JP2553939B2 - Communication cable failure location detection method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improvement in a method for detecting a failure position when a failure occurs in a communication cable. Particularly, it relates to a processing method for improving accuracy.

[Conventional technology]

Conventionally, as a measuring device for detecting a failure point of a communication cable, a pulse tester or a failure position measuring device by measuring a cable input impedance is known for a metal cable.

The pulse tester emits a pulse from one end of the cable and captures the reflected wave that is reflected at the failure point and returns to the measuring instrument. If the round trip time of the pulse is T and the propagation speed of the line is V, the position D of the failure point can be obtained as D = (1-2) (T × V). However, the round-trip time T of the pulse cannot be clearly defined because the reflected pulse waveform becomes smooth. In particular, when a branch or a heterogeneous cable is connected to the cable, the pulse is reflected in a complicated manner at the connection point or the terminal of the cable, making it difficult to distinguish it from the pulse at the failure point, and it is practically impossible to set the time T. It will be possible. As one method for solving this, some of the inventors of the present application have proposed a device for finding a failure point by measuring the input impedance (or admittance) of the cable, and the same applicant as the present application filed a patent application (see (Kaisho 63-33604).

The conventional example will be briefly described. FIG. 5 is an explanatory view thereof, in which the balanced cable 1 (two round-trip lines) has a failure point 2,
When the resistor Z ₂ fails in the form of being connected to the line, the input admittance measuring device 3 measures from the input terminal 3 of the cable.

According to the electric circuit theory, the input admittance from the cable input terminal 11 as seen from the right side of the figure can be calculated, and if there is a failure at the line length l ₀ , the propagation constant γ, the characteristic impedance Z ₀ , and the distance l ₁ from the measurement end. Then the input admittance Y _0X is Becomes If the cable failure point is unknown,
If the distance to the fault point is l ₁ ′ and l ₁ ′ is substituted for l ₁ in the equation (1), the input admittance Y _0X ′ of the same equation can be obtained. Therefore, if Y _R ＝ Y _0X ′ −Y _0X (2) is found and the admittance Y _R is observed while changing the distance l ₁ , Y _R = 0 when l ₁ ′ ＝ l ₁ is matched. , The distance l ₁ to the failure point can be obtained. In fact, Y _{0X in} equation (1) cannot be obtained because the distance l ₁ is unknown, but since Y _0X can be measured, the second term on the right side of equation (2) is the measurement of the input admittance. The value, Y _0X ′, is the calculated value of the input admittance using equation (1).

FIG. 6 is an explanatory view of a cable with a branch,
Distance l point 11 cable 4 from _'2 are branched from the input terminal 11. In this case, the point 11 'to calculate the input impedance viewed cable 4 side from when the input impedance Z _b, point 11 as FIG. 7' an equivalent circuit connected impedance Z _b on. In FIG. 7,
Since the input impedance looking from the point 11 to the right of the figure can be easily calculated, the distance l ₁ to the fault point can be determined even if there is a branch.

[Problems to be Solved by the Invention]

As described above, the method of finding the failure point by measuring the input impedance of the cable was shown.
This method has the following drawbacks. That is, equation (1)
, The propagation constant γ and the characteristic impedance Z ₀
Is used in the calculation, but even for cables with the same core diameter, these constants γ and Z ₀ have some variations from cable to cable. Therefore, it was found that this variation affects the fault point estimation error when determining the actual fault point of the cable, and an error of about 10% occurs in some cases. The error of 10% has an error of 200 m when the failure point is 2 km, which makes it difficult to find the failure point on the actual road.

An object of the present invention is to improve this, and to provide an accurate measurement method capable of reducing an error due to a variation due to a cable constant.

[Means for solving the problem]

The present invention utilizes the above-mentioned method of detecting a fault point by measuring the input admittance of the cable, but instead of calculating the input admittance using the standard propagation constant γ and characteristic impedance Z ₀ , Actually measure the input admittance of the surrounding non-failed core wire (hereinafter referred to as "concentric wire"), correct the input admittance calculation based on this measurement result, and reduce the error in the distance to the failure point. It is characterized by

[Action]

In the present invention, when a faulty core wire occurs, an unused concentric core wire is taken out from the cables mounted in the same cable bundle as the faulty core wire, and the input admittance is measured. On the other hand, the input admittance of the concentric line is calculated using the equation (1). However, since the conscience line is not broken down,
Z ₂ = ∞ and l ₁ = l ₀ may be set. In this way, the calculated input admittance and the measured input admittance are concentric lines and have no unknowns, so they should completely match. However, a slight deviation actually occurs.
The reason for this is that the standard values used in the calculation of the propagation constant γ and the characteristic impedance Z ₀ used in the equation (1) are slightly different from those of the actually measured cable.

However, when trying to measure the propagation constant γ and characteristic impedance Z ₀ of the cable that is actually being measured, it is necessary for the worker to short-circuit or open the terminal at the end opposite to the measurement end. However, if the cable is branched, it is necessary to remove the branch, making it virtually impossible to measure. Therefore, the standard constants γ and Z ₀ used for the calculation cannot be determined with an actual cable.

Therefore, since the measured input admittance is the true input admittance, the calculated input admittance is multiplied by the coefficient δ so that the input admittance calculated using the standard constants γ and Z ₀ matches the measured input admittance. . For example, the calculated input admittance is 100 (S)
If the measured input admittance is 102 (S), then δ = 1.02. When the input admittance is a complex number, the coefficient δ is also a complex number. Using this coefficient δ, the calculated value of the input admittance obtained by appropriately setting the distance l ₁ at the failure point of the failure core is multiplied by the coefficient δ to correct. The difference between this corrected value and the input admittance of the fault core is measured, and the distance l ₁ to the fault point is obtained from the value when the difference approaches 0. In the present invention, the above correction is different from the conventional example.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of the present invention. The fault core wire 1 is assumed to have the impedance Z ₂ inadvertently inserted at the fault point 2 at the distance l ₀ . Reference numeral 3 is an input admittance measuring device. Reference numeral 5 is another concentric 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 an arithmetic means for assembling a cable configuration to be measured by a program, and standard data such as a propagation constant and a specific impedance can also be used. Reference numeral 9 is a computing means for calculating the input admittance of the concentric wire 5, reference numeral 10 is a memory for storing the input admittance measurement value of the concentric wire 5, reference numerals 11, 22 and 33 are switches for connecting the cable and the measuring instrument 3, respectively, and reference numeral 12
Is a comparing means for comparing the calculated value 9 of the concentric-core input admittance and the measured value 10, reference numeral 13 is an arithmetic means for extracting and storing the change coefficient δ compared by the comparing means 12, and reference numeral 14 is for calculating the input admittance of the faulty core wire. Calculation means, reference numeral 15 is calculation means 14
The calculating means for correcting the calculated value of the input admittance of the fault core wire by the coefficient of change δ obtained by the calculating means 13, and the reference numeral 16 is a memory for storing the input admittance measurement value of the fault core wire, and the reference numeral 17
Is a comparison means for comparing the calculated value of the fault core wire input admittance corrected by the calculation means 15 with the measured value of the fault core wire input admittance of 16, and the reference numeral 18 indicates whether or not these comparisons match (or the difference between them is predetermined. A value 19 or less), a reference numeral 19 is a calculation means for changing the distance to the failure point and calculating the input admittance by the calculation means 14 again,
Reference numeral 20 is a display unit for displaying the distance to the failure point when the coincidence is determined by the calculating means 18.

In this embodiment, first, when a failure occurs, a non-failed concentric core wire 5 in the same cable as the cable core wire 1 is appropriately selected. How to choose this concentric wire 5 is the broken cable 1
As long as they have the same conductor diameter and substantially the same length as the above, they do not have to have the same length or the same branch. For example, if the broken core wire 1 is 2 km, the selected concentric wire 5 may be 1.8 km, and if the branch length is 500 m, the selected concentric wire 5 may also branch at the same position. The length may be slightly different, such as 600m. The conscience line 5 thus selected is determined.

After such preparation, first, the switch of the measuring device 3 is connected to the concentric wire 5, the input admittance of the concentric wire 5 is measured, and the data is stored in the memory 10. On the other hand, the cable configuration of the concentric wire 5 is read from the database 7, the cable configuration is created on the program by the calculating means 8, and standard propagation constants and characteristic impedances are extracted. Then, the calculating means 9 calculates the input admittance in that state. The comparing means 12 compares the calculated value of the calculating means 9 with the measured value of the memory 10.

Generally, the calculated value of the input admittance of the cable having the same configuration as the cable of the concentric wire 5 should agree with the measured value because there is no failure in the concentric wire 5 anywhere.
Therefore, if we take the ratio of the calculated input admittance Y _0C and the measured value Y _0m , However, since the propagation constant and characteristic impedance are slightly different from the actual cable, Y _0m / Y _0c is slightly shifted from 1 Becomes Here, the change coefficient δ may be a complex number. This change coefficient δ is extracted by the calculating means 13 and stored.

Next, the switch 33 is pushed to the fault core side, the input impedance of the fault core 1 is measured, and the result is stored in the memory 16. On the other hand, the cable configuration of the faulty core wire 1 is read from the database 7, the cable configuration is assembled by the calculating means 8 and the input admittance is calculated by the calculating means 14 using the standard values of the propagation constant and the characteristic impedance. Computing means 14
When calculating the input admittance at, the failure point is set at an appropriate place because the failure point is unknown.

Next, the change coefficient δ stored in the calculating means 13 is taken out from the calculation result of the calculating means 14, multiplied by the calculating means 15, corrected, and stored. This calculating means 15 and the measured value of the memory 16 are compared with each other.
The comparison is performed at 17, and the fault point position is moved until they match or the difference between them is minimized, and the operation or comparison of 14 → 15 → 17 → 18 is executed again. Then, the obtained result is displayed on the display unit 20 and the distance to the failure point is determined.

Since the calculation of the input admittance used to obtain the distance to the failure point is corrected by the coefficient δ of the equation (4), the standard propagation used in the configuration of the communication cable obtained by the calculating means 8 is used. The calculation based on the constant and the characteristic impedance is corrected to obtain the correct fault point distance.

An example of the calculation method that is actually performed is shown below. For simplification of calculation, the failure core line is set to 1 and the concentric core line is set to 5, as shown in FIG. Here, the four-terminal constant (F
Matrix) is [F] _S. This [F] _S is derived from a standard propagation constant and characteristic impedance.

It is assumed that a fault point impedance Z ₂ is added to the terminal portion of this four-terminal constant as shown in FIG. The input admittance at that time is based on the circuit theory. Becomes On the other hand, the four-terminal constant far. Here, A, B, C, and D are unknowns. When there is nothing at the end of the conscience, that is,
When the terminal is open, the input admittance Y _in is Then, as shown in Fig. 2, if the same impedance Z ₂ as the failure point is added to the concentric line, the input admittance Y ₁ is Becomes Substituting equation (8) into equation (9) Here, A, B, and D of the formula (10) are four-terminal constants of the formula (7), but they have not been determined yet. Y _in is determined by measuring the input admittance of the conscience line. However, many calculations lead to the following:

(I) D / A is close to 1 at a low frequency of several KHz, and is almost equal to D _S / A _S calculated from the standard propagation constant and characteristic impedance. That is Becomes

If Z ₂ > 10kΩ Therefore Even if, the denominators of equation (10) are almost equal.

From the conditions (i) and (ii), the admittance Y ₁ ′ is Can be expressed as In equation (12), all constants are determined, so that the admittance Y ₁ ′ is obtained. Therefore, the change coefficient δ of the equation (4) is determined as follows.

This equation (13) will be used as δ. An example of estimating the fault position with an actual cable by the above method is shown below.

FIG. 3 shows the cable structure used in the experiment, and shows two reciprocating conductors by one line. 1.5km from the measurement end (left end)
There is a 0.2km branch cable at the point.

Fig. 4 shows the failure estimation error when failure occurred at 0.5, 1.0, and 1.7 km points (when artificially caused) in this cable. The failure was Z ₂ = 10 kΩ.
FIG. 4 shows the error when estimating the distance to the failure point on the horizontal axis and the distance to the failure point on the horizontal axis. The Δ mark indicates the result of the conventional example method, and the X mark indicates the result of correction of the calculation according to the present invention.

This result shows that the present invention can significantly reduce the error. The result shows that the input impedance is obtained at a certain frequency, but the failure point may be estimated by obtaining the input impedance at a plurality of frequencies, and this method can reduce the influence of noise or the like generated at a specific frequency. Is also possible.

[Effects of the Invention] As described above, according to the present invention, the error from the standard value of the cable constant is corrected, and the distance to the fault point of the cable can be estimated with high accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 2 is an explanatory view showing a faulty core wire and a good core wire in the circuit. Figure 3 shows the equivalent circuit of the cable used in the test. FIG. 4 is a diagram showing the measurement results according to the present invention in comparison with the conventional method. FIG. 5 is an explanatory diagram for measuring the input admittance of the cable including the failure point. FIG. 6 is an explanatory diagram of a faulty core wire having a branch. Figure 7 shows the equivalent circuit. 1 ... Failure core wire, 2 ... Additional impedance simulating failure point, 3 ... Input admittance measuring device, 4 ... Branching cable, 5 ... Concentric wire, 6 ... Measuring device according to the present invention,
7: Database section containing cable information, 8,
9, 10, 12 to 19 ... Each calculation means or comparison means by a program calculation circuit, 20 ... Display section.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-55-59349 (JP, A) JP-A-53-95245 (JP, A) JP-A-60-142274 (JP, A) JP-A 64-- 6769 (JP, A)

Claims (1)

(57) [Claims] 1. An admittance at one end of a communication cable suspected of causing a failure is measured at one or a plurality of frequencies, and a constant of the communication cable is used to determine the admittance that should appear at the one end with respect to a virtual failure position. In the communication cable failure position detection method, in which the virtual failure position when the calculated admittance and the measured admittance substantially match at each frequency is estimated as the failure position of the communication cable. Determine the propagation constant γ and characteristic impedance Z ₀ of the standard from the configuration, and measure the input admittance at one end of a communication cable that is mounted in the same cable bundle as the communication cable suspected of causing a failure and has no failure, The input admittance at one end of the fault-free communication cable is Calculate based on the value, calculate the coefficient δ that is the ratio of this calculated value and the measured input admittance, calculate the input admittance of the communication cable suspected of occurrence of failure based on the above standard value, and calculate this value. The coefficient δ
The input admittance of the communication cable suspected of the occurrence of the failure is measured and the measured admittance is compared with the input admittance of the communication cable suspected of the occurrence of the failure corrected by the coefficient δ. Characteristic communication cable failure location detection method.