A cable joint positioning circuit with automatic impedance matching

Abstract

This invention discloses a cable joint positioning circuit with automatic impedance matching, belonging to the field of power equipment. The circuit comprises a programmable resistor R1 connected to the pulse output terminal on its left and serving as the load connection terminal on its right; a programmable resistor R2 connected in parallel to the load connection terminal; and a microcontroller (MCU) whose pins are connected to the control pins of a high-voltage DC source, a high-voltage relay, a high-speed sampling circuit, and programmable resistors R1 and R2, respectively. This MCU controls the output voltage of the high-voltage DC source, the switching on and off of the relay, reads data from the high-speed sampling circuit, and controls the resistance value of the programmable resistors. This invention automatically adjusts the resistance values ​​of programmable resistors R1 and R2 according to the degree of impedance mismatch, achieving bidirectional impedance matching between the pulse output terminal and the cable under test. This results in a smooth and clean waveform, making it easier to identify the characteristic reflected waves of the joint, improving the accuracy and range of joint positioning, and reducing the probability of misidentification or missed identification.

Description

Technical Field

[0001] This invention belongs to the field of power equipment technology, and more specifically, relates to a cable intermediate joint positioning circuit with automatic impedance matching. Background Technology

[0002] Power cables have advantages such as not occupying ground space, being unaffected by the external environment, being simple and convenient to operate, requiring little maintenance, and having low operating costs. They are gradually replacing overhead lines and are widely used in urban power distribution networks. When laying cables in the field, cables that are several kilometers or even tens of kilometers long are composed of sections of cable and cable joints. Therefore, cable joints, as points of structural discontinuity, are also weak points in the insulation of power cables. With increasing service life, insulation performance deteriorates and fails, further leading to cable accidents and seriously affecting the reliability of power grid supply.

[0003] To reduce the difficulty of cable inspection, it is often necessary to effectively locate and inspect intermediate joints with relatively weak insulation, so as to replace problematic joints in a timely manner and increase the reliability of power grid operation. At the same time, with the operation and maintenance and expansion of the power grid, the number of intermediate joints is gradually increasing, which will cause the number and location of cable joints shown in the original planning drawings to differ from the actual situation.

[0004] Precisely locating cable joints is crucial for several reasons. First, it allows workers to anticipate the distribution of cable joints, enabling them to focus their inspections on weakly insulated joints when cable faults occur. Second, it allows for the timely updating of cable distribution maps that are no longer accurate due to power grid expansion and maintenance. Therefore, there is an urgent need for a device capable of accurately locating cable joints.

[0005] The impedance of the cable body differs significantly from that of the pulse forming line. Without impedance matching, the incident square wave pulse voltage signal will be reflected at the cable's inlet. Firstly, the pulse signal on the measured object is a refracted signal with a smaller amplitude than the original generated square wave pulse signal, resulting in a reduced amplitude of the reflected wave at the joint, making it difficult to identify. Secondly, the reflected wave generated at the inlet will be re-inputted to the measured object as an incident wave, causing waveform distortion, and the characteristic signal of the reflected wave at the joint will be buried in the clutter. Therefore, an impedance matching network is needed to simplify the waveform process, enabling more accurate positioning of the characteristic signal at the intermediate joint, thus improving the device's positioning accuracy and practicality. Summary of the Invention

[0006] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a cable intermediate joint positioning circuit with automatic impedance matching. Its purpose is to automatically realize bidirectional impedance matching between the pulse output end and the cable under test, so as to make the waveform flat and clean and easy to identify the characteristic reflected wave of the intermediate joint, thereby solving the technical problems of low accuracy and limited range of existing joint positioning.

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

[0008] The high-voltage DC source V0 is used to provide high-voltage DC.

[0009] The pulse forming line PFL has its first end core connected to the high voltage output terminal of the high voltage DC source, and its first and last end shielding layers are grounded to store energy and form a square wave pulse voltage signal.

[0010] The high-voltage relay K1 has its left side connected to the end core of the pulse forming line PFL, and its right side serves as the pulse output terminal for controlling the output of pulses.

[0011] A programmable resistor R1 is connected in series with the output circuit, with its left side connected to the pulse output terminal and its right side serving as the load connection terminal.

[0012] A programmable resistor R2, with one end connected to the load connection terminal and the other end connected to ground, is used in conjunction with the programmable resistor R1 to achieve impedance matching between the pulse output terminal and the test cable serving as the load.

[0013] A high-speed sampling circuit is connected in parallel to the pulse output terminal for acquiring waveforms;

[0014] The microcontroller (MCU) has its pins connected to the control pins of the high-voltage DC source V0, the high-voltage relay K1, the high-speed sampling circuit, and the programmable resistors R1 / R2. It is used to control the output voltage of the high-voltage DC source V0, control the opening and closing of the high-voltage relay K1, read the data of the high-speed sampling circuit, and control the resistance values ​​of the programmable resistors R1 and R2 to achieve bidirectional impedance matching between the pulse output terminal and the cable under test.

[0015] In one embodiment, the impedance-matched cable joint positioning circuit is divided into two parts each time it operates: a pre-test and a formal test.

[0016] During the pre-test, the microcontroller (MCU) reads the data from the high-speed acquisition circuit to obtain the degree of impedance mismatch between the pulse output terminal and the cable under test.

[0017] During formal testing, the microcontroller (MCU) adjusts the resistance values ​​of programmable resistors R1 and R2 according to the degree of impedance mismatch, and then performs the test. By reading the data from the high-speed acquisition circuit, the arrival time of the reflected wave at the intermediate connector is obtained, and the intermediate connector can be located by combining the wave velocity.

[0018] In one embodiment, during pre-testing, the resistance values ​​of the programmable resistors R1 and R2 are in their initial state.

[0019] In one embodiment, in order to achieve equal impedance on both sides of the pulse output terminal, the impedance on both sides of the load connection terminal is equal.

[0020] The programmable resistors R1 and R2, together with the pulse forming line impedance Z1 and the impedance Z2 of the cable under test, must satisfy the following:

[0021] In one embodiment, the pulse forming line (PFL) is used to generate a square wave pulse voltage signal. When the high-voltage pulse forming line is switched on to the object under test, a square wave pulse voltage signal with a certain amplitude and pulse width will be applied to the object under test. The amplitude is 1 / 2 of the voltage of the pulse forming line, and the pulse width is twice the quotient of the forming line length and the wave speed. The equivalent impedance of the circuit on the left side of the pulse output terminal is the wave impedance of the pulse forming line (PFL).

[0022] In one embodiment, the microcontroller (MCU) controls the level of the adjustment pin of the high-voltage DC source V0 through its DAC function, thereby controlling the output voltage of the high-voltage source and adjusting the amplitude of the square wave pulse voltage signal output by the pulse output terminal.

[0023] In one embodiment, the high-voltage relay K1 is a high-voltage wet reed relay.

[0024] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0025] This invention achieves bidirectional impedance matching between the pulse output terminal and the cable under test by adjusting the size of the programmable resistor, thereby making the waveform flat and clean, making it easy to identify the characteristic reflected waves of the intermediate joint, improving the accuracy and range of joint positioning, and reducing the probability of joint misjudgment and omission. Attached Figure Description

[0026] Figure 1 This is a topology diagram of the cable intermediate joint positioning circuit with automatic impedance matching according to an embodiment of the present invention;

[0027] Figure 2 This is a schematic diagram of the waveform when impedance mismatch is pre-tested according to an embodiment of the present invention;

[0028] Figure 3 This is a waveform diagram of impedance matching during a formal test in an 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, the cable joint positioning circuit with automatic impedance matching according to an embodiment of the present invention includes:

[0031] High-voltage DC source V0;

[0032] Pulse forming line (PFL): Its first end core is connected to the high voltage output terminal of the high voltage DC source, and its first and last end shields are grounded;

[0033] High-voltage relay K1: Its left side is connected to the end core of the pulse forming line, and its right side serves as the pulse output terminal;

[0034] Programmable resistor R1: Its left side is connected to the pulse output terminal, and its right side serves as the load connection terminal;

[0035] Programmable resistor R2: One end is connected to the load connection terminal, and the other end is connected to ground;

[0036] High-speed sampling circuit: connected in parallel at the pulse output terminal;

[0037] The pins of the microcontroller (MCU) are connected to the control pins of the high-voltage DC source V0, the high-voltage relay K1, the high-speed sampling circuit, and the programmable resistors R1 / R2.

[0038] like Figure 1 As shown, in order to achieve bidirectional impedance matching between the pulse output terminal and the cable under test, that is, to achieve equal impedance on the left and right sides of the pulse output terminal and equal impedance on the left and right sides of the load connection terminal.

[0039] The equivalent impedance on the left side of the pulse output terminal is the pulse forming line wave impedance Z1; the equivalent impedance on the right side is: ① programmable resistor R1 ② the parallel equivalent impedance of the measured cable wave impedance Z2 and the programmable resistor R2 (Z2 / / R2), and the series equivalent impedance of the two.

[0040] The equivalent impedance on the left side of the load connection terminal is: ① the series equivalent impedance of programmable resistor R1 and pulse forming line waveform impedance Z1 (R1+Z1) ② the parallel equivalent impedance of programmable resistor R2; the equivalent impedance on the right side is the waveform impedance Z2 of the cable under test.

[0041] Therefore, R1, R2, the pulse forming line impedance Z1, and the measured cable impedance Z2 must satisfy the relationship in equation (1):

[0042]

[0043] After solving the equations, the relationship between R1, R2, Z1 and Z2 is shown in equation (2).

[0044]

[0045] During the pre-test, the pulse output terminal is impedance mismatched with the cable under test. Programmable resistor R1 is 0Ω, and programmable resistor R2 is 1kΩ. When the high-voltage relay K1 closes, it outputs a square wave pulse voltage signal with a fixed pulse width and amplitude U0. Due to the impedance mismatch, the square wave pulse voltage signal is reflected at the load connection terminal. The waveform acquired by the high-speed acquisition circuit at this time is as follows: Figure 2 As shown. The reflected wave with an amplitude of -U1 formed by the first reflection will be incident again as the incident wave and be reflected back into the cable under test, forming a second reflected positive wave with an amplitude of U2. This process repeats until the energy of the traveling wave is completely consumed in several reflections. According to the wave process of the traveling wave on the transmission line, U0, U1 and U2 satisfy the relationship shown in equation (3):

[0046]

[0047] The pulse forming line is manually selected and determined, and its wave impedance Z1 is a known parameter, typically 50Ω or 75Ω. The cable under test is unknown, and its wave impedance Z2 is an unknown parameter, typically between 20 and 30Ω. After the data acquisition module acquires the values ​​of U0, U1, and U2, the value of Z2 can be calculated according to one of the equations in equation (3), and then substituted into equation (2) to calculate the values ​​of the programmable resistors R1 and R2.

[0048] After pre-testing, the microcontroller (MCU) controls the programmable resistors R1 and R2 to adjust to their calculated values ​​before proceeding with the formal test. At this point, the pulse output terminal and the cable under test have achieved bidirectional impedance matching, and the waveform acquired by the high-speed acquisition circuit is as follows: Figure 3 The time Δt required for each cable joint to reach the pulse output terminal is collected. n Each cable joint can be located by combining the propagation speed of the traveling wave on the cable.

[0049] In summary, this invention obtains the impedance mismatch between the pulse output terminal and the cable under test through pre-testing, and then adjusts the size of the programmable resistor to achieve bidirectional impedance matching between the pulse output terminal and the cable under test. This results in a smooth and clean waveform, making it easier to identify the characteristic reflected waves of the intermediate joint, improving the accuracy and range of joint positioning, and reducing the probability of joint misjudgment and missed judgment.

[0050] 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 cable intermediate joint positioning circuit with automatic impedance matching, characterized in that, include: The high-voltage DC source V0 is used to provide high-voltage DC. The pulse forming line PFL has its first end core connected to the high voltage output terminal of the high voltage DC source, and its first and last end shielding layers are grounded to store energy and form a square wave pulse voltage signal. The high-voltage relay K1 has its left side connected to the end core of the pulse forming line PFL, and its right side serves as the pulse output terminal for controlling the output of pulses. A programmable resistor R1 is connected in series with the output circuit, with its left side connected to the pulse output terminal and its right side serving as the load connection terminal. A programmable resistor R2, with one end connected to the load connection terminal and the other end connected to ground, is used in conjunction with the programmable resistor R1 to achieve impedance matching between the pulse output terminal and the test cable serving as the load. A high-speed sampling circuit is connected in parallel to the pulse output terminal for acquiring waveforms; The microcontroller (MCU) has its pins connected to the control pins of the high-voltage DC source V0, the high-voltage relay K1, the high-speed sampling circuit, and the programmable resistors R1 / R2. It is used to control the output voltage of the high-voltage DC source V0, control the opening and closing of the high-voltage relay K1, read the data of the high-speed sampling circuit, and control the resistance values ​​of the programmable resistors R1 and R2 to achieve bidirectional impedance matching between the pulse output terminal and the cable under test. The impedance-matching cable joint positioning circuit operates in two parts each time: a pre-test and a formal test. During the pre-test, the microcontroller (MCU) reads data from the high-speed sampling circuit to determine the impedance mismatch between the pulse output and the cable under test. During the formal test, the MCU adjusts the resistance values ​​of programmable resistors R1 and R2 based on the impedance mismatch and performs the test again. By reading data from the high-speed sampling circuit, the arrival time of the reflected wave at the joint is obtained, and the joint can be located by combining this with the wave velocity. To ensure equal impedance on both sides of the pulse output, the impedance on both sides of the load connection is also equal. The programmable resistors R1 and R2, together with the pulse forming line impedance Z1 and the impedance Z2 of the cable under test, must satisfy the following: .

2. The cable intermediate joint positioning circuit with automatic impedance matching as described in claim 1, characterized in that, During the pre-test, the resistance values ​​of the programmable resistors R1 and R2 are in their initial state.

3. The cable intermediate joint positioning circuit with automatic impedance matching as described in claim 1, characterized in that, The pulse forming line (PFL) is used to generate a square wave pulse voltage signal. When the high-voltage pulse forming line is closed to the object under test, a square wave pulse voltage signal with a certain amplitude and pulse width will be applied to the object under test. The amplitude is 1 / 2 of the voltage of the pulse forming line, and the pulse width is twice the quotient of the forming line length and the wave speed. The equivalent impedance of the circuit on the left side of the pulse output terminal is the wave impedance of the pulse forming line (PFL).

4. The cable intermediate joint positioning circuit with automatic impedance matching as described in claim 1, characterized in that, The microcontroller (MCU) controls the level of the adjustment pin of the high-voltage DC source V0 through its DAC function, thereby controlling the output voltage of the high-voltage source and adjusting the amplitude of the square wave pulse voltage signal output by the pulse output terminal.

5. The cable intermediate joint positioning circuit with automatic impedance matching as described in claim 1, characterized in that, The high-voltage relay K1 is a high-voltage wet reed relay.

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