EP1929488B1

EP1929488B1 - Yoke structure for the lamination core of a static electrical machine, composed of unwelded cut-to measure members

Info

Publication number: EP1929488B1
Application number: EP05802418A
Authority: EP
Inventors: Gianfranco Colombini
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-09-27
Filing date: 2005-09-27
Publication date: 2009-11-11
Anticipated expiration: 2025-09-27
Also published as: WO2007036956A1; ES2336585T3; EP1929488A1; ATE448554T1; DE602005017678D1

Abstract

A yoke structure for supporting and compressing the magnetic lamination core (32) of a static electrical machine, comprises at least four stress traverses (1-2, 34) tightened in pairs over the top branch and over the bottom branch of a lamination pack (32). Each stress traverse (1, 2, 3, 4) is composed of at least two tubular members (9) of rectangular cross section, parallel and spaced from one another and joined together by a plurality of brackets (11) having side wings with apertures to slidely receive there through the tubular members (9). At least two pairs of brackets (11) constitute supporting and blocking brackets for the resin body (29) encapsulating the windings of the electrical machine. The two outermost brackets (11) of each stress traverses (1, 2, 3,4) receive their said wings stress washers (12) for tie rods (5, 6, 7, 8) used to tighten the stress traverses.

Description

The present invention relates in general to static electrical machines having a laminated ferromagnetic core composed of packed laminae of high permeability material and resin encapsulated windings.
The structural architecture of inductors, transformers, autotransformers and similar static electrical machines, for rated powers ranging from few tens of kVA to about 2000 kVA, includes yoke structures designed with adequate size and mechanical properties for pressing together the laminated magnetic core and for supporting the weight of the electrical machine.
The yoke structures are practically stress structures, typically using threaded bolts or tie rods, the main purpose of which is to compress the lamination core of the machine, after its final recomposition after having installed the resin body or bodies containing the windings of the machine, to provide means for sustaining and blocking in position the resin encapsulated coils, as well as to stably sustain the whole machine and provide a support for the electrical connection terminals, hoisting eyelets, cable hanging brackets, main plates and alike accessories.
Document US 5 267 393 discloses such a yoke structure having the features of the preamble of claim 1.
Typically, these yoke structures are carpentry products, commonly fabricated in specialized work shops, using steel members, cut to measure and welded together according to a work shop drawing provided by the electrical machine designer.
These stress structures of welded steel must be provided with holes in precisely defined positions in order to permit a correct assembling and mounting of the functional elements of the electrical machine, of the tie rods and accessories.
Very often, the construction of these stress structures is outsourced and even when built within the factory of the electrical machinery manufacturer, their construction, transport and assembly are burdensome because of the weight and large size of these structures, for machines of relatively large power. They are hardly movable by hand, that is without the aid of hoists and/or the intervention of an adequate number of workers.
Moreover, the predominant practice of outsourcing the fabrication of these welded steel structures implies uncontrolled delivery problems, dimensional imprecisions that may compromise the ability to meet contractual delivery times of the electrical machine.
This relatively heavy welded structures provided with a multitude of precisely located holes for the passage of tie rods and bolts for the mechanical connection of components during the phase of final assembly of the machine, must be pre-treated and coated according to customer's specifications in order to confer them resistance to corrosion. Even these surface treatments of relatively heavy and encumbering metal structures of welded steel may be rather laborious and onerous both in terms of times of treatment and costs.
Finally, apart certain tradesmanship expedients for simplifying the construction while fulfilling the design geometric tolerances, these structures are intrinsically hardy standardizable.
From the above representation, it is evident the need and/or usefulness of permitting an economically favorable realization of these yoke structures with appropriate mechanical characteristics, even for machines of relatively large power, directly by the electrical machine manufacturer, by using a limited number of easily standardized components of size and weight such to remain possible for a single person to manually handle them, and that may be joined together with simple operations without requiring any welding nor drilling precisely located holes and finally to be set in place and easily tightened to complete the assembly of the machine, without the need of hoisting apparatuses or the intervention of a plurality of workmen.
These important objectives, a remarkable simplification of the design and weight reduction of these stress structures of a static electrical machine are achieved by a yoke structure of this invention according to the characterizing features of claim 1.
In practice, a yoke structure for pressing the lamination core and for sustaining a static electrical machine is composed, according to the present invention, of tubular members having a generally rectangular or square cross section, cut to measure according to need, and a plurality of special slidable brackets of substantially identical structure, that are slid over at least a pair of identical tubular members, holding them parallel and spaced from each other.
The separation gap between the two rectangular or square cross section tubular members, parallely passing through respectively aligned apertures present in two parallel side wings of each bracket, permits the passage therethrough of threaded tie rods for pressing the magnetic core and other fastening bolts while planar bases of source of the brackets slidely engaged along the pair of parallel tubular members, constitute support and/or blocking jaws of a resin body or bodies encapsulating the windings or coils of the electrical machine.
Even the mechanical connection to the structure of rest feet of the machine, optionally equipped with fixed or caster wheels, may be conveniently established by cooperating pairs of the same standardized slidable brackets, one of which may be fixed onto a rest foot and the other slid over the tubular members of a bottom traverse of the joke structure tightening the lower portion or branch of the lamination core of the machine with their respective parallel side wings purposely interleaved.
The invention overcomes the above noted drawbacks and factor of cost; fulfilling the above remarked needs and/or usefulness.
The invention is defined in the annexed claims.

Figure 1 is a threedimensional view of a yoke structure made according to the present invention.
Figure 2 is an exploited threedimensional view of the yoke structure of Figure 1.
Figure 3 , 4 and 5 are plan, elevation and side views of the yoke structure of the preceding figures.
Figures 6 and 7 are two threedimensional views of a transformer employing a yoke structure of the lamination core and of support of the resin bodies on which are encapsulated the transformer windings.
Figure 8 is a plan view of the transformer of Figures 6 and 7.

A sample embodiment of a yoke structure of this invention is depicted in Figures 1 to 5, in which the same numerical references are used for the same parts and details of the structure.
According to this embodiment, the yoke structure is composed of four stress traverses 1, 2, 3 and 4, that may be tightened in pairs by threaded tie rods 5, 6, 7 and 8, respectively over the upper portion (the pair of traverses 1 and 2) and over the lower portion (the pair traverses 3 and 4) of the lamination core of the transformer that is not shown in this first series of figures that illustrate exclusively the components of the yoke structure in their coordinated function. Those other functional elements of the electrical machine are shown in a successive series of figures.
Each of the four stress traverses 1, 2, 3 and 4, is composed of two tubular members 9 having a rectangular or square cross section, parallel and spaced from one another, to the cut ends of which plugs or caps 10 of plastic may be forcibly applied to shield the sharp edges generated when cutting to measure the tubular members 9 from a stock of rectangular or square tubes of commercial length that may be kept in store.
The two tubular members 9 are joined, kept parallel and spaced one from the other by a plurality, six in the sample embodiment illustrated, of structurally identical rackets 11, each having a planar base portion and two parallel side wings spaced from each other, each having two spaced apertures of shape and size suitable to slidely receive therethrough the two tubular members 9, that are inserted through the respective aligned apertures of the two parallel side wings of the brackets 11.
Therefore, the brackets 11 are freely shiftable to an appropriate position along the pair of tubular members over which they are slid.
The central pair of brackets 11 and (for the sample embodiment shown of a three phase transformer) the other two pairs of brackets 11 of each stress traverse, constitute cantilever jaws structures for supporting and/or blocking the resin body containing the resin encapsulated coils (primary and secondary windings of coil phase), as will be better described later with reference to the other sequence of Figures 6, 7 and 8.
The two extreme side brackets 11 of each stress traverse accommodate, between their respective side wings engaged over the tubular members, stress washers 12 for a respective threaded tie rod 5, 6, 7 and 8, passing through the separation gap between the two tubular members 9 composing the stress traverse and that are eventually tensioned by tightening the respective nuts 13, in order to compress the laminated core of the transformer along the upper and lower portions of the lamination core.
The brackets 11 are practically identical and interchangeable, and may be used for composing the upper pair of stress traverses 1 and 2 and for composing the lower pair of traverses 3 and 4.
This aspect, coupled to the fact that the brackets 11 may be slidely shifted to a correct position along the two tubular members 9 constituting the relative stress traverse and eventually fixed in a correct position by simple set screws, permits an outstanding level of standardization.
In practice, two or few more sizes of tubes 9 used for composing the stress traverses and two or few more standardized sizes of slidable brackets 11 such to provide for appropriate mechanical characteristics and sizes of the aligned apertures through the spaced parallel side wings for the different sizes and mechanical characteristics of the different tubes 9 that may be cut to the required length according to the design needs of the machine, allows to compose yoke structures for a broad range of electrical machines, designed for rated powers that may generally be between 50 and 2000 kVA, thus minimizing the inventory of components to manage.
The necessary mechanical connection between the top stress traverses 1 and 2 and the bottom stress traverses 3 and 4, are also realized without requiring weldings but using, even for this purpose, components that can be easily standardized, without requiring precise drillings of the stress traverses to be joined.
In the sample embodiment shown, the mechanical connection between a top stress traverse and the bottom stress traverse (on the same side of the machine) is established by three flat steel risers 14, the constitution of which can be better observed in the exploded view of Figure 2.
The hole 15 at the bottom end of the risers 14 may be threaded to receive the fastening screw 16 passing through the separation gap between the two tubular members constituting the bottom stress traverse 3 and 4, using a washer 17.
The hole 18 at the top end of the riser 14 receives a bolt 19 connecting it to the end of a hoisting eyelet 20 or of a connection member 20' that can be preinstalled on the inner surface of the top stress traverse by tightening the screw 21 passing through the separation gap between the two tubular members 9 that compose the top stress traverse 1 and 2, which tightens the hoisting eyelet 20 or joining member 20' against the inner surface of the two tubular members 9 composing the stress traverse.
According to the preferred embodiment shown in the figures, the clamping of the lamination core of the machine takes place through elastic spacers 22 of distribution-transmission of the stress that may be made of corrugated steel sheet. The profile and height of the ondulations and the mechanical and elastic properties of these corrugated spacers 22 are designed such to practically prevent a direct abutment of the flat connecting risers 14 and of the rear of the brackets 11 onto the lamination core.
Another positive effect of the use of these corrugated elastic spacers 22 is to determine a separation gap between the stress traverse and the planar surface of the first lamination of the core of the magnetic core. This favors heat dissipation by avoiding to hinder or disturb the natural convective circulation of ambient air through the separation gap and through the corrugations of the elastic spacers 22.
The peculiar design of the bracket 11 facilitates the realization of rest feet 23 and 24, if required. Though they may be composed by using the same tubular members of rectangular cross section used for constituting the four stress traverses of the yoke structure, other steel profiles may be used as in the sample embodiment illustrated in the figures, where the rest feet are realized by employing pairs of steel channels, respectively 23' and 24'.
The channels 23' and 24' of each pair are mechanically joined by a plurality of common bridging brackets 25 having a series of predrilled or stamped holes 26.
Even in this case, the mechanical connection of the two feet 23 and 24 to the bottom pair of stress traverses 3 and 4 of the yoke structure is realized in a outstandingly simple manner, without requiring any welding and/or precise drilling, by employing for this purpose four additional brackets 11' inserted in an upside down position over the tubular members 9 of the bottom traverses 3 and 4 together with the innermost brackets of the two side pairs of brackets, by interleaving their respective side wings, as may be easily observed in the figures.
The feet 23 and 24 are positioned such that a predrilled hole 26 of the bridging brackets 25 of the feet is in alignment with one of the predrilled holes present through the flat base of the bracket 11', purposely installed in an upside down position, thus permitting the mechanical connection by tightening the bolt 27 passing through the hole 26 of the bridge-like bracket 25 and through the hole 28 of the base of the upside down mounted additional bracket 11'.
According to the preferred embodiment shown, the brackets 11 and 11', in particular the profile of the two parallel side wings of the brackets has a trapezoidal shape. This facilitates access and the assembly and blocking operations of the resin bodies of the windings and the necessary recomposition of the top branch of the lamination core of the machine, together with the feature that both the hoisting eyelet 20 and the connecting members 20' may be rotated down by loosening the bolts 19, in order to eliminate "obstructions" during the recomposition of the lamination of the top arm of the magnetic core.
Figures 6 and 7 are threedimensional views from different points of observation and Figure 8 is a plan view of a three-phase transformer, completely assembled, having a yoke structure that can be composed and assembled with singularly lightweight components without requiring any weldings nor precise drillings of holes according to the present invention.
As may be observed in the figures, the resin bodies 29 of the resin encapsulated windings for the three phases of the transformer, are sustained and blocked stably in position by using, for each resin body of respective primary and secondary windings of one phase of the machine, four radially shaped gaskets or facings of plastic material 30, preinstalled on the planar base portions of the respective brackets 11.
After positioning the resin bodies 29 onto the respective four supporting brackets 11 provided with suitably shaped plastic facings 30, engaged along the bottom yoke traverses 3 and 4, the resin bodies 29 are blocked by positioning the four retention brackets 11 also provided with the shaped plastic facings 30, and advancing and tightening the blocking screws 31.
Of course, after having completed the installation of the resin bodies 29 of the windings of the three-phase transformer, the top branch of the lamination core constituting the magnetic core 32 of the machine is recomposed.
Finally, also the pair of top stress traverses 1 and 2 of the yoke structure may be finally tightened by acting on the respective tie rods 5 and 6.
None of the four tightening tie rods 5, 6, 7 and 8 crosses the magnetic lamination core thus preventing problems of electrical isolation of stray currents induced in the ferromagnetic core. The tie rods act on the extremities of the stress traverses that extend beyond the profile of the lamination core 32.
It has been found that tightening, by interposing the above described elastic elements 22, that is effected by tightening the two tie rods at respective ends of the composite stress traverses, is significantly more effective, by being implemented against an elastic reaction force of the slightly cambered stress members, determined by precalendering the cut-to-source size tubular members 9. Through a dedicated mechanical testing campaign it has been verified that by imparting to the tubular members 9 of rectangular cross section, cut to measure, a certain camber such to determine, in absence of load, a maximum deflection at the center point of the length of the member comprised, in terms of the ratio deflection/length, between 0,005 and 0,015 (from 0,5 to 1,5%) and by assembling the curved members with convex surface facing the lamination core to be compressed, the tightening is more effective and the size of the tubular members may be safely reduced for minimizing their weight.
All the components of the yoke structure of the invention, are preferably of steel of goods mechanical characteristics, preferably of a steel having a relatively high yield point.
The outstanding level of standardization that is made possible by the constitution of the yoke structure of the present invention, renders economical to maintain adequate inventories of prefabricated components, already treated against corrosion, thus preventing delaying situations that are often encountered with the traditional welded carpentry technique of the prior art for the final coating treatments of the structures fabricated ad hoc.
The sample embodiment shown in Figures 6, 7 and 8, related to a three-phase transformer for electric energy distribution having a rated maximum power handling capability of 630 kVA, with a 20.000 V isolation.
The profile of the lamination core 32 had a height of 1.235 mm, a width of 1.170 mm and the core had a diameter of 210 mm.
The square cross section tubular members 9 were of F 360 steel, with a size of 30mm x 30mm and wall thickness of 3 mm. They were pre-calendered such to produce at midpoint a maximum deflection of 15 mm, corresponding to a ratio deflection/length of the tubular members of 0,01 (1%).
The brackets 11, 11' were made of steel plate having a thickness of 3 mm, a height of the side wings of 105 mm, and a separation distance between the two side wings of 60 mm.
The threaded tie rods 5, 6, 7 and 8 were spaced by 20 mm from the lamination core.
The stress washers 12 were fabricated with welded steel flat band having a width of 75 mm and a thickness of 8 mm.

Claims

A yoke structure for supporting and compressing the magnetic lamination core (32) of a static electrical machine, comprising at least four stress traverses (1-2, 3-4) tightened in pairs by threaded tie rods (5, 6, 7, 8), respectively over the top branch and over the bottom branch of a lamination pack constituting said magnetic core (32), at least four sustaining and blocking brackets of at least a resin body containing windings of the electrical machine, cantilevering from the pair of stress traverses tightened over said bottom branch of the lamination core and from the pair of stress traverses tightened over the top branch of the core,
characterized in that
each of said stress traverses (1, 2, 3, 4) is composed of at least two tubular members (9) of rectangular or square cross section, parallel and spaced from one another and joined together by a plurality of brackets (11) having at least two parallel side wings, each having at least two apertures spaced and of shape suitable to slidely receive there through said tubular members (9), parallely inserted through aligned apertures of the parallel side wings of the brackets (11) that are slidely positionable along the length of said tubular members (9);

at least two pairs of said brackets (11) slidely engaged over said parallel spaced tubular members of each of said pairs of stress traverses (1-2, 3-4) constituting said supporting and blocking brackets of said resin body (29);

the two outermost brackets (11) of each of said stress traverses (1, 2, 3,4) receiving, between said parallel side wings engaged over said tubular members (9), stress washers (12) for a respective tie rod (5, 6, 7, 8), passing through the separation gap between the two parallel tubular members (9) of two opposing stress traverses (1-2, 3-4), tensioned for compressing the lamination core along said top and bottom branches of the magnetic lamination pack (32).
The yoke structure according to claim 1, characterized in that the ends of said stress traverses (1-2, 3-4) carrying said outermost brackets (11), project beyond the profile of said lamination core (32) and said threaded tie rods (5, 6, 7, 8) remain external to said magnetic core (32).
The yoke structure according to claim 1, characterized in that said tubular members (9) parallel and spaced from one another constituting said stress traverses (1, 2, 3, 4) are cambered such to have at mid point a maximum deflection comprised between 0,5% and 1,5% of their length.
The yoke structure according to claim 1, characterized in that each stress traverse (1, 2, 3, 4) composed of said parallel spaced tubular members (9) comprises at least six of said brackets (11) with aligned side wing apertures slidely inserted over the tubular members (9);
at least two of said brackets (11) of the stress traverses (3, 4) tightened over the bottom branch of the lamination core (32) are fixed in a certain position by a set screw or equivalent fastening element and respectively connected with one and with the other of two feet (23, 24) of the yoke structure.
The yoke structure according to claim 4, characterized in that each of said feet (23, 24) is composed of a pair of parallel spaced channel-shaped members (23', 24') joined by a plurality of bridging brackets (25), the innermost pair of bridging brackets (25') being mechanically coupled to said two brackets (11) of said traverses (3, 4) tightened over the bottom arm of the lamination core (32).
The yoke structure according to claim 1, characterized in that said side wings of said brackets (11) have a trapezoidal profile with maximum width corresponding a right angle bending edge of said wings in respect to a flat base portion of the brackets and said brackets (11) are inserted over the respective tubular members, with the flat base portion facing toward the mid plane of the height of the magnetic core (32).
The yoke structure according to claim 5, characterized in that said mechanical couplings are established by four additional brackets (11') slidely inserted in pairs and in an upside down position along the tubular members (9) of one (3) and the other (4) stress traverse, respectively, and interleaving their parallel side wings with the side wings of said two brackets (11) fixed in position.