EP0172494B1 - Method for manufacturing epoxy resin-embedded windings for transformers - Google Patents

Abstract

1. Method for manufacturing coils, embedded in cast resin, for transformers, - according to which, spools (1), lying one behind another in the axial direction, of the coil are wound each for itself and independently of one another, - according to which, one insulating material mat respectively, serves, in a radial direction, as a brace (2, 3) between an inner casing (5) of the casting mould and the spools (1), as well as between the spools (1) and an outer casing (6) of the casting mould, - according to which, the spools (1) are fixed in an axial direction by frictional contact on the inner brace (2), - according to which, the inner (5) and the outer casing (6) of the casting mould are fixed between mould en walls (10), - according to which, casting with a horizontal mould in an evacuated chamber, follows through a slit (8), parallel to the axis, in the outer casing (6) of the casting mould, and - according to which, the hardening of the cast resin mass follows, at least partly, in the mould with increased temperature and with atmospheric or higher pressure, characterised in that, - the insulating material mats comprise fabric of non-twisted loose glass fibre bundles (15, 16), crossed and impregnated with hardenable artificial resin, - individual threads (17), twisted in themselves, of shrinkable artificial resin are worked into this fabric along zig-zag lines lying substantially in the fabric plane, - the twisted threads (17) in the insulating material mat shrink, during the hardening of the artificial resin mass, introduced through the impregnating, before the insulating materiel mat is brought into the casting mould, and telescope the glass fibre bundles (15, 16) at their intersections, lying in the points of the zig-zag line, to form knotlike swellings, and in that, - these swellings clamp the spools (1) in the casting mould.

Description

The invention relates to a method for producing windings for transformers embedded in cast resin according to the preamble of claim 1.

With the increasing use of cast resin transformers, the optimization of the materials used, in particular the amount of cast resin used, becomes increasingly important. For this reason, an equally good exploitation of the advantageous electrical and the equally advantageous mechanical properties of the cast resin molding material is sought. Small wall thicknesses of the cast resin body bring additional thermal advantages, so that the power limit up to which transformer windings can be cast with cast resin can be increased.

EP-A-0031576 already discloses a process for producing windings for electrical devices embedded in casting resin, according to which impregnated, corrugated insulating mats serve as spacers for fixing the electrical device parts to be encased in the casting mold. These insulating material mats remaining in the casting resin body at the same time bring about reinforcement for the casting resin molding material, which increases the mechanical strength of the casting resin molding material.

With this known method, windings are also cast from coils lying one behind the other in the axial direction, the casting preferably being carried out in a lying position in an evacuated chamber through an axially parallel slot in the outer jacket of the casting mold, and then the curing of the casting resin composition is at least partially in the form even when increased Temperature and at atmospheric or higher pressure.

To carry out the known method, however, spacers or reinforcing inserts in a very large number of different dimensions are required, which in turn require a large number of expensive auxiliary tools for their production. In practice, in order to limit the number of auxiliary tools required for the production of the spacers, only spacers are produced in certain dimensions that are graduated with respect to one another, so that the electrical and mechanical strength of the cast resin body is often not fully utilized. In order to reduce the number of auxiliary tools required and to approximately utilize the electrical and mechanical load capacity of the casting resin body, it is known from EP-A-0103237 to reduce the radial height of a corrugated and impregnated inner spacer by permanent deformation to the desired dimension of the casting resin body wall thickness. by spreading an inner jacket of the casting mold in the radial direction, its axially parallel edges overlapping in the circumferential direction sliding on one another.

However, the production of the corrugated spacers has proven to be relatively complex since a large number of special tools is still required for the large number of required shaft dimensions. In addition, when using these corrugated spacers, there are also relatively large, undesirable displacements in the circumferential direction between the coils of the winding on the one hand and on the other hand individual wave crests of the spacers.

The invention is therefore based on the object of improving the method known from EP-A-103237 in such a way that displacements of the spacers with respect to the coils and damage to the insulation of the coils which may be caused thereby are avoided and that the economy is achieved by further reducing the number of required special tools is further increased.

• - dass die als Abstandshalter eingesetzten Isolierstoffmatten aus Gewebe aus unverdrillten, lockeren, gekreuzten und mit aushärtbarem Kunstharz getränkten Glasfaserbündeln bestehen,
• - dass einzelne in sich verdrillte Fäden aus schrumpffähigem Kunstharz entlang von im wesentlichen in der Gewebeebene liegenden Zick-Zack-Linien in dieses Gewebe eingearbeitet sind,
• - dass die verdrillten Fäden in der Isolierstoffmatte während der Aushärtung der durch die Tränkung eingebrachten Kunstharzmasse vor dem Einbringen der Isolierstoffmatte in die Giessform schrumpfen und die Glasfaserbündel an deren in Spitzen der Zick-Zack-Linie liegenden Kreuzungsstellen zu knotenähnlichen Verdickungen zusammenschieben und
• - dass diese Verdickungen die die Transformatorwicklungen darstellenden Spulen in der Giessfoi m einklemmen.

According to the invention, this object is achieved when the method mentioned at the outset is carried out by

• - that the insulating material mats used as spacers consist of fabric made of untwisted, loose, crossed and fiberglass bundles impregnated with hardenable synthetic resin,
• that individual twisted threads made of shrinkable synthetic resin are worked into this fabric along zigzag lines lying essentially in the plane of the fabric,
• - That the twisted threads in the insulating mat shrink during the hardening of the synthetic resin mass introduced by the impregnation before the insulating mat is introduced into the casting mold and push the glass fiber bundles together at their crossing points in the zigzag line to form knot-like thickenings and
• - That these thickenings pinch the coils representing the transformer windings in the casting mold.

According to advantageous design features of the invention, it is provided that the distance between some of the untwisted glass fiber bundles remains equal to the multiple of the width of these glass fiber bundles and that in the insulating mats used two adjacent warp threads are pushed against each other at their crossing point with a weft thread by one of the twisted threads, in that the twisted thread crosses all the weft threads on the same side of the fabric opposite the warp thread pushed by it at the respective crossing point and by the twisted thread on the other side of the fabric leading back and forth between these crossing points.

Further advantageous design features of the invention consist in that the insulating mats protrude beyond the winding at both ends in the axial direction, that epoxy resin filled or unfilled is used as the casting resin and that the casting mold and / or the winding are preheated, with the impregnation Already hardened synthetic resin compound introduced into the insulating mats remains firm.

The method according to the invention is very advantageous, since it enables transformer windings cast in cast resin to be produced in an economical and easily adaptable manner to different boundary conditions, because the thickened portions pushed together by the individual, twisted, shrunk threads from the untwisted, loose glass fiber bundles through the hardened impregnating resin composition What is certain is that they reliably hold the coils in the casting mold, but on the other hand, due to their loose structure, they can be compressed before the windings are overloaded.

• Fig. einen Quer- und
• Fig.2 einen achsparallelen Längsschnitt durch eine zum Umgiessen vorgesehene Transformatorwicklung in stark verkleinertem Massstab.
• Fig.3 zeigt ein als Isolierstoffmatte vorgesehenes Gewebe aus unverdrillten Glasfaserbündeln in annähernd natürlicher Grösse.

The method according to the invention is explained in more detail with reference to a drawing. It shows:

• Fig. A cross and
• 2 shows an axially parallel longitudinal section through a transformer winding provided for encapsulation on a greatly reduced scale.
• FIG. 3 shows an approximately natural size woven fabric made of untwisted glass fiber bundles as an insulating material mat.

Coils 1 for a transformer winding, for example a high-voltage winding, are wound individually and independently of one another in a manner known per se on special devices. All coils 1 to be embedded in a common cast resin block lie in the radial direction between an inner spacer 2 and an outer spacer 3.

The spacers 2 and 3 in turn consist of insulating material mats made of woven fabric made of untwisted, loose glass fiber bundles 15 and 16 impregnated with curable synthetic resin. The glass fiber bundles represent 15 warp threads and the glass fiber bundles 16 weft threads in the fabric Lines strongly twisted threads 17 made of shrinkable synthetic resin are incorporated.

Instead of glass fiber bundles, the insulating material mats can also be made from bundles of other electrically non-conductive fibers.

Before being cut to size and before being used as a spacer, the fabric is treated, for example by heating, in such a way that the synthetic resin introduced by the impregnation is finally and completely cured and at the same time the twisted threads 17 shrink. As a result, the glass fiber bundles 15 and 16 are pushed together in the corner points of the zigzag lines to form thickenings which, although very hard, give way more than the coils 1 as a result of a certain remaining porosity under a pressure load.

In the fabric example shown in FIG. 3, two glass fiber bundles 15 representing warp threads are each pressed together by a thread 17 and form a thickening at each intersection with a glass fiber bundle 16 representing a weft thread, this thickening being greater than it would be in simple fabric without shrunken threads 17 .

An inner jacket 5 of a casting mold is pressed onto the thickenings of the inside of the inner spacer 2 in the direction of the arrows 4. The pressing force required for this is transmitted to the inner jacket 5 in a manner known per se by strips or other devices displaced on cones or on inclined planes. To reduce the friction and to prevent tension in the circumferential direction, 5 balls or rollers are attached to the strips, not shown, along the lines of contact with the inner casing.

The inner jacket 5 is spread so far, with slight deformation of the inner spacer 2, regardless of diameter tolerances, that the thickness of the gap to be filled with casting resin just withstands the electrical and / or mechanical stress to be expected of the casting resin molding material during operation. Based on this, the dimensioning of the inner spacer 2, in particular with its thickenings, is designed with regard to the mechanical load to be expected. At higher nominal voltages, it is often expedient to provide several insulating mats radially one above the other as spacers 2 and / or 3 instead of a single insulating mat in a manner not shown.

Bandages, not shown, placed around the outer spacer 3, further increase the mechanical strength of the cast resin body in the circumferential direction. These bandages also make it possible to set the thickness of the gap held by the outer spacer 3 independently of the diameter tolerances on the coils 1.

Around the winding arrangements of the coils 1, the inner spacer 2 spread against them from the inside and the inner jacket 5, as well as the outer spacer 3 bandaged from the outside around the coils 1, an outer jacket 6 of a casting mold is placed, which essentially depends on the thickenings of the supports outer spacer 3 or on the comprehensive bandages. In the outer jacket 6, an axially parallel bulge 7 is provided, which forms a reinforcement on the cast resin body for receiving the winding leads and connection contacts. A slot 8 is provided opposite or offset at a certain angle from the bulge 7, which is flanked by wall strips 9 which are bent approximately in the radial direction and at the same time serves as a vent and as a pouring opening of the casting mold.

The end faces of the casting mold are closed by end mold walls 10, the side of which facing the inner shell 5 and the outer shell 6 is covered with a layer 11 of elastic material. The end mold walls 10 are pressed with their layer 11 by an anchor plate 13 each so strongly against the end edges of the inner shell 5 and the outer shell 6 that they are pressed into the elastic layer 11. The necessary for this Such pressing force for the anchor plates 13 is applied by nuts 14 on a tie rod 12.

The arrangement of coils 1, the inner spacer 2 and the outer spacer 3, which is thus embedded in the casting mold from the inner jacket 5, the outer jacket 6 and the end mold walls 10, is evacuated to a perfect vacuum in a chamber (not shown) and then poured out with pure epoxy resin or with an epoxy resin mixture containing up to 75% filler. Depending on the prevailing conditions, the shape, the coils 1 and / or the casting resin mass are preheated.

Following the filling of the casting mold with casting resin compound, it is exposed to atmospheric pressure or a higher pressure, so that the excess casting resin compound from the funnel formed by the wall strips 9 is pressed into the casting mold until the casting resin body has completely solidified.

Claims (6)

1. Method for manufacturing coils, embedded in cast resin, for transformers,

- according to which, spools (1), lying one behind another in the axial direction, of the coil are wound each for itself and independently of one another,

- according to which, one insulating material mat respectively, serves, in a radial direction, as a brace (2, 3) between an inner casing (5) of the casting mould and the spools (1), as well as between the spools (1) and an outer casing (6) of the casting mould,

- according to which, the spools (1) are fixed in an axial direction by frictional contact on the inner brace (2),

- according to which, the inner (5) and the outer casing (6) of the casting mould are fixed between mould end walls (10),

- according to which, casting with a horizontal mould in an evacuated chamber, follows through a slit (8), parallel to the axis, in the outer casing (6) of the casting mould, and

- according to which, the hardening of the cast resin mass follows, at least partly, in the mould with increased temperature and with atmospheric or higher pressure, characterised in that,

- the insulating material mats comprise fabric of non-twisted loose glass fibre bundles (15, 16), crossed and impregnated with hardenable artificial resin,

- individual threads (17), twisted in themselves, of shrinkable artificial resin are worked into this fabric along zig-zag lines lying substantially in the fabric plane,

- the twisted threads (17) in the insulating material mat shrink, during the hardening of the artificial resin mass, introduced through the impregnating, before the insulating material mat is brought into the casting mould, and telescope the glass fibre bundles (15, 16) at their intersections, lying in the points of the zig-zag line, to form knot- like swellings, and in that,

- these swellings clamp the spools (1) in the casting mould.

2. Method according to claim 1, characterised in that, the distance between non-twisted glass fibre bundles (15, 16), not telescoped by the threads (17), remains equal to a multiple of the breadth of these glass fibre bundles (15, 16).

3. Method according to claim 1 and 2, characterised in that, in the insulating material mats used, two adjacent warp threads (15) respectively are pushed against one another at their intersection with a weft thread (16), by one of the twisted threads (17), in that the twisted thread (17) crosses all weft threads (16) on the same fabric side, which lies opposite to the warp thread (15), pushed by the twisted thread (17), at the respective intersection, and in that the twisted thread (17) is led back and forth respectively between these intersections on the other fabric side.

4. Method according to claim 1 to 3, characterised in that, insulating material mats representing the braces (2, 3) overhang the coil at both ends in an axial direction.

5. Method according to claim 1 to 4, characterised in that, epoxy resin filled with quartz powder, or pure epoxy resin, is used as casting resin.

6. Method according to one of claims 1 to 5, characterised in that, the cast resin mould and/or the coil are pre-heated, and in that the artificial resin mass, introduced into the insulating material mats through the impregnating, remains firm thereby, as a result of previous hardening.

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