US 3772565 A
Electrical ballast provides regulation of the operating wattage for gaseous discharge lamps such as high pressure sodium lamps over the entire life of the lamp. Ballast comprises a high leakage reactance transformer having primary and secondary windings on different core portions with a magnetic shunt between the windings, slots in the core under the secondary winding, and a capacitor connected in series with the secondary winding. The transformer is constructed so that its leakage reactance is from two to four times the capacitive reactance provided by the series capacitor. The control of the leakage reactance is obtained by provision of a predetermined cross-sectional area of the magnetic shunt in combination with a non-magnetic gap.
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Description (OCR text may contain errors)
United States Patent [191 Lenz et al.
[ 1 Nov'. 13, 1973 Filed:
LAMP BALLAST DEVICE Inventors: James E. Lenz, Hendersonville;
Wayne R. Neal, Fletcher, both of NC.
Int. Cl. H05b 41/391 Field of Search 315/100, 138, 276,
Assignee: General Electric Company July 28, 1972 Appl. No.1 275,947
References Cited UNITED STATES PATENTS 3,684,921 8/1972 DeLeon 315/276 Primary Examiner-Alfred L. Brody Att0rneySidney Greenberg et al.
[5 7] ABSTRACT Electrical ballast provides regulation of the operating wattage for gaseous discharge lamps such as high pressure sodium lamps over the entire life of the lamp. Ballast comprises a high leakage reactance transformer having primary and secondary windings on different core portions with a magnetic shunt between the windings, slots in the core under the secondary winding, and a capacitor connected in series with the secondary winding. The transformer is constructed so that its leakage reactance is from two to four times the capacitive reactance provided by the series capacitor. The control of the leakage reactance is obtained by provision of a predetermined cross-sectional area of the magnetic shunt in combination with a nonmagnetic gap.
10 Claims, 4 Drawing Figures LAMP BALLAST DEVICE The present invention relates to electrical ballast devices for gaseous discharge lamps, and more particularly concerns a ballast device for regulating power to high pressure gaseous discharge lamps throughout their operational life.
Certain high pressure discharge lamps, such as high intensity sodium arc discharge lamps of known type, tend to vary in voltage over the life of the lamp. For example, a 250 watt high pressure sodium lamp with a nominal voltage rating of 100 volts will vary from 85 to 115 volts when new, while its voltage at end of life (drop-out voltage) may rise to 160 volts or more. It is necessary; therefore, for the ballast apparatus used with such lamps to compensate for such lamp voltage variation as well as line voltage variations in order to provide stabilized lamp operation over the life of the lamp and to avoid premature lamp failure or malfunction.
While certain types of ballast devices have heretofore been used or suggested to provide for such results, these devices have had certain drawbacks, such as being unduly limited to particular line voltages, being useful only on well-regulated distribution circuits, or requiring large, cumbersome, or expensive ballast transformer structures and associated circuit components in order to provide satisfactory results.
It is an object of the present invention to provide an improved ballast apparatus for controlling the operation of gaseous discharge lamps, especially of high pressure sodium vapor type, which avoids the above and other disadvantages of prior known ballast devices.
It is a particular object of the invention to provide a ballast apparatus of the above type which satisfactorily regulates power to high pressure sodium vapor lamps while compensating for line and lamp voltage variations over the life of the lamp, and which may be made of smaller size and at less expense than known ballast devices heretofore used for such lamps.
It is still another object of the invention to provide a ballast apparatus of the above type which is useful for regulating power to various types of high pressure gaseous discharge lamps.
Other objects and advantages will become apparent from the following description and the appended claims.
With the above objects in view, the present invention in a broad aspect relates to a ballast apparatus for operating a gaseous discharge device from an alternating current source comprising, in combination, a transformer having a core of magnetic material providing a closed magnetic circuit, primary winding means on a first portion of the core and secondary winding means on a second portion of the core adapted to be connected in series with the gaseous discharge device, the second portion of the core having a reduced area to provide a localized saturated portion, a capacitor connected in series with the secondary winding means and having sufficient capacitive reactance for limiting current to the gaseous discharge device, and means such as a magnetic shunt between the primary and secondary winding means for providing leakage reactance of the transformer which is between two to four times the capacitive reactance of the capacitor.
The invention will be better understood from the following description taken in conjunction with the accompanying drawing, in which:
FIG. 1 is a schematic diagram of a ballast device illustrating an embodiment of the invention;
FIG. 2 is a graph showing the lamp volt-watt characteristics of the ballast apparatus of the invention as compared to the characteristics of known types of ballasts;
FIG. 3 is a graph illustrating variations in lamp voltwatt characteristics with variation in leakage reactance of the ballast apparatus, and indicating control of such variation in accordance with a modification of the invention; and
FIG. 4 is a circuit diagram representing an equivalent circuit for the FIG. 1 device and modifications thereof.
Referring now to the drawing, and particularly to FIG. 1, there is shown a ballast apparatus constructed in accordance with the invention and comprising a transformer 1 having a closed magnetic core 2 of the U-I type formed of a stack of magnetic steel laminations. The primary winding 3 of transformer 1 comprises winding 3a wound on one leg of core 2 in series with winding 3b wound on the opposite leg of core 2, and is connected to terminals 4 of a source of altemat- -ing current. Secondary winding 5 of the transformer I similarly comprises windings 5a and 5b connected in 6 and at its other side to supply line 21 as shown. The
portion of primary coil 3b between tap 8 and supply line 21 thus provides for a common voltage which is additive to the voltage of the secondary winding and serves to improve the power factor of the ballast circuit which preferably should be at least percent.
The portions of transformer core 2 lying under the secondary winding coils 5a, 5b are formed with slots 9,10 to provide a reduced cross-section of the secondary core in an amount producing localized saturation of these restricted core portions during operation of the circuit, thereby providing the desired secondary magnetizing reactance for controlling current to the lamp in the circuit shown, and for controlling other characteristics of the circuit as explained below.
Capacitor 6 provides leading current in the secondary circuit and thereby assists in establishing the desired saturation in the secondary core portions for regulating power in the secondary circuit, in a manner understood by those versed in the art.
Magnetic shunt 11 is arranged extending across the space or window 20 of core 2 between primary winding 3 and secondary winding 5 for providing leakage reactance in the transformer. Shunt ll typically comprises an assembly of superposed magnetic laminations and is spaced at its opposite ends from the opposite core legs by non-magnetic gaps l3, 14 which may be air gaps or spaces occupied by insulating spacer material such as kraft paper.
For the purpose of starting the lamp, an auxiliary starting circuit will usually be associated with the operating circuit shown, but the starting circuit has been omitted from the illustrated circuit for the sake of simplicity, since it will not affect the operation of the described circuit. Such a starting circuit is disclosed, for example, in the co-pending application of Nuckolls,
Ser. No. 674,508 filed Oct. 11, 1967, and assigned to the same assignee as the present invention, and also disclosed in the U.S. Pat. to Attewell No. 3,407,334.
The relationships involved in the operation of the FIG. 1 ballast device as explained below will be better understood by reference to the equivalent circuit shown in FIG. 4, wherein X is the leakage reactance between the primary and secondary windings controlled by the magnetic shunt, X is the secondary magnetizing reactance controlled by the slots in the secondary portions of the core, X is the capacitive reactance, V is the common voltage described above, V is the secondary winding voltage, V is the secondary magnetizing reactance voltage, and E is the total secondary magnetizing voltage.
FIG. 2 graphically shows the lamp volt-watt (V-W) characteristic obtained by a ballast constructed in accordance with the present invention (Curve C) as compared to the V-W characteristic (Curve A) obtained from a conventional regulated-output or autotransformer regulator ballast for mercury vapor lamps, and to the V-W characteristic (Curve B) obtained from a known so-called peak-lead ballast used for metal halide lamps. A principal difference between the ballast provided by the present invention (herein referred to as a modified-lead ballast) and the above-mentioned known ballasts is that in the modified-lead ballast of the invention the relative size of the leakage reactance X of the ballast is greater than the capacitive reactance X provided by the capacitor in series with the lamp. The conventional lead ballasts are characterized by a value of X L which is not greater than X and is usually in the range of 0.75 to 1.0 times the value of X While such a value provides good power factor and regulation of lamp watts to compensate for variations in line voltage, it is unsatisfactory for use with high pressure sodium lamps due to their unstable voltage characteristic as described. it has been found in accordance with the invention that the value of X must be in the range of about 2 to 4 times that of X in order to achieve the desired results.
There is graphically shown in F l6. 2 a tolerance box defined by the boundaries of maximum lamp watts (W Max), minimum lamp watts (W Min), maximum lamp volts (V Max), and minimum lamp volts (V Min) within which it has been determined by test that the lamp VW curve should be located in order to ensure proper operation of the lamp over its normal life. Lamp specifications require that for a ballast to meet the lamp operating requirements, its characteristic curve must intersect each of the lamp voltage limit lines at points between the wattage limit lines and must remain between these wattage limit lines throughout the full range of lamp voltage. Also shown in the FIG. 2 graph is the point N designating the typical nominal (rated) watt and volt values of a high pressure sodium lamp. Operation of the sodium lamp with either of the conventional ballasts represented by Curves A and B will result in premature destruction of the lamp, since in each case the lamp wattage increases to an intolerable degree as the lamp volts rise with increasing age of the lamp. On the other hand, the V-W characteristic Curve C of the modified lead ballast of the invention provides stable lamp operation within tolerable wattage limits throughout the life of the lamp, and with line voltage variation of at least i percent.
While control of the V-W characteristic by the above described means largely compensates for the unstable voltage characteristics of sodium lamps, other structural features of the ballast transformer and associated circuit should be properly controlled to provide the optimum combination of ballast properties such as line power factor, lamp crest factor and the lamp drop-out voltage (i.e., the lamp voltage at the end of life) to produce the best practical results. Thus, variations in the features of common volts, number of secondary winding turns, and size of the secondary core slots are considered, along with the amount of leakage reactance X in constructing a ballast with optimum properties. The qualitative effect of changes in such features on the operating parameters of the ballast is shown in Table I below, it being understood that a decrease of the listed variable will produce a change opposite to that indicated and that the blanks in the Table indicate little or no effect:
The references to shift of the V-W characteristic in the Table are with regard to the form of the lamp V-W curve in the tolerance box such as shown in FIGS. 2 and 3.
Because of the increased leakage reactance of the ballast due to the relative amount of X provided in comparison to X and large slots in the secondary portion of the core increasing the primary magnetizing current, a lagging current is produced in the primary circuit which results in a relatively low line power factor. To improve the power factor under these conditions, a common voltage is provided as described previously which is of sufficient value to raise the power factor to at least percent.
A significant factor in shaping of the lamp V-W characteristic curve which does not appear in Table l is the effect of saturation of magnetic shunt l1 controlling leakage reactance X, As the lamp volts increase, the leakage flux through the shunt 11 increases and, depending on the cross-section of the shunt, it will start into magnetic saturation at some value of lamp volts. The effect of this saturation is to greatly reduce the value of leakage reactance X It can be seen from Table I that a high value of X is desirable to produce a-steep rise on the lamp V-W characteristic (shift the front of the curve to the left) so that the curve enters the front side of the lamp V-W tolerance box. However, it has been found that a high value of X also causes the tail of the V-W curve to drop faster and decreases the value of the lamp drop-out volts. Thus, it is desirable in certain cases to provide a high value of X on the front of the V-W curve and a somewhat lower value on the tail of the curve.
This desired changein X can be accomplished by providing a cross-sectional area of shunt 11 such that it starts to saturate at about the value of lamp volts producing maximum lamp watts. Thus, a high value of X (no saturation) is maintained throughout the front of the V-W curve to the peak value. Further increase of lamp volts beyond this point causes the shunt to start into saturation, automatically reducing X to raise the tail of the V-W curve and increase the lamp drop-out volt value, which prolongs the lamp life. This effect is illustrated in the graph of FIG. 3, wherein typical V-W curves of low and high X are respectively depicted, and showing in interrupted lines the raised tail T of the high X curve produced by controlled shunt saturation as described above. Such a result may be achieved by decreasing the cross-sectional area of shunt 11 or by narrowing air gaps 13, 14 or by a combination of these steps.
By way of example, there is set forth below specific dimensions and other features of a ballast device such as shown in FIG. 1 which has provided satisfactory results in accordance with the invention, it being understood that the invention is not intended to be limited by the specific values listed:
Ballast for 1000 watt sodium (Lucalox) lamp operating at 120 X 240 volts, 60 Hz.
Core U-l formed of M5 steel laminations inches Lamination thickness 0.012 Lamination width 4.0 Core leg width 1.33 Core window width 1.34 Height of U 5.35 Overall core height 6.68 Core stack height 2.73 Core secondary slots (2) 1.04 X 0.125 Shunt Laminations of M45 steel Lamination thickness 0.0185 Shunt width (across 1.283 window) Shunt length 2.74 Shunt stack height 1.01 Shunt cross-section 2.66 in Total air gap 0.058 in Primary winding 2 coils:
connected series for 240V. connected parallel for 120 V. Each coil l28 turns, 0.0571 inch dia. copper wire tap at 91 turns (coil No. 1 only) Secondary winding 2 coils: connected in series Each coil 290 turns, 0.0571 inch dia. copper wire Electrical values:
X 248 ohms X 102 ohms 26 mt'd. cap. X 107 ohms (X secondary magnetizing reactance) Open circuit voltage 400 volts RMS 885 volts Peak Line Power Factor 94% Lamp Crest Factor 1.52 Common Volts 84.5
While in the usual case the desired leakage reactance is obtained by providing a particular cross-sectional area of the magnetic shunt 11 and/or length of the nonmagnetic gap, it is also possible to use a conventional close coupled transformer and obtain the desired leakage reactance by use of an auxiliary induction coil of suitable indictuve reactance connected in series with the secondary winding 5. It is also possible to obtain the desired secondary magnetizing reactance by use of an auxiliary induction coil of suitable inductive reactance connected in parallel across the combination of secondary winding in series with the leakage reactance. Such alternative arrangements will be evident from the FIG. 4 equivalent circuit wherein the induction coils designated X and X may represent respectively the aforementioned auxiliary induction coils. The term leakage reactance as used herein is intended to refer to the leakage reactance provided by magnetic shunt 11 in the FIG. 1 device or the reactance provided by the induction coil X shown in the FIG. 4 circuit.
It will also be understood that although the invention has been described with respect to a ballast transformer core of U-l configuration, the transformer employed may be of other types, such as a shell-type transformer in which the primary and secondary windings are disposed on the central leg of the three-leg core.
Furthermore, instead of closed slots 9,10 as shown, slots opening at an edge of the core under the secondary winding may be employed, and the number, size, arrangement and shape of the slots may be different from those shown without departing from the scope of the invention.
It will also be understood that while the described ballast apparatus is particularly adapted for use with sodium vapor lamps for the reasons mentioned above, it may also be used with satisfactory results with other types of lamps such as mercury vapor, metal halide and other gaseous discharge lamps.
While the present invention has been described with reference to particular embodiments thereof, it will be understood that numerous modifications may be made by those skilled in the art without actually departing from the scope of the invention. Therefore, the appended claims are intended to cover all such equivalent variations as come within the true spirit and scope of the invention.
What we claim as new and desire to secure by Letters Patent of the United States is:
l. Ballast apparatus for operating a gaseous discharge device from an alternating current source comprising, in combination, a transformer having a core of magnetic material providing a closed magnetic circuit, primary winding means on a first portion of said core and secondary winding means on a second portion of said core adapted to be connected in series with the gaseous discharge device, means for providing a predetermined secondary magnetizing reactance, a capacitor connected in series with said secondary winding means and having sufficient capacitive reactance for limiting current to the gaseous discharge device, and means for providing leakage reactance in the ballast apparatus which is between two and four times the capacitive reactance of said capacitor.
2. Ballast apparatus as defined in claim 1, said leakage reactance means comprising magnetic shunt means between said primary and said secondary winding means in combination with non-magnetic gap means between said core and said magnetic shunt means.
3. Ballast apparatus as defined in claim 2, including a restricted cross-sectional area in the secondary portion of said core to provide localized saturation thereof for reducing the secondary magnetizing reactance.
4. Ballast apparatus as defined in claim 1, and means connecting said secondary winding means to said primary winding means for providing a predetermined voltage additive to said secondary winding means for improving the line power factor.
5. Ballast apparatus as defined in claim 2, and means connecting said secondary winding means to said primary winding means for providing a predetermined voltage additive to said secondary winding means for providing a line power factor of at least 90 percent.
6. Ballast apparatus as defined in claim 5, and a high pressure gaseous discharge sodium lamp connected in series with said capacitor.
7. Ballast apparatus as defined in claim 2, said magnetic shunt means having a predetermined crosssectional area and said gap means having a predetermined length for providing controlled saturation of said magnetic shunt means for producing a characteristic volt-watt curve for said gaseous discharge device which has a relatively steep front and a relatively flat tail.
8. Ballast apparatus as defined in claim 1, said leakage reactance means comprising an induction coil connected in series with said secondary winding means.
9. Ballast apparatus as defined in claim 1, said secondary magnetizing reactance means comprising an induction coil connected in parallel with said secondary winding means.
10. Ballast apparatus as defined in claim 1, said leakage reactance means comprising a first induction coil connected in series with said secondary winding means, said secondary magnetizing reactance means comprising a second induction coil connected in parallel with said series connected secondary winding means and first induction coil.