US2831953A - Apparatus for radio frequency transformer control of electrical energy - Google Patents

Description

April 2, 1958 J. G. D. MANWARING 2,831,953

APPARATUS FOR RADIO FREQUENCY TRANSFORMER CONTROL OF ELECTRICAL ENERGY 2 Sheets-Sheet 1 Filed Feb. 10, 1955 w o V :QI M 2 ATTORNEY p l 1958 J. G. D. MANWARING 2,831,953

APPARATUS FOR RADIO FREQUENCYTRANSFORMER CONTROL OF ELECTRICAL ENERGY Filed Feb. 10, 1955 2 Sheets-Sheet 2 n t 8 S La.

(l/ll/ /'/////l (D INVENTOR. Jwfla BY KTTorNEY high-voltage insulation.

United States Patent APPARATUS FOR RADIO FREQUENCY TRANS- FORMER CONTROL OF ELECTRICAL ENERGY.

Joshua G; D. Manwaring, Medfield, Mass. Application February 10, 1955, Serial No. 487,344

4 Claims. 01. 219-1055 This invention relates to methods and apparatus for controlling electrical energy by means of transformers and, more particularly, this invention is concerned with improvements in radio frequency transformers, including those employed in induction heating, radio transmitting and various other commercial applications.

In conventional induction heating methods and apparatus, there exists a problem of long standing. This problem arises in connection with attempts to furnish a maximum of energy transfer in a transformer which necessarily involves providing for a relatively high fiux linkage and, at the same time, providing for adequate These requirements, in many cases, are not satisfactorily met in conventional devices. For example, in one type of transformer mostcommonly employed, a transformer primary is comprised by a tubular copper conductor formed into coils. One end of the conductor is at high potential, being connected to an R. F. high-voltage power supply; the other end is at ground potential. Around the outside of-these coils is arranged a secondary consisting of a split cylindrical copper sleeve. A' work coil is connected to and supported on either side of the split in the .secondary in a substantially centrally located position and, within definite coupling limits, supplies high amperage 'low voltage output for induction heating. 7

In such a structure, increased coupling can, of course, be achieved by wrapping 'the secondary tightly around the primary coils, but this is impractical because of the materially greater insulation problem induced and increased coupling in this way is not feasible. Either an appreciable air insulation spacing by itself or a very small air spacingwith the use of solid insulation on the primary must be utilized. However,,even with both an air spacing and the use of solid insulation on the primary, there is not achieved sufiicient protection to avoid a relatively rapid deterioration of the solid insulation material. Thus, neither maximum coupling nor satisfactory insulation is accomplished to a degree which meets many commercial requirements.

From extensive study of the foregoing considerations and the problem indicated, there evolved the several objectives of the present invention which include the object of generally providing improved methods and means for coupling electrical energy, as well as the more specific objectives of dealing with the conbined coupling and insulation problem indicated in connection with induction heating; of devising methods and means for increasing transformer coupling and improving efficiency; of reducing voltage insulation problems; and of developing greater primary coil stability in transformer type energy transfer.

As a starting point in' attempting to achieve these objectives, it was first conceived that a method might be devised to reduce insulation difiiculties without coupling reduction taking place and, possibly, with coupling being increased. In an effort to reduce insulation difliculty, there "was devised a split disc type secondary element of very 0 with the secondary located at or very near to the ground potential or low voltage end of the primary coil, zero potential existed between the primary and secondary and, therefore, a zero spacing of secondary to primary could be employed at such a point. However,.couplingin this I was materially decreased.

It was then conceived that the basic idea of decreasing insulation need and simultaneously increasing coupling might be further implemented by utilizing the disc type secondary of short axial length at a zero potential point for at least one of two associated primary coils whose respective magnetic flux might, in some way, be controlled to produce stronger inductive effects. I

In thus attempting to employ a disc type secondary of short axial length with two primary coils, there was first tried an arrangement whereby high potential, for example 5,000 volts, was applied to each of two primary coils. The flux of the two coils were developed separately but in close proximity to one another with the high potential side of one coil being very near to the low potential side of member coil. The disc secondary was located approximately around those points at which the'first of the two coils was at ground potential. 4

It'was found that the two primary coils could be controlled so that instead of producing, as would be expected, two separate flux patterns, each of which patterns would have a region of maximum intensity in the center of each 'coil section, there was produced actually a combined or overlapping pattern of flux furnished from each pri- ,mary coil so that the flux of each coil were, in a considerable degree, made additive to one another. However, the region of overlapping pattern of flux, it was found, tended to become centralized approximately around those points at which the first primary coil was at minimum potential but the second primary coil was at maximum potential. Since the disc secondary, when placed in position around the first coil, as near as possible to point of zero potential, was necessarily located very close to the second coil at points of high potential, there was still an insulation problem. p

. It was further conceived at this time that it might be possible to join the two coils together with high potential being applied at outer ends of the respective coils but with each coil connected so as to have a common center ground. In this way, the centrally located disc secondary might then realize decreased need for insulation at zero potential point of each coil and, yet, utilizing increased flux strength from both coils. This arrangement was attempted unsuccessfully with one conthe split disc located at a point very close to the common central ground. The reason for lack of success was due to the fact that the coils were disposed in bucking relationship and their magnetic fields cancelled out.

It was then discovered that, by winding two coil components at two sides of the disc secondary in such a manner that each coil extended away from the secondary from a common central ground and in the same direction of turning in each instance so as to comprise mirror images of one another, the coils would no longer be bucking and there could successfully be achieved a striking increase in coupling at relatively low potential and 3 with insulation difficulties being held to a minimum. This d1scovery constituted a very essential part of the present invention.

From this discovery, it was thereafter conceived that this stronger coupling effect might be still further augmented by selectively controlling the shape and location of the primary coils with respect to the secondary. This last concept, it was found, could be successfully embodied by employing two primary coils of the mirror image type described; enclosing the coils at their common ground point with a disc type secondary; and forming each coil component in a spiralling or dished conformation in order to bring the constituent turns of each component in close proximity to the secondary at opposite sides thereof and, preferably, in a manner such that the axial spacing of each primary turn from adjacent secondary disc surface varies proportionately with change in triadial spacing of said turns from the axis of the secondary In its broadest aspect, therefore, my invention is based on the discovery that I may provide for an unusual and surprisingly large increase in coupling of magnetic flux by passing R. F. high-voltage impulses along two primary mirror image type coils which are joined together at a common ground point and which are centrally enclosed by a split disc type secondary of short axial length and, preferably, a disc whose spacing from constituent turns of each of the coils increases proportionately with increase in radial spacing of the turns from the central axis of the secondary disc. i i

The nature of the invention may be more fully understood and appreciated from the following detailed description of a preferred embodiment selected for purposes of illustration and shown in the accompanying drawings, in which Fig. 1 is a plan view of the transformer apparatus of the invention shown independently of electrical circuitry and coolant connections;

Fig. 2 is a cross-section taken on the line 2-2 of Fig. l; and

Fig. 3 is another cross-section taken on the line 3-3 of Fig. 1.

Referring more in detail to the transformer structure shown in the drawings, I have, in general, illustrated an arrangement of disc type secondary element of short axial length and two mirror image type primary coils located at either side of the secondary disc to comprise an induction heater structure of commercially acceptable nature.

Numerals 2 and 2' indicate the two primary coil components whose outer ends are connected by a conductor 2a. Numeral 4 indicates the secondary disc element. This secondary disc element 4 consists of a split annular body of short axial length and formed from a low resistance material such as copper. The split ends of the annular body 4 are provided with electrical output members 6 and 8. These members 6 and 8 have supported therethrough two sections of a high current type work coil member 10, which sections are made up of tubular copper conductor portions whose ends are detachably connected by threaded couplings to respective tubular extremities 12 and 12 of a coolant conduit 12. This conduit member is secured to the secondary 4 and extends around its outer peripheral edge, as shown in Fig. l. A coolant, such as water, is supplied and removed through the connecting ends 14 and 16 which are, in tum, connected to a suitable supply source.

The primary coil components 2 and 2 may, for example, consist of a continuous length of copper tubing which is folded or bent over upon itself to provide a common junction or meeting point 20, as shown in Figs. 1 and 2. The two components are arranged in the form of two dished or axially displaced spiralling coils so that the turns of each coil project outwardly from either side of the secondary 4 and extend in the .4 same direction to thus constitute mirror images of one another.

The two outer ends of the coils are connected to a source of R. F. power of relatively high potential, such as 5,000 volts, and each coil is grounded at a common ground point through a ground strap 18 attached to the junction 20. Power is delivered to the coils as R. F. high-voltage impulses which are conducted along the surface of these tubular coils. A coolant, such as water, is circulated through the coils from a suitable supply source which may be taken from the same source of supply for cooling the secondary member. Each turn of the primary coils is covered with a solid type insulation material which provides limited insulation with optimum induction effects and, in addition, each of the primary turns are supported upon spacing wedges 22 located at several points around the two opposite surfaces of the secondary disc 4, as best shown in Figs. 2 and 3. These wedging members thus control the degree of axial displacement of the respective primary coils from adjacent secondary surfaces and thus provide a convenient means of decreasing the spacing of the primary coils with decreasing voltage potential which ranges from a maximum at the outer peripheral edges of the secondary to a minimum at the inner peripheral edges thereof.

The structure described is characterized by several important and novel features all of which combine to produce relatively heavy current carrying capacity with small loss. The principal feature to be noted is that the secondary in the particular position in which it is arranged relative to the primary is adapted to produce a very strong coupling of magnetic flux. This is because the secondary occurs in the center of the primary in the first instance and, in the second instance, the arrangement is such that much less voltage insulation is required to avoid trouble. By bringing the primary very close to the secondary, as is achieved by having two sets of spiralling coils at either side of the secondary, a maximum of coupling is achieved at all points with the adequate amount of voltage insulation being provided for. However, it is pointed out that there is a voltage condition which is at its maximum in entering the primary where the spacing of the dish spiralling coils is greatest and the voltage tapers to a minimum where the spacing of the two sets of coils is at a minimum or nearly zero magnitude.

In typical forms of the apparatus of the invention, measurements have been made of the Q or figure of merit of the transformer coils, i. e., the ratio at any frequency of actual inductive reactance of the coils to the actual resistance at that frequency. These measurements have shown materially increased values of Q over those of conventional transformer arrangements of comparable nature. It was found, for instance, that, if the flux from a conventional coil of ten turns on a two-inch diameter was represented by the figure 10, to obtain a similar flux by my method, two coil sections of six turns each would be needed with the flux additive to each other and the R. F. voltage being fed into the ends and taken out of the center. This meant that, for the same amount of flux and a coil of approximately the same size and shape, with my method, the D. C. ohmic resistance was approximately one-quarter of the conventional coil and, as a result, Q, or quality factor, was increased by a multiple of four.

Another extremely important feature in the construction described is the freedom from loss of stability in the coils in the presence of greatly increased coupling of the magnetic flux. By grounding the primary in its center loop portion and by providing for the spiralling coils extending in the same direction away from a common groundpoint, there is achieved, to a large extent, elimination of parasitic oscillations and excessive heating of the secondary. It will be observed that the leads on both sides of these primary coils which are mirror images of each other are connected together and are taken 05 in the same direction which leads to perfect symmetry, and this is of great importance in H. F. work where even short inductances are of great consideration.

In typical applications of induction heating utilizing the above described method and apparatus, very striking results may be obtained as is evidenced by the following examples.

Example 1 Titanium in the form of a' Ai-inch diameter rod was required to be heated to a temperature of 3450 F. Employing the induction heater of the invention, the rod of titanium was brought to the indicated temperature in /2 second with a power available of 5 kilowatts. So far as is known, there is no commercial apparatus available for forming suchan operation.

Example II in one commercial manufacturing process, it was required to continuously harden small saw blade elements by bringing these blades to a hardening temperature of 1600 F. as rapidly as possible. Employing the method and apparatus of the invention, these saw blades were hardened at a temperature of 1600 F. and at a rate of 60 feet per minute of stock. The best performance observed by conventional equipment employed for this purpose was heating to 1600 F. at the rate'of 17 feet per minute.

Example III In a required commercial operation, it was necessary to heat at rapid rate silvered copper wire, #20. Applicants apparatus provided necessary heating to a temperature of 1000 F. at a rate of 22 feet per minute (5 kilowatts). No comparable heating by prior art devices is known.

Example IV understood that the invention is not limited in its application or in its form of construction and the method and apparatus may be modified and practiced in various ways. For example, the invention, as a transformer, may be used as a coupling device for radio broadcasting with improved efficiency to transfer energy from oscillator to transmission line, from one transformer line to another transformer line of different characteristics, in a trans former line to radiating elements for other antennas. Also, the primary and secondary elements may be desired to be used as a step-down transformer, in which case the secondary disc becomes the primary.

Thus, from the foregoing description, it will be seen that I have provided an important and novel method and to the secondary electrical conductor and extending away 1" m the common ground point in the same direction whereby high voltage impulses applied to the primary will produce flux paths for the two coils, which flux paths combine in series and are additive, and the said spacedapart coils of the primary electrical conductor being arranged in the form of a conical helices so that the axial spacing of constituent turns of each of the coils from the adjacent secondary electrical conductor varies proportionately with change in radial spacing of said turns from the axis of the said secondary electrical conductor.

2. Transformer apparatus for induction heating and comprising in combination a secondary electrical conductor, said secondary electrical conductor including a disk member having an opening located centrally therethrough to define an annular body portion, said disk member being split at one point and presenting circumferentially spacedapart ends, electrical terminal members solidly fixed to said spaced-apart ends of the disk member, a primary electrical conductor consisting of two spaced-apart coils supported at opposite sides of the secondary electrical conductor, said coils being j ined together with a common central ground point and having their outer ends connected to a common terminal, each of said coils having its turns extending away from the common ground point in the same direction in order to cause high voltage impulses applied on the primary to induce llux paths around the two coils with each flux path being in series and additive, and said secondary electrical conductor comprising a tubular conductor element located around the outer periphery of the said disk and extending through References Cited in the file of this patent UNITED STATES PATENTS 891,496 Luschka June 23, 1908 1,382,905 Gravell June 28, 1921 2,181,899 Kennedy Dec. 5, 1939 2,355,560 Roberds Aug. 8, 1944 2,366,290 Rudd Jan. 2, 1945

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