US2793326A

US2793326A - Ballast transformer for electric discharge devices

Info

Publication number: US2793326A
Application number: US474100A
Authority: US
Inventors: Charles E Strecker
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1954-12-09
Filing date: 1954-12-09
Publication date: 1957-05-21
Anticipated expiration: 1974-05-21

Description

i 21, 1957 I c. E. STRECKER 2,793;326

BALLAST TRANSFORMER FOR ELECTRIC DISCHARGE DEVICES Filed Dec. 9, 1954 2 Sheets-Sheet 1 //7 1/922 tor Char/6S 5 Strife/f9;

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1957 c. E. STRECKER 2,793,326

BALLAST TRANSFORMER FOR ELECTRIC DISCHARGE DEVICES Filed Dec. 9, 1954. 2 Sheets-Sheet 2 /z71 ez72for: Char/es 5 Sit/"eater".

1 fittorney.

United States Patent BALLAST TRANSFORMER FOR ELECTRIC DISCHARGE DEVICES Charles E. Strecker, Danville, Ill., assignor to General Electric ompany, a corporation of New York Application December 9, 1954, Serial No. 474,100

4 Claims. (Cl. 315-257) This invention relates to electric discharge devices, and more particularly to ballast transformers for use in starting and operating circuits for such devices.

It is a characteristic of electric discharge devices, 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 conveniently available. When electric discharge devices are operated on alternating current, it is conventional practice to'provide a single high reactance ballast transformer to perform two functions, i. e., limit the current and pro vide a high initial starting voltage. Such a transformer provides a high open circuit voltage for starting and also, by virtue of its high reactance, provides impedance during normal operation to limit the current flow.

A high reactance transformer is one in which the primary and secondary coils are loosely coupled, so that when the transformer is carrying load there is a substantial amount of leakage flux, and the voltages induced in the coils by this leakage flux cause the transformer to have a relatively high effective series reactance, commonly known as leakage reactance. The conventional way of constructing such a transformer is to arrange the primary and secondary coils on difierent parts of the magnetic core and to provide a magnetic shunt between the coils 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 a desired value. The high starting voltage is frequently achieved by using a transformer with the coils connected as an autotransformer, i. e., the primary and secondary coils are connected in series so that their voltages are additive.

It has been found that there is a variety of applications where it is most desirable that a pair of electric discharge devices be used in one circuit and with one transformer. It will be readily apparent that such an arrangement permits considerable saving of space and equipment where two or more devices are to be used. In such arrangements, rather-than provide the exceedingly high voltage which would be necessary if the lamps were started simultaneously it is customary to provide circuits whereby the lamps will be lighted in sequence. In such circuits, the transformer is generally provided with a pair of secondary coils, one of which is connected across the first lamp to be lighted and the other of which is connected across the second lamp to be lighted. It has been found, however, that such circuits often require that a very high voltage be impressed across the first secondary coil in order to light the first lamp, and that once thefirst discharge device has been ignited the voltage across the first secondary coil increases to an even greater value thereby becoming even more undesirable. Such high voltages are far in 6SS of those which would perice mit economical and compact design of the coils without any fear of failure thereof. Thus, it is most desirable to maintain the voltage drop across the secondary coils at a value sufficient to start their associated electric discharge devices in sequence but little, if any, in excess of that value. It is, of course, also necessary that the coils provide suflicient impedance to limit the currents to the desired value when the electric discharge devices are in operation.

It is therefore an object of this invention to provide an improved ballast transformer which will incorporate the advantages set forth above.

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 particul arity in the claims annexed to and forming a part of this specification.

This invention, in one embodiment thereof, provides a ballast transformer for use in a starting and operating circuit for a pair of electric discharge devices. The transformer includes a capacitor adapted to be connected in series with one of the devices, and is provided with a core, a primary coil adapted to be connected to a source of alternating current, and a pair of serially connected high leakage reactance secondary coils wound on the core and adapted to be connected across the one destarts, one of the secondary coils is adapted to remain connected across it for current control purposes while the other secondary coils adapted to be connected in 'autotransformer relation with the primary coil across the other device in order to start it.

In :a preferred modification of the invention, a third secondary coil is provided in tightly coupled relation to the primary coil. This third coil is in series relation with the other two, and its voltage is subtractive with respect to the other two. The three coils are adapted to be connected across the one device, and the net voltage is sufiicient to cause it to start. Subsequent to starting of the one device, the operation is the same as before.

In the drawing, I

Figure 1 is a schematic diagram of a circuit including a ballast transformer constructed in accordance with the preferred embodiment of this invention;

Figure 2 is a schematic illustration of a circuit including a ballast transformer constructed in accordance with the other embodiment of this invention;

Figure 3 is a voltage vector diagram after one dis-- Referring now to Figure 1, there is shown a circuit including a preferred ballast transformer for operating a pair of electric discharge devices 1 and 2, such as fluo-v rescent lamps for instance. Lamp 1 is provided with a pair of electrodes 3 and 4 and lamp 2 has a similar pair of electrodes 5 and 6. While the electrodes shown in connection with the lamps 1 and 2 of Figure 1 are of the cold cathode start" type, that is, no preheating of the electrodes is provided, it will, of course, be understood that such preheating may be provided if so desired.

A ballast transformer, generally indicated by the nu meral 7, has a core 14, and positioned thereon is a primary coil 8 connected "across a pair of lines 9 and 10 which are adapted to lead to a source of alternating current (not shown). Transformer 7 is further provided with a secondary coil 11 positioned on core 14 so as to be tightly coupled to primary coil 8. The tight coupling may be effected by winding coil 11 on the same leg as coil 8, either in the same core opening or in a different core opening without a leakage gap therebetween as is well known in the art. In addition, second and third

secondary coils

12 and 13 are also Wound on the core 14 of transformer 7. Each of these latter secondary coils is provided with a loose coupling to the primary coil 8, that is, they are of the high leakage reactance variety to supply the necessary impedance to limit the current during operation of the lamps. The high reactance may be obtained by the use of leakage gaps, such as are indicated schematically at 15 and 16, as is well known in the art. As shown by the instantaneous polarities indicated in Figure 1, the voltage across coil 11 is subtractive with relation to the voltages across

coils

12 and 13 respectively. Lamp 1 is connected in series with a capacifor 17, and through secondary coil 13, in series with lamp 2.

When it is desired to start lamp 1, there is impressed across the lamp a voltage drop determined by the voltages of

coils

11, 12 and 13 in combination with, as previously stated, the voltage of coil 11 being subtractive. However, the net voltage is sutficient to start the lamp, and it will be observed that both

secondary coils

12 and 13 are used for the starting of lamp 1 so that an extremely high voltage across either one of these two secondary coils is not required.

Referring now to Figure 3, the voltage relationships after the starting of lamp 1 are set forth. It will be seen that ample voltage is provided in order to start lamp 2 and that this voltage is supplied without an unusually high voltage appearing across any one of the secondary coils. It will further be observed from Figure 3 that the presence of closely coupled winding 11 permits a relatively small voltage across secondary coil 12 during the subsequent starting of lamp 2.

Referring now to Figure 4, the voltage vectors of the different components of the circuit are shown when both lamps 1 and 2 are in operation. It will be apparent that both

coils

12 and 13 have voltages across them which are maintained well within desirable limits during operation, as opposed to the very high voltages frequently encountered during operation in the loosely coupled secondary coils of previous circuits of this type. It will be observed that the inclusion of the additional tightly coupled coil 11 permits the previously described changes in voltage through the

coils

12 and 13 to be effected without any unnecessary or undesirable reduction in impedance because the subtractive voltage is achieved through a tightly coupled coil which has little effect insofar as the reactance is concerned.

During operation, the current passes through lamp 1, capacitor 17, coil 13, and lamp 2; it will be observed that the lamps are operated in series, and that coil 13 provides the required impedance, with the capacitor providing the power factor correction made desirable by the presence of the impedance.

Referring now to Figure 2 of the drawmg, a second embodiment of this'invention will be described using like numerals for like parts. The principal difference between the Figures 1 and 2 is that the tightly coupled secondary coil 11 of Figure 1 has been omitted in the ballast transformer shown in Figure 2. As before, loosely coupled

secondary coils

12 and 13 are so arranged that they are connected across lamp 1 with their voltages being additive for starting purposes. When it is desired to start lamp 1, the voltages of coils 1 2 and 13 will be additive across the lamp so that the undesirablesituation of an tr m ly hi h vo tag a ss a in l 91 s elim nat as before. Referring now to Figured, which shows the voltage situation after the lighting of the first lamp, it

will be observed that, as with the previous circuit, ample voltage is provided across lamp 2 in order to cause ignition thereof. Referring now to Figure 6, it will be observed that, once both lamps have been started, the voltages across

coils

12 and 13 are maintained within satisfactory limits. The achievement of these relatively low voltages permits, of course, a more economical construction without forfeiting the advantages of this type of circuit.

It will be seen from the foregoing description that the two baliast transformers set forth in the drawing each. provide a sequence starting and series operation of two electric discharge devices wherein, at all points of starting and during operation, the voltages across the secondary coils are maintained within satisfactory levels so that adequate voltage is present for the purpose to be fulfilled, and yet a highly economical structure is available because the voltage is maintained at a value no higher than that necessary. While specific embodiments of the invention have been set forth in the drawings and in the above description, it will of course be apparent that improvements and modifications may be made without departing from the scope of the invention as defined in the appended claims.

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

c l. A ballast transformer for a pair of electric discharge devices comprising a capacitor adapted to be connected in series with one of said devices, a core, a primary coil wound on said core and adapted to be connected to a source of alternating current, a pair of serially connected high leakage reactance secondary coils wound on said core and adapted to be connected across said one device, said secondary coils being so wound that their voltages are additive thereby to start said one device, one of said secondary coils being adapted to be connected in autotransformer relation with said primary coil across said other device atfer starting of said one device thereby to start said other device.

2. A ballast transformer for a pair of electric discharge devices comprising a capacitor adapted to be connected in series with one of said devices, a core, a primary coil wound on said core and adapted to be connected to a source alternating current, a pair of serially connected high leakage reactance secondary coils wound on said core and adapted to be connected across said one device, said secondary coils being so wound that their voltages are additive thereby to start said one device, one of said secondary coils being adapted to be connected in autotransformer relation with said primary coil across said other device after starting of said one device thereby to start said other device, said one secondary coil being adapted to connect in series with said devices during operation thereof thereby to limit current flow therethrough.

, 3. A ballast transformer for a pair of electric discharge devices comprising a capacitor adapted to be connected in series with one of said devices, a core, a primary coil wound on said core and adapted to be connected to a source of alternating current, three secondary coils wound on said core, two of said secondary coils being of the high leakage reactance type and being so Wound that their voltages are additive, the third of said secondary coils being tightly coupled to said primary coil and being so wound that its voltage is subtractive with relation to the first two of said secondary coils, said secondary coils being connected in series and being adapted to be connected across said first device, said three secondary coils having anet voltage when so connected sufl'lcientto start said first device, one of said high leakage reactance secondary coils being adapted to be connected in autotransformer relation with said primary coil across said other device after starting of said one device thereby to start said other device.

-4. A ballast transformer for a pair of electric discharge devices comprising a capacitor adapted to be connected in series with one of said devices, a core, a primary coil Wound on said core and adagJted to be connected to a source of alternating current, three secondary coils wound on said core, two of said secondary coils being of the high leakage reactance type and being so wound that their voltages are additive, the third of said secondary coils being tightly coupled to said primary coil and being so wound that its voltage is subtractive with relation to the first two of said secondary coils, said secondary coils being connected in series and being adapted to be connected across said first device, said three secondary coils having a net voltage when so connected sufficient to start said first device, one of said high leakage reactance secondary coils being adapted to be connected in autotransformer relation with said primary coil across said other device after starting of said one device, said one high leakage reactance secondary coil being adapted to be connected in series with said devices and between the same during operation thereof thereby to limit current flow therethrough.

References Cited in the file of this patent UNITED STATES PATENTS 2,683,243 Feinberg July 6, 1954