US2390800A - Transformer - Google Patents

Description

Dec. 11, Q J. MADSEN 2,390,800

TRANS FORMER Filed May 13, 1942 INVENTOR Car/ J'Madse/z M5 ATTORNEY Patented Dec. 11 1945 TRANSFORMER Carl J. Madsen, Baltimore, Md., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application May 13, 1942, Serial No. 442,767

4 Claims.

My invention relates to electrical transformers, and more particularly to the construction of such transformers for use in supplying electric energy to areas in which high-intensity, high-frequency energy is transmitted, such as for supplying energy to lights on radio towers used in broadcasting.

Radio towers are commonly used as the radiating elements of modern antenna arrays. When so used, the base of the tower is insulated from ground and in operation is often several thousand volts above ground potential. Towers of the heights commonly used require illumination in accordance with government requirements. One means of supplying power for different purposes is through the use of a transformer mounted at ground potential adjacent to the radio tower. When a transformer is operated in a high energy intensity radio frequency field, and/or with the secondary at high potential radio frequency, it is necessary that the transformer must have (1) low electrostatic capacity between the secondary winding and the primary winding and. between the secondary winding and ground; (2) low loss with respect to radio frequency potentials which may he induced in the secondary; (3) absence of series or parallel resonant circuits with resge ct to radio frequency throughout the frequency band for which it is designed; and i) l loss with respect to radio frequency currents which pass secondary to ground, winding, core case.

in titlepast it has been common practice to provide a transformer having primary and cndary -windings spaced apart a considerable disiance to reduce the electrostatic capacity be= tween them and to connect an electrostatic shield to each winding. These shields are so placed as to be on the adjacent faces of the closely associated windings. Normally the primary winding and the transformer core are connected to ground potential so that these parts are at ground potential with respect to the radio frequency field. The secondary winding is mechanically insulated from the primary winding and is commonly wound as a spool of conductor having the conventional layer upon layer winding with a number of turns of either round or rectangular wire in each layer, the conductors being insulated with enamel, cotton, sill: or glass or some similar material. Multiple layer windings, each layer having several turns, are frequently used to reduce the eifective condenser area of the secondary winding. windings of this type, however, often develop series resonant or the v. n

parallel resonant circuits at some frequency in the broadcast hand. .These resonant effects are caused by the distributed capacitance in the winding and between the winding and the shield and other parts of the apparatus. Such resonant effects cause comparatively high energy loss and also adds unpredictable capacity effects into the adjustment of the antenna arrays with which they are associated.

In accordance witi the present invention, a secondary winding is employed formed or a flat ribbon shaped conductor wound spirally layer upon layer having a single turn per layer nd having a low loss material, excepting the a cent turns. The insulating low loss separating or insulating the adjacent turns be a thin strip of polystyrene, Cellophane, tape, enamel, other suitable varnishes or condenser "paper or the like. This type of winding construction gives exceptionally high capacity between tune of the winding maintaining the ct tire winding ,at substantially the same radio frequency potential. it becomes minecessary, therefore, to provide a shield for the winding as the inner turn performs the function of shield. This construction winding has a lower effective capacitance to the primary winding and ground an equivalent winding and shield in which the winding is wound layer upon layer of silty of turns per layer. s is caused y the smaller overall ding winch is possible because of the simplified mechanics cti object o to provide a timer having ln h capacit ween winding turns so to maintain the en ire winding at substantially the same radio ireuuency potential.

It is a further object of the invention to provide a secondary winding having lower effective capacitance to the primary winding and ground of the transformer than a having the equivalent current carrying capacity Wound layer upon layer with a plurality of turns per layer to-' gether with an electrostatic shield connected thereto.

Gther objects and advantages of the invention will be apparent from the following description or certain preferred embodiments thereof, reference being had to the drawing, in which:

Figure 1 is a diagrammatic view showing a lighting transformer connected to a radio tower;

Fig. 2 is a view partly in section showing a construction organized in accordance with the invention;

vii.

active area of Fig. 3 is a sectional view taken along line III-III of Fig. 2; and

Fig. 4 is a view partly in section, of a modified transformer structure.

Referring to the drawing, the numeral I identifies a radio tower which may be mounted above ground and insulated therefrom by insulating material 2. A source of illumination 3 is provided at the top of the tower and is supplied through a transformer 4 mounted near the base of the tower and having a primary winding connected by conductor 6 to a commercial source of electric energy and a secondary winding 1 connected through conductors 8 to the illuminating source 3. A shield 9 is shown between the primary and secondary windings, 5 and I, the shield 9, the transformer casing 4 and the winding 5 being connected to ground at I0.

Referring to Figs, 2 and 3, the transformer core I| provides a closed magnetic loop having winding legs I2 and I3 upon which are positioned primary windings I4 and I5 connected in series through conductor I6 and to a source of electric energy through conductors 6. Electrostatic shields I1 and I8 are provided about the windings I4 and I5, respectively, which extend about the windings and between the primary windings and the secondary windings.

Secondary windings I9 and are provided about the winding core legs I2 and I3 spaced both from the primary windings l4 and I5, respectively, and from the core legs. These windings are supported upon a plurality of supporting rods 2| which are preferably made from low loss insulating material, such as isolantite, insanol or polystyrene compounds, which have lower loss characteristics than Micarta or similar insulating material. The winding coils I9 and 20 are formed by winding a fiat ribbon conductor 24 between layers of insulation 25 and positioning it about the supporting brackets or rods 2|. The winding will have a length 26 substantially equal to the width of the ribbon 24 from which the winding is wound. The two windings I9 and 20 are connected together by a conductor 21 and to the secondary conductors 8 supplying the energy to the load. As illustrated, the secondary windings are positioned about portions 28 of the winding legs l2 and I3, respectively, adjacent one end thereof while the primary windings I4 and I5 are positioned about portions 29 adjacent the opposite ends thereof.

' Referring to the form of the invention shown in Fig. 4, a .core 4| is provided having winding legs 42 and 43 about which are positioned spools of insulating material having body portions 53 and 54 and end portions 44 and 45. Primary windings 46 and 41 connected in series are positioned adjacent the opposite ends of the two core legs Hand 43 and secondary windings 55 and 56 are positioned adjacent the remaining two opposite ends and connected in series. The secondary windings are supported upon rods 49 extendin between the ends 44 and 45 of the spool shaped insulating structures, and upon which the terminal members SI and 52 of the secondary winding may be clamped. The structures of the individual windings 55 and 56 are similar to the secondary windings I9 and 20 shown in Figs. 2 and 3, and the windings 46 and 41 may also be similar to windings I9 and 20, that is, formed by winding a ribbon of conducting material between layers of low loss insulatin material, or these windings may be of the layer upon layer type of construction corresponding to windings I9 and 20 in Fig.

2. The type of construction shown in Fig. 4

shows a somewhat more compact arrangement.

/ 0f the primary and secondary windings than that shown in Fig. 2. In transformers of conventional design, that is, having both primary and secondary windings formed of the layer upon layer type with a plurality of turns per layer and each provided with an electrostatic shield, the effective secondary and primary capacities have been shown to range from 50 to 120 microfarads depending upon the physical arrangement of the windings and other transformer parts. Such transformers usually exhibit resonant effects in or near the conventional broadcast band of frequencies. The calculated radio frequency losses in a typical installation have been several hundred Watts.

In a design corresponding to Fig. 2' having the same voltampere rating, the secondary to primary capacityn anges from values of 30 to 43 microfarads with various arrangements of the transformer parts. The calculated losses at radio frequency in a typical application was less than watts. No resonant effects have been noted in or near the broadcast band of radio frequency.

The form of the primary winding used has comparatively little effect although some improvement results from the use of a fiat ribbon type winding as distinguished from the layer upon layer with multiple turns per layer type of winding. Materials such as Bakelite, varnishes, polystyrene solutions, enamel, etc., have been successfully used as a separating and insulating medium.

It will be apparent to those skilled in the art that modifications in the specific structure illustrated and described may be employed within the spirit of my invention, and I do not wish tobe limited other than by the scope of the appended claims.

I claim as my invention:

1. In an electrical transformer for transmitting electric energy in a high-energy; high-frequency field. an arrangement of the elements of the transformer characterized by providing low electrostatic capacity between the transformer primary and secondary windings and between the secondary winding and ground, and absence of series or parallel resonant characteristics throu hout a band of high frequency radiations, said structure comprising a magnetic core loop havingtwo Winding legs, a high-voltage winding and a low-voltage winding thereon, the high-voltage winding comprising two winding coils having much less length than the winding legs, one coil being Wound on each leg and positioned adjacent the one end of the leg, the winding coils being connected in series and each winding coil being provided with an electrostatic shield substantially surrounding the edges of the Winding coil and ponding to the length of the winding. the lowvoltage windings being positioned about the opposite ends of the winding legs of the core than the high-Voltage winding.

2. In an electrical transformer for transmitting electric energy in a high-energy, high-frequency field, an arrangement of the elements of the transformer characterized by providing low electroaso soo static capacity between the transformer primary and secondary windings and between the secondary winding and ground, and absence of series or parallel resonant characteristics throughout a band of high-frequency radiations, said structurecomprising a magnetic core loop having two parallel winding legs, a high-voltage wlndingcomprising two-winding coils positioned about opposite ends of the winding legs and connected in series, each coil comprising a plurality of windin turns placed layer upon layer closely about the core winding leg, a low-voltage winding comprising two winding coils connected in series positioned about the remaining two opposite ends of the winding legs in spaced relation from the highvoltage winding coils, said low-voltage winding coils each comprising a plurality of winding turns of flat conducting ribbon wound turn upon turn to provide one turn per layer, and anelectrostatic shield about each coil of the high-voltage winding and extending along the sides thereof facing the high-voltage winding and the low-voltage winding each comprising two winding coils having much less length than the winding 1888. one winding coil being on each leg and positioned adjacent the ends of the two legs, each winding coil being provided with an electrostatic shield substantially surroimdingtheedgesofwindingooilandthe end thereof facing the associated coil of the lowvoltage winding, the low-voltage winding being formed of two single turn layer winding coils connected in series one wound on each winding leg of the core and having a much less length than the length of the core and formed of continuous strips of conductor wound layer upon layer between strips of insulating material, the strips hav-- ing a width corresponding to the length of the winding, the low-voltage winding coils being positioned about the ends of the winding legs of the core opposite to the coils of the high-voltage winding.

4. In an electrical transformer for transmitting electric energy in a high-energy, high-frequency field, an arrangement of the elements of the transformer characterized by providing low electrostatic capacity between the transformer primary and secondary windings and between the secondary winding and ground and absence of series or parallel resonant characteristics throughout a band of high-frequency radiations, said upon turn to provide one turn Der layer positioned structure comprising a magnetic core loop having two parallel winding legs, a high-voltage winding comprising two winding coils positioned about op- DOsite ends of the winding less and connected in series, each coil comprising a plurality of winding turns of flat conducting ribbon wound turn closely about the core winding leg, a low-voltage winding comprising two winding coils connected in series positioned about the remaining two onpcsite ends of the winding legs in spaced relation from the high-voltage winding coils, said lowvoltage winding coils each comprising a plurality of winding turns of flat conducting ribbon wound turn upon turn to provide one turn per layer, and an electrostatic shield about each coil of the highvoltage winding and extending along the sides thereof facing the low-voltage winding.

CARL J. MADBEN.

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