JPH0354311B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a grounding resistance measuring device used for measuring grounding resistance in ultra-high voltage substations, switching stations, etc.

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
The secondary winding side of the is connected to the grounding network N, which is the system to be measured, through the switching switch S ₂ and the switching switch S ₂ and the ammeter A.
A voltmeter V is connected between and zero potential, and the autotransformer _T1 adjusts the current value I flowing through the ammeter A, and the indicated value of the voltmeter V when the switch _S2 is switched left and right is _E1 , The grounding resistance R is determined by reading _E2 .

In this case, when the equipment is in operation and the floating potential (indication value of voltmeter V when I = 0) is Eo, the vector composition relationship shown in Figure 2 is established. From this, the grounding resistance R can be found. In other words, the ground 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 fluctuates easily depending on the surrounding conditions but also lacks reproducibility.
The conventional apparatus described above, which is greatly affected by E ₀ , has the disadvantage that accurate measurement results cannot be obtained.

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 influence of floating potential E ₀ by temporarily shutting down the substation or switchyard; Since this is not easy, it is necessary to lower the grounding resistance to the level that will be required in the future during construction before the start of operation, which has the disadvantage of requiring upfront investment.

This invention was made to eliminate the above-mentioned drawbacks, and even when various equipment is in operation, the floating potential E ₀
An object of the present invention is to provide a grounding resistance measuring device that can measure grounding resistance with high accuracy without being affected by

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

In FIG. 3, 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 has one output terminal connected to auxiliary ground, and the other output terminal connected to the system to be measured, for example, a grounding network 7, via an ammeter 6, and a constant current Icos (ωt− θ).

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.

Next, its effect will be explained.

Now, reference signals Acosωt and Asinωt are generated from the oscillator 4.
is given to the voltage measuring device 8, and the constant current amplifier 5
Assuming that a constant current Icos (ωt−θ) is applied through the ammeter 6, the voltage measuring section 8 receives the floating potential E ₀ cosω ₀ t and the measurement signal as the measurement input V.
V=E ₀ cosω ₀ t+IRcos(ωt-θ) is obtained by superimposing IRcos(ωt-θ). This measurement input V is applied to multipliers 811, 8
12 and are multiplied by the reference signal. Then, from the multiplier 811, x=AV・cosωt=AVE ₀ /2 {cos(ω ₀ +ω)t+co
s(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+si
n(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 synchronized with the reference signal is left, thereby obtaining x=ARI/2cosθ and y=ARI/2sinθ. Furthermore, these outputs x and y are squared by a squarer 8
31,832 to the adder 84 and √
(x) ₂ + (y) ² is obtained, and when this is calculated via the square rooter 85, √() ² + () ² = ARI/2(√ ²
- sin ² θ) = ARI/2, and the indicated value E = ARI/2 at the voltage measuring section 8 is obtained. Here, I in the indicated value ARI/2 is the output current of the constant current amplifier 5, 6 can be read directly, and A can be added arbitrarily, so if A=2, R=E/I, and from the above indicated value, the grounding 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 ground resistance R can be calculated, floating potentials can be eliminated even when equipment at 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. 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 a value that will be required in the future. The upfront investment required for this can be suppressed.

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
This is applied to the adder 84 via the square rooter 85 to obtain the indicated value ARI/2. For example, as shown in FIG. After switching each wave separately, it is applied to the adder 9, where xcosωt+ysinωt=√ ² + ² cos{ωt−cos− ¹ y/x
} is obtained, passed through a bandpass filter 10, and then detected by a detection circuit 11 to obtain the indicated value.
It may be possible to obtain ARI/2. 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 ground resistance measuring device that can measure the ground resistance R with high precision without being affected by the floating potential E ₀ even when various equipment is in operation.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an example of a conventional ground resistance measuring device, FIG. 2 is a vector diagram for explaining the device, and FIG. 3 is a schematic configuration diagram showing an example of the present invention. FIG. 4 is a block diagram showing a voltage measuring section used in the same embodiment, and FIG. 5 is a schematic configuration diagram showing another embodiment of the present invention. 1...power supply, 2...switch, 3...fuse, 4...
Oscillator, 5... constant current amplifier, 6... ammeter, 7... 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.

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 converts the current into a current with a constant amplitude and supplies it to the grounding system under test, and a voltage drop caused by the current flowing through the grounding resistance of the grounding system under test and a floating potential having a commercial frequency are superimposed. and a means for multiplying the measured signal by the first reference signal and a means for multiplying the measured signal by the second reference signal, and extracts only each DC component from each of these outputs. 1. A grounding resistance measuring device characterized by comprising an arithmetic means for taking out, squaring and adding these 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. The earth resistance measuring device according to claim 1 or 2, wherein the calculation means uses a narrow band low-pass filter as a means for extracting only the DC component. 4. The earth resistance measuring device according to any one of claims 1 to 3, wherein the calculation means includes a squarer, an adder, and a square rooter for squaring each of the DC component amplitude values. .