EP3400602B1

EP3400602B1 - Multilayer winding transformer

Info

Publication number: EP3400602B1
Application number: EP16700012.4A
Authority: EP
Inventors: Gianluca BUSTREO; Miljenko Hrkac; Cristiano GREGGIO; Roberto Zannol
Original assignee: ABB Power Grids Switzerland AG
Current assignee: Hitachi Energy Ltd
Priority date: 2016-01-04
Filing date: 2016-01-04
Publication date: 2021-09-01
Anticipated expiration: 2036-01-04
Also published as: WO2017118472A1; EP3400602A1

Description

BACKGROUND

Technical field

The present invention relates to an electrical transformer, in particular to a multilayer winding transformer adopting non-uniform insulation. According to a standard definition (see for example International Electrotechnical Commission IEC 60076-3), a "uniform insulation" is the insulation of a transformer winding having all its ends connected to terminals with the same rated insulation level. On the contrary, a "non-uniform insulation" is the insulation of a transformer winding having a neutral terminal end for direct or indirect terminal to earth and designed with an insulation level which is lower than the insulation level of the line terminal.
Furthermore, the present invention is mainly focused on transformers for high or relatively high voltage applications, where disc type windings are commonly used, having a winding rated power approximately up to 25-30MVA.

Description of the Related Art

High voltage applications typically employ transformers having disc windings. In this kind of windings, the electric field between the turns and discs is distributed in such a way that the use of insulation material is minimal.
In such transformers the clearances (also known as 'ducts') between the winding with the highest rated voltage and the other windings are chosen sufficiently ample to guarantee successful tests and safe operation. Figure 1 schematically shows a common non-uniformly insulated disc winding transformer 100 having a High-Voltage (HV) winding 101 and a low-voltage (LV) winding 102 (it is to be noted that only half view is given and that the winding symmetry axis is indicated by a dotted line). A clearance 107, usually named "main duct", is located between the HV winding 101 and the LV winding 102. In the HV winding 101 a set of discs 103', 103",103"'... , each having a defined number of turns 104', 104", ... , are connected in series, to bridge the top end terminal 105, where the tension is applied, with the lower end terminal 106, which is either the earth in single phase or three phases star-connected systems or simply the Neutral in three phases star-connected systems. The foregoing description shows that disc windings uniformly distribute the electrical potential mainly in the axial direction A whilst the electrical potential variation is relatively low in the radial direction R. The applied electric potential at the winding top end terminal 105 is transferred, with relatively little reduction, to the same winding portion facing the Low Voltage winding (point 108 in Figure 1). Therefore, the main duct 107 is substantially called to withstand the High Voltage section full rated electrical potential difference with respect to the Low Voltage section.
Moreover, the disc windings construction involves long production times. A known electrical transformer is disclosed in document US 4,326,181 A .

BRIEF SUMMARY OF THE INVENTION

The object of the present invention is therefore to provide an electrical transformer for high or relatively high voltage applications, which is alternative to common disc winding transformers featured by a sufficient compactness and a short construction time.
This and other objects achieved by an electrical transformer in accordance with claim 1.
Dependent claims define possible advantageous embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the transformer according to the invention will be more apparent from the following description of a preferred embodiment and of its alternatives given as a way of an example with reference to the enclosed drawings in which:

Figure 1 shows schematically a winding arrangement of a disc winding transformer according to the known art;
Figure 2 shows schematically a winding arrangement of a multilayer winding transformer according to a possible embodiment of the invention;
Figure 3 shows schematically a winding arrangement of a multilayer winding transformer according to an example not being covered by the claimed invention;
Figure 4 shows schematically a winding arrangement of a multilayer winding transformer according to an example not being covered by the claimed invention;
Figure 5 shows a schematic partial sectional view of a possible executive arrangement of the multilayer winding transformer according to the example shown in Figure 4;
Figure 6 shows an enlarged perspective view of a portion of the transformer shown in Figure 5.

DETAILED DESCRIPTION

In the following detailed description identical components have the same reference numbers, regardless of whether they are shown in different embodiments of the present invention or in different examples not being covered by the claimed invention. Furthermore, in order to clearly and concisely disclose the present invention, the drawings may not necessarily be to scale and certain features of the invention may be shown in somewhat schematic form.
With reference to the annexed Figures 2-6, an electrical transformer winding arrangement is indicated with the reference number 1. The transformer provided with the winding arrangement 1 is mainly destined to be used in high or relatively high voltage applications and in particular adopts non-uniform insulation, according to the definitions given above.
Electrical transformer comprises a core 20 and one or more winding assemblies mounted to the core 20 itself. For example, in the case of a single-phase transformer, there is only one winding assembly whilst for three-phase applications there are three winding assemblies.
Considering the single-phase case for simplicity, the winding assembly comprises a low voltage (LV) winding 2 and a high voltage (HV) winding 3. According to the embodiments of the invention or to the examples not being covered by the claimed invention shown in the Figures, HV winding 2 and LV winding 3 are concentrically arranged around a core portion. The representations of Figure 2, 3, 4 and the executive view of Figure 5 show half of the winding arrangement 1 cross section, wherein the longitudinal axis, marked by a dotted line, corresponds to the winding arrangement 1 cylindrical symmetry axis. The cylindrical clearance 15 between the HV winding 3 and the LV winding 2 is commonly referred to as "main duct".
The HV voltage winding 3 comprises a first winding section 4 and a second winding section 5, connected together by an electrical junction 6. First 4 and second 5 winding sections are arranged next one to the other and coaxially along direction A of the HV winding 3. With reference to the normal conditions of use of the transformer 1, the first winding section 4 can correspond to an axially top HV winding section and the second winding section 5 can correspond to an axially bottom HV winding section of the HV winding 3.
The so arranged first winding section 4 and second winding section 5, advantageously, are separated by an axial gap 10 between said sections in the HV winding axial direction A.
The first 4 and the second 5 winding sections are of the so-called "multilayer" or "barrel" type. In particular, each of the first 4 and the second 5 winding sections comprises an electrically insulated conductor 7 wound for example over a limb supporting the HV winding 3 itself. In each winding section the conductor 7 is wound to form a plurality of layers 9', 9".... The different layers 9', 9"... are arranged radially, i.e. along direction R, one on top to the other. Each layer 9', 9"... has a predetermined number of turns 16', 16" formed by the wounded conductor 7 in the axial direction A of the HV winding. Advantageously, the first 4 and the second 5 winding sections have the same overall number of turns (i.e. the sum of turns of all the layers). Still more advantageously, in each of the first 4 and the second 5 winding sections the total number of turns is greater than the number of the layers so to reduce the overall radial size, which in particular can be less than the radial size of a disc winding designed for the same rated voltage and current.
In general, multilayer/barrel windings require less construction time as compared to a disc winding for the same rated voltage and current.
According to possible arrangements (see for example alternative arrangements shown in Figures 2-3), in the first 4 and second 5 winding sections, the number of turns per each layer 9', 9" ... is the same. However, according to an alternative arrangement (see, for example, the schematic representation in Figure 4 and the corresponding executive arrangement shown schematically in Figure 5), in each of the first 4 and the second 5 winding sections, both the radially innermost and outermost layers have less turns than the remaining intermediate layers. The reduced number of turns at innermost and outermost layers allows to increase in the intermediate layers the electric strength by a thicker insulation of the winding edges, where the local electric field enhancement results in an increased risk of electric discharge ignition. Layers with less turns are conventionally called "graded layers".
The first winding section 4 comprises a first terminal 11, which is located radially external, and a second terminal 12 which is located radially internal in the first winding section 4 itself. In the same manner, the second winding section 5 comprises a first terminal 13 which is located radially external and a second terminal 14 which is located radially internal in the second winding section 5 itself.
The first winding section radially external terminal 11 is normally the HV winding 3 entrance, where the electric potential is applied, and is usually connected to a line terminal of the transformer. Advantageously, the first winding section radially external terminal 11 is located axially outward with respect to the HV winding 3 itself, such that the electric strength towards grounded parts is the highest.
The second winding section radially internal terminal 14 is normally the HV winding 3 exit, and can be connected to a transformer tap-changer or directly to a neutral terminal or to earth. The second winding section radially internal terminal 14 is axially external with respect to the HV winding in a position which is axially opposite to the first winding section radially external terminal 11. In other words, referring again to the transformer normal conditions of use, the second winding section radially internal terminal 14 is preferably located in an axially lower position both of the second winding section 5 and of the overall HV winding 3.
The first winding section radially internal terminal 12 is joined to the second winding section radially external terminal 13 by the electrical junction 6. The first winding section radially internal terminal 12 and the second winding section radially external terminal 13 can be axially differently positioned in the respective winding section (i.e. in the axially upper or lower part of the respective section) and consequently the electrical junction 6 can be either outside the axial gap 10 (as in the embodiment depicted in Figures 2) or within it (as in the examples not being covered by the claimed invention depicted in Figures 3 and 4, as well as in Figure 5), as will be described hereinafter.
With reference to Figure 2, a winding arrangement according to a possible embodiment of the transformer is here below detailed. According to the invention, the first winding section radially internal terminal 12 and the second winding section radially external terminal 13 are axially external with respect to the whole HV winding 3, and are in opposite positions. In other words, with reference to the normal conditions of use, the first winding section radially internal terminal 12 and the second winding section radially external terminal 13 are respectively located in the axially upper part of the HV winding 3 (and of the first winding section 4) and in the axially lower part of the HV winding 3 (and of the second winding section 5). According to the invention, the electrical junction 6 is located outside the axial gap 10.
In the winding arrangement according to this embodiment, the electrical potential decays almost linearly along the turns 16', 16"... of the layers 9', 9", from the first section radially external terminal 11 down to the second section radially internal terminal 14. This happens both in a quasi-stationary regime (at a normal power frequency, i.e. 50 or 60 Hz) and during transients (typically, lighting and switching impulses during tests and normal operation). Consequently, due to the preferred equal subdivision of the turns between the first 4 and the second 5 winding sections, in correspondence of the radially inner side of the HV winding 3, which typically faces the radially outer side of the LV winding 2, there is half of the Voltage level which is applied at the first section radially external terminal 11, which is the High Voltage winding entrance. The main duct 15, then, can have a reduced radial dimension with respect to a disc winding designed for the same rated Voltage and Current. Therefore, in comparison to the disc winding type, the multilayer/barrel winding assembly here described can be smaller, due to the overall reduced radial dimension, and with reduced weight.
Additionally, the winding arrangement 1 according to the above described embodiment provides a substantially constant potential difference along the axial gap 10 between the first 4 and second 5 winding sections. Indeed, as explained above, in both the first 4 and second 5 winding sections, the electric potential with respect to ground decreases radially from the outside to the inside, at substantially the same rate. Therefore the electric potential difference between the first 4 and second 5 winding sections is fairly constant. This would not happen, for example, if the first section 4 radially internal terminal 12 were connected to the second section 5 radially internal terminal 14, and if the second section 5 radially external terminal 13 were connected to the earth, or to the transformer neutral terminal or to the tap changer. In this case there would be almost the total rated winding voltage across the axial gap 10, in correspondence of the winding sections outer edges that face the axial gap 10.
According to the invention, in the embodiment described with reference to the Figure 2, the number of layers of each of the first 4 and second 5 winding section is even.
In accordance with a further possible example not being covered by the claimed invention, the number of layers of each of the first 4 and second 5 winding section is odd. In this case, the first 4 and the second 5 winding sections can be differently configured and connected. Examples of this configuration are given in Figures 3-4. According to this example, the first section radially internal terminal 12 and the second section radially external terminal 13, which are bridged together, both face the internal axial gap 10. In this case, differently to what disclosed with reference, for example, to the embodiment shown in Figure 2, the electrical junction 6 can be located in the axial gap 10.
In the configuration described above, graded layers are preferably located both in the first 4 and in the second 5 winding sections, respectively in the outermost and innermost layers, in order to decrease the electric stress located at the winding sections edges facing the axial gap 10 (see example not being covered by the claimed invention in Figure 4) and in correspondence of the electrical junction 6 between the winding sections. However, alternatively, the number of turns can be the same in each layer (see example not being covered by the claimed invention in Figure 3).
The executive arrangement shown in Figure 5 corresponds to the example not being covered by the claimed invention schematically shown in Figure 4. It is to be noted that only half of the winding arrangement, in section, is depicted, and that the dotted line represents the symmetric axis. Figure 4 shows that the radially innermost layer and the radially outermost layer of each of the first 4 and the second 5 sections have a number of turns lower than the number of turns of the intermediate layers. Moreover, the electrical junction 6, preferably embodied by a bent conductor 22, still more preferably wrapped by a convenient amount of creep paper, is located in the axial gap 10 between the first 4 and the second 5 sections.
Figure 6 shows an enlarged view of a portion of the HV winding 3 according to the example not being covered by the claimed invention of Figure 5, where the conductor 22 forming the electrical junction 6 is located. In particular, in Figure 6, only the second winding section 5 is shown, whilst the first winding section is not shown. The conductor 22 extends in the axial gap 10 and, starting from the second section radially external terminal 13, is curved in axial direction towards the first winding section 4 (not shown in Figure 6), and radially towards the transformer core (not shown in Figure 6) since the first section radially internal terminal 12 is radially internal with respect to the second section radially external terminal 13.
To the above-mentioned embodiments of the transformer with the winding arrangement according to the invention, the skilled person, in order to meet specific current needs, can make several additions, modifications, or substitutions of elements with other operatively elements, without however departing from the scope of the appended claims.

Claims

An electrical transformer comprising a core (20) and one or more winding assemblies mounted to the core, each winding assembly comprising a low voltage winding (2) and a high voltage winding (3),
wherein the high voltage winding (3) comprises a first winding section (4) and a second winding section (5) arranged consecutively in the axial direction (A) of the high voltage winding (3) and connected through an electrical junction (6), the first (4) and the second (5) winding sections comprising insulated conductors (7) in multilayer arrangements wherein a plurality of conductor layers (9', 9"...), each having one or more turns (16', 16"...) in said axial direction (A), are wounded on top of one another in the radial direction (R) of the high voltage winding (3), each of the first (4) and second (5) winding sections having a radially external terminal (11, 13) and a radially internal terminal (12, 14), wherein:
- the first winding section (4) radially internal terminal (12) is connected to the second winding section (5) radially external terminal (13) through said electrical junction (6);

- the first winding section (4) radially external terminal (11) is the high voltage winding (3) entrance;

- the second winding section (5) radially internal terminal (14) is the high voltage winding (3) exit,

wherein the first winding section (4) and the second winding section (5) are arranged so to form an axial gap (10) in said axial direction (A) of the high voltage winding (3),

wherein the first winding section (4) radially internal terminal (12) is axially external with respect to said high voltage winding (3) and the second winding section (5) radially external terminal (13) is axially external with respect to said high voltage winding (3), axially opposite to said first winding section (4) radially internal terminal (12),

wherein said electrical junction (6) between the first (4) and the second (5) winding sections is located outside said axial gap (10),

wherein the number of layers (9', 9"...) of each of said first (4) and second (5) winding section is even.
Electrical transformer according to claim 1, wherein the high voltage winding (3) and the low voltage winding (2) are concentrically arranged.
Electrical transformer according to claim 1 or 2, wherein said first winding section (4) and said second winding section (5) have the same number of turns (16', 16"...).
Electrical transformer according to any of the preceding claims, wherein in each of said first (4) and second (5) winding sections the number of turns (16', 16"...) of each of said layers (9', 9") is greater than the overall number of layers.
Electrical transformer according to any claim 1-4, wherein in each of said first (4) and second (5) winding sections each layer (9', 9"...) has the same number of turns (16', 16"...).
Electrical transformer according to any claim 1-4, wherein in each of said first (4) and second (5) winding sections the radially innermost layer and the radially outermost layer have a number of turns (16', 16"...) lower than the number of turns (16', 16"...) of the intermediate remaining layers.
Electrical transformer according to any of the preceding claims, wherein the first winding section (4) radially external terminal (11) is axially external with respect to said high voltage winding (3) and the second winding section (5) radially internal terminal (14) is axially external with respect to said high voltage winding (3), axially opposite to said first winding section radially external terminal (11).