A method and system for distinguishing ferromagnetic resonance and arc high-resistance grounding faults in transmission lines

Abstract

The present invention proposes a method for distinguishing between ferromagnetic resonance and arc high-resistance grounding faults in transmission lines. The method extracts the impedance properties of the ground branch for identification. The power frequency ferromagnetic resonance is biased towards the inductive property of the ground branch, while the arc high-resistance grounding fault is biased towards the resistive property of the ground branch. There is a significant difference between the two, and the method can accurately distinguish between ferromagnetic resonance faults and arc high-resistance grounding faults.

Description

Technical Field

[0001] The present invention belongs to the field related to power system distribution line protection, and in particular relates to a method and system for distinguishing ferromagnetic resonance and arc high-resistance grounding faults of transmission lines. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] In recent years, the integration of large numbers of distributed power sources and the construction and application of AC / DC hybrid power grids have led to the increasing scale of traditional AC transmission lines. To ensure the safe operation of power systems, frequent switching and maintenance of transmission lines can easily induce single-phase series ferroresonance in neutral-grounded systems. The resulting overvoltage and overcurrent can easily degrade the insulation of power equipment, leading to serious accidents such as explosions, seriously threatening the safety of the power system and personnel.

[0004] Similar nonlinear faults or disturbances also exist in actual system operation, such as arc-flash high-resistance grounding faults. The significant nonlinear characteristics of arcs cause the phase voltage waveform in transmission lines to exhibit rectangular waveform distortion, with spectral characteristics of high-frequency harmonics. Furthermore, when the arc burns stably, the voltage and current exhibit power frequency periodic characteristics, similar to the time-frequency characteristics of power frequency ferromagnetic resonance in a neutral-grounded system. This makes it difficult for relay protection devices to quickly identify power frequency ferromagnetic resonance and arc-flash high-resistance grounding faults.

[0005] Due to the high frequency of ferromagnetic resonance and arc-flash high-resistance grounding faults, which pose a high risk to power systems, scholars at home and abroad have conducted extensive research on this topic. Ferromagnetic resonance detection can be divided into detection methods that extract feature quantities from the time domain and the frequency domain. Ferromagnetic resonance has a variety of characteristic modes, making it difficult to ensure the reliability of the detection method. Furthermore, due to the influence of the transformer's nonlinear excitation characteristics, the differential state equation cannot obtain a complete time-domain analytical solution, making it difficult to set the detection threshold. For arc-flash high-resistance grounding fault detection, methods such as the concavity method and the harmonic method have been proposed from the time and frequency domain perspectives. However, these methods rely heavily on accurate modeling of arc distortion characteristics. However, all of these studies focus on a single disturbance or fault, while in actual power grids, both disturbances often occur one after another, and existing methods are at risk of failure. Summary of the Invention

[0006] In order to overcome the deficiencies of the above-mentioned prior art, the present invention provides a method and system for distinguishing between ferromagnetic resonance and arc high-resistance grounding faults in transmission lines. By extracting the impedance properties of the ground branch for identification, the power frequency ferromagnetic resonance is biased towards the inductive nature of the ground branch, while the arc high-resistance grounding fault is biased towards the resistive nature of the ground branch impedance. There is an obvious difference between the two, and the method and system can accurately identify whether a ferromagnetic resonance fault or an arc high-resistance grounding fault has occurred.

[0007] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions: a method for distinguishing between ferromagnetic resonance and arc high-resistance grounding faults in a transmission line, comprising:

[0008] Step 1: Real-time acquisition of phase voltage and phase current within the power frequency cycle of the transmission line grounding system and Fourier transform of each are performed to obtain the total harmonic distortion rate of the phase voltage and phase current. If the total harmonic distortion rate exceeds the set threshold, it is preliminarily determined to be a ferroresonance or arc high-resistance grounding fault.

[0009] Step 2: After filtering the collected phase voltage and phase current, a normalized volt-ampere characteristic curve is drawn. Based on whether the characteristic angle of the normalized volt-ampere characteristic curve exceeds the threshold angle, it is determined whether a ferroresonance fault or an arc high-resistance grounding fault has occurred.

[0010] Furthermore, in step 1, specifically:

[0011] Calculate the effective value of the phase current collected in each power frequency cycle. If the calculated current effective value is greater than the preset current value, it is marked as the starting point of the power frequency cycle;

[0012] Fourier transform is performed on the phase voltage and phase current in the power frequency cycle after the starting point of the power frequency cycle to calculate the total harmonic distortion rate of the phase voltage and the total harmonic distortion rate of the phase current.

[0013] Furthermore, in step 1: when the total harmonic distortion rate exceeds the set threshold, and the voltage power frequency component amplitude is the highest, followed by the high-frequency harmonic amplitude, it is preliminarily determined that ferromagnetic resonance or arc high-resistance grounding fault has occurred.

[0014] Furthermore, in step 2, a Chebyshev filter is used to perform low-pass filtering on the collected phase voltage and phase current.

[0015] Furthermore, in step 2, determining whether a ferromagnetic resonance fault or an arc high-resistance grounding fault occurs based on whether a characteristic angle of the normalized volt-ampere characteristic curve exceeds a preset value specifically includes:

[0016] Draw a volt-ampere characteristic curve based on the phase voltage and phase current measured in real time;

[0017] Based on the first vector formed by the maximum phase voltage point and the origin in each power frequency cycle on the volt-ampere characteristic curve, the second vector formed by the maximum phase current point and the origin, and the characteristic angle of the normalized volt-ampere characteristic curve formed by the first vector and the second vector, it is determined whether it is a ferromagnetic resonance fault or an arc high-resistance grounding fault based on whether the characteristic angle of the normalized volt-ampere characteristic curve exceeds the threshold angle.

[0018] Furthermore, the threshold angle is set to 45 degrees. If the characteristic angle of the normalized volt-ampere characteristic curve exceeds 45 degrees, it is determined to be power frequency ferromagnetic resonance; if the characteristic angle of the normalized volt-ampere characteristic curve does not exceed 45 degrees, it is determined to be an arc high-resistance grounding fault.

[0019] A second aspect of the present invention provides a system for distinguishing between ferromagnetic resonance and arc high-resistance grounding faults in transmission lines, comprising:

[0020] Preliminary determination module: This module is configured to: collect phase voltage and phase current in the power frequency cycle of the transmission line grounding system in real time and perform Fourier transform on them respectively to obtain the total harmonic distortion rate of the phase voltage and phase current. If the total harmonic distortion rate exceeds the set threshold, it is preliminarily determined to be a ferromagnetic resonance or arc high-resistance grounding fault;

[0021] The identification module is configured to: draw a normalized volt-ampere characteristic curve after filtering the collected phase voltage and phase current, and distinguish whether a ferromagnetic resonance fault or an arc high-resistance grounding fault occurs based on whether a characteristic angle of the normalized volt-ampere characteristic curve exceeds a threshold angle.

[0022] A third aspect of the present invention provides a computer-readable storage medium.

[0023] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the method for distinguishing between ferromagnetic resonance and arc high-resistance grounding faults of a transmission line as described above.

[0024] A fourth aspect of the present invention provides a computer device.

[0025] A computer device includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, the steps of the method for distinguishing between ferromagnetic resonance and arc high-resistance grounding faults in a transmission line as described above are implemented.

[0026] One or more of the above technical solutions have the following beneficial effects:

[0027] The present invention overcomes the defect that the periodic characteristics of power-frequency ferromagnetic resonance and arc-light high-resistance grounding fault with nonlinear characteristics are similar to the frequency domain characteristics and cannot be accurately identified. The identification is carried out by extracting the impedance properties of the ground branch. The power-frequency ferromagnetic resonance is more inductive to the ground branch, while the arc-light high-resistance grounding fault is more resistive to the ground branch impedance. The two have obvious differences, and the filtering link can greatly reduce the interference effect of noise, so that the identification method has higher reliability and sensitivity.

[0028] Advantages of additional aspects of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0030] Figure 1 It is a simulation topology diagram of the power transmission line in the present invention;

[0031] Figure 2 (a) is a schematic diagram of the normalized volt-ampere characteristic curve of the power frequency ferromagnetic resonance of the simulation data in the present invention;

[0032] Figure 2 (b) is a schematic diagram of the normalized volt-ampere characteristic curve of the arc high-resistance grounding simulation data in the present invention;

[0033] Figure 3 This is a schematic diagram of impedance differences in the volt-ampere characteristic curve of simulation data in the present invention;

[0034] Figure 4 It is the normalized volt-ampere characteristic curve of the measured arc high-resistance grounding fault. DETAILED DESCRIPTION

[0035] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0036] It should be noted that the terms used herein are for describing particular embodiments only and are not intended to limit the exemplary embodiments according to the present invention.

[0037] In the absence of conflict, the embodiments of the present invention and the features thereof may be combined with each other.

[0038] The overall idea proposed by the present invention is as follows: In view of the difference between the impedance characteristics of the ground branch caused by ferromagnetic resonance and arc high-resistance grounding fault, the present invention proposes a method for distinguishing the characteristics of the normalized volt-ampere characteristic curve composed of phase voltage and phase current. The impedance of the ground branch caused by ferromagnetic resonance is more inductive, while the impedance of the ground branch caused by arc high-resistance grounding fault is more resistive. There is an obvious difference between the two, and it is possible to accurately distinguish whether it is a ferromagnetic resonance fault or an arc high-resistance grounding fault.

[0039] Example 1

[0040] This embodiment discloses a method for distinguishing between ferromagnetic resonance and arc high-resistance grounding faults in a transmission line, including:

[0041] Step 1: Real-time acquisition of phase voltage and phase current within the power frequency cycle of the transmission line grounding system and Fourier transform of each are performed to obtain the total harmonic distortion rate of the phase voltage and phase current. If the total harmonic distortion rate exceeds the set threshold, it is preliminarily determined to be a ferroresonance or arc high-resistance grounding fault.

[0042] Step 2: After filtering the collected phase voltage and phase current, a normalized volt-ampere characteristic curve is drawn. Based on whether the characteristic angle of the normalized volt-ampere characteristic curve exceeds the threshold angle, it is determined whether a ferroresonance fault or an arc high-resistance grounding fault has occurred.

[0043] The present invention uses a mutual inductor to collect phase voltage and phase current signals in real time, draws a normalized volt-ampere characteristic curve, and extracts impedance characteristics to distinguish between a ferromagnetic resonance fault and an arc high-resistance grounding fault.

[0044] In step 1, the phase voltage u and phase current i are continuously sampled, and the effective value I of the phase current in each power frequency cycle is calculated. When I>I set When , it marks the starting point of the power frequency cycle of the overcurrent. set The value is taken as 120% to 140% of the rated current. The effective value of the current I is calculated as follows:

[0045]

[0046] Where ΔT is the sampling time interval, i m is the instantaneous value of the current sampling at the mth time interval within the power frequency cycle, and S is the number of samples in one power frequency cycle.

[0047] Perform Fourier transform on the phase voltage and phase current within the power frequency cycle after the starting point, and calculate the total harmonic distortion rate THD of the phase voltage and phase current respectively. If the total harmonic distortion rate THD of the phase voltage or phase current is greater than THDset, it is suspected that a ferromagnetic resonance or arc high-resistance grounding fault has occurred. set To set the threshold, the THDset value should be higher than the harmonic distortion during normal operation and lower than the minimum harmonic distortion rate of an arc high-resistance grounding fault. The harmonic distortion of a transmission line during normal operation is less than 3%. Statistics show that the minimum harmonic distortion rate of the phase current of an arc high-resistance grounding fault is 5.3%. Therefore, the THDset value should be between 3 and 5%.

[0048] Furthermore, if the amplitude of the power frequency component of the voltage is the highest, followed by the amplitude of the high-frequency harmonics, it is preliminarily determined that a ferromagnetic resonance fault or an arc high-resistance grounding fault has occurred.

[0049] The calculation formula for the total harmonic distortion rate THD of the phase voltage is:

[0050]

[0051] Among them, U1 is the voltage fundamental amplitude, U2, U3...U n are the amplitudes of the voltage harmonics respectively. Similarly, the total harmonic distortion rate of the phase current can be calculated.

[0052] In step 2, a Chebyshev filter is used to perform low-pass filtering on the phase voltage and phase current data, with a cutoff frequency of 2000 Hz.

[0053] Draw the volt-ampere characteristic curve in a two-dimensional plane for the filtered phase voltage and phase current, and connect the maximum phase voltage point P1 and the maximum phase current point P2 in the power frequency cycle with the origin O to form two vectors The angle formed by the two vectors constitutes the characteristic angle θ of the normalized volt-ampere characteristic curve, and the threshold angle is set to θ set , if θ>θ set , it is determined that the power frequency ferromagnetic resonance occurs, if not, it is determined that the arc high resistance grounding fault occurs. set Set to 45 degrees, the calculation formula for θ is:

[0054]

[0055] The method further includes step 3: performing total harmonic distortion detection on the phase voltage and phase current of the next power frequency cycle. If the total harmonic distortion rate determination method in step 1 is not satisfied, the method ends; otherwise, the phase voltage and phase current signals of the next power frequency cycle are subjected to cyclic identification using the method in step 2.

[0056] like Figure 1 As shown, a method for identifying power frequency ferromagnetic resonance and arc high-resistance grounding faults in a transmission line in this embodiment uses power frequency ferromagnetic resonance and arc high-resistance grounding fault simulation data generated in a 110kV neutral point direct grounding system, and applies the above-mentioned method to the simulation data for identification.

[0057] The above-mentioned method for identifying power frequency ferromagnetic resonance and arc high-resistance grounding faults of transmission lines is verified by using simulation data and actual recording data. The normalized volt-ampere characteristic curve characteristics extracted from the simulation data and actual recording data are as follows: Figure 2 and Figure 3 As shown, it can be seen that the power frequency ferromagnetic resonance and arc high-resistance grounding fault impedance characteristics of the method proposed in the present invention have obvious identifiability, which can ensure the reliability of the identification method. At the same time, the filtering link in the identification method greatly increases the sensitivity to noise.

[0058] Example 2

[0059] This embodiment provides a system for distinguishing between ferromagnetic resonance and arc high-resistance grounding faults in transmission lines, including:

[0060] Preliminary determination module: This module is configured to: collect phase voltage and phase current in the power frequency cycle of the transmission line grounding system in real time and perform Fourier transform on them respectively to obtain the total harmonic distortion rate of the phase voltage and phase current. If the total harmonic distortion rate exceeds the set threshold, it is preliminarily determined to be a ferromagnetic resonance or arc high-resistance grounding fault;

[0061] The identification module is configured to: draw a normalized volt-ampere characteristic curve after filtering the collected phase voltage and phase current, and distinguish whether a ferromagnetic resonance fault or an arc high-resistance grounding fault occurs based on whether a characteristic angle of the normalized volt-ampere characteristic curve exceeds a threshold angle.

[0062] Example 3

[0063] The purpose of this embodiment is to provide a computer-readable storage medium.

[0064] A computer-readable storage medium stores a computer program, which executes the steps of the above method when executed by a processor.

[0065] Example 4

[0066] The purpose of this embodiment is to provide a computing device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the above method when executing the program.

[0067] The steps involved in the above embodiments 2, 3, and 4 correspond to those in embodiment 1. For detailed implementation, please refer to the relevant description of embodiment 1. The term "computer-readable storage medium" should be understood to mean a single medium or multiple media that includes one or more instruction sets; it should also be understood to include any medium that can store, encode, or carry an instruction set for execution by a processor and cause the processor to perform any method of the present invention.

[0068] Those skilled in the art will appreciate that the modules or steps of the present invention described above can be implemented using a general-purpose computer device. Alternatively, they can be implemented using program code executable by a computing device, which can then be stored in a storage device and executed by the computing device. Alternatively, they can be fabricated into separate integrated circuit modules, or multiple modules or steps can be fabricated into a single integrated circuit module for implementation. The present invention is not limited to any specific combination of hardware and software.

[0069] Although the above describes the specific embodiments of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without any creative work are still within the scope of protection of the present invention.

Claims

1. A method for distinguishing ferromagnetic resonance and arc high-resistance grounding faults in transmission lines, characterized by: include: Step 1: Real-time acquisition of phase voltage and phase current within the power frequency cycle of the transmission line grounding system and Fourier transform of each are performed to obtain the total harmonic distortion rate of the phase voltage and phase current. If the total harmonic distortion rate exceeds the set threshold, it is preliminarily determined to be a ferroresonance or arc high-resistance grounding fault. Step 2: After filtering the collected phase voltage and phase current, a normalized volt-ampere characteristic curve is plotted. Based on whether the characteristic angle of the normalized volt-ampere characteristic curve exceeds a threshold angle, a ferroresonance fault or an arc high-resistance grounding fault is determined. In step 2, determining whether a ferromagnetic resonance fault or an arc high-resistance grounding fault occurs based on whether a characteristic angle of the normalized volt-ampere characteristic curve exceeds a preset value specifically includes: Draw a volt-ampere characteristic curve based on the phase voltage and phase current measured in real time; Based on the first vector formed by the maximum phase voltage point and the origin in each power frequency cycle on the volt-ampere characteristic curve, and the second vector formed by the maximum phase current point and the origin, and the characteristic angle of the normalized volt-ampere characteristic curve formed by the first vector and the second vector, it is determined whether it is a ferromagnetic resonance fault or an arc high-resistance grounding fault based on whether the characteristic angle of the normalized volt-ampere characteristic curve exceeds a threshold angle; The threshold angle is set to 45 degrees. If the characteristic angle of the normalized volt-ampere characteristic curve exceeds 45 degrees, it is determined to be power frequency ferromagnetic resonance; if the characteristic angle of the normalized volt-ampere characteristic curve does not exceed 45 degrees, it is determined to be an arc high-resistance grounding fault.

2. A method for distinguishing between ferromagnetic resonance and arc high-resistance grounding faults in a transmission line as claimed in claim 1, characterized in that The specific steps in step 1 are: Calculate the effective value of the phase current collected in each power frequency cycle. If the calculated current effective value is greater than the preset current value, it is marked as the starting point of the power frequency cycle; Fourier transform is performed on the phase voltage and phase current in the power frequency cycle after the starting point of the power frequency cycle to calculate the total harmonic distortion rate of the phase voltage and the total harmonic distortion rate of the phase current.

3. A method for distinguishing between ferromagnetic resonance and arc high-resistance grounding faults in a transmission line as claimed in claim 1, characterized in that In step 1: When the total harmonic distortion rate exceeds the set threshold, and the voltage power frequency component amplitude is the highest, followed by the high-frequency harmonic amplitude, it is preliminarily determined that a ferromagnetic resonance or arc high-resistance grounding fault has occurred.

4. A method for distinguishing between ferromagnetic resonance and arc high-resistance grounding faults in a transmission line as claimed in claim 1, characterized in that: In step 2, a Chebyshev filter is used to perform low-pass filtering on the collected phase voltage and phase current.

5. A system for distinguishing between ferromagnetic resonance and arc high-resistance grounding faults in a transmission line, based on a method for distinguishing between ferromagnetic resonance and arc high-resistance grounding faults in a transmission line according to any one of claims 1 to 4, characterized in that: include: Preliminary determination module: This module is configured to: collect phase voltage and phase current in the power frequency cycle of the transmission line grounding system in real time and perform Fourier transform on them respectively to obtain the total harmonic distortion rate of the phase voltage and phase current. If the total harmonic distortion rate exceeds the set threshold, it is preliminarily determined to be a ferromagnetic resonance or arc high-resistance grounding fault; The identification module is configured to: draw a normalized volt-ampere characteristic curve after filtering the collected phase voltage and phase current, and distinguish whether a ferromagnetic resonance fault or an arc high-resistance grounding fault occurs based on whether a characteristic angle of the normalized volt-ampere characteristic curve exceeds a threshold angle.

6. A transmission line ferromagnetic resonance and arc high-resistance grounding fault identification system as claimed in claim 5, characterized in that In the identification module, a volt-ampere characteristic curve is drawn based on the phase voltage and phase current measured in real time; Based on the first vector formed by the maximum phase voltage point and the origin in each power frequency cycle on the volt-ampere characteristic curve, the second vector formed by the maximum phase current point and the origin, and the characteristic angle of the normalized volt-ampere characteristic curve formed by the first vector and the second vector, it is determined whether it is a ferromagnetic resonance fault or an arc high-resistance grounding fault based on whether the characteristic angle of the normalized volt-ampere characteristic curve exceeds the threshold angle.

7. A computer-readable medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the method for distinguishing between ferromagnetic resonance and arc high-resistance grounding faults in a transmission line as claimed in claims 1 to 4 are implemented.

8. A computer device comprising a processor, a memory, and a computer program stored in the memory and capable of running on the processor, characterized in that: When the processor executes the program, the steps of the method for distinguishing between ferromagnetic resonance and arc high-resistance grounding faults in a transmission line as claimed in any one of claims 1 to 4 are implemented.

Images