DC system grounding insulation fault detection method and system

Abstract

The invention relates to a DC system grounding insulation fault detection method and system. The method comprises the steps of determining whether an insulation fault exists in a DC system; when the DC system has the insulation fault, inputting a low-frequency current signal to the DC system and the ground; collecting an alternating current signal of a preset collection point on each branch in the direct current system; respectively carrying out signal separation processing on each alternating current signal so as to separate out a specific frequency signal in each alternating current signal; and according to the parameter of each specific frequency signal, determining a fault branch. According to the invention, the branch where the DC system insulation fault is located can be efficiently and accurately positioned, and the problem that partial feeder lines of the DC system are low in ground insulation and cannot be positioned is solved.

Description

Technical Field

[0001] The invention relates to the technical field of direct current insulation monitoring in nuclear power plants, and in particular to a method and system for detecting grounding insulation faults in direct current systems. Background Art

[0002] DC systems are widely used in nuclear power plants. They are widely distributed, have complex operating conditions, and are greatly affected by environmental factors. Therefore, when the insulation of the DC system is reduced, it will have an adverse effect on the lines and equipment. At the same time, equipment aging and accidental contact by personnel may also cause the insulation of the DC system to be damaged and the terminals to be short-circuited, thereby causing the insulation of the system to decrease, and then cause grounding faults. Although existing methods can detect whether there is an insulation fault in the DC system, the grounding fault in the DC system is irregular and changes quickly. At the same time, some branches may have redundant backup lines, etc., which makes it difficult to quickly locate the redundant backup lines or branches that have faults. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a method and system for detecting grounding insulation faults in a DC system.

[0004] The technical solution adopted by the present invention to solve the technical problem is: constructing a DC system grounding insulation fault detection method, comprising:

[0005] Determine if there is an insulation fault in the DC system;

[0006] When an insulation fault occurs in the DC system, a low-frequency current signal is input to the DC system and the ground;

[0007] Collecting AC signals of preset collection points on each branch of the DC system; wherein each branch is configured as follows: when the branch is of the first branch structure, the main line of the branch and the branches connected to each redundant backup line of the branch are all set as preset collection points of the branch; when the branch is of the second branch structure, the main line of the branch is set as the preset collection point of the branch, and a current sensor is set at each preset collection point; the first branch structure is that there is at least one redundant backup line on the branch, and the second branch structure is that there is no redundant backup line on the branch;

[0008] Performing signal separation processing on each of the AC signals to separate a specific frequency signal from each of the AC signals; wherein the specific frequency signal is a current component whose frequency has an error within a set range with respect to the frequency of the low-frequency current signal;

[0009] The branch where the fault occurs is determined according to the parameters of each of the specific frequency signals.

[0010] Preferably, the step of determining the branch where the fault occurs according to the parameters of each of the specific frequency signals comprises:

[0011] Parameter analysis and processing are performed on the parameters of each of the specific frequency signals, including: determining whether the amplitude of the specific frequency signal is greater than a first set current threshold value; when the amplitude of the specific frequency signal is greater than the first set current threshold value, determining that the branch corresponding to the current sensor that collects the AC signal is a branch with a ground fault.

[0012] Preferably, the parameter analysis process further includes:

[0013] When the amplitude of the specific frequency signal is not greater than the first set current threshold, determining whether the branch structure of the branch corresponding to the AC signal is the second branch structure;

[0014] When the branch structure of the branch corresponding to the AC signal is the second branch structure, determining whether the amplitude of the specific frequency signal is less than the second set current threshold, if the amplitude of the specific frequency signal is less than the second set current threshold, adding a plurality of new collection points on the branch, wherein each of the new collection points is configured to be provided with a current sensor;

[0015] respectively collecting the AC signals of the multiple newly added collection points, and recording each current signal collected from the newly added collection point as a sub-AC signal;

[0016] Superimposing the AC signal with each of the sub-AC signals to obtain a superimposed AC signal;

[0017] Performing signal separation processing on the superimposed AC signal to separate a specific frequency signal from the superimposed AC signal;

[0018] Determine whether the amplitude of the specific frequency signal of the superimposed AC signal is greater than a first set current threshold. When the amplitude of the specific frequency signal of the superimposed AC signal is greater than the first set current threshold, determine that the branch corresponding to the AC signal is a branch with a ground fault.

[0019] Preferably, the parameter analysis process further includes:

[0020] When the amplitude of the specific frequency signal is not greater than the first set current threshold, determining whether the branch structure of the branch corresponding to the AC signal is the first branch structure;

[0021] When the branch structure of the branch corresponding to the AC signal is the first branch structure, the specific frequency signal in each of the AC signals corresponding to the branch is set and analyzed to determine whether the branch corresponding to the AC signal has a grounding fault based on the analysis result; the set analysis and processing includes phase difference analysis and / or correlation analysis.

[0022] Preferably, the phase difference analysis includes:

[0023] respectively calculating the absolute value of the phase difference between each of the specific frequency signals and the low-frequency current signal;

[0024] For each of the phase difference absolute values, the following is performed: determining whether the phase difference absolute value is greater than a set phase difference threshold; when the phase difference absolute value is greater than the set phase difference threshold, determining that the redundant backup line or main line of the specific frequency signal corresponding to the phase difference absolute value is a branch with a capacitor degradation fault.

[0025] Preferably, the correlation analysis includes:

[0026] Performing overlap analysis on each of the specific frequency signals and the low-frequency current signal respectively to obtain an overlap coefficient that can represent the similarity between the specific frequency signal and the low-frequency current signal;

[0027] For each of the overlap coefficients, the following is performed: determining whether the overlap coefficient is less than a set overlap coefficient threshold; when the overlap coefficient is less than the set overlap coefficient threshold, determining that the redundant backup line or main line of the specific frequency signal corresponding to the overlap coefficient is a branch with a capacitor degradation fault.

[0028] Preferably, the phase difference analysis further comprises:

[0029] When the absolute value of the phase difference is not greater than the set phase difference threshold, determining that the redundant backup line or the main line of the specific frequency signal corresponding to the absolute value of the phase difference is not a branch with a fault;

[0030] The correlation analysis also includes:

[0031] When the coincidence coefficient is not greater than the set coincidence coefficient threshold, it is determined that the redundant backup line or the main line of the specific frequency signal corresponding to the coincidence coefficient is not a branch with a fault.

[0032] Preferably, the low-frequency current signal is a sinusoidal wave signal; and / or the frequency range of the low-frequency current signal is 0.05 Hz to 2.5 Hz.

[0033] The present invention also constructs a DC system grounding insulation fault detection system, comprising:

[0034] A control terminal comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the method for detecting ground insulation fault in a DC system according to any one of claims 1 to 8 when executing the computer program; and

[0035] A plurality of current sensors are arranged one-to-one at each preset collection point.

[0036] Preferably, the DC system grounding insulation fault detection system further includes:

[0037] The handheld insulation meter is used to detect the AC signal of the faulty branch after the faulty branch is determined, and locate the fault point based on the flow direction of the AC signal of the faulty branch.

[0038] The implementation of the present invention has the following beneficial effects: a method for detecting grounding insulation faults in a DC system is provided. When an insulation fault occurs in the DC system, a low-frequency current signal is input to the DC system and the ground, and an AC signal of a preset collection point on each branch in the DC system is collected. Then, each AC signal is subjected to signal separation processing to separate a specific frequency signal from each AC signal. Finally, the branch where the fault occurs is determined according to the parameters of each specific frequency signal. The branch where the insulation fault of the DC system is located can be accurately located efficiently, and the problem that some feeders of the DC system have low insulation to the ground and cannot be located is solved. The power supply reliability of key sensitive equipment is improved, the hidden dangers of machine tripping and reactor tripping are reduced, and it is helpful to improve the nuclear safety and power generation reliability of nuclear power plant units. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0040] Figure 1 is a program flow chart of a method for detecting a grounding insulation fault in a DC system in some embodiments of the present invention;

[0041] Figure 2 is a branch circuit structure diagram of a DC system in some embodiments of the present invention;

[0042] Figure 3 is a waveform diagram of an AC signal and its corresponding specific frequency signal in some embodiments of the present invention;

[0043] Figure 4 It is a schematic diagram of the structure of a DC system grounding insulation fault detection system in some embodiments of the present invention. DETAILED DESCRIPTION

[0044] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0045] It should be noted that the flowcharts shown in the accompanying drawings are only exemplary and do not necessarily include all the contents and operations / steps, nor do they have to be executed in the order described. For example, some operations / steps can be decomposed, while some operations / steps can be combined or partially combined, so the actual execution order may change according to actual conditions.

[0046] The block diagrams shown in the accompanying drawings are merely functional entities and do not necessarily correspond to physically independent entities. That is, these functional entities may be implemented in software form, or in one or more hardware modules or integrated circuits, or in different networks and / or processor devices and / or microcontroller devices.

[0047] The present invention provides a method for detecting grounding insulation fault in a DC system, which can efficiently and accurately locate the position of a branch circuit with a fault in the DC system. Figure 1 As shown, the DC system grounding insulation fault detection method may include step S10, step S20, step S30, step S40 and step S50.

[0048] Step S10 includes: determining whether there is an insulation fault in the DC system. In this step, it is possible to determine whether there is an insulation fault in the DC system by existing methods, such as using a DC bridge method to measure the insulation resistance of the DC system to determine whether an insulation fault occurs. Of course, it is also possible to use existing DC power grid insulation detection equipment to determine whether there is an insulation fault in the DC system. As long as it is possible to determine whether there is an insulation fault in the DC system, there is no limitation on what equipment or method is used. It should be noted that although executing step S10 can determine whether there is an insulation fault in the DC system, it is impossible to quickly determine the precise location of the branch with the insulation fault.

[0049] Step S20 includes: when there is an insulation fault in the DC system, inputting a low-frequency current signal to the DC system and the ground. In this step, since the low-frequency current signal is an AC signal, and the DC system outputs a DC signal, the frequency difference of the two signals is obvious and will not interfere with each other. Therefore, while the DC system supplies power to the load, the low-frequency current signal can be input to the DC system and the ground without affecting the operation of the load, that is, the present invention can achieve online detection.

[0050] In some embodiments, the low-frequency current signal can be a sinusoidal wave signal. The sinusoidal wave signal has the advantages of being easy to generate and control, can be provided by an existing waveform generator or circuit, and has good anti-interference ability. It is particularly suitable for environments where the stray capacitance and stray inductance of distribution systems such as nuclear power plant DC systems are highly uncertain, which helps to improve detection accuracy.

[0051] Since the DC system is widely distributed, there is a large amount of stray capacitance between the cable and the ground. If the frequency of the low-frequency current signal is too high, it is easily affected by the stray capacitance and causes signal attenuation or distortion, affecting the detection accuracy. Therefore, in some embodiments, the frequency range of the low-frequency current signal is preferably 0.05Hz to 2.5Hz.

[0052] Step S30 includes: collecting AC signals from preset collection points on each branch in the DC system; wherein each branch is configured as follows: when the branch is of the first branch structure, the main line of the branch and the branches connected to the redundant backup lines of the branch are all defined as preset collection points of the branch; when the branch is of the second branch structure, the main line of the branch is defined as the preset collection point of the branch, and a current sensor is respectively set at each preset collection point; the first branch structure is that there is at least one redundant backup line on the branch, and the second branch structure is that there is no redundant backup line on the branch.

[0053] See also Figure 2 The branches corresponding to load 1 in Figure A and Figure B, and load 2 in Figure B and Figure C are all the second branch structure. It can be understood that the common point of the second branch structure is that the load and the DC system can only form a power supply circuit through the main line (that is, two power supply lines), that is, there is only a single power supply circuit between the load and the corresponding DC system.

[0054] See also Figure 2 , the branch 10 in Figure A is not only connected to the load 2, but also connected to the load N in Figure A through the cable 11, so the branch 10 is the first branch structure, and the cable 11 corresponds to the redundant backup line of the branch 10, so the AC signal of the preset collection point on the branch 10 includes the current sensor CT2 on the branch 10 (that is, the current sensor CT2 in Figure A) and the current sensor CT on the main line of the load N in Figure A N (i.e. the current sensor CT in Figure A N ) measured value. The branch 20 in Figure B is not only connected to the load N, but also connected to the DC system in Figure B through the redundant backup line 21 and the redundant backup line 22, so the branch 20 is also the first branch structure, so the AC signal of the preset collection point on the branch 20 includes the current sensor CT in Figure B N and current sensor CT N-1 The branch 30 in Figure C is not only connected to the load N, but also connected to the branch 40 through the redundant backup line 31 and the redundant backup line 32, so the branch 30 is also the first branch structure, so the AC signal of the preset collection point on the branch 30 includes the current sensor CT in Figure C N And the measured value of the current sensor CT1. In addition, the current sensor can be an existing current transformer, and of course other forms of current measuring devices can be used instead, as long as they can collect AC signals.

[0055] Step S40 includes: performing signal separation processing on each AC signal to separate a specific frequency signal from each AC signal; wherein the specific frequency signal is a current component whose frequency has an error within a set range with respect to the frequency of the low-frequency current signal.

[0056] It should be noted that the detection principle of the present invention is to input a low-frequency current signal between the DC system and the ground as a test signal. When an insulation fault occurs in a branch, the component signal of the test signal on the faulty branch will be significantly different from the change in impedance to the ground if compared with the branch without the fault. The present invention determines whether the corresponding branch is faulty by analyzing the parameter changes of the component signals on each branch that are similar or even equal to the low-frequency current signal. However, since the DC system may be affected by the external environment and load, the power supply network may be coupled with interference noise of various frequencies, and these interference noises will be collected by the current sensor. That is, the AC signal collected by the current sensor is actually a composite signal doped with various noises and interferences. Please refer to Figure 3 , Figure D is the waveform of the AC signal collected at a preset collection point after a low-frequency current signal with a frequency of 0.1 Hz is input into the DC system in some embodiments; and Figure E corresponds to the waveform of the specific frequency signal obtained after the AC signal in Figure D is subjected to signal separation processing (fast Fourier transform). It can be seen that the implementation of this step can specifically extract the specific frequency signal with a frequency similar to or even equal to that of the AC signal, so as to subsequently perform targeted analysis on the parameters of the specific frequency signal, thereby improving the detection accuracy.

[0057] In some embodiments, the signal separation process can be realized by existing algorithms such as fast Fourier transform, wavelet transform, empirical mode decomposition and wavelet packet decomposition. Since the present invention is mainly used in the DC system of a nuclear power plant, and the DC system is usually monitored in real time for a long time (i.e., steps S10 to S50 are executed cyclically) so that when a fault in the DC system is found, it can be discovered in time to avoid the impact of load power failure on the operation of the nuclear power plant, the signal separation process preferably uses an algorithm that is easy to implement, efficient, stable and mature, so this embodiment preferably uses fast Fourier transform to realize signal separation process.

[0058] In some embodiments, the setting range is from -10% to 10%.

[0059] Step S50 includes: determining the branch where the fault occurs according to the parameters of each specific frequency signal. In this step, the parameters of the specific frequency signal include but are not limited to the amplitude, phase and other parameters of the specific frequency signal.

[0060] In some embodiments, the faulty branch may be determined by executing the following steps: performing parameter analysis on the parameters of each specific frequency signal, the parameter analysis including:

[0061] Determine whether the amplitude of the specific frequency signal is greater than a first set current threshold. When the amplitude of the specific frequency signal is greater than the first set current threshold, determine that the branch corresponding to the current sensor that collects the AC signal is a branch with a ground fault.

[0062] It can be understood that the branches of the DC system are connected in parallel with each other. When an insulation fault occurs in a branch, the impedance of the branch to the ground suddenly drops, which will cause the current of the AC signal shunted to the branch to increase. That is, the amplitude of the specific frequency signal on the branch will be significantly greater than the amplitude of the specific frequency signal on the normal branch. Therefore, when the amplitude of a specific frequency signal is greater than the first set current threshold, it can be determined that the branch corresponding to the current sensor that collects the AC signal is the branch where a ground fault occurs. It should be noted that due to the differences in specific circuit structures, number of branches, etc. of different DC systems, the current amplitude of the low-frequency current signal input between the DC system and the ground varies according to local conditions. Usually, the number of branches in the DC system is positively correlated with the current amplitude of the low-frequency current signal, and the actual current amplitude of the specific frequency signal on each branch is affected by both the current amplitude of the low-frequency current signal and the impedance to the ground when the DC system is normal. Therefore, the amplitude of the low-frequency current signal and the first set current threshold are usually customized by the staff based on the on-site situation. Considering that there may be multiple branch insulation faults in the same DC system, the first set current threshold is configured to be no less than 1 / 5 of the current amplitude of the low-frequency current signal. Optionally, the current amplitude range of the low-frequency current signal is 0.5A to 2A.

[0063] In some embodiments, the parameter analysis processing may also include the following steps: when the amplitude of the specific frequency signal is not greater than the first set current threshold, determining whether the branch structure of the branch corresponding to the AC signal is the second branch structure; when the branch structure of the branch corresponding to the AC signal is the second branch structure, determining whether the amplitude of the specific frequency signal is less than the second set current threshold, if the amplitude of the specific frequency signal is less than the second set current threshold, adding multiple new collection points on the branch, wherein each new collection point is configured to be provided with a current sensor; respectively collecting AC signals of the multiple new collection points, and recording each current signal collected from the new collection point as a sub-AC signal; superimposing the AC signal with each sub-AC signal to obtain a superimposed AC signal; performing signal separation processing on the superimposed AC signal to separate the specific frequency signal in the superimposed AC signal; judging whether the amplitude of the specific frequency signal of the superimposed AC signal is greater than the first set current threshold, when the amplitude of the specific frequency signal of the superimposed AC signal is greater than the first set current threshold, determining that the branch corresponding to the AC signal is a branch with a grounding fault.

[0064] In this embodiment, the second set current threshold is less than one Kth of the current amplitude of the low-frequency current signal, where K represents the total number of branches of the detected DC system. When the amplitude of the specific frequency signal corresponding to the AC signal collected by the current sensor on a branch of the second branch structure is less than the second set current threshold, the detected value of the amplitude of the specific frequency signal is already less than the theoretical value, which is an abnormal situation, which may be caused by the failure of the current sensor or the short circuit of the branch. In order to avoid missed judgment, this embodiment adds multiple new collection points and current sensors on the branch, and sets a new collection point on each new collection point to collect the current signal of each new collection point, so as to obtain multiple sub-AC signals corresponding to multiple new collection points. Then, the existing algorithm is used to perform waveform superposition of the AC signal of the branch with multiple sub-AC signals (such as superimposing the AC signal with these sub-AC signals in a two-dimensional coordinate system), so that the superimposed AC signal can be obtained. Then, the superimposed AC signal is subjected to signal separation processing to separate the specific frequency signal in the superimposed AC signal; when the amplitude of the specific frequency signal of the superimposed AC signal is greater than the first set current threshold, it can be inferred that the AC signal threshold is too small due to equipment failure, so the branch corresponding to the AC signal is determined to be the branch with a grounding fault. On the contrary, when the amplitude of the specific frequency signal of the superimposed AC signal is not greater than the first set current threshold, it is determined that the branch corresponding to the AC signal is not the branch with a fault. Further, when the amplitude of the specific frequency signal is not greater than the first set current threshold, not less than the second set current threshold, and the branch structure of the branch corresponding to the AC signal is the second branch structure, it can also be determined that the branch corresponding to the AC signal is not the branch with a fault. It can be understood that this embodiment can improve the detection accuracy of weak AC signals, which helps to improve the detection accuracy of the present invention.

[0065] In some embodiments, parameter analysis and processing may also include the following steps: when the amplitude of the specific frequency signal is not greater than a first set current threshold, determining whether the branch structure of the branch corresponding to the AC signal is a first branch structure; when the branch structure of the branch corresponding to the AC signal is a first branch structure, performing setting analysis and processing on the specific frequency signal in each AC signal corresponding to the branch to determine whether the branch corresponding to the AC signal has a grounding fault based on the analysis results; wherein the setting analysis and processing includes phase difference analysis and / or correlation analysis.

[0066] For branches with the first branch structure, there may be more than two lines in the main line and several redundant backup lines that have insulation faults at the same time, resulting in the amplitudes of specific frequency signals of the AC signals collected by the current sensors on the two faulty lines being no greater than the first set current threshold. To avoid missed judgment, when the amplitude of the specific frequency signal corresponding to the AC signal collected by the current sensor on a branch with the first branch structure is no greater than the first set current threshold, the specific frequency signal will be set for analysis and processing. The set analysis and processing is performed by determining whether the other parameters of the specific frequency signal except the amplitude are normal through phase difference analysis and / or correlation analysis, so as to determine whether the branch is a branch with a grounding fault.

[0067] In some embodiments, the phase difference analysis may include: respectively calculating the absolute value of the phase difference between each specific frequency signal and the low-frequency current signal; for each phase difference absolute value: determining whether the phase difference absolute value is greater than a set phase difference threshold; when the phase difference absolute value is greater than the set phase difference threshold, determining that the redundant backup line or main line of the specific frequency signal corresponding to the phase difference absolute value is a branch with a ground fault; when the phase difference absolute value is not greater than the set phase difference threshold, determining that the redundant backup line or main line of the specific frequency signal corresponding to the phase difference absolute value is not a faulty branch.

[0068] In this embodiment, the phase differences between the specific frequency signals in each AC signal corresponding to the branch and the low-frequency current signal are first calculated to obtain multiple phase differences. After determining the absolute value of the phase difference of the specific frequency signal at each preset acquisition point on the branch, it can be judged one by one whether the absolute value of each phase difference is greater than the set phase difference threshold. When a certain phase difference absolute value is greater than the set phase difference threshold, it is determined that the redundant backup line or main line of the specific frequency signal corresponding to the absolute value of the phase difference is a branch with a capacitor degradation fault. When a certain phase difference absolute value is not greater than the set phase difference threshold, it can be determined that the redundant backup line or main line of the specific frequency signal corresponding to the absolute value of the phase difference is not a branch with a fault. It should be noted that for a branch with the first branch structure, when the amplitude of the specific frequency signal of the AC signal at each preset collection point on the branch is not greater than the first set current threshold, it can be preliminarily determined that there is no serious ground insulation fault in the branch, but when the absolute value of the phase difference of a specific frequency signal is greater than the set phase difference threshold, due to the degradation of the capacitor on the DC system, the phase of the AC signal will be distorted, so it can be inferred that the redundant backup line or the grounding capacitor on the main line corresponding to the specific frequency signal is degraded, thereby causing the DC system's impedance to the ground to decrease, so the staff should replace it in time. It can be understood that this embodiment can accurately determine the line location where the capacitor degradation fault occurs by analyzing the phase of the specific frequency signal at each preset collection point on the branch, which helps the staff to eliminate the impact of capacitor degradation on the DC system and improve the safety and reliability of the DC system.

[0069] Optionally, the phase difference threshold is set to 0.1.

[0070] In some embodiments, the correlation analysis may include: performing overlap analysis on each specific frequency signal and the low-frequency current signal respectively to obtain an overlap coefficient that can represent the degree of similarity between the specific frequency signal and the low-frequency current signal; for each overlap coefficient: determining whether the overlap coefficient is less than a set overlap coefficient threshold; when the overlap coefficient is less than the set overlap coefficient threshold, determining that the redundant backup line or main line of the specific frequency signal corresponding to the overlap coefficient is a branch with a capacitor degradation fault; when the overlap coefficient is not greater than the set overlap coefficient threshold, determining that the redundant backup line or main line of the specific frequency signal corresponding to the overlap coefficient is not a branch with a fault.

[0071] In this embodiment, the overlap between each specific frequency signal and the low-frequency current signal can be analyzed by an existing overlap analysis algorithm to obtain the overlap coefficient. When the overlap coefficient corresponding to a specific frequency signal is less than a set overlap coefficient threshold, the redundant backup line or main line of the specific frequency signal corresponding to the overlap coefficient can be determined as a branch where a capacitor degradation fault occurs. It can be understood that this embodiment can also accurately determine the line location where a capacitor degradation fault occurs by analyzing the waveform of the specific frequency signal at each preset acquisition point on the branch.

[0072] Optionally, the overlap coefficient threshold is set to 85%.

[0073] In some embodiments, the DC system grounding insulation fault detection method may also include: after determining the faulty branch (including the branch with the grounding fault and the branch with the capacitor degradation fault), outputting an alarm prompt signal to prompt the staff to handle the fault as soon as possible.

[0074] In some embodiments, if the faulty branch is not determined in step S50, the following steps are performed: resetting the parameters of the low-frequency current signal, and returning to step S20 after resetting the parameters; wherein the parameters of the low-frequency current signal include the frequency and / or current amplitude of the low-frequency current signal. It can be understood that by adjusting the frequency of the low-frequency current signal, it is possible to avoid some DC systems being unable to detect the faulty branch normally due to the large impedance of the AC current signal of a specific frequency, and adjusting the frequency of the low-frequency current signal can avoid this influence; correspondingly, by adjusting the current amplitude of the low-frequency current signal, it is possible to avoid the situation that some DC systems have a large coverage range and a large number of branches, resulting in small component signals obtained by shunting each branch, which leads to a small amplitude of the specific frequency signal and reduces the detection accuracy. Therefore, this embodiment helps to improve the detection accuracy of the present invention.

[0075] It can be understood that the present invention can efficiently and accurately locate the branch where the insulation fault of the DC system is located, solves the problem that some feeders of the DC system have low insulation to the ground and cannot be located, improves the power supply reliability of key sensitive equipment, reduces the risk of machine and reactor tripping, and helps to improve the nuclear safety and power generation reliability of nuclear power plant units.

[0076] like Figure 4 As shown, the present invention also provides a DC system grounding insulation fault detection system, including a control terminal and a plurality of current sensors.

[0077] The control terminal includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of the DC system grounding insulation fault detection method provided in the embodiment of the present invention are implemented.

[0078] The current sensor is arranged one by one at each preset collection point and is connected to the processor.

[0079] In some embodiments, Figure 4 As shown, the DC system grounding insulation fault detection system also includes a handheld insulation meter. The handheld insulation meter is used to detect the AC signal of the faulty branch after determining the faulty branch, and locate the fault point based on the flow direction of the AC signal of the faulty branch.

[0080] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0081] Professionals may further appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in the above description according to function. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians may use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0082] The steps of the method or algorithm described in conjunction with the embodiments disclosed herein may be implemented directly using hardware, a software module executed by a processor, or a combination of the two. The software module may be placed in a random access memory (RAM), a memory, a read-only memory (ROM), an electrically programmable ROM, an electrically erasable programmable ROM, a register, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.

[0083] It can be understood that the above embodiments only express the preferred implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the patent scope of the present invention. It should be pointed out that, for ordinary technicians in this field, the above technical features can be freely combined without departing from the concept of the present invention, and several deformations and improvements can be made, which all belong to the protection scope of the present invention. Therefore, all equivalent changes and modifications made to the scope of the claims of the present invention should belong to the coverage of the claims of the present invention.

Claims

1. A method for detecting grounding insulation fault in a DC system, characterized in that: include: Determine if there is an insulation fault in the DC system; When an insulation fault occurs in the DC system, a low-frequency current signal is input to the DC system and the ground; Collecting AC signals of preset collection points on each branch of the DC system; wherein each branch is configured as follows: when the branch is of the first branch structure, the main line of the branch and the branches connected to each redundant backup line of the branch are all set as preset collection points of the branch; when the branch is of the second branch structure, the main line of the branch is set as the preset collection point of the branch, and a current sensor is set at each preset collection point; the first branch structure is that there is at least one redundant backup line on the branch, and the second branch structure is that there is no redundant backup line on the branch; Performing signal separation processing on each of the AC signals to separate a specific frequency signal from each of the AC signals; wherein the specific frequency signal is a current component whose frequency has an error within a set range with respect to the frequency of the low-frequency current signal; The branch where the fault occurs is determined according to the parameters of each of the specific frequency signals.

2. The method for detecting grounding insulation fault in a DC system according to claim 1, characterized in that: The step of determining the branch where the fault occurs according to the parameters of each of the specific frequency signals comprises: Parameter analysis and processing are performed on the parameters of each of the specific frequency signals, including: determining whether the amplitude of the specific frequency signal is greater than a first set current threshold value; when the amplitude of the specific frequency signal is greater than the first set current threshold value, determining that the branch corresponding to the current sensor that collects the AC signal is a branch with a ground fault.

3. The method for detecting grounding insulation fault in a DC system according to claim 2, characterized in that: The parameter analysis process also includes: When the amplitude of the specific frequency signal is not greater than the first set current threshold, determining whether the branch structure of the branch corresponding to the AC signal is the second branch structure; When the branch structure of the branch corresponding to the AC signal is the second branch structure, determining whether the amplitude of the specific frequency signal is less than the second set current threshold, if the amplitude of the specific frequency signal is less than the second set current threshold, adding a plurality of new collection points on the branch, wherein each of the new collection points is configured to be provided with a current sensor; respectively collecting the AC signals of the multiple newly added collection points, and recording each current signal collected from the newly added collection point as a sub-AC signal; Superimposing the AC signal with each of the sub-AC signals to obtain a superimposed AC signal; Performing signal separation processing on the superimposed AC signal to separate a specific frequency signal from the superimposed AC signal; Determine whether the amplitude of the specific frequency signal of the superimposed AC signal is greater than a first set current threshold. When the amplitude of the specific frequency signal of the superimposed AC signal is greater than the first set current threshold, determine that the branch corresponding to the AC signal is a branch with a ground fault.

4. The method for detecting grounding insulation fault in a DC system according to claim 3, characterized in that: The parameter analysis process also includes: When the amplitude of the specific frequency signal is not greater than the first set current threshold, determining whether the branch structure of the branch corresponding to the AC signal is the first branch structure; When the branch structure of the branch corresponding to the AC signal is the first branch structure, the specific frequency signal in each of the AC signals corresponding to the branch is set and analyzed to determine whether the branch corresponding to the AC signal has a grounding fault based on the analysis result; the set analysis and processing includes phase difference analysis and / or correlation analysis.

5. The method for detecting grounding insulation fault in a DC system according to claim 4, characterized in that: The phase difference analysis comprises: respectively calculating the absolute value of the phase difference between each of the specific frequency signals and the low-frequency current signal; For each of the phase difference absolute values, the following is performed: determining whether the phase difference absolute value is greater than a set phase difference threshold; when the phase difference absolute value is greater than the set phase difference threshold, determining that the redundant backup line or main line of the specific frequency signal corresponding to the phase difference absolute value is a branch with a capacitor degradation fault.

6. The method for detecting grounding insulation fault in a DC system according to claim 5, characterized in that: The correlation analysis includes: Performing overlap analysis on each of the specific frequency signals and the low-frequency current signal respectively to obtain an overlap coefficient that can represent the similarity between the specific frequency signal and the low-frequency current signal; For each of the overlap coefficients, the following is performed: determining whether the overlap coefficient is less than a set overlap coefficient threshold; when the overlap coefficient is less than the set overlap coefficient threshold, determining that the redundant backup line or main line of the specific frequency signal corresponding to the overlap coefficient is a branch with a capacitor degradation fault.

7. The method for detecting grounding insulation fault in a DC system according to claim 6, characterized in that: The phase difference analysis also includes: When the absolute value of the phase difference is not greater than the set phase difference threshold, determining that the redundant backup line or the main line of the specific frequency signal corresponding to the absolute value of the phase difference is not a branch with a fault; The correlation analysis also includes: When the coincidence coefficient is not greater than the set coincidence coefficient threshold, it is determined that the redundant backup line or the main line of the specific frequency signal corresponding to the coincidence coefficient is not a branch with a fault.

8. The method for detecting grounding insulation fault in a DC system according to any one of claims 1 to 7, characterized in that: The low-frequency current signal is a sinusoidal wave signal; and / or the frequency range of the low-frequency current signal is 0.05 Hz to 2.5 Hz.

9. A DC system grounding insulation fault detection system, characterized in that: include: A control terminal comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the method for detecting ground insulation fault in a DC system according to any one of claims 1 to 8 when executing the computer program; and A plurality of current sensors are arranged one-to-one at each preset collection point.

10. The DC system grounding insulation fault detection system according to claim 9, characterized in that: Also includes: The handheld insulation meter is used to detect the AC signal of the faulty branch after the faulty branch is determined, and locate the fault point based on the flow direction of the AC signal of the faulty branch.

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