Non-contact voltage phase detection device and method

Abstract

To provide a non-contact voltage phase detection device capable of accurately detecting the voltage waveform of a power line while reducing a phase error.SOLUTION: A non-contact voltage phase detection device includes capacitive coupling sensors 210, 220 of the R-phase and T-phase that are respectively capacitively coupled with power lines 10, 20 of the R-phase and T-phase of a three-phase AC power supply; detection circuits 310, 320 of the R-phase and T-phase which respectively convert the displacement currents flowing through the capacitive coupling sensors 210, 220 of the R-phase and T-phase into first and second detection voltages; and a differential circuit 130 which calculates the difference between the first and second detection voltages to output the R-T voltage waveform. The device includes a correction circuit which amplifies the detection voltages of the R-phase and T-phase by the amplification ratio being the reciprocal of the capacitance ratio so as to bring the capacitance ratio between the coupling capacitance of the R-phase in a capacitively-coupled part between the power line 10 of the R-phase and the capacitive coupling sensor 210 of the R-phase and the coupling capacitance of the T-phase in a capacitively-coupled part between the power line 20 of the T-phase and the capacitive coupling sensor 220 of the T-phase close to 1:1.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a non-contact voltage phase detection device and method, and more particularly to a non-contact voltage phase detection device and method capable of reducing a phase error of a voltage waveform without directly adjusting the coupling capacitance between a capacitively coupled power line and a capacitive sensor. [Background technology]

[0002] When detecting earth leakage current flowing through load equipment to which voltage is applied from an AC power source, it is necessary to extract and detect the resistive component leakage current (Ior), since the resistive component leakage current (Ior) contained in the leakage current is dangerous due to heat generation.

[0003] The resistive leakage current (Ior) is expressed as follows: In the case of single phase, Ior=Io COS(θ1) In the case of three phase, Ior=Io COS(θ3) / COS(30) Where: Io: Total leakage current θ1: Phase difference between the power supply voltage and leakage current Ior: Resistance leakage current θ3: Phase difference between the RT voltage and leakage current

[0004] For this reason, in order to detect the resistive component leakage current (Ior), in addition to the leakage current, it is necessary to measure the phase difference (θ1, θ3) between the power supply voltage and the leakage current. Conventionally, when measuring the power supply voltage, the detection terminal was directly contacted to the power line to measure the voltage.

[0005] However, to improve safety and ease of operation when measuring the voltage of a live power line, it is desirable to measure the phase relationship between voltage and current in a non-contact manner, without directly contacting the detection terminal with the power line. A known example of such a non-contact measurement method is the capacitive coupling method, in which a capacitive coupling sensor is brought close to a power line from above the wire insulation, capacitively coupling the capacitive coupling sensor to the wire, and the voltage is measured in a non-contact manner by detecting the waveform of the current flowing through the capacitive coupling section.

[0006] An example of a non-contact voltage measurement device using a conventional capacitive coupling method is described in Patent Document 1. In the non-contact voltage measurement device of Patent Document 1, a signal from an oscillator that outputs a signal of a predetermined frequency is applied to a shielded detection electrode of a detection probe (capacitive coupling sensor) that sandwiches a power line, thereby measuring the impedance between the detection electrode and a conductor, and measuring the current flowing out from the detection electrode due to the voltage applied to the conductor, and measuring the voltage applied to the conductor from the current and impedance. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 3158063 Summary of the Invention [Problem to be solved by the invention]

[0008] Incidentally, when detecting the R-to-RT voltage waveform of a three-phase AC power supply, the R-phase and T-phase power lines are capacitively coupled to separate capacitive coupling sensors. In this case, the capacitive coupling value varies greatly due to, for example, slight variations in the thickness of the insulating coating of the power line or slight differences in the force with which the capacitive coupling sensor pinches the power line. Therefore, if the capacitive coupling value between the capacitive coupling sensor and the power line differs between the R-phase side and the T-phase side, a difference occurs in the peak voltages of the detected voltages of the R-phase and the T-phase. As a result, the phase of the R-to-RT voltage waveform shifts to the R-phase side or the T-phase side with the lower detected voltage, causing a phase error in the R-to-RT voltage waveform. An example of a phase error in the RT voltage waveform is shown in Figure 6. In contrast to the phase of the RT voltage waveform when the detected voltages on the T phase side and R phase side are equal as shown in Figure 6(a), the phase of the RT voltage waveform when the detected voltage on the R phase side is lower than the T phase side as shown in Figure 6(b) shifts to the R phase side. As a result, a phase error occurs in the voltage waveform of the output detection signal with respect to the RT voltage waveform.

[0009] When a difference occurs between the peak voltages of the detection voltages on the R phase side and the T phase side, one might think that the phase error would be eliminated if the detection voltage was adjusted so that the difference between these peak voltages was eliminated. However, in reality, in addition to the capacitive coupling part between the power cable and the capacitive coupling sensor, capacitive coupling parts are also formed between the GND and earth of the detection device and between the power cable and the detection device, and the phase currents flowing through these capacitive coupling parts are also added to and detected as the detection voltage. Therefore, it is not easy to eliminate the phase error simply by adjusting the peak voltage difference between the R phase side and the T phase side to eliminate it.

[0010] The present invention has been made in consideration of the above circumstances, and has an object to provide a non-contact voltage phase detection device and method that can reduce phase error and accurately detect the voltage waveform of a power line. [Means for solving the problem]

[0011] A first non-contact voltage phase detection device of the present invention includes a first capacitively coupled sensor capacitively coupled to a first power supply line of a multi-phase AC power supply, a second capacitively coupled sensor capacitively coupled to a second power supply line of the multi-phase AC power supply, a first detection circuit that converts a displacement current flowing through the R-phase capacitively coupled sensor into a first detection voltage, a second detection circuit that converts a displacement current flowing through the second capacitively coupled sensor into a second detection voltage, and a differential circuit that takes a difference between the first detection voltage and the second detection voltage and outputs a voltage waveform between the first and second power supply lines, and further includes an adjustment device that adjusts the first coupling capacitance so that a first coupling capacitance in a capacitive coupling portion between the first power supply line and the first capacitively coupled sensor and a second coupling capacitance in a capacitive coupling portion between the second power supply line and the second capacitively coupled sensor match each other.

[0012] A third non-contact voltage phase detection method of the present invention includes converting a displacement current flowing through a first capacitively coupled sensor capacitively coupled to a first power supply line constituting a power supply line of a multi-phase AC power supply into a first detection voltage, converting a displacement current flowing through a second capacitively coupled sensor capacitively coupled to a second power supply line constituting another power supply line of the multi-phase AC power supply into a second detection voltage, taking a difference between the first detection voltage and the second detection voltage, and generating a voltage waveform between the first and second power supply lines, characterized in that the first coupling capacitance is adjusted so that a first coupling capacitance at a capacitive coupling portion between the first power supply line and the first capacitively coupled sensor matches a second coupling capacitance at a capacitive coupling portion between the second power supply line and the second capacitively coupled sensor.

[0013] Incidentally, the phase error of the R-to-RT voltage waveform can theoretically be eliminated by matching the capacitive coupling values ​​on the R phase side and the T phase side; however, it is necessary to mechanically adjust the coupling capacitance of the capacitive coupling part between the capacitive coupling sensor and the power supply line so that it is the same on the R phase side and the T phase side.

[0014] As a result of further investigation, the inventors of the present invention have found that even if the coupling capacitances on the R phase side and the T phase side are not made to match, the phase of the R-to-R voltage can be approximately detected by adjusting the detection voltage obtained by converting the displacement current flowing through the capacitive coupling part using a downstream amplifier so that the ratio of the coupling capacitances on the R phase side and the T phase side becomes 1:1, as described later in the embodiment. The second and fourth present inventions have been made based on this finding.

[0015] A second non-contact voltage phase detection device of the present invention includes a first capacitively coupled sensor capacitively coupled to a first power supply line of a multi-phase AC power supply, a second capacitively coupled sensor capacitively coupled to a second power supply line of the multi-phase AC power supply, a first detection circuit that converts a displacement current flowing through the first capacitively coupled sensor into a first detection voltage, a second detection circuit that converts a displacement current flowing through the second capacitively coupled sensor into a second detection voltage, and a differential circuit that takes a difference between the first detection voltage and the second detection voltage and outputs a voltage waveform between the first and second power supply lines, and further includes a correction circuit that amplifies the first and second detection voltages by an amplification ratio that is the reciprocal of a capacitance ratio between a first coupling capacitance in a capacitive coupling portion between the first power supply line and the first capacitively coupled sensor and a second coupling capacitance in a capacitive coupling portion between the second power supply line and the second capacitively coupled sensor so that the capacitance ratio approaches 1:1.

[0016] A fourth non-contact voltage phase detection method of the present invention includes converting a displacement current flowing through a first capacitively coupled sensor capacitively coupled to a first power supply line constituting a power supply line of a multi-phase AC power supply into a first detection voltage, converting a displacement current flowing through a second capacitively coupled sensor capacitively coupled to a second power supply line constituting another power supply line of the multi-phase AC power supply into a second detection voltage, taking a difference between the first detection voltage and the second detection voltage, and generating a voltage waveform between the first and second power supply lines, characterized in that the first and second detection voltages are amplified by an amplification ratio that is the reciprocal of a capacitance ratio between a first coupling capacitance in a capacitive coupling portion between the first power supply line and the first capacitively coupled sensor and a second coupling capacitance in a capacitive coupling portion between the second power supply line and the second capacitively coupled sensor so that the capacitance ratio approaches 1:1. Effect of the Invention

[0017] According to the first and third non-contact voltage phase detection devices and methods of the present invention, one or both of the first coupling capacitance and the second coupling capacitance are adjusted so that a first coupling capacitance in a capacitive coupling portion between a first power supply line and a first capacitive coupling sensor matches a second coupling capacitance in a capacitive coupling portion between a second power supply line and a second capacitive coupling sensor. As a result, according to the present invention, the voltage waveform of the power supply line can be detected with high accuracy while reducing phase errors.

[0018] In addition, in the second and fourth non-contact voltage phase detection devices and methods of the present invention, the first and second detection voltages are amplified by an amplification ratio that is the reciprocal of a capacitance ratio between a first coupling capacitance in a capacitive coupling portion between a first power supply line and a first capacitive coupling sensor and a second coupling capacitance in a capacitive coupling portion between a second power supply line and a second capacitive coupling sensor, so that the capacitance ratio approaches 1:1. As a result, according to the present invention, the phase of the voltage between the first and second power supply lines can be approximately detected with high accuracy by adjusting the detection voltage converted from the displacement current flowing through the capacitive coupling section in a downstream amplifier without directly adjusting the coupling capacitance of the capacitive coupling section between the capacitive coupling sensor and the power supply line. [Brief description of the drawings]

[0019] [Figure 1] FIG. 2 is a schematic diagram of a non-contact voltage phase detector of the present invention connected to a leakage current detector. [Diagram 2] FIG. 2 is a block diagram for explaining a basic configuration excluding a correction circuit in the non-contact voltage phase detection device of the present invention. [Diagram 3] This is an equivalent circuit when the three-phase power line of the basic configuration shown in Figure 2 is connected. [Figure 4] FIG. 4 is a partial enlarged view of the equivalent circuit shown in FIG. [Diagram 5] FIG. 1 is a block diagram of a non-contact voltage phase detection device according to an embodiment of the present invention. [Figure 6] FIG. 11 is an explanatory diagram of the phase error of the voltage between TR when the capacitive coupling value between the capacitance sensor and the power supply line is different on the R phase side and the T phase side, where (a) shows the voltage waveform when the signal levels on the R phase side and the T phase side are the same, and (b) shows the voltage waveform when the signal level on the R phase side is lower than the signal level on the T phase side. [Figure 7] FIG. 4 is a schematic diagram of a second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a non-contact voltage phase detection device and method according to the present invention will be described with reference to the drawings.

[0021] 1 shows a schematic diagram of the non-contact voltage phase detector of the present invention connected to a leakage current detector. The non-contact voltage phase detector of this embodiment constitutes an adapter for detecting the leakage current of a resistive component with a leakage current detector 500 (for example, a product name IOR500 manufactured by Sanwa Electric Instruments Co., Ltd.).

[0022] 1, the adapter is composed of a device main body 100, and first and second capacitive coupling sensors 210 and 220 connected to the device main body 100. The first and second capacitive coupling sensors 210 and 220 have a clip shape, and are capacitively coupled to the R-phase and T-phase power supply lines 10 and 20, respectively, of a three-phase AC power supply by clamping them. The device main body 100 outputs phase information of the RT voltage to a voltage input terminal of the leakage current detecting device 500 .

[0023] With reference to FIG. 2, a basic configuration of the non-contact voltage phase detection device of this embodiment excluding the correction circuit will be described. The non-contact voltage phase detection device shown in FIG. 2 includes, in addition to the first and second capacitive coupled sensors 210 and 220, the following structures included in the device main body 100: an R-phase detection circuit 110 that converts the displacement current flowing through the R-phase capacitive coupled sensor 210 into an R-phase detection voltage; a T-phase detection circuit 120 that converts the displacement current flowing through the T-phase capacitive coupled sensor 220 into a T-phase detection voltage; and a differential circuit 130 that takes the difference between the R-phase detection voltage and the T-phase detection voltage and outputs an R-phase voltage waveform.

[0024] The first and second detection circuits 110 and 120 are CR circuits constituted by capacitors and resistors having the same characteristic values, and output R-phase and T-phase detection voltage waveforms that lead in phase with the actual RT voltage.

[0025] 2 further includes a low-pass filter 140 made up of a variable resistor and a capacitor for adjusting the phase of the R-T voltage waveform output from the differential circuit 130. In the low-pass filter 140, the amount of phase delay is adjusted by changing the resistance value of the variable resistor.

[0026] The voltage waveform output from low-pass filter 140 is amplified by amplifier 156 and then output to a voltage input terminal of leakage current detection device 500 .

[0027] Next, prior to describing the correction circuit of the non-contact voltage phase detection device of this embodiment, a phase error of the R-to-R voltage of a three-phase power supply with the S-phase power supply line grounded will be described. FIG 3 shows an equivalent circuit of the non-contact voltage phase detector of FIG 2 with B-type grounding. The symbols in FIG 3 represent the following elements. FIG 4 is a partially enlarged view of the equivalent circuit shown in FIG 3.

[0028] C1: R-phase capacitive coupling sensor C2: T-phase capacitive coupling sensor C3, C4: Capacitors for signal attenuation C5: Coupling capacitance between the GND of the device body and earth C6: Coupling capacitance between the GND and R phase of the device body C7: Coupling capacitance between the GND and T phase of the device body R1~R4: Resistance for signal ATT R: RS phase voltage T: TS phase-to-phase voltage VR: R-phase detection voltage (waveform with the voltage between the R-phase and adapter GND attenuated) VT: T-phase detection voltage (waveform with the voltage between the T-phase and adapter GND attenuated) VE: Voltage between the adapter's GND and earth

[0029] In the following explanation, the B-class ground resistance is ignored (0 Ω) because it is a value that is sufficiently small compared to the impedance of C1 and C2. The impedances of R1 to R4 are ZR1 to ZR4. The impedances of C1 to C7 are ZC1 to ZC7. Although the detected voltage and impedance are vector values, for convenience, dots and the like are omitted.

[0030] (1) First, calculate the voltage VE of the device body to ground. (1-1)R phase The combined impedance ZR of CR (R1, R2, C3) for the R-phase detection circuit ATT is calculated using the following formula (1). ZR ATT =(ZR1+ZR2)ZC3 / (ZR1+ZR2+ZC3)...(1) The composite impedance ZR' between the R phase and the adapter GND via the R phase capacitive coupling sensor (C1, R1, R2, C3) is calculated by the following equation (2). ZR' = ZC1 + ZR ATT (2) The combined impedance ZR between the R phase and the adapter GND (ZR', C6) is calculated by the following equation (3). ZR = ZR' ZC6 / (ZR' + ZC6) (3)

[0031] (1-2)T phase The combined impedance ZT of CR (R3, R4, C4) for the T-phase detection circuit ATT is calculated using the following formula (4). ZT ATT =(ZR3+ZR4)ZC4 / (ZR3+ZR4+ZC4)...(4) The combined impedance ZT' of the detection circuit (C2, R3, R4, C4) between the T phase and the adapter GND is calculated by the following equation (5). ZT' = ZC2 + ZT ATT (5) Formula for calculating the combined impedance ZT between the T phase and adapter GND (ZT', C6) ZT = ZR' ZC7 / (ZT' + ZC7) (6) The combined impedance ZE between the adapter GND and earth is calculated using the following equation (7). ZE=ZC5 (7)

[0032] (1-3) Voltage to earth VE Calculate the voltage to earth VE using ZR, ZT, and ZE calculated using equations (3), (6), and (7) above. According to Kirchhoff's law, the relationship between the currents IR, IT, and IE flowing through ZR, ZT, and ZE is expressed by the following equation (8). IR+IT=IE···(8) In addition, IR, IT, and IE can be expressed from the circuit by the following equations (9). IR=(R-VE) / ZR, IT=(T-VE) / ZT, IE=VE / ZR...(9) Calculate VE by substituting equation (9) into equation (8). VE=(ZE ZT R+ZE ZR T) / (ZE ZT+ZE ZR+ ZT ZR)...(10)

[0033] Here, when calculating VE, ZR contains a component C6, ZT contains a component C7, and ZE contains a component C5. Therefore, it can be seen that the value of VE also changes due to the coupling capacitances (C5, C6, C7) other than the coupling capacitances C1 and C2 of the first and second capacitive coupling sensors.

[0034] (2) Next, calculate the R and T phase ATT voltage VR-VT that is actually detected by the adapter. VR is the voltage between RS minus VE, which is ZC1 and ZR ATT This voltage is then divided by ZR1 and ZR2, resulting in a voltage that is expressed by the following equation (11). VR = (R-VE) (ZR ATT / ZR)(ZR1ZR2 / (ZR1+ZR2))...(11) VT is the voltage between TS, T minus VE, which is ZC2 and ZT. ATT This voltage is then divided by ZR3 and ZR4, resulting in a voltage that is expressed by the following equation (12). VT=(T-VE)(ZR ATT / ZT)(ZR3ZR4 / (ZR3+ZR4))...(12) The desired value is the voltage between VR and VT, so by subtracting (12) from (11), we get VR-VT=(R-VE)(ZR ATT / ZR)(ZR1ZR2 / (ZR1+ZR2))-(T-VE)(ZR ATT / ZT)(ZR3ZR4 / (ZR3+ZR4))...(13) When equation (13) is summarized in VE, it is expressed as the following equation (14). VR-VT=(ZR ATT / ZR)(ZR1 ZR2 / (ZR1+ZR2))R-(ZR ATT / ZT)(ZR3ZR4 / (ZR3+ZR4))T+{(ZR ATT / ZT)(ZR3ZR4 / (ZR3+ZR4))-(ZR ATT / ZR)(ZR1ZR2 / (ZR1+ZR2))}VE···(14)

[0035] From the above equation (14), if the values ​​of ZC1 and ZC2 are different, ZR ≠ ZT, and therefore the voltage division ratio of R and T changes, making it impossible to obtain an accurate phase between VR and VT. Furthermore, from the above equation (14), when ZR≠ZT, the value in the parentheses surrounding VE does not become 0, and therefore VE affects the phase of VR-VT. In particular, since VE is affected by the coupling capacitances C5, C6, and C7 other than the first and second capacitive coupling sensors, the phase error increases.

[0036] (2-1) Here, a case where the coupling capacitance values ​​(C1, C2) of the first and second capacitive coupling sensors are the same capacitance value will be described. Here, if it is assumed that the coupling capacitances C1, C2 of the first and second capacitive coupling sensors and R1 to R4, C3, and C4 of the CR for the detection circuit are all the same value, then The following equations (15) to (17) hold. Since C1 = C2 (= CS), ZC1 = ZC2 = ZCS (15) Since R1 = R2 = R3 = R4 (= RA), ZR1 = ZR2 = ZR3 = ZR4 = ZRA (16) Since C3 = C4 (= CA), ZC3 = ZC4 = ZCA (17) From the above equations (1), (4), (16), and (17), the following equation (18) is obtained. ZR ATT =ZT ATT (=Z ATT (18) From equations (2), (5), and (18), the following equation (19) holds. ZR = ZT (= ZA) (19) By substituting equations (15) to (19) into equation (14), the following equation (20) is obtained. VR - VT = (Z ATT / ZA)(ZRA ZRA / (ZRA+ZRA))R-(Z ATT / ZA)(ZRA ZRA / (ZRA+ZRA))T+{(Z ATT / ZA)(ZRA ZRA / (ZRA+ZRA))-(Z ATT / ZA)(ZRA ZRA / (ZRA+ZRA))}VE···(20) Rearranging this gives the following equation (21). VR-VT=(Z ATT / ZA)(ZRA ZRA / (ZRA+ZRA))(RT)...(21)

[0037] From the above formula (21), the detection waveform of VR-VT is not affected by VE. The RT voltage is determined only by the relationship between the coupling capacitance of the capacitive coupling sensor and the resistance and capacitance of the detection circuit. Here, the resistance and capacitance for the detection circuit can be known constants. Therefore, if the constant of CR for the detection circuit can be set to the same value for the R phase and the T phase, and if the coupling capacitance of the capacitive coupling sensor can be set to the same capacitance value for the R phase and the T phase, it can be seen that the voltage phase between RT can be accurately detected.

[0038] In this way, if the coupling capacitance of the capacitive coupling sensors for the R and T phases is the same, the signal levels of the R and T phases will be the same, eliminating phase errors between the R-to-R voltage and the detection signal. In addition, errors caused by phase currents flowing due to the coupling capacitance between the GND and earth of the device body, and between the R and T phases will theoretically also be eliminated.

[0039] However, as will be explained below, an approximate value can be obtained by multiplying the downstream amplifier (here, the R phase side) by a coefficient k that makes the capacitance ratio of the R phase and T phase capacitive coupling sensors 1:1, even if adjustment is not made so that the coupling capacitance of the R phase and T phase capacitive coupling sensors are the same.

[0040] (2-2) A case where the sensor coupling capacitance values ​​(C1, C2) are different and the level of the detection signal is adjusted in the subsequent stage will be described. First, when the detection CR has the same constant for the R phase and the T phase, but the coupling capacitances of the first and second capacitive coupling sensors are different (C1 ≠ C2), ZC1 = k ZC2 (22) The VR signal is multiplied by a coefficient k such that: In an actual circuit, this means that the VR signal is amplified by an amplifier by a factor of k.

[0041] Meanwhile, mathematically, this is equivalent to multiplying equation (11) by coefficient k. In this case, since the detection circuit CR is the same constant for the R phase and the T phase, substituting ZATT and ZRA from equations (16) and (18) gives the following equation (23). VR = (R-VE) (Z ATT / ZR)(ZRA ZRA / ZRA+ZRA)...(23) In addition, for the equation calculated for VT using equation (12), since the detection CR is the same constant for the R phase and the T phase, from equations (16) and (18), Z ATT ,ZRA, we obtain the following equation (24). VT=(T-VE)(Z ATT / ZT)(ZRA ZRA / ZRA+ZRA)...(24) If VR-VT is used in equations (23) and (24), the following equation (25) is obtained. VR-VT=(ZRA ZRA / ZRA+ZRA){(ZATT / ZR)kR-(Z ATT / ZT)T+((Z ATT / ZT)-(ZATT / ZR)k)VE}···(25) In addition, regarding equations (2) and (5), since CR for the detection circuit is the same constant for the R phase and the T phase, the following equation (26) is obtained from equation (18). ZR=ZC1+Z ATT (26) ZT = ZC2 + Z ATT (27) By substituting the above equations (26) and (27) into equation (25), we obtain the following equation (28). VR-VT=(ZRA ZRA / (ZRA+ZRA)){(ZATT / (ZC1+Z ATT ))kR-(Z ATT / (ZC2+Z ATT ))T+((Z ATT / (ZC2+Z ATT ))-(Z ATT / (ZC1+Z ATT ))k)VE}···(28)

[0042] Here, the denominator ZC1+Z ATT , ZC2+ZT ATT Regarding actual use, ATT Since the value of is negligibly small compared to the values ​​of ZC1 and ZC2, it can be approximated as shown in the following equations (29) and (30). ZC1+Z ATT ≒ZC1···(29) ZC2+Z ATT ≒ ZC2 (30) By substituting the above equations (29) and (30) into equation (28), we obtain the following equation (31). VR-VT≒(ZRA ZRA / (ZRA+ZRA)){(Z ATT / ZC1)kR-(Z ATT / ZC2)T+((Z ATT / ZC2-(Z ATT / ZC1)k)VE}···(31) Furthermore, by substituting equation (22): ZC1 = kZC2 into ZC1 in equation (31), the following equation (32) is obtained. VR-VT≒(ZRA ZRA / (ZRA+ZRA)){(Z ATT / kZC2)kR-(Z ATT / ZC2)T+((Z ATT / ZC2-(Z ATT / k ZC2)k)VE}···(32) In the above equation (32), the coefficient k is cancelled out in the numerator and denominator, and VE is also subtracted to become 0, so by rearranging this, we obtain the following equation (33). VR-VT ≒ (ZRA ZRA / (ZRA+ZRA))(Z ATT / ZC2)(RT) ···(33)

[0043] From the above equation (33), the voltage waveform of VR-VT is not affected by VE, and the voltage waveform is determined only by the relationship between the coupling capacitance of the capacitive coupling sensor and the resistance and capacitance of the detection circuit. In addition, the resistance and capacitance of the detection circuit can be set to known constants. Therefore, by setting the constant of the CR for the detection circuit to the same value for the R phase and the T phase, and adjusting the GAIN of the ratio of the coupling capacitance of the first and second capacitive coupling sensors for one or both of the R phase and the T phase, the voltage phase between RT can be detected as an approximate value.

[0044] Based on the above findings, as shown in Fig. 5, the non-contact voltage phase detection device of this embodiment includes a correction circuit in the device body shown in Fig. 1 in addition to the configuration shown in Fig. 2. The correction circuit amplifies the first and second detection voltages by an amplification ratio that is the reciprocal of the capacitance ratio so that the capacitance ratio between the first coupling capacitance in the capacitive coupling part between the R-phase power line 10 and the R-phase capacitive coupling sensor 210 and the second coupling capacitance in the capacitive coupling part between the T-phase power line 20 and the T-phase capacitive coupling sensor 220 approaches 1:1. For example, when the capacitance ratio is X:Y, the amplification ratio of the first detection voltage: the second detection voltage is amplified by an amplification ratio of Y:X.

[0045] In this embodiment, in order to check the capacitance ratio of the electrostatic coupling capacitance of the R-phase and T-phase capacitive coupling sensors 210 and 220, a correction circuit outputs a signal having a detection signal frequency different from the commercial frequency of the three-phase AC power supply, and measures the signal current returning via earth and the R-phase and T-phase power supply lines 10 and 20.

[0046] To achieve this, the correction circuit includes an oscillator circuit 310 that outputs a signal current having a signal frequency (for example, 500 Hz to 1 kHz) different from the frequency (50 Hz or 60 Hz) of the multi-phase AC power supply to R-phase and T-phase power supply lines 10 and 20, respectively, via a ground, a first variable amplifier 321 that amplifies or decreases the R-phase detection voltage, a second variable amplifier 322 that amplifies or decreases the T-phase detection voltage, a comparison circuit 330 that compares the voltage of the signal frequency component of the R-phase detection voltage with the voltage of the signal frequency component of the T-phase detection voltage, and an amplification factor correction circuit 350 that corrects the amplification factor of one or both of the first and second variable amplifiers 321 and 322 depending on the comparison result of the comparison circuit 330 so that the voltage of the signal frequency component of the first detection voltage matches the voltage of the signal frequency component of the second detection voltage.

[0047] As a result, based on the above findings, the phase error of the RT detection voltage is corrected by adjusting the amplification factor of one or both of the downstream first and second variable amplifiers 321 and 322, rather than directly adjusting the capacitance ratio itself of the R-phase and T-phase capacitive coupling sensors 210 and 220. The signal frequency is not particularly limited as long as it is different from the power supply frequency, but it is preferable that the signal frequency is sufficiently different from the power supply frequency so that it can be extracted separately from the power supply frequency.

[0048] However, the voltage of the return signal of the signal frequency changes depending on the surrounding conditions. Therefore, in this embodiment, whether or not the capacitance ratio is consistent is determined based on the ratio of the difference (the voltage difference between the signal frequency components of the detection voltages of the R phase and the T phase) to the total signal amount (the sum of the voltages of the signal frequency components of the detection voltages of the R phase and the T phase).

[0049] For this purpose, the correction circuit further includes an adder circuit 340 that adds the first detection voltage and the second detection voltage. The comparison circuit 330 obtains as a comparison result a ratio of the difference between the voltages of the signal frequency components of the first and second detection voltages, the difference of which is taken by the differential circuit, to the sum of the voltages of the signal frequency components of the first and second detection voltages added by the addition circuit 340. When the ratio exceeds a predetermined value, the amplification factor correction circuit 350 corrects the amplification factor of one or both of the R-phase and T-phase variable amplifiers 321 and 322.

[0050] An example of the operation of the non-contact voltage phase detection device of this embodiment will be described below. The oscillator circuit 310 amplifies a signal current having a signal frequency different from the frequency (50 Hz or 60 Hz) of the three-phase AC power supply to about ±40 V by an amplifier 311 and outputs it from a copper plate 312 installed inside the device body 100. The output signal is capacitively coupled to the ground or the R-phase and T-phase power supply lines 10 and 20, respectively, and a signal current flows. The signal current may be a phase current that does not pass through the earth but is capacitively coupled to the output circuit and the power supply line.

[0051] The signal currents flowing through the R-phase and T-phase power supply lines 10 and 20 return to the device main body 100 (see FIG. 1) via the R-phase and T-phase capacitive coupling sensors 210 and 220. The R-phase and T-phase signal currents are converted into R-phase and T-phase detection voltages, respectively, by detection resistors and capacitors of first and second detection circuits 110 and 120 in the device main body 100.

[0052] If the detected voltage of the R phase and the detected voltage of the T phase are at the same level, the capacitance values ​​of the capacitive coupling sensors of the R phase and T phase can be considered to be at the same level. In other words, if the difference between the detected voltage of the R phase and the detected voltage of the T phase is zero, the capacitance values ​​of the capacitive coupling sensors of the R phase and T phase can be considered to be at the same level.

[0053] However, the voltage of the return signal changes depending on the surrounding conditions. As a result, even if the voltage difference between the signal frequency components of the detected voltages of the R and T phases is the same, for example, 0.1 mV, if the total amount of the return signal frequency components is 10 mV, the capacitance ratios can be considered to be at roughly the same level. However, if the sum (total amount) of the detected voltages of the R and T phases is 0.2 mV, the capacitance ratios cannot be considered to be at the same level.

[0054] Therefore, in this embodiment, when determining whether the capacitance values ​​match, the capacitance ratio is determined to be equal or not based on the ratio of the difference (the difference in voltage between the signal frequency components of the detection voltages of the R phase and T phase) to the total signal amount (the sum of the voltages of the components of the detection voltages of the R phase and T phase).

[0055] To this end, in this embodiment, the differential amplifier 130 determines the difference between the detected voltage of the R phase and the detected voltage of the T phase, the detection circuit 342 detects only the signal frequency component, converts the differential signal frequency component to a DC voltage value and outputs it to the comparison circuit 330. In addition, the adder circuit 340 determines the sum (total amount) of the voltages of the signal frequency components of the detected voltages of the R phase and the T phase, and the detection circuit 344 converts the total signal frequency component to a DC voltage value and outputs it to the comparison circuit 330.

[0056] If the ratio of the difference calculated by the differential amplifier 130 to the total amount calculated by the adder circuit 340 is equal to or less than a predetermined value (e.g., 10%), the comparator circuit 330 determines that the capacitance ratio of the coupling capacitances of the R phase and the T phase matches. On the other hand, if the ratio exceeds a predetermined value (e.g., 10%), it determines that the capacitance ratios do not match.

[0057] If the comparison circuit 330 determines that the capacitance ratios do not match, the amplification factor correction circuit 350 corrects the amplification factors (GAIN) of one or both of the R-phase and T-phase variable amplifiers (amplifiers) 321 and 322 at the trigger period of the trigger oscillation circuit 360 (13 Hz) according to the capacitance ratio as a comparison result output from the comparison circuit 330. For example, when the signal strength on the R phase side is small, the amplification factor of the R phase variable amplifier is increased so that the signal strength ratio becomes 1:1, that is, so that the outputs of the signal frequency components of the detection voltages of the R phase and T phase become approximately equal. On the other hand, when the signal strength on the R phase side is large, the amplification factor of the R phase variable amplifier is decreased so that the signal strength ratio approaches 1:1.

[0058] As a result, instead of directly adjusting the capacitance of the R-phase and T-phase capacitively coupled sensors, the phase error of the R-phase voltage can be approximately corrected by adjusting the signal intensity ratio to approach 1:1 in the downstream R-phase and T-phase amplifiers 321 and 322.

[0059] Next, a second embodiment of the present invention will be described with reference to Fig. 7. Fig. 7 is a partially enlarged schematic diagram of a first capacitive coupling sensor 210. 2, the non-contact voltage phase detection device of this embodiment includes an adjustment device that adjusts the first coupling capacitance so that the first coupling capacitance in the capacitive coupling portion between the R-phase power line 10 and the first capacitive coupling sensor 210 matches the second coupling capacitance in the capacitive coupling portion between the T-phase power line and the second capacitive coupling sensor 220. Here, a description of the basic configuration shown in FIG. 2 is omitted. The adjustment device includes an actuator 212 that adjusts the distance between the internal electrode 211 of the first capacitive coupling sensor 210 and the R-phase power line 10 so that the first detection voltage and the second detection voltage match. The actuator 212 receives the output of the differential circuit 130 shown in FIG. 2, and displaces the internal electrode 211 in accordance with the input voltage. As a result, feedback is applied, and the position of the internal electrode 211 is adjusted so that the first detection voltage and the second detection voltage match. This allows the voltage waveform of the power line to be detected with high accuracy while reducing phase error.

[0060] The above describes embodiments of the leakage current detection device and earth leakage current detection method of the present invention, but the leakage current detection device and earth leakage current detection method of the present invention are not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention. For example, in the above embodiment, an example has been described in which the phase error of the R-to-RT voltage of a three-phase power supply is corrected, but the present invention can also be applied to power supplies other than three-phase power supplies. Furthermore, in the above-described embodiment, an example in which two capacitive coupling sensors are used has been described, but the present invention can also be applied to a case in which three or more capacitive coupling sensors are used. [Industrial Applicability]

[0061] The present invention can be used to detect earth leakage current, particularly to measure the resistive component leakage current (Ior) contained in the leakage current, as well as to measure active power, reactive power, and power factor in a power meter, and can also be used in a phase detector. [Explanation of symbols]

[0062] 10 R-phase power line 20 T-phase power line 100 Device body 130 Differential Circuit 140, 141, 142 Low-pass filters 143 Changeover switch 152 Clamp Circuit 154 Comparator 156 Amplifier 210 R-phase capacitive coupling sensor 211 Internal electrode 212 Actuator 220 T-phase capacitively coupled sensor 310 Oscillator Circuit 311 Amplifier 312 Copper plate 321 First variable amplifier 322 Second variable amplifier 330 Comparison circuit 340 Addition Circuit 341,343 Bandpass Filter (BPF) 342,344 Detector circuit 350 Amplification factor correction circuit (digital position meter) 500 Leakage current detection device

Claims

1. a first capacitive coupling sensor that is capacitively coupled to a first power supply line of the multi-phase AC power supply; a second capacitive coupling sensor that is capacitively coupled to a second power supply line of the multi-phase AC power supply; a first detection circuit that converts a displacement current flowing through the first capacitive coupling sensor into a first detection voltage; a second detection circuit that converts a displacement current flowing through the second capacitive coupling sensor into a second detection voltage; a differential circuit that calculates a difference between the first detected voltage and the second detected voltage and outputs a voltage waveform between the first and second power supply lines; A non-contact voltage phase detection device comprising: and an adjustment device that adjusts the first coupling capacitance so that a first coupling capacitance in a capacitive coupling portion between the first power supply line and the first capacitive coupling sensor matches a second coupling capacitance in a capacitive coupling portion between the second power supply line and the second capacitive coupling sensor. A non-contact voltage phase detection device comprising:

2. The adjustment device includes an actuator that adjusts one or both of a distance between an electrode of the first capacitive coupling sensor and the first power supply line and a distance between an electrode of the second capacitive coupling sensor and the second power supply line so that the first detection voltage and the second detection voltage are equal to each other. A non-contact voltage phase detection device comprising:

3. a first capacitive coupling sensor that is capacitively coupled to a first power supply line of the multi-phase AC power supply; a second capacitive coupling sensor that is capacitively coupled to a second power supply line of the multi-phase AC power supply; a first detection circuit that converts a displacement current flowing through the first capacitive coupling sensor into a first detection voltage; a second detection circuit that converts a displacement current flowing through the second capacitive coupling sensor into a second detection voltage; a differential circuit that calculates a difference between the first detected voltage and the second detected voltage and outputs a voltage waveform between the first and second power supply lines; A non-contact voltage phase detection device comprising: a correction circuit that amplifies the first and second detection voltages by an amplification ratio that is the reciprocal of a capacitance ratio between a first coupling capacitance in a capacitive coupling section between the first power supply line and the first capacitive coupling sensor and a second coupling capacitance in a capacitive coupling section between the second power supply line and the second capacitive coupling sensor so that the capacitance ratio approaches 1:

1. A non-contact voltage phase detection device comprising:

4. The correction circuit includes: an oscillator circuit that outputs a correction signal having a signal frequency different from a frequency of the multi-phase AC power source; a first variable amplifier that amplifies or decreases the first detection voltage; a second variable amplifier that amplifies or decreases the second detection voltage; a comparison circuit that compares a voltage of the component of the signal frequency of the first detection voltage with a voltage of the component of the signal frequency of the second detection voltage; an amplification factor correction circuit that corrects the amplification factor of one or both of the first and second variable amplifiers in accordance with a comparison result of the comparator circuit so that a voltage of the signal frequency component of the first detection voltage and a voltage of the signal frequency component of the second detection voltage match; The non-contact voltage phase detection device according to claim 3 , further comprising:

5. an adder circuit that adds the first detection voltage and the second detection voltage; the comparison circuit determines, as a comparison result, a ratio of a difference between a voltage of the signal frequency components of the first detection voltage and the second detection voltage, the difference of which is calculated by the differential circuit, to a sum of a voltage of the signal frequency components of the first and second detection voltages, the sum of which is calculated by the adder circuit; The amplification factor correction circuit corrects the amplification factor of one or both of the first and second variable amplifiers when the ratio exceeds a predetermined value.

3. The non-contact voltage phase detection device according to claim 2.

6. converting a displacement current flowing through a first capacitively coupled sensor that is capacitively coupled to a first power supply line constituting a power supply line of the multi-phase AC power supply into a first detection voltage; converting a displacement current flowing through a second capacitively coupled sensor that is capacitively coupled to a second power supply line constituting another power supply line of the multi-phase AC power supply into a second detection voltage; A non-contact voltage phase detection method for generating a voltage waveform between the first and second power supply lines by calculating a difference between the first detected voltage and the second detected voltage, One or both of the first coupling capacitance and the second coupling capacitance are adjusted so that a first coupling capacitance in a capacitive coupling portion between the first power supply line and the first capacitive coupling sensor and a second coupling capacitance in a capacitive coupling portion between the second power supply line and the second capacitive coupling sensor are matched. A non-contact voltage phase detection method comprising:

7. converting a displacement current flowing through a first capacitively coupled sensor that is capacitively coupled to a first power supply line constituting a power supply line of the multi-phase AC power supply into a first detection voltage; converting a displacement current flowing through a second capacitively coupled sensor that is capacitively coupled to a second power supply line constituting another power supply line of the multi-phase AC power supply into a second detection voltage; A non-contact voltage phase detection method for generating a voltage waveform between the first and second power supply lines by calculating a difference between the first detected voltage and the second detected voltage, The first and second detection voltages are amplified by an amplification ratio that is the reciprocal of a capacitance ratio between a first coupling capacitance in a capacitive coupling portion between the first power supply line and the first capacitive coupling sensor and a second coupling capacitance in a capacitive coupling portion between the second power supply line and the second capacitive coupling sensor so that the capacitance ratio approaches 1:

1. A non-contact voltage phase detection method comprising:

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