US3160784A

US3160784A - Safety systems in apparatus for operating electric discharge devices

Info

Publication number: US3160784A
Application number: US435753A
Authority: US
Inventors: Charles E Strecker
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1954-06-10
Filing date: 1954-06-10
Publication date: 1964-12-08
Anticipated expiration: 1981-12-08

Description

Dec. 8, 1964 C E. STRECKER SAFETY sYsTEMs' IN APPARATUS FOR OPERATING ELECTRIC DISCHARGE DEVICES Filed June 10, 1954 INVENTOR. Char/es E. Str'e c/rer:

ms A122; 0 r-ney.

United States Patent 3,16tl,784 SAFETY SYTEMS IN APhARATUS FER GPER- ATENG ELECTRIC DHSCGE DEVICES Charles E. Strecker, Fort Wayne, Ind., assignor to General Electric Company, a corporation of New York Filed lune 19, 1954, Ser. No. 435,753 13 Claims. (Cl. 315-478) This invention relates to electric discharge devices and more particularly to transformers for starting and operating 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 these two functions, i.e., current limiting and the provision of 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 I 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 coils on diiferent 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. In the past, the high starting voltage has frequently been achieved by using a transformer with the coils connected as an autotransformer, i.e., the primary and secondary are connected in series so that their voltages are additive.

It will be seen that, since the output voltage may be reduced after the device has started, the autotransformer connection may become unnecessary and, in fact, undesirable. This results from the fact that a person handling the device and having one electrode thereof connected to ,the line may complete a circuit through himself to ground, fire the device, and thus receive a lethal shock. This danger is not present where the secondary and primary are substantially isolated during operation of the device. Also, while autotransformer connections have greatly aided in the starting of discharge devices, such connections result in a relatively high voltage between the discharge device and ground. This arrangement is dangerous because of the possibility that a person working on the discharge device (for example, replacing it) may act as a ground from the high voltage side of the device to, for instance, the grounded fixture, and thereby cause and the like.

3,160,784 Fatented Dec. 8, 1964 a possiblylethal current flow. It is, therefore, desirable to provide means which will limit the current flow from the device to ground to a value which is safe for human beings. It will also be seen that it is advantageous to have the primary and secondary of the transformer connected as an autotransformer for the starting operation and as substantially isolated transformer for the operation of the device. For optimum etficiency this change should be automatic and not require additional switches In addition to these features, a highresistance ground connection from the line to the fixture is desirable so that if the grounded side of the line should open the transformer cannot be excited through ground.

It is, therefore, an object of this invention to provide an improved starting and operating circuit for an electric discharge device which will incorporate the desirable features 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 particularity in the claims annexed to and forming a part of this specification.

This invention, in one embodiment thereof, provides a transformer having the secondary connected to the electrodes of an electric discharge device. The primary and the secondary of the transformer are connected in series, so that their open circuit voltages are additive, by means of a line containing a fairly high resistance, which is preferably on the order of at least one megohm. The additive voltages of the primary and the secondary will be applied to one of the electrodes of a discharge device which is adapted to be placed in capacitive relation to a conducting fixture grounded to one side of the line. A fairly small current will flowfrom the electrode to the fixture, and this small current will bring about increased ionization in the area about the electrode. The circuit may be completed by grounding the fixture to one side of the line. The increased ionization, which may be in co-operation with heating of the electrodes, will cause a breakdown of the gas contained within the device.

Once the device starts, the amount of current between the first electrode and the fixture becomes even smaller as the secondary voltage decreases, and the device will be in a closed circuit with the secondary. When this occurs,

the only way for a circuit to be completed" between instances where the fixture of the device will not normally be grounded. I

As explained thus far, the circuit has a low power factor since no correction has been made. In a modification of this invention, the improvements may be applied to a high power factor circuit by connecting a condenser across a portion of the secondary.

charge device incorporating the desirable features of this invention; and

FIGURE 2 is a schematic diagram of a high power factor transformer for a discharge device which also incorporates the improvements of this invention. 7

Referring now to, FIGURE 1 of the drawing, there is shown a voltage, step-up transformer, generally indicated by the numeral 1. This transformer has a core, schematically indicated at 2, and is preferably provided with a'leakage leg, schematically indicated at 3, to provide a high reactance construction as is well known in the art. A primary coil 4 and a high voltage secondary coil 5 are arranged on the core 2; Depending upon the characteristics of the magnetic circuit desired, secondary 5 may be all on the side of leakage leg 3 remote from primary 4 or may be partly arranged on the same side of leakage leg 3 as the primary 4. Transformer 1 is a high reactance transformer, as indicated by the inclusion of a leakage leg 3, so that the load current will be limited to the desired value once the discharge device is started. Secondary 5 preferably has in series therewith, or as a part thereof, a pair of auxiliary secondaries 6 and 7 for a purpose tov be explained below. Primary 4 is connected across a source (not shown) of alternating current voltage (generally on the order of 115 volts) by a pair of lines 8 and 9. Line 9, which is the normally grounded side of the line, is grounded to fixture -10 of the device by a ground 11 containing a high resistance 12 which is preferably on the order of at least one megohm. A line 13 connects the end of primary 4 which is connected to the ungrounded side of the supply line 8 to one end. of secondary 5; line 13 also includes a high resistance 14, which is. also preferably on the order of at least one megohm. An electric discharge device 15, such as a fluorescent lamp, has a pair of

electrodes

16 and 17 sealed therein. Electrode 16 is connected across portion 6 of the secondary by lines 18 and 19, and electrode 17 is connected across portion 7 of the. secondary by lines 20 and 21.

When lines 8 and 9 are connected across the source of alternating current, the current will flow through primary 4 so as to, excite the secondary 5. The open circuit voltage resulting in secondary 5 will be a function of the number of turns of the secondary with respect to the number of turns of the primary 4. In addition to the open circuit voltage produced in secondary 5, the voltage across primary 4 will be. added thereto by connection of the secondary and primary through line 13. There will, there fore, be a relatively'high voltage applied to electrode 16 of the lamp 15 with reference to grounded line 9 and fixture 10. Fixture 10 isarranged to act with electrode 16 as a capacitor, and a relatively small current will pass primary or the secondary. It is also possible to omit these sections and provide a cold cathode starting arrangement, as is well known in the art. The heating of

electrodes

16 and 17 and the ionization of the gas around electrode 16 will break down the gas in device 15, and the current will arc across between the'electrodes to start the device. In a typical one-lamp assembly, the secondary starting voltage will be on the order of 200 volts which with the primary voltage, produces approximately 315 volts between electrode 16 and grounded fixture 10. It will, however, be understood thatthis invention is not limited to circuits involving these values.

Once the circuit has been completed between

electrodes

16 and 17, the lamp will be kept in operation by secondary 5 which will be in a closed circuit with the device 15. This occurs because, after the completion of the circuit across the electrodes, the amount of current between electrode 16 and fixture 10 becomes infinitesimal with relation to the current between

electrodes

16 and 17 and there is, therefore, only a very minor circuit, from a current standpoint, completed through the ground 11. Consequently, trans-former 1 will, for practical purposes, act as" an ordinary high reactance isolated transformer with secondary 5 being excited by primary 4 to produce suflicient current to keep device 15 in operation. The secondary voltage will drop, once the arc is struck between

electrodes

16 and 17, to diminish even further the current flow throughrthe fixture 10. The inclusion of high resistance 12 in ground 11 has the effect that if the 'line 9 should be opened, it will not be possible to excite the transformer through the ground 11.

It will be seen from the foregoing that this circuit provides a high voltage for the starting of device 15 by connecting primary 4 and secondary 5 as an autotransformer, and that full protection against shock hazard, in the form'of resistance 14, is provided during this connection. The autotran-sformer connection permits the secondary to be far smaller than would be possible otherwise, and the circuitry provided insures that this connection will cease to be effective once the device has started thereby completing the protection against shock hazard (by means of resistances 12 and 14).

The embodiment of FIGURE 2 will now be explained, usinglike numerals for, those parts which correspond to parts described in FIGURE 1. The main, difference in the embodiment of FIGURE 2 is the provision in the secondary

Softwo parts

22 and 23, with a capacitor 24 being connected across part 23 which is wound. on the same portion of the core as primary 4. Part 23 of the secondary acts as a power factor correcting winding and provides additional starting aid. The capacitor 24 is made sufficiently large to provide essentially unity power factor. All other features of the circuit shown in FIG- URE 2' are similar to those of FIGURE 1, and the operation is the same as that of the circuit of FIGURE 1 with the single exception of the power factor correcting winding andcapacitor,

. It will be understood that while both circuits shown utilize a ballast transformer having a high reactance, the invention may be' used advantageously where a low reactance transformer is used and other ballasting means areprovided- It will also be understood that while both circuits described show a single electric discharge device, it is possible touse two or more lamps in, for instance, a lead-lag circuit by' providing additional leads to the extra electrodes from an additional secondary.

Also, while a rapid start circuit has been shown, that is,

is connected to line 9 by ground 11. During this time,

electrode 16 is being heated as a result of the output of SGOUOH- 6 of thesecondary, and electrode 17 is being heated as a result of the output of section 7 of the secthe electrodes are heated both before and after starting, the inventionmay be advantageously applied to atrigger start circuit, where the heating of the electrodes issubstantially eliminated after starting, and to other types of electrode connections, such as those provided in the cold cathode startingmethodr V Therefore, while this. invention has been explained by describing a particular embodiment 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 I claim as new and desire to secure by Letters Patent of the United States is:

1. Ballast transformer apparatus for starting and oper ating a fluorescent lamp mounted in a conductive fixture and having two spaced electrodes at the respective ends of said lamp comprising, a high reactance transformer including a magnetic core having a primary winding and a high voltage secondary winding thereon and 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 pair of output lines on said secondary winding for respective connection to the electrodes of said lamp, a high resistance connected between the high voltage end of said primary winding and the low voltage end of said secondary winding, said windings being wound and connected in volt age adding relation, and means for connecting the low voltage end of said primary winding in circuit with said conductive fixture whereby said transformer apparatus provides autotransformer type starting voltage and isolated transformer type running voltage for said lamp.

2. The ballast transformer apparatus of claim 1 wherein said means for connecting the low voltage end of said primary winding in circuit with said fixture comprises a high resistance.

3. The ballast transformer apparatus in claim 1 wherein a capacitor is connected across at least a portion of said secondary winding for improving the power factor of said transformer apparatus.

4. The ballast transformer apparatus of claim 1 wherein said high resistance is of the order of at least one megohm.

5. Ballast transformer apparatus for starting and operating a hot cathode type fluorescent lamp mounted in a conductive fixture and having two spaced electrodes at the respective ends of said lamp comprising, a high reactance transformer including a magnetic core having a primary winding and a high voltage secondary winding thereon and means providing leakage reactance between said primary and secondary windings, a pair of input lines on said primary winding for connection to a source of alterating current, a first pair of output lines connected to one end portion of said secondary winding for connection across one of the electrodes of said lamp and a second pair of output lines connected to the other end of said secondary winding for connection across the other elec trode of said lamp whereby said secondary winding is connected in parallel with said lamp and provides heating voltages for the electrodes thereof, a high resistance connected between the high voltage end of said primary Winding and the low voltage end of said secondary winding, said windings being wound and connected in voltage adding relation, 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 said secondary windings during starting, the current through said fixture circuit being minor with reference to the current through said lamp from said secondary winding after starting thereof.

6. The ballast transformer apparatus of claim 5 wherein said means for connecting the low voltage end of said primary winding in circuit with said fixture comprises a high resistance.

7. The ballast transformer apparatus of claim 6 wherein both said high resistances are of the order of at least one megohm.

8. In combination, a conductive fixture, a fluorescent lamp mounted alongside said fixture, a high reactance ballast transformer comprising a magnetic core having a primary winding and a high voltage secondary winding thereon, said secondary winding being connected in parallel with said lamp, a high resistance connected between I 6 the high voltage end of said primary winding and the low voltage end of said secondary winding, said windings being wound and connected in voltage adding relation, and an electric circuit connecting the low voltage end of said primary winding to said conductive fixture.

9. In combination, a conductive fixture, a hot cathode type fluorescent lamp mounted adjacent said fixture, a

high reactance transformer comprising a magnetic core having a primary winding thereon .and a high voltage secondary winding thereon, a first portion'of said secondary winding at one end thereof being connected across one electrode of said lamp, a second portion of said secondary winding at the other end thereof being connected across the other electrode of said lamp, a capacitor connected across at least a portion of said secondary winding, a high resistance connected between the high voltage end of said primary winding and the low voltage end of said secondary winding, and a second high resistance connected between the low voltage end of said primary winding and said conductive fixture.

10. A system for igniting and operating at least one gaseous discharge lamp from a source of AC. voltage substantially less than the igniting voltage of the said lamp which comprises, an iron core transformer having a primary winding and at least one secondary winding inductively coupled thereto to have a voltage induced in the secondary winding, an elongate gaseous discharge lamp in circuit with the secondary winding, a fixture supporting said lamp and having an elongate, grounded metal part thereof extending along the length of said lamp contiguous and capacitively coupled therewith, a high ohmage resistor connected between one terminal of the primary winding and one terminal of said lamp and providing a connection with said circuit electrically separating the primary and said circuit, the second terminal of the pri mary winding being grounded, the primary winding being connected across said source, the secondary winding being connected to the lamp to provide igniting and operating voltage therefor, the instantaneous open circuit voltage sense of said primary winding relative to said lamp and secondary winding being such as to provide an augmenting additive starting voltage for said lamp, said resistor having a value such as to provide a substantial electrical connection between the primary winding and the circuit, including the secondary winding while limiting current flow through the system to a relativeley safe value.

11. Apparatus for igniting and operating at least one fluorescent discharge lamp which comprises, a source of relatively low A.C. voltage, a fluorescent discharge lamp and a fixture supporting the same, metallic starting aid means arranged in capacitive relation to the discharge lamp and metallically connected with said fixture, a transformer having an iron core and a primary winding, and two secondary windings in electromagnetic relation thereon, the primary winding being connected across the source and having one terminal thereof metallically connected with said fixture, the first secondary winding being closely coupled with the primary winding and the second secondary winding being loosely coupled relative to the primary winding and connected in series with the fluorescentdischarge lamp and having one terminal thereof making a juncture with one terminal of the fluorescent discharge lamp, a high ohmage isolating resistor in series with the first secondary winding and together therewith connected between the second terminal of the primary and the said juncture, with the first secondary winding in voltage aiding relation to the primary winding, the combined voltage of said primary and first secondary windings being applied between said metallic starting aid means and said fluorescent lamp, but excluded from the operating circuit of said lamp.

12. A structnre as claimed in claim 11 in which the References Cited in the file of thispatent second secondary winding is in additive voltage rel-ation- UNITED STATES PATENTS vship to the primary and first secondary windings considering a series circuit containing all of said windings, where- 1814499 Von Wedel 7 July 14, 1931 by during starting its voltage will aid the voltage of said 2,010,879 MUtSaeYS 13, 1935 primary, and first-secondary Winding, the voltages of the 21141842 111mm! P 19, 1938 three windings being applied between said metallic start. 2,392,213 H l Nov. 17, 1942 ing aid means and said fluorescent discharge lamp. 2,372,357 Setchell P 1945 13. A structure as claimed in Claim 11 in which the 2,446,152 Alford July 27, 1948 source comprisesa conventional power line having a 2,552,111 y 8, 1951 grounded side and the first terminal of said primary wind- 2,565,234 a- Allg- 1951 2,683,240 Strange July 6, 1954 ing is conneeted to said grounded side of said line.

Claims

1. BALLAST TRANSFORMER APPARATUS FOR STARTING AND OPERATING A FLUORESCENT LAMP MOUNTED IN A CONDUCTIVE FIXTURE AND HAVING TWO SPACED ELECTRODES AT THE RESPECTIVE ENDS OF SAID LAMP COMPRISING, A HIGH REACTANCE TRANSFORMER INCLUDING A MAGNETIC CORE HAVING A PRIMARY WINDING AND A HIGH VOLTAGE SECONDARY WINDING THEREON AND 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 PAIR OF OUTPUT LINES ON SAID SECONDARY WINDING FOR RESPECTIVE CONNECTION TO THE ELECTRODES OF SAID LAMP, A HIGH RESISTANCE CONNECTED BETWEEN THE HIGH VOLTAGE END OF SAID PRIMARY WINDING AND THE LOW VOLTAGE END OF SAID SECONDARY WINDING, SAID WINDINGS BEING WOUND AND CONNECTED IN VOLTAGE ADDING RELATION, AND MEANS FOR CONNECTING THE LOW VOLTAGE END OF SAID PRIMARY WINDING IN CIRCUIT WITH SAID CONDUCTIVE FIXTURE WHEREBY SAID TRANSFORMER APPARATUS PROVIDES AUTOTRANSFORMER TYPE STARTING VOLTAGE AND ISOLATED TRANSFORMER TYPE RUNNING VOLTAGE FOR SAID LAMP.