JP2006271026A - Leakage current suppression circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a leakage current suppression circuit that can cope with not only the case that an S phase of a three-phase power supply is earthed but also the case that a neutral point between an R phase and the S phases is earthed. <P>SOLUTION: In a device that comprises capacitors connected between the three-phase AC power supply of the S phase and the earth, or between the neutral connecting point between the R phase and the S phases, a primary coil of a transformer T1 is connected between the S phase and the R phase of the three-phase AC power supply, a primary coil of a transformer T2 is connected between the S phase and a T phase, secondary coils of the transformers T1, T2 are V-connected to each other with polarities reverse to those of primary sides, and secondary outputs of the transformers T1, T2 are connected to the earth via the capacitors. The S phase at the primary side of the transformer T1 and an S' phase at a secondary side are connected to each other, or the S phase of the transformer T1 and an R' phase at a secondary side are connected in accordance with the earthing mode of the three-phase AC power supply, or the R phase at the primary side of the transformer T1 is connected to the S' phase at the secondary side. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a leakage current suppression circuit, and more particularly to suppression of low frequency leakage current.

Conventionally, as this type of leakage current suppression circuit, for example, “a capacitor that is connected between a commercial AC power source in which any one phase is grounded and an electronic device, or between each phase and ground, is provided in the electronic device. A transformer primary coil is connected between a ground line and a non-ground line of the commercial AC power supply with respect to a leakage current flowing to the ground through the capacitor, and a series body of the secondary coil and the capacitor of the transformer Is connected between the ground line of the commercial AC power supply and the ground, so that a current equal to the leakage current in an opposite phase is supplied between the ground line of the commercial AC power supply and the ground. Current reduction circuit "has been proposed (for example, Patent Document 1).
Japanese Patent No. 2895604 (Claim 1, FIG. 4)

  In the three-phase 200V power supply in Japan, S-phase grounding is common, but it may be applied as a single-phase three-wire power supply by grounding the midpoint between the R and S phases of the three-phase power supply. The circuit of Document 1 has a problem that it cannot cope with such a grounding form.

  The present invention has been made to solve the above-described problems, and can cope with not only the S-phase grounding but also the case where the midpoint between the RS phases of the three-phase power source is grounded. An object is to provide a leakage current suppressing circuit.

  The leakage current suppression circuit according to the present invention includes a three-phase AC power source in which any one phase (S) is grounded, or a three-phase AC power source in which a midpoint between two phases (S · R) is grounded, and a ground. In which the primary coil of the first transformer is connected between the ground phase (S) and the other phase (R) of the three-phase AC power source. The primary coil of the second transformer is connected between the phase (S) and the other phase (T), and the secondary coils of the first and second transformers are V-connected in the opposite polarity to the primary side. In addition, the secondary side outputs of the first and second transformers are connected to the ground via capacitors, respectively, and the primary phase of the first transformer is grounded according to the grounding mode of the three-phase AC power source ( S) and the secondary side ground phase (S ′), or the primary side of the first transformer , One phase (S) of the two phases (S · R) and the other phase (R ′) on the secondary side are connected, or the other phase (R on the primary side of the first transformer) ) And one phase (S ′) on the secondary side.

  According to the present invention, in the case of a three-phase AC power source in which any one phase (S) is grounded, the primary-side ground phase (S) and the secondary-side ground phase (S ′) of the first transformer. In the case of a three-phase AC power source in which the midpoint between the two phases (S and R) is grounded, one phase (S) on the primary side of the first transformer and the other side on the secondary side Phase (R ′) or the other phase (R) on the primary side of the first transformer and one phase (S ′) on the secondary side. The leakage current generated by the secondary coil of the transformer is equal in magnitude and opposite in phase to the leakage current flowing into the ground via a capacitor connected between each phase and the ground. Leakage current flowing in can be suppressed. Even when the power supply is grounded differently, the leakage current can be effectively canceled and suppressed by changing the connection as described above.

Embodiment 1 FIG.
FIG. 1 is a circuit diagram showing an arrangement example of a leakage current suppressing circuit and a load circuit according to Embodiment 1 of the present invention, and FIG. 2 is a circuit diagram showing details of the leakage current suppressing circuit of FIG. In the first embodiment, an AC power source with the S phase grounded is targeted, and a case where the primary S phase and the secondary S ′ phase of the transformer T1 of the leakage current suppression circuit are connected will be described.

  As shown in FIG. 1, the R phase 1, S phase 2 and T phase 3 of the three-phase power supply supply power to the load 25 via the reactors 4, 5, 6 and the reactors 4, 5, 6 respectively. In addition, it is connected to the ground 21 through capacitors 15, 16, and 17. Leakage current suppression circuit 26 is arranged between reactors 4, 5, 6 and load 25.

  As shown in FIG. 2, the leakage current suppression circuit 26 includes transformers T1 and T2. The primary winding terminal 7 of the transformer T1 is connected to the R phase 1 through the reactor 4. The other primary winding terminal 8 of the transformer T1 and one primary winding terminal 11 of the transformer T2 are connected, and are connected to the S phase 2 via the reactor 5. The other primary winding terminal 12 of the transformer T2 is connected to the T phase 3 via the reactor 6.

  A capacitor 18 is connected to the secondary winding terminal 9 of the transformer T1, and a capacitor 19 is connected to the secondary winding terminal 10 of the transformer T1 and the secondary winding terminal 13 of the transformer T2. A capacitor 20 is connected to the next winding terminal 14, and the capacitors 18 to 20 are each connected to a ground 21. In this example, the primary winding terminal 8 of the transformer T1 and the primary winding terminal 11 of the transformer T2, and the secondary winding terminal 10 of the transformer T1 and the secondary winding terminal 13 of the transformer T2 are switched on the primary side. And a secondary connection switching terminal (hereinafter referred to as a terminal) b.

  Here, the transformers T1 and T2 have a one-to-one turns ratio between the primary and the secondary, and the polarities are indicated by black dots in the figure. The winding terminals 7 and 10 of the transformer T1 and the windings of the transformer T2 The terminal 11 and the winding terminal 14 are configured to have the same polarity. That is, the transformers T1 and T2 are V-connected, and the primary side and the secondary side have opposite polarities. Capacitors have primary capacitors 15, 16 and 17 and secondary capacitors 18, 19 and 20 all having the same capacity.

  The leakage current suppression circuit 26 of FIG. 2 is configured as described above, and in order to cancel the leakage current flowing into the ground via the primary side capacitors 15 and 17, the phase opposite to the leakage current on the secondary side. The leakage current that finally flows into the earth 21 is canceled and suppressed. In the leakage current suppression circuit 26, since the S phase 2 is grounded, no current flows into the capacitors 16 and 19. Although FIG. 2 shows a V-connection using two transformers T1 and T2, it goes without saying that the same effect can be obtained by using a Δ-connection using three transformers. Here, in order for the capacitors 18 and 20 on the secondary side of the transformers T1 and T2 to pass equivalent antiphase currents to the capacitors 15 and 17 on the primary side, it is necessary to pay attention to the frequency characteristics. In other words, if the leakage inductance of the transformers T1 and T2 is 0, the leakage current is canceled out in the entire frequency range. That is, this circuit including the primary side capacitors 15 to 17 as a noise filter is connected. It's the same as not, and it's meaningless. The point is that due to the effect of the leakage inductance, the canceling effect of the secondary side capacitor works on the power supply frequency, and only the primary side capacitor works in the region affecting the noise terminal voltage of 150 kHz or higher. . For this purpose, the leakage inductance and the resonance frequency of the capacitor are set to several tens of kHz. In addition, in order to obtain a desired characteristic, it is necessary to sufficiently increase the primary-secondary coupling coefficient as a characteristic of the transformers T1 and T2 itself. 85 "or more.

  Since the primary side capacitors 15 to 17 need to have a low impedance of 150 kHz or more with respect to the power source impedance, the capacitor capacitance is 0 when considering 50 uH of LISN used for noise terminal voltage measurement as a reference. 0.025uF or more is required. The larger the L value of reactors 4-16, the smaller the capacitor capacity. Considering the above, when the primary and secondary capacitors 15 to 20 are set to 0.1 uF, the sum of the primary and secondary leakage inductances of the transformers T1 and T2 is about 0.1 to 0.5 mH. desirable.

  FIG. 3 is a vector diagram showing primary and secondary input / output voltages of the transformers T1 and T2. The R phase and R 'phase, and the T phase and T' phase are in opposite phases, centering on the S phase = S 'phase, which is the ground phase, and the currents flowing from there to the capacitor connected to the ground 21 are also opposite in phase. Since they are the same size, they are offset. In this way, as shown by the dotted line in FIG. 1, high-frequency noise current leaking from the load 25 via the capacitor 27 is circulated by the primary-side capacitors 15 to 17, and the primary-side capacitors 15 and 17 are connected. The leakage current of the flowing power supply frequency is offset by the currents from the capacitors 18 and 20 in the leakage current suppression circuit 26, and combined to suppress the leakage current.

Embodiment 2. FIG.
FIG. 4 is a circuit diagram showing a configuration in the case where the above leakage current suppression circuit 26 is applied to an AC power source having an R-S phase midpoint grounding. In this example, the midpoint between the R phase 22 and the S phase 23 of the three-phase AC power supply is connected to the ground 21. In this example, the primary winding terminal 8 of the transformer T1 and the secondary winding terminal 9 of the transformer T1 are connected to each other via a terminal a and a secondary-side connection switching terminal (hereinafter referred to as a terminal) c. ing. Except for these points, the circuit configuration of FIG. 4 is the same as that of FIG.

  In the configuration of FIG. 2, since the S phase 2 is the ground phase, the capacitors 16 and 19 did not function. However, when the midpoint shown in FIG. 4 is the ground phase, a voltage is applied to all the capacitors, Current flows. In FIG. 4, the primary winding terminal 8 of the transformer T1 and the secondary winding terminal 9 of the transformer T1 are connected via the terminals a and c, but the primary winding terminal 7 of the transformer T1 is connected to the transformer T1. Even if the connection is changed to the secondary winding terminal 10, a similar circuit is formed (see FIG. 5).

  FIG. 5 is a circuit diagram showing a modification of FIG. When a primary connection switching terminal (hereinafter referred to as a terminal) d connected to the primary winding terminal 7 of the transformer T1 is provided and the midpoint shown in FIG. b. By connecting in this way, as is clear from the vector diagram of FIG. 6 described later, the ground between the R phase and the S phase is connected to the R phase (primary winding terminal 7) and the S ′ phase (of the transformer T1). When the secondary winding terminal 10) is connected to the same potential, the S phase (primary winding terminal 8 of the transformer T1) and the R ′ phase (secondary winding terminal 9 of the transformer T1) also have the same potential.

  FIG. 6 is a vector diagram showing primary and secondary input / output voltages of the transformers T1 and T2. The R phase and R 'phase, the S phase and the S' phase, and the T phase and the T 'phase are reversed from each other about the midpoint of the R phase-S phase, which is the ground phase, and connected to the ground 21 from there. Since the currents flowing in the capacitors are the same in opposite phases, they are canceled out. By doing so, the high-frequency noise current via the capacitor 27 in FIG. 1 is recirculated by the primary-side capacitors 15 to 17, and the leakage current of the power supply frequency flowing through the primary-side capacitors 15 to 17 is the above leakage. The currents from the capacitors 18 to 20 in the current suppression circuit 26 cancel each other and merge to suppress the leakage current.

Embodiment 3 FIG.
In the present invention, as is apparent from the description of the first and second embodiments described above, the connection between the primary side and the secondary side of the transformer T1 that is V-connected is changed according to the grounding mode of the three-phase AC power supply. The determination process will be described as a third embodiment.

  FIG. 7 is a flowchart showing a process of determining the primary-secondary connection of the transformer T1 according to the grounding mode of the three-phase AC power supply. When the power is turned on immediately after the installation of the device, the primary and secondary of the transformer T1 are connected after confirming the ground phase of the three-phase power supply without connecting the primary and secondary of the transformer. This is because the leakage current increases conversely when the grounding condition and the primary-secondary connection of the transformer T1 are unmatched. Specifically, at the time of shipment in step S1, the primary-secondary state of the transformer T1 is not connected, and the process proceeds to step S2. In step 2, it is determined whether or not the connection power source is a three-phase three-wire power source with S-phase grounding. Otherwise, go to step 3. In step 3, it is determined whether or not the connected power source is a three-phase three-wire power source with RS phase midpoint grounding. Otherwise, go to Step 6. In Step 4, the primary S phase and the secondary S 'phase of the transformer T1 are connected (terminals a and b are connected), and the process proceeds to Step 7. In step 5, the primary side S phase of the transformer T1 and the secondary side phase other than the S phase are connected (terminals a and b are connected or terminals d and b are connected), and the process proceeds to step 7. In Step 6, the process proceeds to Step 7 in a state where the primary and secondary sides of the transformer T1 are not connected. In step 7, the power is turned on so that the operation of the device can be started.

It is the circuit diagram which showed the example of arrangement | positioning of the leakage current suppression circuit and load circuit which concern on Embodiment 1 of this invention. FIG. 2 is a circuit diagram illustrating details of a leakage current suppressing circuit of FIG. 1. It is a voltage vector diagram in Embodiment 1 of this invention. It is the circuit diagram which showed the detail of the leakage current suppression circuit which concerns on Embodiment 2 of this invention. FIG. 5 is a circuit diagram showing a modification of the leakage current suppression circuit of FIG. 4. It is a voltage vector figure in Embodiment 2 of this invention. It is the flowchart which showed the process of determining the connection between the primary and secondary of a transformer according to the grounding aspect of a three-phase alternating current power supply.

Explanation of symbols

1-3, 22-24 ... AC power supply, 4-6 ... Reactor, 15-20, 27 ... Capacitor, 7-14 ... Transformer input / output line, 28 ... R-phase power supply line 29 ... S phase power supply line, 30 ... T phase power supply line, 25 ... load, 21 ... earth, 26 ... leakage current suppression circuit, a, b, c, d ... Transformer primary / secondary side connection switching terminal, S1, S4, S5, S6, S7 ... processing block, S2, S3 ... determination block, T1, T2 ... transformer

Claims (3)

Capacitors connected between each phase of the three-phase AC power source with one phase (S) grounded or the three-phase AC power source with the middle point between the two phases (RS) grounded In the equipment provided,
A primary coil of the first transformer is connected between the ground phase (S) and the other phase (R) of the three-phase AC power supply, and between the ground phase (S) and the other phase (T). The primary coil of the second transformer is connected to the secondary coil, and the secondary coils of the first and second transformers are V-connected in the opposite polarity to the primary side, and the secondary side outputs of the first and second transformers are connected. Each is connected to the ground via a capacitor,
Depending on the grounding mode of the three-phase AC power source, the primary-side ground phase (S) and the secondary-side ground phase (S ′) of the first transformer are connected, or the primary primary of the first transformer Of any one of the two phases (R · S) and the other secondary phase (R ′), or the other primary side of the first transformer. A leakage current suppressing circuit comprising: connecting a phase (R) and one phase (S ′) on the secondary side.   2. The leakage current suppression circuit according to claim 1, wherein the coupling coefficient of each of the first and second transformers is 0.85 or more. 3. The leakage current suppression circuit according to claim 1, wherein a resonance frequency due to a leakage reactance of the first and second transformers and a capacitance of the primary and secondary capacitors is in a range of several tens of kHz.

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