Novel T-shaped branch cable fault positioning method

Abstract

The invention relates to a novel T-type branch cable fault positioning method, and the method carries out the feature reflection extraction of a cable fault point based on a pseudo-random sequence with high anti-interference performance and a traveling wave reflection method for the sequential modulation of multi-frequency sinusoidal signals, and combines the filtering effect of a specific magnetic ring on a high-frequency signal. The fault positioning of the multi-branch cable is realized; a set of fault positioning system capable of performing fault positioning and fault type judgment on T-type multi-branch cable faults is constructed, fault information is reflected by means of a spread spectrum time domain reflection method, a shielding magnetic ring and a remote controller are designed, and on-off control is performed on the magnetic ring so that detection signals can pass in a controllable manner; respective detection of different branches is realized; the method has the advantages of realizing multi-branch cable fault positioning, accurately providing fault information in real time and maintaining stable operation of the cable.

Description

Technical Field

[0001] The invention belongs to the technical field of cable fault location, and in particular relates to a novel T-branch cable fault location method. Background Art

[0002] The power grid line is relatively complex, and there are T-shaped branches in the line. Compared with the single-branch cable, the detection signal reflection will overlap at the branch and cannot be distinguished, resulting in the inability to determine the fault location of the T-shaped cable. As the cable ages, the cable is damaged by aging corrosion and mechanical stress, resulting in breakage, damage, short circuit and other damage, which will affect the operation efficiency of the power system and eventually lead to cable failure. If the fault location cannot be found and repaired in time, it will have a serious impact on the power system. In order to maintain the safe and stable operation of the power supply, relying on manual troubleshooting in the context of large-scale cable laying is time-consuming, labor-intensive and inefficient, and is far from meeting the actual needs of T-shaped multi-branch cable fault troubleshooting. At present, power cable fault detection is mainly studied on the premise of a single cable. Although there is also a multi-branch cable fault detection, the location and branch of the fault in different cable branches can be distinguished without separate detection and processing of the cable branches, but this detection strategy still has certain limitations. Therefore, it is very necessary to provide a new T-shaped branch cable fault location method that can realize multi-branch cable fault location, provide fault information in real time and accurately, and maintain stable operation of the cable. Summary of the invention

[0003] 1. Technical issues

[0004] In view of the above-mentioned existing technical status, this application mainly addresses the following technical problems:

[0005] 1. In the T-shaped branch part of the line, the detection signal reflections will overlap at the branch and cannot be distinguished, resulting in the inability to determine the fault location of the T-shaped cable;

[0006] 2. In the context of large-scale cable laying, manual troubleshooting is time-consuming, labor-intensive and inefficient, and is far from meeting the actual needs of T-type multi-branch cable troubleshooting;

[0007] 3. Currently, power cable fault detection is mainly studied on the premise of a single cable. Although multi-branch cable fault detection is also used, this detection strategy still has certain limitations.

[0008] (II) Technical solution

[0009] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide a novel T-branch cable fault locating method which can realize multi-branch cable fault locating, provide fault information accurately in real time, and maintain stable operation of the cable.

[0010] The object of the present invention is achieved by: a novel T-branch cable fault location method, the method comprising the following steps:

[0011] Step 1: Generation of detection signal;

[0012] Step 2: Collect the reflected detection signal and the incident signal and process them by cross-correlation algorithm to obtain the fault peak, and obtain the fault location information based on the wave velocity and reflection time;

[0013] Step 3: Use a multi-branch fault detection strategy to detect different branches separately.

[0014] Furthermore, the generation of the detection signal in step 1 is specifically as follows: based on the characteristic impedance variation characteristics of the cable, it is proposed to use an M sequence and a 10 MHz sinusoidal signal to perform binary phase shift keying modulation to generate a detection signal, Where A is the carrier amplitude; f is the carrier frequency; t is the time; T c is the duration of the PN sequence symbol; g(t) is the width of T c , the amplitude is a n The pulse, a n The value is 0 or 1, the probability of taking 1 is p, and the probability of taking 0 is 1-p.

[0015] Furthermore, the fault location information in step 2 is specifically:

[0016] R 12 (τ)=E[x1(n)x2(n+τ)]=E[s(n)(as(n-d+τ)+v(n+τ))]=aR ss (τ-d)+R sv (τ).

[0017] Furthermore, the step 3 is specifically as follows: based on the characteristic that the detection signal frequency is above 10M, a special magnetic ring is used to filter out the high-frequency signal, and a magnetic ring that can be controlled to close and open is installed at the branch; a PT2262 wireless signal transmitting circuit and a PT2272 wireless signal receiving circuit are used to control the closing of the magnetic ring of the electric telescopic push-pull rod to filter out the high-frequency signal and to allow the high-frequency signal to pass through when it is opened; and the signal is controlled to pass to realize separate detection of different branches.

[0018] A novel T-branch cable fault location system executes the novel T-branch cable fault location method as described above. The system includes a level conversion module and a multiplication modulation module. The level conversion module is used to perform level conversion on a unipolar non-return-to-zero code to generate a bipolar non-return-to-zero code; the multiplication modulation module is used to perform multiplication modulation on a bipolar non-return-to-zero code and a sinusoidal carrier to generate a detection signal, and the modulated signal is injected into the cable for detection.

[0019] Furthermore, the system also includes a reflection signal processing module, which is used in step 2 of the novel T-branch cable fault locating method according to claim 1; the reflection signal processing module includes a sampling circuit and a main control chip.

[0020] Furthermore, the sampling circuit adopts an AD9481 chip; and the main control chip adopts a PGL22G FPGA chip.

[0021] Furthermore, the system also includes a branch fault detection device, which is a magnetic ring installed at the branch and can be controlled to close and open.

[0022] Furthermore, the magnetic ring includes a shielding magnetic ring and a push-pull device. The shielding magnetic ring is a caliper-type structure composed of two semi-annular magnetic materials, and an air gap is formed at the contact points of the two ends of the shielding magnetic ring. The shielding function can be controlled by pushing the pushing device.

[0023] Furthermore, the system also includes a control device, which includes a wireless remote control switch and a relay switch.

[0024] (III) Beneficial effects

[0025] 1. The present invention constructs a fault location system that can determine the fault branch, accurately locate the fault, and determine the fault type of a T-type multi-branch cable fault;

[0026] 2. Detection signal generation: Based on the characteristic impedance change characteristics of the cable, it is proposed to use M sequence and 10MHz sinusoidal signal to modulate and generate detection signals; collect the reflected detection signal and the incident signal for cross-correlation algorithm processing to obtain the fault peak, and obtain the fault location information based on the wave speed and reflection time;

[0027] 3. Multi-branch fault detection strategy: Based on the characteristics of the detection signal frequency being above 10M, a special magnetic ring is used to filter out high-frequency signals, and a magnetic ring with controllable closing and disconnection is installed at the branch; a PT2262 wireless signal transmitting circuit and a PT2272 wireless signal receiving circuit are designed to control the closing of the magnetic ring of the electric telescopic push-pull rod to filter out high-frequency signals and disconnect to allow high-frequency signals to pass; the signal is controlled to pass, realizing the detection of specific and known branches. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of multiplier modulation of the present invention.

[0029] Figure 2 It is a schematic diagram of the detection signal generated by the sine wave and m-sequence modulation of the present invention.

[0030] Figure 3 It is the correlation diagram between the reflection and incident signals of the present invention.

[0031] Figure 4 It is a schematic diagram of the controllable magnetic ring device of the present invention.

[0032] Figure 5 It is a schematic diagram of the branch detection system arrangement of the present invention.

[0033] In the figure: 1-1, unipolar non-return-to-zero coding (pseudo-random sequence) 1-2, bipolar non-return-to-zero coding (random sequence after bipolar conversion (only contains -1 and 1)) 1-3, sinusoidal carrier (10MHz sinusoidal signal) 1-4, detection signal generated by multiplication modulation 4-1, push-pull device 4-2, shielded magnetic ring (closable magnetic ring) 5-1, wireless control switch transmitting end 5-2, A branch wireless switch receiving end and relay switch 5-3, push-pull switch structure 5-4, cable 5-5, shielded magnetic ring 5-6, wireless switch receiving end and relay switch A at branch B, cable A branch B, cable B branch. DETAILED DESCRIPTION

[0034] The present invention relates to a traveling wave reflection method based on a pseudo-random sequence with strong anti-interference ability and sequentially modulated multi-frequency sinusoidal signals to extract characteristic reflections of cable fault points, and realizes the positioning of multi-branch cable faults by combining the filtering effect of a specific magnetic ring on high-frequency signals.

[0035] The present invention is further described below in conjunction with embodiments and / or drawings.

[0036] Example 1

[0037] like Figure 1-5 As shown, a novel T-branch cable fault location method comprises the following steps:

[0038] Step 1: Generation of detection signal;

[0039] In the present invention, the generation of the detection signal is specifically as follows: relying on the traveling wave reflection principle to represent the waveform of the fault characteristics, a 32-bit pseudo-random (PN) sequence and a 10MHz sinusoidal signal binary phase shift keying modulation are used to generate the detection signal; an AD9708 digital-to-analog conversion circuit is used to generate the detection signal and inject it into the cable;

[0040] The PN sequence selects an m sequence with good autocorrelation and cross-correlation as the modulation signal, which is generated by an n-stage shift register with linear feedback whose feedback function only contains modulo-2 addition operations but no nonlinear operations; the period is selected as 2 n -1, n = 5 code sequence, after the pseudo-random sequence generator generates the PN sequence, BPSK modulation (binary phase shift keying modulation) is performed with the sinusoidal signal, and the phase of the keyed carrier is changed according to the baseband pulse; Where A is the carrier amplitude; f is the carrier frequency; t is the time; T c is the duration of the PN sequence symbol; g(t) is the width of T c , the amplitude is a n The pulse, a n The value is 0 or 1, the probability of taking 1 is p, and the probability of taking 0 is 1-p; the unipolar non-return-to-zero code (1-1) is level-converted to generate a bipolar non-return-to-zero code (1-2), which is multiplied and modulated with a sinusoidal carrier (1-3) to generate a detection signal (1-4), and the modulated signal is injected into the cable for detection.

[0041] Step 2: Collect the reflected detection signal and the incident signal and process them by cross-correlation algorithm to obtain the fault peak, and obtain the fault location information based on the wave velocity and reflection time;

[0042] In the present invention, the fault location information is specifically: using the AD9481 chip to design a sampling circuit, collecting and processing the signal and transmitting it to the FPGA main control chip PGL22G; using the cross-correlation operation, the transmission signal and the reflection signal are defined as follows: In the formula, s(n) is the transmitted signal, x2(n) is the reflected signal, d is the delay time of the reflected signal, a is the attenuation coefficient, v(n) is the interference; n is a discrete time index, which represents a time or position index in the signal; the transmitted signal and the reflected signal are cross-correlated to obtain: R 12 (τ)=E[x1(n)x2(n+τ)]=E[s(n)(as(n-d+τ)+v(n+τ))]=aR ss (τ-d)+R sv (τ), where R ss (τ-d) is the cross-correlation result between the incident detection signal and the reflected detection signal; R sv (τ) is the cross-correlation result of the transmitted signal and the noise, which is 0; τ is a time offset or delay, which determines the sliding alignment of the two signals; assuming that v(n) is an ideal Gaussian noise, the test signal s(n) and the noise v(n) are uncorrelated, and Rsv(τ) = 0, then the cross-correlation function of x1(n) and x2(n) can be simplified to: R 12 (τ) = aR ss (τ-d), R 12 The (τ) function waveform will have an obvious peak point at the time t=d, and the delay time and position of the reflected signal can be calculated based on the horizontal coordinate of the peak point.

[0043] Step 3: Use a multi-branch fault detection strategy to detect different branches separately.

[0044] In the present invention, step 3 is specifically as follows: based on the characteristic that the detection signal frequency is above 10M, a special magnetic ring is used to filter out the high-frequency signal, and a magnetic ring that can be controlled to close and open is installed at the branch; a PT2262 wireless signal transmitting circuit and a PT2272 wireless signal receiving circuit are used to control the closing of the magnetic ring of the electric telescopic push-pull rod to filter out the high-frequency signal and to allow the high-frequency signal to pass through when it is opened; and the signal is controlled to pass, so as to realize separate detection of different branches.

[0045] The present invention is a novel T-branch cable fault locating method. In use, based on the limitations of existing detection strategies, the present invention can distinguish the locations and branches of faults existing in different cable branches without separate detection and processing of cable branches. The present invention improves the detection strategy, and extracts characteristic reflections of cable fault points based on a traveling wave reflection method that modulates a pseudo-random sequence with strong anti-interference ability and a multi-frequency sinusoidal signal in sequence, and combines the filtering effect of a specific magnetic ring on high-frequency signals to achieve detection and positioning of multi-branch cable faults, and can provide fault information in real time and accurately, maintain stable operation of cables, and reduce troubleshooting time and costs. The present invention has the advantages of locating multi-branch cable faults, providing fault information in real time and accurately, and maintaining stable operation of cables.

[0046] Example 2

[0047] like Figure 1-5 As shown, a novel T-branch cable fault location system is intended to construct a fault location system that can determine the fault branch, accurately locate the fault, and determine the fault type of a T-type multi-branch cable fault. The fault information is reflected by the spread spectrum time domain reflectometry method, and a shielded magnetic ring and a remote controller are designed to control the switch of the magnetic ring so that the detection signal can pass in a controllable manner, thereby realizing separate detection of different branches. Specifically, the system executes the novel T-branch cable fault location method as described above, and the system includes a level conversion module and a multiplication modulation module. The level conversion module is used to perform level conversion on a unipolar non-return-to-zero code to generate a bipolar non-return-to-zero code; the multiplication modulation module is used to perform multiplication modulation on the bipolar non-return-to-zero code and a sinusoidal carrier to generate a detection signal, and the modulated signal is injected into the cable for detection.

[0048] The system further comprises a reflection signal processing module, which is used in step 2 of the novel T-branch cable fault location method as claimed in claim 1; the reflection signal processing module comprises a sampling circuit and a main control chip.

[0049] The sampling circuit adopts AD9481 chip; the main control chip adopts PGL22G FPGA chip.

[0050] The system further comprises a branch fault detection device, which is a magnetic ring installed at the branch and capable of being controlled to be closed and opened.

[0051] In the present invention, according to the filtering characteristics of the magnetic ring for high-frequency signals, a magnetic ring device that can be controlled to close and open is installed at the branch; the wireless control relay switch controls the closing of the magnetic rings at different branches to filter out the high-frequency signals and the opening to allow the high-frequency signals to pass through, and the controllable passage detection of the signal is performed.

[0052] The magnetic ring includes a shielding magnetic ring and a push-pull device. The shielding magnetic ring is a caliper-type structure composed of two semi-annular magnetic materials, and an air gap is formed at the contact points of the two ends of the shielding magnetic ring. The shielding function can be controlled by pushing with the help of a pushing device.

[0053] In the present invention, the shielding magnetic ring (4-2) adopts a caliper design and is composed of two semi-ring-shaped magnetic materials. An air gap is formed at the contact point between the two ends of the ring. The shielding function can be controlled by pushing the pushing device (4-1). According to the requirement that the equivalent resistance of the magnetic ring should match the bus wave impedance, the equivalent inductance value is determined to be about 0.3uF through experiments. The cable wave impedance is 65Ω, ρ is the resistivity of the ferrite material; h is the width of the magnetic ring; r1 and r2 are the inner and outer diameters of the magnetic ring respectively; μ0 is the magnetic permeability in a vacuum, μ r is the relative magnetic permeability; According to the cable size and formula, the material of the magnetic ring can be determined to be ferrite. The inner and outer diameters of the shielding magnetic ring are 50mm and 80mm respectively, and the width of the magnetic ring is 15cm.

[0054] PT2262 chip and PT2272 chip are selected for the design of switch signal transmitting module and receiving module to realize remote control of relay switch on and off and realize the opening and closing of magnetic ring; the magnetic ring disconnection distance is designed to be 2cm.

[0055] The system also includes a control device, which includes a wireless remote control switch and a relay switch.

[0056] In the present invention, the specific operation is as follows: before transmitting the detection signal, the wireless remote control switch (5-1) is controlled according to the detected branch, and when the A branch is detected, the 1-on key of the wireless remote control switch (5-1) is pressed, and the push-pull device (4-1) of the remote control relay switch (5-2) performs a push-open action to push the magnetic ring away, so that the signal can pass through the A branch, and the detection signal is transmitted. The detection result is the fault condition of the A branch; the detection operation of the B branch is the same as the detection operation of the A branch.

[0057] The novel T-branch cable fault locating system of the present invention can realize separate detection of each branch of the online T-branch cable, without power off and using multiple sets of equipment to detect different branches. It only needs to perform online isolation injection of signals on one end side, and through wireless relay switch control, separate detection of different branches can be realized, thereby improving the efficiency of multi-branch cable fault detection.

[0058] The present invention is a novel T-branch cable fault locating method. In use, based on the limitations of existing detection strategies, the present invention can distinguish the locations and branches of faults existing in different cable branches without performing separate detection and processing on cable branches for multi-branch cable fault detection. The present invention improves the detection strategy, extracts characteristic reflections of cable fault points based on a traveling wave reflection method modulated in sequence by a pseudo-random sequence with strong anti-interference performance and a multi-frequency sinusoidal signal, and combines the filtering effect of a specific magnetic ring on high-frequency signals to achieve detection and positioning of multi-branch cable faults, and can provide fault information in real time and accurately, maintain stable operation of the cable, and reduce troubleshooting time and costs. In addition, the present invention aims at the problem that faults in online multi-branch cables are difficult to detect and fault branches are difficult to determine, and proposes to use a controllable shielding magnetic ring to selectively pass signals through different branches of the T-type cable, thereby achieving separate detection of specific branch faults of the multi-branch cable. In the T-type multi-branch cable fault detection, it is not necessary to use multiple sets of equipment, and it is not necessary to perform invasive damage to the cable at the branch. The present invention has the advantages of locating multi-branch cable faults, providing fault information in real time and accurately, and maintaining stable operation of the cable.

Claims

1. A novel T-branch cable fault location method, characterized in that: The method comprises the following steps: Step 1: Generation of detection signal; Step 2: Collect the reflected detection signal and the incident signal and perform cross-correlation algorithm processing to obtain the fault peak, and obtain the fault location information based on the wave speed and reflection time; Step 3: Use a multi-branch fault detection strategy to detect different branches separately.

2. A novel T-branch cable fault location method as claimed in claim 1, characterized in that: The generation of the detection signal in step 1 is specifically as follows: according to the characteristic impedance change characteristics of the cable, it is proposed to use an M sequence and a 10MHz sinusoidal signal to perform binary phase shift keying modulation to generate a detection signal, Where A is the carrier amplitude; f is the carrier frequency; t is the time; T c is the duration of the PN sequence symbol; g(t) is the width of T c , the amplitude is a n pulse.

3. A novel T-branch cable fault location method as claimed in claim 1, characterized in that: The fault location information in step 2 is specifically: R 12 (τ)=E[x1(n)x2(n+τ)]=E[s(n)(as(n-d+τ)+v(n+τ))]=aR ss (τ-d)+R sv (t)。 4. A novel T-branch cable fault location method as claimed in claim 1, characterized in that: The step 3 is specifically as follows: based on the characteristic that the detection signal frequency is above 10M, a special magnetic ring is used to filter out the high-frequency signal, and a magnetic ring that can be controlled to close and open is installed at the branch; a PT2262 wireless signal transmitting circuit and a PT2272 wireless signal receiving circuit are used to control the closing of the magnetic ring of the electric telescopic push-pull rod to filter out the high-frequency signal and to allow the high-frequency signal to pass through when it is opened; and the signal is controlled to pass to realize separate detection of different branches.

5. A novel T-branch cable fault location system, which executes the novel T-branch cable fault location method according to any one of claims 1 to 4, characterized in that: The system comprises a level conversion module and a multiplication modulation module. The level conversion module is used for level conversion of unipolar non-return-to-zero code to generate bipolar non-return-to-zero code; the multiplication modulation module is used for multiplying and modulating the bipolar non-return-to-zero code with a sinusoidal carrier to generate a detection signal, and the modulated signal is injected into the cable for detection.

6. A novel T-branch cable fault location system as claimed in claim 5, characterized in that: The system further comprises a reflection signal processing module, which is used in step 2 of the novel T-branch cable fault location method as claimed in claim 1; the reflection signal processing module comprises a sampling circuit and a main control chip.

7. A novel T-branch cable fault location system as claimed in claim 6, characterized in that: The sampling circuit adopts AD9481 chip; the main control chip adopts PGL22G FPGA chip.

8. A novel T-branch cable fault location system as claimed in claim 5, characterized in that: The system further comprises a branch fault detection device, which is a magnetic ring installed at the branch and capable of being controlled to be closed and opened.

9. A novel T-branch cable fault location system as claimed in claim 8, characterized in that: The magnetic ring includes a shielding magnetic ring and a push-pull device. The shielding magnetic ring is a caliper-type structure composed of two semi-annular magnetic materials, and an air gap is formed at the contact points of the two ends of the shielding magnetic ring. The shielding function can be controlled by pushing with the help of a pushing device.

10. A novel T-branch cable fault location system as claimed in claim 5, characterized in that: The system also includes a control device, which includes a wireless remote control switch and a relay switch.

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