REDUCTION IN LOAD CURRENT.