Active detection cable fault location method based on controllable current transformer

Abstract

The present invention proposes an active detection cable fault location method based on a controllable converter, comprising: when a fault occurs, controlling the controllable converter to output two sinusoidal voltages of different preset frequencies; obtaining the voltage and current phasors at the head end of the cable line at the two preset frequencies, and using the voltage and current phasors to construct a set of circuit equations from the head end of the cable to the fault point; and solving the set of circuit equations simultaneously to obtain the fault distance from the fault point to the head end of the cable. This method does not require additional pulse injection equipment or communication between the two ends of the cable. It is suitable for metallic faults and high-resistance faults, has strong anti-interference capabilities, and is computationally simple. While ensuring accurate and reliable fault location, it can be implemented based on existing cable configurations, reducing implementation costs.

Description

Technical Field

[0001] The present invention belongs to the technical field of power systems, and in particular relates to an active detection type cable fault location method based on a controllable converter. Background Art

[0002] Compared to overhead lines, cable lines are safer, more reliable, more concealed, and more durable, making them widely used in urban power grids. However, when underground cables fail, fault inspection is extremely difficult. Therefore, developing accurate and reliable fault location solutions is crucial for reducing inspection workload, expediting power supply restoration, and improving power supply reliability.

[0003] Currently, traditional fault location methods are mainly divided into two types: two-end fault location and single-end fault location. Two-end fault location primarily uses the time difference between the traveling wave head reaching the measurement devices at both ends of the transmission line, the length of the transmission line, and the propagation speed of the traveling wave in the cable line to determine the fault distance. As can be seen, the accuracy of this fault location solution relies on high-precision time calibration at both ends of the cable line, resulting in a high implementation cost. Single-end fault location, on the other hand, has high requirements for the sampling environment. Its basic principle is to penetrate the cable fault point with high voltage, use instruments to collect and record the current traveling wave signal generated by the fault point, and use a linear current coupler to collect the current traveling wave signal in the cable. The fault distance is calculated by analyzing the time it takes for the current traveling wave signal to travel between the measurement end and the fault point. However, this method requires a high sampling frequency. Since the reflected pulse from the fault point is often difficult to distinguish from interference during distance measurement, it is sensitive to noise. It also requires additional pulse injection equipment. Therefore, existing fault location solutions still have the disadvantages of high implementation cost and unsatisfactory results. Summary of the Invention

[0004] To address the shortcomings and deficiencies in the existing technologies, and in light of the recent high proportion of renewable energy access and the high proportion of power electronic equipment used in power systems, and considering the increasing number of controllable devices in the system to construct a more accurate and reliable fault location solution, the present invention proposes an active detection cable fault location method based on a controllable converter, comprising:

[0005] When a fault occurs, the controllable converter is controlled to output two sinusoidal voltages with different preset frequencies;

[0006] Obtain the voltage phasors and current phasors generated by sinusoidal voltages of different preset frequencies at the head end of the cable line, and use the voltage phasors and current phasors to construct a circuit equation group from the head end of the cable to the fault point;

[0007] The circuit equations are solved simultaneously to obtain the fault distance from the fault point to the cable head end.

[0008] Optionally, the controllable converter includes a main circuit and a control system, the main circuit is used to realize AC-DC conversion in the cable, and the control system is used to generate control pulses for controlling the AC-DC conversion.

[0009] Optionally, the main circuit includes a rectifier circuit, an inverter circuit, an AC conversion circuit and a DC conversion circuit.

[0010] Optionally, when a fault occurs, controlling the controllable converter to output two sinusoidal voltages with different frequencies includes:

[0011] superimposing an additional control signal on an original basic control signal at an input end of the controllable converter;

[0012] The control system of the controllable converter generates a control pulse according to a superimposed signal generated by the basic control signal and the additional control signal;

[0013] Through the main circuit of the controllable converter, a sinusoidal voltage is generated at the output end of the controllable converter according to the control pulse;

[0014] The sinusoidal voltage generated at the output end is fed back to the input end of the controllable converter in real time, and the additional control signal is adjusted according to the feedback result until two sinusoidal voltages with different preset frequencies are generated at the output end.

[0015] Optionally, obtaining voltage phasors and current phasors generated at the head end of the cable line by sinusoidal voltages of different preset frequencies includes:

[0016] The voltage signal and current signal are collected at the head end of the cable, and the voltage phasor and current phasor corresponding to two preset frequencies are extracted from the voltage signal and current signal based on the Fourier algorithm.

[0017] Optionally, the method of constructing a circuit equation group from the cable head end to the fault point using voltage phasors and current phasors includes:

[0018] At the beginning of the cable, the voltage phasor U of the fault phase at frequency p and frequency q is obtained respectively. pa 、U qa , and the current phasor I of the fault phase at frequency p and frequency q pa , I qa ;

[0019] Establish a circuit equation group for the voltage drop from the cable head end to the fault point, and substitute the measured voltage and current phasors into the circuit equation group to obtain:

[0020]

[0021] Among them, I p0 , I q0are the current phasors of the zero sequence of the line at frequency p and frequency q, respectively, and k pz 、k qz are the zero-sequence compensation coefficients corresponding to frequency p and frequency q, respectively, p 、z q are the line positive sequence impedance at frequency p and frequency q respectively, x is the fault distance to be solved, y1 and y2 are unknown real parameters related to the cable, j represents the imaginary unit, ω p 、ω q are the angular frequencies corresponding to frequency p and frequency q, respectively, R Σ is the total resistance of the cable, L Σ is the total inductive reactance of the cable, R N is the resistance from the fault point to the end of the cable, L N R is the inductive reactance from the fault point to the end of the cable, f is the transition resistance.

[0022] Optionally, the simultaneous solution of the circuit equations to obtain the fault distance from the fault point to the cable head end includes:

[0023] With x, y1, and y2 as unknown real numbers, the circuit equations are transformed into four real linear equations, which are:

[0024]

[0025] Among them, real represents the real part, and imag represents the imaginary part;

[0026] Based on the least squares method, the fault distance x in the real linear equation is solved.

[0027] The beneficial effects brought about by the technical solution provided by the present invention are:

[0028] There is no need for additional pulse injection equipment, nor is there any need for communication at both ends of the cable. It is suitable for metallic faults and high-resistance faults, has strong anti-interference capabilities, and is simple to calculate. While ensuring accurate and reliable fault location, it can achieve fault location based on the existing cable configuration structure, reducing implementation costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solution of the present invention, the following is a brief introduction to the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0030] Figure 1 A schematic flow chart of an active detection cable fault location method based on a controllable converter proposed in an embodiment of the present invention;

[0031] Figure 2 Schematic diagram of the control principle of the controllable converter in an embodiment of the present invention;

[0032] Figure 3 Schematic diagram of the circuit principle at the fault point of the cable in an embodiment of the present invention. DETAILED DESCRIPTION

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0034] The terms "first," "second," "third," "fourth," and so forth (if any) in the description and claims of the present invention and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a particular order or sequential sequence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of the present invention described herein can be implemented in sequences other than those illustrated or described herein.

[0035] It should be understood that in various embodiments of the present invention, the size of the sequence number of each process does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0036] It should be understood that in the present invention, "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or apparatuses.

[0037] It should be understood that in the present invention, "multiple" refers to two or more. "And / or" is only a description of the association relationship of associated objects, indicating that three relationships can exist. For example, and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. The character " / " generally indicates that the previous and next associated objects are in an "or" relationship. "Contains A, B and C", "Contains A, B, C" means that A, B, and C are all included, "Contains A, B or C" means that one of A, B, and C is included, and "Contains A, B and / or C" means that any one, any two, or any three of A, B, and C are included.

[0038] It should be understood that, in the present invention, "B corresponding to A," "B corresponding to A," "A corresponds to B," or "B corresponds to A" means that B is associated with A and B can be determined based on A. Determining B based on A does not mean determining B based solely on A; B can also be determined based on A and / or other information. A and B match when the similarity between A and B is greater than or equal to a preset threshold.

[0039] Depending on the context, "if" as used herein may be interpreted as "when" or "when" or "in response to determining" or "in response to detecting."

[0040] The following specific embodiments are used to describe the technical solution of the present invention in detail. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described in detail in some embodiments.

[0041] Example 1

[0042] like Figure 1 As shown, this embodiment proposes an active detection cable fault location method based on a controllable converter, including:

[0043] S1: When a fault occurs, the controllable converter is controlled to output two sinusoidal voltages with different preset frequencies;

[0044] S2: Obtain the voltage phasors and current phasors generated by sinusoidal voltages of different preset frequencies at the head end of the cable line, and use the voltage phasors and current phasors to construct a circuit equation group from the head end of the cable to the fault point;

[0045] S3: Solve the circuit equations simultaneously to obtain the fault distance from the fault point to the cable head end.

[0046] Traditional fault location solutions can be categorized into single-ended and dual-ended fault location. Dual-ended fault location requires communication between the two terminals and high-precision time alignment, which is costly. Single-ended fault location can be further categorized by the fault location algorithm into traveling wave and fault analysis methods. The traveling wave method requires a high sampling frequency, is sensitive to noise, and requires additional pulse injection equipment, increasing implementation costs. The fault analysis method is simple, economical, and easy to implement, but faces the challenge of insufficient information and difficulty solving high-resistance faults.

[0047] Therefore, in order to address the above drawbacks, this embodiment takes into account the high proportion of renewable energy access and the high proportion of power electronic equipment used in power systems in recent years, and utilizes a large number of controllable converters in cable lines to construct a more accurate and reliable fault location solution.

[0048] In this embodiment, the controllable converter includes a main circuit and a control system. The main circuit is used to achieve AC / DC conversion in the cable and specifically includes a rectifier circuit, an inverter circuit, an AC conversion circuit, and a DC conversion circuit. The control system is used to generate control pulses for controlling the AC / DC conversion and is specifically a closed-loop feedback control system composed of a microprocessor.

[0049] Based on the basic structure of the controllable converter, when a fault occurs, Figure 2 The feedback control principle shown in the figure controls the controllable converter to output two sinusoidal voltages with different frequencies, including:

[0050] superimposing an additional control signal on an original basic control signal at an input end of the controllable converter;

[0051] The control system of the controllable converter generates control pulses based on the superimposed signal generated by the basic control signal and the additional control signal. A sinusoidal voltage is generated at the output of the controllable converter via the main circuit of the controllable converter in response to the control pulses. Specifically, the control pulses are used to control the turning off of switching devices in the main circuit of the controllable converter, thereby generating sinusoidal waves of different waveforms at the output of the main circuit. Specifically, sinusoidal voltages of corresponding frequencies are generated at the output of the controllable converter.

[0052] The sinusoidal voltage generated at the output end is fed back to the input end of the controllable converter in real time, and the additional control signal is adjusted according to the feedback result until two sinusoidal voltages with different preset frequencies are generated at the output end.

[0053] In this embodiment, the two different preset frequencies are 100Hz and 150Hz. The voltage signal and current signal are collected at the head end of the cable. Since there are 100Hz and 200Hz excitation sources in the cable line, that is, controllable converters that generate 100Hz and 150Hz sinusoidal voltages, the measured voltage and current signals will have stable 100Hz and 200Hz components. This embodiment can extract the voltage phasor U corresponding to 100Hz and 200Hz based on the commonly used Fourier algorithm. pa 、U qa and the current phasor I pa , I qa .

[0054] like Figure 3 In the cable route shown, the total impedance of the cable from the beginning to the end is R Σ +jωL Σ , assuming that a fault occurs at a distance x from the beginning of the cable, the total impedance from the fault point to the end of the cable is R N +jωL N , at this time the transition resistance at the fault point is R fTransition resistance is a kind of instantaneous resistance, which means when an electrical device has a phase-to-phase short circuit or a relative short circuit, the resistance through which the short circuit current flows from one phase to another or from one phase to the ground. Figure 3 The circuit principle shown in the figure lists the circuit equations from the cable head end to the fault point at two frequencies p = 100 Hz and q = 200 Hz, specifically:

[0055]

[0056] Among them, U pa 、U qa are the voltage phasors of the fault phase at frequency p and frequency q obtained at the cable head end, I pa , I qa are the current phasors of the fault phase at frequency p and frequency q obtained at the cable head end, I p0 , I q0 are the current phasors of the zero sequence of the line at frequency p and frequency q, respectively, and k pz 、k qz are the zero-sequence compensation coefficients corresponding to frequency p and frequency q, respectively, p 、z q are the positive sequence impedance of the line at frequency p and frequency q respectively, x is the fault distance to be solved, I pf , I qf are the current phasors at the fault point at frequency p and frequency q respectively.

[0057] According to the current distribution relationship at the fault point, we have:

[0058]

[0059] Among them, ω p 、ω q are the angular frequencies of frequency p and frequency q, respectively. Since the total reactance of the line and system is generally much larger than the resistance, especially at high frequencies, ignoring high-order small quantities, substituting equation (2) into equation (1) can be simplified to the following circuit equations:

[0060]

[0061] Among them, y1 and y2 are unknown real parameters related to the cable, j represents the imaginary unit, R Σ is the total resistance of the cable, L Σ is the total inductive reactance of the cable, R N is the resistance from the fault point to the end of the cable, L N is the inductive reactance from the fault point to the end of the cable.

[0062] Equation (3) is then considered as a complex linear equation group about x, y1, and y2. Therefore, in this embodiment, the circuit equation group (3) is converted into four real linear equations:

[0063]

[0064] Where real represents the real part and imag represents the imaginary part. In formula (4), the voltage and current related variables are all known quantities measured in the cable line. The line positive sequence impedance z p 、z q And the zero sequence compensation coefficient k pz 、k qz All cable line parameters are known; only x, y1, and y2 are unknown variables. Finally, using x, y1, and y2 as unknown real numbers, the least squares method is used to solve the real linear equation for the fault distance x. The least squares method is a mathematical optimization technique that seeks the optimal solution to a system of linear equations by minimizing the sum of squared errors. This example uses MATLAB to solve the system of equations using the least squares method.

[0065] This implementation rationally utilizes controllable devices in new power systems, considers transition resistance, and rationally simplifies the system impedance model, creating a more accurate and reliable fault location solution. Furthermore, the fault location method proposed in this embodiment requires no additional pulse injection equipment or communication between the two terminals. It is applicable to metallic and high-resistance faults, exhibits strong anti-interference capabilities, can be implemented using a relatively low sampling frequency, and is computationally simple, ensuring accurate and reliable fault location.

[0066] The serial numbers in the above embodiments are for description only and do not represent the order of assembly or use of the components.

[0067] The above descriptions are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An active detection cable fault location method based on a controllable converter, characterized in that: The active detection cable fault location method comprises: When a fault occurs, the controllable converter is controlled to output two sinusoidal voltages with different preset frequencies; specifically, the following steps are performed: superimposing an additional control signal on an original basic control signal at an input end of the controllable converter; generating a control pulse through a control system of the controllable converter according to a superimposed signal generated by the basic control signal and the additional control signal; generating a sinusoidal voltage at an output end of the controllable converter according to the control pulse through a main circuit of the controllable converter; Feeding back the sinusoidal voltage generated at the output end to the input end of the controllable converter in real time, and adjusting the additional control signal according to the feedback result until two sinusoidal voltages with different preset frequencies are generated at the output end; Obtain the voltage phasors and current phasors generated by sinusoidal voltages of different preset frequencies at the head end of the cable line, and use the voltage phasors and current phasors to construct a circuit equation group from the head end of the cable to the fault point; Solve the circuit equations simultaneously to obtain the fault distance from the fault point to the cable head end; The circuit equation group from the cable head end to the fault point is constructed using voltage phasors and current phasors, including: At the beginning of the cable, the voltage phasor U of the fault phase at frequency p and frequency q is obtained respectively. pa 、U qa , and the current phasor I of the fault phase at frequency p and frequency q pa , I qa ; Establish a circuit equation group for the voltage drop from the cable head end to the fault point, and substitute the measured voltage and current phasors into the circuit equation group to obtain: Among them, I p0 , I q0 are the current phasors of the zero sequence of the line at frequency p and frequency q, respectively, and k pz 、k qz are the zero-sequence compensation coefficients corresponding to frequency p and frequency q, respectively, p 、z q are the positive sequence impedance of the line at frequency p and frequency q respectively, x is the fault distance to be solved, y1 and y2 are unknown real parameters related to the cable, j represents the imaginary unit, ω p 、ω q are the angular frequencies corresponding to frequency p and frequency q, respectively, R Σ is the total resistance of the cable, L Σ is the total inductive reactance of the cable, R N is the resistance from the fault point to the end of the cable, L N R is the inductive reactance from the fault point to the end of the cable, f is the transition resistance; The simultaneous solution of the circuit equations to obtain the fault distance from the fault point to the cable head end includes: The circuit equations are converted into four real linear equations, which are: Among them, real represents the real part, and imag represents the imaginary part; With x, y1, and y2 as unknown real numbers, the fault distance x in the real linear equation is solved based on the least squares method.

2. The active detection cable fault location method based on a controllable converter according to claim 1, characterized in that: The controllable converter includes a main circuit and a control system. The main circuit is used to realize AC-DC conversion in the cable, and the control system is used to generate control pulses for controlling the AC-DC conversion.

3. The active detection cable fault location method based on a controllable converter according to claim 2, characterized in that: The main circuit includes a rectifier circuit, an inverter circuit, an AC conversion circuit and a DC conversion circuit.

4. The active detection cable fault location method based on a controllable converter according to claim 1, characterized in that: The method of obtaining voltage phasors and current phasors generated by sinusoidal voltages of different preset frequencies at the head end of the cable line includes: The voltage signal and current signal are collected at the head end of the cable, and the voltage phasor and current phasor corresponding to two preset frequencies are extracted from the voltage signal and current signal based on the Fourier algorithm.

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