JP2000014006A - Harmonic wave filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve further the absorption rate of a harmonic current flowing in the neutral line of a power supply transformer. SOLUTION: A harmonic wave filter 11 absorbs a same phase harmonic current which flows in the neutral line 4 of a 3-phase 4-wire system power supply transformer 1. A 3-phase 4-wire system filter transformer 6 which has a Δ-connection on its secondary side and has a Y-connection with a neutral is provided in the filter 11. The primary side Y-connection of the filter transformer 6 is connected to distribution lines 2a-2c of the respective phases. A filter device 10 which is composed of a capacitor 8 and a reactor 9 and practices series resonance with a required harmonic frequency is provided between the primary neutral 1 of the filter transformer 6 and the neutral line 4. A reactor 12 is inserted into the neutral line 4 of the power supply transformer 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a harmonic filter, and more particularly, to a harmonic filter for absorbing a common mode harmonic current flowing in a neutral line of a three-phase four-wire system.

[0002]

2. Description of the Related Art In order to supply electric power to a single-phase load, a three-phase four-wire circuit as shown in FIG. 3 is sometimes used in an office building or the like. In this three-phase four-wire circuit, it is assumed that the loads 3a to 3c connected to the three-phase power distribution lines 2a to 2c of the power transformer 1 are loads that easily generate harmonics of a personal computer, a television, and OA equipment. Even if the loads 3a to 3c of the phase distribution lines 2a to 2c are balanced, the load 3a
To 3c, a large amount of in-phase harmonic current (particularly third harmonic current) flows through the neutral line 4 of the power transformer 1.

When a large amount of harmonic current flows through the neutral wire 4 of the power transformer 1 as described above, the neutral wire 4 is overheated. Need to be raised. However, it has been very difficult to construct indoor wiring facilities in a building to replace the electric wires.

As another means, in order to absorb a harmonic current flowing through the neutral line 4 of the power transformer 1, an LC filter (see FIG. 1) is connected between each of the three-phase power distribution lines 2a to 2c and the neutral line 4. (Not shown) is considered to be the most economical, but in this case, it is not a preferable means since excessively advanced reactive power is supplied to the power supply during the steady operation.

Accordingly, the present applicant has prevented the large amount of common-mode harmonic current generated from the single-phase rectifier load from flowing through the neutral line of the power transformer without supplying excessively leading reactive power to the power supply side. (Japanese Patent Application Laid-Open No. 6-165381).

The harmonic filter 5 includes a three-phase four-wire filter transformer 6 having a Δ connection on the secondary side and a Y connection with a neutral point on the primary side, as shown in FIG. The primary side Y connection of each of the three-phase distribution lines 2a to 2c
And the primary neutral point 7 of the filter transformer 6
And a neutral line 4 and a filter element 10 composed of a series circuit of a capacitor 8 and a reactor 9 and resonating in series with a desired harmonic.

According to the harmonic filter 5, since the filter element 10 is disposed in the zero-phase circuit between the primary neutral point 7 of the filter transformer 6 and the neutral line 4, the fundamental wave current becomes neutral. Since the current does not flow to the point, the fundamental wave voltage is not applied to the filter element 10. As a result, it is possible to absorb the harmonic current flowing through the neutral wire 4 of the power transformer 1 without supplying the excessively advanced reactive power to the power supply side.

[0008]

By the way, in the above-described conventional harmonic filter 5 (Japanese Patent Laid-Open No. 6-165381), the absorption rate of the harmonic current flowing through the neutral line 4 of the power transformer 1 is improved. Power transformer 1
In addition, there is a limit in circuit design due to the leakage impedance of the filter transformer 6, the reactance of the capacitor 8 and the reactor 9 of the filter element 10, and the like.

Here, the capacitor 8 of the filter element 10
Assuming that the frequency is tuned to the frequency of the harmonic current that the reactor 9 wants to absorb, the shunt ratio between the harmonic current flowing through the filter transformer 6 and the harmonic current flowing through the neutral conductor 4 is determined by the filter transformer 6 and the power transformer 1. Is determined by the ratio of the leakage impedances. Therefore, the harmonic current flowing through the neutral wire 4 still flows by the ratio of the leakage impedance between the filter transformer 6 and the power transformer 1.

In view of the above-mentioned problems, the present applicant has improved the previously proposed harmonic filter, and has as its object to further improve the absorptivity of the harmonic current flowing through the neutral wire of the power transformer. I do.

[0011]

As a technical means for achieving the above-mentioned object, the present invention provides a harmonic for absorbing a common-mode harmonic current flowing through a neutral wire of a three-phase four-wire power transformer. The filter has the following features. A three-phase four-wire filter transformer having a Δ connection on the secondary side and a Y connection with a neutral point on the primary side, and connecting the primary side Y connection of the filter transformer to each of the three-phase distribution lines, Between the primary neutral point of the filter transformer and the neutral line,
A filter element that resonates in series with the desired harmonic is arranged, and a reactor is inserted and connected to the neutral wire of the power transformer. A three-phase four-wire filter transformer having a Δ connection on the secondary side and a Y connection with a neutral point on the primary side, and connecting the primary side Y connection of the filter transformer to each of the three-phase distribution lines, Connect the primary neutral point of the filter transformer to the neutral line,
A filter element that opens a part of the secondary Δ-connection and resonates in series with a desired harmonic is arranged, and a reactor is inserted and connected to the neutral wire of the power transformer.

In the harmonic filter according to the present invention, since the filter element is disposed in the zero-phase circuit between the primary neutral point of the filter transformer and the neutral line, the primary neutral point of the filter transformer is provided. Since no fundamental current flows through the filter element, no fundamental wave voltage is applied to the filter element, and no excessively advanced reactive power is supplied to the power supply side.

[0013] Further, since the shunt ratio of the harmonic current to the filter transformer and the power transformer is determined by the ratio of the leakage impedance of the filter transformer and the power transformer, a reactor is connected to the neutral line of the power transformer. Accordingly, the harmonic current flowing through the filter transformer increases, so that the absorption rate of the harmonic current can be improved.

It is desirable that the above-mentioned filter element is constituted by a series circuit of a capacitor and a reactor, or a capacitor.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the harmonic filter according to the present invention will be described in detail below. The same parts as those in FIG. 4 are denoted by the same reference numerals.

The harmonic filter 11 of the embodiment shown in FIG.
Is for absorbing the in-phase harmonic current flowing through the neutral wire 4 of the three-phase four-wire power transformer 1, and has a Δ connection on the secondary side,
A three-phase four-wire filter transformer 6 having a Y-connection with a neutral point on the primary side is provided, and the primary side Y of the filter transformer 6 is provided.
While connecting the connection to each of the three-phase distribution lines 2a to 2c,
A filter element 1 comprising a series circuit of a capacitor 8 and a reactor 9 between a primary neutral point 7 and a neutral line 4 of a filter transformer 6 and performing series resonance for a desired harmonic.
0 and the reactor 1
2 is inserted and connected. The filter element 1
Although not shown, “0” can be constituted by only a capacitor.

Next, a harmonic filter 1 according to another embodiment will be described.
1 'is shown in FIG. The harmonic filter 11 'shown in FIG.
Is provided with a three-phase four-wire filter transformer 6 having a Δ connection on the secondary side and a Y connection with a neutral point on the primary side, and the primary side Y connection of the filter transformer 6 is connected to each of the three-phase distribution lines 2a. ~ 2
c, the primary neutral point 7 of the filter transformer 6 is connected to the neutral line 4, a part of the secondary Δ connection is opened, and a filter element 10 that resonates in series with a desired harmonic. And the reactor 12 is inserted into the neutral wire 4 of the power transformer 1.

In the harmonic filters 11 and 11 'in these two embodiments, the filter element 10 is arranged in a zero-phase circuit between the primary neutral point 7 and the neutral wire 4 of the filter transformer 6. Therefore, the fundamental current does not flow through the primary neutral point 7 of the filter transformer 6, so that the filter element 10
Does not apply the fundamental wave voltage, and does not supply excess phase leading reactive power to the power supply side.

If the capacitor 8 and the reactor 9 of the filter element 10 are tuned to the frequency of the harmonic current to be absorbed, the shunt ratio of the harmonic current to the filter transformer 6 and the power transformer 1 is determined by the filter transformer. 6 is determined by the ratio of the leakage impedances of the power transformer 1 and the power transformer 1. Since the reactor 12 is connected to the neutral line 4 of the power transformer 1, the harmonic current flowing through the filter transformer 6 increases. The absorptivity of the wave current can be improved, and the harmonic current flowing through the neutral line 4 of the power transformer 1 becomes very small.

[0020]

For example, in the conventional circuit shown in FIG. 4, for example, if the frequency of a harmonic current desired to be absorbed by the capacitor 8 and the reactor 9 of the filter element 10 is tuned,
Since the shunt ratio of the harmonic current to the power transformer 1 and the filter transformer 6 is determined by the ratio of the leakage impedance of the power transformer 1 and the filter transformer 6, the power transformer 1 is set to 1000 kVA and% Z = 5%.
(6.6 kV / 105 V), the filter transformer 6 is 75
Assuming that 0 kVA and% Z = 3% (6.6 kV / 105 V), the respective leakage amounts are 1.753 μH (secondary conversion) and 1.404 μH (first conversion) (however, the pureness of the filter element 10 is not changed). Ignore the resistance). Therefore, the shunt amount of the harmonic current into the filter transformer 6 is 1.753 / (1.753 + 1.404) ４０４56%.

On the other hand, in the circuit of the present invention shown in FIG. 1, if the value of the reactor 12 is, for example, the same value as the above-mentioned leakage impedance of the power transformer 1, the shunt of the harmonic current to the filter transformer 6 becomes (1) 0.753 × 2) / (1.753 × 2 + 1.404)
≒ 71%, and the amount of shunts to the filter transformer 6 increases, so that it is possible to improve the absorptivity of the harmonic current.

[0022]

According to the present invention, in addition to the three-phase four-wire filter transformer and the filter element that resonates in series with respect to a desired harmonic, a reactor is inserted and connected to the neutral wire of the power transformer. Since the amount of the shunt of the harmonic current to the filter transformer can be increased, the absorptivity of the harmonic current flowing through the neutral line of the power transformer can be further improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a harmonic filter according to the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the present invention.

FIG. 3 is a basic circuit diagram of a three-phase four-wire circuit.

FIG. 4 is a circuit diagram showing a conventional example of a harmonic filter.

[Explanation of symbols]

 2a-2c Each phase distribution line 3a-3c Load 4 Neutral wire 6 Filter transformer 7 Neutral point 8 Capacitor 9 Reactor 10 Filter element 11 Harmonic filter 11 'Harmonic filter

Claims (4)

[Claims] 1. A harmonic filter for absorbing in-phase harmonic current flowing through a neutral line of a three-phase four-wire power transformer, wherein a Δ connection is provided on the secondary side, and a Y having a neutral point is provided on the primary side. A three-phase four-wire filter transformer having a connection is provided. The primary-side Y connection of the filter transformer is connected to each of the three-phase power distribution lines, and a primary neutral point of the filter transformer and a neutral line are provided between the three neutral points. A harmonic filter, wherein a filter element that resonates in series with a desired harmonic is arranged, and a reactor is inserted and connected to a neutral line of the power transformer. 2. A harmonic filter for absorbing in-phase harmonic current flowing through a neutral wire of a three-phase four-wire power transformer, wherein a Δ connection is provided on the secondary side and a neutral point Y is provided on the primary side. A three-phase four-wire filter transformer having a connection, a primary Y-connection of the filter transformer being connected to each of the three-phase distribution lines, and a primary neutral point of the filter transformer being connected to a neutral wire; A harmonic filter, characterized in that a filter element that opens a part of the secondary Δ-connection and resonates in series with a desired harmonic is arranged, and a reactor is inserted and connected to a neutral wire of the power transformer. 3. The filter element according to claim 1, wherein the filter element comprises a series circuit of a capacitor and a reactor.
Or the harmonic filter according to 2. 4. The harmonic filter according to claim 1, wherein the filter element is a capacitor.