JPS61251776A - Measuring instrument for earth resistance - Google Patents

Abstract

PURPOSE:To detect real earth resistance by subtracting the current of an earth system which is connected to an earth system to be detected from a current flowing through the latter system. CONSTITUTION:Earth networks 121 and 122 of other electric stations are connected to an earth network 7 through aerial earth wires. A current transformer 13 is connected between a constant current amplifier 5 and the earth network 7 to detect a current I flowing through the earth network 7 and current transformers 141 and 142 are connected between the earth network 7 and other earth networks 121 and 122 to detect currents I1 and I2 flowing through the earth networks 121 and 122. An adder 15 is connected to output terminals of the current transformers 13, 141, and 142 and the currents I1 and I2 flowing to other earth systems are subtracted from the current I flowing to the earth system to be measured, thus obtaining a current I0. The current I0 is the earth current of this electric station and the current voltage V is measured by a voltage measuring part 8 to measure only the earth resistance of this electric station with high precision.

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.
, heats F are connected to an isolation transformer T via an autotransformer T1, and the secondary winding side of this transformer T is connected to a selector switch S2. Connect to the grounding network that is the system to be measured via ammeter A, connect voltmeter V between this grounding network N and zero potential, and adjust the current value I flowing through ammeter A with autotransformer TI. The indicated value B1 of the voltmeter V when the switch S2 is switched left and right. The grounding resistance R is determined by reading E and E, respectively.

In this case, when the electric station is in operation and the floating potential (min = 0
When the indicated value of the voltmeter V at the time of E is E, the vector composition relationship shown in FIG. 2 is established, and from this, the ground resistance R is obtained. In other words, the grounding resistance is determined by the floating potential E in addition to the readings Fli, Fli of the voltmeter V and the readings Fli of the ammeter A.

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

Therefore, in the past, in order to minimize the influence of the floating potential ffo, the current flowing through the ammeter A was increased, but this not only increased the transformer capacity unnecessarily, but also made the device larger. It also becomes expensive. On the other hand, when measuring ground resistance, a temporary total power outage is performed at electrical stations such as substations and switchyards, and 1 floating potential E
It is possible to eliminate the effects of 2. However, since it is not easy to cause a complete power outage to substations and switchyards that are in operation, it is necessary to lower the connection resistance to the level that will be required in the future during construction before commencing operation. The disadvantage is that this requires t investment.

In view of these conventional circumstances, the present applicant filed an earlier application (Japanese Patent Application No. 58-75262) to develop a grounding resistor with high precision without being affected by the floating potential Eo even when the electrical station is in operation. We are proposing a grounding resistance measuring device that can measure ground resistance.

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

In the figure, 1 is a power supply, and even if an oscillator 4 is connected to this power supply 1 via a switch 2 and a heater 3, the oscillator 4
outputs the Acos&It and As1rsQIt signals as the first and second reference signals.

At this time, the frequencies ω of these signals are set to be slightly different from the line commercial frequency ω0 in order to reduce errors due to frequency differences.

A current generating means such as a constant current amplifier 5 is connected to the oscillator 4. 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, for example, a grounding network 7, and a constant current I cos (ω is - θ) is constantly applied 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, the measuring section 8 is supplied with a measuring force V as shown in FIG. 4, and receives a reference signal Acosωt from the oscillator 4.

Multipliers 811 and 812 to which As1nωt are given separately
, narrowband low-pass filters 821, 822 to which the outputs x, y of these multipliers 811, 812 are given, squarers 831, 832, to which outputs x, y of these low-pass filters 821, 822 are given, these squarers 831, 83.
It has an adder 84 that adds the outputs of 2 and a squarer 85 that squares the output of the adder 84.

In this case, the oscillator 4 now generates the reference signal Acosωt.

Assuming that As1nωt is applied to the voltage measuring device 8, and a constant current 1cos (ω is - θ) is applied from the constant current amplifier 5 through the ammeter 6, the voltage measuring unit 8 receives the measured human power V. The floating potential Eocosωo1 and the measurement signal IRcos (ω and 0 are superimposed, V+++=Eocosω, t−1−IRcos (ω is one θ) are obtained. This measurement force V is applied to the multipliers 811 and 812.
are respectively given and multiplied by the reference signal. Then multiplier 8
11 is obtained, and multiplier 812 is obtained. Then, when these outputs x and y are given to low-pass filters 821 and 822, the AC component of each term of s''ty is attenuated, leaving only the DC component that has been synchronously detected with the reference signal, thereby obtaining. The output x of these DC component amplitude values,
y is given to the adder 84 via the squarer 831, 832 to obtain x+y, and when this is calculated via the squarer 85, it can be directly read with the ammeter 64 as the output current of 5, and A is arbitrarily determined. Therefore, if it is A-2, then R-E/
I, and the grounding resistance R can be easily calculated from the above indicated value.

Therefore, with such a configuration, even when the various equipment of the floating potential switchyard is in operation, the grounding resistance R can be measured with high precision without being affected by the floating potential E0.

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. .

For this reason, in substations and switchyards that operate under such conditions, when measuring the ground resistance with the above-mentioned measuring device,
The measurement will include all the grounding resistances of other electrical stations connected via the aerial grounding wire, as well as the grounding resistances of steel towers along the way, and there is a risk that the true grounding resistance of your own electrical station cannot be measured. be.

This invention was made in order to eliminate the above-mentioned drawbacks, and it is possible to measure the true ground resistance of one's own electrical station with high accuracy while it is in operation without being affected by the floating potential E0. 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 ground system to be measured, for example, the ground network 7.

Grounding networks 121 and 122 are connected to this grounding network 7 as grounding systems for other electrical stations connected via aerial grounding wires or the like. 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 grounding network 7, so that the current (2) flowing from the constant current amplifier 5 to the grounding network 7 is detected. Similarly, current transformers 141 and 1 are installed as current detection means on the lines between the grounding network 7 and the grounding networks 121 and 122 of other electrical stations, respectively.
42 and connect each grounding network 12 of the other electric station from the grounding network 7.
Current flowing through 1,122 11. I.

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. Furthermore, the voltage measuring section 8 in FIG. 5 is the same as that in FIG. 4, and the explanation here will be omitted.
It can be seen that the ground resistance can be measured without being affected by zero. 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 2. ．． 2m, 2. is the impedance of each line, Ro is the grounding network 7 to be measured (the resulting grounding resistance, R1, R is the grounding network 1λ1,
112 is the ground resistance.

However, in Figure 6 The relationship always holds true.

Therefore, the grounding resistance can be found from the beginning, but as it stands, the grounding resistance of other electrical stations is also included, so the true grounding resistance cannot be obtained.

Therefore, first of all, if we pay attention to (in Equation 13), this current flow leaks into the earth over a wider area than the grounding network 7 and cannot be directly measured, but the current flow detected by the current transformer 13 shown in Fig. 5, Similarly, based on the currents I, , I, respectively detected from the current transformers 141 and 142, I, =i-I, -I, ......
...-(3) That is, it is obtained as the output of the adder 15. Then, substitute this into equation (2). Then, a relationship is established.

As a result, adder 15 outputs crab first. Measure this 1
If the output of the constant current amplifier 5 is adjusted so that 0 becomes, for example, IA, and then the voltage V is determined as ÷÷1,000 + 1°, the grounding system to be measured, that is, the grounding network 7 of the electrical station to be measured. This means that the ground resistance of the two can be measured separately.

Therefore, in this way, the alternating current component including the floating potential Eo can be removed, and only the indicated value necessary for measuring the grounding resistance hole 0 of the grounding system to be measured at the own electric station can be calculated, so that the substation or switchyard can Even during operation, only the grounding resistance R6 of the own electric station can be measured with high precision without being affected by the floating potential Eo. This reduces the conventional floating potential E. In order to reduce the effect of can also be suppressed.

It should be noted that the present invention is limited only to the above-mentioned embodiments and can be implemented with appropriate modifications within the scope of the invention.

For example, in the above example, the multipliers 811 and 812 of the voltage measuring section 8 are supplied with the measurement power (2) and the reference signals Acosωt and As1nωt.

Although y is obtained, instead of this, the measured human power V may be directly switched using a square wave having a frequency ω. In addition, in the above description, in the voltage measuring section 8, the outputs x and y of the low-pass filters 821 and 822 are converted to the square
The output x and y are given to the adder 84 through the square waveform generator 84 and then added to the square waveform generator 85 to obtain the indicated value, for example, as shown in FIG. After switching each separately and feeding it to the adder 9, the fundamental wave component and harmonic component x cos ωt −1 − ys in ωt + harmonic component are obtained,
The indicated value may be obtained by passing only the fundamental wave component through the band-pass filter 10 and then detecting it at the detection circuit 11. 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 filters 831, 832... Squarer 84, 9... Adder 85...
・Squarer 1゛0... Bandpass filter 11
...Detection circuit 13,141,142...Current transformer 15...Adder Fig. 1 EZ EaE/ Fig. 3 Fig. 4 Fig. 5 17Z Fig. 6 Fig. 7

Claims (5)

[Claims] (1) Has a frequency slightly different from the commercial frequency and is 9
oscillating means for generating first and second reference signals having a 0° phase difference; and current generating means for receiving one of the reference signals, converting it into a current of constant amplitude and applying it to the grounding system under test. , detects the current flowing through the grounding system under test and the current flowing from the grounding system under test to another grounding system connected to this grounding system, and detects the current flowing through the grounding system under test from the other grounding system. means for detecting a current obtained by subtracting the current flowing through the grounding system; means for multiplying the measurement signal by the first reference signal; and means for multiplying the measurement signal by the second reference signal.
It is characterized by comprising means for multiplying by a reference signal, and a calculation means for extracting only each DC component from each of these outputs, squaring and adding these two DC component amplitude values, and obtaining a square root value. Earth resistance measuring device. (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 current detecting means includes a plurality of current transformers and an adder that adds the outputs of these current transformers with different polarities. Earth resistance measuring device. (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 earthing resistor 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. measuring device.