JPH03180771A - Earthing resistance measurement method - Google Patents

Abstract

PURPOSE:To easily perform a connection test of cable metal sheath and a grounding resistance measurement for both terminals at the same time and to attain a drastic reduction of the working time by measuring a loop resistance of return line of an induction shielding cable to the earth. CONSTITUTION:When a constant voltage E driven by a transmitter 17 is impressed to a return circuit to the earth constituting of the metal sheath 1 of induction shielding cable and grounding devices 2, 3 of both terminals thereof by using a current transformer 15, a circuit current I is made to flow. The loop resistance of return circuit to the earth, R+(RE1+RE2) is measured by means of detecting the circuit current I with a current transformer 16 and an ammeter 18. Since the resistance R of metal sheath 1 is already known according to the sort of cables, the total value of grounding resistances of both terminals, RE1+RE2 is obtained. In the case the metal sheath 1 is not connected, the circuit current I is not detected and the disconnection can be decided, so the connection test is as good as performed at the same time. Then, the measuring time is reduced to about 1/20 as compared with the conventional measuring method, and also the workability is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for conducting a continuity test of an induction shielding cable metal sheath and at the same time easily measuring the grounding resistance of both terminals.

[Conventional technology and issues to be solved]

Induction shielding cables are used for the purpose of reducing induced voltage from power transmission lines, etc., so for cable maintenance, it is necessary to ensure that there are no breaks in the earth return circuit, which consists of the cable metal sheath and the ground at both ends. It is also necessary to maintain the total ground resistance of both terminals of the metal sheath below the required resistance value.

For this reason, conventionally, two measurements were performed: a continuity test of the metal sheath and a ground resistance measurement of both terminals.

The conventional measurement method and its drawbacks are described below.

First, a method for testing the continuity of the metal sheath shown in FIG. 3 will be described. l is induction shielding cable metal sheath, 2,
3 is a ground, 4 and 5 are ground wires, and 6 is an insulation resistance meter. The metal sheath continuity test method involves cutting off the ground wire 4 at one end, inserting an insulation resistance meter 6 between the ground wire 4 and the ground 2, and checking the continuity of the metal sheath l. For this reason, it takes time and effort to temporarily disconnect the grounding wire, and if a ground fault occurs on a power transmission line while the grounding wire is disconnected, the cable core is This has the disadvantage that an excessive voltage is generated in the inductive shielding cable, and the inductive shielding cable cannot perform its original function.

Next, a method for measuring the ground resistance of both terminals shown in FIG. 4 will be described. The same symbols as in Fig. 3 indicate the same things, and 7
is temporary grounding, 8 and 9 are auxiliary grounding rods, 10.11, 12.1
3 is a lead wire, and 14 is a ground resistance meter.

While securing the grounding of the induction shielding cable metal sheath l by connecting the grounding wire 4 and the temporary grounding 7 using the lead wire IO, disconnect the grounding wire 4 on the side closer to the grounding 2 from this grounding point. do.

Next, drive the auxiliary ground rods 8.9 50 m and 100 m apart from the ground 2, respectively, and connect the lead wire Il.

12.13 were connected to the terminals E, P, and C of the ground resistance meter 14, and a current I was passed between E and C to find the ground resistance R=V/I from the voltage V between E and 2.

For this reason, the conventional grounding resistance measuring method requires driving in the auxiliary grounding rods 8 and 9 and laying the temporary grounding 7, which has the drawback of requiring a long time for measurement work. Furthermore, recently, due to the density of buildings and the expansion of road pavement, it has been difficult to secure a place for driving the temporary grounding rod 7 and the auxiliary grounding rods 8, 9.

The purpose of the present invention is to solve the drawbacks of the two conventional measurement methods mentioned above, namely, the continuity test of the metal sheath and the measurement of the ground resistance of both ends, and to be able to carry out the two measurements simultaneously. The objective is to provide a measurement method.

[Means to solve the problem]

The present invention measures the loop resistance of the earth return path constituted by the metal sheath of an inductive shielding cable and the ground at both ends thereof, and easily measures the earthing resistance of the cable metal sheath from this loop resistance measurement value. The most important feature.

〔Example〕

Figure 1 shows an embodiment of the present invention, where ■ is an induction shielding cable metal sheath, 2 and 3 are grounding, 4.5 is a grounding wire, and 15
．． 16 is a divisible current transformer, 17 is a transmitter,
18 is an ammeter.

When the constant voltage E driven by the transmitter 17 is applied using the current transformer 15 to the earth return circuit constituted by the induction shielding cable metal sheath l and the ground 2 and 3 at both terminals, the earth return circuit When a circuit current I flows, the following equation is established.

E/I=R+ (REI+RE2) (1) Here, R is the resistance of the cable metal sheath l, RE I I
RE 2 are the ground resistances of ground 2 and ground 3, respectively.

Therefore, if the drive voltage E is constant, the earth return circuit loop resistance R+ (RE l +
RE2) can be measured. Here, since the resistance R of the cable metal sheath is known depending on the cable type, the sum of the grounding resistances of both terminals RE1 + RE2
(The grounding resistance of an inductive shielding cable is defined by the sum of the grounding resistances of both terminals).

Note that if the induction shielding cable metal sheath is not conductive, it is possible to determine a disconnection because the circuit current (■) is not detected, and a continuity test is performed at the same time.

As a result of measuring the ground resistance of the currently used induction shielding cable sheath according to the above embodiment, it was confirmed that the measurement results according to the present invention and the measurement results according to the conventional method were in good agreement. In addition, compared to the 2 hours required by the conventional measurement method, the measurement time of the present invention is approximately 1/20 of that time.
Workability has also improved.

FIG. 2 shows another embodiment of the present invention, where l is the induction shielding cable metal sheath, 2.3 is the ground, 4°5 is the grounding wire,
19 is a current measuring section using a split type current transformer, 2
0 is a voltage measuring section, and 21 is a divider. In order to operate this, the current measuring section 19 is used to measure the current I which is constantly flowing by induction from the power transmission line into the earth return circuit constituted by the metal sheath of the induction shielding cable and the ground at both terminals. Using the voltage measuring unit 20, measure the voltage V between the ground 2 of the terminal of the metal sheath of the induction shielding cable caused by this current and the far point, and using the divider 21, measure the voltage V between the metal sheath of the induction shielding cable The ground resistance V/I=R81 at the end of the sheath piece can be determined. Furthermore, the ground resistance RE2 of the other terminal can be measured by repeating the same measurement procedure.

As a result of measuring the grounding resistance of a metal sheath of an inductive shielding cable currently in use according to another embodiment of the present invention, it was confirmed that the measurement results according to this embodiment and the measurement results according to the conventional method were in good agreement. Furthermore, compared to the conventional measuring method which required about 40 minutes, the measurement time in this application example is about 1/20 of that time, and the workability is also improved.

〔Effect of the invention〕

As explained above, by measuring the loop resistance of the ground return path of the inductive shielding cable, the continuity test of the cable metal sheath and the ground resistance of both terminals can be performed without the need for disconnecting the ground wire, temporary grounding, or auxiliary grounding rod. This method has the advantage that measurements can be performed simultaneously and easily, and working time can be significantly shortened. Another advantage is that ground resistance can be measured even in locations where temporary grounding and driving of auxiliary grounding rods are difficult due to road pavement.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the invention. FIG. 2 shows another embodiment of the invention. FIG. 3 shows a conventional method for testing continuity of a metal sheath of an induction shielding cable, and FIG. 4 shows a conventional method for measuring ground resistance at both ends of an induction shielding cable. l...Induction shielding cable metal sheath, 2, 3...
・Grounding, 4, 5...Grounding wire, 6...Insulation resistance meter, 7
...temporary grounding, 8,9...auxiliary grounding rod, 10, l resistance meter, 17 window, 2 1.12.13...lead wire, 14...grounding 15.
16...Dividable current transformer...Emitter, 1
8... Ammeter, 19... Current side 0... Voltage measuring section, 21... Divider.

Claims (2)

[Claims] (1) A split current transformer is used to flow a current driven at a constant voltage into a part of the earth return circuit, which is made up of the metal sheath of the inductive shielding cable and the ground at both ends. Detect the current flowing in the return circuit with another split current transformer, measure the loop resistance of the earth return circuit based on the ratio of the driving constant voltage and the detected current, and calculate the earth resistance of both terminals from this loop resistance measurement value. A grounding resistance measuring method characterized by: (2) A split current transformer detects the current flowing in the earth return circuit, which is made up of the metal sheath of the inductive shielding cable and the ground at both terminals, and this current connects the earth to the ground at one terminal. A grounding resistance measuring method, characterized in that the grounding resistance of the one terminal is determined by measuring the potential difference generated between the two terminals with a voltage measuring section and calculating the ratio between the measured voltage and the detected current using a divider. .