WO2003019588A1

WO2003019588A1 - Multiphase electrical induction machine of the static type

Info

Publication number: WO2003019588A1
Application number: PCT/IT2001/000450
Authority: WO
Inventors: Daniele Fornara
Original assignee: F.D.U.E.G. S.R.L.
Priority date: 2001-08-24
Filing date: 2001-08-24
Publication date: 2003-03-06

Abstract

Described herein is a multiphase electrical induction machine of the static type, for example a transformer or a reactor, with a column-type core, wherein at least the axes of the larger sections of the columns are parallel to and coincident with respective generatrices of at least one cylindrical surface having as directrix a closed line.

Description

Title: "MULTIPHASE ELECTRICAL INDUCTION ^% MACHINE OF THE STATIC

TYPE" Technical field of the invention

The present invention relates to a multiphase electrical induction machine and, in particular, a static electrical machine with a "column- type" core, such as a multiphase transformer or a multiphase reactor, having an improved structure as compared to the corresponding electrical machines of a known type. Background of the invention As is well known in the prior art, transformers are static electrical machines that comprise an electrical circuit generally consisting of one or more windings magnetically concatenated together via a ferromagnetic core. In the most common case at least two windings are provided for each phase, namely a primary winding and a secondary winding, whereas, in the particular case where a single winding is present for each phase, the transformer is defined as "autotransformer".

Reactors are electrical machines which are constructively similar to transformers and are provided with a single two-terminal winding set on a ferromagnetic core for each phase. In what follows, for convenience of description, reference will be made basically to multiphase transformers, even though the same principles of the invention can be identically applied also to multiphase reactors and to multiphase autotransformers. The main types of transformers known in the art can be basically distinguished into transformers with a shell-type core and transformers with a column-type core.

In transformers with a shell-type core, the windings are surrounded by closed core elements having a substantially rectangular shape. The multiphαse transformers that fall into this category, albeit affording a certain versatility in the relative arrangement of the electrical and magnetic circuits associated to each phase, nevertheless have very high production costs due to the particular shape that must be imparted on the core elements.

In fact, as is known, transformer cores are made up of a pack of laminations made ,of ferromagnetic material, which are electrically insulated from one another. In the case of shell-type cores it is thus necessary to provide shaped elements, which are generally made up of two separate parts that must then fit together with high precision, or which are formed by assembling packs of laminations until the parts that will enable the substantially rectangular shape of the core elements to be made are formed. In multiphase transformers with a column-type core, the magnetic circuit consists of a plurality of parallel columns, with the respective axes lying on one and the same plane, set between at least one pair of yokes. The primary and secondary windings of each phase are arranged on at least one column, and also additional columns without windings may possibly be provided. For example, with reference to three-phase transformers, the cores can be made with three columns (one for each phase), or else five columns, of which two end columns are without windings.

Transformers with a column-type core are relatively more economical to produce, and thus more widespread, as compared to transformers with a shell-type core because the columns and the yokes can be made of packs of rectilinear laminations.

However, one of the main drawbacks of known multiphase transformers with a column-type core is represented by their encumbrance in the dimension parallel to the plane on which the axes of the columns lie. ln addition, with this known arrangement it is difficult to carry out an effective cooling of the electrical and magnetic circuits during operation of the transformer, above all at the central section of the transformer. These problems are even more accentuated when the transformers are designed to be installed in transformer rooms, control cabinets, or, in any case, inside the casings of apparatus to which they are connected. In fact, in addition to the space available which is necessarily limited for the installation of the transformer, there must also be provided additional solutions for its cooling.

In view of what has been said, an object of the present invention is to provide a multiphase electrical induction machine, with a column-type core, that has overall dimensions smaller 'than the corresponding machines of a known type. Another object of the present invention is to provide a multiphase electrical machine of the type referred to above which enables a more effective cooling of the electrical and magnetic circuits. A further object of the present invention is to provide a multiphase electrical machine of simpler and more economical construction. Disclosure of the invention

The above objects are achieved, according to the present invention, thanks to a multiphase electrical induction machine, of the type comprising at least one magnetic circuit formed by a plurality of parallel columns set between at least two yokes, and at least one electrical circuit consisting of electrical insulated conductors wound on at least part of the columns, characterised in that at least the axes of the larger sections of the columns are parallel to and coincident with respective generatrices of at least one cylindrical surface having as directrix a closed line. The- expression "cylindrical surface" must be here understood in the widest sense of analytical geometry, namely as a surface through each point of which there passes a generatrix that lies on the surface itself, and in which all the generatrices are parallel to one another. As a result, the overall dimensions of an electrical machine with a column-type core according to the invention, whether this be a transformer or a reactor, are considerably reduced as compared to the corresponding machines of a known type. According to a possible embodiment of the invention, the axes of the core columns for each phase are arranged in positions spaced at equal distances to each other, as occurs, for example, in the case where the directrix is a circumference or, in other words, if the parallel axes of the columns are arranged so that they pass through the vertices of an equilateral triangle. According to a preferential aspect of the present invention, the yokes between which the columns are set have a shape substantially tending to that of a cylinder with a circular or polygonal base. The yokes thus made can be advantageously provided each with at least one central through hole. This enables particularly effective circulation of a cooling fluid through the central holes of the two yokes, thus enabling uniform cooling of all the sections of the electrical and magnetic circuits.

The yokes are preferably made of one or more laminations consisting of ferromagnetic material in the form of a ribbon of appropriate width, namely of a width equal to the height of the yoke according to the design requirements. The ribbon is spirally wound on special templates until the desired shape and dimensions are obtained. The economic advantage of this solution lies in the fact that it is possible to use lamination windings already commercially available in this form. It is thus not necessary to cut the material to size in the necessary length, as is the case for the yokes of corresponding machines of a known type. In this way, a process is avoided which, in addition to the cost entailed, causes stressing of the material at the cut. As compared to transformers of a known type, in which the laminations of the yokes must be packed in close mutual contact by means of stay rods that are electrically insulated from the laminations themselves, the wound laminations which form the yokes of the transformer according to the invention are kept compact by means of a metal strap which grips the external periphery of the yoke.

The idea of the present invention can be applied to any type of multiphase electrical induction machine with a column-type core, for example also to transformers in which further columns without windings are provided, as likewise to transformers with integrated reactors. In this latter case, the magnetic circuit further comprises the columns of the cores of integrated reactors associated with at least one of the windings of each phase, and the columns of the cores of the integrated reactors are set between the yokes themselves of the magnetic circuit. Means for circulating a forced flow of a cooling fluid for the electrical and magnetic circuits, for example fans, pumps or the like, can be advantageously provided.

In addition, a housing can also be provided which enables to house the electrical and magnetic circuits inside it. In addition to confining the space for circulation of the cooling fluid, a housing made of appropriate material, for example stainless steel, enables reduction of the dispersion in air of the magnetic flux.

In general, given the same power and performance as compared to known transformers, for the transformer according to the invention there has been found the possibility of limiting further the weight of the core mαde of ferromagnetic material, with evident advantages from the point of view of the production costs.

In the course of tests conducted with a transformer made according to the present invention, there was further found a considerable reduction in the harmonics of the third order and higher. This advantageously enables limitation of the size or of the number of possible filters which must be provided for eliminating said harmonics. Brief description of the drawings

The invention will be now described below in greater detail, with reference to the annexed schematic drawings, in which:

- Figure 1 is a simplified perspective view of a transformer according to a possible embodiment of the present invention;

- Figure 2 is a cross-sectional view of the transformer shown in Figure 1 ;

- Figure 2A is a cross-sectional view of a detail of the transformer shown in Figures 1 and 2;

- Figure 3 is a cross-sectional view that illustrates another possible embodiment of a transformer according to the present invention; and

- Figure 4 is a cross-sectional view that illustrates a further possible embodiment of the present invention. Modes for carrying out the invention

In the following description particular reference will be made to a three- phase transformer and, in particular, a three-phase transformer of the integrated-reactor type, as example of a multiphase electrical induction machine according to the present invention. It should, however, be emphasised that the same principles may be equally applied to multiphase reactors, to transformers without integrated reactors, as well as to transformers with more than three phases (for example, six-phase transformers), it being well known to persons skilled in the art how the windings of the electrical circuits must be arranged on the columns of the magnetic circuit. With reference firstly to Figures 1 and 2, a three-phase transformer according to the present invention comprises three sets of electrical and magnetic circuits, designated by the reference numbers 1 , 2 and 3, respectively, the terminals of the electrical conductors coming out of each set not being shown for clarity of representation. Set 1 comprises, in particular, a column 15 made up of a number of packs of laminations having different dimensions to obtain a section of the "step" type, which enables approximation as far as possible to a section having a circular shape, such as the one represented in Figure 2A.

On column 15 there are concentrically arranged a secondary winding 12 and a primary winding 1 1 , which constitute the parts of the electrical circuit corresponding to the phase of set 1. In addition to the necessary insulating materials 30 (some of which may be seen only in Figure 1 ) that bind the windings, protection elements 10 are placed between the edges of the column 15 and the secondary winding 12, as well as spacer elements 20 are placed between the primary winding 1 1 and the secondary winding 12. In addition to guaranteeing the necessary degree of safety in insulation, elements 10 and 20 enable the formation of gaps designed to favour the natural or forced circulation of a cooling fluid that laps the column 15, as well as the windings 1 1 and 12. In the embodiment illustrated in Figure 2, the cores of the integrated reactors, which also are made in the form of columns 16 consisting of a number of packs of laminations of different cross section, are concatenated with the primary winding 1 1 and arranged in positions diametrically opposite to the column 15. Also for columns 16, protection elements 10 are provided arranged on the edges of the columns themselves. Sets 2 and 3 for the other two phases are built in a way identical to that of set 1. In other words, set 2 comprises a column 25 on which the concentric secondary winding 22 and primary winding 21 are arranged, as well as a pair of columns 26 of the integrated reactors that are concatenated with the primary winding 21. The same applies to set 3, in which the concentric primary winding 31 and secondary winding 32 are arranged on a column 35, with a pair of columns 36 concatenated to the primary winding 31. Also in sets 2 and 3 the protection elements 10 and the spacer elements 20 are present. As may be noted from the schematic representation of Figure 2, the axes 18, 28 and 38 (perpendicular to the plane of the figure) of the respective columns 15, 25 and 35 are arranged in positions equidistant from one another, for example in correspondence of generatrices of a cylindrical surface or, in other words, at the vertices of an equilateral triangle. In this case, also the axes of the columns 16, 26, and 36 have the same distribution along a cylindrical surface, where the base of the cylinder is circular or polygonal, for example that of an irregular hexagon. This arrangement gives to the transformer a particularly compact shape and limited overall dimensions. The magnetic circuit of a transformer according to the present invention further comprises a pair of yokes 50 substantially having the shape of a cylinder with a circular or polygonal base, possibly provided with a central through hole 55. Even though it is not clearly visible in the figures, the yokes 50 are made up of one or more laminations wound in the appropriate shape and gripped on the outside by means of a metal strap along the outer perimeter of the yoke. The yokes 50 themselves are moreover set in close contact with the columns 16, 26 and 36 to close also the magnetic circuits of the integrated reactors. The possible presence of the central hole 55, in at least one or in both of the yokes 50, enables more effective and uniform cooling of all the sets 1 , 2 and 3 by means of circulation of a cooling fluid, possibly set in circulation by appropriate means.

The yokes 50 are mounted in close contact with the columns 15, 25, and 35 by means of plates 51 and corresponding stay rods 52. As compared to column transformers of a known type, there is no longer any need for stay rods with the sole function of gripping the pack of laminations of the yokes. Other possible embodiments of a multiphase transformer according to the present invention are illustrated in Figures 3 and 4.

In the embodiment illustrated in Figure 3, columns 1 15, 125 and 135 consist of a single pack of laminations having a substantially rectangular shape, with concentric windings similar to the ones already described with reference to Figure 1 , and with columns 1 16, 126 and 136 of the integrated reactors that are concatenated to the respective primary windings. In a way similar to the previous embodiment, the axes 1 18, 128 and 138 of columns 1 15, 125 and 135, respectively, are equidistant and arranged according to generatrices of a cylindrical surface, as also are the axes of the columns 1 16, 126 and 136 of the integrated reactors. Each set 101 , 102 and 103 thus presents a section tapered towards the centre of the structure of the transformer. Given the same dimensions in plan view of the yokes 50 with respect to the previous embodiment, this arrangement offers the additional advantage of making available possible additional columns 100 without windings between the two yokes 50. The section of the additional columns 100 (represented by way of example by dashed lines) may also be other than the approximately circular one represented in Figure 3 and can be adapted for guaranteeing optimal circulation of the magnetic flux. As is known in the prior art, the presence of columns without windings cαn enable a magnetic circuit to be made similar to the one obtainable from the construction of transformers with shell-type cores. Also in the embodiment of Figure 4, even though this is not expressly represented, it is possible to envisage the arrangement of further columns without windings.

Columns 215, 225 and 235 of the sets 201 , 202 and 203 are made up of two distinct packs of laminations, whilst columns 216, 226 and 236 of the integrated reactors are set alongside the previous ones and are again concatenated with the respective primary windings of the respective set. All the columns represented are set between two yokes 50 like the ones described previously.

In this case, since each column 215, 225, 235 is made up of two distinct packs of different sections, it is improper to refer to a single axis of the column. However, it may be noted that the axes 218, 228 and 238 of the packs of laminations of larger dimensions lie on a first cylindrical surface, as likewise the axes 219, 229 and 239 of the packs of laminations of smaller dimensions lie on a second cylindrical surface. Even though this is not expressly represented, yokes 50 can also have a slightly different shape from the circular one (for example, a polygonal shape) and may be made up of ribbon-shaped laminations of different widths. This second possibility may become necessary for guaranteeing the most favourable conditions of circulation of the magnetic flux in order to obtain, at least in certain areas, portions of yoke having a height substantially the same as that of the sections of the columns in contact with the yokes themselves in those areas.

Various modifications may be made to the embodiments illustrated herein purely by way of example, without departing from the scope of the present invention. In particular, an electrical machine according to the present invention can be enclosed in a housing of any shape, for exαmple of α cylindrical shape, made of a material that enables limitation of dispersion in air of the magnetic flux, for example stainless steel.

In addition, it is possible to provide means, possibly integrated with the structure of the machine, for circulating a forced flow of a heat- exchange fluid, for example air, oil or similar fluids already adopted in the art, in order to guarantee cooling of the electrical and magnetic circuits in the machine.

Claims

1. A static-type multiphase electrical induction machine, comprising at least one magnetic circuit formed by a plurality of parallel columns set between at least two yokes, and at least one electrical circuit consisting of one or more insulated electrical conductors wound on at least part of said columns, characterised in that at least the axes of the larger sections of said columns are parallel to and coincident with respective generatrices of at least one cylindrical surface having as directrix a closed line.

2. A machine according to Claim 1 , wherein the axes of said columns are arranged in positions spaced at equal distances to each other.

3. A machine according to Claim 1 , Wherein said directrix is a circumference.

4. A machine according to Claim 1, wherein the axes of said columns are arranged at the vertices of a polygon.

5. A machine according to Claim 1 , wherein said at least two yokes have substantially the shape of a cylinder with a circular or polygonal base.

6. A machine according to Claim 5, wherein at least one or both of said at least two yokes are provided with at least one central through hole.

7. A machine according to Claim 1 , wherein said at least two yokes are each made from one or more laminations wound and gripped on the outside by a peripheral strap.

8. A machine according to Claim 1 , further comprising means for circulating a forced flow of a cooling fluid for said electrical circuit and said magnetic circuit.

9. A machine according to Claim 1 , further comprising a housing for sαid electrical circuit and said magnetic circuit.

10. . A machine according to any of Claims 1 to 9, wherein said machine is a multiphase electrical transformer.

1 1. A machine according to Claim 10, wherein at least one primary winding and at least one secondary winding of said electrical circuit are associated to each of said columns, and wherein said magnetic circuit further comprises the columns of the cores of reactors integrated with at least one of said windings.

12. A machine according to Claim 1 1 , wherein the columns of the cores of said integrated reactors are set between said at least two yokes.

13. A machine according to any of Claims 1 to 9, wherein said machine is a multiphase reactor.