JPH0467631B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a grounding resistance measuring device used for measuring grounding resistance in electrical stations such as ultra-high voltage substations and switchyards.

In ultra-high voltage substations and switchyards, so-called grounding connections are made to protect equipment and ensure safe handling.

In this case, a limit value is determined for the resistance between the earth and the ground due to such a ground connection, and it must be kept below the specified value at all times.

For this reason, various measuring devices have been conventionally considered for measuring such ground resistance.

Figure 1 shows an example of a conventional ground resistance measuring device of this type, in which a commercial frequency power supply AC (=200V) is connected to an isolation transformer _T2 via a switch _S1 , a fuse F, and an autotransformer _T1 . This transformer T ₂
Connect the secondary winding side of the autotransformer to the grounding network that is the system to be measured via the changeover switch S ₂ and the ammeter A, and connect the voltmeter V between the grounding network N and zero potential.
The grounding resistance R is determined by adjusting the current value I flowing through the ammeter A at _T1 and reading the indicated values _E1 and _E2 of the voltmeter V when the switch _S2 is switched left and right. There is.

In this case, if the electric station is in operation and the floating potential (indication value of voltmeter V when I = 0) is E ₀ , the vector composition relationship shown in Fig. 2 holds, From this, the ground resistance R can be determined. In other words, the grounding resistance R is determined by the floating potential E ₀ in addition to the indicated values E ₁ and E ₂ of the voltmeter V and the indicated value I of the ammeter A.

However, as is well known, the floating potential E ₀ not only tends to fluctuate depending on the surrounding conditions but also lacks reproducibility, so the above-mentioned device, which is greatly affected by the floating potential E ₀ , has the disadvantage that accurate measurement results cannot be obtained. It was hot.

Therefore, in the past, in order to minimize the influence of the floating potential E ₀ , the current I flowing through the ammeter A was increased, but this only increased the size of the device because the transformer capacitance increased unnecessarily. However, it becomes expensive in terms of price. On the other hand, when measuring ground resistance, it is possible to remove the effects of floating potential E ₀ by temporarily causing a complete power outage at electrical stations such as substations and switchyards. Since it is not easy to cause a complete power outage, it is necessary to lower the connection resistance to the level that will be required in the future during construction before starting operation, which has the disadvantage of requiring upfront investment.

In view of these conventional circumstances, the present applicant proposed in an earlier application (Japanese Patent Application No. 59-75262 (Japanese Unexamined Patent Publication No. 59-200974)) that the floating potential is
We are proposing a grounding resistance measuring device that can measure grounding resistance with high accuracy without being affected by E ₀ .

That is, this device is constructed as shown in FIG.

In the figure, 1 is a power source, and an oscillator 4 is connected to this power source 1 via a switch 2 and a fuse 3. This oscillator 4 outputs the Acosωt and Asinωt signals as first and second reference signals. At this time, the frequencies ω of these signals are set to be slightly different from the commercial frequency ω ₀ of the line in order to reduce errors due to frequency differences.

The oscillator 4 is provided with current generating means, such as a constant current amplifier 5.
are connected. This amplifier 5 is provided with the first or second reference signal and converts it into a current with a constant amplitude.One output terminal is auxiliary grounded, and the other output terminal is connected via an ammeter 6. It is connected to a grounding system to be measured, such as a grounding network 7, and a constant current Icos (ωt-θ) is constantly supplied via an ammeter 6.

A voltage measuring section 8 is connected between the grounding network 7 and the zero potential as a calculation means. A reference signal from the oscillator 4 is given to this measuring section 8 . in this case,
As shown in FIG. 4, the measurement section 8 receives a measurement input V and receives a reference signal from the oscillator 4.
Multiplier 81 to which Acosωt and Asinωt are given separately
1,812, a narrow band low-pass filter 8 to which the outputs x and y of these multipliers 811 and 812 are given.
21,822, these low pass filters 821,
A squarer 831 is given the output of 822,
832, an adder 84 that adds the outputs of these squarers 831 and 832, and a squarer 85 that squares the output of the adder 84.

By doing this, the reference signal from oscillator 4 is now
Assuming that Acosωt and Asinωt are given to the voltage measuring device 8, and a constant current Icos (ωt-θ) is given from the constant current amplifier 5 through the ammeter 6, the voltage measuring section 8 has a measurement input V floating potential as
V = E ₀ cos ω ₀ t + IRcos (ωt - θ) is obtained by superimposing E ₀ cos ω ₀ t and the measurement signal IRcos (ωt - θ). This measurement force V is calculated by multipliers 811, 81
2 and multiplied by the reference signal. Then, from the multiplier 811, x=AV・cosωt= AVE ₀ /2 {cos(ω ₀ +ω)t+cos(ω ₀ +ω)t}
+AIR/2{cos(2ωt-θ)+cosθ} is obtained, and from the multiplier 812, y=AV・sinωt=AVE _0/2 {sin(ω ₀ +ω)t+sin(ω ₀ -ω)t}
+AIR/2{sin(2ωt−θ)+sinθ} is obtained. Then, when these outputs x and y are given to low-pass filters 821 and 822, x,
Among the terms of y, the AC component is attenuated and only the DC component that has been synchronously detected with the reference signal is left, resulting in =ARI/2cosθ, =ARI/2sinθ. Furthermore, the outputs x and y of these DC component amplitude values are given to an adder 84 via squarers 831 and 832 to obtain +, which is then passed through a squarer 831 and 832 to an adder 84.
√() ² () ² = ARI/2(√ ² + ²
)=ARI/2, and the indicated value E=ARI/2 at the voltage measuring section 8 is obtained.

Here, I at the indicated value ARI/2 can be directly read with the ammeter 6 as the output current of the constant current amplifier 5, and A can be determined arbitrarily, so if A=2, R=E/I Therefore, from the above indicated value, the ground resistance R
can be easily calculated.

Therefore, with such a configuration, the floating potential
Since AC components including E ₀ can be removed and only the indicated value ARI/2 required for measuring the ground resistance R can be calculated, stray potentials can be eliminated even when equipment in substations and switchyards is in operation.
This means that the grounding resistance R can be measured with high precision without being affected by E ₀ at all.

By the way, electrical stations such as substations and switchyards may be installed in multiple locations depending on the scale of the power system, and these multiple electrical stations are connected to each other via aerial grounding wires after the start of operation. .

Therefore, when measuring the grounding resistance using the above-mentioned measuring device at substations and switchyards that operate under such conditions, it is possible to measure the grounding resistance of other electrical stations connected via the aerial grounding wire or the grounding resistance of other electrical stations along the way. The measurement will include all the grounding resistance of steel towers, etc., and there is a risk that the true grounding resistance at your own electrical station cannot be measured.

This invention was made in order to eliminate the above-mentioned drawbacks, and it is possible to measure the true ground resistance at one's own electrical station with high precision without being affected by the floating potential E ₀ while in operation. The purpose is to provide a measuring device.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 5 shows a schematic configuration diagram of the same embodiment, and the same parts as in FIG. 3 are given the same reference numerals.

In this case, the other output terminal of the constant current amplifier 5 is directly connected to the grounding system to be measured, for example, the grounding network 7.

A grounding network 121 is connected to this grounding network 7 as a grounding system for other electrical stations connected via an aerial grounding wire or the like.
122 is connected. Although the illustrated example shows a case where two systems are connected to other electric stations, other electric stations may be connected, and a grounding system such as a steel tower may also be used.

A current transformer 13 is connected as a current detection means to the line between the constant current amplifier 5 and the ground network 7, so that the current I flowing from the constant current amplifier 5 to the ground network 7 is detected. Similarly, current transformers 141 and 142 are connected to the lines between the grounding network 7 and the grounding networks 121 and 122 of other electric stations as current detection means, respectively.
Each grounding network 121, 12 of an electric station other than the grounding network 7
The currents I ₁ and I ₂ flowing through the two terminals are detected respectively.

An adder 15 is connected to the output terminals of these current transformers 13, 141, and 142. In this case, the adder 15 is configured to generate an addition output _I0 obtained by subtracting the outputs of the current transformers 13, 141, and 142.

The rest is the same as in FIG. 3, and the explanation here will be omitted. Further, the voltage measuring section 8 in FIG. 5 is also the same as that in FIG. 4, and the explanation here will be omitted.

Therefore, it can be seen that the ground resistance measuring device constructed in this manner can also measure the ground resistance without being affected by the floating potential E ₀ by following the above-mentioned FIGS. 3 and 4. Therefore, here we will discuss the point that only the grounding resistance of the grounding system to be measured at the own electrical station, excluding the resistance of the grounding systems of other electrical stations, can be measured.

Incidentally, FIG. 5 can be represented by an equivalent circuit shown in FIG. 6. Here, Z ₀ , Z ₁ , and Z ₂ are the impedances of each line, R ₀ is the ground resistance due to the grounding network 7 to be measured, and R ₁ and R ₂ are the grounding resistances due to the grounding networks 121 and 122 of other electrical stations, respectively. be.

Therefore, in Fig. 6, I〓=I〓 ₀ +I〓 ₁ +I〓 ₂ V〓=R ₀ I〓 ₀ = (Z ₁ +R ₁ )I〓 ₁ = (Z ₂ +R ₂ )I〓 ₂ ...( 1) …(2) relationship always holds true.

Therefore, I=V/R ₀ +V/Z ₁ +R ₁ +V/Z ₂ +R ₂ , and I/V=1/R ₀ +1/Z ₁ +R ₁ +1/Z ₂ +R ₂ is obtained. As a result, the ground resistance can be found from V/I, but as it is, the ground resistance of other electrical stations is included, so the true ground resistance cannot be obtained.

Therefore, first of all, if we focus on I ₀ in equation (1), this I ₀ flows out into the earth over a wide range from the grounding network 7 and cannot be directly measured, but it can be detected by the current transformer 13 shown in Fig. 5. Current I〓, currents I ₁ and I ₂ similarly detected from current transformers 141 and 142, respectively.
Based on I〓 ₀ =I〓−I〓 ₁ −I〓 ₂ (3) In other words, it is obtained as the output of the adder 15. Then, substitute this into equation (2). Then, R ₀ =V/I ₀ =V/I-I-I ₂ (4), and |R ₀ |=|V/I ₀ |=|V|/|I ₀ | holds true.

As a result, the output I〓 ₀ of the adder 15 is first measured, and the constant current amplifier 5 is applied so that this I〓 ₀ becomes, for example, 1A.
By adjusting the output of , and then measuring the voltage V〓, it becomes possible to separately measure the grounding resistance of the grounding system to be measured, that is, the grounding network 7 of the electrical station to be measured.

Therefore, by doing this, you can remove the alternating current component including the floating potential E ₀ and calculate only the indicated value necessary for measuring the grounding resistance R ₀ of the grounding system to be measured at your own electrical station. Even when the switchyard is in operation, only the grounding resistance R ₀ of the own electrical station can be measured with high precision without being affected by the floating potential E ₀ . This makes it possible to make the device smaller and cheaper than the conventional method that increases the transformer capacitance to reduce the influence of the floating potential E ₀ , and also lowers the grounding resistance to the value that will be required in the future. It is also possible to suppress the upfront investment required for this purpose.

It should be noted that the present invention is not limited to the above-mentioned embodiments, but can be implemented with appropriate modifications without changing the gist. For example, in the above case, the multiplier 81 of the voltage measuring section 8
1,812 is the measurement input V and the reference signal Acosωt,
Although Asinωt is given and x and y are obtained, instead of this, the measurement input V may be directly switched with a square wave of frequency ω. Furthermore, in the above description, the low pass filter 82 is used in the voltage measuring section 8.
1,822 output, squarer 831,832
The output is given to the adder 84 through the square waveform generator 84, and then added to the squarer 85 to obtain the indicated value.For example, as shown in FIG. After switching, when fed to the adder 9, the fundamental wave component and harmonic component xcosωt+ysinωt+harmonic component=√ ² + ² cos{ωt−
tan ⁻¹ (y/x)}+harmonics, pass only the fundamental wave component through the bandpass filter 10, and then detect the wave at the detection circuit 11 to obtain the indicated value. Further, in the above description, a constant current output is obtained from the constant current amplifier 5, but this output does not necessarily have to be a constant current.

As described above, according to the present invention, it is possible to provide a grounding resistance measuring device that can measure the true grounding resistance of one's own electric station with high precision while in operation.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram showing an example of a conventional grounding resistance measuring device, Fig. 2 is a vector diagram for explaining the device, and Figs. 5 is a schematic configuration diagram showing an embodiment of the present invention, FIG. 6 is an equivalent circuit diagram for explaining the embodiment, and FIG. 7 is a schematic diagram showing an embodiment of the present invention. It is a schematic block diagram which shows another Example. 1...power supply, 2...switch, 3...fuse, 4...
Oscillator, 5... Constant current amplifier, 7, 121, 122
...Grounding network, 8...Voltage measuring section, 811, 812...Multiplier, 821, 822...Low pass filter, 83
1,832...squarer, 84,9...adder, 85...
Square rooter, 10... Band pass filter, 11... Detection circuit, 13, 141, 142... Current transformer, 15... Adder.

Claims (1)

[Claims] 1. Oscillating means for generating first and second reference signals having a frequency slightly different from the commercial frequency and having a phase difference of 90 degrees from each other; a current generating means that converts the current into a current with a constant amplitude and supplies it to the grounding system under test; the current flowing through the grounding system under test; and the current flowing from the grounding system under test to other grounding systems connected to this grounding system. and a means for detecting the current obtained by subtracting the current flowing through the other earthing system from the current flowing through the earthing system to be measured; A measurement signal on which a voltage drop and a floating potential having a commercial frequency are superimposed is provided, and the measurement signal includes means for multiplying the measurement signal by the first reference signal and means for multiplying the measurement signal by the second reference signal. A ground resistance measuring device characterized in that it is equipped with arithmetic means for extracting only each DC component from each of these outputs, squaring and adding the two DC component amplitude values, and obtaining a square root value. 2. The earth resistance measuring device according to claim 1, wherein the current generating means comprises a constant current amplifier that generates a constant current. 3. Claim 1, wherein the current detection means includes a plurality of current transformers and an adder that adds the outputs of these current transformers with different polarities.
The earth resistance measuring device according to item 1 or 2. 4. The earth resistance measuring device according to any one of claims 1 to 3, wherein the calculation means uses a narrow band low-pass filter as a means for extracting only the DC component. 5. The earth resistance measuring device according to any one of claims 1 to 4, wherein the calculation means includes a squarer, an adder, and a square rooter for squaring each of the DC component amplitude values. .