JPH03115982A - Fault position locating method for communication cable - Google Patents

Abstract

PURPOSE:To reduce an error due to variance in the constant of the cable by correcting the calculation of input admittance according to the measurement result of the input admittance of a normal conductor at the periphery of a faulty conduction and reduce an error in the distance to a fault point. CONSTITUTION:A measuring instrument 3 is connected to the good conductor 5 to measure the input admittance and its data is stored in a memory 10. The cable constitution of the good conductor 5 is read out of a data base 7 and an arithmetic means 9 calculates the input admittance in the state. Then the input impedance of the faulty conductor 1 is measured and stored in a memory 16. The cable constitution of the faulty conductor 1, on the other hand, is read out of the data base 7 and an arithmetic means 14 calculates its input admittance. A comparing means 17 compares the measured values of the arithmetic means 15 and memory 16 with each other and moves a fault point position until they become equal to each other or the difference between the both is minimized, and the obtained result is displayed on a display part 20 to determine the distance to the fault point.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a method for locating a failure location when a failure occurs in a communication cable. In particular, it relates to a processing method that improves accuracy.

[Conventional technology]

Conventionally, as measuring instruments for detecting failure points in communication cables, pulse testers and failure position measuring devices that measure cable input impedance have been known for metal cables.

A pulse tester sends out a pulse from one end of the cable,
This captures the reflected wave that is reflected at the failure point and returns to the measuring instrument. If the pulse round trip time is the propagation speed of the T1 line as V, the location of the fault point can be found as D-(1/2>(TxV). However, the pulse round trip time T is the reflected pulse waveform. It cannot be determined clearly because it becomes a rounded line.In particular, when branches or different types of core wires are connected to a cable, the pulses are reflected in a complicated manner at the connection point or the cable terminal, and the pulses at the failure point are reflected. This makes it difficult to distinguish, and it becomes virtually impossible to determine the time T. As a way to solve this problem, some of the inventors of the present invention have proposed measuring the input impedance (or admittance) of the cable to detect failures. A device for finding points was proposed, and the same applicant as the present application filed a patent application (Japanese Patent Application No. 63-33604).

The conventional example will be briefly described. Figure 5 is an explanatory diagram of this, and shows that balanced cable 1 (two round trips) is at failure point 2,
When the resistor Z2 is connected to the line and fails, the input admittance measuring device 3 performs measurement from the input terminal 3 of the cable.

According to electric circuit theory, the input admittance when looking from the cable input terminal 11 to the right side of the figure can be calculated, and the line length is l. , propagation constant γ, characteristic impedance Z. , if there is a failure at a distance of 110 points from the measurement end, the input admittance is Y. X
becomes (1). If the failure point of the cable is unknown, the distance to the failure point is set to β1', and the formula (1) is ! .

By substituting β1' into , the input admittance Yo of the same formula
x' is obtained. So YR= YOX' YOX
Find (2), distance! If the admittance YR is observed while changing 1, YR-0 will be obtained when β1'=β1, so the distance 11 to the failure point can be determined. Actually distance! , so Y in equation (1). Although X cannot be found,
Since YoX can be measured, the second term on the right side of equation (2) is the measured value of input admittance, and y o x' is the equation (
This is the calculated value of the input admittance using 1).

FIG. 6 is an explanatory diagram in the case of a cable with a branch, in which the cable 4 is branched from a point 11' at a distance of 12 from the input terminal 11. In this case, if the input impedance viewed from the point 11' to the cable 4 side is calculated and the human input impedance is Z, an equivalent circuit will be obtained in which the impedance Z is connected to the point 11' as shown in FIG. In FIG. 7, since the input impedance viewed from point 11 to the right of the figure can be easily calculated, it is possible to similarly determine the distance 11 to the fault point even if there is a branch.

[Problem to be solved by the invention]

As described above, a method for determining the failure point by measuring the input impedance of the cable has been shown, but this method has the following drawbacks.

That is, as shown in equation (1), the propagation constant T and the characteristic impedance Z. are used in the calculation, but even for cables with the same core diameter, these constants γ and Zo vary somewhat from cable to cable. Therefore, when determining the actual failure point of a cable, this variation affects the error in estimating the failure point, and in some cases it has been found that an error of about 10% occurs.

An error of 10% means that if the failure point is at a 2km point, there is an error of 200m, making it difficult to find the failure point on the actual road.

The present invention improves this, and aims to provide a measurement method that can reduce errors caused by variations in cable constants and has even higher accuracy.

[Means to solve the problem]

The present invention utilizes the fault point detection method by measuring the input admittance of the cable described above, but the propagation constant γ and the characteristic impedance Z are standard. Instead of calculating the input admittance using It is characterized by correcting the error in the distance to the failure point and reducing the error in the distance to the failure point.

[Operation] In the present invention, when a faulty core occurs, an unused good wire is taken out of the cables mounted in the same cable bundle as the faulty core, and its input admittance is measured. on the other hand,
The input admittance of the line of conscience is calculated using equation (1). However, since the conscience line is not broken, Z2 in equation (1)
−ω, pl−β. And it is sufficient. In this way, the calculated input admittance and the measured input admittance should match perfectly, since they are lines of conscience and there is no unknown quantity. However, in reality, a slight deviation occurs. The reason for this is the propagation constant γ and characteristic impedance Z used in equation (1). This is because the standard value used for calculation is slightly different from the actual cable being measured.

The propagation constant γ and characteristic impedance Z of the cable that are actually being measured. When trying to measure cables, it is necessary for the operator to go to the opposite end of the cable and short-circuit or open the terminals, and if the cable has branches, it is necessary to remove the branches. This makes measurement virtually impossible. Therefore, the standard constants γ and Zo used for calculation cannot be determined for the actual cable.

Therefore, since the measured input admittance is the true input admittance, the calculated input admittance is multiplied by a coefficient δ so as to match the measured input admittance. For example, the calculated human admittance is 100 (S)
and the measured input admittance is 102 (S)
If so, it becomes δ-1.02.

Note that when the input admittance is a complex number, the coefficient δ is also a complex number. Using this coefficient δ, the distance f of the faulty core at the fault point! , is corrected by multiplying the calculated input admittance by a coefficient δ. The difference between this corrected value and the measured value of the input admittance of the failed core is calculated.
The distance β1 to the failure point is determined from the value when the difference becomes 0. The present invention differs from the conventional example in that the above correction is performed.

〔Example〕

FIG. 1 is a block diagram of an embodiment of the present invention. Faulty core wire 1 is the distance! . Assume that an impedance Z2 is inadvertently inserted at failure point 2 of .

Reference numeral 3 is an input admittance measuring device. Reference numeral 5 is another conductor wire mounted in the same bundle as the cable 1. Reference numeral 6 is a block diagram showing an example of the present invention. Reference numeral 7 is a database that records the structure and configuration of the cable. Reference numeral 8 is a calculation means for assembling the configuration of the cable to be measured by a program, and standard data on propagation constants and specific impedances can also be used. Reference numeral 9 is a calculation means for calculating the input admittance of the conductor 5, reference numeral 10 is a memory for storing the measured value of the input admittance of the conductor 5, reference numerals 11, 22, and 33 are switches connecting the cable and the measuring device 3, respectively, and reference numeral 12 is a Reference numeral 13 indicates a comparison means for comparing the calculated value 9 of the good conductor input admittance with the measured value 10, reference numeral 13 indicates an arithmetic means for extracting and storing the variation coefficient δ compared by the comparison means 12, and reference numeral 14 indicates the manual admittance of the faulty conductor. Calculating means 15 corrects the failed fiber human admittance value calculated by the calculating means 14 by the change coefficient δ obtained by the calculating means 13. Reference numeral 16 stores the input admittance measurement value of the failed fiber. A memory, reference numeral 17, is a comparison means for comparing the calculated value of the failed fiber human force admittance corrected by the calculation means 15 and the measured value of the failed fiber human force admittance of 16, and reference numeral 18 is a comparison means for comparing whether the compared values match or not. 19 is a calculation means for changing the distance to the failure point and causing the calculation means 14 to calculate the input admittance again. Reference numeral 20 is a calculation means 18 for determining whether the difference is equal to or less than a predetermined value. This is a display section that displays the distance to the fault point when it is determined.

In this embodiment, when a failure occurs, a non-faulty conductor 5 within the same cable as the cable core 1 is appropriately selected. The good wire 5 may be selected as long as it has the same conductor diameter and approximately the same length as the faulty cable 1, and does not have to be exactly the same length or have the same branches. For example, failed core 1
is 2km, then the selected line of conscience 5 is 1.8km.
Alternatively, if the length of the branch is 500 m, the selected conscience line 5 may also have a branch at the same position but have a slightly different length, such as 600 m. In this way, the selected line of conscience 5 is determined.

After making these preparations, first place the measuring device 3 on the line of conscience 5.
connect the switch, measure the 0 input admittance of the conductor 5, and store the data in the memory 10. On the other hand, the cable configuration of the good wire 5 is read from the database 7, the cable configuration is created on a program by the calculation means 8, and the standard propagation constant and characteristic impedance are extracted. Then, the calculation means 9 calculates the input admittance of that state. A comparator 12 compares the calculated value of the calculation means 9 and the measured value of the memory 10 .

In general, the calculated value of the input admittance for a cable with exactly the same configuration as the cable of good conductor 5 should match the measured value since there is no fault in any part of good conductor 5. Therefore, the calculated human admittance value is Y. C and measured value Y. When taking that ratio, the propagation constant and characteristic impedance are slightly different from the actual cable, so Yoa/Yo
c is slightly deviated from 1. Here, the variation coefficient δ may be a complex number. This change coefficient δ is extracted by the calculation means 13 and stored.

Next, the switch 33 is turned to the failed core side, the human power impedance of the failed core 1 is measured, and the result is stored in the memory 16. On the other hand, the cable configuration of the failed core wire 1 is read from the database 7, the cable configuration is assembled by the calculating means 8, and the input admittance thereof is calculated by the calculating means 14 using the standard values of the propagation constant and characteristic impedance. When the input admittance is calculated by the calculating means 14, the failure point is not known, so the failure point is placed at an appropriate location.

Next, the change coefficient δ stored in the calculation means 13 is taken out from the calculation result of the calculation means 14, multiplied by the calculation means 15, corrected, and stored. The comparison means 17 compares the measured values of the calculation means 15 and the memory 16, moves the fault point position until they match or the difference between the two is minimized, and then repeats 14→
15 → 17 → 18 operations or comparisons are executed. The obtained results are then displayed on the display unit 20 to determine the distance to the failure point.

Since the input admittance calculation used to determine the distance to the fault point is corrected by the coefficient δ in equation (4), the standard propagation constant used in the communication cable configuration determined by the calculation means 8 The correct fault distance can be obtained by correcting calculations based on characteristic impedance and characteristic impedance.

An example of the calculation method actually performed is shown below. In order to simplify the calculation, the faulty core wire is designated as 1 and the good wire is designated as 5, as shown in FIG. Here, the four-terminal constant (F matrix) of the cable section of the faulty core is [F]. This [F] is assumed to be derived from standard propagation constants and characteristic impedances.

Assume that a fault point impedance Z2 is added to the terminal end of this four-terminal constant as shown in FIG.

According to circuit theory, the input admittance at that time is s C50 2 Ys - (6) s AS+ 2 3 becomes.

On the other hand, let us consider the four-terminal constant of the conscience wire. Note that A, B, C, and D are unknown numbers here. When nothing is connected to the terminal end of the line of conscience, that is, when the terminal is open, the input admittance Yi becomes Yl, ,; If the same impedance Z2 is added, the input admittance Y1 will be.

Substituting equation (8) into equation (9) yields 4. Here, A, , B, and D of 200 are the four-terminal constants of equation [7], but they have not been determined yet. Y and h are determined by actually measuring the input admittance of the line of conscience. However, the following can be determined by many calculations.

From the eight quasi-propagation constants and characteristic impedance, A
It becomes S.

Z, >1. OkΩ If Therefore Δ 5 Even so, the denominators of formula 00 are almost equal.

From the conditions (i) and (ii), admittance ¥1' can be expressed as. Since all the constants are determined in equation (12+), admittance ¥1' is obtained. Therefore, the variation coefficient δ of equation (4) is determined as follows.

S This equation α will be used as δ. An example of estimating the fault location in an actual cable using the above method is shown below.

Figure 3 shows the cable structure used in the experiment, with two reciprocating conductors shown by one line. 1.5k from the measurement end (left end)
At point m, there is a branch cable of 0.2 km.

In this cable, 0,5.1.0.1.7 km
Figure 4 shows the failure estimation error when a failure occurs at each point (at 6:00 when it was caused artificially). In addition, the failure occurred in Z2
-10 was set to Ω. In Figure 4, the horizontal axis shows the distance at which the failure occurred.
The vertical axis shows the error when estimating the distance to the failure point.

The Δ mark is the result obtained by the conventional method, and the X mark is the result obtained by correcting the calculation according to the present invention.

This result shows that the present invention can significantly reduce errors. This result shows that although the human input impedance was determined at one frequency, it is also possible to estimate the failure point by determining the input impedance at multiple frequencies, and that this method can reduce the effects of noise that occurs at a specific frequency. is also possible.

〔Effect of the invention〕

As described above, according to the present invention, errors in cable constants from standard values are corrected, making it possible to estimate the distance to a cable failure point with high accuracy.

4,

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 2 is an explanatory diagram showing a faulty core wire and a good wire in terms of an electrical circuit. Figure 3 shows the equivalent circuit of the cable used in the test. FIG. 4 is a diagram showing measurement results according to the present invention in comparison with a conventional method. FIG. 5 is an explanatory diagram for measuring the input admittance of a cable including a failure point. FIG. 6 is an explanatory diagram of a failed core with branches. Figure 7 shows its equivalent circuit. 1...Faulty core wire, 2...Additional impedance simulating the fault point, 3...Input admittance measuring device, 4...
・Branch cable, 5... Good wire, 6... Measuring device according to the present invention, 7... Database section containing cable information, 8.9.10.12-19... Based on program calculation circuit Each calculation means or comparison means, 20...display section.

Claims (1)

[Claims] 1. Measure the impedance of one end of a communication cable where a fault is suspected to occur at one or more frequencies, and use the constants of the communication cable to determine the impedance that should appear at the one end with respect to a hypothetical fault position. is calculated for the frequency, and a virtual fault position when the calculated impedance and the measured impedance almost match for each frequency is estimated as the fault position of the communication cable. Measure the impedance of one end of a fault-free communication cable that is mounted in the same cable bundle as the communication cable in which the fault is suspected to occur, at the frequency, and calculate the impedance of the fault-free communication cable from the measured value of the fault-free communication cable. A method for detecting a fault location in a communication cable, characterized by correcting a calculation result of impedance that should appear.