A method for detecting high voltage cables by contact-type electric coupling and electromagnetic wave injection

Abstract

The present application relates to a detection method for a high-voltage cable with contact-type electrically coupled electromagnetic wave injection, comprising the following steps: before the power cable is put into operation, the core at the end of a phase cable is connected to the sheath by a connecting line, the core at the head end of the cable line is connected to a resonant voltage source, a pulse signal is injected into it, and a return signal is received at the sheath at the head end; according to various parameters of the access cable, the amplitude frequency, bandwidth and sampling point of the excitation signal are initially determined, and the linear resonant system makes the loop reach a resonant state; the return signal of the cable is received, and combined with the return signal measured when the power cable is fault-free, and the abnormal signals corresponding to various faults, a comparative analysis is performed to determine whether the core line of the cable to be tested is correct and whether there is an abnormality in the sheath topology. The present application realizes the injection of electromagnetic waves without power outages in the high-voltage cable to determine the path of the high-voltage cable.

Description

Technical Field

[0001] The present application relates to the field of high-voltage cable monitoring, and in particular to a method for detecting high-voltage cables with contact-type electrically coupled electromagnetic wave injection. Background Art

[0002] High-voltage cables have gradually replaced overhead lines to become the backbone of urban power transmission and distribution networks. In recent years, the number of newly built high-voltage cables has maintained an annual growth rate of 10%. Before a new cable is put into operation, it is necessary to determine the path and verify the sheath topology. At present, there is no method based on linear resonance contact electric coupling electromagnetic wave injection into high-voltage cables, and it is impossible to achieve cable path determination and sheath topology verification based on electromagnetic wave injection methods. Summary of the invention

[0003] The purpose of the embodiments of the present application is to provide a method for detecting high-voltage cables using contact-type electrically coupled electromagnetic wave injection. This technology uses electromagnetic wave injection and the principle of linear resonance to transfer electromagnetic energy into the cable, thereby achieving rapid and accurate detection of the cable path and sheath topology.

[0004] To achieve the above objectives, this application provides the following technical solutions:

[0005] The present application provides a method for detecting a high voltage cable by contact-type electrically coupled electromagnetic wave injection, comprising the following steps:

[0006] Before the power cable is put into operation, the core at the end of one phase of the cable is connected to the sheath using a connecting wire, and the core at the head end of the cable line is connected to the resonant voltage source, a pulse signal is injected into it, and a return signal is received at the sheath at the head end;

[0007] According to the parameters of the access cable, the amplitude frequency, bandwidth and sampling point of the excitation signal are initially determined, and the linear resonance system makes the loop reach the resonance state;

[0008] The return signal of the receiving cable is combined with the return signal measured when the power cable is fault-free and the abnormal signals corresponding to various faults to compare and analyze whether the core line of the cable to be tested is correct and whether there is any abnormality in the sheath topology.

[0009] The linear resonance system is composed of an inverter circuit, a resonance compensation network and a transmitter. In order to improve the adaptability of the system, a resonance loop in a voltage-type dual-frequency control pulse combination control system is introduced.

[0010] The voltage type dual frequency control pulse adopts PH and PL pulses to work, and the average input current of the converter is:

[0011]

[0012]

[0013] Where Vin and V0 are the input voltage and output voltage DC values, L is the inductance,

[0014] Therefore, the energy delivered at the converter input is:

[0015]

[0016]

[0017] Therefore, within the pulse sequence cycle period T consisting of μH high-frequency control pulse PH and μL low-frequency control pulse PL, the average input power of the dual-frequency controlled DCM Buck converter is:

[0018]

[0019] If the converter conversion efficiency is η, substituting equation (3) into equation (5) yields the output power:

[0020]

[0021] By transforming the above formula, we can get the ratio of the number of high-frequency and low-frequency control pulses in the pulse sequence cycle:

[0022]

[0023] By adjusting the frequency of the control frequency pulse signal, high-precision control of the operating frequency of the resonant circuit can be achieved.

[0024] The comparative analysis of whether the core line of the cable to be tested is correct and whether the sheath topology is abnormal is specifically as follows:

[0025] When the sheath line topology is abnormal, when the pulse signal encounters an impedance mismatch point, its reflection coefficient ρ is

[0026]

[0027] Where: ZT is the characteristic impedance of the signal transmission end; ZO is the characteristic impedance of the signal terminal. The transfer function between the input signal and the reflected signal of the line is expressed as

[0028]

[0029] Where: P is the number of paths along which the injected signal is reflected back to the injection point; gi is the product of the refraction and reflection coefficients generated by the impedance mismatch point encountered by the signal during transmission along path i; γ is the propagation coefficient of the traveling wave signal in the cable; di is the total distance of path i. The impulse response signal at the injection point can be expressed as

[0030]

[0031] Since the injected signal is a narrow pulse signal, the corresponding signal frequency is relatively high, and the corresponding propagation coefficient γ can be regarded as unchanged. The inverse Fourier transform is performed on the signal to obtain the corresponding response signal after the pulse signal is injected into the system, as follows:

[0032]

[0033] When there is an abnormality in the topology of the sheath line, it can be regarded as a change in the impedance of the line, which will affect the transfer function, and the cable path and sheath topology can be determined.

[0034] Compared with the prior art, the beneficial effects of this application are:

[0035] The present invention realizes a cable path determination and sheath topology verification technology based on electromagnetic wave injection method. This technology transfers electromagnetic energy into the cable by electromagnetic wave injection and utilizes the linear resonance principle to realize rapid and accurate detection of the cable path and sheath topology. Compared with the traditional testing method, the present invention has the following advantages: easy operation, no need to cut or disassemble the cable, reducing the risk of damage to the equipment; able to detect abnormal conditions of the cable path and sheath topology, providing guarantee for the safe operation of power facilities. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0037] Figure 1 A flow chart of the method of this application;

[0038] Figure 2 An equivalent circuit model diagram of the linear resonant system of the present application;

[0039] Figure 3 A precise control diagram of the resonant frequency of this application;

[0040] Figure 4 This is the high voltage cable detection principle diagram of this application. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings.

[0042] The terms "comprises," "comprising," or any other variation thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes the element.

[0043] The terms "first", "second", etc. are only used to distinguish one entity or operation from another entity or operation, and should not be understood as indicating or implying relative importance, nor should they be understood as requiring or implying any such actual relationship or order between these entities or operations.

[0044] like Figure 1 As shown, a method for detecting a high voltage cable by contact-type electrically coupled electromagnetic wave injection comprises the following steps:

[0045] Before the power cable is put into operation, the core at the end of one phase of the cable is connected to the sheath using a connecting wire, and the core at the head end of the cable line is connected to the resonant voltage source, a pulse signal is injected into it, and a return signal is received at the sheath at the head end;

[0046] According to the parameters of the access cable, the amplitude frequency, bandwidth and sampling point of the excitation signal are initially determined, and the linear resonance system makes the loop reach the resonance state;

[0047] The return signal of the receiving cable is combined with the return signal measured when the power cable is fault-free and the abnormal signals corresponding to various faults to compare and analyze whether the core line of the cable to be tested is correct and whether there is any abnormality in the sheath topology.

[0048] The linear resonance system is composed of an inverter circuit, a resonance compensation network and a transmitter. In order to improve the adaptability of the system, a resonance loop in a voltage-type dual-frequency control pulse combination control system is introduced.

[0049] The voltage type dual frequency control pulse adopts PH and PL pulses to work, and the average input current of the converter is:

[0050]

[0051]

[0052] Where Vin and V0 are the input voltage and output voltage DC values, L is the inductance,

[0053] Therefore, the energy delivered at the converter input is:

[0054]

[0055]

[0056] Therefore, within the pulse sequence cycle period T consisting of μH high-frequency control pulse PH and μL low-frequency control pulse PL, the average input power of the dual-frequency controlled DCM Buck converter is:

[0057]

[0058] If the converter conversion efficiency is η, substituting equation (3) into equation (5) yields the output power:

[0059]

[0060] By transforming the above formula, we can get the ratio of the number of high-frequency and low-frequency control pulses in the pulse sequence cycle:

[0061]

[0062] By adjusting the frequency of the control frequency pulse signal, high-precision control of the operating frequency of the resonant circuit can be achieved.

[0063] The comparative analysis of whether the core line of the cable to be tested is correct and whether the sheath topology is abnormal is specifically as follows:

[0064] When the sheath line topology is abnormal, when the pulse signal encounters an impedance mismatch point, its reflection coefficient ρ is

[0065]

[0066] Where: ZT is the characteristic impedance of the signal transmission end; ZO is the characteristic impedance of the signal terminal. The transfer function between the input signal and the reflected signal of the line is expressed as

[0067]

[0068] Where: P is the number of paths along which the injected signal is reflected back to the injection point; gi is the product of the refraction and reflection coefficients generated by the impedance mismatch point encountered by the signal during transmission along path i; γ is the propagation coefficient of the traveling wave signal in the cable; di is the total distance of path i. The impulse response signal at the injection point can be expressed as

[0069]

[0070] Since the injected signal is a narrow pulse signal, the corresponding signal frequency is relatively high, and the corresponding propagation coefficient γ can be regarded as unchanged. The inverse Fourier transform is performed on the signal to obtain the corresponding response signal after the pulse signal is injected into the system, as follows:

[0071]

[0072] When there is an abnormality in the topology of the sheath line, it can be regarded as a change in the impedance of the line, which will affect the transfer function, and the cable path and sheath topology can be determined.

[0073] This patent can determine the path of high-voltage cables and verify the sheath topology through a contact-type electrically coupled electromagnetic wave injection method. This method is based on the linear resonance phenomenon and utilizes the characteristics of electromagnetic wave propagation in high-voltage cables. By injecting a pulse signal into the core-sheath loop through a linear resonance system through a DC voltage power supply, when the resonant loop matches the resonant frequency of the high-voltage cable, the electromagnetic wave produces a linear resonance effect in the cable. This means that the energy of the electromagnetic wave will propagate in the cable and gradually increase, forming a transmission channel with less attenuation. Subsequently, the return signal of the core-sheath loop in the resonant state is obtained by testing the receiving device, and the path of the cable and the topological structure of the sheath are determined based on these signals. This patent proposes a detection method for high-voltage cables with contact-type electrically coupled electromagnetic wave injection, which is simple to operate, highly safe and has excellent accuracy. This is of great significance for the construction of urban cable lines, and can improve work efficiency and ensure personnel safety. At the same time, this method provides a new solution for cable status detection before commissioning, which can accurately determine the path and sheath topology, and provide strong technical support for the safe and stable operation of power cables.

[0074] 1) Linear resonant system

[0075] The linear resonant system consists of an inverter circuit, a resonant compensation network and a transmitter. Figure 2 It is the equivalent circuit model of the linear resonant system, where U is the DC voltage source, L and RL are the inductance and resistance of the core-sheath loop respectively, and the single-phase full-bridge inverter circuit converts the DC power supply into a pulse signal to excite the resonant loop. When the operating frequency of the system is the same as the resonant frequency of the resonant loop, the system's power transmission efficiency and transmission power are the highest. In order to avoid detuning of the resonant loop, that is, the resonant frequency is not equal to the operating frequency of the system, it is necessary to tune and control the resonant loop. This can be achieved by controlling the conduction angle of the drive signals G5 and G6 of the switch tubes S5 and S6, thereby controlling the charging and discharging of the tuning capacitor C1, generating an equivalent tuning capacitor C, and then changing the total equivalent capacitance value of the tuning circuit. By compensating the resonant loop with this variable capacitor, the resonant state of the circuit can be maintained. The variable capacitor tuning circuit is composed of a pair of reverse series-connected switch tubes S5 and S6 and a tuning capacitor C1, which are then connected in parallel with a fixed capacitor C2, as shown in FIG. Figure 2 The selection of parallel capacitors is mainly based on the simplicity of the tuning circuit network circuit and the purpose of achieving the capacitance value of the entire resonant capacitor network by adjusting the capacitance value of capacitor C2 alone.

[0076] When the switches S1 and S4 in the single-phase full-bridge inverter circuit are turned on and S2 and S3 are turned off, the transmitter current flows from point 1 to point 2, and the switch S5 controls the charging and discharging of the tuning capacitor C1. When the switches S2 and S3 in the single-phase full-bridge inverter circuit are turned on and S1 and S4 are turned off, the transmitter current flows from point 2 to point 1, and the switch S6 controls the charging and discharging of the tuning capacitor C1.

[0077] 2) Input pulse signal

[0078] The resonant circuit in the control system is controlled by voltage-type dual-frequency control pulse combination, such as Figure 3 As shown, by introducing two pulse signals of different frequencies into the resonant circuit, precise control of the resonant frequency is achieved. A pulse signal of a reference frequency is introduced into the resonant circuit as a reference signal, which is usually a stable low-frequency signal. Then, a pulse signal of a control frequency is introduced, and its frequency can be adjusted as needed. After appropriate processing, these two pulse signals are input into the resonant circuit.

[0079] By controlling the frequency of the frequency pulse signal, the operating frequency of the resonant circuit can be accurately adjusted to match the required target frequency. The period and duty cycle of the high-frequency control pulse PH are controlled by VMBF (voltage-type dual-frequency controller) to be TH and TH respectively; the period and duty cycle of the low-frequency control pulse PL are TL and DL respectively.

[0080] 3) Direct connection method

[0081] The present invention proposes a non-destructive testing method for high-voltage cables by injecting contact-type electrically coupled electromagnetic waves, which is used to determine the path of high-voltage cables and verify the sheath topology. This method connects the core and sheath loops, uses the linear resonance principle to transfer electromagnetic wave energy to the cable line to be tested, and then determines the cable line and sheath topology through the return signal. Figure 4 As shown. Short-circuit the cable core and sheath grounding wires at the end of the cable, and disconnect the double-end grounding wires of the cable line, so that a core-sheath loop is formed inside the cable. Under the action of the pulse signal source, the generated pulse wave will enter the cable through the core and sheath loop. When there are abnormalities in the cable path and sheath topology, the propagation path, attenuation and reflection of the electromagnetic wave inside the device will change. These changes can be used to determine whether the device is faulty by measuring the transmission characteristics of the injected signal.

[0082] The basic principle of this implementation method is: when electromagnetic waves encounter interfaces or structural changes inside the cable, reflection or refraction may occur, affecting signal transmission. Electromagnetic waves gradually weaken when propagating in the cable, and this attenuation will lead to a decrease in signal strength. Therefore, by measuring the characteristics of electromagnetic waves propagating in high-voltage cables, the linear resonance phenomenon and the method of injecting pulse signals can be used to determine the high-voltage cable path and verify the sheath topology.

[0083] The selection of the injection signal frequency can be achieved through a linear resonance system. Figure 2 The variable capacitor tuning circuit in the circuit controls the conduction angle of the drive signals G5 and G6 of the switch tubes S5 and S6, thereby controlling the charging and discharging of the tuning capacitor C1, generating an equivalent tuning capacitor C, and then changing the total equivalent capacitance value of the tuning circuit. By using this variable capacitor to compensate the resonant circuit, the resonant state of the circuit can be maintained. In addition, a feedback system is introduced to deal with possible abnormalities in the line, and a voltage-type dual-frequency control pulse combination is used to control the resonant circuit in the power system, such as Figure 3 As shown, by introducing two pulse signals of different frequencies into the resonant circuit, precise control of the resonant frequency is achieved.

[0084] This patent is used to determine the path and sheath topology verification before the new cable is put into operation, so the core wire of the cable can be operated during measurement. Therefore, this embodiment proposes to inject a pulse signal into the cable core, and the core and sheath form a signal loop, and receive the return signal at the sheath on the same side of the injection point, such as Figure 4 shown.

[0085] The above description is only an embodiment of the present application and is not intended to limit the protection scope of the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for detecting a high voltage cable by contact-type electric coupling electromagnetic wave injection, characterized in that: The following steps are involved: Before the power cable is put into operation, the core at the end of one phase of the cable is connected to the sheath using a connecting wire, and the core at the head end of the cable line is connected to the resonant voltage source, a pulse signal is injected into it, and a return signal is received at the sheath at the head end; According to the parameters of the access cable, the amplitude frequency, bandwidth and sampling point of the excitation signal are initially determined, and the linear resonance system makes the loop reach the resonance state; Receive the return signal of the cable, combine it with the return signal measured when the power cable is fault-free, and the abnormal signals corresponding to various faults, and compare and analyze whether the core line of the cable to be tested is correct and whether there is any abnormality in the sheath topology; The linear resonant system is composed of an inverter circuit, a resonant compensation network and a transmitter. In order to improve the adaptability of the system, a resonant circuit in a voltage-type dual-frequency control pulse combination control system is introduced; The voltage type dual frequency control pulse adopts PH and PL pulses to work, and the period and duty cycle of the high frequency control pulse PH are T H , D H ; The period and duty cycle of the low-frequency control pulse PL are T L , D L , the average input currents of the converters are: Where V in and V0 are the input voltage and output voltage DC values ​​respectively, L is the inductance, Therefore, the energy delivered at the converter input is: Therefore, within the pulse sequence cycle period T consisting of μH high-frequency control pulse PH and μL low-frequency control pulse PL, the average input power of the dual-frequency controlled DCM Buck converter is: If the converter conversion efficiency is η, substitute equation (3) into equation (5) to obtain the output power: By transforming the above formula, we can get the ratio of the number of high-frequency and low-frequency control pulses in the pulse sequence cycle: By adjusting the frequency of the control frequency pulse signal, high-precision control of the resonant circuit operating frequency can be achieved; The comparative analysis of whether the core line of the cable to be tested is correct and whether the sheath topology is abnormal is specifically as follows: When the sheath line topology is abnormal, when the pulse signal encounters an impedance mismatch point, its reflection coefficient ρ is Where: Z T is the characteristic impedance of the signal transmission end; Z O is the characteristic impedance of the signal terminal, and the transfer function between the input signal and the reflected signal of the line is expressed as Where: P is the number of paths along which the injected signal is reflected back to the injection point; g i is the product of the refraction and reflection coefficients generated by the impedance mismatch point encountered by the signal during transmission along path i; γ is the propagation coefficient of the traveling wave signal in the cable; d i is the total distance of path i, and the impulse response signal of the injection point can be expressed as Since the injected signal is a narrow pulse signal, the corresponding signal frequency is relatively high, and the corresponding propagation coefficient γ can be regarded as unchanged. The inverse Fourier transform is performed on the signal to obtain the corresponding response signal after the pulse signal is injected into the system, as follows: When there is an abnormality in the topology of the sheath line, it can be regarded as a change in the impedance of the line, which will affect the transfer function, and the cable path and sheath topology can be determined.

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