US2474395A - High-frequency transformer - Google Patents

Description

June 28, 1949. EARLY ET AL 2,474,395

HIGH-FREQUENCY TRANSFORMER Filed Sept. 20, 1945 attorney.

Patented June 28, 1949 HIGH-FREQUENCY TRANSFORMER Harold 0. Early, Beaverton, and William G. Dow

and Robert Ohlsson, Ann Arbor, Mich., assignors to General Motors Corporation, Detroit,

Mich., a corporation of Delaware Application September 20, 1945, Serial No. 617,614

Claims. 1

This invention relates to electrical transformers and more specifically to electrical transformers for use with high frequency electrical power. It is of course well known that the problems attendant transformer design are radically differ" ent when the same is to be used on a high frequency power installation than when the same is to be used on ordinary commercial power which is usually of a frequency of 60 cycles. As the frequency increases the problems of iron and copper loss vary considerably, the hysteresis and eddy current factors of the former take on added importance and the skin effect of high frequency current varies the copper consideration. Therefore in proceeding from commercial low frequencies to for example frequencies in the radio broadcast band an entirely different set of considerations for transformer design are found. The transformers usually are air core though in some instances may be provided with a coznminuted or laminated iron core which is formed of small particles isolated from each other. in radio equipment however the amount of current and energy being handled is relatively small.

There has recently been considerable activity in the fields of high frequency heating and weld ing and in such a system the amount of current utilized is relatively large and the previouslymentioned high frequency transformers incapable of handling the load. It was therefore necessary to design transformer means to supply the heavy current heating and welding equipment at advanced frequencies.

It is therefore an object of our invention to provide transformer means for operation at frequencies and very high currents.

It is a further object of our invention to provide a high frequency transformer for heavy currents such for example as for welding.

It is a still further object of our invention to provide a design for high frequency heavy duty transformers in which the skin and proximity effects of high frequency current are taken into consideration.

With these and other objects in view which will become apparent as the specification proceeds, our invention will be best understood by refer" ence to the following specification and claims and the illustrations in the accompanying drawings, in which:

Figure 1 is a perspective view of a transformer winding and terminal arrangements embodying our invention;

Figure 2 is a front elevation of a portion of the winding per se taken on the line 2-2 of Fig. 1;

Figure 3 is an enlarged end view of the winding and terminal plates, parts being broken away and shown in section to illustrate the connection of the windings and plates; and

Figure 4 is an enlarged sectional View through a portion of the terminal plates.

There are a number of points in such design that must be taken into Consideration for proper final construction. The first of these is that since high frequency current is used both the skin effect and the so called proximity effect will be present in the conductors. The skin effect causes current to tend to flow along the surface of the conductor and the proximity effect makes the skin effect more pronounced in two adjacent conductors in which the current is flowing in opposite directions. In other words the current tends to pile up on the surface of a conductor adjacent another in which the current is flowing in the opposite direction. These effects can be used to advantage to decrease losses by providing large surface areas between adjacent turns of primary and secondary, as by using fiat conductors, and yet the total volume of the winding will be less than if some other cross section of conductors were used.

The second consideration is that the leakage flux must be very low for various reasons par ticularly to aid in keeping the size of the transformer small. It has been pointed out above that the optimum cross section for the conductor is flat from a high frequency standpoint and of course this could be manufactured by forming the windings. In order to produce interlinked windings with a minimum leakage, edge winding is used with the primary and secondary turns completely interleaved. This provides a very low leakage flux.

The third consideration is that the primary inductance must be adequately large in a high frequency transformer or the magnetizing current will be excessive. To provide this the diameter of the windings must be large or the axial length short. By using the edge wound construction the axial length is kept to a minimum so that a smaller diameter winding can be used than would otherwise be the case. In general, these principles apply to either air core or iron core transformer construction and if iron core is used then following these principles may result in economy.

While the above considerations relate to the windings per se a part also relates to the conductors connected to the windings and which provide connection thereto. Flat parallel surare rigidly secured cooling fins faces are used to prevent excessive current pil ing up and attendant losses.

In welding transformers or others capable of handling high currents, the ratio of primary to secondary turns is usually large and it is not unusual to have the secondary consist of plurality of single turns in parallel to carry heavy current. Such a transformer is illustrated in the accompanying drawings but it is desired to state that this is merely exemplary of one form of applicants invention and that the same could be applied to transformers of different ratios.

The primary in the present illustration consists of a continuous helical coil 2 formed of a flat member shaped into a coil around its major dimension. The flat sides are coated or covered with any suitable insulating means i to maintain the turns electrically isolated. The helical turns are stretched out or axially spaced far enough apart so that a single secondary turn may be inserted between each primary turn, thus providing in general a continuous hecal primary winding and alternate single turn second-- ary coils between each primary turn.

The single secondary coils or turns are shown in Fig. 2 in which the primary coil begins at the upper left hand corner of the figure and then appears again as the first full turn and as each alternate turn thereafter. turn such as G, 8, ll], l2, etc., starts and ends at approximately the center and the ends are offset so that the turn will fit between the primary turns. The adjacent ends of successive secondary turns are oppositely notched as at so that they may overlap to a certain degree but since the contour of each turn is helical the two ends of one turn are not in juxtaposition but rather the ends of one turn overlap and are adjacent to the opposite ends of the turns on either side thereof.

There are also rigidly secured to each end of each turn outwardly projecting flat conductor strips I5, I3, 213, 22, etc., that are twisted so that their outer ends lie in a horizontal plane, the two adjacent strips connected to the ends of two coils being in spaced parallel relation through.- out their surfaces to keep the current spread over a large surface area by utilizing the skin and proximity effects of high frequency cur rents and maintains the inductance loop as small as possible. At several places around the periphery of each of the secondary coils there In the present instance three of these are shown. Each fin has a central opening 25 therein, and tubes 23, through which coolant circulates, project through an aligned series of fins tocool the same.

It will be noted with respect to Fig. 2 that the terminals H5, H1, 25!, etc., of the secondary turns are grouped into two parallel series one above the other. It is desired to provide as convenient terminal facilities as possible for a o plication of the power of the transformer to a load and since as reviously mentioned this is for high frequency installation the skin, proximity and inductive loop effects are taken into consideration in electrode or output terminal design. For some applications it is desirable to provide surfaces upon which pieces to be welded can be rested and this type application is illustrated in this instance. The simplest manner in which this could be accomplished would be to connect all of the terminal strips connected to one end Each secondary of each secondary turn to one plate and all of the others to a second plate in close but spaced relation thereto. One plate would then be longer than the other to provide a step with the two different elevations providing power output and upon which parts could be laid for welding. This however is not mechanically feasible, for the terminal strips when twisted would be too close together so two series at different elevations are used.

All of the uppermost strips in the upper series Iii, 22, etc., are conductively connected to a large sheet 36 and all of the lower strips of the upper series to a second sheet 32 which is insulated from the first sheet by an insulating layer 34. A third sheet 35 is connected to the third series of contacts it, etc., and lies parallel to the second sheet. The terminal strips connected to sheets 32 and '35 are so poled that current will be flowing in the same direction in these two so they are not insulated from each other. The lowest row of strips Zil, etc., are connected to a bottom plate 33 which, as in the case of the two .top sheets, is insulated from the sheet 38 above it by a layer of insulating material 40.

Since therefore the polarity of the top and bottom sheets Eli and 38 is the same these can be connected together and the ultimate result is two deck plates or electrodes to which the Work can be applied. This is accom'p ished by integral side panels 42 extending from sheet 38 to sheet 30 and insulated from the two intermediate sheets by a layer of insulation 44 as best shown in Fig. 4. The assembly of plates is secured together by suitable bolts it properly insulated from one set of sheets or plates. Intermediate sheet 32 is extended beyond the remaining sheets and it with the upper sheet form the work surfaces for application of parts to be welded as shown at 48 and 58.

We therefore have provided a transformer for use on high frequency current in which the inductance loops formed by the conducting portions of the leads to the work are kept to a minimum, the skin effect and attraction of currents flowing in opposite directions has been fully utilized to provide an efficient device, the primary inductance is high and the leakage flux low, and the size kept to a minimum.

We claim:

1. In transformer means for use with high frequency current, a primary winding in the form of a helix with the turns axially separated, a plurality of single turn secondary windings interposed between the primary turns to form a cylindrical member, the ends of one secondary turn lying adjacent the ends of each secondary turn on opposite sides thereof, conductor strips connected to the ends of each secondary turn, which will result in associated pairs of strips, each pair of strips lying in spaced parallel relation throughout their length and twisted intermediate their ends so that the planes of the opposite ends of each strip are at right angles toeach other and a plurality of parallel spaced conductive plates connected to the extending series of strip ends.

2. In transformer means for use with high frequency current, a primary winding in the form of a helix with the turns axially separated,- a plurality of single turn secondary windings interposed between the primary turns to form a cylindrical member, the ends of I one secondary turn lying adjacent the ends of each secondary turn on opposite sides thereof, conductor strips connected to each end of each secondary turn forming associated pairs of strips, each pair of strips lying in spaced parallel relation throughout their length and twisted from a position parallel to the faces of the turns to one at right angles thereto to form separate series and a plurality of parallel spaced conductive plates each connected to a series of extending ends of the strips.

3. In transformer means for use with high frequency current, a primary winding in the form' of a helix with the turns axially separated, a plurality of single turn secondary windings interposed between the primary turns to form a cylindrical member, the ends of one secondary turn lying adjacent the ends of each secondary turn on opposite sides thereof, conductor strips connected to each end of each secondary turn resulting in a series of closely spaced parallel pairs, said strips being twisted so that their extending ends are at right angles to their inner ends but that they remain parallel to the other one of the pair throughout their lengths to utilize the proximity efiect and a plurality of conductive terminal plates connected to the extending ends.

4. In transformer means for use with high frequency current, a primary winding in the form of a helix with the turns axially separated, a plurality of single turn secondary windings interposed between the primary turns to form a cylindrical member, the ends of one secondary turn lying adjacent the ends of each secondary turn on opposite sides thereof, conductor strips connected to each end of each secondary turn, a plurality of superimposed plates of conductive material connected to the conductor strips, insulating material separating a portion of the plates, conductive means interconnecting other of said plates so that two plates of opposite polarity are provided at the locale to support the work,

5. In transformer means for use with high frequency current a multi-turn primary windin in the form of a helix with axial spacing between turns, a plurality of single turn secondary windings interposed one between each pair of primary turns, conductor strips radially extending from each secondary terminus in parallel pairs, first conductive means connected to a portion of these strips to connect one end of each secondary turn, second conductive means connected to the remaining strips to connect the opposite secondary ends, said first and second conductive means being mechanically supported in major dimension juxtaposition but electrically insulated from each other to utilize throughout the principle of proximity current flow to decrease loss.

HAROLD C. EARLY. WILLIAM G. DOW. ROBERT OHLSSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,394,044 Stephens Oct. 18, 1921 1,506,320 Northrup Aug. 26, 1924 1,880,199 Gebhard et al. Oct. 4, 1932 2,325,810 Strickland Aug. 3, 1943 2,378,884 Seifert June 19, 1945 FOREIGN PATENTS Number Country Date 372,475 Germany Mar. 28, 1923

Images