Substation dc system insulation state detection method based on magnetic coupling common mode injection

Abstract

The application discloses a kind of based on magnetic coupling common mode injection substation DC system insulation state detection method, comprising: S1.through the common mode of magnetic coupling non-contact to the specified place of substation DC system's DC bus injection wideband excitation signal;S2.real-time acquisition kth line feeder after step S1 injection wideband excitation signal feeder head time domain current signal;S3.to the feeder head time domain current signal of kth line feeder by frequency domain analysis, its corresponding resonance characteristic parameter is extracted;S4.based on the change of resonance characteristic parameter to construct comprehensive decision index D k ;S5.according to comprehensive decision index D k To each line feeder insulation state variation degree is judged;The application does not depend on existing system control interface, can independently implement detection, meets the substation DC system insulation on-line detection scene of strict power supply requirement;And without measuring system voltage signal and carrying out phase alignment processing, reliable evaluation to DC system insulation state is realized.

Description

Technical Field

[0001] This invention relates to the field of insulation condition monitoring of DC systems in substations, and specifically to a method for detecting the insulation condition of DC systems in substations based on magnetic coupling common-mode injection. Background Technology

[0002] As the core support platform for power supply to secondary equipment, the DC system of a substation directly affects the reliability of protection and control devices due to its insulation operating status. Currently, bridge testing or low-frequency response characteristics are commonly used in engineering to assess the system's insulation status. These methods rely on steady-state parameters for analysis. Under complex electromagnetic environments, steady-state parameters or low-frequency detection signals are easily affected by power frequency and harmonic interference, leading to a decrease in signal-to-noise ratio and limited detection sensitivity. To ensure measurement accuracy, existing technologies typically require the addition of filtering, signal conditioning, and synchronization processing modules, increasing system complexity. Furthermore, detection schemes relying on synchronous voltage and current measurements require high phase matching accuracy, and in actual operation, judgment deviations are easily generated due to asynchronous sampling or time delay errors. As system capacity and the number of circuits increase, parameter distribution characteristics become more complex, and the superposition effect of measurement errors and interference significantly amplifies, causing small-amplitude insulation anomaly signals to be easily submerged, making it difficult to achieve timely early warning.

[0003] Patent CN220040715U discloses a substation DC system grounding fault monitoring system. It uses a combination of unbalanced bridge detection and low-frequency signal injection to monitor and locate grounding faults in the substation DC system. The unbalanced bridge detection method can only determine whether the overall insulation level of the DC system is abnormal, but cannot determine the specific faulty feeder. It must be combined with the low-frequency signal injection method to achieve accurate location. However, the low-frequency signal injection method itself has obvious shortcomings. The amplitude of the injected low-frequency signal is low. If there is electromagnetic interference or harmonic noise in the DC system, the signal is easily covered up. Therefore, additional filtering and amplification circuits are required, which further increases the structural complexity of the entire monitoring system.

[0004] The invention patent application with publication number CN116859289A proposes a grounding fault detection device for a DC system in a substation. It uses an active low-pass filter to process the current signal and constructs an integrated detection architecture that integrates current and voltage sampling, filtering and amplification, AD conversion, data processing, and communication functions to achieve signal acquisition and analysis. However, signal phase alignment is difficult, and fault location depends on the phase matching of voltage and current signals. The two signals will produce different degrees of phase delay after passing through different filtering and amplification stages, which reduces the accuracy of fault feeder location. Moreover, the device parameters are easily affected by the environment, which can easily lead to signal distortion and affect the detection stability.

[0005] Patent application CN117741353A discloses an online insulation detection method for variable frequency motor systems. This method injects a common-mode excitation signal by controlling the inverter switch during motor shutdown or startup, and then detects the motor's insulation status using specific high-frequency / medium-frequency common-mode characteristics. This method uses the inverter as the excitation source, has a direct physical connection to the system's electrical circuit, and requires control access to the inverter, essentially performing online insulation detection on the variable frequency motor system in a quasi-online manner. However, substation DC power supply differs from variable frequency motor systems; its reliability requirements are extremely high, and power outages are not permitted. Online monitoring is necessary, and substation DC systems typically do not have inverters. Although some substations are equipped with frequency converter bridges, theoretically allowing the injection of common-mode signals into the DC system, grid maintenance personnel often lack control access. Therefore, this technology cannot be applied as an online insulation detection solution for substation DC systems where power outages are not permitted and can be implemented independently.

[0006] Therefore, the applicant hopes to find a technical solution to address the above technical problems. Summary of the Invention

[0007] In view of this, the purpose of this invention is to provide a method for detecting the insulation status of a substation DC system based on magnetic coupling common-mode injection. This method does not rely on existing system control interfaces and can be implemented independently, meeting the requirements of online insulation detection in substation DC systems with stringent power supply requirements. Moreover, it only requires the acquisition of frequency domain current signals at the feeder head end and the analysis of spectral characteristics, without the need to measure system voltage signals or perform phase alignment processing. This simple approach efficiently achieves a reliable assessment of the insulation status of the DC system.

[0008] The technical solution adopted in this invention is as follows:

[0009] An insulation status detection method for a substation DC system based on magnetic coupling common-mode injection includes the following steps:

[0010] S1. Inject a broadband excitation signal into a designated location on the DC bus of the substation's DC system via a non-contact common-mode method using magnetic coupling. The designated location of this DC bus is at the power output terminal and at the tap front of each feeder. Through electromagnetic coupling, this wideband excitation signal... It is converted into common-mode excitation current and injected into the DC bus and distributed to each feeder;

[0011] S2. Real-time acquisition of the wideband excitation signal injected into the k-th feeder in step S1. The time-domain current signal at the beginning of the feeder k represents the number of the feeder, and n is the total number of feeders;

[0012] S3. Time-domain current signal at the beginning of the k-th feeder. Through frequency domain analysis, the corresponding resonant characteristic parameters are extracted;

[0013] S4. Using the resonant characteristic parameters of the k-line feeder under normal operating conditions as a reference, a comprehensive judgment index D is constructed based on the changes in the resonant characteristic parameters to characterize the degree of change in the insulation state of the feeder. k ;

[0014] S5. Based on the comprehensive judgment index D k This is used to determine the degree of change in the insulation status of each feeder.

[0015] Preferably, in step S3, the resonant characteristic parameters include the peak resonant frequency. Feeder head current amplitude Current phase at the feeder head In step S4, the resonant characteristic parameters under normal operating conditions include the peak resonant frequency under normal operating conditions. 0. Normal state feeder head current amplitude 0. Normal state feeder head current phase 0.

[0016] Preferably, in step S3, the frequency domain analysis includes:

[0017] For the time-domain current signal at the feeder head Performing a Fourier transform yields its corresponding frequency domain representation function:

[0018] ;in, This represents the frequency domain current signal at the beginning of the feeder. The Fourier transform formula is given; the relationship between the frequency domain current signal at the feeder head and its corresponding resonant characteristic parameters is as follows:

[0019] j represents The imaginary unit;

[0020] ;

[0021] .

[0022] Preferably, in step S4, the comprehensive judgment index D k The calculation formula is:

[0023] ;

[0024] + + =1;

[0025] in,

[0026] for and The absolute value of the difference between 0 and 0 represents the amount of change in the current peak resonant frequency relative to the peak resonant frequency under normal operating conditions. for and The absolute value of the difference between 0 and 0 represents the change in the current amplitude at the feeder head end relative to the current amplitude at the feeder head end under normal operating conditions. for and The absolute value of the difference between 0 and 0 represents the amount of change in the current phase at the feeder head end relative to the current phase at the feeder head end under normal operating conditions.

[0027] This is a weighting coefficient for the change in peak resonant frequency; This is the weighting coefficient for the current amplitude at the feeder head end; This is the weighting coefficient for the phase of the current at the beginning of the feeder.

[0028] Preferably, =0.4±0.03; =0.3±0.02; =0.3±0.02.

[0029] Preferably, in step S1, a broadband excitation signal is injected into a designated location on the DC bus of the substation's DC system via a magnetically coupled non-contact injection device. The magnetically coupled non-contact injection device includes a magnetic ring that is non-contactly sleeved around the outer periphery of the positive and negative conductors at a designated location on the DC bus and is electromagnetically coupled to the conductors. An injection coil, also electromagnetically coupled to the magnetic ring, is wound around the magnetic ring. The injection coil is connected to a broadband excitation source signal source and is used to inject a broadband excitation signal into the positive and negative conductors at the designated location on the DC bus in a magnetically coupled non-contact common-mode manner. .

[0030] Preferably, the frequency band of the wideband excitation source signal is set to 500Hz-20kHz.

[0031] Preferably, in step S2, a current sensor is installed at the beginning of both the positive and negative conductors of each feeder to collect the time-domain current signal at the beginning of each feeder in real time. The bandwidth of the current sensor at least covers the frequency band of the wideband excitation signal source.

[0032] Preferably, an insulation condition assessment unit is provided, which is connected to the current sensor configured on each feeder line to receive the time-domain current signal at the feeder head end of each feeder line. Frequency domain analysis and resonance characteristic parameter extraction were performed on it, and a comprehensive judgment index D was constructed to characterize the degree of change in the insulation state of the feeder. k .

[0033] Preferably, a balanced bridge and a filter are sequentially provided between the power output terminal and the tap changer of each feeder, wherein...

[0034] The balancing bridge is connected between the positive and negative conductors of the DC bus and is grounded;

[0035] The filter device is connected between the positive and negative conductors of the DC bus and is grounded;

[0036] The power supply side of the DC system in the substation is balanced and filtered by a balancing bridge and a filter device.

[0037] The designated location of the DC bus is at the rear end of the filter device and at the tap front end of each feeder.

[0038] Each feeder is the return line for the loads of various electrical equipment connected to the DC system of the substation.

[0039] The key technical mechanism and beneficial effects of this application are mainly as follows: This application achieves broadband common-mode excitation injection of the DC bus and its feeders through non-contact magnetic coupling. Then, it calculates the resonant characteristic parameters of the frequency domain current signal at the feeder head end by performing differential calculation on the variables of the resonant characteristic parameters, thereby constructing a comprehensive judgment index D to characterize the degree of change in the insulation state of the feeder. k This invention enables quantitative assessment and anomaly identification of the insulation status of DC systems. It can specifically determine changes in insulation status such as insulation degradation, grounding faults, and early defects during DC system operation, and output corresponding insulation status judgment results. The solution provided in this application does not rely on existing system control interfaces and can be implemented independently, meeting the stringent online insulation detection scenarios of substation DC systems. In addition, this application only needs to collect the frequency domain current signal at the feeder head end and perform spectral feature analysis during the detection process, without measuring the system voltage signal or performing phase alignment processing. This simple solution efficiently achieves a reliable assessment of the insulation status of DC systems.

[0040] Furthermore, this application does not require the installation of electrical connection structures for signal injection during implementation, and features good structural isolation and high operational safety; at the same time, it does not generate differential mode components, does not disturb the normal power supply circuit of the system, and ensures the continuous and stable operation of the DC system. Attached Figure Description

[0041] Figure 1 This is a flowchart illustrating the steps of the method for detecting the insulation status of a substation DC system based on magnetic coupling common-mode injection, as described in a specific embodiment of this application.

[0042] Figure 2 This is a schematic diagram of the structure of the substation DC system insulation status detection system based on magnetic coupling common mode injection according to a specific embodiment of this application;

[0043] Figure 3 This is the system simulation experimental platform built according to the specific embodiments of this application;

[0044] Figure 4 yes Figure 3 The waveform diagram of the frequency domain response curve of feeder 2 at the feeder head end under different degrees of insulation aging conditions is shown in the system simulation experimental platform.

[0045] Figure 5 for Figure 3 The diagram shows the variation of the current amplitude at the feeder head end of feeder 2 under different degrees of insulation aging conditions in the system simulation experimental platform shown.

[0046] Figure 6 for Figure 3 The figure shows the peak resonant frequency variation of feeder 2 under different degrees of insulation aging in the system simulation experimental platform. Detailed Implementation

[0047] Please refer to the above. Figure 1 and Figure 2 As shown, this embodiment proposes a method for detecting the insulation status of a substation DC system based on magnetic coupling common-mode injection. Preferably, in this embodiment, a balanced bridge and a filter device are sequentially provided between the power output terminal and the tap changer of each feeder.

[0048] The balanced bridge is connected between the positive and negative conductors of the DC bus and is grounded;

[0049] The filter device is connected between the positive and negative conductors of the DC bus and is grounded;

[0050] The power supply side of the DC system in the substation is balanced and filtered by a balancing bridge and a filter device.

[0051] The DC bus is located at the rear end of the filter device and the front end of the tap of each feeder.

[0052] Each feeder is the return line for the loads of the electrical equipment connected to the DC system of the substation. Figure 2 Specifically, two feeders are shown, one feeder connected to load 1 and the other feeder connected to load 2.

[0053] In this embodiment, the method for detecting the insulation status of a substation DC system includes the following steps:

[0054] S1. Inject a broadband excitation signal into a designated location on the DC bus of the substation's DC system via a non-contact common-mode method using magnetic coupling. The designated location of this DC bus is at the power output terminal and at the tap front of each feeder. Through electromagnetic coupling, this wideband excitation signal... The current is converted into a common-mode excitation current and injected into the DC bus and distributed to each feeder; preferably, in this step S1, a broadband excitation signal is injected into a designated location on the DC bus of the substation DC system through a magnetically coupled non-contact injection device. The magnetically coupled non-contact injection device 2 includes a magnetic ring that is non-contactly sleeved around the outer periphery of the positive and negative conductors at a designated location on the DC bus and is electromagnetically coupled to the conductors. An injection coil that is electromagnetically coupled to the magnetic ring is wound around the magnetic ring. The injection coil is connected to a broadband excitation source signal source 1 and is used to inject a broadband excitation signal into the positive and negative conductors at the designated location on the DC bus in a common-mode manner using magnetic coupling non-contact. Preferably, in this embodiment, the frequency band of the wideband excitation source signal is set to 500Hz-20kHz.

[0055] S2. Real-time acquisition of the wideband excitation signal injected into the k-th feeder in step S1. The time-domain current signal at the beginning of the feeder k represents the number of the feeder line, and n is the total number of feeders; preferably, in step S2, a current sensor 3 is installed at the beginning of the positive and negative conductors of each feeder line to collect the time-domain current signal at the beginning of each feeder line in real time. Among them, the bandwidth of the current sensor 3 at least covers the frequency band of the wideband excitation signal source;

[0056] S3. Time-domain current signal at the beginning of the k-th feeder. Through frequency domain analysis, the corresponding resonance characteristic parameters are extracted; preferably, in this step S3, the resonance characteristic parameters include the peak resonant frequency. Feeder head current amplitude Current phase at the feeder head In step S4, the resonant characteristic parameters under normal operating conditions include the peak resonant frequency under normal operating conditions. 0. Normal state feeder head current amplitude 0. Normal state feeder head current phase 0; Frequency domain analysis includes:

[0057] For the time-domain current signal at the feeder head Performing a Fourier transform yields its corresponding frequency domain representation function:

[0058] ;in, This represents the frequency domain current signal at the beginning of the feeder. The Fourier transform formula is given; the relationship between the frequency domain current signal at the feeder head and its corresponding resonant characteristic parameters is as follows:

[0059] j represents The imaginary unit;

[0060] ;

[0061] ;

[0062] S4. Using the resonant characteristic parameters of the k-line feeder under normal operating conditions as a reference, a comprehensive judgment index D is constructed based on the changes in the resonant characteristic parameters to characterize the degree of change in the insulation state of the feeder. k Preferably, in step S4, the comprehensive judgment index D k The calculation formula is:

[0063] ;

[0064] + + =1;

[0065] in,

[0066] for and The absolute value of the difference between 0 and 0 represents the amount of change in the current peak resonant frequency relative to the peak resonant frequency under normal operating conditions. for and The absolute value of the difference between 0 and 0 represents the change in the current amplitude at the feeder head end relative to the current amplitude at the feeder head end under normal operating conditions. for and The absolute value of the difference between 0 and 0 represents the amount of change in the current phase at the feeder head end relative to the current phase at the feeder head end under normal operating conditions.

[0067] This is a weighting coefficient for the change in peak resonant frequency; This is the weighting coefficient for the current amplitude at the feeder head end; This is the weighting coefficient for the phase of the current at the beginning of the feeder.

[0068] Preferably, =0.4±0.03; =0.3±0.02; =0.3±0.02.

[0069] S5. Based on the comprehensive judgment index D k To determine the degree of change in the insulation condition of each feeder; among them, the comprehensive judgment index D k The higher the value, the greater the degree of insulation degradation of the feeder currently being tested; preferably, in practice, a preset threshold can be set, which is determined by the comprehensive judgment index D. k The insulation status of each feeder is compared with a preset threshold, and the degree of change in insulation status is determined based on the comparison results. Once the preset threshold is exceeded, it means that the insulation status of the feeder being tested has deteriorated significantly.

[0070] Preferably, in this embodiment, an insulation condition assessment unit 4 is provided, which is connected to the current sensor 3 configured on each feeder line to receive the time-domain current signal at the feeder head end of each feeder line. Frequency domain analysis and resonance characteristic parameter extraction were performed on it, and a comprehensive judgment index D was constructed to characterize the degree of change in the insulation state of the feeder. k .

[0071] To enable those skilled in the art to better understand the technical solutions of this invention, based on the above implementation schemes, the following specific embodiments will be proposed in conjunction with the accompanying drawings of the embodiments of this invention. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0072] Based on the above implementation scheme, this application embodiment specifically constructs an experimental platform for simulating a substation DC system. Please refer to [link / reference]. Figure 3 The system simulation experimental platform shown uses a DC power supply with a rated voltage U of 110V as the DC bus power supply, and a balanced bridge is set at the power supply output terminal (specifically by...). Figure 3 The resistor R shown BAL1 and resistance R BAL2 Please provide further details regarding the composition of R. BAL1 and R BAL2 The specific electrical component names and filtering devices (specifically, those provided by the manufacturer) Figure 3 The capacitor C shown FIL1 and capacitor C FIL2 Please provide further details regarding the composition of C. FIL1 and C FIL2The corresponding specific electrical component name is used to establish a balanced resistance channel between the DC bus and ground and suppress high-frequency interference to simulate the ground balance and filtering conditions of the power supply side of the substation DC system.

[0073] In the system simulation platform, the DC bus is connected to three feeders (i.e., cable feeders) at its rear end. Figure 3 Feeders 1, 2, and 3 shown are used to simulate a typical multi-circuit outgoing connection configuration in a substation DC system. In this embodiment, each feeder consists of a KVVP control shielded cable of different lengths and a corresponding load R. Load1 R Load2 R Load3 The configuration is used to represent the connection status of electrical equipment loads such as protection devices and control devices in the field DC system.

[0074] Under the above experimental conditions, the magnetically coupled non-contact injection device MCNCIU was magnetically coupled non-contactly connected to the outer periphery of the positive and negative conductors at a designated location on the DC bus (located at the rear end of the filter device and the front end of the taps of each feeder). A broadband transient excitation signal was injected into the cable at the designated location on the DC bus in a magnetically coupled non-contact common-mode manner. Current sensors are arranged at the beginning of the positive and negative conductors of feeders 1, 2, and 3, respectively, specifically including... Figure 3 The first current sensor CS1, the second current sensor CS2, the third current sensor CS3, the fourth current sensor CS4, the fifth current sensor CS5, and the sixth current sensor CS6 are shown; and an equivalent fault resistance (i.e., a fault resistance) is set at the beginning of the positive conductor of feeder 2. Figure 3 The “simulated fault location” shown in the figure, Figure 4 , Figure 5 and Figure 6 The "normal" shown refers to Figure 3 (No equivalent fault resistance is set at the simulated fault location shown); the specific parameter configurations are shown in Table 1 below:

[0075] Table 1

[0076] The wideband excitation signal is acquired by various current sensors. The time-domain current signal generated at the feeder head end is used for subsequent frequency-domain analysis and resonance characteristic parameter extraction, thereby constructing a comprehensive judgment index D to characterize the degree of change in the insulation state of the feeder. k ;

[0077] For details, please refer to Figure 4 As shown, in Figure 3On the system simulation platform shown, the MCNCIU injects a square wave rising edge broadband transient excitation signal into a designated location on the DC bus cable using a magnetically coupled, non-contact common-mode method. The time-domain current signal at the feeder head end of feeder 2 is acquired by the third current sensor CS3, and frequency-domain analysis is performed to extract its corresponding resonant characteristic parameters. Figure 4 It can be seen that as the severity of the fault increases, the frequency domain response curve of the feeder head of feeder 2 generally shows a trend of shifting to the upper left, that is, the current amplitude at the feeder head increases. Gradually increase, while the peak resonant frequency The voltage gradually decreases. This phenomenon indicates that as insulation deteriorates or fault resistance decreases, the system's equivalent impedance decreases, thereby enhancing the response strength of the magnetically injected signal and leading to an increase in current amplitude; through Figure 4 The variation pattern shown indicates that the peak resonant frequency and the amplitude of the feeder head current are highly sensitive to the degree of fault and can be used as important characteristic parameters to characterize the insulation status of DC bus feeders.

[0078] To further illustrate the implementation effects of this application, please refer to the following: Figure 5 As shown, in Figure 3 On the system simulation platform shown, the MCNCIU sends a broadband square wave excitation signal to a designated location on the DC bus cable in a magnetically coupled, non-contact common-mode manner. Utilizing the inherent broadband spectral characteristics of the square wave's rising edge, each rising edge trigger is sampled as a set of independent analysis samples (a total of 50 sets are used). Figure 5 The horizontal axis of the signal is used to collect the time-domain current signal at the beginning of feeder 2 through the third current sensor CS3. Frequency domain analysis is then performed on this signal to extract the corresponding amplitude of the feeder's beginning current. Figure 5 It can be seen that as the severity of the fault increases, the amplitude of the feeder head current extracted by each group of samples shows a monotonically increasing trend, proving that it has good consistency and repeatability.

[0079] To further illustrate the implementation effects of this application, please refer to the following: Figure 6 As shown, in Figure 3 On the system simulation platform shown, the MCNCIU sends a broadband square wave excitation signal to a designated location on the DC bus cable in a magnetically coupled, non-contact common-mode manner. Utilizing the inherent broadband spectral characteristics of the square wave's rising edge, each rising edge trigger is sampled as a set of independent analysis samples (a total of 50 sets are used). Figure 6 The horizontal axis of the signal is used to collect the time-domain current signal at the beginning of feeder 2 through the third current sensor CS3. Frequency domain analysis is then performed on this signal to extract its corresponding peak resonant frequency. Figure 6It can be seen that as the degree of fault intensifies, the peak resonant frequency of the feeder head current extracted by each group of samples shows a monotonically decreasing trend, proving that it has good consistency and repeatability.

[0080] Based on the above implementation, in order to achieve quantitative determination of the insulation status of feeders, a comprehensive judgment index is constructed. It is determined by the peak resonant frequency offset (i.e., ), the change in current amplitude (i.e. ) and phase change (i.e. The weighted fusion is obtained, specifically expressed as: In this embodiment, the weights of each parameter are set as follows: w1=0.4, w2=0.3, w3=0.3.

[0081] In the actual judgment process, the normal operating condition (i.e., normal operating state) is used as the reference benchmark. Differential calculations are performed on each resonance characteristic parameter, and a comprehensive judgment index is constructed based on the above-described implementation scheme of this application. Since this indicator reflects the deviation relative to the normal state, under normal operating conditions... Theoretically, it is close to 0. Based on this, 0 can be directly used as the criterion: when A small fluctuation around zero is considered normal; when... Furthermore, as the value increases, it is determined to be an insulation abnormality, and its magnitude can further characterize the severity of the fault. The higher the value, the more severe the fault.

[0082] Table 2

[0083] 200kΩ Correct judgment 94% 100kΩ Correct judgment 98% 47kΩ Correct judgment 100% 10kΩ Correct judgment 100%

[0084] The calculation method for the judgment accuracy in Table 2 above is as follows: under each fault condition, through repeated experiments, the proportion of the number of times the judgment result is consistent with the actual state to the total number of samples is counted.

[0085] In summary, a comprehensive judgment index based on the weighted calculation of multiple feature parameters is proposed. This method effectively integrates frequency, amplitude, and phase information, exhibiting higher accuracy and robustness compared to using a single feature parameter. Experimental results demonstrate that this method achieves high accuracy under varying fault conditions, validating its effectiveness and reliability in online detection of DC bus insulation status.

[0086] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0087] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for detecting the insulation status of a substation DC system based on magnetic coupling common-mode injection, characterized in that, Includes the following steps: S1. Inject a broadband excitation signal into a designated location on the DC bus of the substation's DC system via a non-contact common-mode method using magnetic coupling. The designated location of this DC bus is at the power output terminal and at the tap front of each feeder. Through electromagnetic coupling, this wideband excitation signal... It is converted into common-mode excitation current and injected into the DC bus and distributed to each feeder; S2. Real-time acquisition of the wideband excitation signal injected into the k-th feeder in step S1. The time-domain current signal at the beginning of the feeder k represents the number of a certain feeder, and n is the total number of feeders; S3. Time-domain current signal at the beginning of the k-th feeder. Through frequency domain analysis, the corresponding resonant characteristic parameters are extracted; In step S3, the resonant characteristic parameters include the peak resonant frequency. Feeder head current amplitude Current phase at the feeder head ; S4. Using the resonant characteristic parameters of the k-th feeder under normal operating conditions as a reference, a comprehensive judgment index D is constructed based on the changes in the resonant characteristic parameters to characterize the degree of change in the insulation state of the k-th feeder. k In step S4, the resonant characteristic parameters under normal operating conditions include the peak resonant frequency under normal operating conditions.

0. Normal state feeder head current amplitude 0. Normal state feeder head current phase 0; S5. Based on the comprehensive judgment index D k To determine the degree of change in the insulation status of the k-th feeder.

2. The method for detecting the insulation status of a substation DC system based on magnetic coupling common-mode injection according to claim 1, characterized in that, In step S3, the frequency domain analysis includes: For the time-domain current signal at the feeder head Performing a Fourier transform yields its corresponding frequency domain representation function: ;in, This represents the frequency domain current signal at the beginning of the feeder. The Fourier transform formula is given; the relationship between the frequency domain current signal at the feeder head and its corresponding resonant characteristic parameters is as follows: j represents The imaginary unit; ； 。 3. The method for detecting the insulation status of a substation DC system based on magnetic coupling common-mode injection according to claim 1, characterized in that, In step S4, the comprehensive judgment index D k The calculation formula is: ； + + =1； in, for and The absolute value of the difference between 0 and 0 represents the amount of change in the current peak resonant frequency relative to the peak resonant frequency under normal operating conditions. for and The absolute value of the difference between 0 and 0 represents the change in the current amplitude at the feeder head end relative to the current amplitude at the feeder head end under normal operating conditions. for and The absolute value of the difference between 0 and 0 represents the amount of change in the current phase at the feeder head end relative to the current phase at the feeder head end under normal operating conditions. This is a weighting coefficient for the change in peak resonant frequency; This is the weighting coefficient for the current amplitude at the feeder head end; This is the weighting coefficient for the phase of the current at the beginning of the feeder.

4. The method for detecting the insulation status of a substation DC system based on magnetic coupling common-mode injection according to claim 3, characterized in that, =0.4±0.03； =0.3±0.02； =0.3±0.02。 5. The method for detecting the insulation status of a substation DC system based on magnetic coupling common-mode injection according to claim 1, characterized in that, In step S1, a broadband excitation signal is injected into a designated location on the DC bus of the substation's DC system via a magnetically coupled non-contact injection device. The magnetically coupled non-contact injection device includes a magnetic ring that is non-contactly sleeved around the outer periphery of the positive and negative conductors at a designated location on the DC bus and is electromagnetically coupled to the conductors. An injection coil, also electromagnetically coupled to the magnetic ring, is wound around the magnetic ring. The injection coil is connected to a broadband excitation source signal source and is used to inject a broadband excitation signal into the positive and negative conductors at the designated location on the DC bus in a magnetically coupled non-contact common-mode manner. .

6. The method for detecting the insulation status of a substation DC system based on magnetic coupling common-mode injection according to claim 5, characterized in that, The frequency band of the wideband excitation source signal is set to 500Hz-20kHz.

7. The method for detecting the insulation status of a substation DC system based on magnetic coupling common-mode injection according to claim 5, characterized in that, In step S2, a current sensor is installed at the beginning of both the positive and negative conductors of each feeder to collect the time-domain current signal at the beginning of each feeder in real time. The bandwidth of the current sensor at least covers the frequency band of the wideband excitation signal source.

8. The method for detecting the insulation status of a substation DC system based on magnetic coupling common-mode injection according to claim 1, characterized in that, An insulation condition assessment unit is set up, which is connected to the current sensor configured on each feeder line to receive the time-domain current signal at the feeder head end of each feeder line. Frequency domain analysis and resonance characteristic parameter extraction were performed on it, and a comprehensive judgment index D for characterizing the degree of change in the insulation state of the k-th feeder was constructed. k .

9. The method for detecting the insulation status of a substation DC system based on magnetic coupling common-mode injection according to claim 1, characterized in that, A balanced bridge and a filter device are sequentially installed between the power output terminal and the tap changer of each feeder. The balancing bridge is connected between the positive and negative conductors of the DC bus and is grounded; The filter device is connected between the positive and negative conductors of the DC bus and is grounded; The power supply side of the DC system in the substation is balanced and filtered by a balancing bridge and a filter device. The designated location of the DC bus is at the rear end of the filter device and at the tap front end of each feeder. Each feeder is the return line for the loads of various electrical equipment connected to the DC system of the substation.

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