GB2221101A - Iron core for electromagnetic apparatus - Google Patents

Abstract

An iron core for electromagnetic apparatus, such as transformers, throttles and magnetic voltage regulators, has at least two yoke 13 wound from soft magnetic strip material and spaced from each other by at least three laminated spacers 11 which adjoin counter abutment points on the yokes through their end faces. The yokes are mechanically held together by tension screws 18, strips 19 and nuts 20. The screws 18 pass through gaps between the spacer 11 and a winding 16. <IMAGE>

Description

IRON CORE FOR ELECTROMAGNETIC APPARATUS The invention relates to iron cores for electromagnetic apparatus, such as transformers, throttles, magnetic voltage regulators and similar apparatus with at least two annular yokes wound from soft magnetic strip material and spaced from each other to house in between at least three spacers which adjoin counter abutment points of the yokes through their end faces which serve as abutment points.

The disadvantage of the iron cores of this kind known up until now has been that they produce loud noises with higher magnetic flux densities, have high iron losses and a high apparent power requirement. When avoiding these disadvantages it is necessary to have lower magnetic flux densities, thus lower output or large iron cross-sections and frequently recesses in the core for guiding the tension elements.

The present invention is based on the problem of avoiding the said disadvantages and providing an iron core of the kind mentioned at the beginning which - even with high flux densities - has a substantially reduced noise development and is distinguished by a lightweight compact construction, low losses and easy magnetizability.

This is achieved in accordance with the invention in that the mechanical connection between the spacers and the yokes is produced by tension elements, such as tension screws or tension belts with screw ends, placed directly along the spacers so that the iron cross-section is not reduced by recesses. The cross connection is provided by tension parts such as tension plates, which are mounted above and below each yoke so that they can take up the tension pressure of the fastening between the yokes and spacers.

Easy magnetizability despite high flux densities can be achieved if the abutment points of the spacers and/or the counter abutment points of the yokes are ground and then reprocessed to remove the ground edges which have been formed. The measures according to the invention ensure that a practically complete surface contact is made over the contact faces between the wound yokes and the spacers so that an optimum field transition is guaranteed between the individual core parts. Furthermore removing the metallic connections between the individual sheet metal layers or windings which may be formed during the grinding process prevents a magnetic and also electric short circuit from appearing in the iron core so that the vortex currents can be reduced to a minimum and an unacceptably high heating level is avoided.Furthermore the mechanical stability of the iron core can be improved by the full surface contact between the abutment and counter abutment points of the individual core parts, and in addition noises in the iron core due to vibrations can be avoided, even with high flux densities.

The reprocessing which is carried out after grinding to remove any material bridges which may have been formed is preferably a chemical treatment which can be applied in particular to the abutment points of the spacers.

Electrolytic removal, a scraping or trowelling process or even a jet-cleaning process such as for example sand blasting, can all be considered as ways of removing the material bridges or ground edges However as already mentioned chemical removal is preferred.

It can be particularly advantageous for the functionning of the electromagnetic apparatus fitted with an iron core according to the invention if the wound yokes are subjected to heat treatment at least in the area of the counter abutment points by which they adjoin the abutment points of the spacers. Then any changes in structure which may have been caused by the grinding process can be practically eliminated so that the electromagnetic properties originally present can be reproduced in these areas. It can be particularly expedient if after grinding, the wound yokes are subjected to a temperature above the Curie temperature, at least in the area of the counter abutment points, so that on cooling down the crystallographic or electromagnetic properties originally present once more exist in these areas.In many cases it can be particularly advantageous if, after grinding, the wound yokes are subjected as a whole to a heat treatment such as an annealing process, which can be carried out above the Curie temperature since this then not only eliminates any structural changes caused by the grinding but also removes the tensions introduced into the strip material during winding.

To facilitate winding of the yokes it can also be expedient if the soft magnetic strip material forming the wound yoke is subjected to an annealing process prior to winding. The yokes wound in this way can then be processed as already described and subjected if required to a heat treatment or thermal processing.

Furthermore it can be expedient when manufacturing the iron core according to the invention if at least the yokes are flamed with an oxygen-enriched flame, at least in the area of the counter abutment points, wherein the yokes could have been subjected to an annealing process prior to this flaming process. Flaming the counter abutment points with an oxygen-enriched flame can also in a simple way remove any material bridges which may have been formed between the individual winding layers during the grinding process.

However these material bridges formed by the ground edges or grinding chips can also be removed in a similar way to that described already in connection with the spacers. The spacers can also be subjected, at least in their abutment point areas, to a heat treatment or thermal processing, in a similar way to the yokes. The abutment points can thus be flamed for example instead of being chemically treated.

It can be particularly advantageous for the design of the iron core if the wound yokes have a circular shape wherein the spacers can be evenly distributed round the circumference of the circular yokes in order to obtain a symmetrical design of the iron core relative to the length of the line of magnetic force or flux.

It can be particularly expedient for the manufacture of the iron core if the spacers consist of sheet metal laminae which are made into core blocks. The blocks can thereby be designed so that they have a cross-section, such as a square cross-section, adapted to the internal recess of the coils or coil body.

It can be particularly advantageous for the function of an electromagnetic apparatus fitted with an iron core according to the invention if the ratio of the iron crosssection of a spacer to the iron cross-section of a yoke is approximately 1:0.6 to 0.8. It can furthermore be expedient if the wound yokes have an at least approximately square cross-section.

It is furthermore advantageous if at least the spacers are made from strip or sheet material which is grain-orientated wherein the main electromagnetic direction of the spacers runs at least approximately at right angles to the counter abutment points of the yoke. Although the yokes can be made from grain-orientated sheet metal material, in many cases it can be particularly advantageous if a doubletextured material is used, thus a material with two main magnetic directions or an amorphous magnetic material, since this can reduce the deflection resistance in the iron core for the lines of force or magnetic flux when passing from the spacers into the yokes and vice versa.

Furthermore it can be advantageous for the design of an iron core according to the invention if the individual winding layers of the yokes and the individual layers or laminae of the spacers run parallel to each other wherein it can then also be advantageous if the laminae of the spacers are aligned at least approximately tangential to the layers of the wound yokes, thus pointing practically in the circumferential direction.

The iron core can be held together easily by mechanical connecting the spacers to the yokes by means of tension armatures, such as tension screws, which each run between a spacer and an electro-winding provided thereon and are tensioned towards each other by tension plates running across the wound yokes on the outside of the iron core. To reduce the vortex losses or iron losses, tension armatures and/or tension plates are used which are insulated relative to the iron core. The mechanical connection between the spacers and yokes can be simply produced by means of circular rings or discs placed on the yokes on the outside of the iron core and biassed towards each other by tension armatures such as tension screws, whereby the spacers. are clamped between the yokes.

A reduction in the vortex losses and iron losses can also be achieved by making the tension armatures and/or the tension plates and/or the tension rings from a noneltromagnetic material such as eg aluminium or chromenickel-steel, eg V2A.

The invention will now be explained in detail with reference to Figures 1 to 6 in which: Figures 1 and la show a way of mechanically connecting the yokes and spacers of an iron core according to the invention; Figures ib and lc show a further possibility of connecting the yokes and spacers of an iron core; and Figures 2 to 6a show further structural embodiments of iron cores according to the invention.

Figures 1 and la illustrate a means for fastening the yokes 12 and spacers 11, of which only one is shown. The spacers 11 clamped between the annular yokes 13 hold an electric coil 16. A free space 17a,17b is provided radially inwards and radially outwards between the coils 16a or the coil body 16b holding same and the spacer 11 housed therein whereby the tension elements in the form of screws extend through the free spaces. Tension means in the form of tension strips 19 are placed on the areas of the screws 18 projecting over the annular yokes 13 and are tensioned against the outer faces of the annular yokes 13 by means of nuts 20.To keep an approximately even tension over the individual winding layers of the annular yokes 13, the latter can be levelled at least in the contact area of the tension means 19 in a similar way to that described in connection with the abutment points and counter abutment points 4 according to Figure 2. The tension strips 19 can be made of a non-electromagnetic material or insulating layers can be provided at least between the tension plates 19 and annular yokes 3. Instead of individual tension strips 19 it is also possible to use circular tension means extending over the circumference of the yokes 13 and provided with corresponding recesses for passing through the threaded ends of the screws 18. Assembly is simplified by the latter step since the number of individual elements required can be reduced.

With the fastening system for securing the yokes 13 and spacers 11 in Figures 1b and 1c, the lower yoke 13 lies on a circular ring plate 19a which has threaded bores 20a into which the threaded ends of the tension armatures 18 can be fitted. The support plate 19a also has three projections or cams 20b evenly distributed round the circumference and, viewed circumferentially, provided between the threaded bores 20a. The projections 20b each have an axial recess 20c which can serve to hold the fastening screws. The electromagnetic apparatus shown in part in Figures Ib and lc can thus be easily fastened to a support structure by the plate 19a. The upper yoke 13 is fixed by tension strips 19 and nuts 20 in a similar way to that described in connection with Figures 1 and la.

For clarity the upper yoke 13 is not shown in the plan view of Figure ic.

The iron core illustrated in Figure 2 has three spacers 1 which are block-shaped or cubed and consist of laminated sheets la which are connected together eg by adhesive connection through fired lacquer. At their ends the spacers 1 have head or end faces 2 which form abutment points which become adjoined by the counter abutment points 4 of the annular yokes 3 which are designed as a ring band core. The spacers 1 contained beteween the two annular yokes 3 are evenly distributed round the circumference of the yokes.

The end faces 2 of the yokes which ensure the connection for the field transition to the annular yokes 3 are ground and then chemically treated to remove any ground edges which may have been formed.

The annular yokes 3 are ground at least in the area of their counter abutment points 4 wherein in a simple way the entire side of the annular yokes 3 facing a spacer 1 can be ground. After grinding, the annular yokes are thermally treated to remove any possible ground edges and to recrystallize the strip material. It is thereby expedient if the annular yokes are heated to a temperature which is higher than the Curie temperature of the material used.

In the illustrated embodiment the spacers 1 are designed so that the iron cross-section is practially square whilst the iron cross-section of the annular yokes 3 is rectangular.

To this end the layer height k of the laminae la corresponds to the width k of one such lamina la and the strip width h of the wound annular yokes 3 is less than the wound width of the annular yokes which corresponds approximately to the layer height b of the laminae la It is expedient if the ratio of the width b of the spacers 1 running tangentially to the annular yokes 3 and corresponding in the illustrated embodiment according to Figure 2 to the width of a lamina la, to the height h of an annular yoke 3 is approximately 1:0.6 to 0.8. Furthermore by levelling the abutment points 2 and counter abutment points 4 it is possible to produce a defined air space between at least one spacer 1 and annular yoke 3 by inserting eg a small insulated plate of defined thickness between such abutment point 2 and counter abutment point 4.

It can be expedient if a similarly defined air gap is provided at all three spacers whereby precisely the same inductivity or precisely the same throttle effect can be obtained in the transition area between all three spacers 1 and a yoke 3.

Figures 3 and 3a show a possible modification of the iron core illustrated in Figure 2. With this modified iron core, magnetic scattering yokes 25 are mounted between the spacers 21, these yokes consisting in the illustrated embodiment of laminated layers. An air gap or space 26 is provided by means of an intermediate layer between the scattering yokes 25 and the spacers 32 so that a longitudinal throttle effect is produced when the primary and secondary windings are mounted on the or each spacer 21 on different sides of a scattering yoke. This arrangement can be used in a.c. transformers with a high short circuit voltage and in an a.c. regulator, eg a transformer with stabilizing vibration circuit winding and an approximately trapezoidal current curve at the output.

As can be seen in particular from Figure 3, the laminae of the scattering yokes 25 run approximately at right angles to the laminae of the spacers 21 so that they cross in grid-like fashion. The scattering yokes 25 can however also be designed and mounted so that their sheet layers run parallel to the sheet layers of the spacers 21.

The iron core shown in Figure 4 represents a further development of the iron core shown in Figure 3. As already described in connection with Figure 3, the shunt yokes 35 also have a defined throttle distance 36 from the spacers 31. The annular scattering yoke 33a adjoins the spacer parts 31 practically without any air gap. A further wound yoke 33 is provided at the ends of the spacer parts 31 remote from the scattering yoke 33a. Laminated core parts 31b are mounted on the side of the scattering yoke 33a remote from the spacer parts 31 and seen in the axial direction 37, are practically flush with the spacer parts 31. The core parts 31b are mounted axially between the scattering yoke 33a and a further annular yoke 33b.

Figures 5 and Sa-show a further embodiment of the iron core shown in Figure 2. With the modified iron core, the spacers 41 provided between the two annular yokes 43 have a multi-stepped cross-section. This design is advantageous for round electro coils since a higher iron filling factor can be achieved in the electro coil.

The design for an iron core illustrated in Figure 6 is suitable for a combination of a transducer with a transformer electrically switched in at the output side.

This design of iron core thus allows both functions or both appliances to be combined or integrated into a single unit wherein an alternating current connection can be used.

The spacer parts 51 housed between the two annular yokes 53 and 53a each house half of a primary winding whilst secondary windings are provided on the spacer parts Sla.

The spacer parts 51a are housed anxially between the two annular yokes 53a, 53b. The spacer parts 56 are likewise provided axially between the annular yokes 53a, 53b and are mounted in the circumferential direction between the spacer parts 51a. A direct current control coil is mounted on these spacer parts 56. The central part of the core which is defined by the annular yokes 53a, 53b is d.c. premagnetized to a greater or lesser extent according to the level of control of the d.c. spacers 56 and thus forms a greater or lesser obstruction for the main magnetic flux produced by the primary side. In this way a variable secondary voltage corresponding to the winding ratio between the primary and secondary windings can be induced in the secondary windings. As can be seen from Figure 6 the iron core is designed so that it is practically symmetrical either side of the spacer parts 51a and 56.

The iron cores illustrated in the drawings are designed so that the individual winding layers of the yokes and the individual layers or sheet metal laminae of the spacers run parallel to each other, with the laminae of the spacers aligned at least approximately tangential to the layers of the wound yokes.

The iron cores illustrated in Figures 2 to 6a could be held together as described in connection with figures 1 to lc

Claims (1)

1. CLAIMS: 1. An iron core for an electromagnetic apparatus, which core comprises at least two yokes wound from a magnetic material and held spaced apart from one another by at least one lamellar spacer member which contacts the yokes through its end faces to provide abutment areas to the spacer member and the yokes, an electro-winding provided on the spacer member and tensioning means passing between the spacer member and the winding thereon to provide the mechanical connection between the yokes and the spacer member.

   2. An iron core as claimed in claim 1, wherein there are at least three spacer members.

   3. An iron core a claimed in either of claims 1 or 2, wherein the tensioning means includes plate like members provided on the axially outer faces of the yokes.

   4. An iron core as claimed in any one of the preceding claims, wherein the yokes are annular in shape and the lamellar spacer members extend axially between the annuli.

   5. An iron core as claimed in any one of the preceding claims, wherein the abutment areas of the yokes and/or the ends of the spacer member are ground and then re-processed to remove ground edges which may have been formed.

   6. An iron core as claimed in claim 5, wherein the reprocessing is chemical.

   7. An iron core as claimed in any one of the preceding claims, wherein at least the abutment areas of the yokes have been subjected to heat treatment.

   8. An iron core as claimed in claim 7, wherein after grinding, the wound yokes have been subjected to a temperature above the Curie temperature.

   9. An iron core as claimed in any one of the preceding claims, wherein the wound yokes undergo annealing after grinding.

   10. An iron core as claimed in any one of the preceding claims, wherein the yokes are made from a strip material which has undergone an annealing process prior to winding.

   10. An iron core as claimed in any one of the preceding claims, wherein at least the abutment areas of the yokes have been flamed with an oxygen-enriched flame after annealing.

   12. An iron core as claimed in any one of the preceding claims, wherein the spacers comprise sheet metal laminae made into core blocks.

   13. An iron core as claimed in any one of the preceding claims, wherein the ratio of the iron cross-section of one spacer to the iron cross-section of a yoke is approximately 1 : 0.6 to 0.8.

   14. An iron core as claimed in any one of the preceding claims, wherein the spacers have an approximately square cross-section.

   15. An iron core as claimed in any one of the preceding claims, wherein the tensioning means are insulated from the yokes and the spacers.

   16. An iron core as claimed in any one of the preceding claims, wherein tensioning means providing the mechanical connection between the spacers and the yokes includes rings or discs provided on the axially outward face of the yokes.

   17. An iron core as claimed in any one of the preceding claims, wherein the tensioning means are made from a nonelectromagnetic material.

   18. An iron core as claimed in claim 16, wherein the nonelectromagnetic material is a light metal, such as aluminium.

   19. An iron core as claimed in any of the preceding claims, wherein the individual winding layers of the yokes and the individual layers or laminae of the spacers rum parallel to each other.

   20. An iron core as claimed in any one of claims 1 to 18, wherein the sheet metal laminae of the spacers are aligned at least approximately tangential to the layers of the wound yokes.

   21. An iron core substantially as herein before described.

   22. An iron core substantially as herein before described with respect to any one of the accompanying drawings.

   23. An electromagnetic apparatus incorporating an iron core as claimed in any one of the preceding claims.