US2410624A - Transformer apparatus - Google Patents

Description

Nov. 5,1946. 'u 2,410,624

TRANSFORMER APPARATUS Original Filed April 10, 1940 Patented Nov. 5, 1946 TRANSFORMER ArrAaA'rus Charles Philippe Boucher, Paterson, N. J., asslgnor, by mesne assignments, to National!!!- ventions Corporation, a corporation of New Jersey Original application April 10, 1940, Serial No. 328,970. Divided and this application February '7, 1941, Serial No. 377,922

1Claim. 1

My application for patent is a division of my co-pending application Serial No. 328,970, filed April 10, 1940. and entitled Transformer apparatus, now U. S. Letters Patent 2.312.867 of March 2, 1943, and the invention relates to electrical transformer apparatus, and more particularly to electrical transformer apparatus for supplying two or more negative loads, as, for example, in the operation of a luminescent tube system.

One of the objects of my invention is to provide simple, practical and thoroughly reliable trans former apparatus for supplying a plurality of separate negative loads and for ensuring automatically that substantialiy no voltage difference exists between the secondary circuits throughout the entire cycle of operation, and also that the currents in the various circuits are substantially the same.

Another object is to provide compact, inexpensive and highly efficient transformer apparatus for supplying a plurality of negative loads and for energizing in a dependable manner the remainder of said'loads after one or more of them has struck.

Another object of my invention is to provide a transformer system in which negative loads of either equal or unequal resistances may be operated from the same transformer.

A further object of my invention is the provision of a transformer apparatus of the character described which lends itself to rapid, efficient and economical production employing a minimum of different parts and requiring a minimum of skill in construction, installation and repair.

Another object is the provision of transformer apparatus of the character indicated which is peculiarly adapted to withstand the varying-conditions encountered in actual use, including shortcircuiting and grounding, of the whole or parts of the apparatus, without damage to the apparatus and the consequent necessity for shut-down and replacement or repairs.

Another object is the provision of high voltage transformer apparatus of the character indicated which supplies a plurality of separate loads in such a way as to require a minimum amountof insulation.

Other objects will be obvious inpart and in part pointed out hereinafter.

f The invention accordingly consists in the combination of elements, features of construction,

, and arrangement of parts, and in the several operational steps, all as described herein, the scope of the application of which is indicated in the app nded claim.

As conducive to a clearer understanding of certain features of my invention, it may be noted at this point that in the operation of a luminescent sign or display employing one or more lumines cent gas filled tubes of desired size and configuration, high potential electrical energy is required. Ordinarily the desired high potential electrical energy is supplied by alternating-current transformer apparatus connected to a standard single phase sixty cycle source at either one hundred and ten volts or two hundred and twenty volts. In order to supply the highest possible potential across the terminals of a tube without exceeding the maximum potential to ground permitted by the fire underwriters, it has been the practice to energize each tube from two coils having their one ends grounded placing the coils in series and their other ends connected to the tubc By this arrangement, each coil section may have induced in it a potential of about seven thousand five ing an operating potentials, each tube must have its own separate secondary winding. To use a separate transformer for each tube would result in an exceedingly high cost of equipment. Furthermore, the cost of the labor for installing equipment using a transformer for each tube would be obiectionably high because a separate charge is made for each connection to the source of supply.

In transformers I have heretofore designed for operating a luminescent sign or display, these objections are removed by placing two or more secondary windings in series upon a transformer core. Each winding comprises two coils and energizes one negative load. Each coil has associated with it a magnetic by-pass of high reluctance which limits the flow of current through the coil to a safe value. The major portion of the main magnetic flux passes through the bypass when the current flowing through the coil reaches such a value that it generates a counter- In order that the magnetomotive force which i sufllcient to buck most of the main mix. As' a consequence of the coils being mounted in series on the core, when the counter-magnetomotive force of one coil causes the main flux to be by-passed through a shunt, the flux then interlinking the remaining coils is no greater than it was before the first coil became loaded. In fact, due to the increased reluctance of its path, the flux coursing through the core will be somewhat diminished in amount. Consequently, the remaining coils will not have as high voltages induced in them 'as if they had become loaded first. Moreover, the instant at which the load of the remaining coils becomes operative lags substantially behind the time of striking of the first load.

One of the objects of my present invention therefore is to overcome the difficulties noted above and assure a substantially simultaneous striking of luminescent tubes although of slight inequalities in voltage ratings.

It may be noted further that in the operation of a luminescent tube sign or display, conditions may be encountered which cause a short-circuiting of part or all of the apparatus. This may be caused by fog, rain, ice or other moist weather conditions in an atmosphere containing dust, mild sulphur-bearing agents in industrial areas, or salty particles near the seashore. The apparatu may also be subjected to a certain amount of shock and vibration. Furthermore, it is not uncommon for insects to pack themselves around the tube electrodes and in between them and the supporting metallic structure, thus providing a conductive path around the tube. Under these conditions of operation, the tubes frequently become short-circuited from terminal to terminal or from terminal to ground.

Under the conditions of short-circuit, certain heretofore known and/or used transformer apparatus, unless specially designed to accommodate an excess current, is inclined to excessive heating which results in the ultimate charring and burning of the insulation and the destruction of the transformer apparatus, necessitating shutdown and replacement or repair. This situation is especially prevalent in certain heretofore known and/or used transformer apparatus having the secondary winding grounded at its midpoint. When a luminescent tube energized by such transformer apparatus becomes grounded at one terminal, as indicated above, excessive current is inclined to flow in one half of the secondary winding while no current flows in the other half of the winding. The flow of excessive current damages the winding unless it is designed to carry this heavy current. Such a design, of course, requires larger, heavier, and more expensive coils.

Accordingly, another object of my invention is to provide a transformer apparatus which is inexpensive in construction, employing windings of minimum necessary current-carrying capacity and of minimum cost, and yet. which is of such construction as to reliably withstand the many varying conditions encountered in actual. practical use.

Referring now more particularly to the practice of my invention, attention is invited to the figure of the drawing in which there is shown a transformer embodying certain features of my invention. The transformer comprises the longitudinal core bars 93 and 94, upon which are mounted primary and secondary windings as noted below, and also the short core members 0| and 92 interposed between the ends of the longitudinal bars. The bar 93 has a central extension 830. which abuts the bar 04. Bar 93 also has integral shunt arms 93b and 930 whichextend closely toward but do not abut bar Bl, forming therewith air-gaps GI and G2. The member 9| interposed between the end part 93d of bar 93 and longitudinal bar 9| forms a magnetic path of low reluctance, the core parts being held in firm contact by the band I03, preferably of magnetic material. Likewise, the member 92 interposed between the end part 930 of bar SI and the bar forms another magnetic path of low reluctance, the core parts being held together by the band I04 which also preferably is of magnetic material.

The primary coil P is mounted on the central extension 93a of bar 93 and is energized from the source of alternating current electrical energy 96 through leads 9! and 98.

Secondary coil Si is mounted on the end part 93d of bar 93 at the point where a space is formed between part 9311 and bar 94 and between shunt arm 53b and member 9|. One terminal of coil Si is grounded to the core at 99 and its other terminal is connected by lead I00 to one terminal of a negative load. Coil S2 is mounted on the end part 930 of bar 93 at the point where a space is formed between part 93c and bar 94 and between shunt arm 93c and member 92. One terminal is connected to load by conductor NH. The other terminal of coil S2 is grounded to the core at I02. Coils SI and S2 may be connected either in series-aiding or in series-opposition relationship, the transformer being more particularly designed for the operation of a load comprising a series of tubes, TI and T2, grounded at their approximate mid-point, as at I08. The load must be grounded at its approximate midpoint, or connected from the mid-point to the mid-point of the coils, as by the lead I01, if the coils ar connected in series-opposition in order that two complete circuits will be formed, one for each half of the load and it corresponding secondary coil. Where the coils are connected in series-aiding relationship. the grounded at its mid-point to form a complete circuit for each half of the load with its secondary coil but this is inclined to cause an unbalanced operating condition for the transformer and for this reason ordinarily is omitted.

The coils SI and S2 have induced in them voltages high enough to energize their respective portions of the load at substantially the same instant, where a bucking connection is used and the load mid-point is connected to the common connection of the two coils as by grounding them. There is substantial equality between the output voltages of the secondary coils. No danger exists of excessive current flowing through either coil because of the peculiarmagnetic shunt construction provided. Perfectly safe and economical operation is assured for all conditions of short-circuiting, grounding, or open-circuiting of all or any part of the load of one or both coils.

In the event of a short circuit occurring across the whole secondary winding, the coursing of the magnetic flux through the core of the transformer apparatus is substantially the same as it is during the conductive periods of its load. The amount of current flowing in the winding in this condition of operation is about the same as that encountered under normal operating conditions. In neither condition of operation does this curload may berent rise to such excessive values as to cause objectionable heating and damage to the coils.

In the event that only one coil section of the secondary winding becomes grounded, the flow of an excessively high current in this coil section is effectively prevented by the major portion of the magnetic flux coursing along a path of intermediate reluctance provided by a, shunt arm and its associated air-gap. This path extends around and excludes the short-'circuited section. The portion of the total magnetic flux that interlinks the primary winding with the short-circuited coil section, that is the minor portion of the flux, is substantially the same as that interlinking these two under normal operating conditions or under short-circuited operating conditions of the entire secondary winding. In all instances, the electromotive forces induced in the secondary winding are not so great as to cause the flow of an excessively high current in the coil sections of this winding.

The transformer of the figure has internal shuntpaths which will not be appreciably affected by the casing. The casing, being opposite only a small portion of the air-gap, willhave little bridging effect. Thus good air-gap control is possible. of simpler parts, which can be readily manufactured and assembled.

My transformer has the advantages of compactness of construction, symmetry of flux and current distribution, and safe operationunder conditions of short and'open circuits. Furthermore, for a single tube load, or a load comprising two .or more tubes not grounded at their midpoint, where the secondary coils are connected series-aiding, a high'output potential is obtained with nevertheless no more than a safe maximum potential to ground. Where the load comprises two or more tubes which are grounded at their mid-point and the secondary coils are connected in series opposition, a condition of balanced voltages and currents across the two halves of the load will obtain. There will be dependable operation of each half of the load and a minimum time lag will exist between the striking of the,

two halves. Dielectric discharge between the two halves of the load is eliminated. Moreover, the transformer is made of a minimum number of relatively simple parts which are readily assembled. Finally, the advantage of an internal shunt construction, that is, a minimum oi, fringing tdthe casing, is obtained.

Thus it will be seen that there has been provided in this invention transformer apparatus in which the various objects hereinbefore noted, together with many practical advantages thereof, are successfully achieved. It will be seen that my transformerv apparatus is exceedingly compact and rugged in construction and that it lends .itself to inexpensive and efficient commercial production and installation, employing a mini- Moreover, the transformer is made mum of different shaped core members and re quiring a minimum of expensive dies, tools and equipment in its construction. It will be seen, further, that luminescent tubes of the maximum length energizable by any existing equipment approved by the fire underwriters are energized by my transformer without there being present any of the tube puncturing dielectric discharges frequently encountered in the use of present equipment. Moreover, my transformer meets the requirements of fire underwriters in that the potential from no point to ground substantially exceeds 7500 volts. In the operation of my transformer there is no'pos sibility of overloading and consequent damage to the secondary winding in the event of accidental rounding of either .one or both coil sections of these windings.

While I have illustrated transformers having only one or two secondary windings and two or four coils, it is to be understood that three or more windings may be employed with associated core portions and shunts, the additional secondary windings and core members being mounted out from the plane of the construction shown in the drawing for example. With the number of windings illustrated, however, the transformer apparatus is exceptionally compact and yet, because of the peculiar core construction and the relation of this core to the secondary winding, it is fully protected from damage under the various conditions encountered in use. The compactness and coil protection feature assures an inexpensive, efficient and thoroughly reliable piece of apparatus.

As many possible embodiments may be made of my invention and as many changes may be made in the embodiments hereinbefore set forth, it will be understood that all matter described herein, or shown in the accompanying drawing, is to be interpreted as illustrative, and not in a limiting sense.

Iclaim:

In electrical transformer apparatus of the character described, in combination, two substantially parallel linear core members, one of said linear members having intermediate its ends a central extension joining said other linear member and two shunt arms one on either side of said central extension, extending toward but not abutting said other linear member and forming therewith magnetic shunt paths including aps of high reluctance; two end core members connecting said linear core members exteriorly of said shunt arms, the connected members forming two closed magnetic circuits with said central extension;

a primary winding mounted on said central extension; and two sec-'

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