Non-contact cable fault on-line detection positioning method

Abstract

The invention discloses a non-contact cable fault online detecting and positioning method. According to the non-contact cable fault on-line detection positioning method, a detection signal is coupled to a cable to be detected based on an inductive coupler, non-contact detection can be carried out on a cable fault point, and the operation process of the method is shown in a figure 2 in the specification. Compared with a traditional cable fault detection and positioning method, direct contact with the cable is not needed, the application scene is greatly enriched, and the operation difficulty is simplified. Meanwhile, non-contact detection can be carried out in the working state of the cable, so that online detection is realized. Meanwhile, the signal time delay can be accurately extracted by the detection signal secondary cross-correlation algorithm provided by the invention, and accurate positioning of the cable fault is realized.

Description

Technical Field

[0001] The present invention relates to the field of cable fault detection, and particularly to a non-contact on-line cable fault detection and location method. Background Art

[0002] At present, cable fault detection is widely used in fields such as electric power and communication. Cables are usually installed underground or under the sea. When a cable fails, how to quickly and conveniently detect the cable fault is a very important problem that needs to be solved urgently. Traditional cable fault detection methods mainly rely on contact technologies. Usually, detection equipment needs to be directly connected to the cable, and the change of voltage, current or impedance is measured to judge the fault point. Although such methods have certain advantages in detection accuracy, their application scenarios are limited. Contact detection methods usually require power outage operations and the cable needs to be exposed, resulting in complex and time-consuming operation processes, and it is easy to damage the cable. Power outage detection will cause huge economic losses. Contact detection methods are also not applicable to buried cables, dangerous environments or cable systems that are difficult to access.

[0003] To overcome these problems, in recent years, non-contact detection technologies have gradually developed. By detecting outside the cable, direct interference with the cable is avoided. However, existing non-contact technologies usually rely on external sensors to sense weak changes in the electromagnetic field of the cable, but their sensitivity and accuracy are relatively low. Especially in long-distance transmission cables and complex cable networks, it is difficult to accurately locate the fault point. In addition, existing non-contact methods have complex equipment and high costs, which limit their large-scale application.

[0004] Therefore, there is an urgent need in the market for a cable fault detection technology that can achieve high-precision fault location under non-contact conditions, has a simple structure and low cost. This technology should be able to effectively overcome the deficiencies of existing contact and non-contact detection technologies, and provide a more convenient and reliable fault detection solution especially in complex environments. Summary of the Invention

[0005] The purpose of the present invention is to provide a non-contact on-line cable fault detection and location method.

[0006] The technical solution for achieving the purpose of the present invention is as follows:

[0007] A non-contact on-line cable fault detection and location method, the specific steps are as follows:

[0008] The first step: Install an inductive coupler:

[0009] 1.1 First, determine the detection start section and end section of the cable 11 to be detected, then open the buckles 10, 15 of the inductive couplers A, B, sleeved them to the corresponding cable positions, and lock the buckles 10, 15.

[0010] 1.2 As Figure 2 shown, connect the signal terminal 1 of the signal generator and the ground terminal 2 to the signal receiving terminal 3 and the signal receiving ground 4 of the high-frequency signal power amplifier respectively; after the signal is amplified by the high-frequency signal power amplifier, connect the signal output terminal 5 of the high-frequency signal power amplifier to the signal terminal 7 of the inductive coupler A, and connect the signal output ground 6 of the high-frequency signal power amplifier to the signal grounds 8 and 9 of the inductive coupler A; connect the signal terminal 12 of the inductive coupler B to the signal terminal 16 of the signal receiver, and connect the signal grounds 13 and 14 of the inductive coupler B to the signal ground 17 of the signal receiver.

[0011] Step 2: Use high-frequency signals for fault detection

[0012] The signal generator outputs a pre-designed signal. After being amplified by the signal power amplifier, it is injected into the cable through the inductive coupler A. As the signal passes through the cable, it will carry cable fault information. The signal is received from the end of the cable through the inductive coupler B and then sent to the signal receiver for further signal processing.

[0013] Step 3: Perform signal processing

[0014] In cable fault location, the principle of quadratic cross-correlation operation is simple and has strong anti-noise ability. Assume the signal model is:

[0015]

[0016] The quadratic cross-correlation calculation process is as Figure 3 shown:

[0017] Assume the autocorrelation function of signal x1(n) is R 11 (n), the cross-correlation function of signal x1(n) and signal x2(n) is R 12 (n), and the autocorrelation function of signal x1(n) is R 11 (n) is:

[0019] R 11 (τ) = E[x1(n)x1(n + τ)]

[0020] = E[s(n)(αs(n + τ) + v(n + τ))]

[0021] = E[αs(n)s(n + τ) + s(n)v(n + τ)]

[0022] = αR ss (τ) + R sv (τ)

[0023] x1(n) is the test signal, v(n) is the noise, α is the attenuation coefficient, and the autocorrelation is still a function of time, achieving the maximum value at τ = 0.

[0024] The cross-correlation function of signals x1(n) and x2(n) is R 12 (n) is shown as follows. x1(n) is the test signal, x2(n) is the reflected signal, v(n) is the noise, α is the attenuation coefficient, and d is the delay time of the reflected signal:

[0025] R 12 (τ) = E[x1(n)x2(n + τ)]

[0026] = E[s(n)(αs(n + τ - d) + v(n + τ))]

[0027] = E[αs(n)s(n + τ - d) + s(n)v(n + τ)]

[0028] = αR ss (τ - d) + R sv (τ)

[0029] Assume that the autocorrelation function of signal x1(n) is R 11 (n), and the cross-correlation function of signal x1(n) and signal x2(n) is R 12 (n). According to the cross-correlation formula, the second-order cross-correlation can be expressed as:

[0030]

[0031] Similar to the basic cross-correlation, when τ = d, the second-order cross-correlation function reaches the maximum value. At this time, by finding the position of this point on the abscissa, the time-delay estimation of the signal can be obtained. Description of the Drawings

[0032] Figure 1 is the structural diagram of the inductive coupler in the present invention. Figure 2 is the schematic diagram of the device connection in the present invention. Figure 3 is the flowchart of Step 3 in the present invention. Figure 4 、 Figure 5 、 Figure 6 、 Figure 7 and Figure 8 are the example diagrams in the specific implementation manner. Specific Implementation Manner

[0033] The present invention will be further described below in conjunction with the embodiments.

[0034] As Figure 1 shown, the inductive coupler is used to achieve non-contact signal injection and reception, with simple operation and strong reliability. Its structure and usage are as follows:

[0035] The inductive coupler is generally cylindrical, and the hollow part in the middle (9) is used to pass the cable. The solid outer shell body is composed of two parts (6) and (7), and the two parts (6) and (7) are separated and assembled through the buckles (5) and (6); there are strip-shaped protrusions (8) on (6) and (7) to increase the friction force, which is convenient for the installation and disassembly of the inductive coupler; the signal input terminal (1) is used to input signals, generally connected to a signal generator, etc., and the signal ground ports (2) and (3) are connected to the signal ground. If (1), (2), and (3) are correctly connected, the inductive coupler can couple the signal to the cable passing through (9).

[0036] When this patent conducts non-contact on-line detection of cable faults, the connection method is as shown in the appendix Figure 2 As shown. The signal terminal (1) of the signal generator and the signal ground (2) are respectively connected to the signal receiving terminal (3) and the signal ground receiving terminal (4) of the high-frequency signal power amplifier. The signal output terminal (5) of the high-frequency signal power amplifier and the signal output ground (6) are respectively connected to the signal terminal (7) and the signal ground (8) and (9) of the inductive coupler A. The inductive coupler A and the inductive coupler B are sleeved on both ends of the cable to be tested (11). The signal terminal (12) of the inductive coupler B is connected to the signal receiving terminal (16) of the signal receiver, and the signal ground (13) and (14) of the inductive coupler B are connected to the signal ground (17) of the signal receiver. After the overall connection is completed, it can be used to test and locate the faults of the cable (11).

[0037] Conduct non-contact cable fault detection: Output a test signal through the signal generator, amplify the signal power through the high-frequency signal power amplifier, then the signal is coupled to the cable (11) through the inductive coupler A, and then the inductive coupler B receives the signal from the cable (11) and transmits it to the signal receiver for the next signal processing. The signal processing flow is as shown in the appendix Figure 3 As shown.

[0038] In this example, a 400m cable is used, and an open circuit fault is set at 137m. The incident signal x1(n) is a signal modulated by a 5th-order m sequence and a 20MHz sine signal, as Figure 4 shown, and the reflected signal is as Figure 5 shown.

[0039] Assume that the autocorrelation function of the signal x1(n) is R 11 (n), the cross-correlation function of the signal x1(n) and the signal x2(n) is R 12 (n), and the autocorrelation function of the signal x1(n) is R 11 (n) is:[[]]

[0040] R 11 (τ) = E[x1(n)x1(n + τ)]

[0041] = E[s(n)(αs(n + τ) + v(n + τ))]

[0042] = E[αs(n)s(n + τ) + s(n)v(n + τ)]

[0043] = αR ss (τ) + R sv (τ)

[0044] The obtained autocorrelation result R 11 (n) is as Figure 6 shown.

[0045] The cross - correlation function of signal x1(n) and signal x2(n) is R 12 (n) as shown in the following equation:

[0046] R 12 (τ) = E[x1(n)x2(n + τ)]

[0047] = E[s(n)(αs(n + τ - d) + v(n + τ))]

[0048] = E[αs(n)s(n + τ - d) + s(n)v(n + τ)]

[0049] = αR ss (τ - d) + R sv (τ)

[0050] The obtained cross - correlation result R 12 (n) is as Figure 7 shown.

[0051] The autocorrelation function of signal x1(n) is R 11 (n), and the cross - correlation function of signal x1(n) and signal x2(n) is R 12 (n). According to the cross - correlation formula, the second - order cross - correlation can be expressed as:

[0052]

[0053] Similar to the basic cross - correlation, when τ = d, the second - order cross - correlation function reaches the maximum value. At this time, by finding the position of this point on the abscissa, the time - delay estimation of the signal can be obtained. The obtained second - order cross - correlation result is as Figure 8 shown. It can be seen from the result that the detected fault point is at about 135.3 m, with an absolute error of 1.7 m and a relative error of 1.25% compared with the actual situation, and the effect is good. The method of this patent can effectively detect cable faults in a non - contact manner.

[0054] According to the actual situation, appropriately adjust the waveforms and signal - processing algorithms used for detection to make them more suitable for guiding on - site engineering work.

Claims

1. A non-contact on-line cable fault detection and location method, characterized by including the following simulation and test steps: Step 1: Install an inductive coupler for non-contact signal injection and reception, including 1.1: The structure of the inductive coupler is shown in Figure 1. It is cylindrical as a whole, and the hollow part (9) in the middle is used to pass the cable. The solid outer shell body consists of two parts (6) and (7), and the two parts (6) and (7) are separated and assembled through the buckles (5) and (6); there are strip-shaped protrusions (8) on (6) and (7) to increase the friction force, which is convenient for the installation and disassembly of the inductive coupler; the signal input terminal (1) is used to input signals, generally connected to a signal generator, etc., and the signal ground ports (2) and (3) are connected to the signal ground. If (1), (2), and (3) are connected correctly, the inductive coupler can couple the signal to the cable passing through (9). 1.2: As shown in Figure 2, connect the signal terminal 1 and the ground terminal 2 of the signal generator to the signal receiving terminal 3 and the signal receiving ground 4 of the high-frequency signal power amplifier respectively; the signal is amplified by the high-frequency signal power amplifier, connect the signal output terminal 5 of the high-frequency signal power amplifier to the signal terminal 7 of the inductive coupler A, and connect the signal output ground 6 of the high-frequency signal power amplifier to the signal ground 8 and 9 of the inductive coupler A; first open the buckle 11 of the inductive coupler A, sleeved it at the signal injection point of the cable, and then close the buckle 11. First open the buckle 15 of the inductive coupler B, sleeved it at the signal output point of the cable, and then close the buckle 15. The test cable is shown as 11 in Figure 2; connect the signal terminal 12 of the inductive coupler B to the signal terminal 16 of the signal receiver, and connect the signal ground 13 and 14 of the inductive coupler B to the signal ground 17 of the signal receiver; Step 2: Use the modulated high-frequency signal for testing, including 2.1: Use the signal generator to output the modulated high-frequency signal. This signal passes through the high-frequency signal power amplifier, and then the signal is non-contact injected into the signal injection point of the cable through the inductive coupler A. The signal passes through the cable and will carry the fault information of the cable, as shown in Figure 2; 2.2: Use the signal receiver to receive the cable signal output. The signal flowing through the cable is transmitted to the signal receiver through the inductive coupler B to complete signal processing and extract the cable fault information, as shown in Figure 2; Step 3: Signal processing to extract cable fault information, including In cable fault location, the principle of the second-order cross-correlation operation is simple and has strong anti-noise ability. Assume the signal model is: The second-order cross-correlation calculation process is shown in Figure 3: Suppose the autocorrelation function of the signal x1(n) is R 11 (n), and the cross-correlation function between the signal x1(n) and the signal x2(n) is R 12 (n). The autocorrelation function of the signal x1(n) is R 11 (n) is: R 11 R(τ) = E[x1(n)x1(n + τ)] = E[s(n)(αs(n + τ)+v(n + τ))] = E[αs(n)s(n + τ)+s(n)v(n + τ)] = αR ss (τ) + R sv (τ) x1(n) is the test signal, v(n) is the noise, α is the attenuation coefficient, and the autocorrelation is still a function of time, and it reaches the maximum value at τ = 0; The cross-correlation function of signals x1(n) and x2(n) is R 12 (n) is shown as follows, where x1(n) is the test signal, x2(n) is the reflected signal, v(n) is the noise, α is the attenuation coefficient, and d is the delay time of the reflected signal: R 12 R(τ) = E[x1(n)x2(n + τ)] = E[s(n)(αs(n + τ - d)+v(n + τ))] = E[αs(n)s(n + τ - d)+s(n)v(n + τ)] = αR ss (τ - d) + R sv (τ) Suppose the autocorrelation function of the signal x1(n) is R 11 (n), and the cross-correlation function between the signal x1(n) and the signal x2(n) is R 12 (n). According to the cross-correlation formula, the second-order cross-correlation can be expressed as: R RR (τ) = E[R 11 (n)R 12 (n + τ)] = E[R x1x1 (n)(R x1x1 (n + τ - d)+ R x1v (n + τ))] Similar to the basic cross-correlation, when τ = d, the second-order cross-correlation function reaches the maximum value. At this time, find the position of this point on the abscissa to obtain the time delay estimation of the signal; According to the above steps 1, 2, and 3, non-contact on-line detection of cable faults can be realized.

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