US2736841A - Electromagnetic switching means - Google Patents

Description

Feb. 28, 1956 H. w. LORD 2,736,841

ELECTROMAGNETIC SWITCHING MEANS Filed Aug. 24, 1951 His Attorney.

United States Patent() ELECTROMAGNETIC SWITCHING MEANS Harold W. Lord, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application August 24, 1951, Serial No. 243,486

6 Claims. (Cl. 315-174) My invention relates to frequency selective electromagnetic switching systems, and more particularly to carrier current switching systems especially adapted to control electric discharge lamps and the like.

When discharge lamps, such as fluorescent lamps or the like, are connected in multiple, or parallel, circuit relation for street lighting applications, it may be desirable to control the energization and de-energization of the lamps remotely, as by a carrier current electromagnetic switching system.

It has been common practice to connect electric discharge lamps in parallel circuit relation to a pair of supply conductors through separate ballast-type autotransformers each having one extended secondary winding loosely coupled to the primary winding to provide a ballast impedance for the connected lamp, and a second extended secondary winding closely coupled to the primary winding with a power factor correction capacitor connected across the closely coupled secondary winding or across that secondary winding and a part or all of the primary winding. The power frequency is commonly 60 cycles per second, and a commonly-utilized carrier frequency superimposed upon the supply conductors has been 720 cycles per second. 4 l

With the foregoing arrangement, when it has been sought to control a carrier frequency responsive switching device or relay connected for energization across the supply conductors, it has been found that the power factor correction capacitor has provided such a low impedance atthe carrier frequency that it virtually short-circuits the conductors, and thus so limits the voltage at carrier frequency that the relay has failed to operate.

- and improved carrier current switching system for electric discharge lamps and the like.

More specifically, it is an object of my invention to provide means for preventing the power factor correction capacitor in a discharge lamp ballast transformer from effectively short circuiting the supply conductors for voltages of carrier frequency.

In carrying out my invention in one form, I provide a lamp ballast of the auto-transformer type, wherein a primary winding is adapted to be connected across the supply conductors through a carrier frequency responsive relay, a pair of oppositely extending secondary windings are connected in series circuit relation with the primary winding at opposite ends thereof, and a power factor correction capacitor is connected across the primary and one of the secondary windings, the discharge lamp .load being connected across the primary winding and the other extended secondary winding. If desired, of course, the relay contacts may be connected in the transformer output circuit. I so arrange the primary and secondary windings upon the ballast transformer that a relatively large leakage inductance is provided between the pri- W 2,736,841 ce Patented Feb. 28, 1956 mary winding and the secondary winding associated with the lamp, thereby to provide a ballast iimpedance for the lamp. Between the primary winding and the secondary winding associated with the power factor correction capacitor, I provide an appreciable but relatively small amount of leakage inductance, so that for power frequency voltages the shunt path through the capacitor is effectively of capacitive reactance, while for carrier frequency voltages the small leakage inductance is such that the shunt path through the capacitor is effectively inductive in nature. This second leakage inductance, the reactance of which is small at power frequency but large at carrier frequency, thus acts as a series inductance in y the capacitor circuit and serves to limit the current through v to such auto transformers whether the power factor correction capacitor be connected across only the associated secondary winding or across that winding in series with a part or all of the primary winding. Also, the two secondary windings may extend from the same end rather than from opposite ends of the primary winding.

My invention itself will be more fully understood and its various objects and advantages further appreciated by referring now to the following detailed specification, taken in conjunction with the accompanying drawing, in which Fig. 1 is a schematic circuit diagram of a frequency selective discharge lamp switching system embodying my invention; and Fig. 2 is a diagrammatic cross-sectional representation of a lamp ballast transformer having the primary and various secondary windings arranged thereon in accordance with my invention.

Referring now to the drawing, and more particularly to Fig. 1, I have there shown an electric discharge lamp supply and switching system comprising a pair of supply conductors 1 having connected thereto in parallel circuit relation a source 2 of alternating electric current supply of power frequency, for example 60 cycles per second, and a source 3 of alternating electric current supply of an appreciably higher carrier frequency, for example 720 cycles per second. A pair of electric discharge lamps 4 having terminals 4a and 4b are adapted to be energized in parallel circuit relation from the power conductors 1, each through an associated relay 5 having normally an open contact 5a and a tuned actuating winding 5b. The actuating windings 5b are connected for energization across the supply conductors 1 and are selectively responsive to the carrier frequency from the source 3.

For energizing the lamps 4 in parallel circuit relation, I provide for each lamp a ballasting auto-transformer having a primary winding 6 and a pair of opp'ositely extending secondary windings 7 and 8 connected in series circuit relation with the primary winding. Each primary winding 6 has a pair of input terminals 6a and 6b which are adapted to be connected to the supply conductors 1 through the normally open contact 5a of the associated relay 5. Each auto-transformer is of the iron core type and is provided with a core 9, having the windings 6, 7 and 8 mounted thereon. Both secondary windings 7 and 8 on each transformer are loosely coupled to the primary winding 6, insofar as an appreciable leakage reactance is provided between the primary winding and each secondary winding. As best shown at Fig. 2, this leakage reactance is provided by magnetic shunts interposed between the windings, a shunt 9a being interposed between the primary winding 6 and the secondary winding 8 and a shunt 9b being interposed between the primary winding 6 and the secondary winding 7. The core and the magnetic shunts are schematically indicated at Fig. 1 and are diagrammatically illustrated at Fig. 2, wherein the windings 6, 7 and 8 are shown in cross-sectional view. It will be noted from Fig. 2 that the magnetic shunt 9a between the primary winding 6 and the secondary winding S, across which the lamp load is adapted to be connected, is of relatively large section, so that these windings are quite loosely coupled and the leakage reactance therebetween is appreciable even at the low power frequency. On the other hand, the magnetic shunt 9b between the primary winding 6 and the secondary winding 7 is of relatively small section, and the windings 6 and 7, while loosely coupled insofar as some appreciable leakage reactance is intentionally provided therebetween, are more closely coupled than are the windings 6 and 8. Thus, the leakage reactance between the windings 6 and 7 is of small, and indeed of relatively inappreciable value, at the low power frequency, but is of appreciable value at the high carrier frequency.

Referring now more particularly to Fig. l, it will be observed that a power correction capacitor llt) is connected across the primary winding 6 and the extended secondary winding 7 in series circuit relation. A terminal 8a at the end of the secondary winding 3 and the terminal 6a of the primary winding constitute a pair of output terminals for the transformer, across which the lamp 4 is connected. lt will of course be understood by those skilled in the art that in the general case the lamp terminals 4a and 4b represent load terminals between which there may be connected any desired type of electric load device, the electric discharge lamps 4 being shown by way of illustration, since my invention is particularly well adapted for use in conjunction with a load of this type. It will be further understood that if desired the relay contacts 5a may be connected between the load terminals and the transformer output terminals.

It will now be apparent that in operation, when the high carrier frequency is applied to the power conductors l, the load relays 5 are energized and close their contacts 5a, thereby to connect the discharge lamps 4 to the supply conductors through their respective auto-transformers. Upon such connection, the lamps 4 are energized from the power frequency source 2 through the transformer windings 6 and 8. As is well understood by those skilled in the art, the leakage reactance between windings 6 and 8 of each transformer, which is relatively large at power frequency, serves as a series ballast impedance for the associated discharge lamp 4. The leakage reactance between the windings 6 and 7 is relatively low at power frequency, so that it has no appreciable effect upon the power factor corrective action of the capacitor lt). For the high carrier frequency currents, however, the leakage reactance between the windings 6 and '7 is of high value, while the capacitive reactance of the capacitor l@ is lower for the high carrier frequency currents than for the low frequency `power currents. By proper selction of constants, the leakage reactance between the windings 6 and 7 is made less than the reactance of the capacitor itl for power frequency currents and greater than the reactance of capacitor 10 for carrier frequency currents, so that this leakage revactance serves as a current limiting impedance in series with tht` capacitor 1t) for high carrier frequency currents, but has no appreciable effect upon the power frequency currents.

While i have described a preferred embodiment of my :invention by way of illustration, many modifications will loccur to those skilled in the art and I therefore wish to have it understood that l intend in the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

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

li in a frequency selective electromagnetic switching system for energizing an electric load device at the lower of two frequencies from a pair of supply conductors having connected thereto in parallel circuit relation two sources of -alternating current supply of appreciably different frequencies, an auto-transformer having loosely coupled primary and secondary windings'providing a leakage reactance between said windings which is relatively inappreciable at said lower source frequency but which is appreciable at said higher source frequency, said autotransformer having a pair of output terminals adapted to be connected to said load device and said primary winding having a pair of input terminals adapted to be connected to said supply conductors, a capacitor connected across at least said secondary winding, and having at said lower source frequency a reactance which is greater than said leakage reactance and which at said higher source frequency is less than said leakage reactance so that said leakage reactance serves as a current limit impedance in series with said capacitor for said higher source frequency but has no appreciable effect upon current ow at said lower source frequency and electromagnetic switching means connected to energize said load device through said transformer, said switching means being adapted to be connected for energization to said supply conductors and being selectively responsive to the higher of said source frequencies.

2. In a frequency selective electromagnetic switching system for energizing an electric load device at the lower of two frequencies from a pair of supply vconductors having connected thereto in parallel circuit relation two sources of alternating electric current supply of appreciably different frequencies, an auto-transformer having a primary winding and an extended secondary winding connected in series circuit relation therewith and loosely magnetically coupled thereto, said auto-transformer having a pair of output terminals adapted to be connected to said load device and said primary winding having a pair of input terminals adapted to be connected to said supply conductors, a capacitor connected across at least said secondary winding, said capacitor having a capacitive reactance greater than the inductive leakage reactance between said primary and secondary windings at the lower said frequency but less than said leakage reactance at the higher said frequency, and electromagnetic switching means connected to energize said load device through said transformer, said switching means being adapted to be connected for energization to said supply conductors and being selectively responsive to said higher frequency;

3. In a carrier current electromagnetic switching sysstem for energizing an electric load device at power frequency from a pair of supply conductors having connected thereto in parallel circuit relation a low frequency source of power current supply and a high frequency source of carrier current supply, an auto-transformer having a primary winding and an extended secondary winding connected in series circuit relation, therewith, said auto-transformer having a pair of output terminals adapted to be connected to said load device and said primary winding having a pair of input terminals adapted to be connected to said'supply conductors, magnetic shunt means interposed between said primary and secondary windings to provide a leakage reactance therebetween, a capacitor connected across at least said secondary winding, said capacitor having a capacitive reactance 'greater than said leakage reactance at said power frequency but less than said leakage reactance at said carrier frequency, and electromagnetic switching means connecting said I input terminals to said supply conductors, said switchcoupled thereto, said primary winding having a pair of input terminals adapted to be connected to the supply conductors, the leakage rea/.trance between one of said secondary windings and said primary winding being appreciable even at the lower of said source frequencies, the leakage reactance between the other of said secondary windings and said primary winding being relatively inappreciable at the lower of said source frequencies but being appreciable at the higher of said source frequencies, a capacitor connected across said primary winding and said other of said secondary windings and having relative to the leakage reactance between said other secondary winding and said primary winding, a capacitive reactance which at said lower source frequency is greater than said last mentioned leakage reactance and renders its circuit effectively of capacitive reactance and which at said higher source frequency is less than said last mentioned leakage reactance and renders its circuit effectively of inductive reactance limiting high frequency current ow therethrough, a pair of output terminals on said auto-transformer having connected therebetween said primary winding and said one of said secondary windings and adapted to be connected to the load device, and electromagnetic switching means connected to energize the load device through said transformer, said switching means being adapted to be connected for energization to said supply conductors and being selectively responsive to the higher of said source frequencies.

5. In a frequency selective electromagnetic switching system for energizing an electric discharge load device at the lower of two frequencies from a pair of supply conductors having connected thereto in parallel circuit relation two sources of alternating electric current supply of appreciably different frequencies, any auto-transformer having a primary winding and a pair of oppositely extending secondary windings connected in series circuit relation therewith and loosely magnetically coupled thereto, said primary winding having a pair of input terminals adapted to be connected to said supply conductors, a capacitor connected across said primary Winding and one of said secondary winds, said capacitor having a capacitive reactance greater than the inductive leakage reactance between said primary winding and said one secondary winding at the lower said frequency but less than said leakage reactance at the higher said frequency, a pair of output terminals on said auto-transformer having connected therebetween said primary winding and the other said secondary winding and adapted to be connected to said load device, the leakage reactance between said primary winding and said other secondary winding providing a load ballast impedance at said lower frequency,

and electromagnetic switching means connected to energize said load device through said transformer, said switching means being selectively responsive to said higher frequency and being connected for energization to said input terminals.

6. lnr a carrier current electromagnetic switching system for energizing an electric discharge lamp load at power frequency from a pair of supply conductors having connected thereto in parallel circuit relation a low frequency source of power current supply and a high frequency source of carrier current supply, an auto-transformer having a primary winding and a pair of oppositely extending secondary windings connected in series circuit relation therewith, said primary winding having a pair of input terminals adapted to be connected to said supply conductors, magnetic shunt means interposed between said primary winding and a first of said secondary Windings to provide therebetween a first inductive leakage reactance of low value at said power frequency, a capacitor connected across said primary and first secondary windings, said capacitor having a capacitive reactance greater than said first leakage reactance at said power frequency but less than said lirst leakage reactance at said carrier frequency, magnetic shunt means interposed between said primary winding and the other of said secondary windings to provide therebetween a second inductive leakage reactance of higher value than said first inductive leakage reactance at said power frequency, a pair of output terminals having connected therebetween said primary and said other secondary winding and adapted to be connected to said discharge lamp, and electromagnetic switching means connecting said input terminals to said supply conductors, said switching means being selectively responsive to said carrier frequency and being adapted to be connected for energization to said input terminals, whereby said second leakage reactance ballasts said lamp and said iirst leakage reactance limits capacitor current upon carrier frequency application.

References Cited in the file of this patent UNITED STATES PATENTS 1,969,498 Bivens Aug. 7, 1934 1,994,603 Blatterman Mar. 19, 1935 2,025,471 Osborne Dec. 24, 1935 2,212,198 Sola Aug. 20, 1940 2,358,725 Mauerer Sept. 19, 1944 2,486,307 Mauerer Oct. 25, 1949 2,487,092 Bird Nov. 8, 1949 2,509,188 Feinberg May 23, 1950 2,565,234 Ilker Aug. 21, 1951

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