High-voltage cable grounding loop resistance live detection device and method

Abstract

The invention belongs to the technical field of power equipment detection, and relates to a high-voltage cable grounding loop resistance live detection device and method, and the device comprises a signal injection unit, a head end detection unit, a tail end detection unit and a host system. The signal injection unit and the head end detection unit are installed on a grounding wire at the head end of a detected high-voltage cable, the tail end detection unit is installed on a grounding wire at the tail end of the detected high-voltage cable, and the host system is in communication connection with the signal injection unit, the head end detection unit and the tail end detection unit. An injection signal waveform measured by the head end detection unit and a receiving signal waveform measured by the tail end detection unit are fitted by applying a vector fitting algorithm, a receiving signal waveform parameter matrix and an injection signal waveform parameter matrix are calculated, and the sum of all resistances in the receiving signal waveform parameter matrix is the loop resistance of the high-voltage cable grounding system. According to the invention, high-efficiency and high-precision live detection of the grounding loop resistance of the high-voltage cable is realized.

Description

Technical Field

[0001] This invention belongs to the field of power equipment testing technology, specifically relating to a live detection device and method for the resistance of a high-voltage cable grounding circuit. Background Technology

[0002] High-voltage cables, with their safety, reliability, and aesthetic appeal, have become an essential component of power transmission networks. Their safe and stable operation is crucial for improving the reliability of power system operation. However, high-voltage cables are mostly buried underground and often operate in high-temperature and high-humidity environments. Their grounding systems are prone to problems such as lead corrosion, metal rust, and partial circuit breaks, leading to a significant increase in loop resistance, affecting grounding reliability, causing local potential rise, damaging cable insulation, and inducing breakdown faults. Therefore, conducting high-voltage cable grounding system inspections and effectively assessing the grounding system connection status is a prerequisite for ensuring the safe and stable operation of high-voltage cables.

[0003] The loop resistance value is directly related to the health status of the high-voltage cable grounding system. Defects such as lead corrosion, metal rust, and partial open circuits can all lead to a significant increase in the loop resistance value of the grounding system. Currently, commonly used methods for detecting loop resistance value require a current source and a detection unit connected in series in the high-voltage cable grounding loop for injection and measurement of a power frequency-like signal. However, the grounding system state cannot be changed while the high-voltage cable is in operation, and the power frequency-like signal is easily affected by the cable's operating voltage and current, so it is generally only used for offline detection. In recent years, some scholars and companies have proposed using an inductive method to inject high-frequency signals and use the ratio of the injected signal voltage to the response signal current to obtain the loop resistance value of the high-voltage cable grounding system. This method can achieve live detection without disconnecting the cable while eliminating the cable's operating voltage and current signals. However, high-frequency signals are extremely sensitive to stray inductance and capacitance in the cable grounding system, affecting the detection accuracy. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a live detection device and method for the resistance of high-voltage cable grounding loops, thereby achieving efficient and high-precision live detection of the resistance of high-voltage cable grounding loops.

[0005] The technical solution of the present invention is: a method for detecting the resistance of a high-voltage cable grounding loop under live conditions, wherein a head-end detection unit and a tail-end detection unit are installed on the grounding wires at the head and tail ends of the high-voltage cable under test, respectively; the equivalent network of the high-voltage cable grounding system is formed by the parallel connection of the conductor axial impedance and the conductor radial admittance, the axial impedance is formed by the series connection of the conductor resistance and the conductor mutual inductance, and the radial admittance is formed by the parallel connection of the leakage conductance and the equivalent capacitance; the head-end detection unit measures the injected signal waveform e(t), and the tail-end detection unit measures the received signal waveform x(t), the relationship between the received signal waveform x(t) and the injected signal waveform e(t) satisfies the formula (1), and the received signal waveform parameter matrix A and the injected signal waveform parameter matrix B can be calculated by using a vector fitting algorithm based on the formula (1); (1); The sum of all resistances in the received signal waveform parameter matrix A is the loop resistance of the high-voltage cable grounding system.

[0006] Further preferably, in the equivalent network of the high-voltage cable grounding system, the resistance R0 of the 0th conductor segment is connected in series with the inductance L0 of the 0th conductor segment; the resistance R1 of the 1st conductor segment is connected in parallel with the inductance L1 of the 1st conductor segment; the resistance R2 of the 2nd conductor segment is connected in parallel with the inductance L2 of the 2nd conductor segment, and so on, with the resistance R of the Mth conductor segment... M With the inductance L of the Mth segment of the conductor M The segments are connected in parallel, and each segment is connected in series. The equivalent capacitance C0 of segment 0 is connected in parallel with the leakage conductance G0 of segment 0; the equivalent capacitance C1 of segment 1 is connected in series with the leakage conductance G1 of segment 1; the equivalent capacitance C2 of segment 2 is connected in series with the leakage conductance G2 of segment 2, and so on. The equivalent capacitance C0 of segment N is connected in parallel with the leakage conductance G0 of segment 0. N With the leakage conductance G of the Nth segment N The segments are connected in series, and the segments are connected in parallel.

[0007] This invention also provides a live detection device for the grounding circuit resistance of a high-voltage cable, comprising: a signal injection unit, a head-end detection unit, an end-end detection unit, and a host system; the head-end and end-end of the high-voltage cable under test are respectively connected to cable terminals, and the head-end and end-end of the high-voltage cable under test are respectively grounded through grounding wires; the signal injection unit and the head-end detection unit are installed on the grounding wire at the head-end of the high-voltage cable under test, and the end-end detection unit is installed on the grounding wire at the end-end of the high-voltage cable under test; the host system is communicatively connected to the signal injection unit, the head-end detection unit, and the end-end detection unit; a monitoring and calculation module is deployed in the host system for processing the waveform data detected by the head-end detection unit and the end-end detection unit; the monitoring and calculation module is also used to control the signal injection unit to inject a double exponential wave into the high-voltage cable under test through the electric field coupling method of the control signal injection unit.

[0008] In a further preferred embodiment, the signal injection unit mainly consists of a signal generation circuit and a signal injection antenna. The output terminal of the signal generation circuit is connected to the input terminal of the signal injection antenna. The signal generation circuit mainly consists of a sinusoidal signal generation circuit, a push-pull power amplifier circuit, a transformer rectifier circuit, and an LC oscillation circuit connected in series.

[0009] Further optimization reveals that the signal injection antenna adopts a dipole antenna structure, with each antenna being teardrop-shaped and consisting of 6 antennas, and the signal is a double exponential wave.

[0010] The beneficial effects of this invention are: 1) This method only requires injecting or detecting a signal on the grounding wire of the high-voltage cable, without changing the connection method of the cable and its grounding system, and the cable does not need to be shut down during the detection process, resulting in high detection efficiency; 2) The injected detection signal is a double exponential wave, which avoids interference from the cable's operating voltage during the detection process and significantly improves the detection accuracy; 3) Compared with existing detection technologies, it does not require a high-power adjustable frequency sinusoidal voltage generator, but only needs to generate a pulse signal with a single waveform, which significantly reduces the equipment manufacturing cost.

[0011] This invention is applicable to live-line detection of the grounding circuit resistance of high-voltage cables. It enables non-destructive, non-contact, efficient, and high-precision live-line detection of the grounding system circuit resistance while the high-voltage cable is in operation, providing a convenient and reliable technical means and equipment for the condition monitoring of high-voltage cable grounding systems, and has broad application prospects. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the high-voltage cable grounding circuit resistance live detection device of the present invention.

[0013] Figure 2 This is a schematic diagram of the signal generation circuit and a schematic diagram of the signal injection antenna structure.

[0014] Figure 3 This is a schematic diagram of the equivalent network structure of a high-voltage cable grounding system. Detailed Implementation

[0015] The invention will now be explained in further detail with reference to the accompanying drawings.

[0016] like Figure 1As shown, a live-line detection device for the grounding loop resistance of a high-voltage cable includes: a signal injection unit, a head-end detection unit, an end-end detection unit, and a host system. The high-voltage cable under test can be equivalently divided into several cable segments, with adjacent cable segments connected by cable joints. The head and end of the high-voltage cable under test are respectively connected to cable terminals and grounded through grounding wires. The signal injection unit and the head-end detection unit are installed on the grounding wire at the head of the high-voltage cable under test, and the end-end detection unit is installed on the grounding wire at the end of the high-voltage cable under test. The host system is connected to the signal injection unit and the head-end detection unit via optical fiber or other communication cables, and to the end-end detection unit via wireless communication methods such as 5G, ensuring the normal operation and communication of all units. A monitoring and calculation module is deployed in the host system to process the waveform data detected by the head-end and end-end detection units. The monitoring and calculation module is also used to control the signal injection unit, injecting a double-exponential high-frequency signal into the high-voltage cable under test through the electric field coupling method of the control signal injection unit.

[0017] like Figure 2 As shown, the signal injection unit mainly consists of a signal generation circuit and a signal injection antenna. The output terminal of the signal generation circuit is connected to the input terminal of the signal injection antenna. The signal generation circuit mainly consists of a sine wave signal generation circuit, a push-pull power amplifier circuit, a transformer rectifier circuit, and an LC oscillation circuit connected in series. The sine wave signal generation circuit uses an ICL8038 programmable waveform generator chip and a first waveform adjustment resistor R. S1 Control frequency, second waveform adjustment resistor R S2 Adjust the duty cycle, and adjust the resistor R of the third waveform. S3 To compensate for distortion, the power supply Vcc uses a +5V~+15V DC input and is connected to ground GND. It features a push-pull amplifier circuit composed of two complementary transistors, powered by a +12V~+24V mains power supply (V... dc ) and -12V~-24V symmetrical negative power supply (-V dc The circuit consists of two transistors that alternately conduct to amplify the signal power. The LC oscillator circuit comprises a hollow inductor L... oa Polypropylene capacitor C oa Adjustable resistor R p The signal generation circuit consists of a waveform selection switch SW1 and an output signal V. out The signal injection antenna employs a dipole antenna structure, with each antenna being teardrop-shaped, consisting of six antennas. The signal is a double exponential wave, with a dominant frequency in the range of 1MHz-10MHz. out It is also the input signal V injected into the antenna. in .

[0018] The first-end detection unit and the last-end detection unit have the same structure. They are actually high-frequency current transformers with a detection 3dB bandwidth of not less than 500kHz-50MHz and a detection sensitivity of not less than 3V / A. They have data storage and uploading functions and are used to collect current waveforms.

[0019] The host system, with a structure similar to an industrial control computer, has multiple signal transmission interfaces such as USB, fiber optic, network cable, and mobile signal, and is equipped with a Windows or Linux operating system.

[0020] This invention equates the high-voltage cable grounding circuit to, as follows: Figure 3 The equivalent network of the high-voltage cable grounding system shown is composed of the conductor axial impedance and the conductor radial admittance connected in parallel. The axial impedance is composed of the conductor resistance and the conductor mutual inductance connected in series, and the radial admittance is composed of the leakage conductance and the equivalent capacitance connected in parallel. Figure 3 In the middle, R0~R M These represent the resistances of the wire segments 0 to M; L0~L M The inductances of the wires from segment 0 to M are as follows: the resistance R0 of segment 0 is connected in series with the inductance L0 of segment 0; the resistance R1 of segment 1 is connected in parallel with the inductance L1 of segment 1; the resistance R2 of segment 2 is connected in parallel with the inductance L2 of segment 2, and so on. The resistance R of segment M is... M With the inductance L of the Mth segment of the conductor M Parallel connection, where each segment is connected in series; i (k-1)0 Let i be the starting current of the (k-1)th segment. k0 The starting current of segment k; C0~C N The equivalent capacitance for segments 0 to N is G0~G N The leakage conductance is for segments 0 to N. The equivalent capacitance C0 of segment 0 is connected in parallel with the leakage conductance G0 of segment 0; the equivalent capacitance C1 of segment 1 is connected in series with the leakage conductance G1 of segment 1; the equivalent capacitance C2 of segment 2 is connected in series with the leakage conductance G2 of segment 2, and so on. The equivalent capacitance C0 of segment N is... N With the leakage conductance G of the Nth segment N Series connection, parallel connection of segments; u kO G is the voltage at the end of the k-th segment (potential of point O relative to ground). in For input conductance, C in The input capacitor is M. Larger values ​​for M and N result in smaller measurement errors, but also more complex and time-consuming calculations. Therefore, the values ​​of M and N should not be less than [a certain value]. (in (The length of the high-voltage cable being tested is in 100 meters).

[0021] The circuit grid parameter fitting algorithm, based on the equivalent network of the high-voltage cable grounding system, shows that during signal transmission, the first-end detection unit measures the injected signal waveform e(t), and the last-end detection unit measures the received signal waveform x(t). The relationship between the received signal waveform x(t) and the injected signal waveform e(t) satisfies formula (1). By using the vector fitting algorithm based on formula (1), the received signal waveform parameter matrix A and the injected signal waveform parameter matrix B can be calculated. The sum of all resistances in the received signal waveform parameter matrix A is the loop resistance of the high-voltage cable grounding system, which can directly represent the connection state of the grounding system.

[0022] (1); ; ; ; ; In the formula, A kk Let K be the received signal waveform parameters in the k-th row and k-th column, where k = [1, 2, ..., K], and K is the parameter value. Let be the resistance of the i-th segment of the wire, i = [0, 1, ..., M]. Let J be the leakage conductance of segment j, where j = [0, 1, ..., N]. This is the transpose of the injected signal waveform parameter matrix.

[0023] Both detection units are set to trigger-ready mode. The trigger voltage of the first detection unit is set to 5V, and the trigger voltage of the last detection unit is set to 5V. V (wherein) The length of the high-voltage cable being tested is in 100 meters; if it is less than 100 meters, then... (Setting the value to 1), the maximum amplitude of the high-frequency signal generated by the signal injection unit is set to 50 V, the rise time is 183 ns, and the pulse width is 1920 ns. The injected high-frequency signal is transmitted along the grounding system of the high-voltage cable under test, which sequentially triggers the two detection units to start recording data. The data recording length of the two detection units is 10 μs, and the sampling frequency is 50 MHz. After the data recording is completed, it is uploaded to the host system.

[0024] Set the number of equivalent network cascades for the high-voltage cable grounding system ( Figure 3 (Values ​​of M and N), take M=N= *2200, the injected signal waveform e(t) and the received signal waveform x(t) measured by the end detection unit are obtained. Substitute them into formula (1) and use the vector fitting algorithm to calculate the received signal waveform parameter matrix A and the injected signal waveform parameter matrix B. The resistance of the first to M segments of the conductor (R1, ..., R) in the received signal waveform parameter matrix is ​​then calculated. MThe summation yields the accurate circuit resistance value of the grounding system of the high-voltage cable under test. If the circuit resistance value is greater than 300mΩ, it can be determined that there is a defect in the grounding system of the high-voltage cable under test.

[0025] Following the steps described above, the equipment developed according to this invention was used to test a high-voltage cable approximately 500 meters long, and the resistance value of the grounding loop of the high-voltage cable was found to be 14.8 mΩ. After the line was de-energized, the resistance value of the grounding loop of the line was directly measured using a DC resistance meter and found to be 16 mΩ. Thus, it can be seen that the measurement error of this invention is 7.5%, verifying the effectiveness of this invention.

[0026] Finally, it should be noted that the above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. Therefore, although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention. All technical solutions and improvements that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A method for detecting the resistance of a high-voltage cable grounding circuit under live conditions, characterized in that: A head-end detection unit and an end-end detection unit are installed on the grounding wires at the head and end of the high-voltage cable under test, respectively. The equivalent network of the high-voltage cable grounding system is composed of the parallel connection of the conductor axial impedance and the conductor radial admittance. The axial impedance is composed of the conductor resistance and the conductor mutual inductance connected in series, and the radial admittance is composed of the leakage conductance and the equivalent capacitance connected in parallel. The head-end detection unit measures the injected signal waveform e(t), and the end-end detection unit measures the received signal waveform x(t). The relationship between the received signal waveform x(t) and the injected signal waveform e(t) satisfies formula (1). By using a vector fitting algorithm based on formula (1) to fit the waveform, the received signal waveform parameter matrix A and the injected signal waveform parameter matrix B can be calculated. （1）； The sum of all resistances in the received signal waveform parameter matrix A is the loop resistance of the high-voltage cable grounding system.

2. The method for detecting the resistance of a high-voltage cable grounding circuit under live conditions according to claim 1, characterized in that: In the equivalent network of the high-voltage cable grounding system, the resistance R0 of the 0th conductor segment is connected in series with the inductance L0 of the 0th conductor segment; the resistance R1 of the 1st conductor segment is connected in parallel with the inductance L1 of the 1st conductor segment; the resistance R2 of the 2nd conductor segment is connected in parallel with the inductance L2 of the 2nd conductor segment, and so on, with the resistance R of the Mth conductor segment... M With the inductance L of the Mth segment of the conductor M The segments are connected in parallel, and each segment is connected in series. The equivalent capacitance C0 of segment 0 is connected in parallel with the leakage conductance G0 of segment 0; the equivalent capacitance C1 of segment 1 is connected in series with the leakage conductance G1 of segment 1; the equivalent capacitance C2 of segment 2 is connected in series with the leakage conductance G2 of segment 2, and so on. The equivalent capacitance C0 of segment N is connected in parallel with the leakage conductance G0 of segment 0. N With the leakage conductance G of the Nth segment N The segments are connected in series, and the segments are connected in parallel.

3. A live-line detection device for the resistance of a high-voltage cable grounding circuit, characterized in that: The system includes a signal injection unit, a head-end detection unit, an end-end detection unit, and a host system. The head and end of the high-voltage cable under test are connected to cable terminals, and the head and end of the high-voltage cable under test are grounded through grounding wires. The signal injection unit and the head-end detection unit are installed on the grounding wire at the head of the high-voltage cable under test, and the end-end detection unit is installed on the grounding wire at the end of the high-voltage cable under test. The host system is communicatively connected to the signal injection unit, the head-end detection unit, and the end-end detection unit. The host system deploys a monitoring and calculation module to process the waveform data detected by the head-end detection unit and the end-end detection unit. The monitoring and calculation module is also used to control the signal injection unit, injecting a double exponential wave into the high-voltage cable under test through the electric field coupling method of the control signal injection unit.

4. The high-voltage cable grounding circuit resistance live detection device according to claim 3, characterized in that: The signal injection unit mainly consists of a signal generation circuit and a signal injection antenna. The output terminal of the signal generation circuit is connected to the input terminal of the signal injection antenna. The signal generation circuit mainly consists of a sine wave signal generation circuit, a push-pull power amplifier circuit, a transformer rectifier circuit, and an LC oscillation circuit connected in series.

5. The high-voltage cable grounding circuit resistance live detection device according to claim 4, characterized in that: The signal injection antenna adopts a dipole antenna structure, with each antenna being teardrop-shaped and consisting of 6 antennas. The signal is a double exponential wave.

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