A positioning circuit for a cable intermediate joint

Abstract

The application discloses a positioning circuit of a cable intermediate joint and belongs to the technical field of pulse power, which comprises a high-voltage source, two pulse forming lines connected in parallel, the first end wire core of the two pulse forming lines being connected with the high-voltage end of the high-voltage source, and the first end shielding layer of the two pulse forming lines being grounded, a first series branch, one end of the first series branch being connected with the high-voltage end of the high-voltage source, and the other end of the first series branch being grounded, the first series branch comprising a reversed diode D1 and a resistor R1 connected in series, a second series branch, one end of the second series branch being connected with the high-voltage end of the high-voltage source, and the other end of the second series branch being grounded, the second series branch comprising a reversed diode D2 and a resistor R2 connected in series, a third series branch, one end of the third series branch being connected with the terminal wire core of the two pulse forming lines, and the other end of the third series branch being used as a pulse output end, the third series branch comprising a relay K1 and a positive diode D3 connected in series, and a waveform acquisition circuit connected in parallel with the pulse output end and used for detecting the square wave pulse signal of the pulse output end. The application amplifies the characteristic signal at the joint while solving the problem of the mismatch between the pulse output end and the measured cable wave impedance.

Description

Technical Field

[0001] This invention belongs to the field of pulse power technology, and more specifically, relates to a positioning circuit for a cable intermediate joint. Background Technology

[0002] Power cables are widely used in urban power distribution networks. Cables laid in the field, often stretching for several kilometers, are composed of sections of cable spliced ​​together with intermediate joints. These joints, as points of structural discontinuity, are weak points in the insulation of power cables. With increasing service life, they are prone to insulation degradation and failure, leading to cable accidents and severely impacting the reliability of the power grid. Accurately locating cable joints allows workers to know their distribution in advance, enabling focused inspection of weakly insulated joints when cable faults occur. Furthermore, it allows for timely updates to cable distribution maps that are inconsistent with the actual situation due to power grid expansion and maintenance.

[0003] The principle of time-domain reflection is that when a traveling wave is transmitted to a cable joint, the wave impedance of the cable joint is greater than that of the cable body, causing the traveling wave to be reflected at both the beginning and end of each cable joint.

[0004] One principle for generating square wave pulses is the pulse forming line method. After the pulse forming line (PFL) is charged and switched on to the cable under test, a square wave pulse voltage signal of a certain amplitude and pulse width is incident between the cable core and the shield. Based on the principle of time-domain reflection, this square wave pulse voltage signal will generate a pair of positive and negative polarity reflected square waves at each joint of the cable, which are then used as characteristic signals. Based on this characteristic, the arrival time of the characteristic signal at the joint is collected at the pulse output end of the circuit, and combined with the wave velocity, the location of the intermediate joint can be determined. However, because the wave impedance of the pulse forming line is inconsistent with the wave impedance of the cable itself, the traveling wave will be reflected at the pulse output end, and the reflected negative wave will again enter the test object as the incident wave, resulting in a very complex waveform and making it difficult to identify the characteristic signal at the joint. At the same time, as the incident wave propagates along the cable, the signal continuously attenuates, resulting in smaller amplitude reflected waves at more distant joints. Furthermore, the influence of ambient noise during field testing is difficult to ignore, causing the characteristic signal of the intermediate joint with a smaller amplitude to be even buried in the noise signal, making it difficult to identify.

[0005] Therefore, it is necessary to design a circuit structure that can eliminate the influence of reflected negative waves caused by impedance mismatch in order to simplify the wave process and make the waveform of the entire wave process flat and simple. At the same time, it is necessary to further increase the amplitude of the characteristic signal of the intermediate connector to improve the identification of the characteristic signal. Summary of the Invention

[0006] In view of the above-mentioned defects or improvement needs of the prior art, the present invention provides a positioning circuit for cable intermediate joints. Its purpose is to eliminate the adverse effects of impedance mismatch for different types of tested cables and to amplify the characteristic signals at the joint, thereby solving the technical problem of the negative wave reflection caused by impedance mismatch.

[0007] To achieve the above objectives, according to one aspect of the present invention, a positioning circuit for a cable intermediate joint is provided, comprising:

[0008] High voltage source V0;

[0009] The pulse forming lines PFL1 and PFL2 are connected in parallel. The first-end cores of both PFL1 and PFL2 are connected to the high-voltage end of the high-voltage source V0, and the shielding layers at both ends are grounded.

[0010] The first series branch has one end connected to the high-voltage terminal of the high-voltage source V0 and the other end grounded. Starting from the high-voltage terminal of the high-voltage source V0, it includes a series-connected diode D1 and a resistor R1 connected in reverse.

[0011] The second series branch has one end connected to the high-voltage terminal of the high-voltage source V0 and the other end grounded. Starting from the high-voltage terminal of the high-voltage source V0, it includes a series-connected diode D2 and a resistor R2 connected in reverse.

[0012] The third series branch has one end connected to the end core of the pulse forming line PFL1 and the pulse forming line PFL2, and the other end serves as the pulse output terminal, including the series relay K1 and the positive diode D3.

[0013] A waveform acquisition circuit, connected in parallel with the pulse output terminal, generates a square wave pulse signal at the pulse output terminal when the relay K1 closes after the high-voltage source V0 charges the pulse forming lines PFL1 and PFL2. The waveform acquisition circuit detects the amplitude U of the square wave pulse signal. a It is half the voltage source V0, and the pulse width is related to the length of the pulse forming line.

[0014] In one embodiment, the pulse forming lines PFL1 and PFL2 are charged and discharged in parallel simultaneously; the wave impedance of the positioning circuit of the cable intermediate joint from the pulse output end to the outside is the parallel wave impedance of the pulse forming lines PFL1 and PFL2.

[0015] In one embodiment, when the pulse forming lines PFL1 and PFL2 are charged in parallel simultaneously, both diodes D1 and D2 are in a reverse cutoff state.

[0016] In one embodiment, when the reflected positive wave at the intermediate connector reaches the pulse output terminal, the diode D3 is cut off relative to the reflected positive wave.

[0017] In one embodiment, the reflected positive wave undergoes total internal reflection at the cathode of the diode D3, and the reflected positive wave acquired by the waveform acquisition circuit is a signal after total internal reflection superposition, thus doubling the signal strength.

[0018] In one embodiment, when the pulse output terminal and the wave impedance of the cable under test are inconsistent, resulting in a reflected negative wave, diodes D1, D2, and D3 are turned on relative to the reflected negative wave. The reflected negative wave is then guided to the ground through resistors R1 and R2, and no longer affects the subsequent wave process.

[0019] In one embodiment, the resistance value of resistor R1 is consistent with the wave impedance of pulse forming line PFL1; the resistance value of resistor R2 is consistent with the wave impedance of pulse forming line PFL2.

[0020] In one embodiment, a resistor R3 is connected in parallel to ground at the pulse output terminal to discharge rapidly at the end of the pulse output, thereby reducing the fall edge time of the output pulse and thus helping to improve the characteristic signal amplitude at the intermediate junction.

[0021] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0022] (1) The present invention uses two pulse forming lines to charge in parallel, which reduces the impedance mismatch with the cable under test, increases the effective incident pulse voltage amplitude on the cable under test, thereby increasing the amplitude of the reflection characteristic signal at the intermediate joint.

[0023] (2) The negative wave caused by the mismatch between the pulse output terminal and the wave impedance of the cable under test is introduced into the ground through the anti-connection diode and the matching resistor, thus avoiding the adverse effects caused by its subsequent re-incidence as the incident wave to the cable under test.

[0024] (3) The reflected positive wave at the intermediate joint is superimposed on the forward diode at the pulse output end, thereby doubling the intensity of the characteristic signal. The topology of this invention is simple, uses few components, is easy to implement, and amplifies the characteristic signal at the joint while solving the problem of impedance mismatch between the pulse output end and the wave of the cable under test, making the wave process simple and clean, and easy to identify the characteristic signal. Attached Figure Description

[0025] Figure 1 This is a topology diagram of a positioning circuit for a cable intermediate joint provided in an embodiment of the present invention;

[0026] Figure 2 This is an equivalent circuit diagram of the reflected negative wave reaching the pulse output terminal in the positioning circuit of the cable intermediate joint provided in an embodiment of the present invention;

[0027] Figure 3 This is an equivalent circuit diagram of the reflected positive wave reaching the pulse output terminal in the positioning circuit of the cable intermediate joint provided in an embodiment of the present invention;

[0028] Figure 4 This is a topology diagram of a positioning circuit for a cable intermediate joint provided in another embodiment of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0030] like Figure 1 As shown, a positioning circuit for a cable intermediate joint is provided, comprising:

[0031] High voltage source V0;

[0032] The pulse forming lines PFL1 and PFL2 are connected in parallel. The first-end cores of both PFL1 and PFL2 are connected to the high-voltage end of the high-voltage source V0, and the shielding layers at both ends are grounded.

[0033] The first series branch has one end connected to the high-voltage terminal of the high-voltage source V0 and the other end grounded. Starting from the high-voltage terminal of the high-voltage source V0, it includes a series-connected diode D1 and a resistor R1 connected in reverse.

[0034] The second series branch is connected at one end to the high-voltage terminal of the high-voltage source V0 and at the other end to ground. Starting from the high-voltage terminal of the high-voltage source V0, it includes a series-connected diode D2 and a resistor R2 connected in reverse.

[0035] The third series branch is connected at one end to the end core of pulse forming line PFL1 and pulse forming line PFL2, and at the other end as the pulse output terminal, including the series relay K1 and the positive diode D3.

[0036] The waveform acquisition circuit, connected in parallel with the pulse output terminal, generates a square wave pulse signal at the pulse output terminal when the high-voltage source V0 charges the pulse forming lines PFL1 and PFL2, and the relay K1 closes. The waveform acquisition circuit detects the amplitude U of the square wave pulse signal. a It is half the voltage source V0, and the pulse width is related to the length of the pulse forming line.

[0037] The positioning circuit for the cable intermediate joint of this invention includes a high-voltage source V0, diodes D1, D2, and D3, pulse forming lines PFL1 and PFL2, resistors R1 and R2, a relay K1, and a waveform acquisition circuit. The high-voltage source V0 is connected to ground via GND. The first ends of the pulse forming lines PFL1 and PFL2 are connected to the high-voltage end of the high-voltage source V0, and their shielding layers are connected to ground. The first end of the pulse forming line PFL1 is connected to ground via diode D1 and resistor R1. The first end of the pulse forming line PFL2 is connected to ground via diode D2 and resistor R2. The last ends of the pulse forming lines PFL1 and PFL2 are connected to the left side of the relay K1, and their shielding layers are connected to ground. The right side of the relay K1 is connected to the anode of diode D3, and the cathode of diode D3 serves as the pulse output terminal. The waveform acquisition circuit is connected in parallel to the pulse output terminal.

[0038] Figure 1 After the medium- and high-voltage power source charges the pulse forming lines PFL1 and PFL2, when relay K1 closes, it will generate a square wave pulse signal with a certain amplitude and pulse width at the pulse output terminal, with an amplitude U a The pulse width is half that of the high-voltage source V0, and is related to the length of the pulse forming line. Let the impedance of PFL1 be Z1 and the impedance of PFL2 be Z2, then the equivalent outward impedance Z of the circuit topology of this invention is... a As shown in equation (1), Z1 and Z2 are connected in series.

[0039]

[0040] The wave impedance Z of the cable under test b Generally between 20 and 30 Ω, due to Z b and Z a The sizes are inconsistent, and Z a The size can be artificially controlled to be greater than Z. b Within this range, there is an impedance mismatch problem at the pulse output terminal, i.e., Z... b and Z a The issue is the inconsistency in pulse magnitude. The output pulse signal will be reflected at the pulse output end, while the actual pulse signal applied to the cable under test is formed by the refraction of the output pulse signal. The reflected signal will enter from the end of the pulse forming line towards the beginning. The actual pulse signal amplitude U applied to the cable under test... b The amplitude U of the reflected signal f The pulse amplitude U output by the pulse forming line a The relationship between them is shown in equation (2).

[0041]

[0042] As can be seen, reducing the degree of impedance mismatch, i.e., reducing Z... b and Z a The difference can, on the one hand, improve U b The size of the junction increases the intensity of the characteristic signal; on the other hand, it can reduce the size of U. f The size of the reflected negative wave is reduced, thereby minimizing its subsequent impact. Commercially available coaxial cables conforming to national standards and suitable for use as pulse forming lines have a waveform impedance of 50 or 75Ω, significantly different from the actual cable waveform impedance of 20–30Ω. Using two pulse forming lines in parallel can reduce the equivalent waveform impedance of the circuit topology to 30 or 37.5Ω, effectively reducing impedance mismatch.

[0043] Even after reducing the impedance mismatch, a reflected negative wave still incidents from the end of the pulse forming line to the beginning. The equivalent circuit is as follows: Figure 2 As shown, diodes D1, D2, and D3 are in the conducting state relative to this reflected negative wave. Therefore, the reflected negative wave will be guided into the ground through matching resistors R1 and R2 and will no longer affect the subsequent wave process.

[0044] like Figure 3 As shown, after the positive wave of the reflected wave pair from the cable mid-joint reaches the pulse output terminal, the diode D3 is reverse cut off, and the impedance of the circuit relative to this positive wave is infinite. Therefore, the reflected positive wave will be totally reflected by the cathode of the diode D3, thereby achieving the effect of waveform superposition. The amplitude of the reflected positive wave from the mid-joint acquired by the waveform acquisition circuit is doubled.

[0045] In one embodiment, such as Figure 4 As shown, a resistor R3 is connected in parallel to ground at the pulse output terminal.

[0046] In this embodiment, a large high-voltage resistor, namely resistor R3, is connected in parallel at the pulse output terminal. This allows for rapid discharge at the end of the pulse output, thereby reducing the fall edge time of the output pulse and thus helping to improve the characteristic signal amplitude at the intermediate junction.

[0047] In summary, this invention reduces the impedance mismatch with the cable under test by introducing two parallel pulse forming lines into the circuit topology; by connecting a diode and a matching resistor in series at the beginning of the pulse forming line, the remaining negative reflected waves caused by impedance mismatch are directed into the ground, eliminating their subsequent effects; and by connecting a diode in series at the pulse output end, the positive wave signals of the reflected wave pair from the intermediate joint are superimposed, thereby improving the amplitude and distinctiveness of the characteristic signal. Furthermore, this invention has a simple circuit structure, uses few components, and is easy to implement.

[0048] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A positioning circuit for a cable intermediate joint, characterized in that, include: High voltage source V0; The pulse forming lines PFL1 and PFL2 are connected in parallel. The first-end cores of both PFL1 and PFL2 are connected to the high-voltage end of the high-voltage source V0, and the shielding layers at both ends are grounded. The first series branch has one end connected to the high-voltage terminal of the high-voltage source V0 and the other end grounded. Starting from the high-voltage terminal of the high-voltage source V0, it includes a series-connected diode D1 and a resistor R1 connected in reverse. The second series branch has one end connected to the high-voltage terminal of the high-voltage source V0 and the other end grounded. Starting from the high-voltage terminal of the high-voltage source V0, it includes a series-connected diode D2 and a resistor R2 connected in reverse. The third series branch has one end connected to the end core of the pulse forming line PFL1 and the pulse forming line PFL2, and the other end serves as the pulse output terminal, including the series relay K1 and the positive diode D3. A waveform acquisition circuit, connected in parallel with the pulse output terminal, generates a square wave pulse signal at the pulse output terminal when the relay K1 closes after the high-voltage source V0 charges the pulse forming lines PFL1 and PFL2. The waveform acquisition circuit detects the amplitude U of the square wave pulse signal. a It is half the voltage source V0, and the pulse width is related to the length of the pulse forming line.

2. The positioning circuit for the cable intermediate joint as described in claim 1, characterized in that, The pulse forming lines PFL1 and PFL2 are charged and discharged in parallel simultaneously; the wave impedance of the positioning circuit of the cable intermediate joint from the pulse output end to the outside is the parallel wave impedance of the pulse forming lines PFL1 and PFL2.

3. The positioning circuit for the cable intermediate joint as described in claim 2, characterized in that, When the pulse forming lines PFL1 and PFL2 are charged in parallel, both diodes D1 and D2 are in reverse cutoff state.

4. The positioning circuit for the cable intermediate joint as described in claim 1, characterized in that, When the reflected positive wave at the intermediate connector reaches the pulse output terminal, the diode D3 is cut off relative to the reflected positive wave.

5. The positioning circuit for the cable intermediate joint as described in claim 4, characterized in that, The reflected positive wave undergoes total reflection at the cathode of diode D3, and the reflected positive wave acquired by the waveform acquisition circuit is a signal after total reflection superposition, with the signal strength doubled.

6. The positioning circuit for the cable intermediate joint as described in claim 1, characterized in that, When the pulse output terminal and the wave impedance of the cable under test are inconsistent, resulting in a reflected negative wave, diodes D1, D2, and D3 are turned on relative to the reflected negative wave. The reflected negative wave is then guided to the ground through resistors R1 and R2, and no longer affects the subsequent wave process.

7. The positioning circuit for the cable intermediate joint as described in claim 1, characterized in that, The resistance value of the resistor R1 is consistent with the wave impedance of the pulse forming line PFL1. The resistance value of resistor R2 is consistent with the wave impedance of pulse forming line PFL2.

8. The positioning circuit for a cable intermediate joint as described in any one of claims 1-7, characterized in that, A resistor R3 is connected in parallel to ground at the pulse output terminal to discharge quickly at the end of the pulse output, thereby reducing the fall edge time of the output pulse and thus helping to improve the characteristic signal amplitude at the intermediate junction.

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