Method and system for evaluating the safety of cable insulation based on harmonic data preprocessing

Abstract

The application relates to a cable insulation safety evaluation method and system based on harmonic data preprocessing, and the method comprises the following steps: collecting voltage or current data of a cable to be detected; according to the periodic characteristics of harmonics, harmonic data is updated after reaching a preset fixed time each time, the process of the harmonic data updating comprises the following steps: extracting harmonics of the voltage or current data through a wave trap, and compensating the harmonic phase by using a repetitive predictive controller to obtain extracted harmonics; multiplying the extracted harmonics by an amplitude gain module to compensate the harmonic amplitude and obtain optimized harmonics; subtracting the optimized harmonics from the original voltage or current data to obtain fault data; performing traveling wave decoupling on the fault data, and judging the fault type and fault distance of the cable according to the traveling wave signal obtained through decoupling. Compared with the prior art, the application realizes rapid evaluation of cable insulation safety and rapid and accurate positioning when the insulation is damaged.

Description

Technical Field

[0001] This invention relates to the field of cable fault detection technology, and in particular to a method and system for assessing cable insulation safety based on harmonic data preprocessing. Background Technology

[0002] When energy distribution is uneven, long-distance transmission lines are typically required from energy-rich sources to load-concentrated receivers. The complex geographical and climatic environments along these transmission lines mean that insulation damage to transmission cables has become a vulnerable link with a high probability of failure in the power system.

[0003] When cable insulation faults occur, the ability to quickly and accurately identify the type and location of the fault is crucial for ensuring power supply reliability. However, the current power system exhibits a "dual-high" structural characteristic: a high proportion of renewable energy and a high proportion of power electronic equipment connected to the grid. These nonlinear devices introduce high-order harmonics into the grid, resulting in grid voltage and current being rich in background harmonics.

[0004] Existing methods for assessing cable insulation faults primarily involve decomposing the traveling wave signals generated during a cable insulation fault and using an expert database to determine the fault type based on signal characteristics. However, due to the significantly increased voltage and current harmonic content in modern power systems compared to traditional systems, traditional methods often fail to decompose the signals into effective signals, making it impossible to determine the type of cable insulation fault and thus pinpoint its location. Furthermore, while some researchers have proposed artificial intelligence and machine learning methods to train existing data for automatic identification, current approaches still suffer from limitations such as insufficient training sets, low training accuracy, and unreliable performance in practical applications.

[0005] Therefore, how to effectively overcome the impact of voltage and current distortion caused by the connection of a large number of nonlinear devices in modern new power systems with "high" characteristics, and how to achieve rapid assessment of cable insulation safety and rapid and accurate location when insulation is damaged, has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the existing technology by providing a cable insulation safety assessment method and system based on harmonic data preprocessing, overcoming the influence of voltage and current distortion caused by the connection of a large number of nonlinear devices, and realizing rapid assessment of cable insulation safety and rapid and accurate determination when insulation is damaged.

[0007] The objective of this invention can be achieved through the following technical solutions: A method for assessing cable insulation safety based on harmonic data preprocessing includes: Collect voltage or current data of the cable under test; Based on the periodicity of harmonics, harmonic data is updated after each preset fixed time. The process of updating harmonic data includes: extracting harmonics from the voltage or current data using a notch filter, and compensating for the harmonic phase using a repetitive predictive controller to obtain the extracted harmonics; multiplying each extracted harmonic by an amplitude gain module to perform harmonic amplitude compensation to obtain optimized harmonics. The fault data is obtained by subtracting the optimized harmonics from the original voltage or current data. The fault data is decoupled by traveling wave, and the fault type and fault distance of the cable are determined based on the traveling wave signal obtained from the decoupling.

[0008] Furthermore, the harmonics extracted by the notch filter include the 5th, 7th, 9th, and 11th harmonics.

[0009] Furthermore, the expression for the notch filter is: In the formula, The angular frequency of voltage or current data. For the damping ratio, It is a complex frequency.

[0010] Furthermore, the repetitive prediction controller includes: a first subtractor, a first adder, a second delay module, a proportional module, a third adder, a first delay module, and a periodic delay module; The voltage input to the repetitive predictive controller is connected to the input terminals of the first subtractor and the third adder. The third adder outputs the predicted line voltage and is connected to the input terminal of the first delay module. The output terminal of the first delay module is connected to the input terminal of the first adder. The output terminal of the first subtractor is connected to the input terminal of the second adder. The output terminal of the second adder is connected to the input terminals of the periodic delay module and the second delay module. The output terminal of the periodic delay module is connected to the input terminal of the second adder. The output terminal of the second delay module is connected to the input terminal of the proportional module. The output terminal of the proportional module is connected to the input terminal of the third adder.

[0011] Furthermore, the expression for the second delay module is: In the formula, N The number of samples per cycle. N 1 represents the predicted number of switching cycles. To indicate N - N Delay of one sampling period; The expression for the first delay module is: ,express N The delay of one sampling period.

[0012] Furthermore, the expression for the periodic delay module is as follows: In the formula, Q It is a constant less than 1.

[0013] Furthermore, the periodic update process of the harmonic data specifically includes: 1) Determine if the set harmonic update flag is 1; if so, proceed to step 3); otherwise, proceed to step 2. 2) Determine whether the fixed time has been reached. If yes, set the harmonic update flag to 1 and execute step 7); otherwise, execute step 6). 3) Harmonic extraction is performed on the voltage or current data using a notch filter; 4) A repetitive predictive controller is used to compensate for the harmonic phase, and the extracted harmonics are obtained; 5) Multiply each extracted harmonic by the amplitude gain module to perform harmonic amplitude compensation and obtain the optimized harmonics; 6) Set the harmonic update flag to 0; 7) Receive the real-time acquired voltage or current data of the cable under test and return to step 1).

[0014] Furthermore, the process of determining the fault distance includes: By detecting the wavefront of the traveling wave at the fault point from the decoupled traveling wave signal, the time when the traveling wave at the fault point arrives at the detection point is determined, thereby determining the fault distance.

[0015] Furthermore, the method employs wavelet transform to identify the wavefront of the traveling wave during a fault, and uses the Db45 wavelet as the basis function of the wavelet transform.

[0016] The present invention also provides a cable insulation safety assessment system for implementing the cable insulation safety assessment method based on harmonic data preprocessing as described above, comprising: Voltage and current data acquisition module, used to acquire voltage or current data of the cable under test; The harmonic data update determination module is used to update the harmonic data after each preset fixed time period based on the periodic characteristics of the harmonics. The harmonic extraction and compensation module is used to extract harmonics from the voltage or current data using a notch filter, and to compensate for the harmonic phase using a repetitive predictive controller to obtain the extracted harmonics. The gain module is used to multiply the extracted harmonics by the amplitude gain module to perform harmonic amplitude compensation and obtain the optimized harmonics. The distortion reduction module is used to subtract the optimized harmonics from the original voltage or current data to obtain fault data, thereby reducing the distortion rate of the data used for fault type determination. The traveling wave decoupling and phase mode transformation module is used to transform fault data into independent moduli through coordinate transformation; The cable insulation fault type determination module is used to determine the cable insulation fault type based on the mutually independent moduli; and to determine the time when the traveling wave at the fault point arrives at the detection point by detecting the wavefront of the traveling wave at the fault point through wavelet transform. The fault distance calculation module is used to determine the time of the modulus maxima obtained by wavelet transform decomposition based on the time when the traveling wave at the fault point arrives at the detection point, and calculate the fault distance based on the traveling wave method.

[0017] Compared with the prior art, the present invention has the following advantages: (1) In the process of harmonic extraction, the present invention first extracts low-order harmonics from voltage or current data through a notch filter, then compensates the harmonic phase through a repetitive prediction controller, and multiplies each harmonic by an amplitude gain module to compensate the harmonic amplitude, thus overcoming the problem that the notch filter causes the extracted harmonic signal to lag in phase and reduce in amplitude; by subtracting the optimized harmonics from the original data, the harmonics with reduced distortion and containing cable insulation fault information can be obtained, which improves the accuracy of cable insulation safety assessment and can solve the problem that the existing system cannot effectively identify the type of cable insulation fault and cannot accurately locate the subsequent insulation fault point when the grid voltage and current distortion is severe. It is applicable to modern new power systems.

[0018] (2) Since all harmonics are periodic, the repetitive controller of the present invention can make the current signal lead the next period signal, which is convenient to realize phase advance prediction. It has a large amplitude gain at the fundamental wave and each harmonic, which can realize near zero steady-state error prediction and ensure that the amplitude of the predicted harmonics will not increase.

[0019] (3) The present invention takes into account that harmonics are periodic, and their amplitude and content generally do not change in real time. A fixed time is preset for updating harmonic data. The harmonic voltage and current information can be updated adaptively according to the preset time to ensure the accuracy and real-time performance of harmonic voltage and current. Attached Figure Description

[0020] Figure 1 This invention provides a method for assessing cable insulation safety based on harmonic data preprocessing. Figure 2 This is a control block diagram corresponding to a repetitive prediction controller provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the amplitude-frequency characteristics of a repetitive prediction controller provided in an embodiment of the present invention; Figure 4This is a schematic diagram showing the comparison before and after optimization of input current data using the present invention in an embodiment of the present invention, wherein (a) is the original current data waveform and (b) is the current data waveform after subtracting a specific harmonic; Figure 5 This is a schematic diagram comparing the system identification results of a traditional method and the method proposed in this invention in an embodiment of the present invention, wherein (a) is the result that the traditional method cannot effectively identify the fault type, and (b) is the result that the method proposed in this invention can effectively identify the fault type; Figure 6 This is a schematic diagram of wavelet transform for identifying the timing of fault traveling waves in an embodiment of the present invention, wherein (a) is the timing diagram of the first wavefront of the α component of the fault voltage traveling wave at one end of the cable, and (b) is the timing diagram of the first wavefront of the α component of the fault voltage traveling wave at the other end of the cable. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0022] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0023] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0024] Example 1 like Figure 1 As shown, this embodiment also provides a cable insulation safety assessment method based on harmonic data preprocessing, including the following steps: S1: Collect voltage or current data of the cable under test; S2: Based on the periodicity of harmonics, harmonic data is updated after each preset fixed time. The process of updating harmonic data includes: extracting harmonics from voltage or current data using a notch filter, and compensating for harmonic phase using a repetitive predictive controller to obtain the extracted harmonics; multiplying each extracted harmonic by an amplitude gain module to perform harmonic amplitude compensation to obtain optimized harmonics. That is, the system determines whether the harmonic data needs to be updated based on the harmonic update flag. If the flag is 1, the harmonic data needs to be updated. The 5th, 7th, 9th, and 11th harmonics are extracted by a notch filter, and the extracted harmonics are compensated by a repetitive prediction controller and an amplitude gain module. If the harmonic flag is zero, the harmonic data does not need to be updated. The system then determines whether the set harmonic update time interval has been reached. If the preset time has been reached, the harmonic update flag is set to 1. If not, the flag is set to zero. Specifically, it includes the following sub-steps: S201: Determine whether the set harmonic update flag is 1. If yes, proceed to step S203; otherwise, proceed to step S202. S202: Determine whether the fixed time has been reached. If yes, set the harmonic update flag to 1 and execute step S207; otherwise, execute step S206. S203: Harmonic extraction from voltage or current data using a notch filter; S204: The harmonic phase is compensated by a repetitive predictive controller to obtain the extracted harmonics; S205: Multiply the extracted harmonics by the amplitude gain module to perform harmonic amplitude compensation and obtain the optimized harmonics; S206: Set the harmonic update flag to 0; S207: Receive the real-time collected voltage or current data of the cable under test and return to step S201; S3: Subtract the optimized harmonics from the original voltage or current data to obtain the fault data; S4: Decouple fault data using a traveling wave technique; S5: Determine the cable fault type based on the traveling wave signal obtained from decoupling; S6: Wavefront calibration of traveling wave signals based on wavelet transform; S7: Determine the distance to the insulation fault based on the wavefront and traveling wave distance measurement.

[0025] Specifically, for three-phase systems, common harmonics are mainly the 5th, 7th, 9th, and 11th harmonics, which are periodic and show relatively little variation. Therefore, a notch filter is constructed to extract these signals. The notch filter expression is as follows: (1) In the formula The angular frequency of the harmonic signal to be extracted. The damping ratio is denoted as .

[0026] Notch filters cause phase lag and amplitude reduction in the extracted harmonic signals. Therefore, a repetitive predictive controller (RPC) is used to predict the extracted harmonic signals. The expression for the RPC is: (2) In the formula, N is the number of samples in one cycle. Z -N Located on the forward path of the repetitive control. Since harmonics are periodic, repetitive control allows the current signal to lead the signal of the next period, facilitating phase lead prediction. A block diagram of the repetitive predictive controller including the internal model element is attached. Figure 2 As shown.

[0027] Figure 2 middle Q It is a constant less than 1, used to improve the stability of the system during prediction; N 1 represents the predicted number of switching cycles. This is used to predict the detected transmission line voltage. u g For example, the voltage obtained by sampling u g Connected to the inputs of the first subtractor and the third adder; the predicted line voltage u g_F The input terminal of the first delay module is connected to the input terminal of the first adder, the output terminal of the first subtractor is connected to the input terminal of the second adder, the output terminal of the second adder is connected to the input terminals of the periodic delay module and the second delay module, the output terminal of the periodic delay module is connected to the input terminal of the second adder, the output terminal of the second delay module is connected to the input terminal of the proportional module, the output terminal of the proportional module is connected to the input terminal of the third adder, and the output terminal of the third adder is the predicted signal.

[0028] This solution achieves its goal through forward-looking... N The output voltage is predicted in one step to compensate for the inherent delay caused by calculation, sampling and other processes in the system, thereby improving the speed and stability of control.

[0029] A Bode plot of the repetitive controller is attached. Figure 3 As shown, it can be proven that the repetitive controller has a large amplitude gain at the fundamental frequency and each harmonic, indicating that the prediction based on repetitive control can achieve near-zero steady-state error prediction, ensuring that the predicted harmonic amplitude will not increase.

[0030] To address the issue of notch filters reducing the amplitude of specific harmonics, each extracted harmonic is multiplied by an amplitude gain module, and the gain coefficient is corrected based on the actual measured value.

[0031] Considering the periodicity of harmonics, their amplitude and content generally do not change in real time, a fixed time is preset. T set This is used to update harmonic data. When the time reaches... T set After that, the harmonic update flag will be set to 1, so that the harmonic data will be updated in the next interrupt.

[0032] Subtracting the optimized harmonics from the original data yields harmonics with reduced distortion that also include information about cable insulation faults. Taking current as an example... Figure 4 In the image (a), the original current waveform is shown. Figure 4 (b) in the figure represents the current waveform after subtracting the optimized harmonics.

[0033] In actual high-voltage long-distance transmission systems, which are three-phase systems, traveling waves are generated even in the non-faulty phases when a fault occurs, and the wave equations cannot be independent of each other. In order to eliminate electromagnetic coupling between the three-phase lines, this invention decouples the traveling waves based on the phase mode transformation method. The three-phase voltage wave equation with electromagnetic coupling is shown in equation (3): (3) In the formula, L s This represents the self-inductance per unit length of a single-phase transmission line. L m This represents the mutual inductance per unit length between two-phase output lines. Since the off-diagonal elements of the matrix in equation (4) are not zero, the three-phase voltage is transformed as follows: (4) After transformation, the linear modulus component can be obtained. α , β And zero-mode components. Linear mode components, with the conductor as the loop, include... α Quantity in a Phase conductors and b Flow between phase conductors β Quantity in a Phase conductors and c Flow occurs between phase conductors. To facilitate modulus analysis, a... γ The component, which flows between the b-phase conductor and the c-phase conductor, can be represented as... (5) This effectively decouples the traveling wave. The current signal is then transformed using the same decoupling method. The resulting traveling wave signal is then input into an expert assessment system for evaluation, which can then determine the fault type of the power transmission cable.

[0034] When locating a fault, based on the traveling wave method, it is necessary to accurately identify the traveling wave to precisely locate the fault. This invention uses wavelet transform to identify the current traveling wave front during a fault, and selects the Db45 wavelet as the wavelet basis function for traveling wave front detection.

[0035] The filter bank corresponding to the Db45 wavelet belongs to the dual-channel orthogonal mirror filter bank. The frequency domain characteristics of the dual-channel orthogonal mirror filter bank are: (6) In the formula H 0( e jω )and H 1( e jω () represents the orthogonal filter bank corresponding to the Db45 wavelet. Let the signal frequency be... f 1. Sampling frequency is f s Then the number of frequency band division layers ρ It can be represented as: (7) Figure 5 The results of fault identification in cable voltage and current distortion using existing methods and the present invention are presented. It can be seen that the traditional method cannot effectively identify the fault type when the system reports an error, while the system using the present invention can accurately identify the fault type and the fault location.

[0036] Figure 6 Given that the cable voltage and current are rich in harmonics, the present invention uses wavelet to identify the time of the traveling wave front of the fault. Based on the identification time, the cable fault can be calculated using the traveling wave method.

[0037] Example 2 This embodiment provides a cable insulation safety assessment system that implements the cable insulation safety assessment method based on harmonic data preprocessing as described in Embodiment 1, comprising: Voltage and current data acquisition module, used to acquire voltage or current data of the cable under test; The harmonic data update determination module is used to update the harmonic data after each preset fixed time period based on the periodic characteristics of the harmonics. The harmonic extraction and compensation module is used to extract harmonics from voltage or current data using a notch filter and to compensate for the harmonic phase using a repetitive predictive controller to obtain the extracted harmonics. The gain module is used to multiply the extracted harmonics by the amplitude gain module to perform harmonic amplitude compensation and obtain the optimized harmonics. The distortion reduction module is used to subtract optimized harmonics from the original voltage or current data to obtain fault data, thereby reducing the distortion rate of the data used for fault type determination. The traveling wave decoupling and phase mode transformation module is used to transform fault data into independent moduli through coordinate transformation; The cable insulation fault type determination module is used to determine the cable insulation fault type based on mutually independent moduli; and to determine the time when the traveling wave at the fault point arrives at the detection point by detecting the wavefront of the traveling wave at the fault point through wavelet transform. The fault distance calculation module is used to determine the time of the modulus maxima obtained by wavelet transform decomposition based on the time when the traveling wave at the fault point arrives at the detection point, and calculate the fault distance based on the traveling wave method.

[0038] Essentially, the sampling voltage and current data module samples the cable voltage and current as system input; the harmonic data update judgment module determines whether the harmonic data of the cable voltage and current needs to be updated; the harmonic extraction and compensation module extracts specific frequency harmonic voltage and current based on a notch filter after a set time, and performs phase compensation on the data using repeated prediction; the gain module compensates for the amplitude; the distortion reduction module subtracts the original data from the optimized harmonic data to reduce the distortion rate of the data used for fault type judgment; the traveling wave decoupling and phase mode transformation module transforms the three-phase coupled voltage and current vectors into independent moduli through coordinate transformation; the cable insulation fault type judgment module determines the cable insulation fault type through independent moduli; wavelet transform is used to detect the wavefront of the traveling wave when a fault occurs, and is used to determine the time when the traveling wave at the fault point arrives at the detection point, i.e., the time when the modulus maxima point obtained by the fault distance calculation module based on wavelet transform decomposition is used as the time when the traveling wave at the fault point arrives at the detection point, thereby calculating the fault point based on the traveling wave method.

[0039] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for assessing cable insulation safety based on harmonic data preprocessing, characterized in that, include: Collect voltage or current data of the cable under test; Based on the periodicity of harmonics, harmonic data is updated after each preset fixed time. The process of updating harmonic data includes: extracting harmonics from the voltage or current data using a notch filter, and compensating for the harmonic phase using a repetitive predictive controller to obtain the extracted harmonics; multiplying each extracted harmonic by an amplitude gain module to perform harmonic amplitude compensation to obtain optimized harmonics. The fault data is obtained by subtracting the optimized harmonics from the original voltage or current data. The fault data is decoupled by traveling wave, and the fault type and fault distance of the cable are determined based on the traveling wave signal obtained from the decoupling.

2. The cable insulation safety assessment method based on harmonic data preprocessing according to claim 1, characterized in that, The harmonics extracted by the notch filter include the 5th, 7th, 9th and 11th harmonics.

3. The cable insulation safety assessment method based on harmonic data preprocessing according to claim 1, characterized in that, The expression for the notch filter is: In the formula, The angular frequency of voltage or current data. For the damping ratio, It is a complex frequency.

4. The cable insulation safety assessment method based on harmonic data preprocessing according to claim 1, characterized in that, The repetitive prediction controller includes: a first subtractor, a first adder, a second delay module, a proportional module, a third adder, a first delay module, and a periodic delay module; The voltage input to the repetitive predictive controller is connected to the input terminals of the first subtractor and the third adder. The third adder outputs the predicted line voltage and is connected to the input terminal of the first delay module. The output terminal of the first delay module is connected to the input terminal of the first adder. The output terminal of the first subtractor is connected to the input terminal of the second adder. The output terminal of the second adder is connected to the input terminals of the periodic delay module and the second delay module. The output terminal of the periodic delay module is connected to the input terminal of the second adder. The output terminal of the second delay module is connected to the input terminal of the proportional module. The output terminal of the proportional module is connected to the input terminal of the third adder.

5. The cable insulation safety assessment method based on harmonic data preprocessing according to claim 4, characterized in that, The expression for the second delay module is: In the formula, N The number of samples per cycle. N 1 represents the predicted number of switching cycles. To indicate N - N Delay of one sampling period; The expression for the first delay module is: ,express N The delay of one sampling period.

6. The cable insulation safety assessment method based on harmonic data preprocessing according to claim 5, characterized in that, The expression for the periodic delay module is: In the formula, Q It is a constant less than 1.

7. The cable insulation safety assessment method based on harmonic data preprocessing according to claim 1, characterized in that, The periodic update process of the harmonic data specifically includes: 1) Determine if the set harmonic update flag is 1; if so, proceed to step 3); otherwise, proceed to step 2. 2) Determine whether the fixed time has been reached. If yes, set the harmonic update flag to 1 and execute step 7); otherwise, execute step 6). 3) Harmonic extraction is performed on the voltage or current data using a notch filter; 4) A repetitive predictive controller is used to compensate for the harmonic phase, and the extracted harmonics are obtained; 5) Multiply each extracted harmonic by the amplitude gain module to perform harmonic amplitude compensation and obtain the optimized harmonics; 6) Set the harmonic update flag to 0; 7) Receive the real-time acquired voltage or current data of the cable under test and return to step 1).

8. The cable insulation safety assessment method based on harmonic data preprocessing according to claim 1, characterized in that, The process of determining the fault distance includes: By detecting the wavefront of the traveling wave at the fault point from the decoupled traveling wave signal, the time when the traveling wave at the fault point arrives at the detection point is determined, thereby determining the fault distance.

9. A cable insulation safety assessment method based on harmonic data preprocessing according to claim 8, characterized in that, The method employs wavelet transform to identify the wavefront of the traveling wave during a fault, and uses the Db45 wavelet as the basis function of the wavelet transform.

10. A cable insulation safety assessment system that implements the cable insulation safety assessment method based on harmonic data preprocessing as described in any one of claims 1-9, characterized in that, include: Voltage and current data acquisition module, used to acquire voltage or current data of the cable under test; The harmonic data update determination module is used to update the harmonic data after each preset fixed time period based on the periodic characteristics of the harmonics. The harmonic extraction and compensation module is used to extract harmonics from the voltage or current data using a notch filter, and to compensate for the harmonic phase using a repetitive predictive controller to obtain the extracted harmonics. The gain module is used to multiply the extracted harmonics by the amplitude gain module to perform harmonic amplitude compensation and obtain the optimized harmonics. The distortion reduction module is used to subtract the optimized harmonics from the original voltage or current data to obtain fault data, thereby reducing the distortion rate of the data used for fault type determination. The traveling wave decoupling and phase mode transformation module is used to transform fault data into independent moduli through coordinate transformation; The cable insulation fault type determination module is used to determine the cable insulation fault type based on the mutually independent moduli; and to determine the time when the traveling wave at the fault point arrives at the detection point by detecting the wavefront of the traveling wave at the fault point through wavelet transform. The fault distance calculation module is used to determine the time of the modulus maxima obtained by wavelet transform decomposition based on the time when the traveling wave at the fault point arrives at the detection point, and calculate the fault distance based on the traveling wave method.

Images