WO2008153257A1

WO2008153257A1 - Transformer

Info

Publication number: WO2008153257A1
Application number: PCT/KR2007/006607
Authority: WO
Inventors: Myung Hwan Lee
Original assignee: Myung Hwan Lee
Priority date: 2007-06-12
Filing date: 2007-12-18
Publication date: 2008-12-18
Also published as: KR20080109260A; KR100887194B1

Abstract

A toroidal transformer is disclosed. The toroidal transformer includes an R-phase toroidal core, an S-phase toroidal core, and a T-phase toroidal core, which correspond to respective R phase, S phase, and T phase. The part of a main winding of the R-phase toroidal core is wound around one of the two remaining toroidal cores. When the part of the main winding of the R-phase toroidal core is wound around the S-phase toroidal core, the part of the main winding of the S-phase toroidal core is wound around the T-phase toroidal core and the part of the main winding of the T-phase toroidal core is wound around the R-phase toroidal core. When the part of the main winding of the R-phase toroidal core is wound around the T-phase toroidal core, the part of the main winding of the T-phase toroidal core is wound around the S-phase toroidal core, and the part of the main winding of the S-phase toroidal core is wound around the R-phase toroidal core.

Description

Description TRANSFORMER

Technical Field

[1] The present invention relates, in general, to a transformer, and, more particularly, to a transformer using toroidal cores.

[2]

Background Art

[3] Generally, it is known that toroidal transformers have various characteristics that are superior to those of EI transformers.

[4] Compared to the EI transformer, such a toroidal transformer has the most significant advantage in that little leakage magnetic flux is generated, so that it can be used in applications that include sensitive circuits. The toroidal transformer has additional advantage in that the unique structure of the toroidal transformer allows the toroidal transformer to exhibit 15 to 30% higher or more higher efficiency, and that the efficiency of the toroidal transformer increases as the capacity of the toroidal transformer is increased.

[5] In addition, the toroidal transformer has advantages in that it is smaller and lighter than the EI transformer, in that it can be manufactured in various sizes, in that the operational temperature thereof is low, and in that it has considerably low non-load loss.

[6] Despite such excellent characteristics, the toroidal transformer lags behind the EI transformer in actual utilization.

[7] FIG. 1 is a view showing the Neutral Current Eliminator (NCE) of a three-phase four- wire EI transformer. Since the principle thereof is well known, a detailed description thereof is omitted, and only the structure of a traditional EI transformer and a method of winding main windings will be described below.

[8] As shown in FIG. 1, the EI transformer is configured such that main windings are connected to three respective iron cores corresponding to three phases, and each of the three iron cores is connected to the other two iron cores, each functioning as a path for magnetic flux. In this configuration, each of the magnetic fluxes, corresponding to one of the three respective phases, extends along those iron cores, each functioning as a path, and interlinks with the magnetic fluxes of the other phases, thereby balancing the three-phase current.

[9] Further, since the three iron cores, to which the respective main windings corresponding to the three phases are connected, are provided in a single structure, the connection method thereof is variously applied. An example of the connection method is the NCE structure shown in FIG. 1, which shows the state in which the three re- spective phases intersect each other, and each of the phases is connected to the iron cores of the other phases, thereby eliminating zero-phase- sequence component harmonics current that flows through a neutral line due to the three harmonics.

[10] Compared to the EI transformer, despite the above-described excellent characteristics, the toroidal transformer cannot realize the balance of three-phase current, and cannot realize variation in the connection method, unlike that shown in FIG. 1.

[11] That is, the EI transformer for three phases is manufactured to have a single structure, so that variation in connection is freely realized, and the unique structure, shown in FIG. 1, allows flux linkage.

[12] Meanwhile, the reason for the defects of the toroidal transformer is considered to be that only one toroidal core corresponds to one phase because of the characteristics of the structure of the toroidal transformer, so that variation in connection cannot be freely realized. Even when three toroidal cores, which correspond to three respective phases, are layered and then operated, magnetic fluxes thereof interact, thereby entailing various restrictions on the use thereof.

[13] Conventionally, each of the toroidal coils has been configured such that the balance of phase voltage is maintained. That is, a main winding is formed of a single winding, and an incoming winding is directly wound to an outgoing winding, so that voltage is dropped or raised using the voltage tap of a field winding, thereby maintaining balance between the phase voltages by adjusting the voltage tap between phases.

[14] The toroidal coil only has a technique for compensating for a voltage difference, generated by a voltage drop due to the difference between phase currents, using the voltage tap of a field winding. Therefore, as the difference between phase voltages increases, the voltage of the field winding should be configured to have a multilayer structure.

[15] This configuration method causes unnecessary results in that the rate of a coil cost is increased, in that excessive circuit configuration is made and the size of a casing is increased due to the control of a multi- voltage tap, and in that the voltage tap is switched to a manual operation mode due to the complexity of the control, so that these unnecessary results act as obstacles for mass production.

[16] Therefore, all related business enterprises have standardized a single-tap operation or a two-tap operation, so that the original object of the voltage balance has disappeared, with the result that only a power-saving function using a voltage drop operation is regarded as important. For these reasons, the toroidal core is applied to part of the toroidal core market which has enormous potential application possibility.

[17]

Disclosure of Invention Technical Problem

[18] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a toroidal transformer that is capable of performing current phase balance operation based on flux linkage using toroidal cores, each of which has minimal magnetic loss and is stable from the aspect of a core structure.

[19] Another object of the present invention is to provide a toroidal transformer that has improved power efficiency.

[20]

Technical Solution

[21] In order to accomplish the above objects, the present invention provides a transformer, including an R-phase toroidal core, an S-phase toroidal core, and a T- phase toroidal core, which correspond to respective R phase, S phase, and T phase; wherein the part of the main winding of the R-phase toroidal core is wound around one of the two remaining toroidal cores; wherein, when the part of the main winding of the R-phase toroidal core is wound around the S-phase toroidal core, the part of the main winding of the S-phase toroidal core is wound around the T-phase toroidal core and the part of the main winding of the T-phase toroidal core is wound around the R-phase toroidal core; and wherein, when the part of the main winding of the R-phase toroidal core is wound around the T-phase toroidal core, the part of the main winding of the T- phase toroidal core is wound around the S-phase toroidal core, and the part of the main winding of the S-phase toroidal core is wound around the R-phase toroidal core.

[22] Here, one end of each of the main windings of the three-phase toroidal cores is the input terminal of a three-phase input voltage, and the remaining end thereof is connected to a load side. Further, the part of each of the main windings, which are wound around the remaining phase toroidal cores, has the same length within a predetermined error range.

[23] Further, according to another aspect of the present invention, in order to accomplish the above objects, the present invention provides a transformer, including an R-phase toroidal core, an S-phase toroidal core, and a T-phase toroidal core, which correspond to respective R phase, S phase, and T phase; wherein the part of the main winding of the R-phase toroidal core is wound around the S-phase toroidal core and the T-phase toroidal core; wherein the part of the main winding of the S-phase toroidal core is wound around the T-phase toroidal core and the R-phase toroidal core; and wherein the part of the main winding of the T-phase toroidal core is wound around the R-phase toroidal core and the S-phase toroidal core.

[24] Here, each of the in-phase part of one main winding and the out-of -phase parts of remaining main windings is partially wound around a circular core.

[25] Further, according to further another aspect of the present invention, in order to accomplish the above objects, the present invention provides a three-phase four-wire transformer, including a neutral line, and an R-phase toroidal core, an S-phase toroidal core, and a T-phase toroidal core, which correspond to respective R phase, S phase, and T phase; wherein the parts of the neutral line are wound around the R-phase toroidal core, the S-phase toroidal core, and the T-phase toroidal core, and the parts of the neutral line, wound around the R-phase toroidal core, the S-phase toroidal core, and the T-phase toroidal core, are connected in parallel, so that current flowing through the neutral line branches off from the neutral line, flows into the three-phase toroidal cores, and then flows therefrom.

[26] Further, according to still another aspect of the present invention, in order to accomplish the above objects, the present invention provides a toroidal transformer including a single-phase toroidal core and a neutral line; wherein a part of the neutral line is wound around the toroidal core, so that current flowing through the neutral line flows into the toroidal core and then flows therefrom.

[27]

Advantageous Effects

[28] As described above, the present invention provides a toroidal transformer which can effectively perform phase current balance while taking advantage of the excellent characteristics of toroidal cores, and in which power efficiency is excellent.

[29]

Brief Description of the Drawings

[30] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[31] FIG. 1 is a view showing the NCE of a three-phase four- wire EI transformer;

[32] FIG. 2 is a schematic diagram showing a method of connecting the main windings of a toroidal transformer for a three-phase power system according to a first embodiment of the present invention;

[33] FIG. 3 is a view showing the connection method of the toroidal transformer corresponding to that of the schematic diagram of FIG. 2A;

[34] FIGS. 4 to 7 are views showing various modified examples of connection methods, which are different from that according to the first embodiment of the present invention;

[35] FIG. 8 is a schematic diagram showing a method of connecting the main winding of a toroidal transformer for a single-phase power system according to a second em- bodiment of the present invention. [36]

Best Mode for Carrying Out the Invention

[37] The embodiments of the present invention will be described in detail with reference to the accompanying drawings below.

[38] FIG. 2 is a schematic diagram showing a method of connecting the main windings of a toroidal transformer for a three-phase power system according to a first embodiment of the present invention, and FIG. 3 is a view showing the connection method of the toroidal transformer corresponding to that of the schematic diagram of FIG. 2.

[39] For better understanding, FIG. 2 simply shows that an R-phase toroidal core corresponds to a first row, an S-phase toroidal core corresponds to a second row, and a T- phase toroidal core corresponds to a third row, and portions shown as sticks indicate the connection of the main winding.

[40] Referring to FIG. 2, the main winding of the R-phase toroidal core is divided into three portions.

[41] That is, the facts that a first main winding, to which current is led, is connected to the

R-phase toroidal core, that a second main winding is connected to the S-phase toroidal core, and that a third main winding is connected to the R-phase toroidal core can be known. Therefore, R-phase current flows into along the first main winding, flows through the S-phase toroidal core along the second main winding, and then flows through the R-phase toroidal core again.

[42] It can be easily understood that the respective main windings of the S-phase and T- phase toroidal cores are connected using a method corresponding to the method of connecting the main windings of the R-phase toroidal core. That is, the second main winding of the S-phase toroidal core is connected to the T-phase toroidal core, and the second main winding of the T-phase toroidal core is connected to the R-phase toroidal core.

[43] An actual example of the connection method corresponding to that schematically shown in FIG. 2 is shown in FIG. 3. Here, the fact that a pair of main windings 21 and 22, connected to the respective R, S, and T-phase toroidal cores, is connected to the main windings 11 and 12 and 31 to 33 of the respective R, S, and T-phase toroidal cores can be known.

[44] Although not shown in detail in FIG. 2, after three-phase currents flow into the respective first main windings from a three-phase power system, the three-phase currents are supplied to loads connected to the rear ends of the respective third main windings. Here, if the magnitudes of the loads are different from each other, the balance of the three-phase currents is broken. [45] While each of the phase currents, which are different from each other, flows through each of the second main windings, it affects the magnetic fluxes of the other toroidal cores for different phases. That is, while R, S, and T-phase currents intersect each other, they affect the magnetic fluxes of the S, T, and R-phases, so that the magnitudes of the R, S, and T-phase currents are adjusted, thereby realizing phase-current balance even though the balance is not perfect.

[46] Here, a remarkable point is that, even though phase voltages are not adjusted, phase balance, in which magnetic fluxes of the toroidal transformer are interlinked with each other using a unique connection method according to the present invention, occurs.

[47] In addition, a further remarkable point is that, for example, the second main winding of the R-phase does not necessarily need to be connected to one of the S-phase toroidal core and the T-phase toroidal core in Fig. 2. Therefore, even if the second main winding of the R-phase is adjusted to be connected to both the S-phase toroidal core and T-phase toroidal core, it should be understood that this connection method is included in the technical spirit of the present invention.

[48] FIGS. 4 to 7 show various modified examples of connection methods which are different from that of the first embodiment.

[49] When FIG. 4 is compared with FIG. 2, it can be known that the connection direction of the second main winding is changed, and the connection direction does not affect the fact that phase current affects magnetic flux. However, the change of the connection direction only causes a difference in output voltage from the tap voltage of a field winding connected to a main winding.

[50] Therefore, the facts that there is no difference in a method of realizing phase balance even though connection directions are different from each other in the connection methods of FIGS. 4 to 7, and that the connection direction affects the level of voltage output from the tap voltage of a field winding, can be grasped.

[51] Although FIGS. 2 to 7 illustrate only the facts that each of the main windings is divided into three portions and that each of the second main windings is connected to one of the toroidal cores of the other phases, the present invention is not necessarily limited thereto.

[52] That is, each of the main windings may not always be divided using the same ratio, and it is sufficient for part of each of the main windings to be connected to intersect the others so as to affect magnetic fluxes for the other phases. The number of main windings to intersect and be connected with each other and the part of the main winding to intersect and be connected are problems of selection, and they do not affect the essential technical spirit of the present invention.

[53] FIG. 8 is a schematic diagram showing a method of connecting the main winding of the toroidal transformer for a single -phase power system according to a second em- bodiment of the present invention.

[54] As shown in FIG. 8, a toroidal core corresponding to a single phase is illustrated in a first row, a second row indicates a neutral line, and a main winding and other wound portions are illustrated as sticks.

[55] Although not shown, current flowing from the single-phase power system flows into one end of the main winding and flows out though a load terminal via the other end of the main winding. The current flowing through the load terminal flows into one end of the neutral line, which is shown, and flows out through the other end thereof. Since such a configuration of the flow of current is general, a detailed description thereof is omitted.

[56] A remarkable point is that the part of the cable of the neutral line is wound around the toroidal core.

[57] Using the same method as that described in the first embodiment, current flowing through the neutral line affects the magnetic flux of the toroidal core, so that the current flowing through the main winding and the current flowing through the neutral line are adjusted to realize balance.

[58] In order to describe the advantages that can be obtained due to balance, a simple example will be described.

[59] For example, if current corresponding to "1" is supplied to a load which consumes current less than or equal to "1" through a main winding and current corresponding to "0.95" flows out through a neutral line due to an effect such as a power factor, only the current corresponding to "0.95" actually works.

[60] According to the second embodiment of the present invention, the current flowing through the neutral line affects or is affected by the magnetic flux of the main winding, so that the magnitudes thereof are adjusted to realize current balance in the relationship therebetween.

[61] Therefore, in the previous example, current corresponding to "0.98" is supplied to the load and current corresponding to "0.98" flows out due to the balance. Therefore, it can be appreciated that this balance operation results in improved power efficiency compared to the previous example, in which only the current corresponding to "0.95" works.

[62] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

[1] A transformer, comprising: an R-phase toroidal core, an S-phase toroidal core, and a T-phase toroidal core, which correspond to respective R phase, S phase, and T phase; wherein a part of a main winding of the R-phase toroidal core is wound around one of the two remaining toroidal cores; wherein, when the part of the main winding of the R-phase toroidal core is wound around the S-phase toroidal core, a part of a main winding of the S-phase toroidal core is wound around the T-phase toroidal core and a part of a main winding of the T-phase toroidal core is wound around the R-phase toroidal core; and wherein, when the part of the main winding of the R-phase toroidal core is wound around the T-phase toroidal core, the part of the main winding of the T- phase toroidal core is wound around the S-phase toroidal core, and the part of the main winding of the S-phase toroidal core is wound around the R-phase toroidal core.

[2] The transformer according to claim 1, wherein one end of each of the main windings of the three-phase toroidal cores is an input terminal of a three-phase input voltage, and the remaining end thereof is connected to a load side.

[3] The transformer according to claim 1, wherein the part of each of the main windings, which are wound around the remaining phase toroidal cores, has a same length within a predetermined error range.

[4] A transformer, comprising: an R-phase toroidal core, an S-phase toroidal core, and a T-phase toroidal core, which correspond to respective R phase, S phase, and T phase; wherein a part of a main winding of the R-phase toroidal core is wound around the S-phase toroidal core and the T-phase toroidal core; wherein a part of a main winding of the S-phase toroidal core is wound around the T-phase toroidal core and the R-phase toroidal core; and wherein a part of the main winding of the T-phase toroidal core is wound around the R-phase toroidal core and the S-phase toroidal core.

[5] The transformer according to any one of claims 1 to 4, wherein each of an in- phase part of one main winding and out-of -phase parts of remaining main windings is partially wound around a circular core.

[6] A toroidal transformer for a single-phase two- wire system, comprising: a single-phase toroidal core and a neutral line; wherein a part of the neutral line is wound around the toroidal core, so that current flowing through the neutral line flows into the toroidal core and then flows therefrom.