US2791753A - Transformer - Google Patents

Description

United States Patent TRANSFORMER Morris R. Jeppson, Orinda, Calif.

Application December 14, 1953, Serial No. 397,992

5 Claims. (Cl. 336-.-83)

The present invention relates to an improved transformer and is particularly concerned with transformer structure in connection with insulation of the windings thereof.

It is necessary in conventional transformers to insulate the windings one from another and to insulate the Windings from the core upon which they are wound and in the instance of high voltage transformers large amounts of insulation are required to insulate the secondary windings from the core. This insulation multiplies the size of transformers with increased voltage rating in addition to increasing the price thereof. The present invention overcomes the problem of insulating the secondary windings from the core to the extent that insulation need only be provided for substantially the voltage developed across a single winding. The result is that there remains only the insulating of one winding from another, which insulation also suiiices for winding to core insulation. Inasmuch as there may be developed across the secondary winding of a high voltage transformer a voltage of the order of 150 kilovolts or more and the voltage differential between windings may be only of the order of ten kilovolts or less it is apparent that a very real saving and advantage results from the present invention.

The winding-to-core insulation problem in high voltage transformers is overcome in the present invention by the provision in effect of a voltage divider in the form of a magnetic core. Rather than employ a conventional iron core the present invention employs a magnetic material that has a very high electrical resistance and has provision for particular electrical connections between same and the transformer windings.

It is an object of the present invention to provide an improved high voltage transformer.

It is another object of the present invention to provide an improved high voltage transformer having minimum core-to-winding insulation.

It is another object of the present invention to provide an improved 'high voltage transformer of simplified construction.

The present invention is disclosed herein with respect to a single preferred embodiment both as to description and illustration solely for the purpose of clarity. The invention is not limited to the details shown but instead reference is made to the appended claims for a precise definition of the scope of the invention.

The invention is illustrated in the accompanying drawing wherein Figure l is a vertical center section of the transformer and Figure 2 is a horizontal section view taken at 22 of Figure 1.

Considering now the structural details of the invention and referring to the drawing, there is provided a shell 11 which may include a hollow cylinder 12 and end pieces 13 and 14 suitably joined thereto preferably in fluid-tight relation. This shell serves as the container for the transformer and may also serve as a magnetic flux path in which case it is formed of iron, however, in some 2,791,753 Patented May 7, 1957 'ice instances it may be preferable to provide another flux path and to this end there is shown a plurality of ferromagnetic bars 16 disposed longitudinally of the cylinder 12 within same and connected between the ferromagnetic end pieces 13 and 14 about the cylinder axis. Within the shell 11 there is disposed an elongated core 17 lying on the axis of the cylinder and extending between the end pieces 13 and 14. This core is formed of a cubic ferrite having high magnetic permeability and low electrical conductivity, this material sometimes being termed as a magnetic nonmetal and having the general formula MF204 wherein M stands for a bivalent metal ion. The core may if desired be built up of a plurality of pieces suitably bonded together in such a manner as not to impair the permeability thereof. Mounting of the core may be facilitated by the provision of a raised boss 18 formed on the lower end piece 14 and extending axially of the cylinder with a conical boss surface being provided for mating with a conical indentation in the lower core end.

Referring further to the core 17 it is contemplated that same may be formed with a tapered cross section whereby desired voltage distribution may be obtained therealong for the voltage drop per unit length thereof is proportional to the cross sectional area. In the illustrated embodiment the lower half of the core 17 is formed as a circular cylinder while the upper half of the core is formed as an inverted conical section. This conical core section is also formed with an axial inverted conical opening therein extending to the core center and the walls of this cone may be tapered as shown to provide desired voltage distribution characteristics.

Also within the shell 11 and about the core 17 therein there is disposed a primary winding 19 and a secondary winding 21. The primary winding is disposed about the core adjacent the lower end thereof and may actually be disposed about the boss 18 if desired. The secondary winding 21 is disposed about the core between the primary winding and the core center and may consist of a plurality of individual wafer windings, as shown. Suitable insulating spacers 22 may be provided to separate the individual windings, as shown. Electrical connection is made from the ends of the primary winding 19 via lead-through insulators 23 in the lower end piece 14 to a pair of conductors 24 extending externally of the shell 11 and adapted for connection across a power supply providing a varying current whereby same flows through the primary winding to produce charging magnetic flux cutting the conductors of the secondary windings. A complete magnetic path is provided for flux so established through the core 17, end pieces 13 and 14, and bars 16. The end of the secondary winding 21 adjacent the primary winding 19 is electrically connected to the core 17 at this point and the secondary windings are serially connected to establish the upper end of same as the high voltage end. A high voltage lead 26 is disposed axially of the cylinder 12 and of core 17 and extends from well beyond the upper end piece 13 into the core 17 into electrical contact with the center thereof. A conical insulator 27 formed for example of glass or porcelain, as shown, surrounds this lead 26 and mates with the conical depression in the upper half of the core 17 to insulate the high voltage lead from the core and shell. This insulator may have a cylindrical extension above the shell 11 about the lead 26 and may further have, a, peripheral flange extending over the end piece 13 which is apertured to receive same and which may be bolted to this flange, as shown. Electrical connection is made between the high voltage lead 26 and the upper or high voltage end of this secondary winding 21 at the center of the core 17 as by means of extending the 3 winding end through a radial core aperture to the lead 26, also as shown. The interior of the shell 11 may be filled with an insulating material such as oil or a plastic if desired.

'With the primary winding energized as by an alternating current voltage, the current flow therethrough establishes a varying flux that traverses the above-noted complete flux path cutting conductors of the secondary winding to induce a voltage therein. The lower end of the secondary winding 21 is grounded to the core 17 and with a very large number of turns in the secondary winding a very high voltage results at the upper end of the secondary winding. With the structure illustrated there exists a voltage between individual windings of the secondary winding and each winding is insulated for this voltage. There also exists the entire secondary voltage between opposite ends of the secondary winding, as for example some hundreds of kilovolts. With the high voltage end of the secondary winding electrically connected to the core there can exist only the voltage of a single winding between the upper secondary winding and the core, some few kilovolts at the most and thus the individual winding insulation suffices in this respect. Inasmuch as the core 17 is an electrical nonconductor it serves as a voltage divider with one end grounded and the other end at a high voltage and thus substantially the same voltage differential exists between spaced points thereon as between secondary windings equally spaced or at least core area variations or winding spacing may be readily varied, to produce such a result. Consequently then at no point does there exist between secondary winding and adjacent core a high voltage beyond substantially that of a single winding voltage so that no particular winding-core insulation is required other than' regular between-turn winding insulation. Similarly the upper half of the core 17 acts as a voltage divider so that the entire secondary high voltage appears across the upper half of the core. A material saving in insulation thus results.

1 Although a single type of transformer has been illustrated and described various other types of windings may be employed as, for example, center tap grounded or insulated and only variations in relative winding and core disposition are required. Also advantages are found in that theinsulating properties of the core substantially preiclude'eddy currents so that quite high frequency transformer operation may be realized.

' What I claim' is: r

'1. An improved transformer comprising a shell formed of magnetic material, a central core disposed within said shell in connecting relation to opposite ends thereof and formed at least in part of a cubic ferrite having high magnetic permeability and low electrical conductivity,

a primary winding disposed about said core, a secondary Winding disposed about said core and having a high voltage end electrically connected to the ferrite portion of said core at the center thereof and a low voltage end connected to one end of said core, and a high voltage lead connected to said secondary winding at the connection thereof to said core.

2. An improved high voltage transformer comprising an elongated core formed of a cubic ferrite, a ferromagnetic shell about said core and contacting each end thereof, a primary Winding disposed about an end of said core and adapted for electrical energization, a secondary winding disposed about said core between said primary winding and the longitudinal center of said core with each end of said secondary winding electrically connected to said core at one end adjacent the primary Winding and at the other end adjacent the core center, and a high voltage lead connected to said core and secondary winding at said core center.

3. An improved high voltage transformer comprising an elongated member formed of a cubic ferrite having high magnetic permeability and low electrical conductivity, means having a high magnetic permeability extending between ends of said elongated member, first windings disposed about one end of said elongated member, second windings disposed about said elongated member and electrically connected thereto between one end and the center thereof, said elongated member comprising a transformer core and a voltage divider across said second windings, and a high voltage lead connected to the center of said elongated member and to the end of said second windings thereat.

4. An improved high voltage transformer comprising an elongated core member formed of a cubic ferrite and having a cross section tapered outwardly from the center to one end thereof, a high voltage lead extending into said core in insulated relation thereto into electrical connection with the center thereof, a magnetic member extending between ends of said core for providing a complete magnetic path, a primary winding disposed about said core at the untapered end thereof, and a secondary winding disposed about said core between said primary winding and the core center and electrically connected at one end to said core adjacent said primary winding and at the other end to said core and high voltage lead at the core center whereby the voltage differential between the core and each of the turns of said secondary winding is substantially the same and the high voltage end of said secondary winding is insulated from said magnetic member by said core.

5. An improved high voltage transformer comprising i a cylinder having ferromagnetic members extending between ends thereof, a core formed of a cubic ferrite having good magnetic permeability and poor electrical conductivity, said core having a cylindrical portion with an axial conical extension thereof flaring outwardly from the cylinder end with said cylindrical and conical portions having substantially the same axial length and said core being disposed within said cylinder extending between the ends thereof, said core further having an opening in the conical end thereof extending to the core center, an insulator disposed within said core opening and extending therefrom, an electrical conductor disposed within said insulator and extending at the free end therefrom and at the other end into electrical contact with the center of said core, a first winding disposed about said core at the end of its cylindrical portion thereof adjacent the connection thereof to said cylinder and being adapted for electrical energization to produce magnetic flux through said core and cylinder, and a plurality of second windings disposed about said cylindrical core portion between said first winding and said core center, said second windings being electrically connected together with the extreme ends thereof connected one to said core adjacent said first winding and the other to said electrical conductor at said core center and also to the core at the center thereof whereby said core comprises a voltage divider across said second windings and the required insulation between said second windings and said core is minimized.

References Cited in the file of this patent UNITED STATES PATENTS 2,608,610 Thulin Aug. 26, 1952 FOREIGN PATENTS 115,025 Great Britain Apr. 17, 1942

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