US2655623A

US2655623A - Electrical transformer

Info

Publication number: US2655623A
Application number: US149044A
Authority: US
Inventors: William N Parker
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1950-03-11
Filing date: 1950-03-11
Publication date: 1953-10-13
Anticipated expiration: 1970-10-13

Description

Oct. 13, 1953 w. N. PARKER ELECTRICAL TRANSFORMER Filed March 11, 1950 I a v, o I l Ff/11126711112 INVENTOR M/baw NR? 01' ATTORNEY Patented Oct. 13, 1953 ELECTRICAL TRANSFORMER William N. Parker, Lancaster, Pa., assignor to Radio Corporation of America, a corporation of Delaware ApplicationMarch 11, 1950, Serial No. 149,044

1 Claim. 1

My invention relates to transformers and particularly to transformer systems supplying power to a load device requiring high operating current at low voltage.

One instance of a use for such a power supply, and which I shall employ to illustrate my invention, is to supply the heating current for the cathodes of high power electron tubes such as are used in radio transmission.

In such tubes, it is ,common practice to have a number of cathode members, all connected in parallel. It is preferable that these cathode members be directly heated by the passage of current through them. These cathode members are usually relatively short and have a low resistance. Since the resistance is low, a large current is required to produce the heat necessary to maintain the cathodes at emitting temperature. Providing suitable short internal leads of high current carrying capacity presented a problem. One

solution for this problem was the provision of heavy concentric or coaxial rings or cylinders of suitable material to which the cathodes were fastened, such as in the RCA type 5831 tube which is more fully described in copending application Serial No. 81.932, filed March 17, 1949.

For eflicient operation, the apparatus supplying the large current to the cathode leads should follow the same principles as the leads themselves. That is, it should be so arranged that the leads connecting the power supply to the cathode leads are as short as possible and present as small a resistance to the flow of the current as is possible. A convenient apparatus for supplying the current required is a transformer.

Accordingly, it is an object of my invention to provide an improved transformer.

A further object of my invention is the provision of a transformer system for supplying a large current at low voltage-wherein the output terminals are coaxially disposed.

Still another object is to provide a transformer system adapted to be used with high-power electron tubes, particularly with those tubes having concentric or coaxial cathode leads.

In accomplishing these and other objects, I provide a transformer having one or more annular cores of ferromagnetic material. Each of these cores has a toroidal coil wound upon it. These coils constitute the primary of the transformer. The secondary of the transformer comprises a shell of electrically conductive material that substantially surrounds the primary coils. This shell is in the shape of a hollow annulus that is open at one endand has a substantially U-shaped cross-section. In order to provide flexibility in the operating conditions of my system, I prefer the use of several primary' coils. In such case, the ends of the individual coils may be connected to independent external terminals so that they may be connected in different ways, depending on the desired operating condition.

A better understanding of my invention may be had from the following detailed description when read in conjunction with the accompanying drawings in which:

Fig. 1 is a cross-section view of an embodiment of the transformer of my invention.

Fig. 2 is a cross-section view taken along the line 22 of Figure 1.

Fig. 3 shows a modified form of the secondary of the transformer.

Fig. 4 is a fragmentary cross-section view showing another modification of the secondary of the transformer,

Fig. 5 is a fragmentary View, partly in crosssection, showing the transformer of my invention connected to the base portion-of a high-power electron tube.

Fig. 6 is a fragmentary view in cross-section showing the transformer of my invention built into a high-power electron tube, and

Fig. 7 shows in a fragmentary cross-section view, a modification of the transformer structure.

Referring to the drawings in detail, in Figs. 1 and 2 I have shown a plurality of annular core members I of laminated ferromagnetic material. Wound upon each of these cores is a toroidal coil 2. These coils constitute the primary of the transformer. The coils 2 are placed in a hollow annular shell 3. This shell is made of an electrically conductive material, such as copper, and serves as a secondary for the transformer. The shape of the shell substantially takes the form of a pair of spaced apart concentric cylinders, the two cylinders being joined at one end. The primary coils and their associated cores are placed in the space between the inner and outer cylinders. A pair of concentric rings 4 and 5 is formed by the open ends of the cylinders. These rings are the terminals for the secondary of the transformer. The ends of each of the primary windings may be connected to individual or independent external terminals whereby the separate coils may be variously connected, as will be explained later. V

A modified form of the secondary is shown in Fig. 3. Instead of the one-piece, one-turn secondary shown in the other figures, the cylinders are formed by a number of U-shaped copper straps 8. These straps are here shown arranged in groups of two and one strap of each group is serially connected to the other by a connecting strap 9. Thus each pair of straps constitutes a two-turn secondary.

The groups of straps are, in turn, connected in parallel to two contact rings l4 and 15. These rings correspond to the terminal rings & and ,5 of the shell type secondary shown in Figs. 1 and 2. It may be seen that the arrangement shown in Fig. 3 provides a plurality of two-tum secondary windings all connected in parallel. By eliminating the connecting strap 9 and connecting the ends of the U-shaped members 8 directly to the rings 14 and i5 respectively, a plurality of oneturn secondaries is formed. A three or more turn secondary may be provided in a manner similar to that shown and discussed in the twoturn arrangement.

A fragmentary view of the base portion of a high-power electron tube [2 is shown in Fig. 5. One end of each of a plurality of cathodes (not shown) is connected to a contact flange 16. The other ends of the cathodes are connected to a cylindrical member that extends through the base of the tube to form a contact ring H. A set of spring loaded contact fingers l8 provides a convenient means of assuring a good electrical contact between the inner ring 5 of the secondary and the contact ring ll of the tube l2. Suitable clamping devices (9 are provided to secure the tube to the transformer, the outer ring 4 of the transformer making direct electrical contact with the contact flange it of the tube.

Under some conditions of operations, the current in the secondary may be large enough to cause excessive heating of the secondary, To obviate this, I provide a modified construction of the secondary member in which there are intrawall cavities 20, substantially as shown in Fig. 4, through which a fluid coolant may be passed.

When the transformer is used to supply the heating current for the cathodes of electron tubes, it is desirable to be able to control the starting current since the resistance of the cathodes will vary considerably as their temperatures change. I have shown in Fig. 3, one arrangement for controlling the output of the transformer. In the transformer there shown, I provide eleven identical toroidal primaries 2. The

bottom six of these toroids are connected in parallel to a double-pole, double-throw switch 22. One side of the switch 22 is connected to a source of alternating current 26. The other side of the switch 22 is connected to a shorting bar 25. The top five toroids are connected in parallel to a variable auto-transformer 28. The auto-transformer is connected through a reversing switch 30 to the source of alternating current 26.

To initiate the operation of the system, the switch 22 is closed to connect the bottom six toroids to the source of current 26. The autotransformer is adjusted so that its output voltage is in a ratio of 6/5 with its input voltage. The reversing switch 30 is closed to cause the current in the top five toroids to flow in the opposite direction from the current in the bottom six. Since the voltage impressed on the top five primaries is six-fifths of the voltage impressed on the bottom six, the voltage induced in the secondary by each set will be equal. However, since the two sets are bucking each other, the net induced voltage in the secondary will be zero. Now, if the output of the auto-transformer 28 is reduced, the net voltage induced in the secondary will increase. The output of the main transformer will be one-half of its full load output when the output of the auto-transformer 28 is zero. At this point the reversing switch 30 may be closed on its other side. If the output of the auto-transformer is now increased, the current in the upper set of toroids will be aiding that in the lower set. This results in a transformer whose output is continuously variable from zero output to full load while controlling only half of the total power input.

It should be understood that the exact number of toroidal primaries here illustrated is not essential to the carrying out of the foregoing operation. There may be more or fewer primary coils, with the control voltage supplied by the auto-transformer being adjusted accordingly. If conditions are such that not more than half of the total power is required, the switch 22 may be closed on the shorting bar 25. This shortcircuits the lower six primary coils, allowing the upper five coils to supply the power for the load.

In some instances, it may not be desirable to have the output of the transformer variable from zero to full load. Instead, it may be preferable to have the output variable only between certain limits. In such case the control voltage from the auto-transformer could be applied to a fewer number of the primary coils. For example, only one coil may be so connected.

Other adaptations of the transformer include various combinations of parallel and series connection between the individual primary coils. These various combinations provide selection among any of a number of different line voltages that may be applied to the primaries to produce a given output voltage.

Although I have shown and described the primaries as having independent external terminals, the several primary coils may be connected internally in any suitable or desired manner.

While, in most instances, it may be more convenient to have the transformer separable from the tube with which it is associated, it is within the contemplation of my invention to have the transformer built into the tube as I have shown in Fig. 6. The glass side wall 33 of the tube is secured to the transformer secondary through a suitable glass-to-metal seal. This arrangement, with nothing more, would provide an envelope enclosing all of the tube elements as well as the primary coils of the transformer. When the envelope is evacuated, the gas absorbed by the elements in the envelope must be driven off during the evacuating process. The primary coils with their associated cores would have a large quantity of this absorbed gas; and it would ordinarily be diflicult to drive the gas out. However, in order to reduce the difficulties encountered in degasing such a tube, the main or vacuum chamber of the tube is isolated from the primary coils by means of a seal-off member 35. In such an arrangement, the cathodes 31 may conveniently be connected directly across the secondary terminals 4 and 5.

As I have previously indicated, the resistance of the cathodes is considerably-lower when they are cold than when they are heated to operating temperature. If full load voltage is applied to these cathodes while they are cold, excessive current would ordinarily flow through the secondary circuit. In Fig. 7 I show, in addition to the core members, around which the primary coils are wound, an auxiliary annular ferromagnetic core 18. This auxiliary core does not have a primary coil associated with it, but provides a closed magnetic path in the field of the secondary. This introduces sufiicient reactance into the secondary circuit to limit the excessive current that would flow if the full load voltage were applied to the cathodes while they are cold.

From the foregoing, it may be seen that I have provided a new and useful transformer system for supplying low-voltage, high-current loads. The system is particularly adapted for use with those load devices having coaxial or concentric leads.

What I claim is:

A transformer having a plurality of ferromagnetic cores, each of said cores providing a closed magnetic path, a toroidal primary coil wound on each of said cores, a secondary for said transated coils being contained in the space between said cylindrical members, independent external terminals connected to the windings of each 01' said primary coils whereby said primary coils may be variously connected, and an auxiliary annular ferromagnetic core, said auxiliary core being disposed within the outer one of said cylindrical members and axially displaced from said aforementioned cores, thereby introducing a reactance to limit exceedingly high starting currents in said secondary.

WILLIAM N. PARKER.

References Cited in the file of this patent