US2088803A - High reactance transformer - Google Patents

Description

Aug. 3, 1937. F. E. MONTROY HIGH REACTANCE TRANSFORMER 2 Sheets-Sheet 1 Filed Sept. 26, 1955 INVENTOR 37 F. E. MONTROY 2,088,803

HIGH REACTANCE TRANSFORMER Filed Sept. 26, 1935 2 Sheets-Sheet 2 as i I 33 ,/a3 34 v 32-, AW

l/VVENTOR Patented Aug. 3, 1937 UNl-TED STATES PATENT OFFICE I 2,088,803 HIGH REACTANGE SFORMER Frank Edward Montroy, Los Angeles, Calif.

Application September 3 Claims.

This invention relates to a high reactance stepup transformer, and is adapted to a wide range of applications in the electrical art, particularly in connection with loads having negative resist- 5 ance characteristics. It is particularly adaptable to the lighting of gaseous discharge tubes in their numerous applications, the embodiment of the invention herein described and illustrated being a double secondary sign lighting transformer. It 10 is to be understood however, that'the invention is not limited to the particular types illustrated or to the applications described, but may be variously embodied and applied within the purview of the claims, which are to be limited only by 15 the limitations thereby imposed and. by the prior art.

In the manufacture of illuminated gaseous discharge tube displays it is necessary for the contractor to be ready to fill orders for many dif- 20 ferent load combinations, and both for steadily lighted and flashing displays. It is, of course, unavoidable that transformers of different voltage ratings be carried in stock as the range of loads will vary all the way from small window signs 5 requiring a couple of thousand volts, to large displays requiring many transformers of the highest voltage available. However, provision in the transformers which will make them adaptable over a considerable range of conditions will effect a, very considerable saving in the necessary stock of transformers as well as effecting a saving by increased quantity production on a limited number of types.

It is one object of this invention, therefore, to provide a transformer which may be variously operated over a considerable range of load conditions. I have provided a construction in which two secondary coils, each corresponding to a separate primary coil, may be operated in series or in parallel, or independently. Thus, if the coils are connected in series they may be used to light a series connected load of tubing of the sum capacity of both coils. If they be operated in parallel they may be used to light a high intensity tube of high current demand. If they be operated separately the transformer may be used for in-, stallations in which the coils can be connected to independent lights and switched on the primary side with an ordinary low voltage switch 50 or fiasher.- I I It is an object of the invention to accomplish these results without sacrificing any efliciency as compared with the standard stock transformers of the maximum -capacity of the unit and without 55 increasing the expense of manufacture percepti- 26, 1935, Serial No. 42,217

bly. In the manufacture of transformers numerous practical considerationsas to the size and spacing of coils, disposition of the iron, designing of the joints and order of assembly govern the design and are reflected in the total cost. In my invention I have provided a construction which can be easily assembled so as to make the .use of a double primary of no consequence so far as net cost is concerned, thus gaining the advantage of being able to flash the secondaries separately if desired without extra. cost.

It is common practice in discharge tube lighting to ground the middle of the high voltage .winding in order to limit the terminal-to-ground voltage. In this invention I provide for the grounding of the connection between the two high voltage coils when they are operated in series for voltage. When operated in parallel or independently the secondary.v coils which are separately insulated remain ungrounded, unless grounding is indicated for other reasons.

A further object of the invention is to provide a transformer in which vibration and noise are reduced to a minimum. Other objects will be apparent from the following description in connection with the drawings.

The invention is illustrated by the preferred embodiment thereof shown in the drawings, in which:

Figure 1 is a view of a transformer made according to this invention with each of the secondary coils connected to a separate gaseous discharge tube, and with the primary coils con nected to a flashing switch for alternate flashing of the tubes.

Figure 2 is a perspective view of the upper portion of the transformer shown in Figure 1 showing the core joints.

Figure 3 is a diagrammatic illustration of one of my transformers connected for maximum voltage output to a series of tubes.

Figure 4 is a diagrammatic illustration of one of my transformers connected for maximum current output for a single high capacity tube.

Figures 5, 6, and 7 are views of three modified forms of cores suitable for thisinvention.

Numeral I, Figures 1 and 2, indicates the core of the transformer, the primary coils being indicated by 2 and 3, andthe secondary coils by 4 and 5. The core I is composed of a stack of E shaped laminations, 8, 6, etc., and a stack of straight laminations, l, 1, etc., said laminations being so cut and assembled that the stacks dovetail with each other. In this instance I illustrate the joint 8 as formed by interstacking the laminations in groups, thus providing a joint having the advantages of an interstacked joint but easier to assemble than a joint in which the laminations are separately interstacked. In Figure 2 the ends 9a, Illa, and Ila of the legs 9, I0, and II, respectively, may, be seen extending through the openings in the cross bar I. The ends of the legs are thus mortised into the cross bar and held in place by bolts l2, l2, etc., similar bolts being provided to tighten the laminations on the main section of the core. It is also permissible to form the joint by abutting the stacks provided that suitable clamps are used to hold the stacks firmly together. 0r, obviously, the usual alternate stacking of laminations may be employed.

A magnetic shunt I3 is provided between the legs 9 and I0, and separating the coils 2 and 4. A similar shunt i4 is provided between the legs I0 and II, and separating the coils 3 and 5. These shunts are composed of the iron laminations l5, 15, etc., each shunt being wrapped in a "fibre sleeve as indicated by 26 and 21. The shunt assemblies are driven tight between the core legs and bear against the insulating sheets l6, l1, l8, and I! which are wrapped around the coils, thus forming a tight construction of core and coil with a minimum of tendency to vibrate.

The primary coils 2 and 3 are connected to the two point flashing switch 20, which alternately connects the coils to the source of current. In-

stead of an alternate switch any other desired type of switch may be used as the two secondary coils are substantially independent of each other in this circuit arrangement. The secondary coils 4 and 5 are connected to the gaseous discharge tubes 2! and 22 respectively. The primary coils are preferably connected so that their flux is in opposition, the leg in thus serving as a common leg for both coils.

Each primary coil with its corresponding secondary coil and the intervening magnetic shunt will operate with very little cross induction to the other coils. It is to be noted that the secondary coil opposite to the energized primary is shielded by both shunts and the leg Hi. In addition, I have found that the discharge tube itself cooperates with the magnetic shielding within the transformer to prevent current flow in the dead secondary. Thus, a certain minimum voltage must be reached before the tube will convey current. Any inductive effect which might get through to the dead secondary in spite of the shields will be insuflicient to cause current flow unless it is suilicient to raise the potential to the ignition voltage of the tube. These eifects together in all cases, and the shielding effect alone in many cases, can be counted on to produce a transformer which will operate on a flasher with the secondary coils substantially independent.

I have taken advantage of the characteristics of high reactance transformers in another fashion to eifect a reduction of vibration and noise. I have found that by locating the joint 8 between the core sections beyond the secondary coil in that portion of the magnetic path which conveys the minimum average flux a very considerable reduction in vibration and hum is effected. This reduction is considerably more than is to be expected from the mere reduction of the total average flux. This I ascribe to the fact that the rate of change of flux in this region is more gradual than had heretofore been thought. According to the theory of the shunted core transformer generally accepted in the art the shift in the flux is rather sudden, occurring when the tube begins to convey current and the secondary develops a counter motive force. However, it appears that suflicient weight was not given to the magnetic lag which would operate to prevent as sudden a shifting of flux as the theory would indicate. It is probable that careful research will show that the current in the tube rises momentarily to enormous proportions somewhat as has been shown to be the case with incandescent lamps, and that the shifting of the flux is far more gradual than thought. This could easily have passed unnoticed by the workers in the-art as momentary intense currents would be even less harmful in gaseous discharge tubes than in filament lamps.

This discovery has enabled me to design transformers with core joints located so as to be subjected to the minimum rate of change in the flux without interfering with the ready assembly of the units. In Figures 5 and 6 I have shown two types of joint which might be used instead of that shown in Figures 1 and 2. In these views some of the noise reducing feature is sacrificed for the sake of certain advantages in assembly. In Figure 7 I have shown a construction which retains all of the noise reduction feature. In these views the outside legs of the core are indicated by 32 and 33, and the inner leg by 34. The inner leg in Figures 5 and 6 is made integral with the cross bar 36, and in Figure '7 it is split and part is integral with the cross bar 36 and part with the cross bar 35. Being located beyond the shunts 4| and 42 it is in the region of minimum flux change. The end joints in these views are indicated by 38, and the joint in the leg 34 in Figure '7, by 40.

These joints may be made as interlocking joints by interstacking the laminations, or as butt joints. In Figure 3 I have shown a transformer connected to a series of tubes with the secondary coils in series to develop the maximum voltage. To limit the terminal-to-ground voltage a center ground tap 41 is shown from the inter-coil connection to the core. The tubes, indicated by II and 3|, may consist of any number of sections of tubing, letters, etc., as is usual in the art within the capacity of the transformer.

In Figure 4, I show a transformer with the secondary coils connected in parallel to supply a high current flow to the high intensity tube 45.

The terms E shaped laminations", "straight laminations, parallel legs, rectangular cross bar as used in the claims are to be understood in their generic sense as including elements sub stantially equivalent to those thus described and varying only in unimportant particulars.

Having thus described my invention, what I claim is:

1. In a high reactance transformer, a laminated core structure comprising a stack of E shaped laminations and a stack of straight laminations assembled to provide a core having three substantially parallel legs and two cross bars at the ends thereof, each of said cross bars connecting together the like ends of said parallel legs, said laminations being interstacked at the joints, all of said joints being at the like ends of all of the said parallel legs. a primary coil on each of the outer of said parallel legs at the ends thereof distant from said joints, a secondary coil on each of the outer of said parallel legs at the ends thereof near said io and a a e ic shunt bridge positioned between the two coils on each of said parallel outer legs, there being two 75 such bridges, each or said bridges extending from the corresponding outer leg to the inner of said parallel legs.

2. In a high reactance transformer, a laminated core structure comprising a stack of E shaped laminations and a stack of straight laminations assembled to provide a core having three substantially parallel legs and two cross bars at the ends thereof, each of said cross bars connecting together the like ends of said parallel legs, said laminations being interstacked at the joints, all of said joints being at the like ends of all of said parallel legs, a primary coil on each of the outer of said parallel legs at the ends thereof distant from said joints, a secondary coil on each of the outer of said parallel legs at the ends thereof near said joints, and a magnetic shunt bridge positioned between the two coils on each of said parallel outer legs, there being two such bridges, each of said bridges extending from the corresponding outer leg to the inner of said parallel legs, said secondary coils being connected together in series with the common junction grounded to said core. 3. In a high reactance transformer, a core structure comprising two stacks of laminations, the first of said stacks comprising three substantially parallel legs connected together at like ends thereof by a cross bar, and the second of said stacks comprising a rectangular cross bar and positioned to connect the free ends of the said parallel legs together, the joints between the two said stacks being mechanically firm, a primary coil on each of the outer of said parallel legs at the ends thereof distant from said joints, 8. secondary coil on each of the outer of said parallel legs at the ends thereo! near said joints. a magnetlc' shunt bridge extending from each of the outer of said parallel legs to the inner of said parallel legs and between the primary and secondary coils on the corresponding outer legs, said elements being so proportioned and related that upon the connection of each 01' said secondary coils to a gaseous conduction discharge lighting tube, and the connection or either of said primary coils to a source of alternating current adequate to illuminate the tube connected to the corresponiiing secondary coil, the shielding eflect of said magnetic shunt bridges and said inner leg will substantially prevent illumination in the tube corresponding to the unenergized coil.

FRANK EDWARD MON'I'ROY.

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