JPH0434702B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Field of Industrial Application The present invention relates to a distance measuring method to a disconnection point that is effective for detecting a disconnection failure point in, for example, underground or undersea cables.

(b) Prior Art Generally, when a breakage occurs in an insulated cable (such as an electric wire), it is extremely difficult to find the breakage point without removing the cable coating. In particular, underground power cables that are difficult to access directly,
It is almost impossible to know the distance to the point of disconnection in submarine cables, etc. In recent years, methods to solve this problem include introducing pulse voltage into the cable and detecting the delay in reflected voltage, and Although attempts have been made to calculate this by comparing it with the capacity of

(C) Purpose The purpose of the present invention is to provide a cable that includes at least one pair of core wires, even if the cable core wire is covered with an outer jacket, or even if the cable is buried underground or laid on the ocean floor. It is an object of the present invention to provide a distance measuring method to a wire breakage point that can accurately and easily find the wire breakage point.

(d) Configuration In order to achieve the above object, this invention short-circuits one terminal of the pair of wires, and reduces the capacitances CA and CB between each of the pair of wires and another identical target object, and the pair of wires. Measure the capacitance CW of both together and the capacitance CW between the same object, and calculate these measured capacitances CA, CB, CW and the known total length of the cable LT.
From this, the distance LS to the disconnection point is calculated by calculating LS = (CW + CB - CA) · LT / CW.

(e) Examples The present invention will be explained in detail below using examples.

FIG. 1 is a schematic diagram showing an embodiment of the present invention. In the figure, reference numeral 1 denotes a cable for measuring the distance to the disconnection point, which is composed of a pair of core wires 2 and 3 and a shield conductor 4. 5 is a capacitance measuring calculator, which measures the capacitance between each core wire 2, 3 and the shield conductor, and calculates the distance to the disconnection point based on the measured capacitance. One ends A and B of the core wires 2 and 3 are connected to the capacitance measurement calculator 5 via switches SA and SB, respectively, and one ends A and B of the core wires 2 and 3 are connected to the switch SA and SB respectively.
They are commonly connected to each other via SW. Furthermore, during measurement, the other ends of the core wires 2 and 3 are short-circuited (point F). However, a low impedance circuit such as an electronic circuit is connected to the other end, so if it is in a substantially short-circuited state, it can be left as is.

Now, assuming that point D of the core wire 3 is broken, we will explain how to find the distance LS from one end B to point D.

First, switch SA is turned on with switches SW and SB open, and capacitance CA between core wire 2 and shield conductor 4 is measured by capacitance measurement calculator 5. Next, switch SB is turned on, switches SW and SA are turned off, and the capacitance CB between the core wire 3 and the shield conductor 4 is measured. Next, Switch SW
, turn on either switch SA or switch SB, and measure the capacitance CW between the core wires 2 and 3 together and the shield conductor 4. When these capacitances CA, CB, and CW are measured, the capacitance measurement calculator 5 calculates the following formula using the known total cable length LT and the capacitances CA, CB, and CW, which are input separately, and calculates LS= (CW+CB-CA)・LT/CW...(1) Calculate the distance LS from one end A, B to the disconnection point D.

Next, using the above formula (1), the distance LS to the disconnection point is
The reason why can be calculated will be explained.

In Fig. 1, the capacitance CA between point A and the shield conductor 4 is the capacitance CAE of the core wire 2 (point E: the position of the core wire 2 corresponding to the disconnection point D).
CEDF is the capacitance of points EF and DF of the pair of core wires 2 and 3.
Then, CA=CAE+CEDF...(2). On the other hand, the capacitance CB between point B and the shield conductor 4 is the capacitance CBD of BD of the core wire 3.

Also, since the pair of core wires 2 and 3 are symmetrical with respect to the capacitance measurement end, CAE=CBD=CB...(3). The cable 1 has the same shape over its entire area, and the collective capacitance CW of the core wires 2 and 3 is proportional to the length L of the cable. Therefore, if the capacitance per unit length of the cable is Co, then CW=Co×LT...(4) CEDF=Co×LR...(5) However, LR: Distance between DR (EF) . Also, from equation (2), CEDF=CA-CAE...(6) From equations (3) and (6), CEDF=CA-CB...(7) The distance LS from point B to point D, where the wire is disconnected, is LS= LT−LR …(8) Inserting LT and LR from formulas (4) and (5) into this formula (8), LS=CW/Co−CEDF/Co=CW−CEDF/Co …(9) This Inserting the CEDF of equation (7) into equation (9), LS = (CW + CB - CA) / Co ... (10) Also, from equation (4), Co = CW / LT ... (11) This equation (11) When Co is inserted into equation (10), LS = (CW + CB - CA)・LT/CW, and the original equation (1) is obtained. In other words, the known total length LT of cable 1 and the measured capacitance CA,
The distance LS to the disconnection point can be calculated from CB and CW.

An example of a capacitance measuring calculator used in the embodiment of FIG. 1 is shown in FIG. This capacitance measurement calculator is effective when the cable length is long.

In FIG. 2, CX is an unknown capacitance, which is connected in parallel to the power supply 10 and the resistor R by a switch S1.
11 is a comparator which outputs an output signal VG when the input voltage E (terminal voltage of the resistor R) is smaller than the upper limit voltage EO and larger than the lower limit voltage EC.
12 is a pulse train generator that outputs the pulse train signal VP; 13 is a gate circuit that outputs the pulse signal VC from the pulse train generator 12 while the output signal VG is input from the comparator 11; and 14 is a pulse signal from the gate circuit 13. A counter 15 that receives and counts VC is a storage calculation circuit that stores the count value of the counter 14 as a measured capacitance and performs calculations such as the above equation (1).

In this capacitance measurement calculator, first, the switch S1 is turned to the a side, and the capacitance to be measured CX is charged with the voltage ES of the power supply 10. Next, when the switch S1 is turned to the b side, the charge stored in the capacitance to be measured CX is discharged through the resistor R. In this case, the voltage E across the resistor R is from time ts to E as shown in Figure 3a.
It decreases due to the characteristics of = Ese−tc−to/CX・R. Here, to indicates the time when the voltage E reaches the upper limit voltage Eo,
tc indicates the time when the voltage E reaches the lower limit voltage Ec, and from time to to tc, the comparator 11 outputs the output signal VG [see b in Figure 3], and while this output signal VG is applied, The gate circuit 13 outputs a pulse signal VC (see d in FIG. 3). This output pulse signal is counted by the counter 14, and the count value becomes larger as the period from to to tc becomes longer. Since the period from to to tc is proportional to the capacitance to be measured CX, the count value of the counter 14 corresponds to the capacitance to be measured CX, and from that count value, the capacitance to be measured CX You can know. Measure the capacitances CA, CB, and CW shown in Figure 1 as the capacitances to be measured CX,
The pulse count values NA, NB, NW of the counter 14 correspond to the capacitances CA, CB, and CW.
Once obtained, the distance LS to the disconnection point can be calculated from LS=(NW-NA+NB)・LT/NW (12) corresponding to equation (1). Also, instead of measuring the pulse numbers NW, NA, and NB, the times tW, tA, and tB from to to tc in Figure 3 a when each capacitance is connected are measured, and LS = (tW - tA + tB) ・LT /tW...The distance LS to the disconnection point may be calculated from the formula (13). Equation (12) above converts each capacitance into the number of pulses, and Equation (13) converts it into time to calculate the distance LS.

Regarding the measurement of unknown capacitance, as shown in FIG. Other measurement principles may be used to measure the capacitance.

In addition, in the above embodiment, a method for measuring the distance to the disconnection point of a cable that has a pair of core wires and a shield conductor was explained, but even if the cable does not have a shield conductor, it is possible to measure the distance between a pair of core wires and a conduit conductor pipe or the ground. By measuring the capacitance between the two wires, the distance to the disconnection point can be similarly measured.

(f) Effects According to this invention, since only the capacitance at one end of each of the two core wires of the cable and the capacitance at one end when both core wires are bundled are measured, it is easy to measure the distance to the disconnection point. can be measured. Furthermore, since the capacitance can be measured with rotational accuracy, the distance to the disconnection point can also be measured with high accuracy.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing an embodiment of the present invention, Fig. 2 is a block diagram showing an example of a capacitance measurement calculator used in the same embodiment, and Fig. 3 shows the operation of the capacitance measurement calculator. This is a signal time chart for explanation. 1: Cable, 2, 3: Core wire, 4: Shield conductor, 5: Capacitance measurement calculator.

Claims (1)

[Scope of Claims] 1. A method for measuring the distance to a disconnection point in a cable formed by covering a pair of wires with an outer sheath, the method comprising: short-circuiting one end of the pair of wires, and connecting each of the pair of wires to the other end. Capacitance CA, CB between one target object
Then, measure the capacitance CW of both pairs of wires together and the same target object, and calculate the measured CA, CB, CW and the known total length of the cable.
LS=(CW+CB-CA)・LT/CW by LT
By calculating the distance LS to the disconnection point
A method of measuring the distance to the disconnection point that calculates the distance. 2. The distance measuring method to a disconnection point according to claim 1, wherein the same target object is a shield conductor of a cable.