US2962629A

US2962629A - Transformer for electric discharge lamps

Info

Publication number: US2962629A
Application number: US816343A
Authority: US
Inventors: Jeanne E Strecker
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1959-05-27
Filing date: 1959-05-27
Publication date: 1960-11-29
Anticipated expiration: 1977-11-29

Description

Nov. 29, 1960 c. E. STRECKER TRANSFORMER FOR ELECTRIC DISCHARGE LAMPS Filed May 27, 1959 l l l I l I I l I l l United States Patent TRANSFORMER FOR ELECTRIC DISCHARGE LAMPS Charles E. Strecker, deceased, late of Danville, Ill., by Jeanne E. Strecker, executrix, Danville, Ill", assignor to General Electric Company, a corporation of New York Filed May 27, 1959, Ser. No. 816,343

11 Claims. (Cl. 315-97) This invention relates to electric discharge lamps and more particularly to ballast apparatus for starting and operating such lamps.

It is a characteristic of electric discharge lamps, such as fluorescent lamps, that their internal resistance decreases as the current flow therethrough increases. It is, therefore, necessary in the installation of such devices to provide means which will limit the current flow through the device to a safe value. In addition, it may also be desirable to provide a higher voltage for initially starting or causing a discharge in the device than is conventienty available. When electric discharge devices are operated on alternating current, it is conventional practice to provide a single high reactance ballast transformer to perform these two functions, i.e., limit current and provide a high initial starting voltage. Such a transformer provides a high open circuit voltage for starting and also, by virtue of this high reactance, provides impedance during normal operation to limit the current flow.

A high reactance transformer is one in which the primary and secondary windings are loosely coupled so that when the transformer is carrying a load, there is a a substantial amount of leakage flux and the voltages induced in the windings by this leakage flux cause the transformer to have a relatively high effective series reactance, or what is commonly known as leakage reactance. The conventional way of constructing such a transformer is to arrange the primary and secondary windings on different parts of the core and to provide a magnetic shunt between the windings thereby providing a path for the leakage flux. This shunt is usually provided with an air gap so calibrated that the operating current of the secondary coil of the transformer Will be limited to the desired value. The high, starting voltage can be achieved with a high voltage secondary winding, or may be achieved by using a transformer with the primary winding and the operating secondary winding connected in autotransformer relation, i.e., the primary and secondary are connected in series across one of the lamps so that their voltages are additive, as more fully described in my copending application Serial No. 816,342, filed on the same date herewith and assigned to the same assignee as the instant application. However, it is sometimes desirable to produce a higher starting voitage than is available by the utilization of the primary and operating secondary voltages alone. Such a higher starting voltage may be achieved according to the instant invention by utilizing the voltage induced in an auxiliary starting secondary winding across one or more of the lamps during starting thereof.

'When the primary winding and secondary windings are connected in autotransformer relation, it may be desirable that the output voltage be reduced after the device has started; the autotransformer connection at this point may become unnecessary and, in fact, undesirable. Such a transformer which provides autotransformer type starting voltage in a starting aid circuit and isolated transformer type running voltage is more fully described in my co- "ice pending application Serial No. 435,753, filed June 10, 1954, and assigned-to the same assignee as the present invention.

It is, therefore, an object of this invention to provide an improved ballast transformer apparatus for starting and operating electric discharge lamps which will incorporate the desirable features set forth above.

A more specific object of this iIlVI1tlOIl is to provide an improved ballast transformer apparatus for starting and operating electric discharge lamps which will provide a starting voltage across the lamps higher than that available from the primary and operating secondaryopen circuit voltages alone.

Further objects and advantages of this invention will become apparent and the invention will be better understood 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.

This invention, in one embodiment thereof, includes a ballast transformer apparatus having a primary winding, an auxiliary starting secondary winding, and an operating secondary winding on a magnetic core and all connected in series in autotransformer relation so that their voltages are additive and cooperate to start the lamps. Once the lamps have started, however, since the auxiliary starting winding is in series with a low capacity starting capacitor across one of the lamps, only a small amount of current can flow through this winding and, therefore, the auxiliary starting winding does not form a part of the operating,

circuit. The added voltages of the auxiliary-starting secondary and at least the operating secondary are, therefore, applied across at least one lamp during starting thereof. A further feature of the instant invention is that the additive voltages of the primary, auxiliary starting secondary and operating secondary are applied between one of the lamp cathodes and a conductive part of fixture in a starting aid circuit. After starting of the lamps, the ballast transformer apparatus may operate the lamps as an autotransformer or as a substantially isolated secondary transformer.

As explained thus far, the circuit has a low power factor since no correction has been made. The circuit described above would draw lagging current through the transformer. It may be desirable, but not necessary, to draw leading current through the transformer, as, for example, by having a capacitor in series with the operating secondary winding. Or, it may be desirable, but not necessary, to correct the power factor to near unity as, e.g., by connecting a condenser across a portion of the primary winding or equivalent winding.

It will be seen that by using the additive voltage of a starting auxiliary secondary, the operating secondary may be made smaller since the output voltage during starting therefrom need not be as great. Also, this additive voltage of the auxiliary starting secondary, which becomes undesirable once the lamp is started and is operating, is not effective after starting. It will be readily appreciated that since the auxiliary starting winding is substantially ineffective after starting of the lamps, it may be wound of relatively fine wire, and may, if desired, be of relatively high impedance thereby further limiting the current flow therethrough after starting. Since the auxiliary starting winding is substantially ineffective after starting of the lamps, it may be coupled to either the primary winding or the operating secondary winding.

In the drawing,

Figure 1 is a schematic diagram of an improved ballast transformer for operating a pair of serially connected discharge lamps according to the instant invention;

Figure 2 is a schematic diagram of another modification for an improved ballast transformer according to the instant invention for operating a pair of serially connected discharge lamps; and,

Figure 3 is a plan view of the ballasting transformer according to Figure 2.

Referring to Figure 1, there is shown a ballasting transformer apparatus according to the instant invention for starting and operating a pair of serially connected discharge lamps. The ballasting apparatus according to the instant invention includes a magnetic core 1 having a central winding leg 2 and yoke sections 3 and 4 and having a primary winding P, an operating secondary winding 8,, and an auxiliary starting secondary winding S on the winding leg 2. The primary Winding P is loosely coupled to the operating secondary winding S The primary P and the operating secondary winding S may be placed side by side on the central winding leg 2 of the magnetic core 1. thereby resulting in leakage reactance in the magnetic circuit. Where it is desired to increase the magnetic leakage and therefore the leakage reactance of the transformer, this may readily be accomplished by the inclusion of high reluctance flux leakage paths or shunts in the core 1 between the primary P and the operating secondary S It will be understood that, depending upon the design of the transformer, the flux leakage paths may be formed either through nonmagnetic material such as air, or through magnetic material as by the provision of the projecting shunt legs 4a formed on the core 1. This shunt construction results in what is known as a high reactance transformer and the transformer acts to limit the current flow in the circuit including the lamps. This is necessary due to the negative resistance characteristics of the lamps.

The auxiliary starting secondary winding S may be coupled with one of the other windings; as shown in Figures 1 and 3, the starting secondary S is coupled with the primary P, being wound over it. It will be understood, however, that secondary winding S could be placed closely beside one of the other windings in order to obtain the desired coupling.

The primary P has a pair of leads 5, 6 for connection to a source of alternating current 7, 8. As explained above, the low potential side of the normal residential and commercial distribution systems is grounded, as shown at 9. The primary P and operating secondary S are connected through line 10 in autotransformer relation. The other end of the operating secondary S is connected through leads 11 and 12 in series with the auxiliary starting secondary S to form substantially an autotransformer connection therewith. A starting capacitor 13 of relatively low capacitance is inserted in series with the auxiliary starting secondary S between the starting secondary S and the operating secondary the purpose of which will hereinafter be explained. A first cathode heating winding 14, a second cathode heating winding 15, and a third cathode heating winding 16 are also on the magnetic core 1. As shown, cathode heating winding 16 is an extension winding of the primary P; it is to be understood, however, that it may be an isolated secondary.

The ballasting transformer apparatus is connected to operate a pair of serially connected discharge lamps L L Lamp L has a pair of electrodes 17, 18, one in each end thereof. Lamp L has a pair of electrodes 19, 20, one in each end thereof. The lamps L L are in close proximity to a conducting fixture 21 thereby being in capacitive relation therewith. As normally installed, fixture 21 would be grounded through ground 22 thereby being in circuit relation with the low potential line 8 of the supply source (and thereby to the low potential lead 6 of the primary P) through the grounds 9 and 22. However, to insure that the fixture 21 is in fact in electric circuit relation with a low potential line 8 of the supply source, it may be desirable, but not necessary, to connect the low potential lead 6 of the primary P to the ballast case 23 through a high ohmage resistor 24. The ballast case 23 is normally connected, as shown at 25, to the lamp fixture, thereby securing the fixture in electrical circuit with the low potential lead 6 of the primary P and the low potential line 8 of the supply source. A first pair of output leads 25, 26 connect the cathode heating winding 14 to one electrode 19 of lamp L A second pair of output leads 27, 28 connect the cathode heating winding 15 to electrode 20 of lamp L and electrode 17 of lamp L A third pair of output leads 29, 30 connect the third cathode heating winding 16 with electrode 18- of larnpL The low potential lead 6 of the primary P is connected to one output line 29 connected to the third cathode heating winding 15. A series circuit including the auxiliary starting secondary S and the starting capacitor 13 is connected across the second lamp L in parallel therewith by having one end connected to one output line 25 (through.line 12) connected to thefirst cathode heating winding 14 and having its other end connected to output lead 28 connected to cathodeheating winding 15.

A first starting circuit or loop including lamp L consistsof the series circuit including the primary P, the operating secondary S the starting capacitor 13 (through lines 11, 12), the auxiliary starting secondary S and the first lamp L As lamp L has not yet started, it is nonconducting and does not form a part of this starting loop. When leads 5 and 6 are connected across the source of alternating current, the current will flow through the primary P so as to excite the secondaries S and S The open circuit voltage resulting in the secondaries S and 5 will be a function of the number of turns of the secondaries with respect to the number of turns of the primary P. Since lamp L is nonconducting, the additive voltages of the windings are placed across the electrodes 17 and 18 of the first lamp L Prior to the starting of the first lamp L a relatively small starting current is flowing, and the starting capacitor 13 has no substantial effect upon this starting loop, There will, therefore, be a relatively high voltage applied across the electrodes 17, 18 of the first lamp L At the same time, an auxiliary starting aid circuit or loop includes the additive voltages of the primary P, the operating secondary S and the starting secondary S applied to electrode 17 of the first lamp L which is in capacitive relation with the conducting fixture 21. A return ground with conducting fixture 21 is completed through ground 22 to either ground 25 of the ballast case or ground 9 of the low potential line 8. Due to the very high impedance thereof, the relatively high voltage applied between electrode 17 of the lamp and the conducting fixture 21 causes a relatively small current to pass therebetween. This current will preferably be on the order of a few microamps, which is sufiicient to increase substantially the ionization of the gas around the electrode 17 and cause the lamp L to become conducting, and the current will arc across between electrodes 17 and 18.

After the first lamp L has started, a second starting loop including lamp L will consist of the primary P, the first secondary S and the voltage existing at the electrode 17 of the first lamp L There will simultaneously be a relatively high voltage applied between electrode 20 and the conducting fixture 21, through ground 22 and ground 25 or ground 9. As explained above, the gas in lamp 1.2 will ionize causing lamp L to become conductive and the voltage across lamp L issufficient to start the lamp.

Once lamps L and L have both started, the starting capacitor 13 has sufficient impedance that no significant operating current will flow through winding S and the current. through the starting capacitor 13 will be minor with reference to the current through the lamp. The lamps L and L will then operate in a series circuit across the primary P and the operating secondary. S1. Also, after completion of the circuit through the lamps,

because of the high impedance of the capacitive coupling of the lamps and fixture, the amount of current flow from the lamp cathodes to the conducting fixture 21 is infinitesimal with relation to the current through the lamps and there is, therefore, only a very minor circuit, from a current standpoint, completed through the grounds. Transformer 1 will now, for practical purposes, act as an ordinary high reactance autotransformer with the combined voltages of the primary P and operating secondary S producing suflicient current to keep the lamp L and L in operation.

The hallasting transformer of Figure 2 is similar to that illustrated in Figure 1 except that the transformer has its primary and secondary windings connected to operate the lamps in isolated secondary relation rather than in autotransformer relation, as more fully taught in the above referenced copending application Serial No. 435,753. A further modification illustrated in Figure 2 is the inclusion of a capacitor of large capactive reactance in series with the operating secondary S to draw leading current through the lamps. This, of course, is a matter of design and the invention as illustrated in either Figures 1 or 2 may be applied to either a leading or a lagging circuit.

Referring now to Figure 2, there is illustrated the improved ballasting transformer according to the instant invention and comp-rising a magnetic core 1 within a case or housing 23. The magnetic core 1 has wound thereon a primary winding P, an operating secondary winding S and an auxiliary starting secondary winding S also wound on the magnetic core 1 are cathode heating windings 14, 15 and 16. A pair of input leads 5, 6 are connected to the primary P for connection to a source of alternating current 7, 8. As hereinafter explained, the low potential side 8 of the supply source in a normal residential or commercial distribution system would be grounded as indicated by a ground 9. Such a ground, however, is not necessary for the operation of the ballasting trans former providing the low potential side 6 of the primary P is in circuit relationship with the conducting fixture 21 as hereinafter described. The high potential line 5 connected to the primary P is connected to one end of the operating secondary S in autotransformer relation. The line connecting the primary P and the secondary S may include, if desired, a high resistance 31, which will afford certain safety precautions as more fully described in the above referenced copending application Serial No. 435,753. It is to be understood, however, that where the safety precautions afforded by resistance 31 are not needed, resistance 31 may be omitted from the circuit without effecting the operation thereof. Serially connected to the operating secondary S is a power capacitor 32 of sufficient size relative to the inductance of the transformer to draw leading current through the ballasting transformer. It is to be understood, however, that the instant invention is equally applicable to a lagging circuit, for example, as described in connection with Figure 1 above, and that in the event that a lagging circuit is desired, the capacitor 32 may be omitted. The transformer is connected to operate a pair of serially connected discharge lamps L and L The first discharge lamp L has a cathode 17 in one end and another cathode 18 at the other end; the second discharge lamp L has a first cathode 19 in one end and a second cathode 20 in the other end.

The lamps L and L are in close proximity to a conducting fixture 21 and are therefore in capacitive relationship therewith. The conducting fixture 21 may be at the same potential as the low potential line 8. It is customary in normal residential and commercial distribution systems in this country tohave the low potential side of the input line grounded. It is also customary that the.

at the primar Windi g-J l'tm ybs. de ir b e b t necessary, to connect the low potential side 6 of the primary P to the ballast transformer case 23. Since the ballast case is normally mounted on the conducting fixture, this will place the low potential side of the primary winding in circuit with the conducting fixture. It may be desirable, but not necessary, to place a high ohmage resistor 34 in the circuit connecting the low potential side 6 with the case 23. Such a circuit through the ballast case may be desirable or necessary where the low potential side of the supply distribution system is not grounded or where the fixture of the lamp will not normally be grounded, and the high ohmage resistor 34 will afford normal safeguards as more fully explained in my above referenced copending application Serial No. 435,753.

A first pair of output leads 25, 26 are connected across the first cathode heating winding 14 for connection across cathode 19 of lamp L a second pair of

leads

27, 28 extend from the second cathode heating winding 15 for connection across cathode 20 of lamp L and cathode 17 of lamp L and a third pair of output leads 29, 30 extend from the third cathode heating winding 16 for connection across cathode 18 of lamp L The starting capacitor 13 is in series with the auxiliary starting secondary S and has sufiicient impedance to limit the current flow therefrom after the starting of the lamps. The series circuit of the auxiliary starting secondary S and the starting capacitor 13, as shown, has one end connected to one output lead 25 from the first cathode heating winding 14 (through line 12) and has the other end connected to one output lead 28 from the second cathode heating Winding 15.

An auxiliary starting aid circuit is formed of the series loop including the primary P, the high resistance 31, the operating secondary 8,, the power capacitor 32, through lines 11 and 12 to starting capacitor 13, the auxiliarystarting secondary S through line 28, simultaneously to cathode 17 of lamp L and cathode 20 of lamp L to the conducting fixture 21 (which is in capacitive relation with lamps L and L and through electrical circuit 33 and resistance 34 to the low potential end 6 of the primary P. The additive voltages of the primary winding P and the secondary windings S and S are applied between cathodes 17 and 20 and fixture 21.

A first lamp starting loop including lamp L is formed of the operating secondary 8,, the power capacitor 32 through lines 11 and 12 to the starting capacitor 13, the auxiliary starting secondary S to cathode 17 of lamp L to the other cathode 18 of lamp L With no current flowing, the combined open circuit voltages of the secondaries S and S are placed across the lamp L the starting capacitor 13 offers no impedance to the application of voltage between electrodes 17 and 18 as no significant current is flowing through this circuit before the lamp L has started. As explained above, when lines 5 and 6 are connected across the source of alternating current, the current will flow through the primary P, exciting the secondaries S and S and the lamp L will ignite due to the voltage of S and S applied across it and due to the ionization in the area of electrode 17 as a result of the additive voltages of the primary P and the secondaries S and S applied between the electrode 17 and the conducting fixture 21. p I

Once the first lamp L has ignited, a second starting loop including L will be composed of the voltage induced in the operating secondary S less the voltage across lamp L and capacitor 32. This voltage across the electrodes of lamp L in connection with the ionization in the area of electrode 20 due to the additive voltages of the pricuitbecause, after completion of the circuit across electrodes of lamps L and L the amount of current throughv secondary S becomes minor with reference to the current, in the operating secondary. Likewise, the impedance of resistor 31 coupled with the impedance ofiered by the capacitive relation of electrodes 17 and 20 to the conducting fixtures 21 is sufllcicnt to limit the flow of current in this auxiliary starting circuit so that the current flow from the electrodes 17 and 20 to the fixture 21 becomes infinitesimal with relation to the currentbetwcen the electrodes of the respectivelamps and there is, therefore, only a minor circuit, from at current standpoint, completed to the conducting fixture 21. The lamps L and L therefore, operate in closed circuit with the operating secondary S and the power capacitor 32 as a substantially isolated secondary transformer.

It will be understood from the modifications discussed above that the invention may be advantageously used in many different types of lamp circuits. Therefore, while this invention has been explained by describing particular embodiments thereof, it will be apparent that improvements and modifications may be made without departing from the scope of the invention as defined in the appended claims.

What is claimed as new and desired to secure by Letters Patent of the United States is:

1. Ballast transformer apparatus for starting and op erating at least one fluorescent lamp and having two spaced electrodes at the respective ends of said lamp, comprising, a magnetic core having a primary winding and a first secondary winding thereon, output leads for connecting at least the said secondary winding across the lamp, means providing leakage reactance between said windings, a pair of input lines on said primary winding for connection to a source of alternating current, a second secondary winding on said magnetic core, said windings being wound and connected in voltage adding relation, and circuit means including a starting capacitor for connecting said second secondary winding across said lamp in a series starting circuit with at least said first secondary winding, said starting capacitor having sufficient reactance to render said second secondary winding substantially ineffective after said lamp is started.

2. Ballast transformer apparatus for starting and operating at least one fluorescent lamp mounted near a conductive part and having two spaced electrodes at the respective ends of said lamp comprising, a magnetic core having a primary winding and a first secondary winding thereon connected in autotransformer relation, means providing leakage reactance between said windings, output leads for connecting at least the secondary winding across said lamp, a pair of input lines on said primary winding for connection to a source of alternating current, a second secondary winding on said core, said windings being wound and connected in voltage adding relation. circuit means including a starting capacitor for connecting said second secondary winding across said lamp in a series starting circuit with at least said first secondary winding, and circuit means for connecting the low potential end of said primary winding in circuit with said conductive part to form a starting aid circuit thereby to complete an electrical path for said primary winding and said secondary windings during starting, the current through said starting aid circuit being minor with reference to the current through said lamp after starting thereof, said starting capacitor having sufficient reactance to render said second secondary winding substantially ineffective after said lamp is started.

3. Ballast transformer apparatus for starting and operating at least one fluorescent lamp mounted near a conductive part and having two spaced electrodes at the respective ends of said lamp comprising, a magnetic core having a primary winding and a first secondary winding thereon connected in autotransformcr relation,

means providing leakage reactance-betweensaid wind-- ings, output leads for connecting at least the secondary winding across said lamp, a pair of input lines on said primary winding for connection to a source of alternating current, a second secondary winding on said core, said windings being wound and connected in voltage adding relation, and circuit means for connecting the low potential end of said primary winding in circuit with said conductive part to form a starting aid circuit thereby to complete an electrical path for said primary winding and said secondary windings during starting, said circuit means including a starting capacitor for connecting said second secondary winding across said lamp, the current through said starting aid circuit being minor with reference to the current through said lamp after starting thereof, said starting capacitor having suflicicnt reactance to substantially limit the current flow through said second secondary winding and said second secondary winding having a relatively high impedance thereby further limiting the current flow therethrough.

4. Ballast transformer apparatus for starting and operating a pair of serially connected fluorescent lamps mounted in a conductive fixture and having spaced electrodes at their respective ends comprising, a magnetic core having a primary winding and a first secondary winding inductively coupled therewith, means providing leakage reactancc between said windings, output leads for connecting at least said secondary wind ng across said pair of seria ly connected lamps, a pair of input lines on said primary winding for connection to a source of alternating current, a second secondary winding on said core, said windings being wound and connected in voltage add ng relation, and circuit means including a starting capacitorfor connecting said second secondary winding across one of said lamps in a series starting circuit with at least said first secondary winding, said starting capacitor having suflicient reactance to render said second secondary winding substantially ineffective after said lamp is started.

5. Ballast transformer apparatus for starting and operating a pair of serially connected fluorescent lamps mounted in a conduct ve fix ure and having spaced electrodes at their respective ends comprising, a magnetic core having a primary winding and a first secondary winding thereon connected in autotransformer relation, means providing leakage reactance between said windings, output leads for connecting said windings across said pair of serially connected lamps, a pair of input lines on said primary winding for connection to a source of alternating current, a second secondary winding on said core, said windings being wound and connected in voltage adding relation, and circuit means including a starting capacitor for connecting said windings across one of said lamps in a series starting circuit, said starting capacitor having sulficient reactance to render said second secondary winding substantially ineffective after said lamp is started.

6. Ballast transformer apparatus for starting and operating a pair of se ially connected fluorescent lamps mounted in a conductive fixture and having spaced electrodes at their respective ends comprising, a magnetic core having a primary winding, a first secondary winding, a second secondary winding, 21 first cathode heating winding, a second cathode heating winding, and a third cathode heating winding thereon. circuit means connecting the high potential end of said primary winding and the low potential end of said first secondary winding in autotransformer re ation, means providing leakagereactance between said primary winding and said first secondary winding, a first pair of output leads from said first cathode heating winding for connection across one electrode of one of the lamps, a second pair of output leads from said second cathode heating winding for connection to the other cathode of said first lamp and for connection to one cathode of the second lamp, a third pair of output leads from said third cathode heating wind-- ing for connection to the other cathode of said second lamp, circuit means for connecting at least the first secondary winding across said pair of serially connected lamps, a pair of input lines on said primary winding for connection to a source of alternating current, said primary winding and secondary winding being wound and connected in voltage adding relation, a series circuit including a starting capacitor and said first pair of output leads and having its other end connected to one of said second pair of output leads whereby a series starting circuit is formed, and means for connecting the low voltage end of said primary winding in circuit with said conductive fixture thereby to complete an electrical path for said primary and secondary winding during starting, said starting capacitor having sufficient reactance to render said second secondary winding substantially ineffective after said lamps are started.

7. Ballast transformer apparatus for starting and operating a pair of serially connected fluorescent lamps mounted in a conductive fixture and having spaced electrodes at their respective ends comprising, a magnetic core having a primary winding and a first secondary winding thereon, circuit means connecting the high potential end of said primary winding and the low potential end of said secondary winding in autotransformer relation, means providing leakage reactance between said windings, output leads for connecting said windings across said pair of serially connected lamps, a pair of input lines of said primary winding for connection to a source of alternating current, a second secondary winding on said core, said windings being wound and connected in voltage adding relation, and circuit means including a starting capacitor for connecting said second secondary Winding across one of said lamps in a series starting circuit with said primary winding and first secondary winding, and means for connecting the low potential end of said primary winding in circuit with said conductive fixture thereby to complete an electrical path for said windings during starting, the current through said fixture circuit being minor with reference to the current through said lamps after starting thereof, said starting capacitor having sufficient reactance to substantially limit the current flow through said second secondary winding and said second secondary winding having a relatively high impedance thereby further limiting the current flow therethrough.

8. Ballast transformer apparatus for starting and operating a pair of serially connected fluorescent lamps mounted in a conductive fixture and having spaced electrodes at their respective ends comprising, a magnetic core having a primary winding and a first secondary winding thereon, circuit means connecting the high potential end of said primary winding and the low potential end of said secondary winding, means providing leakage reactance between said windings, output leads for connecting said secondary winding across said pair of serially connected lamps, a pair of input lines on said primary winding for connection to a source of alternating current, a second secondary winding on said oore, said windings being wound and connected in voltage adding relation, circuit means including a starting capacitor for connecting said second secondary winding across one of said lamps in a series starting circuit with said first secondary winding, and means for connecting the low potential end of said primary winding in circuit with said conductive fixture thereby to complete an electrical path for said windings during starting, the current through said fixture circuit being minor with reference to the current through said lamps after starting thereof.

9. Ballast transformer apparatus according to claim 8 above wherein said circuit means for connecting the high potential end of said primary winding to the low potential end of said secondary winding includes a high resistance for isolating said primary winding from the operating circuit after said lamps are started.

10. A lighting system comprising, a conductive fixture, at least one fluorescent lamp mounted alongside said fixture, a high reactance ballast transformer comprising a magnetic core having a primary winding and a first secondary winding thereon, circuit means con necting the high potential end of said primary winding and the low potential end of said secondary winding in autotransformer relationship, output leads connecting said lamp to at least said secondary winding, 21 pair of input lines on said primary winding for connection to a source of alternating current, a second secondary winding on said core, said windings being wound and connected in voltage adding relation, and circuit means including a starting capacitor for connecting said second secondary winding across said lamp in a series starting circuit with at least said first secondary winding, said starting capacitor having sufi'icient reactance to render said second secondary winding substantially ineffective after said lamps are started.

11. A lighting system comprising a conductive fixture, a pair of serially connected fluorescent lamps mounted alongside said fixture, a high reactance ballast transformer comprising a magnetic core having a primary winding and a first secondary winding thereon, circuit means connecting the high potential end of said primary winding and the low potential end of said secondary winding in autotransformer relation, output leads for connecting said secondary winding across said pair of serially connected lamps, a pair of input lines on said primary windings for connection to a source of alternating current, a second secondary winding on said core, said windings being wound and connected in voltage adding relation, and circuit means including a starting capacitor for connecting said second secondary winding across one of said lamps in a series starting circuit with said primary and said first secondary windings, said starting capacitor having sufiicient reactance to substantially limit the current flow through said second secondary winding and said second secondary winding having a relatively high impedance thereby further limiting said current flow therethrough.

References Cited in the file of this patent UNITED STATES PATENTS 2,810,100 Strecker Oct. 15, 1957 2,820,180 Feinberg Jan. 14, 1958 2,824,242 Cates Feb. 18, 1958 2,861,217 Feinberg Nov. 18, 1958 2,870,378 Abrahams Jan. 20, 1959