JP4778922B2 - Ground resistance measuring method and ground resistance measuring apparatus - Google Patents

Description

  The present invention relates to a ground resistance measuring method and a ground resistance measuring apparatus for measuring the ground resistance of a ground electrode embedded in the ground without using an auxiliary electrode.

  Conventionally, a three-electrode method has been used as a method for measuring the ground resistance of a ground electrode embedded in the ground. While this method has excellent measurement accuracy, there is a problem in that it is necessary to drive the auxiliary electrode into the ground during measurement.

  On the other hand, in recent years, a ground resistance measurement method that can easily measure the ground resistance without using an auxiliary electrode has been proposed (see, for example, Patent Document 1). As shown in the block diagram of FIG. 17, the measuring device used in this method includes a ground electrode disposed on the ground, a return line disposed on the ground, a coil, and an oscillator inside the device 300. At the time of measurement, as shown in FIG. 18, it is assumed that the impedance between the return line and the ground is only the capacitance C (unknown number), the ground resistance Rg, the internal resistance Ri, and the coil L inside the apparatus. And the impedance at the resonance point in the RLC series resonance circuit composed of the capacitance C.

Specifically, as shown in the flowchart of FIG. 19, the impedance of the series resonant circuit is measured while changing the frequency f of the oscillator (S31). The minimum impedance value is measured as a loop resistance (S32). Since the internal resistance Ri is known, the ground resistance Rg is obtained (S32). This method has recently been put into practical use since the measurement accuracy is good when the ground resistance is in the range of 100Ω to 500Ω.
Japanese Patent No. 2935229

  However, in the case of measuring a lower ground resistance by the conventional single electrode ground resistance measuring method, not only the capacitance C between the return line and the ground but also the influence of the ground return impedance cannot be ignored. The graph of FIG. 20 is a graph showing the measurement accuracy of the ground resistance by the conventional single electrode ground resistance measurement method. Circles in the figure indicate measurement values obtained by the single electrode ground electrode measurement method, and diamonds in the figure indicate measurement errors. The measurement error is an error from the true value when the measured value by the three-electrode method indicated by the straight line in the figure is regarded as the true value.

  As shown by the dotted line arrow in the figure, when the ground resistance of the measurement object is reduced to 100Ω or less in the conventional single electrode ground resistance measurement method, not only the capacitance C between the return line and the ground but also the ground return impedance. Since the influence cannot be ignored, there is a problem that the measurement accuracy is deteriorated because the error is enlarged as compared with the three-electrode method.

  In view of the above problems, it is an object of the present invention to reduce measurement errors caused by ground return impedance and improve measurement accuracy of a low ground resistance.

According to a first aspect of the present invention, there is provided a ground resistance measuring method comprising: a first closed-loop circuit formed between a ground electrode having one end embedded in the ground; an oscillator; and a first metal member disposed on the ground; A second closed loop circuit formed between a ground electrode, the oscillator, the variable inductance element, and a second metal member disposed on the ground; the first metal member; the oscillator; the variable inductance element; A ground resistance measuring method for measuring a ground resistance using a ground resistance measuring device switchable by a switching means with a third closed loop circuit formed with a second metal member, wherein the switching means To switch to the first closed-loop circuit, change the frequency of the oscillator to resonate the first closed-loop circuit, and use an impedance meter to change the first closed-loop circuit between the first metal member and the ground. A first step of measuring a first loop resistance including a ground return impedance of the first and a second closed loop circuit is switched by the switching means, and the frequency of the oscillator is resonated when the first closed loop circuit resonates. While maintaining the frequency, the inductance of the variable inductance element is changed to resonate the second loop circuit, and the impedance measuring instrument includes a second ground return impedance between the second metal member and the ground. A second step of measuring a second loop resistance; and the switching means switches to the third closed loop circuit to maintain the frequency of the oscillator at the frequency when the first closed loop circuit resonates and the variable. The inductance of the inductance element is changed to the inductance when the second closed loop circuit resonates. A third step of measuring a third loop resistance including the first ground return impedance and the second ground return impedance by means of an impedance measuring instrument, and the first and second loop resistances. And a fourth step of calculating a ground resistance by subtracting the third loop resistance from the added value and dividing by 2 .

  In the present invention, a ground resistance measuring device including a ground electrode, one end of which is embedded in the ground, a variable inductance circuit, and a first metal member and a second metal member disposed on the ground is used. The loop resistance is measured while switching to a closed loop circuit of three different paths. In the first closed-loop circuit, the first loop resistance is measured by resonating at a different frequency, and in the second closed-loop circuit, the second loop resistance is measured by resonating by changing the inductance while maintaining the same frequency. In the third closed loop circuit, the third loop resistance is measured while maintaining the same frequency and inductance. Measurement due to ground return impedance depending on the measurement environment such as frequency by calculating the ground resistance derived from the first to third loop resistances measured only by the real component at the resonance point of each closed loop circuit The error can be reduced.

According to a second aspect of the present invention, there is provided a ground resistance measuring method, comprising: a first closed loop circuit formed between a ground electrode having one end embedded in the ground; an oscillator; and a first metal member disposed on the ground; A second closed loop circuit formed between a ground electrode, the oscillator, a variable inductance element, a variable resistor, and a second metal member disposed on the ground; the ground electrode, the oscillator, and the first metal member; And a third closed loop circuit formed between the variable inductance element, the variable resistor, and the second metal member, and measuring a ground resistance using a ground resistance measuring device that can be switched by a switching unit. A method for measuring resistance, wherein the switching means switches to the first closed loop circuit, changes the frequency of the oscillator to resonate the first closed loop circuit, and uses an impedance measuring instrument. A first step of measuring a first loop resistance including a first ground return impedance between the first metal member and the ground, and switching to the second closed loop circuit by the switching means; The second loop circuit is resonated by changing the inductance of the variable inductance element while maintaining the frequency of the second closed loop circuit at the frequency when the first closed loop circuit resonates. Adjusting the second loop resistance to be equal to the first loop resistance by changing the resistance of the variable resistance while measuring the second loop resistance including the second ground return impedance with the ground. Switching to the third closed-loop circuit by the switching means, and the first closed-loop circuit shares the frequency of the oscillator. The first and second loop resistances are equalized while maintaining the frequency at the same time and maintaining the inductance of the variable inductance element at the inductance when the second closed loop circuit resonates. maintaining the value of time, a third step of measuring a third loop resistance including the first earth return impedance and the second earth return impedance by the impedance measuring device, said third loop resistance And a fourth step of calculating the ground resistance by subtracting the value of the first or second loop resistance from the doubled value .

  In the present invention, the variable resistance adjusts the second loop resistance measured in the second closed loop circuit to be equal to the first loop resistance, and the third closed loop circuit is adjusted with respect to the ground resistance. The loop resistance including the first ground return impedance and the second loop resistance including the second ground return impedance can be handled as a parallel circuit connected in parallel, so that the ground resistance can be easily calculated. . In addition, since the third closed loop circuit is a loop circuit that passes through the ground electrode, all three closed loop circuits become loop circuits that pass through the ground electrode, and the loop resistance measured in each circuit is less affected by the ground return impedance. Can do.

According to a third aspect of the present invention, there is provided a ground resistance measuring apparatus, comprising: a first closed loop circuit formed between a ground electrode having one end embedded in the ground; an oscillator; and a first metal member disposed on the ground; A second closed loop circuit formed between a ground electrode, the oscillator, the variable inductance element, and a second metal member disposed on the ground; the first metal member; the oscillator; the variable inductance element; A third closed loop circuit formed between the second metal member and the first closed loop circuit, the second closed loop circuit, and a switching unit capable of switching the third closed loop circuit. The switching means switches to the first closed-loop circuit, changes the frequency of the oscillator to resonate the first closed-loop circuit, and the impedance meter measures the first metal member and the ground. A first loop resistance including a first ground return impedance between the first closed loop circuit and the switching means to switch to the second closed loop circuit, and the frequency of the oscillator when the first closed loop circuit resonates. While maintaining the frequency, the inductance of the variable inductance element is changed to resonate the second loop circuit, and the impedance measuring instrument includes a second ground return impedance between the second metal member and the ground. The second loop resistance is measured, the switching means switches to the third closed loop circuit, the frequency of the oscillator is maintained at the frequency when the first closed loop circuit resonates, and the inductance of the variable inductance element is increased. While maintaining the inductance when the second closed loop circuit resonates, the impedance A third loop resistance including the first ground return impedance and the second ground return impedance is measured by a setting device, and the third loop resistance is calculated from a value obtained by adding the first and second loop resistances. The ground resistance can be calculated by subtracting and dividing by 2 .

According to a fourth aspect of the present invention, there is provided a ground resistance measuring apparatus comprising: a first closed loop circuit formed between a ground electrode having one end embedded in the ground; an oscillator; and a first metal member disposed on the ground; A second closed loop circuit formed between a ground electrode, the oscillator, a variable inductance element, a variable resistor, and a second metal member disposed on the ground; the ground electrode, the oscillator, and the first metal member; And a third closed loop circuit formed between the variable inductance element, the variable resistor, and the second metal member, the first closed loop circuit, the second closed loop circuit, and the third closed loop circuit. Switching means capable of switching, and switching to the first closed loop circuit by the switching means, changing the frequency of the oscillator to resonate the first closed loop circuit, and impedance Measuring a first loop resistance including a first ground return impedance between the first metal member and the ground by a setting device, and switching to the second closed loop circuit by the switching means; Is maintained at the frequency at which the first closed loop circuit resonates, and the second loop circuit is resonated by changing the inductance of the variable inductance element, and the second metal member and the ground are Adjusting the second loop resistance to be equal to the first loop resistance by changing the resistance of the variable resistance while measuring the second loop resistance including the second ground return impedance between Switching to the third closed loop circuit by the switching means, and maintaining the frequency of the oscillator at the frequency when the first closed loop circuit resonates. And maintaining the resistance of the variable resistance at the value when the first and second loop resistances are equal while maintaining the inductance of the variable inductance element at the inductance when the second closed loop circuit resonates, A third loop resistance including the first ground return impedance and the second ground return impedance is measured by an impedance measuring instrument, and the first or second value is calculated from a value obtained by doubling the third loop resistance. The ground resistance can be calculated by subtracting the value of the loop resistance.

  According to the present invention, it is possible to reduce a measurement error caused by the ground return impedance and improve the measurement accuracy of a low ground resistance.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[First Embodiment]
FIG. 1 is a block diagram showing a schematic configuration of a ground resistance measuring apparatus according to the first embodiment. As shown in the figure, the ground resistance measuring apparatus 100 includes a ground electrode 1, an impedance measuring instrument 2, a first return line 3, a second return line 4, a fixed inductor 5, a variable inductor 6, and a switch. 7.

  The ground electrode 1 is disposed in a state of being buried in the ground when measuring the ground resistance. The lead wire 10 is connected to the terminal 7 c of the switch 7.

  The impedance measuring instrument 2 includes an oscillator inside, and can measure the impedance between a pair of measurement terminals while changing the frequency. Here, one measurement terminal is connected to the terminal 7a of the switch 7, and the other measurement terminal is connected to the terminal 7b.

  The first return line 3 is a measurement line in which, for example, a conductive metal line is covered with an insulator as the first metal member. It is placed on the ground when measuring ground resistance.

  The second return line 4 is also a measurement line in which, for example, a conductive metal line is covered with an insulator as the second metal member. It is placed on the ground when measuring ground resistance. Here, for example, members having the same length, shape, and material are used for the first return line 3 and the second return line 4.

  The fixed inductor 5 includes, for example, a coil having an inductance L1 as a fixed value as an inductance element. One end of the fixed inductor 5 is connected to the terminal 7 e of the switch 7, and the other end is connected to the first return line 3.

  The variable inductor 6 has a coil that can change the value of the inductance L2 as a variable inductance element. One end of the variable inductor 6 is connected to the terminal 7 d of the switch 7, and the other end is connected to the second return line 4.

  The switch 7 is connected to the ground electrode 1 through a lead wire 10 and a terminal 7 a connected to one measurement terminal of the impedance measuring instrument 2, a terminal 7 b connected to the other measurement terminal of the impedance measuring instrument 2. Terminal 7 c, a terminal 7 e connected to one end of fixed inductor 5, and a terminal 7 d connected to one end of variable inductor 6. At the time of ground resistance measurement, the first closed loop circuit, the second closed loop circuit, and the third closed loop circuit can be switched as switching means. Here, it is set as the structure which can be switched manually by a measurer.

  The first closed loop circuit is connected to the terminals 7a and 7c and the terminals 7b and 7e by the switch 7, the ground electrode 1 having one end buried in the ground, the oscillator inside the impedance measuring instrument 2, the fixed inductor 5, And the first return line 3 disposed on the ground. As shown in the equivalent circuit of FIG. 2, the first closed-loop circuit includes a ground resistance Rg of the ground electrode 1 disposed on the ground, an inductance L1 of the fixed inductor 5, and a static between the first return line 3 and the ground. This is an RLC series resonance circuit composed of a capacitance C1.

  The second closed loop circuit is connected to the terminals 7a and 7c and the terminals 7b and 7d by the switch 7, the ground electrode 1 having one end buried in the ground, the oscillator inside the impedance measuring instrument 2, the variable inductor 6, , And the second return line 4 disposed on the ground. As shown in the equivalent circuit of FIG. 3, the second closed loop circuit includes a ground resistance Rg of the ground electrode 1 disposed on the ground, an inductance L2 of the variable inductor 6, and a static between the second return line 4 and the ground. This is an RLC series resonance circuit composed of a capacitance C2.

  The third closed loop circuit switches the connection to the terminals 7a and 7d and the terminals 7b and 7e by the switch 7, and the first return line 3 arranged on the ground, the fixed inductor 5, the oscillator inside the impedance measuring instrument 2, And formed between the variable inductor 6 and the second return line 4 disposed on the ground. As shown in the equivalent circuit of FIG. 4, the third closed-loop circuit includes a capacitance C1 between the first return line 3 and the ground, an inductance L1 of the fixed inductor 5, an inductance L2 of the variable inductor 6, 2 is an RLC series resonant circuit composed of a return line 4 and a capacitance C2 between the ground.

  Next, a ground resistance measuring method using the ground resistance measuring apparatus 100 will be specifically described with reference to the flowchart of FIG.

  Prior to the measurement, the measurer places the ground electrode 1 in a state of being buried in the ground, and places the first return line 3 and the second return line 4 on the ground. At this time, it is desirable that the first return line 3 and the second return line 4 are arranged on the ground with a sufficient distance to avoid mutual influence. Here, the first return line 3 and the second return line 4 are arranged on the ground in a state where the angle between them is maintained at a sufficient distance, for example, about 90 degrees.

  Thereafter, the measurer measures the ground resistance while sequentially switching the first closed loop circuit, the second closed loop circuit, and the third closed loop circuit with the switch 7.

As a first step, first, the switch 7 switches to the first closed loop circuit of FIG. Next, the frequency f of the oscillator inside the impedance measuring device 2 is changed to resonate the first closed loop circuit. Then, to measure a first loop resistance R _L1 including the first earth return impedance between the first return line 3 and the earth by the impedance measuring device 2 (S11). Specifically, the frequency at which the impedance measured by the impedance measuring device 2 is minimum is set as the resonance frequency ω ₀ (= 2πf1), and the impedance at that time is measured as the loop resistance R _L1 .

  The impedance Ze (ω) between the return line and the ground is expressed by the following equation (1) as a function of the frequency ω when the real component is Re (Ze (ω)) and the imaginary component is Im (Ze (ω)). It can be expressed as

Ze (ω) = Re (Ze (ω)) + Im (Ze (ω)) (1)
Here, when the impedance between the first return line 3 and the ground is Ze1 (ω), the imaginary component of the impedance Ze1 (ω) is zero in the first loop resistance R _L1 measured at the resonance point. It can be expressed by the following equation (2) including the first ground return impedance _Rε1 .

R _L1 = Rg + Re (Ze1 (ω ₀ ))
= Rg + R _ε1 (2)
As a second step, first, the switch 7 is switched to the second closed loop circuit of FIG. Next, while maintaining the frequency f1 of the oscillator inside the impedance measuring instrument 2 at the frequency ω ₀ (= 2πf1) when the first closed loop circuit resonates, the inductance L2 of the variable inductor 6 is changed to resonate the second loop circuit. Let Then, to measure a second loop resistance R _L2 including the second earth return impedance between the second return line 4 and the ground by the impedance measuring device 2 at the resonance point (S12). Specifically, the inductance L2 is adjusted so that the impedance measured by the impedance measuring device 2 is minimized, and the impedance at that time is measured as the loop resistance _RL2 .

When herein as the impedance between the second return line 4 and the ground Ze2 (omega), the second loop resistance R _L2 measured in resonance point, the imaginary component of the impedance Ze2 (omega) is zero It can be expressed by the following equation (3) including the second ground return impedance _Rε2 .

R _L2 = Rg + Re (Ze2 (ω ₀ ))
= Rg + R _ε2 (3)
As described above, the inductance L2 is adjusted while the frequency ω ₀ (= 2πf1) is kept the same, so that the imaginary component of the impedance Ze2 (ω) is made zero. Accordingly, the second loop resistance _RL2 can be measured at the resonance point even in the second step in which the measurement environment is different from the first step using the first return line 3.

As a third step, first, the switch 7 is switched to the third closed loop circuit of FIG. Next, the frequency of the oscillator inside the impedance measuring device 2 is maintained at the frequency ω ₀ (= 2πf1) when the first closed loop circuit of FIG. 2 resonates, and the inductance L2 of the variable inductor 6 is changed to the second closed loop circuit of FIG. The third loop resistance R _{L3 including} the first ground return impedance and the second ground return impedance is measured by the impedance measuring device 2 while maintaining the inductance when the resonance occurs (S13).

The third loop resistance R _L3 measured here includes the first ground return impedance R _ε1 and the second ground return impedance R _{ε2 at} which the imaginary components of the impedances Ze1 (ω) and Ze2 (ω) are zero. It can be expressed by the following formula (4).

R _L3 = Re (Ze1 (ω ₀ )) + Re (Ze2 (ω ₀ ))
= R _ε1 + R _ε2 (4)
Thus, in each of three different closed loop circuits, it is possible to measure the loop resistance with only the real number component by resonating at the same frequency.

As a fourth step, the ground resistance Rg is calculated based on the first loop resistance R _L1 , the second loop resistance R _L2 , and the third loop resistance R _L3 measured in the first step to the third step (S14). ). Specifically, as represented by the following equation (5), the third loop resistance R _L3 is subtracted from the value obtained by adding the first loop resistance R _L1 and the second loop resistance R _L2, thereby being included in the loop resistance. The ground resistance Rg from which the ground return impedances R _ε1 and R _ε2 are removed is obtained.

Rg = (R _L1 + R _L2 −R _L3 ) / 2 (5)
Thereby, the measurement error resulting from the earth return impedance depending on the measurement environment such as the frequency can be reduced. Therefore, it is possible to accurately measure even a low ground resistance.

  Therefore, according to the first embodiment, the ground resistance measuring device including the ground electrode 1 embedded in the ground, the first return line 3 and the second return line 4 disposed on the ground, and the variable inductor 6. 100 is used to measure the ground resistance while switching to a closed loop circuit of three different paths. The first closed-loop circuit measures the loop resistance by changing the frequency to resonate, the second closed-loop circuit measures the loop resistance by changing the inductance while maintaining the same frequency, and the third closed-loop circuit uses the same Measure loop resistance while maintaining frequency and inductance. By calculating the ground resistance from the loop resistance measured with only the real component at the resonance point of each closed loop circuit, it is possible to reduce the measurement error due to the ground return impedance depending on the measurement environment such as the frequency.

  In the first embodiment, the ground resistance measuring apparatus 100 includes first and second return lines that are measurement lines in which conductive metal wires are covered with an insulator as the first and second metal members. However, the present invention is not limited to this, and at least one of the first metal member and the second metal member is made of a metal plate such as a copper plate and placed on the ground during measurement. It is good also as a structure.

  In the first embodiment, the first closed loop circuit uses the fixed inductor 5 whose inductance is a fixed value as the inductance element. However, a variable inductance element that can change the value of the inductance may be used. In addition, if the first closed loop circuit can resonate only by changing the frequency without using an inductance element, the fixed inductor 5 is not necessarily an essential component.

[Second Embodiment]
Hereinafter, a second embodiment will be described. The basic configuration of the ground resistance measuring device used in the ground resistance measuring method according to the present embodiment is the same as that described in the first embodiment. The following description will focus on differences from the first embodiment.

  The difference from the configuration of the ground resistance measuring device 100 in the first embodiment is that the ground resistance measuring device 200 further includes a fixed resistor 8 and a variable resistor 9, as shown in the block diagram of FIG. The configuration of the third closed loop circuit is different.

  Hereinafter, the configuration of the closed loop circuit switched by the switch 7 will be described with reference to FIGS. In addition, the same number is attached | subjected about the structural member similar to 1st Embodiment.

  The first closed loop circuit is connected to the terminals 7a and 7c and the terminals 7b and 7e by the switch 7, the ground electrode 1 having one end buried in the ground, the oscillator inside the impedance measuring instrument 2, the fixed inductor 5, , Formed between the fixed resistor 8 and the first return line 3 arranged on the ground. As shown in the equivalent circuit of FIG. 7, the first closed loop circuit includes a grounding resistance Rg of the grounding electrode 1 arranged on the ground, an inductance L1 of the fixed inductor 5, a resistance R1 of the fixed resistance 8, and a first return line. 3 is an RLC series resonance circuit including a capacitance C1 between 3 and the ground.

  The second closed loop circuit is connected to the terminals 7a and 7c and the terminals 7b and 7d by the switch 7, the ground electrode 1 having one end buried in the ground, the oscillator inside the impedance measuring instrument 2, the variable inductor 6, , And is formed between the variable resistor 9 and the second return line 4 disposed on the ground. As shown in the equivalent circuit of FIG. 8, the second closed loop circuit includes a grounding resistance Rg of the grounding electrode 1 disposed on the ground, an inductance L2 of the variable inductor 6, a resistance R2 of the variable resistance 9, and a second return line. 4 is an RLC series resonance circuit including a capacitance C2 between 4 and the ground.

  The third closed loop circuit switches the connection to terminals 7a and 7c, terminals 7b and 7e, and 7b and 7d by the switch 7, the ground electrode 1 having one end buried in the ground, the oscillator inside the impedance measuring instrument 2, It is formed between the fixed inductor 5, the fixed resistor 8, the first return line 3 disposed on the ground, the variable inductor 6, the variable resistor 9, and the second return line 4 disposed on the ground. As shown in the equivalent circuit of FIG. 9, the third closed-loop circuit includes a first RLC series resonance circuit including an inductance L1, a resistance R1, and a capacitance C1, an inductance L2, and a variable with respect to the ground resistance Rg. This is a resonance circuit in which a second RLC series resonance circuit including a resistor R2 and a capacitance C2 is connected in parallel. In the present embodiment, the third closed loop circuit is a loop circuit via the ground electrode 1.

  Next, a ground resistance measuring method using the ground resistance measuring apparatus 200 will be specifically described with reference to the flowchart of FIG.

  Here, prior to the measurement, the measurer places the ground electrode 1 in a state of being buried in the ground, and places the first return line 3 and the second return line 4 on the ground. The switch 7 measures the ground resistance while sequentially switching the first closed loop circuit, the second closed loop circuit, and the third closed loop circuit.

  In the first embodiment, the first return line 3 and the second return line 4 are arranged on the ground with a sufficient distance to avoid mutual influence. Then, since all of the first closed loop circuit to the third closed loop circuit are loop circuits via the ground electrode, the measurer must always consider the positional relationship when arranging the first return line 3 and the second return line 4. Convenience is improved.

As a first step, first, the switch 7 switches to the first closed loop circuit of FIG. Next, the frequency f of the oscillator inside the impedance measuring device 2 is changed to resonate the first closed loop circuit. Then, the impedance measuring instrument 2 measures the first loop resistance R _L1 ′ including the first ground return impedance between the first return line 3 and the ground (S21). Specifically, the frequency at which the impedance measured by the impedance measuring device 2 is minimized is measured as the resonance frequency ω ₀ (= 2πf1), and the impedance at that time is measured as the loop resistance R _L1 ′.

Here, when the impedance between the first return line 3 and the ground is Ze1 (ω), the first loop resistance R _L1 ′ measured at the resonance point has zero imaginary component of the impedance Ze1 (ω). It can be expressed by the following equation (2) ′ including the first ground return impedance R _ε1 ′.

R _L1 ′ = Rg + R1 + Re (Ze1 (ω ₀ ))
= Rg + R _ε1 '(2)'
As a second step, first, the switch 7 switches to the second closed loop circuit of FIG. Next, while maintaining the frequency f1 of the oscillator inside the impedance measuring instrument 2 at the frequency ω ₀ (= 2πf1) when the first closed loop circuit resonates, the inductance L2 of the variable inductor 6 is changed to resonate the second loop circuit. Let Then, the second loop resistance R _L2 ′ including the second ground return impedance between the second return line 4 and the ground is measured by the impedance measuring device 2 at the resonance point. At this time, the resistance R2 of the variable resistor 9 is changed so that the second loop resistance R _L2 ′ becomes equal to the first loop resistance R _L1 ′ (S22).
Here, when the impedance between the second return line 4 and the ground is Ze2 (ω), the second loop resistance R _L2 ′ measured at the resonance point has an imaginary component of the impedance Ze2 (ω) of zero. It can be expressed by the following equation (3) including the second ground return impedance R _ε2 ′.

R _L2 ′ = Rg + R2 + Re (Ze2 (ω ₀ ))
= Rg + R _ε2 '(3)'
As described above, the inductance L2 is adjusted while the frequency ω ₀ (= 2πf1) is kept the same, so that the imaginary component of the impedance Ze2 (ω) is made zero. As a result, the second loop resistance _RL2 can be measured at the resonance point even in step 2 where the measurement environment is different from step 1 using the first return line 3.

As a third step, first, the switch 7 is switched to the third closed loop circuit of FIG. Next, the frequency of the oscillator inside the impedance measuring device 2 is maintained at the frequency ω ₀ (= 2πf1) when the first closed loop circuit of FIG. 7 resonates, and the inductance L2 of the variable inductor 6 is changed to the second closed loop circuit of FIG. The resistance R2 of the variable resistor 9 is maintained at a value in which the second loop resistance R _L2 ′ is equal to the first loop resistance R _L1 ′, and the impedance measuring instrument 2 The third loop resistance R _L3 ′ including the first ground return impedance and the second ground return impedance is measured (S23).

The third loop resistance R _L3 ′ measured here is the first ground return impedance R _ε1 ′ in which the imaginary component of the impedance Ze1 (ω) is zero with respect to the ground resistance Rg, and the impedance Ze2 (ω). The second ground return impedance R _ε2 ′ in which the imaginary component is zero can be expressed by the following equation as being connected in parallel.

R _L3 ′ = Rg + (R _ε1 ′ × R _ε2 ′) / (R _ε1 ′ + R _ε2 ′)
Further, in the second step, since the first loop resistance R _L1 ′ and the second loop resistance R _L2 ′ are adjusted to be equal, the following expression (4) ′ is established.

R _L3 ′ = Rg + R _ε1 ′ / 2
= Rg + R _ε2 '/ 2 (4)'
Again, in each of three different closed-loop circuits, the loop resistance can be measured with only real components by resonating at the same frequency.

As the fourth step, the ground resistance Rg is calculated based on the first loop resistance R _L1 ′, the second loop resistance R _L2 ′, and the third loop resistance R _L3 ′ measured in the first step to the third step. (S14). Specifically, as represented by the following equation (5) ′, the third loop resistance R _L3 ′ is subtracted from the value obtained by adding the first loop resistance R _L1 ′ and the second loop resistance R _L2 ′, thereby obtaining a loop. The ground resistance Rg from which the ground return impedances R _ε1 ′ and R _ε2 ′ included in the resistance are removed can be easily obtained.

_{Rg = 2R L3 '- R L1} '
= 2R _L3′− R _L2 ′ (5) ′
Thereby, the measurement error resulting from the earth return impedance depending on the measurement environment such as the frequency can be reduced. Therefore, it is possible to accurately measure even a low ground resistance.

  Therefore, according to the second embodiment, the variable loop adjusts the second loop resistance measured in the second closed loop circuit to be equal to the first loop resistance, and grounds the third closed loop circuit. Since the first loop resistance including the first ground return impedance and the second loop resistance including the second ground return impedance with respect to the resistance can be handled as a parallel circuit connected in parallel, the first The ground resistance can be easily calculated as compared with the embodiment. In addition, the third closed loop circuit is a loop circuit via a ground resistance, and all the three closed loop circuits are loop circuits via a ground resistance, so that the measured loop resistance is less affected by the ground return impedance. be able to. Thereby, since the measurer does not necessarily need to consider the positional relationship when arranging the first return line 3 and the second return line 4, the convenience is improved as compared with the first embodiment.

  In the second embodiment, the ground resistance measuring device 100 is configured to include a measurement line in which a conductive metal wire is covered with an insulator as the first metal member and the second metal member. For example, at least one of the first metal member and the second metal member may be provided with a metal plate such as a copper plate, and may be disposed on the ground during measurement.

[Comparative example]
Next, in order to facilitate understanding of each of the above embodiments, a ground resistance measurement method using a ground resistance measurement device 300 as shown in the block diagram of FIG. 11 as a comparative example, between the return line and the ground. The generated ground return impedance will be described. The ground resistance measuring apparatus 300 of the comparative example includes a ground electrode disposed on the ground, a return line disposed on asphalt paved with a thickness of 3 cm to 40 cm from the ground, a coil, and an oscillator. Prepare for. In the measurement, in the series resonance circuit assuming that the earth return impedance between the return line and the earth is only the capacitance C (unknown number), the ground resistance is calculated from the impedance value measured at the resonance point by changing the frequency. Rg is obtained. Here, the difference (average value) from the three-electrode method is used as a correction table, so that the influence of the ground return impedance is corrected from the obtained value.

  However, the ground return impedance is not only the capacitance C, but also the distance d between the ground and the return line, the ground conductivity σ (0.003 [1 / Ωm] to 0.2 [1 / Ωm]), It depends on parameters such as earth permittivity ε and measuring device frequency f. The ground resistance measuring method of the comparative example has a problem that the ground return impedance cannot be corrected when measuring a ground resistance of 100Ω or less.

  In consideration of the characteristics of the ground return impedance, the present inventor expressed the ground resistance measuring device of the comparative example using a distributed constant circuit. FIG. 12 shows an equivalent circuit thereof.

  FIG. 13 is a graph showing the impedance when the arrow direction is viewed from the oscillator in the equivalent circuit of FIG. The horizontal axis indicates the frequency of the oscillator. Here, the case of Rg + Ri = 10Ω is shown. As shown in the figure, even if the resonance point has the minimum impedance, the value includes an error caused by the ground return impedance.

Furthermore, the error due to the ground return impedance when the ground resistance was measured in the ground resistance measuring device of the comparative example was analyzed. In this case, a physical phenomenon as shown in the left diagram of FIG. 14 occurs between the return line and the ground. (1) current _{I 1} flows through the return line. (2) The magnetic flux Φ generated by the current I ₁ passes through the ground. (3) current I ₂ as magnetic flux direction is generated to cancel out the magnetic fluxes from Φ flows. (4) Magnetic flux Φ ′ is generated in a direction that cancels the magnetic flux Φ.

The right figure of FIG. 14 is an equivalent circuit in which the above physical phenomena (1) to (4) are modeled by a mutual induction circuit. This is expressed as follows.

Here, the impedance Z seen from the power source side is derived as follows.

As described above, both the real component and the imaginary component of the impedance Z are functions of the frequency, and here again, the ground resistance measurement method of the comparative example has a value including an error depending on the frequency.

  Therefore, in order to remove such errors depending on the measurement environment such as the frequency, in the above embodiment, the ground electrode 1 embedded in the ground, the first return line 3 and the second return disposed on the ground. A ground resistance measuring device 100 including a line 4 and a variable inductor 6 is used to measure the ground resistance while switching to a closed loop circuit of three different paths. The first closed-loop circuit measures the loop resistance by changing the frequency to resonate, the second closed-loop circuit measures the loop resistance by changing the inductance while maintaining the same frequency, and the third closed-loop circuit uses the same Measure loop resistance while maintaining frequency and inductance.

Hereinafter, the measurement results of the ground resistance measurement method according to the above embodiment and the ground resistance measurement method of the comparative example are compared. FIG. 15 is a schematic diagram of a measurement system used in an experiment for confirming the effect of the above embodiment. The impedance measuring device 2 used was R3754 manufactured by ADVANTEST, which can measure impedance in the frequency range of 10 kHz to 150 MHz. As the ground electrode 1 to be measured, two ground electrodes having a measurement result of 9Ω and 12Ω by the three-electrode method were used in advance. For the first return line 3 and the second return line 4, measurement lines having the same area of 2 mm ² and the same length of 20 m were used. Thereby, the first loop resistance and the second loop resistance are made equal without using the variable resistance. The first return line 3 and the second return line 4 were arranged on the ground paved with asphalt. An inductance element having a fixed inductance is used for the inductor 5, and a variable inductance element that is variable in the range of inductance 1 mH to 10 mH is used for the variable inductor 6. Switching of the closed loop circuit by the switch 7 was performed manually by the measurer.

  In such a measurement system, the ground resistance was measured by the measurement method according to the first embodiment and the second embodiment.

  FIG. 16 is a graph showing the measurement results. The triangles in the figure indicate the respective measurement results. The diagonal line in the figure shows the measured value by the three-electrode method. The results of measuring 9 Ω and 12 Ω ground resistance are both close to the values measured by the three-electrode method. On the other hand, the measurement result obtained by measuring the ground resistance of 12Ω by the measurement method of the comparative example has a larger error than the measurement value by the three-electrode method. More specifically, the error of the measurement value relative to the true value by the three-electrode method was 140% in the measurement method of the comparative example, whereas the error was greatly improved by 5% in the measurement method according to the present invention. became. That is, according to the present invention, it is possible to reduce the measurement error caused by the ground return impedance and improve the measurement accuracy of the low ground resistance.

[Application example]
In each of the above embodiments, the switch to the first to third closed loop circuits is manually performed by the switch. However, the present invention is not limited to this. For example, a timing signal is sent to the switch. In addition, a control means for transmitting a command for sequentially switching the first to third closed-loop circuits may be provided, and the switching may be performed sequentially based on the command received by the switch. As a result, the user can improve convenience without manually performing the switching operation.

  Furthermore, the control means adjusts the frequency of the oscillator, the inductance of the variable inductance element, and the resistance value of the variable resistance, and the storage means for temporarily storing the first to third loop resistances, and the loop resistance from the storage means. An arithmetic means for reading and calculating the ground resistance may be further provided, and the steps of the ground resistance measuring method described in the above embodiments may be automated.

1 is a block diagram showing a schematic configuration of a ground resistance measurement device according to a first embodiment. FIG. 2 is an equivalent circuit of a first closed loop circuit formed by the ground resistance measuring device of FIG. 1. FIG. 3 is an equivalent circuit of a second closed loop circuit formed by the ground resistance measuring device of FIG. 1. FIG. 6 is an equivalent circuit of a third closed loop circuit formed by the ground resistance measuring device of FIG. 1. It is a flowchart which shows the procedure of the ground resistance measuring method using the said ground resistance measuring apparatus. It is a block diagram which shows schematic structure of the ground resistance measuring apparatus which concerns on 2nd Embodiment. FIG. 7 is an equivalent circuit of a first closed loop circuit formed by the ground resistance measuring device of FIG. 6. FIG. 7 is an equivalent circuit of a second closed loop circuit formed by the ground resistance measuring device of FIG. 6. FIG. 7 is an equivalent circuit of a third closed loop circuit formed by the ground resistance measuring device of FIG. 6. It is a flowchart which shows the procedure of the ground resistance measuring method using the said ground resistance measuring apparatus. It is a block diagram which shows the schematic structure of the ground resistance measuring apparatus of a comparative example. 12 is an equivalent circuit represented by using a distributed constant circuit for the ground resistance measuring apparatus of FIG. 11. 13 is a graph showing impedance when viewing the arrow direction from the oscillator in the equivalent circuit of FIG. 12. 12 is an equivalent circuit that models a physical phenomenon between a return line and the ground when the ground resistance is measured using the ground resistance measuring device of FIG. 11. It is the schematic which showed the measurement system in the effect confirmation experiment by the said 1st and 2nd embodiment. It is a graph which shows the measurement result by the said experiment, and the measurement result of a comparative example. It is a block diagram which shows the schematic structure of the conventional ground resistance measuring apparatus. It is a figure which shows the equivalent circuit of the conventional ground resistance measuring apparatus. It is a flowchart which shows the procedure of the conventional grounding resistance measuring method. It is a graph which shows the measured value by the conventional grounding resistance measuring method, and its measurement error.

Explanation of symbols

1 ... ground electrode 2 ... impedance measuring instrument (frequency variable)
3 ... 1st return line 4 ... 2nd return line 5 ... Fixed inductor 6 ... Variable inductor 7 ... Switch 7a ... Terminal 7b connected to one measuring terminal of impedance measuring instrument ... Connected to the other measuring terminal of impedance measuring instrument Terminal 7c connected to the ground electrode via a lead wire 7d connected to one end of the variable inductor 8e connected to one end of the fixed inductor 8 fixed resistor 9 variable resistor 10 lead Line 100 ... Grounding resistance measuring device (Example 1)
200: Grounding resistance measuring device (Example 2)
300 ... Conventional ground resistance measuring device (comparative example)
f ... frequency f1 ... resonance frequency R _L1 ... first loop resistance R _L2 in the first closed loop circuit second loop resistance R _L3 in the second closed loop circuit third loop resistance Rg in the third closed loop circuit ... ground resistance L1 ... inductance L2 of fixed inductor (coil) ... inductance R1 of variable inductor (coil) ... resistance value L2 of fixed resistance ... resistance value C1 of variable resistance ... electrostatic capacitance between the first return line and the ground Capacitance C2: Capacitance between the second return line and the ground

Claims (4)

A first closed loop circuit formed between a ground electrode having one end buried in the ground, an oscillator, and a first metal member disposed on the ground, the ground electrode, the oscillator, the variable inductance element, and the ground disposed on the ground A second closed loop circuit formed between the second metal member formed, and a first closed loop circuit formed between the first metal member, the oscillator, the variable inductance element, and the second metal member. A ground resistance measuring method for measuring a ground resistance using a ground resistance measuring device that can be switched by a switching means.
The first closed loop circuit is switched by the switching means, the first closed loop circuit is resonated by changing the frequency of the oscillator, and a first ground between the first metal member and the ground is measured by an impedance measuring device. A first step of measuring a first loop resistance including a return impedance;
Switching to the second closed loop circuit by the switching means, and maintaining the frequency of the oscillator at the frequency when the first closed loop circuit resonates, while changing the inductance of the variable inductance element, the second loop circuit A second step of measuring a second loop resistance including a second ground return impedance between the second metal member and the ground by means of an impedance meter;
The switching means switches to the third closed loop circuit, maintains the frequency of the oscillator at the frequency when the first closed loop circuit resonates, and the second closed loop circuit resonates the inductance of the variable inductance element. A third step of measuring a third loop resistance including the first ground return impedance and the second ground return impedance by an impedance meter while maintaining the inductance at the time;
A fourth step of calculating a ground resistance by subtracting a third loop resistance from a value obtained by adding the first and second loop resistances and dividing by 2 ;
A grounding resistance measurement method comprising: A first closed loop circuit formed between a ground electrode having one end buried in the ground, an oscillator, and a first metal member disposed on the ground; the ground electrode, the oscillator, a variable inductance element, and a variable resistor; A second closed loop circuit formed between a second metal member disposed on the ground, the ground electrode, the oscillator, the first metal member, the variable inductance element, the variable resistor, and a second resistor. A third closed loop circuit formed between the metal member and the ground resistance measuring method using a ground resistance measuring device switchable by the switching means to measure the ground resistance,
The first closed loop circuit is switched by the switching means, the first closed loop circuit is resonated by changing the frequency of the oscillator, and a first ground between the first metal member and the ground is measured by an impedance measuring device. A first step of measuring a first loop resistance including a return impedance;
Switching to the second closed loop circuit by the switching means, and maintaining the frequency of the oscillator at the frequency when the first closed loop circuit resonates, while changing the inductance of the variable inductance element, the second loop circuit And the second loop resistance including the second ground return impedance between the second metal member and the ground is measured by an impedance measuring instrument, and the resistance of the variable resistance is changed to change the second resistance. A second step of adjusting a loop resistance to be equal to the first loop resistance;
The switching means switches to the third closed loop circuit, maintains the frequency of the oscillator at the frequency when the first closed loop circuit resonates, and the second closed loop circuit resonates the inductance of the variable inductance element. The resistance of the variable resistor is maintained at the value when the first and second loop resistances are equal while maintaining the inductance at the time, and the first ground return impedance and the second ground are measured by an impedance meter. A third step of measuring a third loop resistance including a return impedance;
A fourth step of calculating a ground resistance by subtracting the value of the first or second loop resistance from a value obtained by doubling the third loop resistance;
A grounding resistance measurement method comprising: A first closed-loop circuit formed between a ground electrode having one end buried in the ground, an oscillator, and a first metal member disposed on the ground;
A second closed loop circuit formed between the ground electrode, the oscillator, the variable inductance element, and a second metal member disposed on the ground;
A third closed loop circuit formed between the first metal member, the oscillator, the variable inductance element, and the second metal member;
Switching means capable of switching between the first closed loop circuit, the second closed loop circuit, and the third closed loop circuit, and
The first closed loop circuit is switched by the switching means, the first closed loop circuit is resonated by changing the frequency of the oscillator, and a first ground between the first metal member and the ground is measured by an impedance measuring device. Measure the first loop resistance including the return impedance,
Switching to the second closed loop circuit by the switching means, and maintaining the frequency of the oscillator at the frequency when the first closed loop circuit resonates, while changing the inductance of the variable inductance element, the second loop circuit And a second loop resistance including a second earth return impedance between the second metal member and the earth is measured by an impedance measuring instrument,
The switching means switches to the third closed loop circuit, maintains the frequency of the oscillator at the frequency when the first closed loop circuit resonates, and the second closed loop circuit resonates the inductance of the variable inductance element. A third loop resistance including the first ground return impedance and the second ground return impedance is measured by an impedance meter while maintaining the inductance at the time,
3. A ground resistance measuring apparatus, wherein a ground resistance can be calculated by subtracting a third loop resistance from a value obtained by adding the first and second loop resistances and dividing by two . A first closed-loop circuit formed between a ground electrode having one end buried in the ground, an oscillator, and a first metal member disposed on the ground;
A second closed loop circuit formed between the ground electrode, the oscillator, a variable inductance element, a variable resistor, and a second metal member disposed on the ground;
A third closed loop circuit formed between the ground electrode, the oscillator, the first metal member, the variable inductance element, the variable resistor, and a second metal member;
Switching means capable of switching between the first closed loop circuit, the second closed loop circuit, and the third closed loop circuit, and
The first closed loop circuit is switched by the switching means, the first closed loop circuit is resonated by changing the frequency of the oscillator, and a first ground between the first metal member and the ground is measured by an impedance measuring device. Measure the first loop resistance including the return impedance,
Switching to the second closed loop circuit by the switching means, and maintaining the frequency of the oscillator at the frequency when the first closed loop circuit resonates, while changing the inductance of the variable inductance element, the second loop circuit And the second loop resistance including the second ground return impedance between the second metal member and the ground is measured by an impedance measuring instrument, and the resistance of the variable resistance is changed to change the second resistance. Adjusting the loop resistance to be equal to the first loop resistance;
The switching means switches to the third closed loop circuit, maintains the frequency of the oscillator at the frequency when the first closed loop circuit resonates, and the second closed loop circuit resonates the inductance of the variable inductance element. The resistance of the variable resistor is maintained at the value when the first and second loop resistances are equal while maintaining the inductance at the time, and the first ground return impedance and the second ground are measured by an impedance meter. Measure the third loop resistance including the return impedance,
A ground resistance measuring apparatus, wherein the ground resistance can be calculated by subtracting the value of the first or second loop resistance from a value obtained by doubling the third loop resistance.

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