Loop impedance tester and loop impedance measuring method

Abstract

To provide a loop impedance tester which improves reliability while suppressing cost, and a loop impedance measuring method.SOLUTION: In a loop impedance tester 1, a current generation unit 6 causes a first AC current ILE1 including a frequency component of a second frequency fs lower than a first frequency fm of a main power source 2 to flow between a live wire L and a ground line E. A VNE voltage acquisition circuit 9 measures a first AC voltage VNE1 between a neutral line N and the ground line E in a state where the first AC current ILE1 is caused to flow between the live wire L and the ground line E. A filter circuit 10 extracts a second AC voltage VNE2 for which a frequency component of the first frequency fm is reduced from the first AC voltage VNE1. Measurement control means 12 calculates impedance ZE of the ground line E from a current value of the first AC current ILE1 and a voltage value of the second AC voltage VNE2 and uses ZE to calculate a loop impedance ZLE.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a loop impedance tester and a loop impedance measuring method. [Background technology]

[0002] In power distribution equipment that supplies AC voltage from the main power source (commercial power source), the loop impedance between the live line L and the ground line E is measured when new electrical wiring is installed, when wiring is changed, during regular inspections, etc., and it is confirmed that the value is within safety specified values. In the power line shown in Figure 1, which includes three wires, a live wire L, a neutral wire N, and a ground wire E, the loop impedance between the live wire L and the ground wire E is the impedance Z of the live wire L. L and the impedance Z of the ground wire E E The sum of (Z L +Z E ).

[0003] Normally, a ground fault circuit interrupter 3 is installed in the power distribution equipment 14. If the live line L and the ground wire E are short-circuited, a leakage current flows through the ground wire E, and the ground fault circuit interrupter 3 detects the current difference between the live line L and the neutral wire N and trips, cutting off the circuit to prevent electric shock and fire. However, if the loop impedance between the live line L and the ground wire E is high, the ground fault circuit interrupter 3 will not operate because there is not enough leakage current to operate it. In that case, it is possible that this could lead to accidents such as electric shock or fire. This is why it is necessary to check the loop impedance between the live line L and the ground wire E.

[0004] Conventionally, the loop impedance between the live line L and the ground line E was measured by passing a large current between the live line L and the ground line E using the energy of the main power source 2 and detecting the voltage drop. The loop impedance between the live line L and the ground line E is small and needs to be measured in 0.01 Ω units, but to measure in 0.01 Ω units with this method, it is necessary to pass a large current of about 6 A between the live line L and the ground line E and detect the voltage drop. In this case, the earth leakage circuit breaker 3 installed in the distribution equipment 14 will trip. Therefore, it is necessary to bypass the earth leakage circuit breaker 3 by connecting the power supply side and the load side of the earth leakage circuit breaker 3 with an electric wire and perform the measurement without tripping the earth leakage circuit breaker 3, which takes time.

[0005] As a means for avoiding this, Patent Document 1 (JP Patent No. 4297774) discloses a method for calculating the loop impedance between the live line L and the ground line E by using a measurement value when a high current flows between the live line L and the neutral line N, not between the live line L and the ground line E, and a measurement value when a low current of 15 mA or less that does not activate the earth leakage circuit breaker 3 flows between the neutral line N and the ground line E. However, this method requires an energy supply source (current source) to be provided in the loop impedance tester for passing a current of 15 mA or less between the neutral line N and the ground line E, which leads to an increase in electronic components and an increase in costs. In addition, although it is possible to use a battery as the energy supply source, noise is often superimposed on the signal between the neutral line N and the ground line E of the power distribution equipment 14, and if the noise is 10 V, for example, a current source capable of outputting 10 V or more must be configured. There is a limit to generating a high output voltage from a dry cell with a voltage of 1.5 V when considering the miniaturization of the loop impedance tester, so there were some power distribution equipment that could not be measured.

[0006] Furthermore, Patent Document 2 (Patent Publication No. 6788259) discloses a method of measuring by passing a low current of 15 mA or less between the live line L and the ground line E, which does not operate the earth leakage circuit breaker 3, without using a neutral line N. However, when measuring the loop impedance in units of 0.01 Ω, it is necessary to separate the measurement signal of 15 mA x 0.01 Ω = 0.15 mV from the voltage of the main power supply 2 of 230 V (in Europe), and since the S / N ratio is very small (the ratio of noise to signal is large), the measurement results vary greatly and are unreliable. As a countermeasure, it is possible to increase reliability by acquiring a large amount of data and averaging it. However, it takes more than 10 seconds to measure, which leads to a decrease in the work efficiency of the inspection work, and it is difficult to obtain the same reliability as the results obtained in Patent Document 1. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 4297774 [Patent Document 2] Patent No. 6788259 Summary of the Invention [Problem to be solved by the invention]

[0008] SUMMARY OF THE PRESENT EMBODIMENTS Accordingly, an object of the present invention is to provide a highly reliable loop impedance tester and a loop impedance measuring method that can reduce costs. [Means for solving the problem]

[0009] A loop impedance tester 1 according to one aspect of the present invention measures a loop impedance Z between a live line L and a ground line E in a power line including a live line L supplying an AC voltage including a frequency component of a first frequency fm, a neutral line N, and a ground line E. LEIn order to measure the impedance of the live line L, the neutral line N, and the ground line E, a loop impedance tester is connected to the live line L, the neutral line N, and the ground line E, and includes a first measurement circuit 15, a current generating unit 6, and a second measurement circuit V NE The device includes a voltage acquisition circuit 9, a filter circuit 10, and a measurement control means 12. The first measurement circuit 15 measures a first voltage value V between the live line L and the neutral line E in a state where no load is connected between the live line L and the neutral line N. LE1 and a second voltage value V between the live line L and the neutral line N with a load resistor R connected between the live line L and the neutral line N. LN2 and a third voltage value V between the live wire L and the ground wire E. LE2 And, measure. The current generating unit 6 generates a first AC current I that includes a frequency component of a second frequency fs that is lower than the first frequency fm between the live line L and the ground line E. LE1 Flush. V NE The voltage acquisition circuit 9 detects a first AC current I between the live line L and the ground line E. LE1 The first AC voltage V between the neutral wire N and the earth wire E with NE1 Measure. The filter circuit 10 is connected to a first AC voltage V NE1 A second AC voltage V obtained by reducing the frequency component of the first frequency fm from NE2 Take out. The measurement and control means 12 measures the value of the load resistance R and the first, second and third voltage values ​​V LE1 , V LN2 and V LE2 and the impedance Z of the live line L L Calculate the first AC current I LE1 and the second AC voltage V NE2 The impedance Z of the ground wire E from the voltage value E Calculate the impedance Z L and Z E from loop impedance Z LE Calculate. [Brief description of the drawings]

[0010] [Figure 1]FIG. 1 is a circuit diagram showing a schematic configuration of a loop impedance tester 1 according to an embodiment of the present invention that is connected to a power distribution facility 14. [Diagram 2] FIG. 2 is a circuit diagram illustrating measurement of the impedance ZL of the live line L in the embodiment of the present invention. [Diagram 3] FIG. 3 is a circuit diagram illustrating measurement of the impedance ZL of the live line L in the embodiment of the present invention. [Figure 4] FIG. 4 is a circuit diagram for explaining measurement of the impedance ZE of the ground line E in the embodiment of the present invention. [Diagram 5] 5(A) to 5(D) are waveform diagrams illustrating a procedure for measuring the impedance ZE of the ground wire E in the embodiment of the present invention. [Figure 6] FIG. 6 is a circuit diagram showing details of the current generating unit 6 shown in FIGS. [Figure 7] 7(A) to 7(H) are waveform diagrams illustrating the operation of the current generating unit 6. In FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. The embodiment described below shows an example of the present invention, and does not limit the contents of the present invention. Furthermore, not all of the configurations and operations described in the embodiment are necessarily essential as the configurations and operations of the present invention. Note that the same components are given the same reference symbols, and duplicated explanations will be omitted.

[0012] <1. Configuration of Loop Impedance Tester 1> FIG. 1 is a circuit diagram showing a schematic configuration of a loop impedance tester 1 according to an embodiment of the present invention, which is connected to a power distribution facility 14. A live line L has an impedance Z L and the neutral conductor N has impedance Z N and the ground wire E has impedance Z E It has an impedance Z L corresponds to the first impedance, and impedance ZE corresponds to the second impedance.

[0013] The loop impedance tester 1 is connected to the live line L terminal 4 L and N terminal 4 connected to neutral wire N N and E terminal 4 connected to ground wire E E The loop impedance tester 1 further includes a switch SW1, a load resistor R, a current generating unit 6, and a V LN Voltage acquisition circuit 7 and V LE Voltage acquisition circuit 8 and V NE The device includes a voltage acquisition circuit 9, a filter circuit 10, an A / D conversion circuit 11, a measurement control means 12, and an input / output means 13. LN Voltage acquisition circuit 7 and V LE The voltage acquisition circuit 8 constitutes a first measurement circuit 15. NE The voltage acquisition circuit 9 constitutes a second measurement circuit.

[0014] The switch SW1 and the load resistor R are connected in series between the live line L and the neutral line N. The switch SW1 is normally off and does not conduct electricity. The switch SW1 is connected to the impedance Z L When measuring, turn it on to connect the main power supply 2 to the load resistance R, and a current I LN (Figure 3) is poured.

[0015] V LN The voltage acquisition circuit 7 is connected between the live line L and the neutral line N, and the voltage value V between the live line L and the neutral line N when the switch SW1 is in the off state is LN1 (Figure 2) and the second voltage value V, which is the voltage value between the live line L and neutral line N when switch SW1 is in the on state. LN2 (Figure 3) and

[0016] V LE The voltage acquisition circuit 8 is connected between the live line L and the ground line E, and acquires a first voltage value V LE1 (Figure 2) and the third voltage value V, which is the voltage value between the live line L and the ground line E when the switch SW1 is in the on state. LE2(Figure 3) and

[0017] The current generating unit 6 is connected between the live line L and the ground line E. The current generating unit 6 is normally off and does not conduct electricity. The impedance Z of the ground line E E When measuring the current, the first AC current I is generated between the live wire L and the ground wire E by using the energy of the main power supply 2. LE1 (Figure 4) is passed. The first AC current I LE1 The current value is limited to 15 mA or less, which is lower than the threshold value that operates the earth leakage breaker 3.

[0018] V NE The voltage acquisition circuit 9 is connected between the neutral line N and the ground line E, and acquires a first AC voltage V NE1 (Figure 4) is obtained.

[0019] The filter circuit 10 is V NE The first AC voltage V acquired by the voltage acquisition circuit 9 NE1 and a second AC voltage V consisting of a voltage signal of a second frequency fs. NE2 (Figure 4) is output.

[0020] The A / D conversion circuit 11 is V LN Voltage acquisition circuit 7, V LE The magnitude of the amplitude of the output signal from the voltage acquisition circuit 8 and the filter circuit 10 is measured and converted into a digital signal.

[0021] The measurement control means 12 controls the switch SW1 and the current generating unit 6, and also calculates the loop impedance Z between the live line L and the ground line E based on the measurement value by the A / D conversion circuit 11. LE Calculate.

[0022] The input / output means 13 includes all or any of a display, an indicator lamp, a speaker, a button, and an operation panel. The input / output means 13 visually notifies the user of the measurement result by displaying it, or audibly notifies the user by outputting a voice, and further receives an instruction to switch between various test modes by inputting an operation from the user.

[0023] <2. Operation of Loop Impedance Tester 1> 2 to 4 show the loop impedance Z between the live line L and the ground line E in the embodiment of the present invention. LE This is a circuit diagram explaining the measurement method of Z LE The measurement method is to measure the impedance Z of the live line L. L (Fig. 2, Fig. 3) and the impedance Z of the ground wire E E (Figure 4) and Z L and Z E 2 to 4 show the same loop impedance tester 1 as in FIG. 1, but some components that are not used in each procedure are omitted.

[0024] <2-1. Impedance Z of live line L L Measurements > <2-1-1. Voltage value V LN1 and the first voltage value V LE1 Measurements > As shown in Figure 2, in a no-load state with switch SW1 off, the voltage V between the live line L and neutral line N is LN1 V LN The voltage is acquired by the voltage acquisition circuit 7. Similarly, the first voltage value V between the live line L and the ground line E in a no-load state is LE1 V LE The voltage is acquired by the voltage acquisition circuit 8. LN1 corresponds to the voltage value of the main power supply 2, and the first voltage value V LE1 corresponds to the sum of the earth voltage and the voltage of the main power source 2. The voltage value V LN1 and the first voltage value V LE1 are measured by the A / D conversion circuit 11 in FIG. 1 and are converted into digital values.

[0025] <2-1-2. Second voltage value V LN2 and a third voltage value V LE2 Measurements > As shown in Figure 3, turn on switch SW1 and connect main power supply 2 to L terminal 4. L and N terminal 4 NThis connects the load resistor R to the live wire L and the neutral wire N. LN With the current flowing, the second voltage value V between the live wire L and the neutral wire N LN2 V LN The voltage is acquired by the voltage acquisition circuit 7. Similarly, the current I LN With current flowing, the third voltage value V between the live wire L and the ground wire E LE2 V LE The second voltage value V LN2 and a third voltage value V LE2 are measured by the A / D conversion circuit 11 and converted into digital values.

[0026] <2-1-3.Z L Calculation of > Second voltage value V LN2 is the current I LN Since this is the voltage across the load resistance R when a current I LN can be calculated using the following formula (1). I LN =V LN2 / R ... (1) To ensure the desired measurement accuracy, the current I LN The value of the load resistor R is set so that the current I LN flows between the live line L and the neutral line N, but does not flow to the earth wire E, so it does not trip the earth leakage breaker 3.

[0027] The third voltage value V LE2 is the earth potential and the current I LN The impedance Z of the load resistance R and neutral line N when N The first voltage value V is the sum of the voltage across the two terminals of the power supply 1 and the voltage across the ground voltage V. LE1 to a third voltage value V LE2 Subtracting this, the impedance Z of the live line L L This is the voltage across both ends. Therefore, Z L is expressed by the following equation (2). Z L =(V LE1 -V LE2 ) / I LN... (2)

[0028] From equation (1) and equation (2), Z L can be calculated using the following formula (3). Z L =(V LE1 -V LE2 ) / (V LN2 / R) =(V LE1 -V LE2 )R / V LN2 ... (3)

[0029] The voltage value of main power supply 2 is V LN1 From the above, the current I LN The second voltage value V is the voltage value across the load resistance R when LN2 Subtracting this, the impedance Z of the live line L L and the impedance Z of the neutral wire N N The voltage across both ends is calculated. Therefore, the loop impedance Z between the live wire L and the neutral wire N is LN is expressed by the following equation (4). Z LN =(V LN1 -V LN2 ) / I LN ... (4)

[0030] From equation (1) and equation (4), Z LN can be calculated using the following formula (5). Z LN =(V LN1 -V LN2 ) / (V LN2 / R) =(V LN1 -V LN2 )R / V LN2 ... (5)

[0031] Z LN is the loop impedance used to calculate the short circuit current that flows when a short circuit occurs between the live line L and the neutral line N. LN is used when selecting an overcurrent protection device, and is used to confirm that the overcurrent protection device trips normally. LETogether with the measurement of Z, equation (5) LN It is also possible to measure

[0032] <2-2. Impedance Z of ground wire E E Measurements > <2-2-1. First AC current I LE1 Generation of > As shown in FIG. 4, a first AC current I, which is a known current, is generated between the live line L and the ground line E from the main power supply 2 via the current generating unit 6. LE1 The first alternating current I LE1 is an AC constant current whose peak value is constant and which is not affected even when the voltage of the main power supply 2 fluctuates, has a half-wave rectified waveform synchronized with the AC voltage of the main power supply 2, and switches the polarity of the half-wave rectification at a second frequency fs (period 1 / fs) which is lower than a first frequency fm (e.g., 50 Hz or 60 Hz) which is the frequency of the main power supply 2. Such a first alternating current I LE1 can be generated using the main power supply 2 as an energy source. This eliminates the need to provide a special current source inside the loop impedance tester 1.

[0033] First alternating current I LE1 Since the first AC current I flows between the live wire L and the ground wire E, it may be detected as a ground fault by the earth leakage circuit breaker 3. Since most earth leakage circuit breakers have a rated sensitivity current of 30 mA, in order to prevent the earth leakage circuit breaker 3 from tripping, the first AC current I LE1 It is desirable to set the current to 15mA or less, which is half the rated sensitivity current.

[0034] <2-2-2. First AC voltage V NE1 Measurement and noise elimination> Next, the first alternating current I LE1 The first AC voltage V between the neutral wire N and the ground wire E when NE1 V NE The first AC voltage V NE1 is the impedance Z of the ground wire E E The first alternating current I LE1This includes the voltage signal generated by the flow of

[0035] However, between the neutral conductor N and the ground conductor E of the power distribution equipment 14, there is often a leakage current flowing through the ground conductor E and a load current flowing from an electrical device to the neutral conductor N. For this reason, the first AC voltage V NE1 The waveform of the first AC current I LE1 The waveform is not completely proportional to the waveform of fm, but contains noise. Normally, the noise component is composed of a signal whose main component is the frequency component of the first frequency fm and also contains harmonic components of the first frequency fm.

[0036] 5(A) to 5(D) show the impedance Z of the ground line E in the embodiment of the present invention. E FIG. 5(A) is a waveform diagram illustrating the measurement procedure of the first AC current I LE1 The waveform of the first AC voltage V NE1 When the frequency of the noise contained in is the same as the first frequency fm as shown in FIG. 5(B), the first AC current I LE1 In proportion to Z E The first AC voltage V NE1 The waveform of the first AC voltage V is shown in FIG. 5(C). By passing this waveform through the filter circuit 10 of FIG. NE1 5(D) is obtained by removing frequency components higher than the second frequency fs from the second AC voltage V NE2 The second AC voltage V NE2 is the impedance Z of the ground wire E E It should be noted that "removing" does not necessarily mean making it completely zero, but also includes reducing the frequency component of the first frequency fm. Second AC voltage V NE2 is measured by the A / D conversion circuit 11 in FIG. 1 and converted into a digital value.

[0037] Here, the noise to be removed is mainly frequency components of the first frequency fm, and since the first frequency fm is higher than the second frequency fs, a low-pass filter can be used as the filter circuit 10. Alternatively, since various noise components including frequency components other than the first frequency fm may be superimposed between the neutral conductor N and the ground conductor E, reliability can be improved by using a band-pass filter or lock-in amplifier that extracts only the signal component of the second frequency fs.

[0038] If a method of simply passing an AC current between the live line L and the ground line E using the main power supply 2 as the energy source is used, the frequency of the AC current will be 50 Hz or 60 Hz, the same as the first frequency fm. In this case, it will be difficult to distinguish between the superimposed noise and the desired signal component when measuring the voltage between the neutral line N and the ground line E, which will lead to a decrease in the reliability of the measurement results. Therefore, in this embodiment, the first AC current I LE1 5(A), the waveform of the first AC voltage V is a half-wave rectified waveform synchronized with the AC voltage of the main power supply 2, and the polarity of the half-wave rectification is switched at a second frequency fs lower than the first frequency fm. NE1 Therefore, noise components mainly having the frequency component of the first frequency fm can be easily removed.

[0039] In addition, the voltage of the main power supply 2 often contains distortion and noise, and is not an ideal sine wave. LE1 is affected by distortion or noise in the waveform of the main power supply 2 and contains distortion and noise just like the voltage of the main power supply 2, the error in the measurement result will also increase. So, the first AC current I LE1 It is desirable that the AC constant current have a constant peak value and are not affected even if the voltage of the main power supply 2 fluctuates.

[0040] <2-2-3.Z E Calculation of > Second AC voltage V NE2is the impedance Z of the ground wire E E The first alternating current I LE1 The first AC voltage V NE1 Since the noise component has been removed from Z E is the first alternating current I LE1 and the second AC voltage V NE2 Using the voltage value, it is expressed by the following equation (7). Z E =V NE2 / I LE1 ... (7)

[0041] As mentioned above, noise is superimposed between the neutral wire N and the ground wire E, but in most cases this noise is no more than about 20V. The impedance Z of the ground wire E is E The first alternating current I LE1 The magnitude of the signal when E When the resistance is 0.01Ω, it is 0.01Ω×15mA=0.15mV, which is very small. However, if we obtain the voltage between the live line L and the ground line E, which includes the 230V of the main power supply 2, Z E Compared to measuring the signal-to-noise ratio, the signal-to-noise ratio has been improved by more than 10 times, enabling more accurate measurements to be performed in a shorter time.

[0042] <2-3.Z L and Z E Calculating the sum of Finally, based on equations (3) and (7), the loop impedance Z between the live line L and the ground line E is calculated. LE is calculated using the following formula (8). Z LE =Z L +Z E =(V LE1 -V LE2 )R / V LN2 +V NE2 / I LE1 ... (8)

[0043] 3. Configuration of current generating unit 6 Fig. 6 is a circuit diagram showing details of the current generating unit 6 shown in Fig. 1 and Fig. 4. The current generating unit 6 includes a full-wave rectifier circuit 61, a comparator 62, a control signal generating unit 63, a D / A converter 64, and a constant current circuit 65.

[0044] The full-wave rectifier circuit 61 is composed of a bridge diode. The AC input terminals 61a and 61b of the full-wave rectifier circuit 61 are connected between the live line L and the ground line E, and the positive output terminal 61c is connected to a constant current circuit 65. The full-wave rectifier circuit 61 outputs a positive pulsating voltage by inverting the negative polarity portion of the AC voltage waveform between the live line L and the ground line E.

[0045] The non-inverting input terminal (+) of the comparator 62 is connected to the live line L, and the inverting input terminal (-) is connected to the ground line E. The output terminal of the comparator 62 is connected to the control signal generating unit 63. The comparator 62 outputs a zero-cross signal including a high or low output voltage according to the polarity of the voltage between the live line L and the ground line E.

[0046] The control signal generating unit 63 is composed of a processing device such as a microcomputer. The control signal generating unit 63 outputs a digital signal for controlling the current waveform of the current flowing through the constant current circuit 65 to the D / A converter 64 in synchronization with the zero cross signal according to a program stored in the memory. The output terminal of the D / A converter 64 is connected to a constant current circuit 65 .

[0047] The constant current circuit 65 includes an operational amplifier 66, a FET 67, and a detection resistor R1. The output terminal of the D / A converter 64 is connected to the non-inverting input terminal (+) of the operational amplifier 66, and the output terminal of the operational amplifier 66 is connected to the gate terminal of the FET 67. The drain terminal of the FET 67 is connected to the positive output terminal 61c of the full-wave rectifier circuit 61, and the source terminal is connected to the detection resistor R1, one side of which is grounded, and the inverting input terminal (-) of the operational amplifier 66. A bipolar transistor may be used instead of the FET 67.

[0048] <4. Operation of current generating unit 6> Figures 7(A) to 7(H) are waveform diagrams illustrating the operation of the current generating unit 6. Figure 7(A) shows the waveform of the voltage between the live line L and the ground line E.

[0049] The waveform of the output voltage of the full-wave rectifier circuit 61 (FIG. 7B) is a waveform obtained by full-wave rectifying the voltage between the live line L and the ground line E. However, the current output from the full-wave rectifier circuit 61 is regulated by the constant current circuit 65.

[0050] The comparator 62 outputs a zero-cross signal (FIG. 7(C)) synchronized with the timing when the polarity of the voltage between the live line L and the ground line E switches at the first frequency fm. The zero-cross signal is composed of a square wave. The zero-cross signal is input to the control signal generator 63.

[0051] The control signal generating unit 63 uses the timing at which the polarity of the zero-cross signal switches at the first frequency fm to generate the first AC current I LE1 The digital signal is input to a D / A converter 64.

[0052] The D / A converter 64 converts the digital signal into an analog voltage signal (FIG. 7(D)). When the waveform of this voltage signal is enlarged, it has a stepped shape as shown in FIG. 7(E). The voltage signal is input to the non-inverting input terminal (+) of the operational amplifier 66.

[0053] The constant current circuit 65 monitors the feedback signal from the detection resistor R1 with the operational amplifier 66, and passes a current (FIG. 7(F)) proportional to the voltage of the voltage signal (FIG. 7(D)) input from the D / A converter 64. This current is a constant current that is not affected by fluctuations in the amplitude of the voltage (FIG. 7(A)) between the live line L and the ground line E.

[0054] When a current flows through the constant current circuit 65, a first AC current I flows between the live line L and the ground line E. LE1 (FIG. 7(G)) flows. The length of each of the periods t1 to t7 shown in FIG. 7(G) corresponds to half the cycle 1 / fm of the main power supply 2. The current flowing through the constant current circuit 65 (FIG. 7(F)) is a unipolar current, but the first AC current I LE1 However, during each of periods t1, t3, and t6, no current flows through the constant current circuit 65, so the output current of the full-wave rectifier circuit 61 is cut off, and the first AC current I LE1 The first AC current I LE1 The timing at which the signal is set to 0 is determined by a digital signal generated by the control signal generating unit 63.

[0055] First alternating current I LE1 By switching the timing at which the first AC current I LE1 For example, the polarity of the first AC current I can be switched at the timing when the subscript attached to t in the periods t1 to t7 is an odd number (for example, t1 and t3), that is, at the timing when the voltage between the live line L and the ground line E becomes positive. LE1 0, and the first AC current I LE1 By passing the first AC current I LE1 On the other hand, when the subscript attached to t becomes an even number (for example, t6), that is, when the voltage between the live line L and the ground line E becomes negative, the first AC current I LE1 is set to 0, and the first AC current I LE1 By passing the first AC current I LE1 The first AC current I LE1 The polarity switching is performed with a period 1 / fs which is longer than the period 1 / fm of the main power supply 2.

[0056] The current generating unit 6 can also be used when the loop impedance tester 1 functions as an earth leakage circuit breaker tester. The earth leakage circuit breaker tester generates a second AC current I as a pseudo leakage current between the live line L and the ground line E. LE2 By passing a current (FIG. 7(H)), the earth leakage breaker 3 of the power distribution facility 14 is tripped, and the time taken from the occurrence of the earth leakage to the tripping is measured.

[0057] Second AC current ILE2 is a first AC current I that is greater than the threshold for tripping the earth leakage circuit breaker 3 and does not include pause periods such as t1, t3, and t6. LE1 However, the second alternating current I LE2 In order to perform accurate measurement, it is desirable that the main power source 2 be a constant AC current with a constant peak value that is not affected by waveform distortion or noise. LE1 According to this embodiment, the first AC current I LE1 The first mode passes an alternating current I LE2 You can switch between a first mode and a second mode.

[0058] <5. Effects of the embodiment> (1) According to the embodiment of the present invention described above, the current generating unit 6 generates a first AC current I between the live line L and the ground line E, the first AC current I including a frequency component of a second frequency fs lower than the first frequency fm of the main power supply 2. LE1 V NE The voltage acquisition circuit 9 detects a first AC current I between the live line L and the ground line E. LE1 The first AC voltage V between the neutral wire N and the earth wire E with NE1 The filter circuit 10 measures a first AC voltage V NE1 A second AC voltage V obtained by reducing the frequency component of the first frequency fm from NE2 The measurement and control means 12 extracts the first AC current I LE1 and the second AC voltage V NE2 The impedance Z of the ground wire E from the voltage value E Calculate Z E Using the loop impedance Z LE Calculate. According to this, the first AC voltage V NE1 A second AC voltage V obtained by reducing the frequency component of the first frequency fm from NE2 By extracting the loop impedance Z LESince the measurement can be performed in a short time and there is no need to provide a special current source, an inexpensive and small loop impedance tester 1 can be realized.

[0059] (2) According to the embodiment of the present invention, the control signal generating unit 63 of the current generating unit 6 generates the first AC current I by utilizing the timing at which the polarity of the voltage between the live line L and the ground line E switches at the first frequency fm. LE1 The polarity of the first input signal is switched at a second frequency fs. According to this, by utilizing the timing at which the polarity of the voltage between the live line L and the ground line E is switched, a control signal synchronized with this timing is generated, and the first AC current I LE1 The polarity of the signal can be switched.

[0060] (3) According to the embodiment of the present invention, the current generating unit 6 generates a first AC current I by switching the timing of cutting off the full-wave rectifier circuit 61 connected between the live line L and the ground line E and the output current of the full-wave rectifier circuit 61 at the first frequency fm. LE1 and a control signal generating unit 63 for switching the polarity of the signal. According to this, the output current of the full-wave rectifier circuit 61 is cut off at the timing when the voltage between the live line L and the ground line E becomes positive, so that the first AC current I LE1 is set to negative polarity, and the output current of the full-wave rectifier circuit 61 is cut off at the timing when the voltage between the live line L and the ground line E becomes negative polarity, thereby generating a first AC current I LE1 can be positive polarity.

[0061] (4) According to the embodiment of the present invention, the control signal generating unit 63 of the current generating unit 6 can be switched between a first mode and a second mode. In the first mode, the first AC current I LE1 The loop impedance Z is reduced by making the current value smaller than the threshold value that trips the earth leakage breaker 3 connected between the live line L and the neutral line N. LE The second mode is a mode that allows measurement of a second AC current I having a current value greater than a threshold between the live wire L and the ground wire E. LE2This is a mode in which the loop impedance tester 1 can function as a ground fault circuit interrupter tester by passing a current through it. According to this, the loop impedance Z LE The measurement function and the function as an earth leakage breaker tester can be switched, and the circuit of the current generating unit 6 can be shared. [Explanation of symbols]

[0062] 1...Loop impedance tester, 2...Main power supply, 3...Earth leakage breaker, 4 L ...L terminal, 4 N ...N terminal, 4 E ...E terminal, 6...Current generator, 7...V LN Voltage acquisition circuit, 8...V LE Voltage acquisition circuit, 9...V NE Voltage acquisition circuit, 10...filter circuit, 11...A / D conversion circuit, 12...measurement and control means, 13...input / output means, 14...power distribution equipment, 15...first measurement circuit, 61...full-wave rectifier circuit, 61a, 61b...AC input terminal, 61c...positive output terminal, 62...comparator, 63...control signal generation unit, 64...D / A converter, 65...constant current circuit, 66...operational amplifier, 67...FET, L...live line, N...neutral line, E...ground line, R...load resistor, R1...detection resistor, SW1...switch

Claims

1. A loop impedance Z between a live line L that supplies an AC voltage including a frequency component of a first frequency fm, a neutral line N, and a ground line E in a power line including the live line L and the ground line E. ＬＥ A loop impedance tester connected to the live line L, the neutral line N, and the ground line E to measure A first voltage value V between the live line L and the neutral line N in a state where no load is connected between the live line L and the neutral line N ＬＥ１ and a second voltage value V between the live line L and the neutral line N in a state where a load resistor R is connected between the live line L and the neutral line N. ＬＮ２ and a third voltage value V between the live line L and the ground line E. ＬＥ２ A first measurement circuit for measuring A first AC current I having a frequency component of a second frequency fs lower than the first frequency fm flows between the live line L and the ground line E. ＬＥ１ A current generating unit that generates a current The first AC current I flows between the live line L and the ground line E. ＬＥ１ A first AC voltage V between the neutral wire N and the ground wire E in a state where ＮＥ１ A second measurement circuit for measuring The first AC voltage V ＮＥ１ A second AC voltage V obtained by reducing the frequency component of the first frequency fm from ＮＥ２ A filter circuit that extracts A measurement control means, The value of the load resistance R and the first, second and third voltage values ​​V ＬＥ１ , V ＬＮ２ and V ＬＥ２ Therefore, the first impedance Z of the live line L Ｌ Calculate The first alternating current I ＬＥ１ and the second AC voltage V ＮＥ２ The second impedance Z of the ground line E is calculated from the voltage value of Ｅ Calculate The first and second impedances Z Ｌ and Z Ｅ from the loop impedance Z ＬＥ Calculate The measurement control means; Including, The current generating unit is a full-wave rectifier circuit including a first AC input terminal connected to the live line L, a second AC input terminal connected to the ground line E, and an output terminal for outputting an output current of one polarity; A control signal generating unit; Including, The control signal generating unit a first process for cutting off the output current when the voltage between the live line L and the ground line E is positive, and for allowing the output current to flow when the voltage between the live line L and the ground line E is negative, thereby making the first AC current I LE1 flowing between the live line L and the ground line E via the first and second AC input terminals negative; a second process for cutting off the output current when the voltage between the live line L and the ground line E is negative, and for allowing the output current to flow when the voltage between the live line L and the ground line E is positive, thereby making the first AC current I LE1 flowing between the live line L and the ground line E via the first and second AC input terminals positive; by utilizing the timing at which the polarity of the voltage between the live line L and the ground line E switches at the first frequency fm, thereby switching the polarity of the first AC current I LE1 at the second frequency fs.

2. The current generating unit further includes a comparator that outputs an output signal according to the polarity of the voltage between the live line L and the ground line E, The control signal generation unit switches between the first processing and the second processing based on the output signal.

2. The loop impedance tester of claim 1.

3. the current generating unit further includes a transistor connected to the output terminal and regulating the output current; The control signal generating unit In the first process, when the voltage between the live line L and the ground line E is positive, the transistor cuts off the output current, and when the voltage between the live line L and the ground line E is negative, the transistor passes the output current; In the second process, when the voltage between the live line L and the ground line E is negative, the transistor cuts off the output current, and when the voltage between the live line L and the ground line E is positive, the transistor passes the output current. The control signal is output so that 2. The loop impedance tester of claim 1.

4. A loop impedance tester connected to a live line L supplying an AC voltage including a frequency component of a first frequency fm, a neutral line N, and a ground line E in a power line including the live line L, the neutral line N, and a ground line E to measure a loop impedance ZLE between the live line L and the ground line E, comprising: a first measurement circuit that measures a first voltage value V LE1 between the live line L and the ground line E in a state where no load is connected between the live line L and the neutral line N, and a second voltage value V LN2 between the live line L and the neutral line N and a third voltage value V LE2 between the live line L and the ground line E in a state where a load resistor R is connected between the live line L and the neutral line N; a current generating unit that causes a first AC current I LE1 including a frequency component of a second frequency fs lower than the first frequency fm to flow between the live line L and the ground line E; a second measurement circuit that measures a first AC voltage V NE1 between the neutral wire N and the ground wire E in a state in which the first AC current I LE1 is flowing between the live wire L and the ground wire E; a filter circuit that extracts a second AC voltage V NE2 by reducing a frequency component of the first frequency fm from the first AC voltage V NE1 ; A measurement control means, calculating a first impedance Z L of the live line L from the value of the load resistance R and the first, second and third voltage values ​​V LE1 , V LN2 and V LE2 ; calculating a second impedance Z E of the ground line E from the current value of the first AC current I LE1 and the voltage value of the second AC voltage V NE2 ; calculating the loop impedance Z LE from the first and second impedances Z L and Z E ; The measurement control means; Including, The current generating unit is The first alternating current I ＬＥ１ The loop impedance Z ＬＥ A first mode enabling the measurement of A second AC current I having a current value greater than the threshold between the live line L and the ground line E. ＬＥ２ a second mode in which the loop impedance tester functions as a ground fault circuit interrupter tester by passing a current A control signal generating unit that can be switched to Loop impedance tester.

5. A loop impedance Z between a live line L that supplies an AC voltage including a frequency component of a first frequency fm, a neutral line N, and a ground line E in a power line including the live line L and the ground line E. ＬＥ A loop impedance measurement method for measuring a loop impedance, comprising: A first voltage value V between the live line L and the neutral line N in a state where no load is connected between the live line L and the neutral line N ＬＥ１ and a second voltage value V between the live line L and the neutral line N in a state where a load resistor R is connected between the live line L and the neutral line N. ＬＮ２ and a third voltage value V between the live line L and the ground line E. ＬＥ２ Measure and A first AC current I having a frequency component of a second frequency fs lower than the first frequency fm flows between the live line L and the ground line E. ＬＥ１ The The first AC current I flows between the live line L and the ground line E. ＬＥ１ A first AC voltage V between the neutral wire N and the ground wire E in a state where ＮＥ１ Measure and The first AC voltage V ＮＥ１ A second AC voltage V obtained by reducing the frequency component of the first frequency fm from ＮＥ２ Take out the The value of the load resistance R and the first, second and third voltage values ​​V ＬＥ１ , V ＬＮ２ and V ＬＥ２ Therefore, the first impedance Z of the live line L Ｌ Calculate The first alternating current I ＬＥ１ and the second AC voltage V ＮＥ２ The second impedance Z of the ground line E is calculated from the voltage value of Ｅ Calculate The first and second impedances Z Ｌ and Z Ｅ from the loop impedance Z ＬＥ Calculate Including, The first AC current I LE1 is A full-wave rectifier circuit including a first AC input terminal connected to the live line L, a second AC input terminal connected to the ground line E, and an output terminal for outputting a unipolar output current, a first process for cutting off the output current when the voltage between the live line L and the ground line E is positive, and for allowing the output current to flow when the voltage between the live line L and the ground line E is negative, thereby making the first AC current I LE1 flowing between the live line L and the ground line E via the first and second AC input terminals negative; a second process for cutting off the output current when the voltage between the live line L and the ground line E is negative, and for allowing the output current to flow when the voltage between the live line L and the ground line E is positive, thereby making the first AC current I LE1 flowing between the live line L and the ground line E via the first and second AC input terminals positive; The polarity of the first AC current I LE1 is switched at the second frequency fs by utilizing the timing at which the polarity of the voltage between the live line L and the ground line E is switched at the first frequency fm. A method for measuring loop impedance by generating a loop impedance.

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