KR20160092788A - Neutral line current remover - Google Patents

Abstract

The present invention relates to a neutral line current remover comprising: a first transformer which forms one closed circuit together with a load system by connecting a primary winding to a neutral line of the load system and connecting a secondary winding to a phase line of an R phase between an electric power system and the load system; a second transformer which forms one closed circuit together with the load system by connecting a primary winding to the neutral line of the load system and connecting a secondary winding to a phase line of an S phase between the electric power system and the load system; and a third transformer which forms one closed circuit together with the load system by connecting a primary winding to the neutral line of the load system and connecting a secondary winding to a phase line of a T phase between the electric power system and the load system. Ratios K_R, K_S and K_T of the first transformer, the second transformer and the third transformer are set to control current I_NS flowing to the electric power system through the neutral line between the first, second, and third transformers and the electric power system, to be 0. According to the above described structure, the transformers are formed between the phase line and the neutral line of the load system, and the winding ratios of the transformers are controlled such that the current dose not flow into the neutral line of the electric power system, thereby allowing the current of the neutral line not to be introduced into the electric power system.

Description

{NEUTRAL LINE CURRENT REMOVER}

More particularly, the present invention relates to a neutral line current flowing from a load system to a power supply system, that is, ) Current and an unbalanced load current.

As nonlinear loads such as computers, printers, copiers, air conditioners, electronic fluorescent lamps and uninterruptible power supplies are increasingly used in apartments, office buildings, buildings, hotels, hospitals, department stores and broadcasting stations, the image minute current generated in the load system becomes neutral line ) To the power supply system.

These neutral currents are the major cause of overheating or burning of power equipment such as transformer, cable, condenser and breaker. Power factor decreases due to power factor reduction and power loss, causing malfunction of control equipment.

Therefore, a method of eliminating the image minute current of the neutral line by adding a zigzag transformer between the neutral line and the phase line is widely used.

FIG. 1A is a connection diagram of a conventional zigzag transformer for eliminating an image minute current, and FIG. 1B is a configuration diagram of a conventional zigzag transformer.

1A, the zigzag transformer 30 is provided between the phase line between the power supply system 10 and the load system 20 and the neutral line of the load system 20. The zigzag transformer 30 is configured such that a video harmonic current flowing from the load system to the power supply system flows into the zigzag transformer 30. When the impedance of the system such as the power impedance and the cable impedance is smaller than the impedance of the zigzag transformer 30, There is a problem of falling.

1B, the zigzag transformer 30 turns two windings on the iron core in opposite directions, and the image minute currents are canceled by reversing the phases, and the normal and negative phase currents are made to have a large vector composition. The image minute impedance is made smaller and the normal minute and reverse phase minute impedances are made larger.

In Patent Publication Nos. 10-0428458 and 10-0493987, a method of removing image minute using a zigzag transformer is illustrated.

In Patent Publication No. 10-0428458, a reactor and a capacitor combination are further connected between a zigzag transformer and a load system to remove harmonic components. In addition, in Patent Publication No. 10-0493987, the image minute blocking reactor is additionally provided to block the image minute current from flowing into the power supply system.

A variety of methods have been used, such as the combination of a zigzag transformer and a power device such as a reactor to enhance the effect of removing the zenith electric current of the zigzag transformer 30 in the same manner as the above document. However, in the above-described method, a reactor or other elements must be added in order to perform impedance matching, so that a considerable difficulty arises in each power equipment.

10-0428458 10-0493987

It is an object of the present invention to provide a neutral current removing device.

The apparatus for removing neutral current according to the present invention is characterized in that primary windings are connected in parallel to the neutral line of the load system and secondary windings are connected to the phase line of R between the power supply system and the load system secondary windings are connected in parallel to form one closed circuit together with the load system; A second transformer in which a primary winding is connected in parallel to a neutral line of the load system and a secondary winding is connected in parallel to a phase line of an S phase between the power supply system and the load system to form one closed circuit together with the load system; And a third transformer in which a primary winding is connected in parallel to the neutral line of the load system and a secondary winding is connected in parallel to a phase line on the T phase between the power supply system and the load system to form one closed circuit together with the load system Lt; / RTI >

Wherein the winding ratio K _R of the first transformer to adjust the current I _NS flowing through the neutral line between the first transformer, the second transformer and the third transformer to the power supply system to zero and improve the phase imbalance, 2 winding ratio K _S of the transformer, and the winding ratio K _T of the third transformer are set in the neutral line current remover (NCR).

 In order to prevent an excessive fault current due to the failure of the load system from flowing into the first transformer, the second transformer, and the third transformer, the phase line of the first transformer and the phase of the R, A first switch disposed between the phase line of the S phase, and the phase line of the third transformer and the T phase; A second transformer, and a third transformer, wherein the first transformer, the second transformer, and the third transformer are connected in parallel to each other to prevent a transient fault current due to the failure of the load system from flowing into the first transformer, 1 transformer, a second transformer, and a second switch connected in parallel with the primary winding of the third transformer.

According to the neutral line current eliminating apparatus described above, the transformer is provided between the phase line and the neutral line of the load system and the winding ratio of the transformer is adjusted so that no current flows through the neutral line of the power supply system. .

In addition, the phase unbalance can be improved by separately controlling the current flowing from the neutral wire current removing device to the phase line by controlling the winding ratios K _R , K _S , and K _T of the transformer.

In addition, by adding a switch in parallel with the primary winding of the transformer of the neutral wire removing device and adding a switch between the secondary winding and the phase line of the transformer, burnout of the transformer due to excessive fault current can be prevented.

Also, unlike a zigzag transformer, it is not influenced by the impedance of the system, so that the neutral current can be removed irrespective of the installation position. In addition, since there is no need to add a separate power device to increase the neutral current removal efficiency, it is easy to maintain, and the installation cost is remarkably reduced.

In addition, unlike the zigzag transformer, it eliminates the unbalanced load current due to the unbalanced load system in addition to the image minute current, thereby reliably eliminating the neutral current.

In addition, since there is no influence of the neutral line current flowing from the other load system to the load system provided with the neutral line current removing device, it is possible to prevent overload and overheating of the neutral line current removing device.

FIG. 1A is a connection diagram of a conventional zig-zag transformer for eliminating an image minute current.
1B is a block diagram of a conventional zigzag transformer.
2A is a connection diagram of a neutral current removing apparatus according to a first embodiment of the present invention.
2B is a configuration diagram of a first transformer, a second transformer, and a third transformer according to the first embodiment of the present invention.
3 is a connection diagram of a neutral current removing apparatus according to a second embodiment of the present invention.
4A is an experimental system diagram of a conventional neutral current removing apparatus using a conventional zig-zag transformer.
4B is a graph showing a neutral current of a neutral current removing apparatus using a conventional zig-zag transformer.
4C is a graph showing a harmonic spectrum of a neutral current removing apparatus using a conventional zig-zag transformer.
5A is an experimental system diagram of a neutral current removing apparatus according to the present invention.
5B is a graph showing the neutral current of the neutral current removing apparatus according to the present invention.
5c is a graph showing a harmonic spectrum of a neutral current removing apparatus according to the present invention.
6 is a block diagram of a method of removing a neutral current according to an embodiment of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail to the concrete inventive concept.

It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Like reference numerals are used for like elements in describing each drawing.

The terms first, second, A, B, etc. may be used to describe various elements, but the elements should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component. And / or < / RTI > includes any combination of a plurality of related listed items or any of a plurality of related listed items.

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, .

On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise.

In the present application, the terms "comprises" or "having" and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component or a combination thereof described in the specification, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Do not.

FIG. 2A is a connection diagram of a neutral current removing apparatus according to the first embodiment of the present invention, and FIG. 2B is a configuration diagram of a first transformer, a second transformer, and a third transformer according to the first embodiment of the present invention.

2A, a neutral current removing apparatus 100 according to the first embodiment of the present invention includes a first transformer 110, a second transformer 120, a third transformer 130, Lt; / RTI >

Hereinafter, the detailed configuration will be described.

The first transformer 110 may be configured such that primary windings are connected in parallel to a neutral line of the load system 20. [

The first transformer 110 may be configured such that secondary windings are connected in parallel to the phase line of the R phase between the power supply system 10 and the load system 20. [

The load system 20, the neutral line of the load system 20, the primary winding of the first transformer 110, the secondary winding of the first transformer 110, the phase line of R and the load system 20 are connected to one closed circuit .

The second transformer 120 can be configured such that the primary winding is connected in parallel to the neutral line of the load system 20 and the secondary winding is connected in parallel to the phase line of the S phase between the power supply system 10 and the load system 20. [ .

Similarly, the load system 20, the neutral line of the load system 20, the primary winding of the second transformer 120, the secondary winding of the second transformer 120, the phase line of the S phase, And constitute a closed circuit.

The third transformer 130 can be configured such that the primary winding is connected in parallel to the neutral line of the load system 20 and the secondary winding is connected in parallel to the phase line on the T phase between the power supply system 10 and the load system 20. [ .

Likewise, the load system 20, the neutral line of the load system 20, the primary winding of the third transformer 130, the secondary winding of the third transformer 130, the phase line on T, .

I _{NL which} is the sum of the neutral line currents I _Rh3 , I _Sh3 and I _Th3 due to the third harmonic flows from the load system 20 through the neutral line of the load system 20. That is, the harmonics of each of the three-phase phase lines are synthesized and output through the neutral line.

The neutral line current is transmitted to the three-phase phase line by the first transformer 110, the second transformer 120, and the third transformer 130, respectively. This neutral current flows through each of the three closed circuits previously formed.

More specifically, I _Rh3 the third harmonic current, I _Sh3, to the primary winding of the first transformer 110, the second transformer 120 and the third transformer 130 by the I _Th3, respectively V1 _NCRTrR, V1 The voltage of _NCRTrS , V1 _NCRTrT is formed. And the voltages of V2 _NCRTrR , V2 _NCRTrS and V2 _NCRTrT are formed in the secondary winding, respectively. If the turns ratio of the first transformer 110, the second transformer 120 and the third transformer 130 are K _R , K _S and K _T , respectively, K _R XI _Rh3 and K _S XI _Sh3 and _KT XI _Th3 are circulated between the load system 20 and the neutral wire current eliminator 100. [ At this time, each harmonic current can be controlled.

That is, according to the Kirchhoff current law (KCL) at the specific branch point of the closed circuit, the flow amount and the inflow amount of the circulating current become equal to each other, so that the neutral line current I _NS can be removed. That is, by adjusting the winding ratios K _R , K _S , and K _T of the neutral line current removing apparatus 100, the third harmonic current is circulated in the closed circuit without flowing the current I _NS to the neutral line of the power supply system 10, I _NS can be removed.

Unlike the conventional method of the zigzag transformer 30, there is no need to consider the impedance, and it is very easy to construct and maintain the facility very simply and conveniently.

Here, the respective winding ratios K _R , K _S , and K _T of the first transformer 110, the second transformer 120, and the third transformer 130 may be set differently, and depending on the setting of each winding ratio, The harmonic current values respectively flowing from the device 110 to the phase lines may be separately controlled. Thus, the winding ratios K _R , K _S , and K _T can be set to be different from each other, so that the respective harmonic currents can be individually controlled, which contributes to the improvement of phase unbalance.

On the other hand, the primary windings of the neutral current removing device 100 are preferably parallel wirings, and each secondary windings is preferably composed of wye connections.

3 is a connection diagram of a neutral current removing apparatus according to a second embodiment of the present invention.

3, the apparatus 200 for removing neutral current according to the second embodiment of the present invention includes a first transformer 210, a second transformer 220, a third transformer 230, a first switch, A second switch 240, and a second switch 250.

Hereinafter, the detailed configuration will be described.

The respective constitutions of the first transformer 210, the second transformer 220 and the third transformer 230 and the formation of the closed circuit are the same as those of the neutral current removing device 100 of FIG.

However, in the second embodiment, the first switch 240 and the second switch 250 are further provided.

The first switch 240 can be configured to be provided between the phase line of the first transformer 210 and the phase of the R phase, the phase line of the second transformer 220 and the phase line of the S phase, and the phase line of the third transformer 230 and the phase of T .

The first switch 240 is configured to prevent or prevent an excessive fault current from flowing into the first transformer 210, the second transformer 220 and the third transformer 230 due to a failure of the load system 20, to be.

The second switch 250 may be configured to be connected in parallel with the primary windings of the first transformer 210, the second transformer 220 and the third transformer 230. When the second switch 250 is closed, the load system 20 and the power supply system 10 are directly connected to each other by the neutral line, and the first transformer 210, the second transformer 220 and the third transformer 230 Neutral current does not flow. Thus, the transient fault current due to the failure of the load system (20) is prevented from flowing into the first transformer (210), the second transformer (220), and the third transformer (230).

The first switch 240 and the second switch 250 cut off the excessive fault current to the neutral line current canceling device 200 and are connected to the first transformer 210 and the second transformer 220, And the third transformer 230 are protected.

FIG. 4A is a graph showing an experimental result of a neutral current removing apparatus using a conventional zig-zag transformer, FIG. 4B is a graph showing a neutral current of a neutral current removing apparatus using a conventional zig- Is a graph showing a harmonic spectrum. 5A is a graph showing the neutral current of the neutral line current removing apparatus according to the present invention. FIG. 5C is a graph showing the harmonics of the neutral line current removing apparatus according to the present invention. Fig.

Referring to FIGS. 4A to 4C and FIGS. 5A to 5C, it can be seen that the present invention clearly improves the removal of the image minute current and the neutral current.

The following Table 1 numerically shows such experimental data.

division Image minute current
(3 harmonic current) Image minute
electric current
Removal rate
(%) Neutral current
(Image min + unbalanced) current Neutral line
electric current
Removal rate
(%) Remarks Power system (A) Load system (A) Power system (A) Load system (A) Zigzag Tr 10.66 29.93 64.38 10.89 30.60 64.41 Conventional technology NCR 0.20 30.22 99.34 0.20 30.61 99.35 Invention technology

As shown in Table 1, the zigzag transformer 30 has an image minute current removal rate of 64.38%, and the neutral current removal device according to the present invention has an image minute current removal rate of 99.34%. It can be seen that the image minute current flowing to the power supply system 10 is reliably removed.

In addition, the zigzag transformer 30 measured the neutral current removal rate at 64.41%, and the neutral current removal device according to the present invention measured the neutral current removal rate at 99.35%. It can be confirmed that the image minute current and the unbalanced load current flowing to the power supply system 10, that is, the neutral current, are reliably removed.

As described above, the neutral current removing device according to the present invention has a remarkably excellent neutral current removing function as compared with the conventional zig-zag transformer 30, and has excellent superiority in design, installation, maintenance, and repair .

6 is a block diagram of a method of removing a neutral current according to an embodiment of the present invention.

Referring to FIG. 6, the principle of neutral current removal according to the present invention is shown.

6, harmonic voltage sources 310, 320, and 330 are shown instead of the transformers 110, 120, and 130, respectively.

As described above, the harmonic current generated in the nonlinear load system 20 flows to the power supply system 10 through the neutral line. When the neutral line current removal device is not installed, the power supply system 10 is supplied with the fundamental wave voltage source V _Rh1 , V _Sh1 , and V _Th1 ) and the harmonic voltage _sources (V _Rh3 , V _Sh3 , and V _Th3 ) are formed. However, installing a neutral current removal device according to the present invention, the fundamental wave voltage source (V _Rh1, V _Sh1, V _Th1) is formed in the power supply system 10 and the harmonic voltage (V _Rh3 ', V _Sh3', V _Th3 ' Are formed in the transformers 110, 120, and 130, respectively.

The core of the present invention is such that the fundamental wave voltage is supplied by the power supply system 10 and the harmonic voltage is supplied by the transformers 110, 120 and 130. That is, the movement of the harmonic voltage source by controlling the winding ratios K _R , K _S , and K _T is the core of the present invention. In particular, the voltage division ratio can be adjusted by setting the winding ratios K _R , K _S , and K _T differently. The connection between the neutral wire and the transformers 110, 120 and 130 is formed in parallel rather than in series and the winding ratios K _R , K _S and K _T of the respective transformers 110, 120 and 130 are respectively set to improve the phase imbalance Lt; / RTI >

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention as defined in the following claims. There will be.

10: power supply system 20: load system
30: zigzag transformer 110: first transformer
120: second transformer 130: third transformer
210: first transformer 220: second transformer
230: third transformer 240: first switch
250: second switch 310: harmonic voltage source
320: Harmonic voltage source 330: Harmonic voltage source

Claims (2)

Primary windings are connected in parallel to the neutral line of the load system and secondary windings are connected in parallel to the phase line of R between the power supply system and the load system so that one A first transformer forming a closed circuit;
A second transformer in which a primary winding is connected in parallel to a neutral line of the load system and a secondary winding is connected in parallel to a phase line of an S phase between the power supply system and the load system to form one closed circuit together with the load system;
And a third transformer in which a primary winding is connected in parallel to the neutral line of the load system and a secondary winding is connected in parallel to a phase line on the T phase between the power supply system and the load system to form one closed circuit together with the load system ,
The first transformer, the second transformer, and the third transformer,
The winding ratio K _R of the first transformer to adjust the current I _NS flowing through the neutral line between the first transformer, the second transformer and the third transformer and the power supply system to zero and improve the phase imbalance, Wherein the winding ratio K _S of the third transformer and the winding ratio K _T of the third transformer are set. The method according to claim 1,
The second transformer and the third transformer to prevent the transient fault current due to the failure of the load system from flowing into the first transformer, the second transformer, and the third transformer, A first switch provided between the phase line, the third transformer and the phase line on the T-phase, respectively;
A second transformer, and a third transformer, wherein the first transformer, the second transformer, and the third transformer are connected in parallel to each other to prevent a transient fault current due to the failure of the load system from flowing into the first transformer, Further comprising a second switch connected in parallel with the primary winding of the first transformer, the second transformer, and the third transformer.

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