CN107576852A - Method and system for measuring characteristic impedance of cable accessory - Google Patents

Abstract

The invention relates to a method and system for measuring the characteristic impedance of a cable accessory. The method includes the steps of: inputting an excitation signal to the terminal to be tested of the cable accessory; collecting a time-domain voltage signal and a time-domain current signal of the cable accessory at the terminal to be tested; wherein, the cable accessory is in open circuit and short circuit Respond to the excitation signal in the state; perform Fourier transform on the time-domain voltage signal and time-domain current signal to obtain a frequency-domain voltage signal and a frequency-domain current signal; according to the frequency-domain voltage signal and frequency-domain current signal, calculate the open circuit impedance and short circuit impedance; calculate the characteristic impedance of the cable accessory according to the open circuit impedance and short circuit impedance. Through this technical scheme, the variable resistance and the frequency characteristics of the characteristic impedance of the cable accessory to be tested are fully considered, and the characteristic impedance measurement of the cable accessory at different frequencies is realized, and the measurement result of the characteristic impedance of the cable accessory is improved.

Description

Method and system for measuring characteristic impedance of cable accessories

technical field

The invention relates to the technical field of power cables, in particular to a method and system for measuring the characteristic impedance of cable accessories.

Background technique

Cable accessories are an important part of the cable line, mainly including cable intermediate joints and cable terminals. The cable joint is used to realize the connection of the cable length and the cross interconnection of the three-phase line, and the cable terminal is used to realize the connection between the cable and other equipment.

In recent years, many high-voltage cable joints have failed when they are closed and transmitted, which has aroused widespread concern. The operating overvoltage usually occurs during the closing process, and the operating overvoltage generally contains rich frequency components. Since the impedance of the cable joint changes with the frequency of the input signal, when the operating overvoltage propagates in the cable line, there may be an obvious mismatch between the joint and the cable impedance at the joint, resulting in multiple occurrences of the operating overvoltage at the joint Wave reflection, resulting in high overvoltage, eventually lead to cable joint breakdown. Therefore, it is necessary to measure the characteristic impedance of cable accessories (including cables) at different frequencies.

In terms of measuring the characteristic impedance of cable accessories, the traditional technology usually uses the electronic voltmeter method to measure the characteristic impedance of cable accessories. This measurement method needs to connect a variable resistor when measuring the characteristic impedance. By adjusting the variable resistor, the voltage values at both ends of the variable resistor and the cable accessory to be tested are equal, so as to obtain the characteristic impedance of the cable accessory to be tested. However, due to the difference in frequency characteristics between the variable resistor and the characteristic impedance of the cable accessory to be tested, it is not accurate to obtain the characteristic impedance of the cable accessory.

Contents of the invention

Based on this, it is necessary to provide a measurement method and system capable of accurately measuring the characteristic impedance of cable accessories to solve the problem of inaccurate measurement methods of the characteristic impedance of the traditional cable accessories.

A method for measuring the characteristic impedance of a cable accessory, comprising the steps of:

Input the excitation signal to the tested end of the cable accessory;

Collecting the time-domain voltage signal and time-domain current signal of the cable accessory at the terminal to be tested; wherein, the cable accessory responds to the excitation signal in an open circuit and a short circuit state;

performing Fourier transform on the time-domain voltage signal and the time-domain current signal to obtain a frequency-domain voltage signal and a frequency-domain current signal;

calculating an open circuit impedance and a short circuit impedance according to the frequency domain voltage signal and the frequency domain current signal;

Calculate the characteristic impedance of the cable accessory according to the open circuit impedance and the short circuit impedance.

A measuring system for characteristic impedance of a cable accessory, comprising:

The signal input module is used to input an excitation signal to the end of the cable accessory to be tested;

A signal acquisition module, configured to acquire a time-domain voltage signal and a time-domain current signal of the cable accessory at the terminal to be tested; wherein, the cable accessory responds to the excitation signal in an open circuit and a short circuit state;

A signal conversion module, configured to perform Fourier transform on the time-domain voltage signal and the time-domain current signal to obtain a frequency-domain voltage signal and a frequency-domain current signal;

A first calculation module, configured to calculate open circuit impedance and short circuit impedance according to the frequency domain voltage signal and frequency domain current signal;

The second calculation module is used to calculate the characteristic impedance of the cable accessory according to the open circuit impedance and the short circuit impedance.

The method and system for measuring the characteristic impedance of the above-mentioned cable accessory, by inputting an excitation signal to the terminal to be tested of the cable accessory, when the cable accessory is in the open circuit and short circuit state, the time domain voltage signal and the response to the excitation signal are obtained at the terminal to be tested. The current signal in the time domain is converted into a voltage signal in the frequency domain and a current signal in the frequency domain, and then the open circuit impedance and short circuit impedance are calculated, and then the characteristic impedance of the cable accessory is calculated using the characteristic impedance of the cable accessory. Through this technical scheme, the variable resistance and the frequency characteristic of the characteristic impedance of the cable accessory to be tested are fully considered, and the characteristic impedance measurement of the cable accessory at different frequencies is realized, and the measurement result of the characteristic impedance of the cable accessory is improved.

Description of drawings

Fig. 1 is the measurement method flowchart of the characteristic impedance of cable accessory of the present invention;

Fig. 2 is a schematic diagram of the measurement circuit of the short-circuit impedance and the open-circuit impedance of the cable accessories;

The flowchart of the application example of the measuring method of the characteristic impedance of Fig. 3 cable accessories;

Fig. 4 is a schematic structural diagram of a measuring system for the characteristic impedance of the cable accessory of the present invention.

Detailed ways

The specific implementation of the method and system for measuring the characteristic impedance of the cable accessory of the present invention will be described in detail below with reference to the accompanying drawings.

With reference to shown in Fig. 1, Fig. 1 is the measurement method flowchart of the characteristic impedance of the cable accessory of the present invention, comprises the following steps:

Step S100, inputting an excitation signal to the end of the cable accessory to be tested.

In this step, the cable accessories are an important part of the cable line. The cable accessories can include cable intermediate connectors and cable terminals. Used to realize the connection between the cable and the device.

As an implementation manner, an excitation signal may be generated by a signal generator, and the excitation signal is loaded to the end of the cable accessory to be tested. A signal generator is a device that can provide electrical signals of various frequencies, waveforms, and output levels. It can be used as an excitation signal source when measuring the characteristics of components.

Specifically, the wire core and the shielding layer of the terminal to be tested of the cable accessory can be led out by a wire, and the signal generator can load the generated excitation signal between the wire core and the shielding layer through the wire. It should be noted that the cable accessory can have two ports, and one of the ports of the cable accessory can be used as the terminal to be tested to measure the characteristic impedance, and then the characteristic impedance of the other port of the cable accessory can be measured. Measurement. The signal generator can provide various required excitation signals according to the measurement requirements of the characteristic impedance of the cable accessories, so that the measurement is more convenient and flexible.

Optionally, the excitation signal generated by the signal generator may be a square wave signal. In this embodiment, the signal generator can generate a square wave signal containing multiple frequency components by adjusting the frequency and rising edge time. Therefore, using the square wave signal as the excitation signal, the characteristic impedance of the cable accessory at multiple frequencies can be obtained through one measurement, making the measurement of the characteristic impedance of the cable accessory more accurate and convenient.

Step S200, collecting the time-domain voltage signal and time-domain current signal of the cable accessory at the terminal to be tested; wherein, the cable accessory responds to the excitation signal in an open circuit and a short circuit state.

In this step, refer to Figure 2, which is a schematic diagram of the measurement circuit of the short-circuit impedance and open-circuit impedance of the cable accessory, wherein, between the core and the shielding layer of the other end opposite to the end of the cable accessory to be tested It can be connected by a wire, and when the wire is disconnected, the cable accessory is in an open circuit state, the cable accessory can respond to the excitation signal in the open circuit state, and the time domain voltage of the cable accessory can be collected at the terminal to be tested signal and time-domain current signal; when the wire is connected, the cable accessory is in a short-circuit state, the cable accessory can respond to the excitation signal in the short-circuit state, and the time domain of the cable accessory can be collected at the terminal to be tested Voltage signal and time domain current signal.

As a specific implementation of the above steps, the time-domain voltage signal of the cable accessory can be collected at the terminal to be tested through the differential voltage input channel of the data acquisition card; acquiring the time-domain current signal of the cable accessory; and acquiring the time-domain current signal acquired by the clamp-type current transformer through the current input channel of the data acquisition card.

Specifically, the data acquisition card may include a differential voltage input channel and a current input channel, and the data acquisition card may collect the signal to be measured at the terminal to be measured by selecting an appropriate number of sampling points and a sampling period, and the signal to be measured may include a time-domain voltage signal and time-domain current signals. The differential voltage input channel of the data acquisition card can collect the time-domain voltage signal by obtaining the differential voltage between the wire core and the shielding layer of the terminal to be tested; The time-domain current signal at the measuring terminal, and the time-domain current signal acquired by the clamp-type current transformer through the current input channel of the signal acquisition card.

Through the above method, the signal acquisition card can quickly and accurately acquire the time-domain voltage signal and time-domain current signal of the cable accessory's response to the excitation signal.

Step S300, performing Fourier transform on the time-domain voltage signal and time-domain current signal to obtain a frequency-domain voltage signal and a frequency-domain current signal.

In this step, the time-domain voltage signal and the time-domain current signal may be transformed using a Fast Fourier Transform (FFT) algorithm to obtain a frequency-domain voltage signal and a frequency-domain current signal. The FFT algorithm can be used to efficiently convert the time-domain voltage signal and the time-domain current signal, and the frequency-domain voltage signal and the frequency-domain current signal can be quickly obtained, thereby improving calculation efficiency.

Step S400, calculating open circuit impedance and short circuit impedance according to the frequency domain voltage signal and frequency domain current signal.

As a specific implementation of this step, the open circuit impedance and short circuit impedance can be calculated according to the frequency domain voltage signal and frequency domain current signal using the following formula:

In the formula, f is the frequency, Z _∞ [f] is the open circuit impedance, U _∞ [f] is the open circuit voltage of the frequency domain voltage signal, I _∞ [f] is the open circuit current of the frequency domain current signal, Z ₀ [f] is the short-circuit impedance, U ₀ [f] is the short-circuit voltage of the frequency-domain voltage signal, and I ₀ [f] is the short-circuit current of the frequency-domain current signal.

Specifically, the frequency domain voltage signal includes an open circuit voltage and a short circuit voltage, the frequency domain current signal includes an open circuit current and a short circuit current, the open circuit impedance can be calculated using the ratio of the open circuit voltage to the open circuit current, and the open circuit impedance can be the The open-circuit impedance of the cable accessories at different frequencies can be calculated by using the ratio of the short-circuit voltage to the open-circuit current, and then the open-circuit impedance of the cable accessories at different frequencies can be obtained.

Through the above embodiment, the open circuit impedance and short circuit impedance of the cable accessory at different frequencies can be obtained simultaneously, so that the measurement of the characteristic impedance of the cable accessory is more accurate.

Step S500, calculating the characteristic impedance of the cable accessory according to the open circuit impedance and the short circuit impedance.

As a specific implementation of this step, the characteristic impedance of the cable accessory can be calculated according to the open circuit impedance and short circuit impedance using the following formula:

In the formula, f is the frequency, Z _c [f] is the characteristic impedance of the cable accessory, Z _∞ [f] is the open circuit impedance, and Z ₀ [f] is the short circuit impedance.

Specifically, the open-circuit impedance may be the open-circuit impedance of the cable accessory at different frequencies, and the short-circuit impedance may be the short-circuit impedance of the cable accessory at different frequencies. According to the open-circuit impedance and the short-circuit impedance, the The above formula calculates the characteristic impedance of this cable accessory at different frequencies.

Combining the technical solutions of the above-mentioned embodiments, according to the measurement requirements of the characteristic impedance of the cable accessory, different types of excitation signal sources can be input to the test end of the cable accessory, and the open circuit and short circuit conditions of the cable accessory can be measured at the test end. , the time-domain voltage signal and time-domain current signal in response to the excitation signal, using Fourier transform to convert the time-domain voltage signal and time-domain current signal into a frequency-domain voltage signal and a frequency-domain current signal, by calculating the open circuit impedance and Short-circuit impedance, the characteristic impedance of the cable accessory at different frequencies can be obtained. The measurement method of this scheme is efficient and flexible, and the characteristic impedance of the cable accessory to be tested at different frequencies can be obtained through one measurement, which makes the measurement of the characteristic impedance of the cable accessory more accurate and convenient, and provides a method that can accurately measure the characteristic impedance of the cable accessory The measurement method provides an important reference for the protection of power cable lines.

In order to clarify the technical solution of the present invention, the application examples of the measurement method are set forth below.

Referring to FIG. 3 , it is a flow chart of an application example of the method for measuring the characteristic impedance of the cable accessory in FIG. 3 .

Step (1): If the middle joint of the cable is cut out separately, the core and shielding layer at both ends of the middle joint can be drawn out. If the middle joint of the cable is connected to a long cable, two measuring points need to be selected at both ends of the cable joint. Use an electric drill to drill holes at two measurement points until the drill bit touches the cable core, and put wires in the two holes so that the wires can effectively contact the high-voltage cable core, and fix the lead wires with adhesive.

In addition, peel off the outer sheath at the coaxial position of the two measuring points to expose the metal shielding layer, weld the two wires to the metal shielding layer at the two measuring points respectively, and wrap the exposed metal shielding layer with insulating tape. Mark the two ends of the middle connector of the high-voltage cable as end A and end B respectively.

Step (2): Short-circuit the wire core at the B end of the high-voltage cable intermediate joint and the shielding layer with a wire, and use a signal generator to add a square wave with a frequency of f ₀ between the wire core at the A end of the cable intermediate joint and the shielding layer wire , In order to make the voltage applied to the middle joint of the cable have more frequency components, try to use a signal generator with a short rising edge time to generate a square wave.

Step (3): Add the core and shielding layer of the A-end of the cable intermediate joint to a differential voltage input channel of the data acquisition card, so as to collect the voltage signal u ₀ [n] of the A-end of the cable accessory.

Add a clamp-type current transformer to the output wire of the signal generator, and add the output terminal of the clamp-type current transformer to the current input channel of the data acquisition card, so as to collect the current signal i ₀ [n ].

For the convenience of calculation, the sampling period of the data acquisition card can be set as T ₀ =1/f ₀ , the number of sampling points can be set as N ₀ =2 ^m , m is a suitable positive integer, and n satisfies 0≤n<N ₀ .

Step (4): short-circuit the B-side of the cable connector collected in step (3), and input the voltage signal u ₀ [n] and current signal i ₀ [n] between the A-side core and the shielding layer into the mathematical software MATLAB in matrix form, Use the FFT algorithm to convert the time-domain discrete signals u ₀ [n], i ₀ [n] into frequency-domain discrete signals U ₀ [kf ₀ ], I ₀ [kf ₀ ], where f ₀ is the square wave of the signal generator Frequency is also the fundamental frequency after discrete Fourier transform, and k satisfies 0≤k<N ₀ , where N ₀ is the number of sampling points.

Step (5): Calculate the short-circuit impedance of the A-end at different frequencies when the high-voltage cable intermediate joint is short-circuited at the B-end Wherein, f ₀ is the square wave frequency of the signal generator, k satisfies 0≤k<N ₀ , and N ₀ is the number of sampling points.

Step (6): Disconnect the wire core at the B end of the high-voltage cable intermediate joint from the wire of the shielding layer and keep it open, and use a signal generator to add a frequency f ₀ between the wire core at the A end of the cable intermediate joint and the wire of the shielding layer. Square wave, ensure that the frequency is consistent with the square wave input in step (2).

Step (7): Add the core and shielding layer of the A-end of the cable intermediate connector to a differential voltage input channel of the data acquisition card, so as to collect the voltage signal u _∞ [n] of the A-end of the cable accessory.

Add a clamp-type current transformer to the output wire of the signal generator, and add the output terminal of the clamp-type current transformer to the current input channel of the data acquisition card, so as to collect the current signal i _∞ [n ]. For the convenience of calculation, the sampling period of the data acquisition card can be set as T ₀ =1/f ₀ , the number of sampling points can be set as N ₀ =2 ^m , m is a suitable positive integer, and n satisfies 0≤n<N ₀ .

Step (8): Input the voltage signal u _∞ [n] and current signal i _∞ [n] between the cable connector B end collected in step 6 into the mathematical software MATLAB in matrix form, and use FFT Algorithm, convert time-domain discrete signals u _∞ [n], i _∞ [n] into frequency-domain discrete signals U _∞ [kf ₀ ], I _∞ [kf ₀ ], where f ₀ is the square wave frequency of the signal generator, It is also the fundamental frequency after discrete Fourier transform, and k satisfies 0≤k<N ₀ , where N ₀ is the number of sampling points.

Step (9): Calculate the open-circuit impedance of the A-end at different frequencies when the middle joint of the high-voltage cable is open-circuited at the B-end Wherein, f ₀ is the square wave frequency of the signal generator, k satisfies 0≤k<N ₀ , and N ₀ is the number of sampling points.

Step (10): Calculate the characteristic impedance of the A-end at different frequencies of the high-voltage cable intermediate joint: Wherein, f ₀ is the square wave frequency of the signal generator, k satisfies 0≤k<N ₀ , and N ₀ is the number of sampling points.

Step (11): For the high-voltage cable intermediate joint, the symmetry is relatively large, and the characteristic impedance of the A terminal is approximately equal to that of the B terminal. For other cable accessories such as cable terminals, just exchange the A terminal with the B terminal and repeat the steps (2)-(10), the characteristic impedance of the B-end of the cable accessory can be obtained.

Compared with the prior art, the present invention can select a suitable signal generator, adjust a suitable frequency and rising edge time, and make the voltage applied to one side of the high-voltage cable accessory contain multiple frequency components, and similarly, the current also contains multiple frequency components. Frequency component, the characteristic impedance of high-voltage cable accessories at multiple frequencies can be obtained in one measurement, which is simple, feasible, and easy to operate. With the help of mathematical tools such as MATLAB, it can conveniently and accurately realize the measurement and calculation of the characteristic impedance of high-voltage cable accessories at different frequencies .

Referring to Fig. 4, Fig. 4 is a schematic structural diagram of a measurement system for the characteristic impedance of the cable accessory of the present invention, including:

A signal input module 100, configured to input an excitation signal to the end-to-be-tested cable accessory;

The signal acquisition module 200 is used for the signal acquisition module, and is used to collect the time-domain voltage signal and the time-domain current signal of the cable accessory at the terminal to be tested; wherein, the cable accessory is connected to the Respond to the stimulus signal;

A signal conversion module 300, configured to perform Fourier transform on the time-domain voltage signal and time-domain current signal to obtain a frequency-domain voltage signal and a frequency-domain current signal;

The first calculation module 400 is used to calculate open circuit impedance and short circuit impedance according to the frequency domain voltage signal and frequency domain current signal;

The second calculation module 500 is configured to calculate the characteristic impedance of the cable accessory according to the open circuit impedance and the short circuit impedance.

In one of the implementation manners, the signal input module may include:

The signal generation unit is used to generate the excitation signal through a signal generator, and load the excitation signal to the terminal to be tested of the cable accessory; wherein, the signal generator adjusts the frequency and rising edge time of the excitation signal .

In another embodiment, the signal acquisition module may include:

A voltage acquisition unit, configured to collect the time-domain voltage signal of the cable accessory at the terminal to be tested through the differential voltage input channel of the data acquisition card;

The current acquisition unit is used to obtain the time-domain current signal of the cable accessory at the terminal to be tested through the clamp-type current transformer; collect the current signal obtained by the clamp-type current transformer through the current input channel of the data acquisition card The time-domain current signal.

In one of the embodiments, the first calculation module may include:

The first calculation unit is configured to calculate the open circuit impedance and the short circuit impedance according to the frequency domain voltage signal and the frequency domain current signal using the following formula:

In the formula, f is the frequency, Z _∞ [f] is the open circuit impedance, U _∞ [f] is the open circuit voltage of the frequency domain voltage signal, I _∞ [f] is the open circuit current of the frequency domain current signal, Z ₀ [f] is the short-circuit impedance, U ₀ [f] is the short-circuit voltage of the frequency-domain voltage signal, and I ₀ [f] is the short-circuit current of the frequency-domain current signal.

In another embodiment, the second calculation module may include:

The second calculation unit is used to calculate the characteristic impedance of the cable accessory according to the open circuit impedance and short circuit impedance by using the following formula:

In the formula, f is the frequency, Z _c [f] is the characteristic impedance of the cable accessory, Z _∞ [f] is the open circuit impedance, and Z ₀ [f] is the short circuit impedance.

The measuring system of the characteristic impedance of the cable accessory of the present invention corresponds to the measuring method of the characteristic impedance of the cable accessory of the present invention one by one, and the technical characteristics and beneficial effects thereof described in the embodiment of the measuring method of the characteristic impedance of the cable accessory are applicable In the embodiment of the measurement system of the characteristic impedance of the cable accessories, it is hereby declared.

Based on the above examples, in one embodiment there is also provided a computer device, the computer device includes a memory, a processor, and a computer program stored in the memory and operable on the processor, wherein the processor executes the The program implements any one of the sleep assistance methods in the above-mentioned embodiments.

Those of ordinary skill in the art can understand that all or part of the processes in the methods of the above embodiments can be implemented through computer programs to instruct related hardware, and the programs can be stored in a non-volatile computer-readable storage In the medium, as in the embodiment of the present invention, the program can be stored in the storage medium of the computer system, and executed by at least one processor in the computer system, so as to realize the measurement method including the characteristic impedance of each cable accessory as described above Example flow. Wherein, the storage medium may be a magnetic disk, an optical disk, a read-only memory (Read-Only Memory, ROM) or a random access memory (Random Access Memory, RAM) and the like.

Accordingly, in one embodiment, there is also provided a storage medium, on which a computer program is stored, wherein, when the program is executed by a processor, a method for measuring the characteristic impedance of a cable accessory as in any one of the above-mentioned embodiments is implemented. .

The various technical features of the above-mentioned embodiments can be combined arbitrarily. To make the description concise, all possible combinations of the various technical features in the above-mentioned embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, should be considered as within the scope of this specification.

The above-mentioned embodiments only express several implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but should not be construed as limiting the patent scope of the invention. It should be pointed out that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent for the present invention should be based on the appended claims.

Claims (10)

1. a method for measuring the characteristic impedance of cable accessories, is characterized in that, comprises the steps: Input the excitation signal to the tested end of the cable accessory; Collecting the time-domain voltage signal and time-domain current signal of the cable accessory at the terminal to be tested; wherein, the cable accessory responds to the excitation signal in an open circuit and a short circuit state; performing Fourier transform on the time-domain voltage signal and the time-domain current signal to obtain a frequency-domain voltage signal and a frequency-domain current signal; calculating an open circuit impedance and a short circuit impedance according to the frequency domain voltage signal and the frequency domain current signal; Calculate the characteristic impedance of the cable accessory according to the open circuit impedance and the short circuit impedance. 2. The method for measuring the characteristic impedance of the cable accessory according to claim 1, wherein the step of inputting the excitation signal to the terminal to be tested of the cable accessory comprises: The excitation signal is generated by a signal generator, and the excitation signal is loaded to the terminal to be tested of the cable accessory; wherein, the signal generator adjusts the frequency and rising edge time of the excitation signal. 3. The method for measuring the characteristic impedance of the cable accessory according to claim 1, wherein the step of collecting the time-domain voltage signal of the cable accessory at the terminal to be tested comprises: The time-domain voltage signal of the cable accessory is collected at the terminal to be tested through the differential voltage input channel of the data acquisition card. 4. the measuring method of the characteristic impedance of cable accessory according to claim 1, is characterized in that, the step of collecting the time-domain current signal of described cable accessory at described terminal to be tested comprises: Obtain the time-domain current signal of the cable accessory at the terminal to be tested through the clamp-type current transformer; collect the time-domain current signal obtained by the clamp-type current transformer through the current input channel of the data acquisition card. 5. The method for measuring the characteristic impedance of the cable accessory according to claim 3 or 4, further comprising: The sampling period and the number of sampling points of the data acquisition card are set; The data acquisition card collects the time-domain voltage signal of the cable accessory according to the sampling period and the number of sampling points. 6. The measuring method of the characteristic impedance of cable accessory according to claim 1, is characterized in that, carry out Fourier transformation to described time-domain voltage signal and time-domain current signal, obtain frequency-domain voltage signal and frequency-domain current signal The steps include: The time-domain voltage signal and the time-domain current signal are converted into the frequency-domain voltage signal and the frequency-domain current signal by using an FFT algorithm. 7. The method for measuring the characteristic impedance of the cable accessory according to claim 1, wherein, according to the frequency-domain voltage signal and the frequency-domain current signal, the steps of calculating the open-circuit impedance and the short-circuit impedance include: Use the following formulas to calculate the open circuit and short circuit impedances: <mrow><msub><mi>Z</mi><mi>&amp;infin;</mi></msub><mo>&amp;lsqb;</mo><mi>f</mi><mo>&amp;rsqb;</mo><mo>=</mo><mfrac><mrow><msub><mi>U</mi><mi>&amp;infin;</mi></msub><mo>&amp;lsqb;</mo><mi>f</mi><mo>&amp;rsqb;</mo></mrow><mrow><msub><mi>I</mi><mi>&amp;infin;</mi></msub><mo>&amp;lsqb;</mo><mi>f</mi><mo>&amp;rsqb;</mo></mrow></mfrac></mrow> <mrow><msub><mi>Z</mi><mn>0</mn></msub><mo>&amp;lsqb;</mo><mi>f</mi><mo>&amp;rsqb;</mo><mo>=</mo><mfrac><mrow><msub><mi>U</mi><mn>0</mn></msub><mo>&amp;lsqb;</mo><mi>f</mi><mo>&amp;rsqb;</mo></mrow><mrow><msub><mi>I</mi><mn>0</mn></msub><mo>&amp;lsqb;</mo><mi>f</mi><mo>&amp;rsqb;</mo></mrow></mfrac></mrow> In the formula, f is the frequency, Z _∞ [f] is the open circuit impedance, U _∞ [f] is the open circuit voltage of the frequency domain voltage signal, I _∞ [f] is the open circuit current of the frequency domain current signal, Z ₀ [f] is the short-circuit impedance, U ₀ [f] is the short-circuit voltage of the frequency-domain voltage signal, and I ₀ [f] is the short-circuit current of the frequency-domain current signal. 8. The method for measuring the characteristic impedance of the cable accessory according to claim 1, wherein, according to the open circuit impedance and short circuit impedance, the step of calculating the characteristic impedance of the cable accessory comprises: Calculate the characteristic impedance of the cable accessories described using the following formula: <mrow><msub><mi>Z</mi><mi>c</mi></msub><mo>&amp;lsqb;</mo><mi>f</mi><mo>&amp;rsqb;</mo><mo>=</mo><msqrt><mrow><msub><mi>Z</mi><mn>0</mn></msub><mo>&amp;lsqb;</mo><mi>f</mi><mo>&amp;rsqb;</mo><msub><mi>Z</mi><mi>&amp;infin;</mi></msub><mo>&amp;lsqb;</mo><mi>f</mi><mo>&amp;rsqb;</mo></mrow></msqrt></mrow> In the formula, f is the frequency, Z _c [f] is the characteristic impedance of the cable accessory, Z _∞ [f] is the open circuit impedance, and Z ₀ [f] is the short circuit impedance. 9. The method for measuring the characteristic impedance of a cable accessory according to claim 1 or 2, wherein the excitation signal is a square wave signal. 10. A measuring system for the characteristic impedance of a cable accessory, characterized in that it comprises: The signal input module is used to input an excitation signal to the end of the cable accessory to be tested; A signal acquisition module, configured to acquire a time-domain voltage signal and a time-domain current signal of the cable accessory at the terminal to be tested; wherein, the cable accessory responds to the excitation signal in an open circuit and a short circuit state; A signal conversion module, configured to perform Fourier transform on the time-domain voltage signal and the time-domain current signal to obtain a frequency-domain voltage signal and a frequency-domain current signal; A first calculation module, configured to calculate open circuit impedance and short circuit impedance according to the frequency domain voltage signal and frequency domain current signal; The second calculation module is used to calculate the characteristic impedance of the cable accessory according to the open circuit impedance and the short circuit impedance.