Method and device for acquiring resonant frequency of alternating-current excitation type oscillation wave of high-voltage cable

Abstract

The invention belongs to the technical field of high-voltage cable insulation state detection, and discloses a high-voltage cable alternating current excitation type oscillation wave resonant frequency obtaining method and device. The acquisition method comprises the following steps: forming a series resonance circuit by an exciting transformer, a resonance reactor and a tested high-voltage cable line; a variable-frequency power supply and a state change-over switch unit are matched to generate a square-wave voltage, and the square-wave voltage acts on the series resonance circuit, so that the tested high-voltage cable line generates a square-wave response; and acquiring voltage data of square wave response generated by the tested high-voltage cable line, and calculating by utilizing the voltage data in the free resonance stage and combining a nonlinear least square method to obtain the resonant frequency of the alternating-current excitation type oscillation wave of the high-voltage cable. According to the technical scheme, the resonant frequency of the alternating-current excitation type oscillation wave of the high-voltage cable can be conveniently, rapidly, efficiently and accurately obtained, and the method has important engineering practical value.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-voltage cable insulation state detection, and in particular relates to a method and a device for acquiring the resonance frequency of an AC excitation type oscillation wave of a high-voltage cable. Background Art

[0002] The high-voltage cable series resonance AC withstand voltage test is the mainstream on-site handover or preventive test at home and abroad. It is the most widely used test method for high-voltage cable insulation status detection, and provides an effective insulation status assessment method for the safe and reliable operation of high-voltage cables. However, the existing traditional series resonance withstand voltage test is an inspection test, which has no diagnostic capability and cannot detect latent insulation defects in high-voltage cables and accessories; therefore, even if the series resonance withstand voltage test is passed, high-voltage cables and accessories may still fail during commissioning or in the initial stage of operation.

[0003] Compared with the above-mentioned high-voltage cable series resonant AC withstand voltage test, the high-voltage cable AC excitation oscillation wave test can include both inspection test and diagnostic test in one test process, and keep the frequency of AC withstand voltage test and the frequency of AC excitation oscillation wave the same, which provides a new test technology and method for on-site insulation status detection of high-voltage cables. Further explanation, the high-voltage cable AC excitation oscillation wave test has neither the switching noise interference of frequency modulation series resonant voltage detection of partial discharge, nor the need to use high-voltage semiconductor switches in the DC excitation oscillation wave test system. In addition, it can also expand the distance of partial discharge detection interval through the double-end detection method, which can meet the requirements of on-site high-voltage cable partial discharge detection and positioning, and can not only reasonably judge the overall insulation strength of the high-voltage cable line, but also expose local insulation defects, especially those that can only be excited under high field strength, so as to discover insulation defects as early as possible and the types and scale of insulation defects.

[0004] The high-voltage cable AC excitation type oscillation wave test system mainly includes a DC energy storage power supply unit, a variable frequency power supply, a state conversion switch unit, an excitation transformer, a resonant reactor, a capacitor voltage divider, a partial discharge detection unit, a data acquisition unit, a control unit, a protection unit, a drive unit and a host computer; wherein, the DC energy storage power supply unit, the variable frequency power supply and the state conversion switch unit constitute a high-voltage cable AC excitation type oscillation wave generating device, which is a key test equipment for the generation of high-voltage cable AC excitation type oscillation waves. At present, in the high-voltage cable AC excitation type oscillation wave test in the existing technical scheme, the sweep frequency technology is mainly used to obtain the resonant frequency of the high-voltage cable line, which has the disadvantages of complex control strategy and low efficiency. Summary of the invention

[0005] The purpose of the present invention is to provide a method and device for obtaining the resonant frequency of an AC-excited oscillation wave of a high-voltage cable, so as to solve one or more of the above-mentioned technical problems. In the technical solution disclosed in the present invention, a square wave response technical means is used to obtain the resonant frequency of a high-voltage cable line, so as to achieve convenient, fast, efficient and accurate acquisition of the resonant frequency of an AC-excited oscillation wave of a high-voltage cable, which has important engineering practical value.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a method for obtaining the resonance frequency of an AC excitation type oscillation wave of a high voltage cable, comprising the following steps: The excitation transformer, the resonant reactor and the tested high-voltage cable line form a series resonant circuit; A square wave voltage is generated by cooperating with a variable frequency power supply and a state conversion switch unit, and the square wave voltage is applied to the series resonant circuit, so that the tested high-voltage cable line generates a square wave response; wherein the square wave response is divided into a forced resonance stage and a free resonance stage; The voltage data of the square wave response generated by the tested high-voltage cable line is obtained, and the voltage data in the free resonance stage is used in combination with the nonlinear least square method to calculate and obtain the resonance frequency of the AC excitation type oscillation wave of the high-voltage cable.

[0007] A further improvement of the acquisition method of the present invention is that in the step of generating a square wave voltage by cooperating between a variable frequency power supply and a state conversion switch unit, The pulse width of the square wave voltage is greater than or equal to 25 ms.

[0008] A further improvement of the acquisition method of the present invention is that in the step of generating a square wave voltage by cooperating between a variable frequency power supply and a state conversion switch unit, Before the variable frequency power supply outputs the square wave voltage, the state conversion switch unit performs a short circuit connection between the variable frequency power supply output and the primary side input of the excitation transformer; When the variable frequency power supply outputs a square wave voltage, the state conversion switch unit performs a short circuit connection between the variable frequency power supply output and the primary side input of the excitation transformer; After the variable frequency power supply outputs the square wave voltage, the state conversion switch unit first opens the variable frequency power supply output and the primary side input of the excitation transformer, and then short-circuits the primary side input of the excitation transformer.

[0009] In a second aspect of the present invention, a device for acquiring the resonance frequency of an AC-excited oscillation wave of a high-voltage cable is provided, which is used to implement the acquisition method described in the first aspect of the present invention, and comprises: an industrial frequency power supply, a DC energy storage power supply unit, a variable frequency power supply, a state conversion switch unit, an excitation transformer, a resonant inductor and a data processing unit; wherein, The industrial frequency power supply, the DC energy storage power supply unit, the variable frequency power supply, the state conversion switch unit and the excitation transformer are connected in series in sequence; wherein the excitation transformer is used to form a series resonant circuit with the resonant reactor and the tested high-voltage cable line; the variable frequency power supply and the state conversion switch unit are used to cooperate to generate a square wave voltage, and apply the square wave voltage to the series resonant circuit, so that the tested high-voltage cable line generates a square wave response; The data processing unit is used to obtain the voltage data of the square wave response generated by the tested high-voltage cable line, and calculate the voltage data in the free resonance stage in combination with the nonlinear least squares method to obtain the resonance frequency of the high-voltage cable AC excitation type oscillation wave.

[0010] A further improvement of the acquisition device of the present invention is that it further comprises: a control unit and a driving unit; The output of the control unit is connected to the driving unit, and the output of the driving unit is connected to a variable frequency power supply and a state conversion switch unit; The driving unit is used to generate a switch device driving signal and control the switching state of the variable frequency power supply and the switching state of the state conversion switch unit according to the instruction of the control unit.

[0011] A further improvement of the acquisition device of the present invention is that it further comprises: a protection unit; The output of the protection unit is connected to the input of the control unit; Among them, the protection unit is used to detect the voltage and current of the switching device of the variable frequency power supply to realize overvoltage and overcurrent protection of the switching device of the variable frequency power supply; the protection unit is used to detect the voltage and current of the switching device of the state conversion switch unit to realize overvoltage and overcurrent protection of the switching device of the state conversion switch unit.

[0012] A further improvement of the acquisition device of the present invention is that it further comprises: a capacitive voltage divider; The capacitive voltage divider is used to measure the oscillation wave voltage of the tested high-voltage cable line in the forced resonance stage and the free resonance stage.

[0013] A further improvement of the acquisition device of the present invention is that the industrial frequency power supply is used to output a 50Hz AC voltage with an effective value greater than or equal to 200V and a capacity greater than or equal to 10kVA.

[0014] A further improvement of the acquisition device of the present invention is that the DC energy storage power supply unit is used to output a DC voltage, the DC voltage amplitude is greater than or equal to 300V, and the stored energy is greater than or equal to 625J.

[0015] A further improvement of the acquisition device of the present invention is that in the step of the variable frequency power supply and the state conversion switch unit cooperating to generate the square wave voltage, Before the variable frequency power supply outputs the square wave voltage, the state conversion switch unit performs a short circuit connection between the variable frequency power supply output and the primary side input of the excitation transformer; When the variable frequency power supply outputs a square wave voltage, the state conversion switch unit performs a short circuit connection between the variable frequency power supply output and the primary side input of the excitation transformer; After the variable frequency power supply outputs the square wave voltage, the state conversion switch unit first opens the variable frequency power supply output and the primary side input of the excitation transformer, and then short-circuits the primary side input of the excitation transformer.

[0016] Compared with the prior art, the present invention has the following beneficial effects: In view of the problems in the prior art of using the complex sweeping frequency technology of the high-voltage cable frequency modulation series resonant circuit to obtain the resonant frequency of the high-voltage cable line, the present invention specifically provides a new method for obtaining the resonant frequency of the high-voltage cable AC excitation type oscillation wave, which uses a simple square wave response to obtain the resonant frequency of the high-voltage cable line, thereby achieving convenient, fast, efficient and accurate acquisition of the resonant frequency of the high-voltage cable AC excitation type oscillation wave, and has important engineering practical value. Further explanatory, the technical solution of the present invention utilizes the uniqueness of the topological structure of the high-voltage cable AC excitation type oscillation wave generating device, and proposes a method for obtaining the resonant frequency of the high-voltage cable AC excitation type oscillation wave. The unique topological structure of the high-voltage cable AC excitation type oscillation wave generating device can utilize its variable frequency power supply and state conversion switch unit to inject square waves into its subsequent resonant circuit, measure the square wave response of the tested cable, and then use the nonlinear least squares method to calculate the oscillation frequency of the square wave response of the tested cable. This resonant frequency is the resonant frequency of the high-voltage cable AC excitation type oscillation wave; at the same time, the control algorithm for controlling the variable frequency power supply and the state conversion switch unit to inject square waves is simple, and the square wave response duration of the tested cable is short, thereby realizing the convenient, fast, efficient and accurate acquisition of the resonant frequency of the high-voltage cable AC excitation type oscillation wave, which has important engineering practical value. Principle explanatory, using the waveform data of the oscillation wave in the free resonance stage, this waveform data is a decaying oscillation waveform, and using the nonlinear least squares method to fit the oscillation frequency of this decaying oscillation waveform, this oscillation frequency is the resonant frequency of the high-voltage cable AC excitation type oscillation wave. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below; obviously, the drawings described below are some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1It is a flow chart of a method for obtaining the resonance frequency of an AC excitation type oscillation wave of a high-voltage cable in an embodiment of the present invention; Figure 2 It is a schematic block diagram of a device for acquiring the resonance frequency of an AC excitation type oscillation wave of a high-voltage cable in an embodiment of the present invention; Figure 3 It is a waveform diagram of a high voltage cable AC excitation type oscillation wave test in a specific embodiment of the present invention; The reference numerals in the figures are explained as follows: 11. Industrial frequency power supply; 12. DC energy storage power supply unit; 13. Variable frequency power supply; 14. State conversion switch unit; 15. Excitation transformer; 16. Resonant inductor; 17. Capacitor voltage divider; 18. Partial discharge detection unit; 19. Data acquisition unit; 21. Control unit; 22. Protection unit; 23. Drive unit; 24. Host computer. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention; it is obvious that the described embodiments and technical solutions are only part of the embodiments of the present invention, not all of the embodiments.

[0020] All other embodiments obtained by those of ordinary skill in the art without creative work based on the technical solutions disclosed in the embodiments of the present invention belong to the scope of protection of the present invention. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device including a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0021] See also Figure 1 The embodiment of the present invention provides a method for obtaining the resonance frequency of an AC excitation type oscillation wave of a high voltage cable, comprising the following steps: Step 1, the excitation transformer 15, the resonant reactor 16 and the tested high-voltage cable line form a series resonant circuit; Step 2, generating a square wave voltage by cooperating with the variable frequency power supply 13 and the state conversion switch unit 14, and applying the square wave voltage to the series resonant circuit, so that the tested high-voltage cable line generates a square wave response; wherein the square wave response is divided into a forced resonance stage and a free resonance stage; Step 3, obtaining the voltage data of the square wave response generated by the tested high-voltage cable line, using the voltage data in the free resonance stage and combining the nonlinear least squares method to calculate, and obtaining the resonant frequency of the high-voltage cable AC excitation type oscillation wave.

[0022] Explanatoryly, in the process of using the complex sweeping technology of the high-voltage cable frequency modulation series resonant circuit to obtain the resonant frequency of the high-voltage cable line, the sweeping technology controls the inverter output frequency to increase linearly with time, and measures the test cable voltage at the same time. The inverter output frequency corresponding to the moment when the test cable voltage amplitude reaches the maximum value is the resonant frequency of the high-voltage cable line. From the principle of the sweeping technology, it can be seen that the control algorithm for realizing the linear increase of the inverter output frequency with time is relatively complex. On the other hand, in order to obtain high-resolution resonant frequency, the sweeping process is generally divided into two times. The first time is coarse adjustment with higher frequency resolution, and the second time is fine adjustment with lower frequency resolution. Therefore, the sweeping technology takes a long time to obtain the resonant frequency and has lower efficiency. The topological structure and test principle of the AC excitation oscillation wave generating device for high-voltage cables are quite different from those of the traditional high-voltage cable frequency modulation series resonant circuit. The AC excitation oscillation wave for high-voltage cables is divided into two stages. The first stage is the forced resonance stage, which is mainly used for high-voltage cable inspection tests. The second stage is the free resonance stage, which is mainly used for high-voltage cable diagnostic tests. The traditional high-voltage cable frequency modulation series resonance has only the forced resonance stage and can only be used for high-voltage cable inspection tests. On the other hand, in the free resonance stage of the AC excitation oscillation wave for high-voltage cables, the switching interference of the variable frequency power supply is isolated by using the state conversion switch unit, thereby improving its partial discharge detection sensitivity.

[0023] The technical solution of the present invention accurately injects a square wave signal of specific parameters into the subsequent resonant circuit by controlling the variable frequency power supply and the state conversion switch unit in the device. This process makes full use of the flexibility of the device topology structure, making the injection of the square wave signal both efficient and controllable. In specific implementation, the square wave signal is first output by the variable frequency power supply, and the state conversion switch unit is used to achieve fast and accurate switching of the signal, thereby injecting the square wave signal into the resonant circuit. This step is the key to ensure the accuracy of subsequent measurements. The present invention uses the mathematical tool of nonlinear least squares method. This method can effectively filter out noise interference by fitting and optimizing the response data, and accurately calculate the oscillation frequency of the square wave response of the tested cable. This frequency is the resonant frequency of the AC excitation type oscillation wave of the high-voltage cable sought by the present invention, which is of vital importance for evaluating the electrical performance of the cable and diagnosing potential faults. It should be emphasized that the method of the present invention has shown significant advantages in the implementation process. The control algorithm is concise and clear, easy to implement, and reduces the complexity of operation. At the same time, due to the short duration of the square wave response, the detection efficiency is greatly improved and the test cycle is shortened. These characteristics together make the technical solution of the present invention convenient, fast, efficient and accurate in obtaining the resonant frequency of the high-voltage cable, greatly improving the operability and practicality in engineering practice. In summary, the present invention not only provides a new idea and method for AC excitation oscillation wave detection of high-voltage cables, but also demonstrates important engineering application value through its unique technical path and significant practical effects, which not only helps to improve the accuracy and efficiency of cable detection, but also provides strong technical support for the safe and stable operation of the power system.

[0024] In a specific embodiment of the present invention, in step 3, the step of using the voltage data in the free resonance stage and combining the nonlinear least squares method to perform calculation specifically includes: Step 1), set the initial parameters of the fitted decay oscillation wave; Step 2), iteratively solve the error function; Step 3), when the variation of the error function is less than the set threshold or reaches the maximum number of iterations, the iteration stops and the oscillation frequency of the attenuated oscillation wave is obtained, that is, the resonance frequency of the high-voltage cable AC excitation oscillation wave.

[0025] See also Figure 2 The embodiment of the present invention provides a device for obtaining the resonance frequency of an AC excitation type oscillation wave of a high-voltage cable, comprising: an industrial frequency power supply 11, a DC energy storage power supply unit 12, a variable frequency power supply 13, a state conversion switch unit 14, an excitation transformer 15 and a resonant inductor 16; in a further optional technical solution, it may also include a capacitive voltage divider 17, a partial discharge detection unit 18, a data acquisition unit 19, a control unit 21, a protection unit 22, a drive unit 23 and a host computer 24, etc.; wherein, The output of the industrial frequency power supply 11 is connected to the input of the DC energy storage power supply unit 12; in a specific exemplary technical solution, the industrial frequency power supply 11 can output a 50Hz AC voltage, an effective value of not less than 200V, and a capacity of not less than 10kVA; The output of the DC energy storage power supply unit 12 is connected to the input of the variable frequency power supply 13; in a specific exemplary technical solution, the DC energy storage power supply unit 12 can output a DC voltage with an amplitude of not less than 300V and a storage energy of not less than 625J; The output of the variable frequency power supply 13 is connected to the input of the state conversion switch unit 14; in a specific exemplary technical solution, the variable frequency power supply 13 can output a square wave voltage with a pulse width of not less than 25ms; The output of the state conversion switch unit 14 is connected to the primary side input of the excitation transformer 15; wherein, before the variable frequency power supply 13 outputs a square wave voltage with a pulse width of not less than 25ms, the state conversion switch unit 14 performs a short circuit connection between the output of the variable frequency power supply 13 and the primary side input of the excitation transformer 15; during the process of the variable frequency power supply 13 outputting a square wave voltage with a pulse width of not less than 25ms, the state conversion switch unit 14 performs a short circuit connection between the output of the variable frequency power supply 13 and the primary side input of the excitation transformer 15; after the variable frequency power supply 13 outputs a square wave voltage with a pulse width of not less than 25ms, the state conversion switch unit 14 performs an open circuit between the output of the variable frequency power supply 13 and the primary side input of the excitation transformer 15, and short circuits the primary side input of the excitation transformer 15; explanatory, the above process is a process in which the state conversion switch unit 14 and the variable frequency power supply 13 cooperate to inject a square wave voltage into the subsequent series resonant circuit, and the function of the state conversion switch unit 14 is to allow the subsequent series resonant circuit to switch from the forced resonance stage of the inverter output to its free resonance stage; The output of the excitation transformer 15 is connected to the resonant reactor 16; wherein the resonant reactor 16 is used to form a series resonant circuit with the tested high-voltage cable line; The output of the capacitive voltage divider 17 is connected to the oscillation wave voltage acquisition channel of the data acquisition unit 19 to measure the oscillation wave voltage of the tested high-voltage cable line in the forced resonance stage and the free resonance stage; the output of the partial discharge detection unit 18 is connected to the partial discharge signal acquisition channel of the data acquisition unit 19 to measure the partial discharge signal of the tested high-voltage cable line in the forced resonance stage and the free resonance stage; The output of the data acquisition unit 19 is connected to the host computer 24 to realize the acquisition of the oscillation wave voltage signal and the partial discharge signal of the AC excitation type oscillation wave test of the high-voltage cable; The output of the control unit 21 is connected to the driving unit 23 to control the switching state of the variable frequency power supply 13 and the switching state of the state conversion switch unit 14; The output of the protection unit 22 is connected to the control unit 21, and the overvoltage and overcurrent protection of the switching device of the variable frequency power supply 13 is realized by detecting the voltage and current of the switching device of the variable frequency power supply 13, and the overvoltage and overcurrent protection of the switching device of the state conversion switch unit 14 is realized by detecting the voltage and current of the switching device of the state conversion switch unit 14; The output of the driving unit 23 is connected to the variable frequency power supply 13 and the state conversion switch unit 14 to realize the generation of the switching device driving signal of the variable frequency power supply 13 and the state conversion switch unit 14; The output of the host computer 24 is connected to the control unit 21, and is used to send an instruction to the control unit 21 to obtain the resonant frequency of the AC excitation type oscillation wave of the high-voltage cable, receive the oscillation wave voltage signal and partial discharge signal of the high-voltage cable AC excitation type oscillation wave test collected by the data acquisition unit 19, and display the waveform of the high-voltage cable AC excitation type oscillation wave in the forced resonance stage and the free resonance stage. The waveform data of the oscillation wave in the free resonance stage is used. This waveform data is an attenuated oscillation waveform. The oscillation frequency of this attenuated oscillation waveform is fitted using the nonlinear least squares method. This oscillation frequency is the resonant frequency of the high-voltage cable AC excitation type oscillation wave, and is displayed.

[0026] Explanatory, the technical solution of the embodiment of the present invention is that before applying the AC excitation type oscillation wave to the cable, the high-voltage cable AC excitation type oscillation wave generating device needs to know the resonant frequency of the subsequent series resonant circuit. The present invention uses the method of injecting square waves to accurately obtain the resonant frequency of the subsequent series resonant circuit without using the frequency sweeping method on the basis of the unchanged hardware topology of the AC excitation type oscillation wave test. However, the hardware topology of the high-voltage cable AC excitation type oscillation wave test also applies a high-voltage oscillation wave to the tested cable and measures the partial discharge signal. The partial discharge signal here is to keep the hardware topology and software configuration of the high-voltage cable AC excitation type oscillation wave test unchanged, and the partial discharge signal has no direct relationship with the acquisition of the resonant frequency.

[0027] In summary, the embodiment of the present invention provides a method for obtaining the resonant frequency of the AC excitation type oscillation wave of the high-voltage cable, which can conveniently, quickly, efficiently and accurately obtain the resonant frequency of the AC excitation type oscillation wave of the high-voltage cable. Explanatory, when performing an AC excitation type oscillation wave test, the high-voltage cable line undergoes a forced resonance stage and a free resonance stage. When the variable frequency power supply efficiently completes the forced resonance stage, an accurate resonant frequency of the high-voltage cable line is required. Therefore, before performing an AC excitation type oscillation wave test on the high-voltage cable line, it is necessary to accurately obtain the resonant frequency of the high-voltage cable line; however. Since the topological structure and test principle of the AC excitation type oscillation wave generating device are significantly different from those of the traditional high-voltage cable frequency modulation type series resonant circuit, there is no need to use the complex frequency sweeping technology of the traditional high-voltage cable frequency modulation type series resonant circuit to obtain the resonant frequency of the high-voltage cable line. The embodiment of the present invention uses a simple square wave response method to obtain the resonant frequency of the high-voltage cable line, which realizes the convenient, fast, efficient and accurate acquisition of the resonant frequency of the AC excitation type oscillation wave of the high-voltage cable, and has important engineering practical value. To further explain, the existing high-voltage cable AC excitation oscillation wave test system mainly includes a DC energy storage power supply unit, a variable frequency power supply, a state conversion switch unit, an excitation transformer, a resonant inductor, a capacitive voltage divider, a partial discharge detection unit, a data acquisition unit, a control unit, a protection unit, a drive unit and a host computer. In the new scheme proposed in the embodiment of the present invention, the existing equipment of the high-voltage cable AC excitation type oscillation wave test system is used to change the pulse width modulation control mode of the variable frequency power supply to generate a simple square wave voltage output (explanatory, corresponding to the aforementioned "the output of the variable frequency power supply is connected to the input of the state conversion switch unit, and the variable frequency power supply can output a square wave voltage with a pulse width of not less than 25ms", the prior art is frequency sweeping, and the control mode of the variable frequency power supply of the present invention is a fixed pulse width control mode. By allowing the variable frequency power supply to output a square wave, the control mode can be simplified), the state conversion switch unit cooperates to make the square wave voltage output by the variable frequency power supply act on the primary side input of the excitation transformer, so that the series resonant circuit composed of the excitation transformer, the resonant inductor and the tested high-voltage cable line is excited by the square wave voltage, and a square wave response will be generated on the tested high-voltage cable line. The voltage waveform data of the square wave response of the tested high-voltage cable line in the free resonance stage is used, combined with the nonlinear least squares method, to accurately obtain the resonant frequency of the high-voltage cable AC excitation type oscillation wave.

[0028] In a specific embodiment of the present invention, a specific method for obtaining the resonant frequency of the AC excitation type oscillation wave of the high voltage cable is as follows: First, the DC energy storage power supply unit 12 is charged by the industrial frequency power supply 11 so that it stores enough energy to complete the square wave response of the series resonant circuit composed of the excitation transformer 15, the resonant reactor 16 and the tested high-voltage cable line; Secondly, the host computer 24 sends an instruction to the control unit 21, and the control unit 21 sends a control signal to the drive unit 23 to make the variable frequency power supply 13 generate a square wave voltage with a pulse width of not less than 25ms; wherein, before, during and after the variable frequency power supply 13 generates the square wave voltage, the control unit 21 sends a control signal to the drive unit 23 to make the state conversion switch unit 14 complete the state conversion, and its specific control timing logic is: before the variable frequency power supply 13 outputs the square wave voltage, the state conversion switch unit 14 executes a short-circuit connection between the output of the variable frequency power supply 13 and the primary side input of the excitation transformer 15; during the process of the variable frequency power supply 13 outputting the square wave voltage, the state conversion switch unit 14 executes a short-circuit connection between the output of the variable frequency power supply 13 and the primary side input of the excitation transformer 15; after the variable frequency power supply 13 finishes outputting the square wave voltage, the state conversion switch unit 14 executes an open circuit between the output of the variable frequency power supply 13 and the primary side input of the excitation transformer 15, and short-circuits the primary side input of the excitation transformer 15; Finally, the square wave voltage generated by the variable frequency voltage acts on the series resonant circuit composed of the excitation transformer 15, the resonant inductor 16 and the tested high-voltage cable line, and a square wave response is generated on the tested high-voltage cable line. The upper computer 24 uses the capacitor voltage divider 17 and the data acquisition unit 19 to collect the square wave response voltage data on the tested high-voltage cable line. The square wave response on the tested high-voltage cable line is also divided into a forced resonance stage and a free resonance stage. The voltage data in the free resonance stage is used in combination with the nonlinear least squares method to accurately obtain the resonant frequency of the high-voltage cable AC excitation type oscillation wave.

[0029] In the technical solution of the embodiment of the present invention, the uniqueness of the topological structure of the high-voltage cable AC excitation type oscillation wave generating device is utilized to achieve convenient, fast, efficient and accurate acquisition of the resonant frequency of the high-voltage cable AC excitation type oscillation wave.

[0030] In a specific embodiment of the present invention, a method for obtaining the resonant frequency of an AC-excited oscillation wave of a high-voltage cable specifically includes the following four steps: Step S1, the DC energy storage power supply unit 12 stores energy, including: using the industrial frequency power supply 11 to charge the DC energy storage power supply unit 12 to 500V, the DC energy storage power supply unit 12 stores energy of not less than 625J, so that it stores enough energy to complete the square wave response of the series resonant circuit composed of the excitation transformer 15, the resonant reactor 16 and the tested high-voltage cable line; Step S2, the variable frequency power supply 13 and the state conversion switch unit 14 output a square wave voltage, including: the host computer 24 sends an instruction to the control unit 21, and the control unit 21 sends a control signal to the drive unit 23 to make the variable frequency power supply 13 generate a square wave voltage with a pulse width of not less than 25ms, and the square wave voltage amplitude is 500V; before, during and after the variable frequency power supply 13 generates the square wave voltage, the control unit 21 sends a control signal to the drive unit 23 to make the state conversion switch unit 14 complete the state conversion, and its specific control timing logic is: Before the variable frequency power supply 13 outputs the square wave voltage, the state conversion switch unit 14 executes a short circuit connection between the variable frequency power supply 13 output and the primary side input of the excitation transformer 15; during the process of the variable frequency power supply 13 outputting the square wave voltage, the state conversion switch unit 14 executes a short circuit connection between the variable frequency power supply 13 output and the primary side input of the excitation transformer 15; after the variable frequency power supply 13 finishes outputting the square wave voltage, the state conversion switch unit 14 executes an open circuit between the variable frequency power supply 13 output and the primary side input of the excitation transformer 15, and short circuits the primary side input of the excitation transformer 15; Step S3, obtaining the resonance frequency of the AC excitation type oscillation wave of the high-voltage cable, including: the square wave voltage generated by the variable frequency voltage acts on the series resonance circuit composed of the excitation transformer 15, the resonant reactor 16 and the tested high-voltage cable line, and a square wave response will be generated on the tested high-voltage cable line. The host computer 24 uses the capacitor voltage divider 17 and the data acquisition unit 19 to collect the square wave response voltage data on the tested high-voltage cable line. The square wave response on the tested high-voltage cable line is divided into a forced resonance stage and a free resonance stage, such as Figure 3 As shown, by using the voltage data in the free resonance stage and combining it with the nonlinear least squares method, the resonant frequency of the AC excitation oscillation wave of the high-voltage cable can be accurately obtained.

[0031] In summary, an embodiment of the present invention discloses a method for obtaining the resonant frequency of an AC-excited oscillation wave of a high-voltage cable. The method utilizes the uniqueness of the topological structure of an AC-excited oscillation wave generating device of a high-voltage cable to achieve convenient, fast, efficient and accurate acquisition of the resonant frequency of an AC-excited oscillation wave of a high-voltage cable, and has important engineering practical value.

[0032] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for obtaining the resonance frequency of an AC excitation oscillation wave of a high voltage cable, characterized in that: The following steps are involved: The excitation transformer (15), the resonant reactor (16) and the high-voltage cable line under test form a series resonant circuit; A square wave voltage is generated by cooperating with a variable frequency power supply (13) and a state conversion switch unit (14), and the square wave voltage is applied to the series resonant circuit, so that the tested high-voltage cable line generates a square wave response; wherein the square wave response is divided into a forced resonance stage and a free resonance stage; The voltage data of the square wave response generated by the tested high-voltage cable line is obtained, and the voltage data in the free resonance stage is used in combination with the nonlinear least square method to calculate and obtain the resonance frequency of the AC excitation type oscillation wave of the high-voltage cable.

2. A method for obtaining the resonance frequency of a high voltage cable AC excitation oscillation wave according to claim 1, characterized in that: In the step of generating a square wave voltage by cooperating with a variable frequency power supply (13) and a state conversion switch unit (14), The pulse width of the square wave voltage is greater than or equal to 25 ms.

3. The method for obtaining the resonance frequency of the AC excitation oscillation wave of a high-voltage cable according to claim 1, characterized in that: In the step of generating a square wave voltage by cooperating with a variable frequency power supply (13) and a state conversion switch unit (14), Before the variable frequency power supply (13) outputs a square wave voltage, the state conversion switch unit (14) performs a short circuit connection between the variable frequency power supply (13) output and the primary side input of the excitation transformer (15); When the variable frequency power supply (13) outputs a square wave voltage, the state conversion switch unit (14) performs a short circuit connection between the output of the variable frequency power supply (13) and the primary side input of the excitation transformer (15); After the variable frequency power supply (13) finishes outputting the square wave voltage, the state conversion switch unit (14) first opens the variable frequency power supply (13) output and the primary side input of the excitation transformer (15), and then short-circuits the primary side input of the excitation transformer (15).

4. A device for obtaining the resonance frequency of an AC excitation oscillation wave of a high voltage cable, characterized in that: Used to implement the acquisition method described in claim 1, comprising: an industrial frequency power supply (11), a DC energy storage power supply unit (12), a variable frequency power supply (13), a state conversion switch unit (14), an excitation transformer (15), a resonant reactor (16) and a data processing unit; wherein: The industrial frequency power supply (11), the DC energy storage power supply unit (12), the variable frequency power supply (13), the state conversion switch unit (14) and the excitation transformer (15) are connected in series in sequence; wherein the excitation transformer (15) is used to form a series resonant circuit with the resonant reactor (16) and the high-voltage cable line under test; the variable frequency power supply (13) and the state conversion switch unit (14) are used to cooperate to generate a square wave voltage, and to apply the square wave voltage to the series resonant circuit, so that the high-voltage cable line under test generates a square wave response; The data processing unit is used to obtain the voltage data of the square wave response generated by the tested high-voltage cable line, and calculate the voltage data in the free resonance stage in combination with the nonlinear least squares method to obtain the resonance frequency of the high-voltage cable AC excitation type oscillation wave.

5. The device for acquiring the resonance frequency of the AC excitation type oscillation wave of a high voltage cable according to claim 4, characterized in that: Also includes: A control unit (21) and a drive unit (23); The output of the control unit (21) is connected to the drive unit (23), and the output of the drive unit (23) is connected to a variable frequency power supply (13) and a state conversion switch unit (14); The drive unit (23) is used to generate a switch device drive signal and control the switch state of the variable frequency power supply (13) and the switch state of the state conversion switch unit (14) according to the instruction of the control unit (21).

6. The device for acquiring the resonance frequency of the AC excitation type oscillation wave of a high-voltage cable according to claim 4, characterized in that: Also includes: Protection unit (22); The output of the protection unit (22) is connected to the input of the control unit (21); The protection unit (22) is used to detect the voltage and current of the switching device of the variable frequency power supply (13) to achieve overvoltage and overcurrent protection for the switching device of the variable frequency power supply (13); the protection unit (22) is used to detect the voltage and current of the switching device of the state conversion switch unit (14) to achieve overvoltage and overcurrent protection for the switching device of the state conversion switch unit (14).

7. The device for acquiring the resonance frequency of the AC excitation type oscillation wave of a high voltage cable according to claim 4, characterized in that: Also includes: Capacitor voltage divider (17); The capacitive voltage divider (17) is used to measure the oscillation wave voltage of the tested high-voltage cable line in the forced resonance stage and the free resonance stage.

8. The device for acquiring the resonance frequency of the AC excitation oscillation wave of a high-voltage cable according to claim 4, characterized in that: The industrial frequency power supply (11) is used to output a 50 Hz AC voltage with an effective value greater than or equal to 200 V and a capacity greater than or equal to 10 kVA.

9. The device for acquiring the resonance frequency of the AC excitation type oscillation wave of a high voltage cable according to claim 4, characterized in that: The DC energy storage power supply unit (12) is used to output a DC voltage, the DC voltage amplitude is greater than or equal to 300V, and the stored energy is greater than or equal to 625J.

10. A device for acquiring the resonance frequency of an AC excitation type oscillation wave of a high voltage cable according to claim 4, characterized in that: In the step of the variable frequency power supply (13) and the state conversion switch unit (14) cooperating to generate a square wave voltage, Before the variable frequency power supply (13) outputs a square wave voltage, the state conversion switch unit (14) performs a short circuit connection between the variable frequency power supply (13) output and the primary side input of the excitation transformer (15); When the variable frequency power supply (13) outputs a square wave voltage, the state conversion switch unit (14) performs a short circuit connection between the output of the variable frequency power supply (13) and the primary side input of the excitation transformer (15); After the variable frequency power supply (13) finishes outputting the square wave voltage, the state conversion switch unit (14) first opens the variable frequency power supply (13) output and the primary side input of the excitation transformer (15), and then short-circuits the primary side input of the excitation transformer (15).

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