JPH0546506B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a grounding resistance measuring method for measuring grounding resistance at a telephone subscriber side.

Conventionally, the three-electrode method (potential drop method) has been generally used as the most reliable method for measuring ground resistance. However, in this method, two auxiliary electrodes must be implanted into the ground at a distance such that the resistance areas of the respective ground electrodes do not overlap. This distance usually extends to 10-20 meters. In addition, in order to implant the ground electrode, a place with exposed soil that is not covered with concrete or the like is required.

However, in the actual subscriber environment,
It is often extremely difficult to secure the above distance and still find a suitable place for pouring.
Moreover, the wiring must be done at a distance during the work, making the wiring work troublesome and requiring an AC power source, which is inconvenient.

The present invention eliminates the above-mentioned drawbacks of the conventional method by connecting a measuring circuit having an ammeter and a voltmeter using a subscriber telephone line, and eliminates the need to install a grounding electrode as an auxiliary grounding electrode on-site. To provide a grounding resistance measuring method capable of easily measuring grounding resistance in an extremely short time without needing to carry out wiring work or carrying a power supply device.

The present invention will be described by way of example with reference to the drawings. FIG. 1 shows lines between a telephone office 1 and a subscriber 2, and the circuits connecting them. On the telephone office 1 side, a station power supply 3 having an electromotive voltage E is provided, and is grounded by a grounding electrode 4. Let this station grounding resistance be R ₀ . A first line 5 and a second line 6 are provided between the telephone office 1 and the subscriber 2. Let the respective DC resistances be r ₁ and r ₂ .

The subscriber 2 is equipped with a protector 7 , the first terminal 8 of which is connected to the first line 5 , and the second terminal 9 of which is connected to the second line 6 . The third terminal 10 is connected to a ground electrode 11. Let this subscriber grounding resistance be _Re . 1st, 2nd, 3rd terminal 8, 9, 10
is further connected to telephone 12.

FIG. 2 shows a ground resistance measuring circuit 13, in which a load resistance 1 is connected between the first terminal 14 and the third terminal 15.
7 (resistance value R _L ) and an ammeter 18 connected in series. Further, the second terminal 19 and the third terminal 15 are connected by a voltmeter circuit having a voltmeter 20. A part of the ammeter circuit and the voltmeter circuit may be shared as shown in the figure.

In the measurement, the first, second, and third terminals 14, 19, and 15 of the ground resistance measuring circuit 3 are connected to the first, second, and third terminals 8, 9, and 10 of the protector 7, respectively. A circuit diagram in this state is shown in FIG. 3 (telephone 12 is omitted). E′ represents the electromotive force due to stray current.

An opening/closing mechanism 1 is provided between the first terminal 8 and the first terminal 14.
6. This opening/closing mechanism 16 connects the first terminal 1 to the first terminal 8 by using a device such as a switch or by manually moving the contacts into and out of contact.
4, or separating the ends of the lead wires connected thereto.

In this case, R _L and the voltmeter 20 are arranged so that the load resistance R L is much larger than r ₁ and the internal resistance of the voltmeter 20 is much larger than r ₂ , R ₀ , and _{R e} .
Choose an internal resistance such that r ₁ and r ₂ can be ignored. Furthermore, by setting R _x =R ₀ +R _e (1), the circuit diagram of FIG. 3 is simplified as shown in FIG. 4.

When making measurements in such a circuit, errors occur due to the influence of stray currents, so it is necessary to remove this influence. For this reason, when making measurements, first the opening/closing mechanism 16 is opened and the voltmeter 20 is opened.
Measure the voltage. If the voltage at that time is V', then R _x is very small compared to the internal resistance of the voltmeter 20, so V'=E' (2) In other words, the electromotive force E' due to the stray current is measured.

Next, close the opening/closing mechanism 16 and measure with the ammeter 18 and voltmeter 20. If the current at that time is I and the voltage is V, then V-E'=R _x I (3) (1 ) and (2), the subscriber side earthing resistance R _e can be determined as R _e =V-V'/i-Ro (4) excluding the influence of stray current.

For this measurement, all you have to do is connect each terminal of the compact earth resistance measuring circuit 13 to each terminal of the protector 7, and then open and close the opening/closing mechanism 16, for example by turning a switch or by manually releasing the contacts. It is extremely simple to perform simple opening/closing operations such as connecting and separating the ends of the lead wires, reading current values and voltage values, and calculating according to (4).

In the above-mentioned embodiment, there is no need to place the ground electrodes one by one on site, there are no drawbacks of the conventional method of placing earth electrodes (large restrictions due to mutual spacing and ground conditions), and there is no need for wiring work. Furthermore, there is no need to carry a power supply device, and measurements can be easily carried out in an extremely short time and without being affected by stray currents.

In the measurement method as in the above embodiment, since the current is a short-time minute current, the polarization effect is small. However, if the influence of polarization is to be eliminated, the following method may be used.

Fig. 5 is a circuit diagram showing a case where there is a polarization effect Do of the station grounding and a polarization effect D _e of the subscriber side grounding.
This corresponds to Figure 3. FIG. 6 is a simplified circuit diagram similar to FIG. 4.

However, D _x = Do + D _e (5).

The relationship between the numerical values when the opening/closing mechanism 16 is closed is as follows:
If the terminal voltage of the polarization effect D _x is V _d , then V = IR _x + V _d + E' (6).

Here, the load resistance R _L is changed and the measurement is performed twice.
The voltage values at that time are V ₁ , V ₂ (according to voltmeter 20),
If the voltage values I ₁ and I ₂ (measured by the voltmeter 18) and the terminal voltages of the polarization effect D _x are V _d1 and V _d2 (not measured),
Since the electromotive force E' of the stray current does not change, V ₁ = I ₁ R _x + V _d1 + E' (7) V ₂ = I ₂ R _x + V _d2 + E' (8) ∴V1−V ₂ = (I ₁ − I ₂ )R _x + (V _d1 −V _d2 ) (9) Here, if V _d i=R _d I _i +V _d (10) then V ₁ −V ₂ = (I ₁ −I ₂ )R _x +R _d (I ₁ −I ₂ ) (11) Therefore, R _x =V ₁ −V ₂ /I ₁ −I ₂ −R _d (12) Here, since R _x >>R _d (13), R Ignoring _d and substituting (1), the subscriber side earthing resistance R _e is calculated as R _e =V ₁ −V ₂ /I ₁ −I ₂ −R _p (14) excluding the influence of polarization. , can be found.

According to the present invention, the grounding resistance is measured using two electrodes, the grounding electrode to be measured and one auxiliary grounding electrode, and the auxiliary grounding electrode is connected to the first line and the second line on the subscriber telephone side. and a ground line, the first line and the ground line are connected by an ammeter circuit comprising a load resistor and an ammeter opening/closing mechanism and connected in series, and the second line and By using a voltmeter circuit with a voltmeter connected to the ground line, the central office power supply and central office ground on the telephone office side can be used as an auxiliary grounding electrode, and grounding can be done on site. There is no need to place electrodes, and therefore there are no problems associated with placing electrodes (securing placement intervals, restrictions on ground surface conditions, etc.), and there is no need for wiring work.
It is possible to provide a grounding resistance measurement method that does not require carrying a power supply device, allows measurement work to be easily carried out in an extremely short time, and also allows measurements to be made without the effects of stray current or polarization. ,
This has an extremely large practical effect.

[Brief explanation of the drawing]

The drawings relate to embodiments of the present invention; Fig. 1 is a circuit diagram of a telephone line, Fig. 2 is a circuit diagram of a grounding resistance measuring device, Fig. 3 is a circuit diagram during measurement, and Fig. 4 is a simplified version thereof. FIG. 5 is a circuit diagram at the time of measurement of another example, and FIG. 6 is a simplified circuit diagram thereof. 1... Telephone office, 2... Subscriber, 3... Station power supply, 4...
Grounding electrode, 5...first line, 6...second line, 7...protector, 8...first terminal, 9...second terminal, 10...third
Terminal, 11... Ground electrode, 12... Telephone, 13... Ground resistance measuring circuit, 14... First terminal, 15... Third terminal, 16... Opening/closing mechanism, 17... Load resistance, 18... Ammeter, 19... Second terminal , 20... Voltmeter.

Claims (1)

[Claims] 1. A method for measuring ground resistance using two electrodes: a grounding electrode to be measured and one auxiliary grounding electrode.
With respect to the line and the ground electrode line, the first line and the ground line are connected by an ammeter circuit comprising a load resistor and an ammeter opening/closing mechanism and connected in series; When using a voltmeter circuit with a voltmeter connected between the line and the ground line, and mainly eliminating the influence of stray current, use the method (1) below to mainly eliminate the influence of polarization. A grounding resistance measurement method characterized by using the method (2) below if the earthing resistance is excluded. (1) The voltages measured by the voltmeter when the connection between the ammeter circuit and the first line is opened and closed by the opening/closing mechanism are V ₁ and V, respectively.
When the current measured by the ammeter with the connection between the ammeter circuit and the first line closed is I, and the grounding resistance on the telephone office side is Ro,
The grounding resistance Re in the grounding line is determined as Re=V-V'/I-Ro. (2) With the connection between the ammeter circuit and the first line closed by the opening/closing mechanism, change the load resistance and measure twice, and set the voltages measured by the voltmeter to V ₁ and V ₂ , the currents measured by the ammeter are I ₁ and I ₂ , and the grounding resistance on the telephone office side is Ro, then the grounding resistance Re in the grounding line is Re=V ₁ −V ₂ /I ₁ −I ₂ −Ro.