A power distribution network fault locating method based on inter-harmonic injection

Abstract

The application discloses a power distribution network fault positioning method based on inter-harmonic injection, and relates to the technical field of power system distribution network relay protection. When an asymmetric grounding fault occurs in a power distribution network, signal injection devices arranged on each feeder inject inter-harmonic signals with different harmonic frequencies into the power distribution network at the same time, a multi-source detection signal network with spatial distribution and different frequencies is formed, a significant energy gathering effect is formed at a fault point, the excellent time-frequency analysis capability of S transform on non-stationary signals is utilized, S transform energy of three-phase first ends of each feeder under each inter-harmonic signal is directly extracted for fault positioning. The method enhances fault characteristics through multi-source and multi-frequency inter-harmonic injection, and in combination with the time-frequency resolution and characteristic extraction capability of S transform, the method can realize grounding fault detection in different penetration rate scenes in an active power distribution network, realize fast fault positioning, and improve the protection sensitivity and fault positioning efficiency of the active power distribution network.

Description

Technical Field

[0001] This application relates to the field of power system distribution network relay protection technology, and in particular to a distribution network fault location method based on interharmonic injection. Background Technology

[0002] Traditional distribution network protection primarily employs a three-stage current protection scheme, whose core design is based on two fundamental assumptions: first, the network structure is radial; and second, the power flow direction is unidirectional, always flowing from the substation to the load end. Under these premises, three-stage current protection can achieve effective fault detection and isolation at a relatively low cost. However, with the large-scale integration of distributed generation (DG), these assumptions are gradually being altered. The introduction of DG, especially inverter-type DG, has transformed the traditional distribution network from a passive network with unidirectional power supply to an active network with bidirectional power flow. When the DG penetration rate exceeds 30%, the malfunction rate of traditional current protection will significantly increase. This is because: the output current of inverter-type DG is affected by the current-limiting control of power electronic devices, and its output fault current amplitude is typically only 1.2 to 2 times the rated current, far lower than the short-circuit current level of traditional synchronous power sources; simultaneously, the complex harmonic environment in the distribution network interferes with the accurate extraction of fault characteristics; furthermore, the emergence of bidirectional power flow renders the original protection logic based on unidirectional discrimination ineffective.

[0003] To address these challenges, existing technologies have proposed various improvement schemes, mainly including the following categories: first, improving traditional current protection, such as blocking protection based on the change in fault current phase angle; second, introducing directional elements, such as dual-setting directional overcurrent protection; and third, adopting communication-assisted protection schemes, such as protection systems based on the wireless token ring network protocol. However, these passive protection methods all rely on the natural response of electrical quantities after a fault, which has inherent limitations. Among them, the steady-state method is easily affected by the arc suppression coil and transition resistance, resulting in insufficient sensitivity; although the transient method has a large fault characteristic amplitude, the transient process has a short duration, making feature extraction difficult and limiting its practicality.

[0004] Against this backdrop, active detection protection technology has attracted widespread attention due to its ability to proactively enhance fault characteristics. This technology improves the identifiability of fault characteristics by actively injecting specific signals (such as harmonics or probe pulses) into the power electronic converter after a fault occurs. Typical solutions include harmonic injection and differential protection based on probe signal injection. However, applying active detection protection to modern distribution networks with complex topologies, numerous branches, dispersed distributed power source access locations, and variable distributed power source penetration rates still faces many challenges. Especially in active distribution networks with high-resistance grounding, the weak and easily interfered fault characteristic signals lead to insufficient protection sensitivity and difficulties in fault location. Summary of the Invention

[0005] This application addresses the aforementioned problems and technical requirements by proposing a fault location method for distribution networks based on interharmonic injection. The technical solution of this application is as follows:

[0006] A method for fault location in distribution networks based on interharmonic injection, the method comprising: When an asymmetrical grounding fault is determined to have occurred in the distribution network, the multiple feeders deployed in the distribution network are utilized. Simultaneously, one signal injection device injects interharmonic signals into the distribution network. Each signal injection device is deployed in On different feeder lines, The interharmonic frequencies of the interharmonic signals injected by each signal injection device are all different, and the integer parameters are... ; By using detection devices deployed at the beginning of each feeder in the distribution network to synchronously acquire the current response signal after the injection of interharmonic signals, the S-transform spectrum of the acquired current response signal is calculated to determine the three-phase current response at the beginning of each feeder in the distribution network. S-transform energy under inter-harmonic signals; According to the three phases at the beginning of each feeder The distribution characteristics of S-transform energy under inter-harmonic signals determine the faulty feeder and faulty phase in the distribution network where asymmetrical grounding faults occur.

[0007] A further technical solution is that the power distribution network fault location method also includes: The current response signal after the injection of interharmonic signals is synchronously acquired using detection devices deployed at the line detection nodes at both ends of each section of each feeder. The S-transform spectrum of the acquired current response signal is calculated to determine the three-phase current response of each feeder in the distribution network. S-transform energy at each line detection node under inter-harmonic signals; After locating the faulty feeder and the faulty phase, based on the faulty phase of the faulty feeder... The S-transform energy at each line detection node under inter-harmonic signals is used to locate the fault section in the faulty phase of the faulty feeder where an asymmetrical grounding fault occurs.

[0008] A further technical solution is to locate the faulty section in the faulty phase of the faulty feeder where an asymmetrical grounding fault occurs, including: The difference in S-transform energy at each line detection node is calculated under the interharmonic signal injected on other feeders for the faulty phase of the faulty feeder. This difference is used as the energy difference between the current two line detection nodes, and the section with the largest energy difference is determined as the faulty section.

[0009] A further technical solution involves identifying the faulty feeder and faulty phase in the distribution network where an asymmetrical grounding fault occurs, including any feeder in the distribution network. : When in the feeder Injecting interharmonic signals At that time, according to the feeder Three-phase interharmonic signals at the beginning Other interharmonic signals The distribution of S-transform energy on the feeder Fault detection is performed on the first three phases; integer parameters Integer parameters and , This is the total number of feeders included in the distribution network; When not in the feeder When injecting interharmonic signals, according to the feeder S-transform energy of the first three phases under arbitrary interharmonic signals combined with energy threshold For feeder Fault detection is performed on the first three phases.

[0010] Its further technical solution is, based on the feeder Three-phase interharmonic signals at the beginning Other interharmonic signals The distribution of S-transform energy on the feeder Fault detection of the first three phases includes: When the feeder Head Interphase harmonic signals The S-transform energy under these conditions is greater than that of the feeder. Head Phase of other interharmonic signals When determining the S-transform energy, the feeder is... Head The phases satisfy the phase equilibrium condition. They represent the feeders respectively Three phases; When the feeder When at least one phase at the head end does not meet the in-phase balance condition, determine the feeder. For the faulty feeder, and according to the feeder Three-phase interharmonic signals at the beginning The distribution of S-transform energy under the condition determines the feeder. The faulty phase in which a ground fault occurs; When the feeder When all three phases at the beginning meet the phase balance condition, determine the feeder. No asymmetrical grounding fault occurred.

[0011] Its further technical solution is, based on the feeder Three-phase interharmonic signals at the beginning The distribution of S-transform energy under the condition determines the feeder. The faulty phases that experience grounding faults include: Using feeders Three-phase interharmonic signals at the beginning Calculate the S-transform energy respectively Phase dispersion coefficients , It is a feeder Head Phase harmonic frequency is Interharmonic signals S-transform energy under the following conditions This indicates taking the minimum value; Determine the discrete coefficients The phase is the feeder The faulty phase that experiences a ground fault. It is the threshold of the discrete coefficients.

[0012] Its further technical solution is, based on the feeder S-transform energy of the first three phases under arbitrary interharmonic signals combined with energy threshold For feeder Fault detection of the first three phases includes: When the feeder At least one phase has an interharmonic signal at the beginning. The S-transform energy is greater than the energy threshold. And much larger than the feeder Other phases at the beginning of the interharmonic signal When determining the S-transform energy, the feeder is... The faulty feeder was identified, and the S-transform energy was determined to be greater than the energy threshold. And the phase with a much higher S-transform energy than other phases is the feeder. The faulty phase that experienced a ground fault; otherwise, determine the feeder. No asymmetrical grounding fault occurred; integer parameters .

[0013] The further technical solution is that the harmonic frequency of the interharmonic signal injected by each signal injection device is less than the resonant frequency of the filter circuit at the output of the signal injection device, and much greater than the fundamental frequency; the harmonic frequency of the interharmonic signal is different from the power frequency, integer multiples of the power frequency, and the inherent background harmonic frequency of the distribution network.

[0014] A further technical solution is that the distribution network fault location method also includes: When multiple signal injection devices are deployed on a feeder, the highest priority signal injection device deployed on the current feeder is used to inject interharmonic signals into the distribution network.

[0015] A further technical solution is that the power distribution network fault location method also includes: Zero-sequence current transformers deployed at the beginning of each feeder are used to detect the real-time zero-sequence current at the beginning of each feeder. If the real-time zero-sequence current at the beginning of at least one feeder exceeds the zero-sequence current over-limit threshold, the system will detect the over-limit. At that time, it was determined that an asymmetrical grounding fault had occurred in the distribution network.

[0016] The beneficial technical effects of this application are: This application discloses a distribution network fault location method based on interharmonic injection. This method employs a multi-source, multi-frequency collaborative injection mechanism. When an asymmetrical grounding fault occurs in the distribution network, signal injection devices deployed on each feeder simultaneously inject interharmonic signals of different harmonic frequencies into the distribution network, forming a spatially distributed, frequency-differentiated multi-source detection signal network. This mechanism fundamentally changes the traditional passive fault characteristic mode of protection, creating a significant energy accumulation effect at the fault point. Furthermore, utilizing the excellent time-frequency analysis capability of S-transform for non-stationary signals, the S-transform energy of the three phases at the beginning of each feeder under each interharmonic signal is directly extracted. The fault is located based on the S-transform energy distribution characteristics. This method enhances fault characteristics through multi-source, multi-frequency interharmonic injection. Combined with the time-frequency resolution and feature extraction capability of S-transform, it can achieve grounding fault detection in active distribution networks under different penetration scenarios, enabling rapid fault location and improving protection sensitivity and fault location efficiency in active distribution networks.

[0017] This method locates the faulty section by comparing the relative magnitudes of the S-transform energy between adjacent detection points on the faulty feeder. It only requires comparing the relative magnitudes of the S-transform energy, has low requirements for the synchronization accuracy between detection devices, does not require precise line parameters, and has strong robustness and field adaptability. It fundamentally breaks through the dependence of traditional ranging methods on high-precision synchronization.

[0018] This method addresses the practical engineering problem in active distribution networks where some feeders are connected to inverter-type distributed power sources and others are purely load feeders. The electrical characteristics of faults in these two types of feeders differ fundamentally, and traditional single-criteria methods are insufficient to address both. A differentiated fault selection criterion system is proposed: For feeders containing grid-connected inverters, an energy imbalance criterion is constructed based on the energy distribution difference between the injected signal from this feeder and the injected signal from other feeders. For feeders without grid-connected inverters, fault identification is performed using the energy threshold of the injected signal from other feeders. This system achieves unified fault selection for feeders with different configurations, making the invention applicable to mixed scenarios with arbitrary penetration rates and configurations in active distribution networks, significantly improving the engineering applicability of the technology.

[0019] This method reuses existing power electronic devices with grid-connected inverters in the distribution network as signal injection devices, including but not limited to inverter-type distributed power sources, active power filters, static var generators, and energy storage converters, without requiring additional dedicated signal injection equipment. Synchronous startup of each feeder injection device is achieved through a communication network, and a priority selection mechanism is introduced to ensure that at most one device injects a signal per feeder, avoiding signal aliasing caused by simultaneous injection from multiple devices, reducing system modification costs, and demonstrating good engineering applicability. Attached Figure Description

[0020] Figure 1 This is a flowchart of a distribution network fault location method based on interharmonic injection in one embodiment of this application.

[0021] Figure 2 This is a flowchart of a distribution network fault location method based on interharmonic injection in another embodiment of this application.

[0022] Figure 3 This is a simulation model diagram of a typical 10kV active distribution network in one example of this application.

[0023] Figure 4 This is a bus voltage waveform diagram from a simulation example of this application.

[0024] Figure 5 This is a simulation example of the present invention, showing the S-transform energy distribution of phase A of feeder 1 under the 420Hz interharmonic signal S2 at various line detection nodes under different transition resistance values. Detailed Implementation

[0025] The specific embodiments of this application will be further described below with reference to the accompanying drawings.

[0026] This application discloses a method for fault location in distribution networks based on interharmonic injection. Please refer to [reference needed]. Figure 1 The flowchart shown illustrates that the power distribution network fault location method includes: Step S1: Monitor whether an asymmetrical grounding fault has occurred in the distribution network. Continue monitoring if no asymmetrical grounding fault has occurred. When it is determined that an asymmetrical grounding fault has occurred in the distribution network, proceed to step S2.

[0027] In one embodiment, such as Figure 2 As shown in the flowchart, zero-sequence current transformers deployed at the beginning of each feeder are used to detect the real-time zero-sequence current at the beginning of each feeder. When the real-time zero-sequence current at the beginning of at least one feeder exceeds the zero-sequence current over-limit threshold, the system will proceed. At that time, it is determined that an asymmetrical grounding fault has occurred in the distribution network. Zero-sequence current exceeding the limit threshold. Custom settings are typically 0.02 to 0.05 times the system's rated current.

[0028] Step S2: When an asymmetrical grounding fault is determined to have occurred in the distribution network, utilize the multiple feeders deployed in the distribution network... Multiple signal injection devices simultaneously inject interharmonic signals into the distribution network, with integer parameters. .

[0029] The distribution network includes 1 feeder, each feeder contains Three-phase. Signal injection devices are deployed on all or some feeders in the distribution network, that is... After an asymmetrical grounding fault occurs, Each signal injection device synchronously starts injection via a communication network. Inter-harmonic signals, this Each signal injection device is deployed in On different feeder lines.

[0030] In actual power distribution networks, one or more signal injection devices are deployed on a single feeder. For example... Figure 3 In the simulation model diagram of a typical 10kV active distribution network, the distribution network includes three feeders, referred to as feeder 1, feeder 2 and feeder 3 respectively. Signal injection devices are deployed on all three feeders. Signal injection device 1 and signal injection device 2 are deployed on feeder 1, signal injection device 3 and signal injection device 4 are deployed on feeder 2, and signal injection device 5 and signal injection device 6 are deployed on feeder 3.

[0031] At most one signal injection device can be used for interharmonic signal injection on each feeder. When multiple signal injection devices are deployed on a single feeder, one device is selected from these devices to inject the interharmonic signal, while the others remain off. In one embodiment, a signal injection device can be randomly selected to initiate interharmonic signal injection, or priorities can be pre-set for multiple signal injection devices on the same feeder, and the highest-priority device deployed on the current feeder can be used to inject the interharmonic signal into the distribution network.

[0032] in addition, The interharmonic signals injected by each signal injection device have different harmonic frequencies, thus forming multi-harmonic injection. The amplitude of each interharmonic signal is set to be 5% lower than the rated voltage at the grid connection point, and the injection duration is 0.2 seconds. To ensure the harmonic injection effect, the harmonic frequencies of the interharmonic signals injected by each signal injection device must meet the following conditions: less than the resonant frequency of the filter circuit at the output of the signal injection device and much greater than the fundamental frequency, at least greater than 5 times the fundamental frequency. In addition, the harmonic frequencies of the injected interharmonic signals are different from the power frequency, integer multiples of the power frequency, and the inherent background harmonic frequencies of the distribution network.

[0033] For example in Figure 3 In the example, a harmonic signal with a harmonic frequency of 368Hz is injected using a signal injection device 1 deployed on feeder 1, a harmonic signal with a harmonic frequency of 420Hz is injected using a signal injection device 3 deployed on feeder 2, and a harmonic signal with a harmonic frequency of 475Hz is injected using a signal injection device 5 deployed on feeder 3.

[0034] Step S3 involves synchronously acquiring the current response signal after the injection of interharmonic signals using detection devices deployed at the beginning of each feeder in the distribution network. The detection devices at the beginning of each feeder are synchronized to ensure a unified time reference; in one example, the sampling frequency of each detection device is 8kHz.

[0035] exist Figure 3 In the example, the current response signal after the injection of interharmonic signals is simultaneously acquired using the detection devices at the beginning of feeder 1 (CB1), the beginning of feeder 2 (CB4), and the beginning of feeder 3 (CB7).

[0036] Step S4: Calculate the S-transform spectrum of the acquired current response signal to determine the three-phase current at the head end of each feeder in the distribution network. S-transform energy under interharmonic signals.

[0037] The S-transform is a time-frequency analysis tool that combines the advantages of the short-time Fourier transform and wavelet transform, offering both good time-frequency resolution and feature extraction capabilities. It is used to directly analyze the acquired feeder data. Head Phase current response signal S-transform can be used to obtain the current response signal in any harmonic interval. harmonic frequencies Time-frequency domain representation :

[0038]

[0039] in, Indicates time, This is the time shift factor. (Integer parameter) , It represents the total number of feeders included in the distribution network. They represent the feeders respectively Three-phase. Integer parameters Interharmonic signals Indicates injection Any one of the inter-harmonic signals.

[0040] This transformation applies a Gaussian window function to the signal, with the window width varying with the harmonic frequency. Changes, harmonic frequencies At lower frequencies, the window is wider, resulting in higher frequency resolution; harmonic frequencies At higher speeds, the window is narrower, resulting in higher time resolution, thus enabling the simultaneous acquisition of current response signals. Local characteristics in the time and frequency domains. Furthermore, the S-transform directly processes the original current response signal, eliminating the need for complex preprocessing and spectral analysis algorithms, thus simplifying the signal processing flow and improving detection efficiency.

[0041] Then, based on the S-transform results, the feeder can be calculated. Head Phase at harmonic frequency Interharmonic signals The S-transform spectrum under the following conditions is used as energy. That is, for interharmonic signals harmonic frequencies The energy of the component is integrated over the time axis to obtain the result at that harmonic frequency. The total energy below.

[0042] For example in Figure 3 In this process, detection device 1 deployed at the beginning of feeder 1 collects the current response signals of the three phases at the beginning of feeder 1 after the injection of inter-harmonic signals. Simultaneously, detection device 2 deployed at the beginning of feeder 2 collects the current response signals of the three phases at the beginning of feeder 2 after the injection of inter-harmonic signals, and detection device 3 deployed at the beginning of feeder 3 collects the current response signals of the three phases at the beginning of feeder 3 after the injection of inter-harmonic signals. The S-transform spectrum is calculated for each phase at the beginning of each feeder, and the form of the S-transform energy of each phase at the beginning of each feeder under each inter-harmonic signal is shown below:

[0043] Step S5, based on the three phases at the beginning of each feeder... The distribution characteristics of S-transform energy under inter-harmonic signals determine the faulty feeder and faulty phase in the distribution network where asymmetrical grounding faults occur.

[0044] This application utilizes signal injection devices deployed on multiple feeders to simultaneously inject interharmonic signals of different harmonic frequencies, forming a multi-source detection signal network with spatial distribution and varying frequencies. This mechanism creates a significant energy accumulation effect at the fault point. In addition, the time-frequency resolution and feature extraction capability of the S-transform enable reliable detection of fault characteristics even under high-resistance grounding conditions of several thousand ohms.

[0045] And considering when When interharmonic signals are injected only into some feeders of the distribution network, the distribution network actually contains two types of feeders: one type with injected interharmonic signals and the other type of feeder that is a pure load feeder without injected interharmonic signals. The fault electrical characteristics of these two types of feeders are fundamentally different, and traditional single criteria cannot adequately address both practical engineering problems. Therefore, a differentiated line selection criterion system is proposed in one embodiment. For example... Figure 2 As shown, for any feeder in the distribution network First, determine the feeder. Which category does it belong to? (1) When in the feeder Injecting interharmonic signals At that time, when the feeder When an asymmetrical grounding fault occurs, the feeder The ground capacitance of the faulty phase is short-circuited, forming a low-impedance path. Interharmonic signals injected from other feeders will preferentially flow into the ground through the faulty phase, causing the feeder to... The S-transform energy of the faulty phase at the beginning is significantly higher than that of the non-faulty phase. And the feeder... Injected interharmonic signals The current mainly flows through the ground capacitance of the non-faulty phases, resulting in higher energy in the non-faulty phases. Therefore, by comparing the energy distribution of each phase under different interharmonic signals, the faulty line and faulty phase can be accurately identified.

[0046] Based on this, according to the feeder Three-phase interharmonic signals at the beginning Other interharmonic signals The distribution of S-transform energy on the feeder Fault detection is performed on the first three phases. Integer parameters. and That is, interharmonic signals It is a feeder Interharmonic signals injected on other feeders besides these.

[0047] Please refer to Figure 2 First, according to the feeder any of the first ends Interphase harmonic signals Other interharmonic signals Determine the distribution of S-transform energy in the feeder Check if an asymmetrical grounding fault has occurred. When the feeder... Head Interharmonic signals injected into the current feeder The S-transform energy under these conditions is greater than that of the feeder. Head Phase of other interharmonic signals When determining the S-transform energy, the feeder is... Head The phase satisfies the phase equilibrium condition.

[0048] When the feeder When all three phases at the beginning meet the above-mentioned intra-phase balance conditions, the feeder is determined. No asymmetrical grounding fault occurred.

[0049] When the feeder When at least one phase at the head end does not meet the in-phase balance condition, determine the feeder. The feeder is faulty. Continue following the feeder's instructions. Three-phase interharmonic signals at the beginning The distribution of S-transform energy under the condition determines the feeder. The faulty phases that experience grounding faults include: Using feeders Harmonic signals of any one of the three phases at the beginning Calculate the S-transform energy respectively Phase dispersion coefficients .in, It is a feeder Head Phase harmonic frequency is Interharmonic signals S-transform energy under the following conditions This indicates taking the minimum value. Then determine. Phase Discrete Coefficient The phase is the feeder The faulty phase that experiences a grounding fault. It is the discrete coefficient threshold, determined empirically based on high-resistance faults. In rare, somewhat unusual cases, when... The discrete coefficients of the phases are all no greater than the discrete coefficient threshold. At that time, the feeder can be directly determined. A high-resistance grounding fault occurred, with the resistance value exceeding the identifiable range. This embodiment can also be applied to feeders. In the event of a two-phase ground fault, the dispersion coefficient of the two phases will be detected. .

[0050] (2) When not in the feeder When an interharmonic signal is injected onto the feeder, the interharmonic signals injected onto other feeders also follow the same propagation pattern, causing the feeders to... The S-transform energy of the interharmonic signals injected into other feeders detected by the faulty phase at the beginning is significantly higher than that of the non-faulty phase. When the fault occurs in the feeder... When other than the feeders, this feeder The energy distribution detected in each phase is relatively uniform. Therefore, based on the feeder... S-transform energy of the first three phases under arbitrary interharmonic signals combined with energy threshold For feeder Fault detection is performed on the first three phases, including: When the feeder At least one phase harmonic signal exists at the head end in any room. The S-transform energy is greater than the energy threshold. And much larger than the feeder Other phases at the beginning of the interharmonic signal When determining the S-transform energy, the feeder is... The faulty feeder was identified. The S-transform energy was determined to be greater than the energy threshold. And the phase with a much higher S-transform energy than other phases is the feeder. The faulty phase that experienced a ground fault; otherwise, determine the feeder. No asymmetrical grounding fault occurred. When the feeder... When a two-phase ground fault occurs, the feeder will be detected. There are two phase interharmonic signals at the beginning. The S-transform energies under these conditions are all greater than the energy threshold. And it is much larger than the inter-harmonic signal of the other phase. The S-transform energy under these conditions can also detect two faulty phases. For example, when the feeder... When a two-phase ground fault occurs (A and B phases), the feeder... Interharmonic signals of phases A and B at the beginning The S-transform energies under these conditions are all greater than the energy threshold. And much larger than the feeder The first C phase in the interharmonic signal The S-transform energies under these conditions are all greater than the energy threshold. .

[0051] After locating the faulty feeder and faulty phase in the distribution network, the faulty section in the faulty phase of the faulty feeder where an asymmetrical grounding fault occurs can be further located. In this embodiment: In addition to the detection device deployed at the beginning of each feeder, detection devices are also deployed at the line detection nodes at both ends of each section of the feeder. For example... Figure 3 In the example, in addition to deploying detection devices at the beginning of feeders 1, 2, and 3 (CB1, CB4, and CB7), detection devices are also deployed at the line detection nodes CB1', CB2, CB2', CB3, and CB3' of feeder 1, at the line detection nodes CB4', CB5, CB5', CB6, and CB6' of feeder 2, and at the line detection nodes CB7', CB8, CB8', CB9, and CB9' of feeder 3.

[0052] In step S3 above, while simultaneously acquiring the current response signal after the injection of interharmonic signals using the detection devices deployed at the beginning of each feeder in the distribution network, the current response signal after the injection of interharmonic signals is also simultaneously acquired using the detection devices deployed at the line detection nodes at both ends of each section of each feeder. Then, the method in step S4 is followed to acquire the current response signal at each line detection node of each feeder. The S-transform spectrum of the current response signal of each phase is calculated to obtain the three-phase current response of each feeder. The S-transform energy at each line detection node under interharmonic signals.

[0053] After locating the faulty feeder and the faulty phase, based on the faulty phase of the feeder... The S-transform energy at each line detection node under inter-harmonic signals is used to further locate the fault section in the faulty phase of the faulty feeder where an asymmetrical grounding fault occurs.

[0054] When the fault point is located within a certain section, the low impedance path presented by the fault grounding point to interharmonic signals leads to a significant difference in the S-transform energy detected on both sides of the section. The energy is higher at the upstream detection point and lower at the downstream detection point. For non-faulty sections, the signal energy detected at both ends is not significantly different. Therefore, by comparing the energy differences at both ends of each section, the faulty section can be accurately located. This involves calculating the difference in S-transform energy at each line detection node under interharmonic signals injected on other feeders for the faulty phase of the faulty feeder, using this difference as the energy difference between the current two line detection nodes, and determining the section with the largest energy difference as the faulty section. The detection results under different interharmonic signals are similar, allowing for fault section location under any interharmonic signal.

[0055] To verify the effectiveness of the method in this application, Figure 3 Taking the typical 10kV active distribution network simulation model diagram shown below as an example, a simulation instance is constructed. The values ​​of each parameter of the distribution network are defined as shown in Table 1 below, and the threshold of the discrete coefficient is taken. : Table 1 Parameters of the Distribution Network

[0056] In one simulation example, please refer to Figure 4 The bus voltage waveform diagram, in Previously, the power distribution network was operating normally. When a phase A ground fault is injected into feeder 1, a transition resistor is set. Under these fault conditions, the method described in this application is used in... An asymmetrical grounding fault was detected in the distribution network, and 368Hz interharmonic signals were injected sequentially into feeders 1, 2, and 3 using signal injection devices 1, 3, and 5.S 1. 420Hz interharmonic signal S 2 and 475Hz interharmonic signals S 3. After detecting the injected interharmonic signals, the S-transform energy data of each phase at the beginning of the three feeders under each interharmonic signal are shown in Table 2 below: Table 2. S-transformation energy when feeder 1 experiences a phase-A ground fault ( )

[0057] In this simulation example, when fault location is performed according to the method of this application: (1) For feeder 1, the harmonic signal of phase A at the beginning of feeder 1 within this feeder. S The S-transform energy at step 1 is less than that of phase A in the interharmonic signal. S 2 and S The S-transform energy at point 3 indicates that phase A at the beginning of feeder 1 does not meet the phase balance condition. Similarly, it can be determined that phase B at the beginning of feeder 1 meets the phase balance condition, and phase C at the beginning of feeder 1 also meets the phase balance condition. Therefore, it can be determined that feeder 1 has an asymmetrical grounding fault and is a faulty feeder.

[0058] Then, the harmonic signal of the three phases at the beginning of feeder 1 at 420Hz is used. S S-transform energy calculation under 2 The dispersion coefficients of the phases are 40.7, 1.0, and 1.08 respectively, and the dispersion coefficient of phase A is greater than the dispersion coefficient threshold. The dispersion coefficients of phases B and C are less than the dispersion coefficient threshold. It can be determined that feeder 1 is the faulty feeder, and phase A is the faulty phase.

[0059] When using the three-phase harmonic signal at the beginning of feeder 1 at 475Hz... S S-transform energy calculation under 3 The phase dispersion coefficients are 38.02, 1.0, and 1.07 respectively, which shows that the results are the same. It can also be determined that feeder 1 is the faulty feeder and phase A is the faulty phase.

[0060] (2) For feeder 2, the harmonic signal of phase A at the beginning of feeder 2 within this feeder. S The S-transform energy under phase 2 is greater than that of phase A in the interharmonic signal. S 1 and S The S-transform energy at point 3 indicates that phase A at the beginning of feeder 1 meets the phase balance condition. Similarly, it can be determined that phase B at the beginning of feeder 1 also meets the phase balance condition, and phase C at the beginning of feeder 1 also meets the phase balance condition. Therefore, it can be determined that no asymmetrical grounding fault has occurred in feeder 2.

[0061] (3) For feeder 3, the harmonic signal of phase A at the beginning of feeder 3 within this feeder.S The S-transform energy under phase 3 is greater than that of phase A in the interharmonic signal. S 1 and S The S-transformation energy at point 2 indicates that phase A at the beginning of feeder 3 meets the phase balance condition. Similarly, it can be determined that phase B at the beginning of feeder 3 also meets the phase balance condition, and phase C at the beginning of feeder 3 also meets the phase balance condition. Therefore, it can be determined that no asymmetrical grounding fault has occurred in feeder 3.

[0062] As can be seen from this simulation example, the fault location results are consistent with the actual fault injection results, indicating that the method of this application can accurately locate asymmetrical grounding faults.

[0063] To further verify the adaptability of the method in this application under high transition resistance conditions, in another simulation example, a C-phase ground fault is injected into feeder 2, and a transition resistance is set. Under these fault conditions, after detecting an asymmetrical grounding fault in the distribution network according to the method of this application, a 368Hz interharmonic signal is sequentially injected into feeder 1, feeder 2, and feeder 3 using signal injection devices 1, 3, and 5. S 1. 420Hz interharmonic signal S 2 and 475Hz interharmonic signals S 3. The S-transform energy data of each phase at the beginning of the three feeders under each interharmonic signal after the injection of interharmonic signals are detected are shown in Table 3 below: Table 3. S-transformation energy when feeder 2 experiences a phase-C ground fault ( )

[0064] In this simulation example, when fault location is performed according to the method of this application: (1) For feeder 1, it can be detected that phases A, B and C at the beginning of feeder 1 all meet the phase balance condition, thus it can be determined that no asymmetrical grounding fault has occurred in feeder 1.

[0065] (2) For feeder 2, it can be detected that phases A and B at the beginning of feeder 2 meet the phase balance condition, but phase C at the beginning of feeder 2 does not meet the phase balance condition. Therefore, it can be determined that feeder 2 is a faulty feeder due to an asymmetrical grounding fault.

[0066] Then, the harmonic signal of the three phases at the beginning of feeder 2 at 368Hz is utilized. S S-transform energy calculation under 1 The dispersion coefficients of the phases are 1.0, 1.0, and 4.32, respectively. The dispersion coefficients of phases A and C are less than the dispersion coefficient threshold. The discrete coefficient of phase C is greater than the discrete coefficient threshold. It can be determined that feeder 2 is a faulty feeder, and phase C is a faulty phase.

[0067] (3) For feeder 3, it can be detected that phases A, B and C at the beginning of feeder 3 all meet the phase balance condition, thus it can be determined that no asymmetrical grounding fault has occurred in feeder 3.

[0068] As can be seen from this simulation example, the fault location results are consistent with the actual fault injection results, proving that the method of this application can also achieve accurate fault location under high transition resistance and has good resistance to transition resistance.

[0069] In another simulation example, a phase-A ground fault is injected into the CB2 and CB2' section of feeder 1, and a transition resistance is applied. Simulation analyses were performed for resistances of 10Ω, 100Ω, 300Ω, 500Ω, 800Ω, and 1000Ω. After determining that feeder 1 was a faulty feeder and phase A was a faulty phase according to the method of this application, different transition resistances were analyzed. Under the given value, the harmonic signal of phase A of feeder 1 at 420Hz S 2. The S-transform energy at each line detection node is as follows Figure 5 As shown. By Figure 5 It can be seen that, by Figure 5 The data shows that in any transition resistance Under the given value, the difference in S-transform energy between line detection node CB2 and line detection node CB2′ is significantly higher than that in other sections. According to the method of this application, the fault section can be accurately located under different transition resistance conditions.

[0070] The above descriptions are merely preferred embodiments of this application, and this application is not limited to the above embodiments. It is understood that other improvements and variations that can be directly derived or conceived by those skilled in the art without departing from the spirit and concept of this application should be considered to be included within the protection scope of this application.

Claims

1. A method for fault location in distribution networks based on interharmonic injection, characterized in that, The power distribution network fault location method includes: When an asymmetrical grounding fault is determined to have occurred in the distribution network, the multiple feeders deployed in the distribution network are utilized. Simultaneously, one signal injection device injects interharmonic signals into the distribution network. Each signal injection device is deployed in On different feeder lines, The interharmonic frequencies of the interharmonic signals injected by each signal injection device are all different, and the integer parameters are... ; By using detection devices deployed at the beginning of each feeder in the distribution network to synchronously acquire the current response signal after the injection of interharmonic signals, the S-transform spectrum of the acquired current response signal is calculated to determine the three-phase current response at the beginning of each feeder in the distribution network. S-transform energy under inter-harmonic signals; According to the three phases at the beginning of each feeder The distribution characteristics of S-transform energy under inter-harmonic signals determine the faulty feeder and faulty phase in the distribution network where asymmetrical grounding faults occur.

2. The method for locating faults in a power distribution network according to claim 1, characterized in that, The power distribution network fault location method also includes: The current response signal after the injection of interharmonic signals is synchronously acquired using detection devices deployed at the line detection nodes at both ends of each section of each feeder. The S-transform spectrum of the acquired current response signal is calculated to determine the three-phase current response of each feeder in the distribution network. S-transform energy at each line detection node under inter-harmonic signals; After locating the faulty feeder and the faulty phase, based on the faulty phase of the faulty feeder... The S-transform energy at each line detection node under inter-harmonic signals is used to locate the fault section in the faulty phase of the faulty feeder where an asymmetrical grounding fault occurs.

3. The method for locating faults in a power distribution network according to claim 2, characterized in that, The fault section in the faulty phase of the faulty feeder where an asymmetrical grounding fault occurs includes: The difference in S-transform energy at each line detection node is calculated under the interharmonic signal injected on other feeders for the faulty phase of the faulty feeder. This difference is used as the energy difference between the current two line detection nodes, and the section with the largest energy difference is determined as the faulty section.

4. The method for locating faults in a power distribution network according to claim 1, characterized in that, Identifying the faulty feeder and faulty phase in a distribution network that experiences an asymmetrical grounding fault includes any feeder in the distribution network. : When in the feeder Injecting interharmonic signals At that time, according to the feeder Three-phase interharmonic signals at the beginning Other interharmonic signals The distribution of S-transform energy on the feeder Fault detection is performed on the first three phases; integer parameters Integer parameters and , This is the total number of feeders included in the distribution network; When not in the feeder When injecting interharmonic signals, according to the feeder S-transform energy of the first three phases under arbitrary interharmonic signals combined with energy threshold For feeder Fault detection is performed on the first three phases.

5. The method for locating faults in a power distribution network according to claim 4, characterized in that, According to the feeder Three-phase interharmonic signals at the beginning Other interharmonic signals The distribution of S-transform energy on the feeder Fault detection of the first three phases includes: When the feeder Head Interphase harmonic signals The S-transform energy under these conditions is greater than that of the feeder. Head Phase of other interharmonic signals When determining the S-transform energy, the feeder is... Head The phases satisfy the phase equilibrium condition. They represent the feeders respectively Three phases; When the feeder When at least one phase at the head end does not meet the in-phase balance condition, determine the feeder. For the faulty feeder, and according to the feeder Three-phase interharmonic signals at the beginning The distribution of S-transform energy under the condition determines the feeder. The faulty phase in which a ground fault occurs; When the feeder When all three phases at the beginning meet the phase balance condition, determine the feeder. No asymmetrical grounding fault occurred.

6. The method for locating faults in a power distribution network according to claim 5, characterized in that, According to the feeder Three-phase interharmonic signals at the beginning The distribution of S-transform energy under the condition determines the feeder. The faulty phases that experience grounding faults include: Using feeders Three-phase interharmonic signals at the beginning Calculate the S-transform energy respectively Phase dispersion coefficients , It is a feeder Head Phase harmonic frequency is Interharmonic signals S-transform energy under the following conditions This indicates taking the minimum value; Determine the discrete coefficients The phase is the feeder The faulty phase that experiences a ground fault. It is the threshold of the discrete coefficients.

7. The method for locating faults in a power distribution network according to claim 4, characterized in that, According to the feeder S-transform energy of the first three phases under arbitrary interharmonic signals combined with energy threshold For feeder Fault detection of the first three phases includes: When the feeder At least one phase has an interharmonic signal at the beginning. The S-transform energy is greater than the energy threshold. And much larger than the feeder Other phases at the beginning of the interharmonic signal When determining the S-transform energy, the feeder is... The faulty feeder was identified, and the S-transform energy was determined to be greater than the energy threshold. And the phase with a much larger S-transform energy than other phases is the feeder. The faulty phase that experienced a ground fault; otherwise, determine the feeder. No asymmetrical grounding fault occurred; integer parameters .

8. The method for locating faults in a power distribution network according to claim 1, characterized in that, The harmonic frequencies of the interharmonic signals injected by each signal injection device are lower than the resonant frequency of the filter circuit at the output of the signal injection device, and much higher than the fundamental frequency; the harmonic frequencies of the interharmonic signals are different from the power frequency, integer multiples of the power frequency, and the inherent background harmonic frequencies of the power distribution network.

9. The method for locating faults in a distribution network according to claim 1, characterized in that, The power distribution network fault location method also includes: When multiple signal injection devices are deployed on a feeder, the highest priority signal injection device deployed on the current feeder is used to inject interharmonic signals into the distribution network.

10. The method for locating faults in a power distribution network according to claim 1, characterized in that, The power distribution network fault location method also includes: Zero-sequence current transformers deployed at the beginning of each feeder are used to detect the real-time zero-sequence current at the beginning of each feeder. If the real-time zero-sequence current at the beginning of at least one feeder exceeds the zero-sequence current over-limit threshold, the system will detect the over-limit. At that time, it was determined that an asymmetrical grounding fault had occurred in the distribution network.

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