Cable fault detection method based on frequency difference of frequency modulated continuous waves

Abstract

The invention relates to a frequency modulated continuous wave (FMCW) frequency difference-based cable fault detection method, which comprises the following steps of: transmitting an FMCW signal to a cable, acquiring a reflected signal, mixing the transmitted signal and the reflected signal, and extracting a lower sideband through a low-pass filter, so as to detect the cable fault based on the frequency modulated continuous wave (FMCW) frequency difference. Performing FFT processing on the obtained signal to obtain a frequency spectrum and a phase spectrum of a difference frequency signal, determining a cable fault position by using the frequency spectrum, and determining a cable fault type by using the phase spectrum; the method is sensitive to slight defects of the cable, and has the advantages of high resolution and strong anti-interference capability; the method has the advantages that frequency difference and phase sensitivity are introduced, the anti-interference capability is high, and live detection is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of cable fault detection, and in particular relates to a cable fault detection method based on frequency modulation continuous wave frequency difference. Background Art

[0002] In distribution networks, especially urban 10kV distribution networks, the application of power cables has become more and more extensive, and plays an irreplaceable role in urban power supply. How to maximize the normal operation of cable lines and improve the operating reliability of cables themselves is related to the safe and reliable operation of urban distribution networks. The detection of faulty cables is particularly important. In the field of cable fault detection, traditional methods often rely on electrical testing and time domain reflection technology. Although effective, their accuracy is limited in complex environments. Therefore, it is very necessary to provide a cable fault detection method based on frequency modulation continuous wave frequency difference, which introduces frequency difference and phase sensitivity, has strong anti-interference ability, and realizes live detection. Summary of the invention

[0003] 1. Technical issues

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

[0005] 1. Traditional methods often rely on electrical testing and time domain reflection technology, which has limited accuracy in complex environments.

[0006] (II) Technical solution

[0007] The purpose of the present invention is to overcome the shortcomings of the prior art and to provide a cable fault detection method based on frequency modulation continuous wave frequency difference, which introduces frequency difference and phase sensitivity, has strong anti-interference ability and realizes live detection.

[0008] The object of the present invention is achieved by: a cable fault detection method based on frequency modulation continuous wave frequency difference, the method comprising the following steps:

[0009] Step 1: Generate an incident FMCW signal;

[0010] Step 2: Connect the obtained FMCW signal to the power divider, keep one output signal as a reference signal for standby use, and inject one output signal from the head end of the cable through a three-terminal circulator as a transmission signal, and obtain the reflected signal at the head end of the cable;

[0011] Step 3: Connect the reflected signal obtained at the head end of the cable to the mixer through a three-terminal circulator, connect the other end of the mixer to the reference signal output by the power divider, mix the reflected signal with the reference signal, and output the signal through a low-pass filter;

[0012] Step 4: sout (t) Perform FFT processing on the signal to obtain the frequency domain signal;

[0013] Step 5: Obtain the maximum peak value of the spectrum result, obtain the signal frequency difference, that is, the horizontal coordinate of the maximum peak value, and combine it with the corresponding formula to obtain the fault location of the cable;

[0014] Step 6: Obtain the phase spectrum results, analyze the phase change trend, and obtain the cable fault type.

[0015] Furthermore, the expression of the incident FMCW signal generated in step 1 is: Where A is the amplitude of the modulation signal; ω 0 (t) is the angular frequency of the cosine signal; For 1 (t) The initial phase of the signal.

[0016] Furthermore, the expression of the reflected signal in step 2 is as follows:

[0017] Among them, α is the signal transmission attenuation factor; t d is the two-way delay to the destination.

[0018] Further, the output signal in step 3 is expressed as: Among them, f b (t) is the frequency difference; For signal s out The phase of (t).

[0019] Furthermore, the frequency domain signal formula in step 4 is: k=0,1,...,N-1, where X[k] represents the frequency domain signal; x[n] represents the signal s out (t) is a discrete form; j is an imaginary unit; N is the number of sampling points, i.e., the signal length of x[n]; k represents each frequency point; It is a complex exponential function that reflects the frequency component of the signal; the calculation formula for the horizontal coordinate of the spectrum graph is as follows: k=0,1,...,N-1, where f[k] is the frequency corresponding to each frequency point k; Δf 0 is the frequency difference between adjacent frequency points on the horizontal axis; f s is the sampling frequency; the ordinate of the spectrum graph is the amplitude of X[k], and the calculation formula is as follows: Where Re(X[k]) and Im(X[k]) are the real and imaginary parts of X[k], respectively; the phase of the phase diagram is the phase of X[k], and the calculation formula is as follows: Finally, the signal spectrum and phase spectrum are obtained.

[0020] Furthermore, the step 5 is specifically as follows: obtaining the maximum peak value of the spectrum result, and obtaining s out (t) Signal frequency difference f b (t), i.e. the horizontal coordinate of the maximum peak value, is combined with the following formula to obtain the fault location D of the cable: Where Δf is the input signal s 1 (t) half bandwidth of frequency modulation; T s is the frequency modulation period; f b is the frequency difference of the result in the previous step; v is the actual wave velocity of the signal transmitted in the cable.

[0021] Furthermore, the cable fault type is determined in step 6 as follows: if the phase turns from a negative angle to a positive angle, and the turning angle is close to 180°, it is an open circuit fault; if the phase turns from a positive angle to a negative angle, and the turning angle is close to 180°, it is a short circuit fault.

[0022] A cable fault detection system based on frequency modulation continuous wave frequency difference adopts the cable fault detection method based on frequency modulation continuous wave frequency difference as described above to realize the cable fault detection function. The system includes a power divider, a three-terminal circulator, a mixer, an oscilloscope, a computer and a signal generator; the power divider includes channel one and channel two; the three-terminal circulator includes a three-terminal circulator inlet, a three-terminal circulator middle port and a three-terminal circulator outlet; the mixer includes mixer inlet channel two and mixer inlet channel one.

[0023] Furthermore, the signal generator is used to generate an incident FMCW detection signal, and the signal generator is connected to a power divider; the power divider is respectively connected to a three-terminal circulator and a mixer; the three-terminal circulator is connected to a mixer, the mixer is connected to an oscilloscope, the oscilloscope is connected to a computer, and the computer is connected to the signal generator.

[0024] Furthermore, the power divider divides the detection signal into an incident signal and a reference signal through channel one and channel two, and respectively connects to the three-terminal circulator inlet and mixer inlet channel one; the three-terminal circulator middle port is connected to the cable head end, outputs the incident signal to the detected cable and obtains a reflected signal; the mixer inlet channel two is connected to the three-terminal circulator outlet, and is used to multiply and mix the reference signal and the reflected signal to obtain a frequency difference and a frequency sum signal;

[0025] The oscilloscope is connected to the mixer outlet to collect data of the mixed signal; the collected data of the oscilloscope is transmitted to the computer to process and analyze the mixed signal, implement low-pass filtering to extract the frequency difference signal, then obtain the frequency difference signal spectrum diagram and phase spectrum diagram, and finally obtain the fault information of the detected cable.

[0026] (III) Beneficial effects

[0027] 1. The present invention is based on the cable fault detection of frequency modulated continuous wave (FMCW) frequency difference, introduces frequency difference and phase sensitivity to detect the cable, and is an emerging cable fault location and diagnosis detection method;

[0028] 2. The present invention transmits an FMCW signal to the cable, collects the reflected signal, mixes the transmitted signal and the reflected signal, extracts the lower sideband through a low-pass filter, and performs FFT processing on the obtained signal to obtain the spectrum and phase spectrum of the difference frequency signal;

[0029] 3. The present invention uses the frequency spectrum to determine the cable fault location and uses the phase spectrum to determine the cable fault type;

[0030] 4. The present invention is sensitive to slight defects of the cable and has the advantages of high resolution and strong anti-interference ability. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the FMCW cable fault detection system of the present invention.

[0032] Figure 2 Schematic diagram of the FMCW incident signal of the present invention.

[0033] Figure 3 This is a diagram of the FMCW reflection signal of the present invention.

[0034] Figure 4 It is a schematic diagram of the low-frequency filtering mixing signal of the present invention.

[0035] Figure 5 It is the amplitude-frequency diagram of the mixing signal of the present invention.

[0036] Figure 6 It is the open circuit phase-frequency diagram of the cable of the present invention.

[0037] Figure 7 It is the phase-frequency diagram of the cable short circuit of the present invention.

[0038] In the figure: 1, channel one 2, channel two 3, three-terminal circulator inlet 4, three-terminal circulator middle port 5, three-terminal circulator outlet 6, mixer inlet channel two 7, mixer inlet channel one 8, three-terminal circulator 9, mixer 10, oscilloscope 11, computer 12, signal generator 13, power divider. DETAILED DESCRIPTION

[0039] Frequency modulated continuous wave (FMCW) technology has made remarkable progress in the field of radar detection and is widely used in automotive anti-collision radar and weather radar. It is favored for its high resolution and strong anti-interference ability. In terms of laser ranging, FMCW laser ranging technology has also gradually matured and can achieve high-precision distance measurement and object recognition, especially in autonomous driving and unmanned aerial vehicle applications. The method of the present invention draws on the successful experience of FMCW technology in the other two fields and is applied to the field of cable fault detection. The method of the present invention can accurately locate the fault location and fault type by sending modulated signals and analyzing the frequency difference of reflected signals. In addition, when the cable is buried at a large depth or the environmental conditions are complex, the method of the present invention has the advantages of strong real-time performance, wide adaptability and high accuracy, and is particularly sensitive to slight defects of the cable, which promotes the progress of cable fault detection technology.

[0040] The present invention is further described below in conjunction with embodiments and / or drawings.

[0041] Example 1

[0042] like Figure 1-7 As shown, a cable fault detection method based on frequency modulation continuous wave frequency difference, the method comprises the following steps:

[0043] Step 1: Generate an incident FMCW signal;

[0044] Furthermore, the expression of the incident FMCW signal generated in step 1 is: Where A is the amplitude of the modulation signal; ω 0 (t) is the angular frequency of the cosine signal; For 1 (t) The initial phase of the signal.

[0045] In the present invention, s 1 (t) The frequency f of the signal is as follows: Among them, f 0 is the starting frequency; K is the frequency modulation slope; the frequency modulation slope is set as follows: Wherein, B is the FM bandwidth and T is a FM period.

[0046] Step 2: Connect the obtained FMCW signal to the power divider, keep one output signal as a reference signal for standby use, and inject one output signal from the head end of the cable through a three-terminal circulator as a transmission signal, and obtain the reflected signal at the head end of the cable;

[0047] Furthermore, the expression of the reflected signal in step 2 is as follows: Among them, α is the signal transmission attenuation factor; t d is the two-way delay to the destination.

[0048] In the present invention, the two-way delay to the target is t d The expression of is as follows: d =2D / v, the frequency of the received signal f τ It can be calculated as follows:

[0049] Step 3: Connect the reflected signal obtained at the head end of the cable to the mixer through a three-terminal circulator, connect the other end of the mixer to the reference signal output by the power divider, mix the reflected signal with the reference signal, and output the signal through a low-pass filter;

[0050] Further, the output signal in step 3 is expressed as: Among them, f b (t) is the frequency difference; For signal s out The phase of (t).

[0051] Step 4: s out (t) Perform FFT processing on the signal to obtain the frequency domain signal;

[0052] Furthermore, the frequency domain signal formula in step 4 is: k=0,1,...,N-1, where X[k] represents the frequency domain signal; x[n] represents the signal s out (t) is a discrete form; j is an imaginary unit; N is the number of sampling points, i.e., the signal length of x[n]; k represents each frequency point; It is a complex exponential function that reflects the frequency component of the signal; the calculation formula for the horizontal coordinate of the spectrum graph is as follows: k=0,1,...,N-1, where f[k] is the frequency corresponding to each frequency point k; Δf 0 is the frequency difference between adjacent frequency points on the horizontal axis; f s is the sampling frequency; the ordinate of the spectrum graph is the amplitude of X[k], and the calculation formula is as follows: Where Re(X[k]) and Im(X[k]) are the real and imaginary parts of X[k], respectively; the phase of the phase diagram is the phase of X[k], and the calculation formula is as follows: Finally, the signal spectrum and phase spectrum are obtained.

[0053] Step 5: Obtain the maximum peak value of the spectrum result, obtain the signal frequency difference, that is, the horizontal coordinate of the maximum peak value, and combine it with the corresponding formula to obtain the fault location of the cable;

[0054] Furthermore, the step 5 is specifically as follows: obtaining the maximum peak value of the spectrum result, and obtaining s out (t) Signal frequency difference f b (t), i.e. the horizontal coordinate of the maximum peak value, is combined with the following formula to obtain the fault location D of the cable: Where Δf is the input signal s 1 (t) half bandwidth of frequency modulation; T s is the frequency modulation period; f b is the frequency difference of the result in the previous step; v is the actual wave velocity of the signal transmitted in the cable.

[0055] Step 6: Obtain the phase spectrum results, analyze the phase change trend, and obtain the cable fault type.

[0056] Furthermore, the cable fault type is determined in step 6 as follows: if the phase turns from a negative angle to a positive angle, and the turning angle is close to 180°, it is an open circuit fault; if the phase turns from a positive angle to a negative angle, and the turning angle is close to 180°, it is a short circuit fault.

[0057] The present invention is a cable fault detection method based on frequency modulated continuous wave frequency difference. During use, the present invention creatively introduces frequency difference and phase sensitivity to detect cables based on the detection method of FMCW signals, which is an emerging cable fault location and diagnosis detection method. The FMCW signal has strong anti-interference ability, can realize live detection of cable faults, and is very sensitive to various types of faults and minor defects, improves the accuracy and sensitivity of cable fault location and diagnosis, and is of great significance to improving the stability of the power supply system. The present invention has the advantages of introducing frequency difference and phase sensitivity, strong anti-interference ability, and realizing live detection.

[0058] Example 2

[0059] like Figure 1-7 As shown, a cable fault detection system based on frequency modulation continuous wave frequency difference adopts the cable fault detection method based on frequency modulation continuous wave frequency difference as described above to realize the cable fault detection function. The system includes a power divider, a three-terminal circulator, a mixer, an oscilloscope, a computer and a signal generator; the power divider includes channel one and channel two; the three-terminal circulator includes a three-terminal circulator inlet, a three-terminal circulator middle port and a three-terminal circulator outlet; the mixer includes mixer inlet channel two and mixer inlet channel one.

[0060] Furthermore, the signal generator is used to generate an incident FMCW detection signal, and the signal generator is connected to a power divider; the power divider is respectively connected to a three-terminal circulator and a mixer; the three-terminal circulator is connected to a mixer, the mixer is connected to an oscilloscope, the oscilloscope is connected to a computer, and the computer is connected to the signal generator.

[0061] Furthermore, the power divider divides the detection signal into an incident signal and a reference signal through channel one and channel two, and respectively connects to the three-terminal circulator inlet and mixer inlet channel one; the three-terminal circulator middle port is connected to the cable head end, outputs the incident signal to the detected cable and obtains a reflected signal; the mixer inlet channel two is connected to the three-terminal circulator outlet, and is used to multiply and mix the reference signal and the reflected signal to obtain a frequency difference and a frequency sum signal;

[0062] The oscilloscope is connected to the mixer outlet to collect data of the mixed signal; the collected data of the oscilloscope is transmitted to the computer to process and analyze the mixed signal, implement low-pass filtering to extract the frequency difference signal, then obtain the frequency difference signal spectrum diagram and phase spectrum diagram, and finally obtain the fault information of the detected cable.

[0063] In the present invention, ① installation of the cable fault detection system: when a fault occurs in the distribution network, the distribution network relay protection device will be induced to operate and disconnect the fault line. At the same time, in order to ensure the safety of maintenance, when eliminating the cable fault, further detection will be performed on whether the fault line is energized;

[0064] After confirming that the cable is completely powered off, follow the Figure 1 Connect various components: the signal source (signal generator) is connected to the power divider 13, the power divider 13 has two outputs, channel 1 is connected to the three-terminal circulator inlet 3, channel 2 2 is directly connected to the mixer inlet channel 1 7, the three-terminal circulator middle port 4 is connected to the cable head end, the three-terminal circulator outlet 5 is connected to the mixer inlet channel 2 6, the mixer 9 outlet is connected to the oscilloscope 10, the oscilloscope 10 collects data and transmits it to the computer 11; confirm that each part is connected correctly, and the cable fault detection system is installed.

[0065] ② Setting of incident FMCW signal: Figure 2 , a FMCW signal with a frequency modulation period of 1ms, a frequency modulation bandwidth of 50MHz, a starting frequency of 1MHz, an initial phase of 0, and an amplitude of 1Vpp is generated through a signal source, and a signal is transmitted every 3ms; it can also be set according to actual needs.

[0066] ③ Cable detection data acquisition: such as Figure 3 , the cable reflected signal is transmitted to the mixer 9, the oscilloscope 10 is turned on, the sampling frequency is set to 500MHz, the horizontal and vertical axis ranges are set appropriately, and the collected data is stored, such as Figure 4 , collect the mixed signal; transmit the collected data to the computer 11 through the serial port to obtain the cable fault information.

[0067] ④ Obtaining the cable fault location: Use the frequency difference between the fault signal collected at the head end of the cable and the reference signal to measure the cable fault location; first use low-pass filtering to extract the lower sideband of the mixed signal collected by the oscilloscope. In this example, a butter low-pass filter is used, the filter order is 4, and the cutoff frequency is set to 2MHz; then perform FFT processing on the filtered difference frequency signal to obtain the amplitude-frequency diagram and phase-frequency diagram; Figure 5 , the amplitude-frequency graph gets a peak value, and the corresponding frequency is the required frequency difference; substitute the frequency difference into the following formula:

[0068] According to the example, the wave velocity v in the cable is 2.094×10 8 m / s,T s is the frequency modulation period, the second step is set to the known 1ms, Δf is half of the frequency modulation bandwidth, the second step is set to the known 25MHz, f b As shown in the figure, it is 48191Hz, and the fault location can be calculated to be 100.9m.

[0069] ⑤ Obtaining the cable fault type: Observe the phase spectrum. At the fault point, the following two situations may occur: (1) If the phase turns from a negative angle to a positive angle, and the turning angle is close to 180°, it is an open circuit fault; (2) If the phase turns from a positive angle to a negative angle, and the turning angle is close to 180°, it is a short circuit fault. The cable fault type is determined.

[0070] According to the example, Figure 6 , the phase at the fault point turns from -49.9° to 128.2°, and the turning angle is close to 180°, which is consistent with an open circuit fault; Figure 7 The phase at the fault point turns from 130.1° to -51.7°, and the turning angle is close to 180°, which is consistent with a short circuit fault.

[0071] Combining the above data processing methods, the fault type and fault distance of the cable can be obtained.

[0072] In summary, the connection mode and functions of each part of the detection system of the present invention are as follows: an FMCW detection signal is generated by a signal generator 12; the detection signal is divided into an incident signal and a reference signal by a power divider 13; the incident signal is output to the detected cable by a three-terminal circulator 8 and a reflected signal is obtained, and the three-terminal circulator 8 can make the signal flow in one direction, separate the incident signal and the reflected signal, and avoid signal aliasing; the reference signal and the reflected signal are multiplied and mixed by a mixer 9 to obtain a frequency difference and a frequency sum signal; the mixed signal data is collected by an oscilloscope 10; the mixed signal is processed and analyzed by a computer 11 to realize low-pass filtering to extract the frequency difference signal, and then the frequency difference signal spectrum diagram and phase spectrum diagram are obtained, and finally the fault information of the detected cable is obtained.

[0073] The present invention is a cable fault detection method based on frequency modulated continuous wave frequency difference. During use, the present invention creatively introduces frequency difference and phase sensitivity to detect cables based on the detection method of FMCW signals, which is an emerging cable fault location and diagnosis detection method. The FMCW signal has strong anti-interference ability, can realize live detection of cable faults, and is very sensitive to various types of faults and minor defects, improves the accuracy and sensitivity of cable fault location and diagnosis, and is of great significance to improving the stability of the power supply system. The present invention has the advantages of introducing frequency difference and phase sensitivity, strong anti-interference ability, and realizing live detection.

Claims

1. A cable fault detection method based on frequency modulation continuous wave frequency difference, characterized in that: The method comprises the following steps: Step 1: Generate an incident FMCW signal; Step 2: Connect the obtained FMCW signal to the power divider, keep one output signal as a reference signal for standby use, and inject one output signal from the head end of the cable through a three-terminal circulator as a transmission signal, and obtain the reflected signal at the head end of the cable; Step 3: Connect the reflected signal obtained at the head end of the cable to the mixer through a three-terminal circulator, connect the other end of the mixer to the reference signal output by the power divider, mix the reflected signal with the reference signal, and output the signal through a low-pass filter; Step 4: s out (t) Perform FFT processing on the signal to obtain the frequency domain signal; Step 5: Obtain the maximum peak value of the spectrum result, obtain the signal frequency difference, that is, the horizontal coordinate of the maximum peak value, and combine it with the corresponding formula to obtain the fault location of the cable; Step 6: Obtain the phase spectrum results, analyze the phase change trend, and obtain the cable fault type.

2. A cable fault detection method based on frequency modulation continuous wave frequency difference as claimed in claim 1, characterized in that: The expression of the incident FMCW signal generated in step 1 is: Where A is the amplitude of the modulation signal; ω0(t) is the angular frequency of the cosine signal; is the initial phase of the s1(t) signal.

3. A cable fault detection method based on frequency modulation continuous wave frequency difference as claimed in claim 1, characterized in that: The expression of the reflected signal in step 2 is as follows: Among them, α is the signal transmission attenuation factor; t d is the two-way delay to the destination.

4. A cable fault detection method based on frequency modulation continuous wave frequency difference as claimed in claim 1, characterized in that: The output signal in step 3 is expressed as: Among them, f b (t) is the frequency difference; For signal s out The phase of (t).

5. A cable fault detection method based on frequency modulation continuous wave frequency difference as claimed in claim 1, characterized in that: The frequency domain signal formula in step 4 is: Among them, X[k] represents the frequency domain signal; x[n] represents the signal s out (t) is a discrete form; j is an imaginary unit; N is the number of sampling points, i.e., the signal length of x[n]; k represents each frequency point; It is a complex exponential function that reflects the frequency component of the signal; the calculation formula for the horizontal coordinate of the spectrum graph is as follows: Where f[k] is the frequency corresponding to each frequency point k; Δf0 is the frequency difference between adjacent frequency points on the horizontal axis; f s is the sampling frequency; the ordinate of the spectrum graph is the amplitude of X[k], and the calculation formula is as follows: Where Re(X[k]) and Im(X[k]) are the real and imaginary parts of X[k], respectively; the phase of the phase diagram is the phase of X[k], and the calculation formula is as follows: Finally, the signal spectrum and phase spectrum are obtained.

6. A cable fault detection method based on frequency modulation continuous wave frequency difference as claimed in claim 1, characterized in that: The step 5 is specifically as follows: obtaining the maximum peak value of the spectrum result, and obtaining s out (t) Signal frequency difference f b (t), i.e. the horizontal coordinate of the maximum peak value, is combined with the following formula to obtain the fault location D of the cable: Where Δf is the half bandwidth of the frequency modulation of the input signal s1(t); T s is the frequency modulation period; f b is the frequency difference of the result in the previous step; v is the actual wave velocity of the signal transmitted in the cable.

7. A cable fault detection method based on frequency modulation continuous wave frequency difference as claimed in claim 1, characterized in that: The cable fault type is determined in step 6 as follows: if the phase turns from a negative angle to a positive angle, and the turning angle is close to 180°, it is an open circuit fault; if the phase turns from a positive angle to a negative angle, and the turning angle is close to 180°, it is a short circuit fault.

8. A cable fault detection system based on frequency modulation continuous wave frequency difference, which uses the cable fault detection method based on frequency modulation continuous wave frequency difference as described in claims 1-7 to realize the cable fault detection function, characterized in that: The system includes a power divider, a three-terminal circulator, a mixer, an oscilloscope, a computer and a signal generator; the power divider includes channel one and channel two; the three-terminal circulator includes a three-terminal circulator inlet, a three-terminal circulator middle port and a three-terminal circulator outlet; the mixer includes mixer inlet channel two and mixer inlet channel one.

9. A cable fault detection system based on frequency modulation continuous wave frequency difference as claimed in claim 8, characterized in that: The signal generator is used to generate an incident FMCW detection signal, and the signal generator is connected to a power divider; the power divider is respectively connected to a three-terminal circulator and a mixer; the three-terminal circulator is connected to a mixer, the mixer is connected to an oscilloscope, the oscilloscope is connected to a computer, and the computer is connected to the signal generator.

10. A cable fault detection system based on frequency modulation continuous wave frequency difference as claimed in claim 9, characterized in that: The power divider divides the detection signal into an incident signal and a reference signal through channel one and channel two, and respectively connects the three-terminal circulator inlet and mixer inlet channel one; the three-terminal circulator middle port is connected to the cable head end, outputs the incident signal to the detected cable and obtains a reflected signal; the mixer inlet channel two is connected to the three-terminal circulator outlet, and is used to multiply and mix the reference signal and the reflected signal to obtain a frequency difference and a frequency sum signal; The oscilloscope is connected to the mixer outlet to collect data of the mixed signal; the collected data of the oscilloscope is transmitted to the computer to process and analyze the mixed signal, implement low-pass filtering to extract the frequency difference signal, then obtain the frequency difference signal spectrum diagram and phase spectrum diagram, and finally obtain the fault information of the detected cable.

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