JPH0445962B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to a transformer with a magnetic core of amorphous material.

Description of the Prior Art In the manufacture of iron-clad transformers, the primary and secondary windings are formed into a common ring with a central opening or window. Two or more rings of core material are cut open and passed through windows in the winding and closed, such that the rings of core material are disposed around and surrounding the winding. One of the problems with steel transformers is that it is difficult to cut and shape the core material without degrading its magnetic properties. To overcome this problem, core transformers have been proposed, in which the magnetic core is formed into a ring, and two or more groups of primary and a secondary winding surrounds the ring. Such core type transformers are large and inefficient from the point of view of material usage. Furthermore, in the aforementioned types and transformers, the heat generated by the windings and magnetic core during operation often results in temperature rises of more than 50°C, and the solid insulating materials in the magnetic core and windings as well as the transformer The rate of deterioration of the liquid coolant in which it is immersed increases. For this reason, transformers of the type described generally result in higher purchase and maintenance costs than would be considered desirable, and also exhibit lower operating efficiency.

SUMMARY OF THE INVENTION The present invention utilizes a plurality of easy-to-assemble segmented links to form an annular segmented winding, thereby making the overall device easy to fabricate and relatively robust in construction. The present invention provides a transformer with excellent heat dissipation efficiency by segmenting such windings and separating each of them from each other around the magnetic core, and furthermore, has low hysteresis loss and low eddy current. By forming the magnetic core with a soft magnetic material, especially amorphous strip material, which has various properties such as loss, low coercive force, high permeability, high saturation value, and small permeability change due to temperature, provides a transformer that is smaller, lighter, more efficient in operation, and more reliable than the use of strips of conventional polycrystalline metal alloys to produce transformers of comparable power capacity. It is.

Furthermore, the invention provides a transformer with an annular segmented secondary winding. The annular segmented secondary winding consists of a plurality of segmented links surrounding the magnetic core and primary coil and interconnected to provide a helical current path. Each split link has a portion that passes through the central opening of the magnetic core and is spaced apart from one another around the core.

The transformer of this invention has important structural features. For a given power capacity, the toroidal core requires less material. Since there is no air gap in the magnetic core, the magnetizing current is reduced. The toroidal core can be easily wound from strip material and is particularly suitable for use with amorphous metal strips. The split links are easily manufactured or cast and press-fit during assembly to form an outer container that strengthens the device and protects the internal core and windings. The segmented configuration of the primary and secondary coils improves heat dissipation and reduces temperature rise. As a result, the transformer of the present invention has smaller dimensions, weight and manufacturing costs, and higher operating efficiency and reliability than conventional transformers.

The invention will be better understood and other advantages will become apparent from the following detailed description of adopted embodiments of the invention and the accompanying drawings.

(Explanation of adopted configuration example) Looking at Figures 1 and 2, it has a 25KVA rating (of course, other ratings are also possible)
A transformer is illustrated. The magnetic core 10 is constructed by stacking a plurality of annular bodies 12. Each toroid 12 is formed from a coiled magnetically permeable strip of material. In the illustrated configuration, seven stacked toroids 12 are used, each of which is approximately 1 inch in height and has an inner diameter of approximately 1 inch.
8.6 inches (approximately 21.84 cm), outer diameter approximately 14.3 inches (approximately
36.32cm). However, as will be appreciated, the number of stacked toroids and the height and inner and outer diameters of each toroid depend on the required efficiency, volume, eddy current reduction requirements, power rating,
It can be changed depending on the frequency, etc. The toroids 12 are separated from each other by an annular insulator 14 which provides the required flexibility at the core's designed operating temperature, typically in the vicinity of 130°C.
Any suitable thermosetting or thermoplastic material exhibiting dielectric strength, tenacity and stability, such as glass cloth, fiberglass, polycarbonate, mica, CAPSTAN, LEXAN, fiber paper, etc. It may be formed of an insulating material. Insulating layer 14 is in the form of a flexible film approximately 1/2 mil (1.27 x 10 ^-3 mm) thick and having inner and outer diameters approximately matching those of toroid 12 . It will be appreciated that insulating layer 14 need not be continuous, but may be in a spaced apart form if desired. Alternatively, the insulating layer can be applied by spraying, coating, etc. without separating it. Furthermore, the magnetic core 10 can take a form other than annular, such as oval, rectangular, square, etc., and can also take a molded structure rather than a wound structure. A similar insulating wrapper 16 is shown, which in this case surrounds the magnetic core 10 on all exterior surfaces, enclosing the magnetic core in the form of an insulating cocoon.

The coiled strip material of the annular body 12 is comprised of a soft magnetic material. Such materials have (a) low hysteresis losses, (b) low eddy current losses, (c) low coercivity, (d) high permeability, (e) high saturation values, and (f) permeability with temperature. It is desirable to have the following characteristics: Commonly used soft magnetic materials in the form of strips, such as high-purity iron, silicon, steel, iron, nickel alloys,
Instead of iron-cobalt alloys, etc., the present invention uses recently available amorphous (glassy) magnetic alloy strip materials. Alloys of this type are at least about 50% amorphous as determined by X-ray diffraction. In this type of alloy, M is at least one of iron, cobalt and nickel, T is at least one transition metal element,
When X is at least one of the metalloid elements of phosphorus, boron, and carbon, (M _60~90 T _0~15
It consists of an alloy with the _formula : Up to 80% of the carbon, phosphorus and/or boron in X may be replaced by aluminum, antimony, beryum, germanium, indium, silicon, tin. When used as transformer cores, such amorphous metal alloys generally exhibit superior properties compared to the conventional polycrystalline metal alloys in common use. A strip of such amorphous alloy is at least about
Preferably, it is 80% amorphous, and even more preferably at least about 95% amorphous.

Preferably, the amorphous magnetic alloy of magnetic core 10 is formed by cooling the melt at a rate of about 10 ⁵ -10 ⁶ ° C./sec. Various well-known techniques can be used to produce rapid-quenched continuous strips. The strip material of magnetic core 10 is typically in the form of a wire or ribbon. This strip material is conveniently prepared by dumping the molten material directly onto a cooling surface or into some type of quenching medium. Such processing techniques do not require intermediate drawing or ribbon forming steps, thereby significantly reducing manufacturing costs.

Desirable amorphous metal alloys for constructing magnetic core 10 typically range from about 200,000 to
Exhibits high tensile strength of 600000 psi (1.35×10 ⁶ to 4.14×10 ⁶ kpa). It is usually used in annealed condition and has a pressure of about 40000 to 80000 psi (2.76 x ¹⁰⁶ to 5.52
x10 ⁶ kpa).

Additionally, depending on the particular composition, the amorphous metal alloy used to form the magnetic core 10 has a temperature of about
160-180 microohm cm (1.6
It exhibits a high electrical resistivity of ~1.8 microohm-meter). Typical conventional substances are approximately 45~
160 microohm cm (0.45~
It has a resistivity of 1.60 microohm-meter). The high resistivity of the amorphous metal alloys defined above minimizes eddy current losses, which are a factor in reducing core losses.

Another advantage of using an amorphous metal alloy to form the magnetic core 10 is that it provides a lower coercive force than conventional compositions of approximately the same metal content, and is therefore more expensive than those with a high nickel fraction. This means that a larger amount of relatively inexpensive iron can be used for the magnetic core 10 compared to the conventional method.

The toroid 12 may be formed by continuous winding on a mandrel (not shown) while tensioning the strip material to provide a tight structure. The number of turns is selected depending on the desired dimensions of the annular body 12. The thickness of the strip material ^of the toroid 12 is preferably in the range of 1 to ² mils. The relatively high tensile strength of the amorphous alloy used here allows strip material with a thickness of 1 to 2 mils (approximately 2.54 x 10 ^-2 to 5.08 x 10 ^-2 mm) to be used without fear of breakage. can do. As will be appreciated, making the strip material relatively thin increases the effective resistivity because there are more boundaries per unit radial length that eddy currents must pass through.

The primary winding is shown as having at least three primary coils 18 surrounding and spaced apart from each other around the magnetic core 10. The illustrated configurations each have approximately 1 inch (approximately 2.54 cm)
There are 18 coils 18 made up of 84 turns of insulated aluminum strip 0.005 inches wide and thick. This configuration provides a 6000 volt primary winding, but other ratings are possible. The number of primary coils 18 used may vary depending on the inner diameter of the magnetic core 10, the width and thickness of the strip material used for each coil, the number of turns per coil, and the desired spacing between each coil. I can do it. The number of primary coils should preferably start from about 10.
In the range of up to 30, more preferably in the range of about 16 to 20. Furthermore, the primary coil 18 has a voltage
It can vary in size depending on power rating, available space, etc., and can have a circular, square or other cross section.

The annular spacers shown on each side of coil 18 may be constructed of any suitable insulating material having sufficient mechanical strength and dielectric strength to withstand the transformer environment.
The phenolic resin or materials described in connection with the insulating layer 14 may be used for the spacers 20 and 21. The inner and outer diameters of annular spacers 20 and 21 are each sufficient to completely cover coil 18. Eighteen ribs 23 are arranged adjacent to the spacers 20 and 21. As shown below,
The annular spacers 20 and 21 are the same, and
Spaced cutouts are provided along the inner and outer circumferences for aligning the secondary windings as described in more detail below. As will be understood, the transformer of this invention is
It can be used as an inductance without a secondary winding and as other electromagnetic devices that utilize a secondary winding.

According to the invention, the transformer includes an annular segmented secondary winding, shown as a multi-turn inner conductor 22 and an outer conductor 24. conductors 22 and 24
are separated by annular spacers 26 and 27 on either side of conductor 22. Annular spacer 26
and 27 may be formed of the same insulating material as the spacers 20 and 21, and have inner and outer diameters that are sized to fit the space inside the conductor 24. Conductors 22 and 24 form a helical winding, with one end of conductor 24 shown as lead 28.

Turning to FIG. 3, a perspective view of a portion of conductors 22 and 24 is shown. As shown, conductor 2
2 and 24 have been removed from the core and pulled apart to show internal details. conductors 22 and 24
is made of aluminum and provides a helical current path. This current path here includes the bottom piece 30, the first
It is formed as a U-shaped member, ie a split link, consisting of a leg 32 and a second leg 34. Legs 32 and 34 are 1/2 inch in diameter, and bottom piece 30 has a rectangular cross section 1 inch in height and 1/2 inch in width. However, their shape and net cross-sectional area can be changed according to the current rating. The circuit of conductor 22 is completed by a jumper 36 which makes a connection between legs 32 and 34. The ends of legs 32 and 34 are tapered and sized to be pushed into tapered holes 37 in the ends of bottom piece 30 and jumper 36. Preferably, the ends of legs 32, 34 and hole 37 each have approximately the same taper angle, thereby maximizing the contact area and contact pressure of their engagement surfaces.
These connections may be grooved or knurled to improve conductivity and mechanical stiffness.

The conductor 24 is composed of a split link consisting of a bottom piece 42, a first leg 44 and a second leg 46, each of which is connected to a member 30, 32,
It has the same cross-sectional dimensions as 34 but has a different length. This length fits snugly around spacers 20 and 21 for conductor 22, and
4 is chosen to fit snugly around spacers 26 and 27. In this configuration, the bottom pieces 30 and 42 are radially aligned and are therefore shorter than their respective jumpers 36 and 40.

The connection between conductors 22 and 24 is made by legs 34 and 4.
This is done by means of a vertical bar 38 with a length intermediate to that of 6. This length allows the upper end of the rod 38 to be connected to the conductor 24.
The conductor 24 is at the same height as the leg 46 of the conductor 2.
2 (not shown in this figure) to form a tightly nested structure. To prevent short circuits between adjacent turns of the conductor 24, the legs 4 are separated by an insulating sleeve 48.
Just cover 6.

4 and 5 schematically illustrate the secondary winding of FIG. 3. In FIG. 4, the spacer 20
(And spacer 21 below which is hidden in the drawing)
is illustrated as having a plurality of notches including an inner notch 50 and an outer notch 52 provided at equal intervals along the inner and outer peripheries. The second leg 34 is along the inner perimeter 54 and the second leg 46 is innermost along the perimeter 56. Upper jumpers 36 and 40, shown in solid lines, and lower pieces 30 and 42, shown in broken lines, provide the connections described above. The foregoing structure can be more easily understood with reference to FIG. 5, which shows the inner doublet wound helically around the magnetic core 10 and connected to the output terminals 60 and 61. A secondary conductor 22 is schematically shown. An outer secondary conductor 24 is also helically wrapped around the magnetic core 10 and connected to terminals 62 and 63 and a center tap 64.

The spiral winding of the secondary conductor 24 is illustrated by the schematic diagram in FIG. For example, the helical winding of conductor 22 is effected by leg 34a depending and connecting to outward extension 30a and then to leg 32a and jumper 36a. Jumper 36a
connects to the next link, leg 34b.
This completes one turn, which progresses in this manner to cover the entire magnetic core. The spiral winding of the outer conductor 24 connects to the bottom piece 42a and then to the outer leg 44a.
This can be understood by considering the inner leg 46a that connects to the inner leg 46a. Next, Jumper 4
0a connects to the next leg 46b. This results in 1
The winding is complete and can be continued to cover the core and winding 22 again.

The inner legs 46 are in contact with each other and with the inner legs 34. The inner leg 34 is the leg 4
into the connections between adjacent ones of 6. However, the legs 34 are spaced apart and the legs 4
6 is provided with an insulating sleeve, so there is no short circuit in the windings.

The aforementioned secondary winding consists of divided windings 22 and 24.
Each winding has 26 turns and 60
It is designed to produce 120 volts in hertz (240 volts total). Of course, other output voltages and frequencies are possible. Members 30, 32
and 34 and members 38, 42 and 44 are pre-assembled and it is envisaged that members 30, 32 and 34 are fitted into corresponding cutouts 50 and 52. Jumpers 36 may then be stretched between the appropriate pairs of legs 32 and 34 and pushed into position either individually or simultaneously. after that,
The members 38, 42 and 44 are connected to the notches 50 and 52.
The jumper 40 may be placed between the appropriate legs 44 and 46 and pushed into position either individually or simultaneously.

Furthermore, as shown in Fig. 10, the secondary winding is composed of a plurality of divided winding sections connected in series and parallel, and the alternate winding section is composed of a wound ribbon conductor. You can also do that. Generally, the number of windings ranges from 10 to 30, and the number of ribbon turns used for each winding is 10.
~100, the ribbon width ranges from 0.5 to 3 cm, and the ribbon thickness ranges from 0.025 to 2 cm. 10th
The example configuration shown has 20 windings each having 28 turns of 1/2 inch wide and 0.040 inch thick ribbon. The 20 winding sections are connected in series and parallel as shown in FIG. In the configuration example shown in Figure 10,
There are 10 windings in parallel across a 0.2 inch (approximately 0.508 cm) cross section.

6 and 7, the primary coil of the transformer of FIG. 1 is illustrated. In FIG. 6, each coil 18 is shown as comprising a split bobbin 70 on which an aluminum strip 72 is wound. The use of bobbin 70 is optional since the individual coils 18 are capable of self-supporting. strip 72
is an insulating layer 74 that prevents short circuits between adjacent windings.
It is equipped with Connections to the coil 18 are made by an inner end 76 and an outer end 78 of the strip 72. A bobbin is basically a channel-shaped member that follows a rectangular trajectory and has a central hole sized to fit around a magnetic core (core 10 in FIG. 1). In this example configuration,
Eighteen coils are used, each having 84 turns of strip material 72. Therefore, 6000
For a primary voltage of volts, each coil 18 will exhibit a voltage drop of approximately 333 volts, which is a reasonable value. However, the potential difference between the first and last coils is 6000 volts, which presents a design limit in the case of adjacency. Therefore, it is preferred to wire and group the coils 18 non-continuously as shown in FIG. As shown, the coil 18 has four quadrants 80, 82,
Grouped into 84 and 86 (arranged in this order),
The coils in each quadrant are connected in series to effectively combine voltages. Coil 18 in quadrant 80 is connected between terminal 88 and lead 90. The coil in quadrant 86 is connected between leads 90 and 92. Coil 18 in quadrant 84 is connected between leads 92 and 94. Coil 18 in quadrant 82 is connected between lead 94 and terminal 96. The foregoing connections effectively combine the voltages in each quadrant. Importantly, the highest potential difference between the terminals of coil 18 exists between terminals 96 and 88, but these terminals are approximately 180 degrees apart. Therefore, there are no excessive electric fields that would cause dielectric breakdown. Furthermore, each coil 1
Since coil 18 has 84 turns and 333 volts are applied thereto, the interlayer potential between each turn of coil 18 is only about 4 volts. This small potential difference is easily handled by the insulating layer 74. coil 18
In an example configuration in which the wire is comprised of layers of conventional multi-turn insulated wire, the potential difference between successive layers will be relatively high.

The aforementioned transformer has a capacity of 25 KVA, a load loss of 240 watts, and a total weight including outer box and oil of 360 lbs.
(approximately 163.3Kg) is a distribution transformer. 165lbs
Using an amorphous alloy core that weighs about 74.8 kg (approximately 74.8 kg) and operates at 13.5 kg gauss, the transformer core loss is only 16 watts. A distribution transformer of the same capacity and load loss with a conventional cruciform design using the same amorphous alloy operating at the same magnetic flux density would have a total weight of 720 lbs. The core would weigh 260 lbs and have a loss of 38 watts. A typical 25 KVA transformer in use today has a silicon-iron core operating at 16 to 17 kilogauss and has a load loss of 300 to 500 watts and a core loss (iron loss) of 90 to 113 watts. are doing. For utilities willing to pay incentives for low core losses and less for low load losses, the best grain-oriented silicon-iron cores are available. The latest 25 KVA design weighs 400 lbs and has a core loss of 87 watts and a load loss of 250 watts. As is apparent from the foregoing, a transformer constructed in accordance with the present invention will have the highest loss penalty and lowest material volume.

Referring to FIG. 8, an alternative link and jumper is shown as link 100 and jumper 102. Link 100 is a round bar formed into a U-shaped member with a right angle bend. these tips 10
4 and 106 are provided with inward facing teeth or serrations. Tips 104 and 106 are sized to fit into holes 108 and 110, respectively, in jumper 102. The jumper 102 is a U-shaped bracket, which in some configurations may be formed from a hollow tube, but in this configuration it is exposed in the middle. Jumper 102 is (with appropriate dimensional adjustments) jumper 3 of FIG.
6 or 40. Ring 100 (with appropriate dimensional adjustments) is attached to member 3
0, 32 and 34 and the link formed by members 42, 44 and 46 can be replaced. As will be appreciated, in another example configuration, link 100
The connection between the jumper 102 and jumper 102 can be made with any suitable fasteners, including nuts and bolts.

Turning to FIG. 9, the finished product is illustrated, with the transformer of FIG. 1 shown in phantom as assembly 112. As will be appreciated, assembly 112 actually has a strong metal exoskeleton (conductors 22 and 24 in FIG. 1), so it withstands shock very well. Assembly 112 may be mounted on any suitable pedestal or pedestal, and the bottom of assembly 112 is left open for cooling. Assembly 112 is shown mounted within a container 114, which may be filled with a cooling medium, such as oil. Because the transformer 112 is a relatively open structure with most of the magnetic core 10 exposed, cooling is greatly facilitated. In particular, coil 18
(FIG. 1), allowing oil to pass through conductors 22 and 24 and into intimate contact with magnetic core 10. High voltage primary voltage connections are made by terminals 118 and 120 mounted on top of high voltage isolation posts 122 and 124, respectively. Struts 122 and 124 are mounted on cover 128 and are continuous to transformer 112 by internal conductors (not shown). cover 128
The container 114 is sealed to prevent oil from leaking. The secondary voltage connection is here output terminal 13
0, 132 and 134, which correspond to terminals 62, 64 and 60 in FIG. It will be appreciated that the overall height of the assembly of FIG. 9 is relatively small due to the annular configuration of the transformer.
Lightning arresters 136 and 138 remove dangerous eddy voltages from terminal 1.
18 and 120, the container 114 is grounded.
can be sidetracked.

It should be appreciated that various modifications may be made to the exemplary configurations adopted above. Current and voltage ratings can be changed by changing the size and number of turns of the conductors in the windings. Various containers can be used to house the transformer. The order of connecting the primary windings can be changed, especially for low voltage devices. Although oil coolant is mentioned in some configurations, other liquid or gas coolants may be used instead. Although the primary winding is shown surrounded by the secondary winding, the arrangement of the windings could be reversed in other configurations. Furthermore, the functions of the primary and secondary windings can also be reversed. The various fixtures shown for supporting and insulating the windings can be reworked or made of different materials depending on the desired dielectric strength, weight, and structural integrity.
Although aluminum conductors are described here, other conductive materials may be used depending on weight, resistivity, and other requirements.

Although the present invention has been described in sufficient detail, it is not necessary to adhere strictly to such detail and one skilled in the art will appreciate that the invention is as defined by the claims. It will be appreciated that various modifications or variations that fall within the scope of the invention may occur.

[Brief explanation of the drawing]

FIG. 1 is an isometric view, partially cut away for illustrative purposes, of a transformer according to the invention. 2 is a sectional view of the main body of the transformer of FIG. 1; FIG. 3 is a perspective view of the windings removed from the transformer of FIG. 1 and separated for illustrative purposes; FIG. 4 is a partial schematic diagram of the secondary winding of the transformer of FIG. 1; FIG. 5 is a schematic diagram of the secondary winding of the transformer of FIG. 1; FIG. 6 is a perspective view of one of the primary coils of the transformer of FIG. 1; FIG. 7 is a schematic diagram showing the interconnection of the primary coils of the transformer of FIG. 1; FIG. FIG. 8 is a side view of a split link and jumper that is different from that shown in FIG. 3. FIG. 9 is a front view of the finished transformer. FIG. 10 is a schematic electrical diagram of a secondary winding having multiple winding sections, each section consisting of multiple layers of strip material. In these figures, 10 is a magnetic core, 12 is an annular body, 14 is an insulating layer, 18 is a primary coil, 20 and 21 are spacers, 22 is an inner conductor, and 24 is an outer conductor (22, 24 are annular segmented secondary forming a winding),
26 and 27 are spacers, 30 is a bottom piece, 32 is a first leg part, 34 is a second leg part (30, 32, 34
(forming a U-shaped member or split link), 36 a jumper, 42 a bottom piece, 44 a first leg, 46
is a second leg (42, 44, 46 form a split link), 40 is a jumper, 50 is an inner notch,
52 is an outer notch, 100 is a link, and 102 is a jumper.

Claims (1)

[Scope of Claims] 1. A magnetic core having a central opening, a primary winding around the magnetic core, and a secondary winding including a plurality of divided links around the magnetic core, the secondary winding comprising a plurality of divided links around the magnetic core. links are mutually spaced apart and interconnected around the magnetic core to provide a helical current path, each of the plurality of segmented links having a portion extending through the central opening of the magnetic core; the secondary winding configured in a transformer, wherein the magnetic core comprises a plurality of magnetically permeable strips of material, each layer of which is made of a metal alloy that is at least 50% amorphous; and wherein the plurality of segmented links are a series of generally U-shaped members, each member having a first leg, a second leg, and a bottom piece, and each member of the members Said first
is electrically connected to the second leg of the next successive member of the group of members by a jumper having a hole, and the first leg and the second leg are the primary winding has an end configured to engage the jumper in the hole by crimping to provide an electrical connection; A transformer characterized in that it is segmented into coils, each of the primary coils being a coiled electrically conductive strip having an insulating layer on at least one side. 2. The transformer according to claim 1, wherein the magnetic core has an annular shape. 3. The transformer according to claim 2, wherein the number of primary coils is in the range of 10 to 30. 4. A transformer as claimed in claim 2, wherein the magnetic core comprises a plurality of layers, each layer consisting of an insulated magnetically permeable strip material. 5. The magnetically permeable strip material is such that M is at least one of the elements iron, cobalt, and nickel, and T is
is at least one of the transition metal elements, and X is at least one of the metalloid elements of phosphorus, boron, and carbon, and the formula M _60~90 T _0~15
A transformer according to claim 1, consisting of a metal alloy having a composition defined by X _10-25 . 6. A transformer according to claim 5, wherein up to 80% of the element X is replaced by at least one of aluminum, antimony, beryum, germanium, indium, silicon and tin. 7. The transformer of claim 6, wherein at least 80% of the magnetically permeable strip material is amorphous. 8. The transformer of claim 1, wherein the secondary winding surrounds the primary winding. 9. The transformer according to claim 2, wherein the primary coil has at least one primary coil discontinuously connected in series between two primary coils having a highest potential and a lowest potential. . 10. The transformer of claim 6, wherein the magnetic core includes a plurality of stacked toroids, each toroid comprised of coiled, uninsulated magnetically permeable strip material. 11 Claims including an annular spacer disposed on the top of the magnetic core and having a plurality of spaced apart notches, the secondary winding being adapted to the plurality of notches. The transformer according to paragraph 1. 12. The transformer according to claim 1, wherein the jumper and the member are provided with a tapered engagement surface so as to maximize the contact pressure between the members.