KR100821705B1 - Earth resistance measurement method by clamp-on type current comparison - Google Patents

Abstract

The present invention relates to a method for measuring ground resistance, the method for measuring ground resistance of each ground wire at a place where at least three ground wires are commonly connected, comprising: (a) clamping a core wound with a coil to each ground wire; Doing; (b) supplying a measurement power source to the coil of the core fastened to one of the ground lines; (c) measuring each ground line flow by detecting a current flowing through a coil of a core mounted on each ground line; (d) repeating steps (b) and (c) to sequentially supply measurement power to the coils of each core and measure each ground line current; And (e) measuring the ground resistance of each ground line by a relationship between the core-side ground line voltage and current to which the measurement power is supplied and the common ground ground current on the core side to which the measurement power is not supplied. By sequentially switching and measuring ground resistance using current changes on the core side where the switch is inserted and the core side where the switch is opened, it is possible to easily measure without complicated work such as sealing the auxiliary electrode. Even accurate measurement of ground resistance can be achieved.

Ground Resistance, Core, Primary Coil, Secondary Coil, Switch, Ammeter

Description

Earth resistance measurement method by clamp-on type current comparison

1 is an illustration of a conventional potential drop measurement method

2 and 3 is an exemplary view of a conventional hook-on measurement method

Figure 4 is an illustration of a grounding resistance measuring apparatus according to the present invention

5 is an equivalent circuit diagram of an earth resistance measuring apparatus according to the present invention.

6 through 8 are circuit diagrams illustrating a method of measuring ground resistance according to the present invention.

<Explanation of symbols for the main parts of the drawings>

10: distribution line 15: neutral point

20: ground booth 30: core

31: primary coil 32: secondary coil

35 measurement power 40 switch

45 ammeter

The present invention relates to a method for measuring ground resistance, and can be easily measured by not using an auxiliary electrode, and more particularly, to a method for measuring ground resistance that enables a more accurate measurement of ground resistance even at a small place.

Distribution lines or other electrical equipment are grounded to discharge abnormal currents or lightning strikes to the ground, thereby ensuring the reliability of the power system and preventing safety accidents such as electric shocks. In general, grounding is performed by connecting a grounding point of a distribution line or an enclosure or grounding line of an electric device to a grounding electrode in the ground. At this time, a ground resistance of approximately several Ω to several hundred Ω is generated by the electrical resistance component between the ground electrode and the ground.

Very low grounding resistance is required for stable discharge of abnormal current and lightning, and grounding method limits the grounding resistance according to the type of grounding work. Since the ground resistance may be changed by various peripheral factors even after the initial construction, it is necessary to periodically measure the ground resistance to maintain a stable power system. Ground resistance is usually measured by artificially applying current through the ground wire, then measuring the voltage and current values to calculate the resistance value by Ohm's law. As a typical method of measuring ground resistance, a potential drop measuring method and a hook-on measuring method have been disclosed.

Figure 1 illustrates a ground resistance measurement method by the conventional potential drop measurement method. Referring to this, the potential drop measurement method, also referred to as a three-point method, the potential auxiliary electrode (P) and the current auxiliary electrode (C) is sealed at a predetermined distance from the ground electrode (E) to be measured, and the C terminal of the measuring device (3) It is a method to find ground resistance by measuring a voltage after passing a constant current. This potential drop measurement method is usually performed at the beginning of the construction of the grounding work, and is suitable for a case where the exact position of the grounding electrode is known. However, there is a problem that it is difficult to apply when the ground booth and the ground electrode are different or in places where the auxiliary electrode is difficult to install. In addition, there is a problem that involves a complicated operation such as sealing the auxiliary electrode.

2 and 3 illustrate a conventional hook-on measurement method. Referring to this, in the ground wire current measuring method, the coil 5 wound around the core is hooked to the ground wire side as shown in FIG. 2, and after applying a power supply to the coil, the current flowing through the ground wire is detected to measure the ground resistance. do. FIG. 3 is a circuit diagram showing the hook-on measuring device 7, wherein the ratio between the measuring power supply Eo and the voltage across the ground resistance E is measured power supply side current Io and ground line side current I. FIG. Using the transformer principle inversely proportional to), it is obtained by the following equation.

This hook-on measurement method is mainly used in a multi-ground method in which a plurality of ground electrodes are connected in parallel. Referring to Figure 2, the ground resistance Rx is calculated by the following equation.

At this time, when there are a large number of multiple grounds ranging from R1 to Rn, compared with Rx, the subsequent parallel synthesized resistance value becomes small enough to be negligible. Therefore, the ground resistance Rx can be obtained only by the voltage E across the ground resistance and the ground line current I. Will be.

However, when there are few common grounding points, the sum of other resistance values connected in parallel cannot be ignored, and there is a problem in that the grounding resistance cannot be obtained by hook-on measurement.

The present invention has been proposed to solve the above problems, so that the ground resistance can be usefully measured at a location where the buried position of the ground electrode is not accurately known or where the auxiliary electrode is difficult to seal, or at a location where the common ground is small. It is an object of the present invention to provide a method of measuring ground resistance.

In addition, an object of the present invention is to provide a method of measuring ground resistance, which allows a relatively small number of ground resistance values of each ground line connected to each other to be more accurately measured using the ground line side current.

In the ground resistance measuring apparatus of the present invention for achieving the above object is a ground resistance measuring apparatus for measuring at least three ground resistance is mounted to a common ground connected to the ground wire, the core is clamped to each ground wire, A coil wound around each core, a switch provided for each core to control supply of measurement power to each coil, and an ammeter connected in series to each coil side to detect a current flowing through each ground line; It is characterized in that the configuration.

Preferably, the coil is wound by winding the primary coil and the secondary coil separately on the primary side and the secondary side of each core, the measurement power is selectively supplied to the primary coil by a switch, the ammeter is 2 And to detect a current induced in the secondary coil.

The measurement power supply is a high frequency power supply having a commercial power frequency or higher.

Ground resistance measurement method of the present invention for achieving the above object is a ground resistance measurement method for measuring the ground resistance of each ground wire in a place where at least three ground wires are commonly connected, (a) coils are wound around each ground wire Clamping the completed core; (b) supplying a measurement power source to the coil of the core fastened to one of the ground lines; (c) measuring each ground line flow by detecting a current flowing through a coil of a core mounted on each ground line; (d) repeating steps (b) and (c) to sequentially supply measurement power to the coils of each core and measure each ground line current; And (e) measuring the ground resistance of each ground line by a relationship between the core-side ground line voltage and current to which the measurement power is supplied and the common ground ground current on the core side to which the measurement power is not supplied. .

Preferably, in the core, the primary coil and the secondary coil are separately wound and wound. In step (b), the measurement power is supplied to the primary coil, and in step (c), the current induced in the secondary coil is supplied. Detect and measure ground line current.

In addition, the step (b) is performed in a state in which the switch is opened to supply the measurement power to one ground line and the supply of the measurement power to the other ground line.

In addition, in step (c), both the ground line side current supplied with the measurement power supply and the ground line side current cut off the measurement power supply are detected.

In one embodiment of the present invention, the step (e) is; (e-1) obtaining a relationship between a current value applied to the parallel ground line from which the measurement power supply is cut off and each ground resistance of the parallel ground line; (e-2) displaying the total combined resistance as a ratio of the supply voltage and the ground line current on the ground line side to which the measurement power supply is supplied; (e-3) Using the relational equation obtained in the above step (e-1), the ground resistance value of the one ground line is measured using the core side ground line voltage and current supplied with the measurement power supply and the common ground ground line current of the core side without the measurement power supply. It is represented by the relational expression of, and the step of obtaining the ground resistance value of the ground line on one side.

If the ground resistance of one ground line is obtained in step (e-3), the method further includes the steps of obtaining ground resistances of the other ground lines using the relational expression of step (e-1).

In another embodiment of the present invention, if there is only one measurement ground line, the method may further include installing two or more virtual auxiliary ground lines before the step (a), and in step (a), the measurement target ground line and each virtual auxiliary ground line may be provided. Clamp the core around the coil.

In another embodiment of the present invention, if there are two measurement ground wires, the method may further include installing one or more virtual auxiliary ground wires before the step (a), and in step (a), each measurement ground wire and each virtual auxiliary earth line may be provided. Clamp the core wound with the ground wire.

In the ground resistance measuring method of the present invention, the measurement power supply is a high frequency power supply having a commercial power frequency or higher.

According to another feature of the present invention, the ground resistance measuring apparatus of the present invention for achieving the above object is at least three or more mounted on a common ground connected to the ground resistance measuring apparatus for measuring ground resistance, wherein A core clamped to each of at least two ground wires, a coil wound around each core, a switch provided for each core to control supply of a measurement power supply to each coil, and connected in series to each coil side And an ammeter for detecting a current flowing in the ground line.

Preferably, the coil is wound around a primary coil and a secondary coil separately on the primary side and the secondary side of each core, the measurement power is selectively supplied to the primary coil by a switch, the ammeter is secondary And to detect a current induced in the coil.

According to another aspect of the present invention, the method of measuring the ground resistance of the present invention for achieving the above object in the ground resistance measuring method for measuring the ground resistance of each ground wire at a place where at least three ground wires are commonly connected, ( o) clamping a core wound with a coil to each of at least two ground wires of the ground wires; (p) supplying measurement power to a coil of the core fastened to one of the ground wires; (q) measuring each ground line flow by detecting a current flowing through a coil of a core mounted on each ground line; (r) calculating the Kirchhoff's law using the current value measured in the step (q) of the ground line current without the core; (s) repeating steps (p) to (r) to sequentially supply measurement power to the coils of each core and measure each ground line current; And (t) measuring the ground resistance of each ground line by a relationship between the core-side ground line voltage and current to which the measurement power is supplied and the common ground ground current on the core side to which the measurement power is not supplied. .

Preferably, in the core, the primary coil and the secondary coil are separately wound and wound. In step (p), the measurement power is supplied to the primary coil, and in step (q), the current is induced in the secondary coil. Is made to measure the ground line current.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings and embodiments. 4 is an exemplary view of a grounding resistance measuring apparatus according to the present invention, FIG. 5 is an equivalent circuit diagram of the grounding resistance measuring apparatus according to the present invention, and FIGS. 6 to 8 illustrate a method of measuring grounding resistance according to the present invention. One schematic.

First, referring to the exemplary diagram of FIG. 4 and the equivalent circuit diagram of FIG. 5, this embodiment illustrates the ground of the neutral point 15 of the distribution line 10, and the ground electrode to be measured is connected to the ground booth 20. Two distribution lines 10 are neutral ground electrodes and ground electrodes of the ground booth 20. The ground resistance of each ground electrode is R1, R2, R3.

The ground resistance measuring apparatus of the present invention is applied to a place where at least three or more ground wires are commonly connected, and a core 30 wound around a coil is clamped to each ground wire. In the present embodiment, three sets of cores 30 are fastened, but three or more sets of cores 30 may be used depending on the number of ground wires. An ammeter 45 is connected to the coil of each core 30 in series, and the measurement power supply 35 is supplied through the switch 40 connected in parallel to this ammeter. Preferably, in order to separate the measuring power supply 35 and the ammeter 45, in the embodiment shown in FIG. 4, the primary coil 31 and the secondary coil 32 are spaced apart from each other in each core 30. And wound around, the measurement power 35 is connected to the primary coil 31 via the switch 40, and the measurement power 35 is selectively supplied by the interruption of the switch 40, and the secondary coil 32 ) Are individually connected in series with an ammeter 45 for detecting each ground line side current. Preferably, the measuring power supply 35 is a high frequency power supply above a commercial power supply frequency in order to eliminate the influence of an external device and detect only the current component by the measuring power supply 35. For example, the measurement power supply 35 has a frequency of 2000 to 3000 kHz.

The method of measuring ground resistance using the ground resistance measuring apparatus of the present invention will be described with reference to the circuit diagrams of FIGS. 6 to 8 as follows.

In the ground resistance measuring method of the present invention, by sequentially switching each switch 40, the measurement power is sequentially supplied to the core 30 fastened to each ground wire, and the secondary coil of the side core 30 to which the measurement power is supplied. The ground resistance of each ground wire is measured by using the change state of the current flowing through the secondary coil 32 of the side core 30 to which the power supply 32 and the measurement power supply are not supplied.

First, when the switch SW1 is put in and SW2 and SW3 are opened, the equivalent circuit as shown in FIG. At this time, the current flowing through each ground line is detected by ammeters A1, A2, and A3. In the circuit diagram of Fig. 6, the ground line current I1 on the side to which SW1 is input is distributed and applied to the ground line side on which SW2 and SW3 are open, and the same voltage is applied across ground resistances R2 and R3. If this is expressed as a formula, it is (I2R2 = I3R3), and the following formula can be obtained.

In the same manner, when SW2 is input and the remaining switches SW1 and SW3 are opened, an equivalent circuit as shown in FIG. 7 is configured. Here, the same voltage is applied to both ends of the ground resistors R1 and R3, and the following equation can be obtained from the formula (I1'R1 = I3'R3).

In addition, when SW3 is input and the remaining switches SW1 and SW2 are opened, an equivalent circuit as shown in FIG. 8 is configured, where the same voltage is applied across the ground resistors R1 and R2, and (I1 " R1 = I2 " R2). In the formula, the following expression can be obtained.

In formula (3), the following formula is obtained,

In equation (2), the following equation is obtained.

Again, in the circuit diagram of Fig. 6, the synthesis resistance Ro of the entire circuit has the following formula.

Then, by substituting the values obtained by the formulas (4) and (5) into R2 and R3 of the formula (6), the following formula (7) is finally calculated to obtain the value of the ground resistance R1.

Referring to Equation (7), the values of the ground resistance R1 are the core side ground line voltage (E) and current (I) to which the measurement power is supplied and the common ground line current (I1 ', I1) to the core side where the measurement power is not supplied. '', I2 '', I3 ').

As described above, the ground resistance measuring method of the present invention detects the current flowing through the ground wires in each state in which the switches SW1, SW2, and SW3 are sequentially switched by the ammeters A1, A2, and A3, Calculate the ground resistances R1, R2, and R3 with constant values by the relationship between the current of the ground line and the current of the ground line that is not supplied with the measurement power supply (Equation (7)).
Therefore, it is not necessary to separate the auxiliary electrode, and even more accurate measurement of the ground resistance can be performed even when the embedding position of the ground electrode is not correct. Meanwhile, in the present embodiment, the case where the three ground wires are connected in common is taken as an example, but the present invention can be applied even if the number of ground wires increases.

The present invention is to measure the ground resistance by fastening three or more sets of cores 30 to each ground line of three or more lines, but the present invention can be applied to the case where one or two ground electrodes are used.

When the number of ground electrodes to be measured is one, two or more auxiliary grounds may be installed to measure the ground resistance by installing the apparatus of the present invention. In this case, as in the conventional potential drop measurement method, there is no need to immerse the auxiliary electrode at a predetermined distance. A virtual ground wire is connected to a nearby water pipe or a metal material, and a total of three wires are provided with a ground wire, and then three sets of cores 30 are connected to each ground wire. The ground resistance can be measured by the fastening method described above. Similarly, when two ground electrodes are measured, one or more auxiliary electrodes may be used.

In addition, the ground resistance measuring apparatus may be applied to other devices connected to the ground booth 20 in common, or to one or two ground electrodes.

For example, in the circuit diagram of FIG. 4, when the ground wire of another electrical device is held in the ground booth 20, the ground resistance R of the electrical device may be further connected in parallel to the ground resistance R3 as indicated by a dotted line in the equivalent circuit diagram of FIG. 5. . In this case, the value of the current flowing through the ground resistor R can be obtained by a calculation formula through the measurement of the current flowing through the ground resistor R3. For example, according to Kirchhoff's law such as I1 = I2 + I3 as shown in FIG. 6, the current of the ground wire to which the core is not fastened can be obtained. According to this method, of course, even when measuring the grounding resistance of a three-wire ground wire, two sets of cores are fastened, and the ground wire current on the side where the core is not fastened can be obtained by Kirchhoff's law. Accordingly, by installing the device of the present invention on the ground line side less than the number of common grounded ground electrode and calculating the remaining ground line current by a formula, it is possible to measure the ground resistance more easily and to make the device compact and portable. I can do it.

The present invention is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes are possible within the scope without departing from the technical spirit of the present invention. It will be apparent to those who have knowledge.

As described above, in the ground resistance measuring method according to the present invention, after the cores are wound around each of the three or more wires, and the measurement power is sequentially supplied to each coil, current values induced in the ground wires are obtained. By measuring the ground resistance by the current distribution ratio, it is possible to measure the accurate ground resistance even when the position of the ground electrode is not accurate. The measurement work is very easy because the auxiliary electrode does not need to be sealed at a certain distance. Therefore, it is effective to measure more accurate ground resistance even in places where there are few grounding points.

In addition, the present invention is based on the measurement of the ground resistance at the place where the three-wire ground wire is arranged, but even in one or two ground electrodes, a virtual ground wire can be measured by surrounding a water pipe or a metal material, and the conventional potential drop Compared to the measurement method, a simple and accurate measurement of the grounding resistance is possible, and unlike the conventional hook-on measuring method, there is an effect that the measurement of the reliable grounding resistance can be performed at a location having a small common ground.

In addition, the present invention measures the ground wire current with a smaller number of clamp core sets than the number of the ground wires to be measured, and the remaining ground wire current is obtained using Kirchhoff's law, which simplifies the operation of measuring the ground resistance and makes the device compact. There is an effect to facilitate the design and portability.

In addition, the present invention has the effect of eliminating interference by an external device by using a high frequency power supply of a commercial power frequency or more as a measurement power supply.

Claims (16)

delete delete delete In the ground resistance measuring method for measuring the ground resistance of each ground wire in a place where at least three ground wires are commonly connected, (a) clamping the cores around which the coil is wound on each ground wire; (b) supplying a measurement power source to the coil of the core fastened to one of the ground lines; (c) measuring each ground line flow by detecting a current flowing through a coil of a core mounted on each ground line; (d) repeating steps (b) and (c) to sequentially supply measurement power to the coils of each core and measure each ground line current; And (e) measuring the ground resistance of each ground line by a relationship between the core-side ground line voltage and current to which the measurement power is supplied and the common ground ground current on the core side to which the measurement power is not supplied. How to measure resistance. The method of claim 4, wherein In the core, the primary coil and the secondary coil are wound separately, and in step (b), the measurement power is supplied to the primary coil, and in step (c), the current is induced in the secondary coil and the ground wire is detected. Earth resistance measuring method characterized in that for measuring the current. The method according to claim 4 or 5, The step (b) is a ground resistance measurement method, characterized in that the switch is supplied in the state of supplying the power supply to the ground line and the other ground wire is opened in the switch to cut off the supply of the measurement power. The method according to claim 4 or 5, The step (c) is a ground resistance measurement method characterized in that it detects both the ground line side current supplied the measurement power supply and the ground line side current is cut off the measurement power supply. The method according to claim 4 or 5, Step (e) comprises; (e-1) obtaining a relationship between a current value applied to the parallel ground line from which the measurement power supply is cut off and each ground resistance of the parallel ground line; (e-2) displaying the total combined resistance as a ratio of the supply voltage and the ground line current on the ground line side to which the measurement power supply is supplied; (e-3) Using the relational equation obtained in the above step (e-1), the ground resistance value of the one ground line is measured using the core side ground line voltage and current supplied with the measurement power supply and the common ground ground line current of the core side without the measurement power supply. The method of measuring ground resistance, comprising the steps of: The method of claim 8, If the ground resistance of the one ground line in the step (e-3) is obtained, further comprising the step of obtaining the ground resistance of the other ground line using the relation of step (e-1). The method according to claim 4 or 5, If there is only one grounding target wire, the method may further include installing two or more virtual auxiliary grounding wires before the step (a), and in step (a), clamp the core wound with the coil to the grounding grounding wire and each virtual auxiliary grounding wire. Grounding resistance measuring method characterized in that the fastening. The method according to claim 4 or 5, In the case of two measurement target ground wires, the method may further include installing one or more virtual auxiliary ground wires before the step (a), and in step (a), a core having coils wound around each measurement ground wire and each virtual auxiliary ground wire. Grounding resistance measuring method characterized in that the clamp is fastened. The method according to claim 4 or 5, The measurement power supply is a ground resistance measurement method, characterized in that the high frequency power supply more than the commercial power frequency. delete delete In the ground resistance measuring method for measuring the ground resistance of each ground wire in a place where at least three ground wires are commonly connected, (o) clamping a core wound with a coil to each of at least two ground wires of the ground wires; (p) supplying measurement power to a coil of the core fastened to one of the ground wires; (q) measuring each ground line flow by detecting a current flowing through a coil of a core mounted on each ground line; (r) calculating the Kirchhoff's law using the current value measured in the step (q) of the ground line current without the core; (s) repeating steps (p) to (r) to sequentially supply measurement power to the coils of each core and measure each ground line current; And (t) measuring the ground resistance of each ground line by a relationship between the core-side ground line voltage and current to which the measurement power is supplied and the common ground ground current on the core side to which the measurement power is not supplied. How to measure resistance. The method of claim 15, In the core, the primary coil and the secondary coil are wound separately, and in step (p), the measurement power is supplied to the primary coil, and in step (q), the ground current is detected by detecting the current induced in the secondary coil. Earth resistance measuring method characterized in that for measuring the current.

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