PARK, Hoonyang (2201-701, Jindalrae Maeul Daewoo APT.Sang-dong, Wonmi-gu, Bucheon-s, Gyeonggi-do 420-030, KR)
Claims
[1] A transformer for attenuating harmonics including a primary coil and a secondary coil, the transfer comprising: a core having a first leg, a second leg, and a third leg; a first winding of the secondary coil which is wound on the first leg, the third leg, the first leg, the third leg, and the first leg in sequence, and is connected to a neutral line; a second winding of the secondary coil which is wound on the second leg, the first leg, the second leg, the first leg, and the second leg in sequence, and is connected to the neutral line; and a third winding of the secondary coil which is wound on the third leg, the second leg, the third leg, the second leg, and the third leg in sequence, and is connected to the neutral line. [2] The transformer for attenuating the harmonics according to claim 1, wherein the first winding is wound at different positions in the first leg and the third leg, wherein the second winding is wound at different positions in the second leg and the first leg, and wherein the third winding is wound at different positions in the third leg and the second leg. [3] The transformer for attenuating the harmonics according to claim 2, wherein the first winding is wound in a direction opposite to each other in the first leg and the third leg, wherein the second winding is wound in a direction opposite to each other in the second leg and the first leg, and wherein the third winding is wound in a direction opposite to each other in the third leg and the second leg. [4] The transformer for attenuating the harmonics according to claim 3, wherein in the secondary coil, the number of winds of the first winding firstly wound on the first leg is the same as the number of winds of the first winding lastly wound on the first leg, the number of winds of the second winding firstly wound on the second leg is the same as the number of winds of the second winding lastly wound on the second leg, and the number of winds of the third winding firstly wound on the third leg is the same as the number of winds of the second winding lastly wound on the second leg. [5] The transformer for attenuating the harmonics according to claim 4, wherein a turn ratio of the first winding wound on the first leg, the third leg, the first leg, the third leg, and the first leg in sequence is 1:1:1:1:1 or 1:2:2:2:1, wherein a turn ratio of the second winding wound on the second leg, the first leg, the second leg, the first leg, and the second leg in sequence is 1:1:1:1:1 or 1:2:2:2:1, and wherein a turn ratio of the third winding wound on the third leg, the second leg, the third leg, the second leg, and third leg in sequence is 1:1:1:1:1 or 1:2:2:2:1.
[6] A transformer for attenuating harmonics including a primary coil and a secondary coil, the transfer comprising: a core having a first leg, a second leg, and a third leg; a first winding of the secondary coil which is wound on the first leg, the second leg, the first leg, the second leg, and the first leg in sequence, and is connected to a neutral line; a second winding of the secondary coil which is wound on the second leg, the third leg, the second leg, the third leg, and the second leg in sequence, and is connected to the neutral line; and a third winding of the secondary coil which is wound on the third leg, the first leg, the third leg, the first leg, and the third leg in sequence, and is connected to the neutral line.
[7] The transformer for attenuating the harmonics according to claim 6, wherein the first winding is wound at different positions in the first leg and the second leg, wherein the second winding is wound at different positions in the second leg and the third leg, and wherein the third winding is wound at different positions in the third leg and the first leg.
[8] The transformer for attenuating the harmonics according to claim 7, wherein the first winding of the secondary coil is wound in a direction opposite to each other in the first leg and the second leg, wherein the second winding of the secondary coil is wound in a direction opposite to each other in the second leg and the third leg, and wherein the third winding of the secondary coil is wound in a direction opposite to each other in the third leg and the first leg.
[9] The transformer for attenuating the harmonics according to claim 8, wherein in the secondary coil, the number of winds of the first winding firstly wound on the first leg is the same as the number of winds of the first winding lastly wound on the first leg, the number of winds of the second winding firstly wound on the second leg is the same as the number of winds of the second winding lastly wound on the second leg, and the number of winds of the third winding firstly wound on the third leg is the same as the number of winds of the second winding lastly wound on the second leg. [10] The transformer for attenuating the harmonics according to claim 9, wherein a turn ratio of the first winding wound on the first leg, the second leg, the first leg, the second leg, and the first leg in sequence is 1:1:1:1:1 or 1:2:2:2:1, wherein a turn ratio of the second winding wound on the second leg, the third leg, the second leg, the third leg, and the second leg in sequence is 1:1:1:1:1 or 1:2:2:2:1, and wherein a turn ratio of the third winding wound on the third leg, the first leg, the third leg, the first leg, and third leg in sequence is 1:1:1:1:1 or 1:2:2:2:1. |
Description
A TRANSFORMER FOR ATTENUATING HARMONICS
Technical Field
[1] The present invention relates to a transformer for attenuating harmonics, and more particularly, to a transformer for attenuating harmonics capable of removing unbalance and the harmonics, and reducing core loss and copper loss by connecting Y type windings of a secondary coil in zigzags by itself in a δ-Y type transformer connection structure. Background Art
[2] In general, an electric transformer, which is an apparatus providing an AC voltage or current by using electromagnetic induction, is connected to a transmission system in series. In such a transformer, there exist load loss (copper loss) caused by a load electrically connected to the transformer and transformer's own no-load loss (core loss) generated regardless of a load. Accordingly, the load loss and the no-load loss should be minimized in order to reduce power loss and increase efficiency of the transformer.
[3] In order to reduce the no-load loss (core loss) of the transformer, a low-loss type amorphous core is used. However, the transformer using the amorphous core is expensive 1.5 times more expensive than a silicon steel transformer and has a limitation in the noise or manufacturing capacity. Accordingly, the transformer using the amorphous core is also limited in consideration of economic efficiency and energy efficiency. In particular, it is difficult to expect reduction of the no-load loss (core loss) in the case when a load factor is equal to or more than 40%.
[4] Meanwhile, the load loss (copper loss) is proportional to the load factor, and harmonics and unbalance occur according to a type of the load, resulting in unnecessary power loss. The harmonics and unbalance increase as use of nonlinear loads such as a computer, a UPS, a rectification device, a lighting apparatus, and office machinery are suddenly increased. The further, the harmonics and unbalance cause various problems including an increase in power loss, overheating and fire of a neutral line, and a dielectric breakdown and operational errors of various apparatuses in the transmission system.
[5] An example of a technique of attenuating harmonic current of the neutral line in order to solve the above-described problems is disclosed in Document 1 (Device for Attenuating Harmonics) described below.
[6] In Document 1, as shown in FIG. 1, a harmonics attenuator 3 is connected between a power supply 1 and a load 2 in parallel, thereby attenuating a harmonic current generated from the load 2. Accordingly, the harmonics attenuator 3 is installed closer
to the load 2 in order to minimize the harmonic current of the neutral line.
[7] Meanwhile, a device for reducing an unbalance current in a three-phase four- wire transmission system is shown in FIG. 2. FIG. 2 is a block diagram illustrating an unbalance reducing device electrically connected to the three-phase four- wire transmission system according to the related art.
[8] As shown in FIG. 2, an unbalance reducing device 6 is connected between a receiving end 4 and a distribution end 5 in series. First and second loads 7a and 7b are connected to the distribution end 5. A harmonic attenuating device 8 a is connected between the distribution end 5 and the first load 7a in parallel. A harmonic attenuating device 8b is connected between the distribution end 5 and the second load 7b in parallel. Accordingly, the unbalance reducing device 6 reduces the unbalance which occurs in the loads 7a and 7b, and equipment in the transmission system, and is deviated between a three-phase average voltage (current) and three-phase voltages (currents).
[9] [Document 1] Korean Registration Patent Publication No. 10-0428459 (registered on
April 10, 2004) Disclosure of Invention Technical Problem
[10] However, in the related art disclosed in FIGS. 1 and 2, since a plurality of harmonics reducing devices and unbalance reducing devices are installed between distribution ends and loads, there is a problem in that installation cost relating thereto increases and securing an installation space is difficult.
[11] In the related art disclosed in FIGS. 1 and 2, there is a problem in that a current flowing on a neutral line becomes larger than a phase current due to the generation of harmonics, causing saturation of a transformer core and a very large harmonic current flows on a primary coil by actuation of a transformer, which causes overheating of the transformer and a trouble of an equipment.
[12] The present invention is made to solve the above-described problems. An object of the present invention is to provide a transformer for attenuating harmonics having a harmonic attenuating function and an unbalance reducing function installed in a transmission system.
[13] Another object of the present invention is to provide a transformer for attenuating harmonics capable of saving investment cost and reducing power loss since a harmonics attenuating device and an unbalance reducing device are not installed between a distribution end and a load. Technical Solution
[14] In order to achieve the above-described objects, a transformer for attenuating
harmonics according to an aspect of the present invention including a primary coil and a secondary coil, which includes a core having a first leg, a second leg, and a third leg; a first winding of the secondary coil which is wound on the first leg, the third leg, the first leg, the third leg, and the first leg in sequence, and is connected to a neutral line; a second winding of the secondary coil which is wound on the second leg, the first leg, the second leg, the first leg, and the second leg in sequence, and is connected to the neutral line; and a third winding of the secondary coil which is wound on the third leg, the second leg, the third leg, the second leg, and the third leg in sequence, and is connected to the neutral line.
[15] In the transformer for attenuating the harmonics according to the aspect of the invention, the first winding of the secondary coil is wound at different positions in the first leg and the third leg, the second winding of the secondary coil is wound at different positions in the second leg and the first leg, and the third winding of the secondary coil is wound at different positions in the third leg and the second leg.
[16] In the transformer for attenuating the harmonics according to the aspect of the invention, the first winding of the secondary coil is wound in a direction opposite to each other in the first leg and the third leg, the second winding of the secondary coil is wound in a direction opposite to each other in the second leg and the first leg, and the third winding of the secondary coil is wound in a direction opposite to each other in the third leg and the second leg.
[17] In the transformer for attenuating the harmonics according to the aspect of the invention, in the secondary coil, the number of winds of the first winding firstly wound on the first leg is the same as the number of winds of the first winding lastly wound on the first leg, the number of winds of the second winding firstly wound on the second leg is the same as th number of winds of the second winding lastly wound on the second leg, and the number of winds of the third winding firstly wound on the third leg is the same as the number of winds of the second winding lastly wound on the second leg.
[18] In the transformer for attenuating the harmonics according to the aspect of the invention, a turn ratio of the first winding wound on the first leg, the third leg, the first leg, the third leg, and the first leg in sequence is 1:1:1:1:1 or 1:2:2:2:1, a turn ratio of the second winding wound on the second leg, the first leg, the second leg, the first leg, and the second leg in sequence is 1:1:1:1:1 or 1:2:2:2:1, and a turn ratio of the third winding wound on the third leg, the second leg, the third leg, the second leg, and third leg in sequence is 1:1:1:1:1 or 1:2:2:2:1.
[19] In order to achieve the above-described objects of the present invention, a transformer for attenuating harmonics according to another aspect of the invention including a primary coil and a secondary coil, which includes a core having a first leg,
a second leg, and a third leg; a first winding of the secondary coil which is wound on the first leg, the second leg, the first leg, the second leg, and the first leg in sequence, and is connected to a neutral line; a second winding of the secondary coil which is wound on the second leg, the third leg, the second leg, the third leg, and the second leg in sequence, and is connected to the neutral line; and a third winding of the secondary coil which is wound on the third leg, the first leg, the third leg, the first leg, and the third leg in sequence, and is connected to the neutral line.
[20] In the transformer for attenuating the harmonics according to the aspect of the invention, the first winding of the secondary coil is wound at different positions in the first leg and the second leg, the second winding of the secondary coil is wound at different positions in the second leg and the third leg, and the third winding of the secondary coil is wound at different positions in the third leg and the first leg.
[21] In the transformer for attenuating the harmonics according to the aspect of the invention, the first winding of the secondary coil is wound in a direction opposite to each other in the first leg and the second leg, the second winding of the secondary coil is wound in a direction opposite to each other in the second leg and the third leg, and the third winding of the secondary coil is wound in a direction opposite to each other in the third leg and the first leg.
[22] In the transformer for attenuating the harmonics according to the aspect of the invention, a turn ratio of the first winding wound on the first leg, the second leg, the first leg, the second leg, and the first leg in sequence is 1:1:1:1:1 or 1:2:2:2:1, a turn ratio of the second winding wound on the second leg, the third leg, the second leg, the third leg, and the second leg in sequence is 1:1:1:1:1 or 1:2:2:2:1, and a turn ratio of the third winding wound on the third leg, the first leg, the third leg, the first leg, and third leg in sequence is 1:1:1:1:1 or 1:2:2:2:1.
Advantageous Effects
[23] As described above, in accordance with a transformer for attenuating harmonics according to the present invention, although a harmonic attenuating device and an unbalance reducing device are not installed in addition a transformer, it is possible to attenuate the harmonics and reduce unbalance.
[24] In accordance with the transformer for attenuating the harmonics according to the present invention, it is possible to reduce manufacturing investment cost accompanied by the installation of the harmonic attenuating device and the unbalance reducing device by instead installing a transformer having a function of attenuating the harmonics.
[25] In accordance with the transformer for attenuating the harmonics according to the present invention, it is possible to improve power quality, protect equipments in a
transmission system, and prevent an electrical accident occurring in the transmission system by installing the transformer having the function of attenuating the harmonics to reduce no-load loss (core loss) and load loss (copper loss). Brief Description of the Drawings
[26] FIG. 1 is a block diagram illustrating a harmonics attenuating device electrically connected to a three-phase four- wire transmission system according to the related art;
[27] FIG. 2 is a block diagram illustrating an unbalance reducing device electrically connected to the three-phase four- wire transmission system according to the related art;
[28] FIG. 3 is a graph illustrating a phenomenon in which a third harmonic current is enlarged on a neutral line of a three-phase four-wire transmission line;
[29] FIG. 4 is a block diagram illustrating a configuration of a δ- Y transformer according to an embodiment of the present invention;
[30] FIG. 5 is a diagram illustrating a winding of a δ- Y transformer according to a first embodiment of the present invention;
[31] FIG. 6 is a diagram illustrating a structure of a δ-Y transformer according to a first embodiment of the present invention;
[32] FIG. 7 is a diagram illustrating a winding of a δ-Y transformer according to a second embodiment of the present invention;
[33] FIG. 8 is a diagram illustrating a structure of a δ-Y transformer according to a second embodiment of the present invention; and
[34] FIG. 9 is a diagram illustrating a winding of a δ-Y transformer according to a third embodiment of the present invention. Best Mode for Carrying Out the Invention
[35] The above-described objects and other objects, and new features of the present invention will become more apparent and readily appreciated from the following description and the accompanying drawings of the specification. Before describing the embodiments of the present invention, a theoretical background of a harmonic current flowing on a neutral line of a three-phase four- wire transmission system will be described first by the use of a third high harmonic which is a zero-phase harmonic.
[36] FIG. 3 is a graph illustrating a phenomenon in which a third harmonic current is enlarged on a neutral line of a three-phase four-wire transmission line. Hereinafter, a symbol written in italics represents a vector.
[37] As shown in FIG. 3, currents flowing on three phases R, S, and T in a balance state are represented by / , / , and / , respectively, in the following Equation 1. In this case, I m represents a level of an AC current flowing on each phase, δ represents a frequency of the AC current flowing on each phase, and t represents a time.
Meanwhile, since 1 , 1 , and / flow while being predeterminedly spaced from each other by a phase difference of 120, a current flowing on a neutral line N is calculated by a sum of the three-phase currents 1 , 1 , and / . The calculation value becomes
Rl Sl Tl
0 as shown in the following Equation 2. [38] Equation 1
[39] fj , . = I inS i nωL. fsi = I 111 S iH(CuI- I 20 °) . h i = I :n s i n(ω1_- 240° )
[40] Equation 2
[41] J f u í /-:; + ■ In = I m sinωl + l m sm(ωi- 1 20° ) + l m sin(ωl-y40°J = 0
[42] However, a third harmonic flowing on the R phase, a third harmonic flowing on the
S phase, and a third harmonic flowing on the T phase have the same phase as each other as shown in Equation 3. Accordingly, a current flows on the neutral line N and a value of the current becomes larger than values of the currents flowing on the three phases R, S, and T, thereby causing an expected damage due to the harmonics.
[43] Equation 3
[44] j Fl + j <} + / 77 = I m sin: < !ωl + I n siπ3(ujt- 1 2O°) + l m shi3t<ϋt-240° )
- Jlnsiiiotυl
[45] In general, a thickness of the neutral line is equal to or smaller than thicknesses of lines of other phases and when a large amount of current flows on the neutral line by the zero-phase harmonics, a cable is overheated. Since the third harmonics have a frequency of 180Hz which is three times more than a fundamental wave as shown in Equation 3 described above, a skin effect in which current density further increases at an edge of the cable occurs. Accordingly, the third harmonics increases a resistance being in inverse proportion to a sectional area by reducing an effective sectional area of a cable on which the current flows. As a result, the third harmonics causes overheating of the cable and reduces a transmission capacity by increasing power loss generated in the cable.
[46] For example, in a transformer which takes charge of loads generating the harmonics, such as a computer, a UPS, a lighting apparatus, and the like, Joule's heat is generated due to superposition of the harmonic current and an increase of the resistance. Accordingly, the transformer which takes charge of the loads generating the harmonics should be manufactured in a capacity twice to 2.5 times larger than a transformer which takes charge of loads which does not generate the harmonics.
[47] Meanwhile, since the current generated by the harmonics does not have an influence on resistance loss (current x resistance), the transformer is designed on the basis of a rated current. However, when the harmonic current is inputted from a load end, a root mean square of the AC current increases, whereby loss generated in the transformer increases.
[48] Equation 4
[49]
[50] (Irms: a root mean square of total current, n: a harmonic degree, and In: a current value of an n-th degree harmonic)
[51] Hereinafter, a configuration of the present invention will be described in detail with reference to the accompanying drawings.
[52] In the description of the present invention, like reference numerals refer to like elements and repetitive description thereof is omitted.
[53] FIG. 4 is a block diagram illustrating a configuration of a δ-Y transformer according to an embodiment of the present invention.
[54] As shown in FIG. 4, a harmonic attenuating transformer 10 according to the embodiment of the present invention is connected in series to a power supply (not shown) outputting three-phase power supplied from a power plant through a transmission line. The harmonic attenuating transformer 10 is electrically connected to a distribution end 13 distributing the supplied three-phase power to loads l la and 1 Ib. In this case, a primary coil of the harmonic attenuating transformer 10 is connected in a δ type and a secondary coil of the harmonic attenuating transformer 10 is connected in a Y type. However, the primary and secondary coils of the harmonic attenuating transformer 10 may be connected using a general method used a technical field which the present invention belongs to unlike the embodiment of the present invention.
[55] The harmonic attenuating transformer 10 has functions of attenuating the harmonics by itself and reducing unbalance of voltages (or currents) generated by the loads l la and 1 Ib. Accordingly, since the harmonic attenuating transformer 10 is installed in the transmission system without needing to install an additional harmonic reducing device and an unbalance reducing device, it is possible to save manufacturing cost and reduce power loss generated in the transmission system.
[56] Next, referring to FIGS. 5 and 6, a configuration of a harmonic attenuating transformer according to a first embodiment of the present invention will be described in more detail.
[57] FIG. 5 is a diagram illustrating a winding of a δ-Y transformer according to a first embodiment of the present invention. FIG. 6 is a diagram illustrating a structure of a δ-Y transformer according to a first embodiment of the present invention.
[58] As shown in FIGS. 5 and 6, a harmonic attenuating transformer 20 according to the first embodiment of the present invention includes a primary coil 21 and a secondary
coil 23, and a core 25 having a first leg 25a, a second leg 25b, and a third leg 25c.
[59] The primary coil 21 is connected in a δ type. A first winding 21a, a second winding
21b, and a third winding 21c of the primary coil 21 are wound on the first leg 25a, the second leg 25b, and the third leg 25c, respectively, in the same direction. In this case, the windings 21a, 21b, and 21c of the primary coil 21 are formed at a turn ratio of 1:1:1. The first to third windings 21a, 21b, and 21c may be wound on the first to third legs 25a to 25c, respectively, once or more.
[60] The secondary coil 23is connected in a Y type at a position other than a position of the primary coil in the legs 25a, 25b, and 25c of the core 25. The secondary coil 23 is wound in zigzags in order to reduce harmonics and unbalance of voltages and currents generated in the transmission system. A current flowing on the secondary coil flows in a direction to attenuate magnetic flux generated in the core 25 by the current flowing on the primary coil 21. A first winding 23 a, a second winding 23b, and a third winding 23c of the secondary coil 23 are wound on the first leg 25a, the second leg 25b, and the third leg 25c of the core 25, respectively.
[61] The first winding 23a of the secondary coil 23 is wound on the first leg 25a, the third leg 25c, the first leg 25a, the third leg 25c, and the first leg 25a in sequence, and is connected to a neutral line N. The second winding 23b of the secondary coil 23 is wound on the second leg 25b, the first leg 25a, the second leg 25b, the first leg 25a, and the second leg 25b in sequence, and is connected to the neutral line N. The third winding 23c of the secondary coil 23 is wound on the third leg 25c, the second leg 25b, the third leg 25c, the second leg 25b, and the third leg 25c in sequence, and is connected to the neutral line N.
[62] In this case, the first winding 23a of the secondary coil 23 is wound at different positions in the first leg 25a and the third leg 25c, and the second winding 23b is wound at different positions in the second leg 25b and the first leg 25a. The third winding 23c is wound at different positions in the third leg 25c and the second leg 25b.
[63] Meanwhile, the first winding 23a of the secondary coil 23 is wound in a direction opposite to each other in the first leg 25a and the third leg 25c. The second winding 23b of the secondary coil 23 is wound in a direction opposite to each other in the second leg 25b and the first leg 25a. The third winding 23c of the secondary coil 23is wound in a direction opposite to each other in the third leg 25c and the second leg 25b. Accordingly, although the intensities of the magnetic flux on the legs 25a, 25b, and 25c are equal to each other, phases of zero-phase currents generated in a load are opposite to each other, whereby the magnetic flux is attenuated, and harmonic and unbalance currents are reduced.
[64] In the secondary coil 23, the number of winds of the first winding 23a firstly wound on the first leg 25a is the same as the number of winds of the first winding 23a lastly
wound on the first leg 25a. The number of winds of the second winding 23b firstly wound on the second leg 25b is the same as the number of winds of the second winding 23b lastly wound on the second leg 25b. The number of winds of the third winding 23c firstly wound on the third leg 25c is the same as the number of winds of the second winding 23c lastly wound on the second leg 25c.
[65] For example, a turn ratio of the first winding 23a wound on the first leg 25a, the third leg 25c, the first leg 25a, the third leg 25c, and the first leg 25a in sequence is 1 : 1 : 1 : 1 : 1. A turn ratio of the second winding 23b wound on the second leg 25b, the first leg 25a, the second leg 25b, the first leg 25a, and the second leg 25b in sequence is 1:1:1:1:1. A turn ratio of the third winding 23c wound on the third leg 25c, the second leg 25b, the third leg 25c, the second leg 25b, and third leg 25c in sequence is 1:1:1:1:1.
[66] Meanwhile, in the case that the primary coil 21 and the secondary coil 23 are connected in the δ type and in the Y type, respectively, a short protection plate 27 may be interposed between the primary coil 21 and the secondary coil 23. In the case that a relatively higher voltage is applied to the primary coil 21 rather than the secondary coil 23, the short protection plate 27 reduces electrical damages occurring to loads 11a and 1 Ib connected the secondary coil 23 to which the lower voltage is applied. The short protection plate 27 prevents harmonics generated between a power supply and the loads l la and 1 Ib from being inputted.
[67] Next, referring to FIGS. 7 and 8, a harmonic attenuating transformer according to a second embodiment of the present invention will be described.
[68] FIG. 7 is a diagram illustrating a winding of a δ-Y transformer according to the second embodiment of the present invention. FIG. 8 is a diagram illustrating a structure of a δ-Y transformer according to a second embodiment of the present invention.
[69] As shown in FIGS. 7 and 8, in a harmonic attenuating transformer 30 according to the second embodiment of the present invention, a turn ratio of a first winding 23a wound on a first leg 25a, a third leg 25c, a first leg 25a, a third leg 25c, and a first leg 25a in sequence is 1:2:2:2:1. A turn ratio of a second winding 23b wound on a second leg 25b, the first leg 25a, the second leg 25b, the first leg 25a, and the second leg 25b in sequence is 1:2:2:2:1. A turn ratio of a third winding 23c wound on the third leg 25c, the second leg 25b, the third leg 25c, the second leg 25b, and third leg 25c in sequence is 1:2:2:2:1.
[70] As a result, it is possible to attenuate harmonics and reduce unbalance by adjusting the phases of AC currents flowing on the windings 23a, 23b, and 23c. Other elements of the harmonic attenuating transformer 30 according to the second embodiment of the present invention are the same as those described in the first embodiment. Therefore,
detailed description thereof is omitted.
[71] Next, referring to FIG. 9, a harmonic attenuating transformer according to a second embodiment of the present invention will be described.
[72] FIG. 9 is a diagram illustrating a winding of a δ- Y transformer according to a third embodiment of the present invention.
[73] As shown in FIG. 9, a harmonic attenuating transformer 40 according to the third embodiment of the present invention includes a primary coil 21 and a secondary coil 23. Each of the primary coil 21 and the secondary coil 23 is wound on a core 25 having a first leg 25a, a second leg 25b, and a third leg 25c.
[74] A first winding 23a of the secondary coil 23 is wound on the first leg 25a, the second leg 25b, the first leg 25a, the second leg 25b, and the first leg 25a in sequence, and is connected to a neutral line N. A second winding 23b of the secondary coil 23 is wound on the second leg 25b, the third leg 25c, the second leg 25b, the third leg 25c, and the second leg 25b in sequence, and is connected to the neutral line N. A third winding 23c of the secondary coil 23 is wound on the third leg 25c, the first leg 25a, the third leg 25c, the first leg 25a, and the third leg 25c in sequence, and is connected to the neutral line N.
[75] The first winding 23a of the secondary coil 23 is wound at different positions in the first leg 25a and the second leg 25b, and the second winding 23b is wound at different positions in the second leg 25b and the third leg 25c. The third winding 23c is wound at different positions in the third leg 25c and the first leg 25a.
[76] Meanwhile, the first winding 23a of the secondary coil 23 is wound in a direction opposite to each other in the first leg 25a and the second leg 25b. The second winding 23b of the secondary coil 23is wound in a direction opposite to each other in the second leg 25b and the third leg 25c. The third winding 23c of the secondary coil 23 is wound in a direction opposite to each other in the third leg 25c and the first leg 25a.
[77] In the secondary coil 23, the number of winds of the first winding 23a firstly wound on the first leg 25a is the same as the number of winds of the first winding 23a lastly wound on the first leg 25a. The number of winds of the second winding 23b firstly wound on the second leg 25b is the same as the number of winds of the second winding 23b lastly wound on the second leg 25b. The number of winds of the third winding 23c firstly wound on the third leg 25c is the same as the number of winds of the second winding 23c lastly wound on the second leg 25c.
[78] For example, a turn ratio of the first winding 23a wound on the first leg 25a, the second leg 25b, the first leg 25a, the second leg 25b, and the first leg 25a in sequence is 1:1:1:1:1 or 1:2:2:2:1. A turn ratio of the second winding 23b wound on the second leg 25b, the third leg 25c, the second leg 25b, the third leg 25c, and the second leg 25b in sequence is 1:1:1:1:1 or 1:2:2:2:1. A turn ratio of the third winding 23c wound on
the third leg 25c, the first leg 25a, the third leg 25c, the first leg 25a, and third leg 25c in sequence is 1:1:1:1:1 or 1:2:2:2:1.
[79] Other elements of the harmonic attenuating transformer 40 according to the third embodiment of the present invention are the same as those described in the first embodiment. Therefore, detailed description thereof is omitted.
[80] Although a few embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the general inventive concept, the scope of which is defined in the appended claims and their equivalents.
[81] For example, even though a harmonic attenuating transformer according to the present invention is connected in a δ-Y type has been described, the above embodiments are not limited thereto, but illustrative in all aspects. In addition, the harmonic attenuating transformer according to the present invention may be applied to all kinds of transformer used at a receiving end or a distribution end.