Extra-high voltage alternating current transmission line ground fault property identification method based on phase difference polar relation

Abstract

The invention discloses an ultra-high-voltage alternating-current transmission line grounding fault property identification method based on a phase difference polar relation, and the method comprises the steps: disconnecting circuit breakers at two ends of a fault phase after the protection of an ultra-high-voltage alternating-current transmission line detects a single-phase grounding fault; the fault phase fast grounding switch is closed, and after the grounding arc is extinguished, the fast grounding switch is disconnected; extracting a fundamental wave phase of a head end voltage of a fault phase line by using an all-phase fast Fourier transform algorithm considering frequency shift compensation and recording the fundamental wave phase as theta 1, and extracting a fundamental wave phase of a tail end voltage of the fault phase line and recording the fundamental wave phase as theta 2; according to the extracted fault phase line head end voltage fundamental wave phase theta1 and the fault phase line tail end voltage fundamental wave phase theta2, calculating the line head end and tail end voltage phase difference delta theta, and according to the polarity of the phase difference delta theta, judging the grounding fault property, and realizing accurate identification of the fault property. According to the method, the grounding fault property of the ultra-high-voltage power transmission line with the high-speed grounding switch can be accurately identified, and an indication is provided for whether reclosing operation is carried out after the fault occurs.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultra-high voltage alternating current transmission, and more specifically, relates to a method for identifying the nature of an ultra-high voltage alternating current transmission line grounding fault based on a phase difference polarity relationship. Background Art

[0002] At present, the research on UHV AC transmission lines mainly focuses on the accurate identification of the nature of ground faults, that is, judging whether the fault disappears before the circuit breaker recloses and then deciding whether to close the circuit. At first, some scholars proposed to use the recovery voltage amplitude characteristics to realize the instantaneous and permanent fault discrimination, that is, to use the coupling voltage size to distinguish permanent faults from instantaneous faults; but the discrimination sensitivity of this criterion is low in long lines and is greatly affected by the system operation mode. More importantly, this criterion is not suitable for transmission lines with shunt reactors. Therefore, for UHV transmission lines with reactors, some scholars have proposed to use the beat frequency characteristics of the reactor current, the current differential principle, the compensation current change characteristics, the model parameter identification, etc. to identify the nature of the ground fault, but the sensitivity is generally low and the ability to withstand transition resistance is poor.

[0003] To this end, the present invention proposes a method for identifying the nature of grounding faults in ultra-high voltage AC transmission lines based on the phase difference polarity relationship. The method has simple judgment criteria, high sensitivity, and high transition resistance resistance, and can provide an indication of whether to perform a reclosing operation after a fault. Summary of the invention

[0004] In view of the above-mentioned defects of the prior art, the present invention provides a method for identifying the nature of grounding faults in ultra-high voltage AC transmission lines based on the phase difference polarity relationship, so that the nature of the grounding fault can be accurately determined and an indication can be provided as to whether a reclosing operation should be performed after the fault.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A method for identifying the nature of a ground fault in an ultra-high voltage AC transmission line based on a phase difference polarity relationship, comprising:

[0007] S1. After the UHV AC transmission line protection detects a single-phase ground fault, it disconnects the circuit breakers at both ends of the faulty phase;

[0008] S2: The fast grounding switch of the fault phase is closed. After the grounding arc is extinguished, the fast grounding switch is opened.

[0009] S3: using the full-phase fast Fourier transform algorithm taking into account frequency shift compensation, extract the fundamental phase of the voltage at the head end of the fault phase line, recorded as θ1, and extract the fundamental phase of the voltage at the end of the fault phase line, recorded as θ2;

[0010] S4: Calculate the voltage phase difference Δθ between the beginning and the end of the line according to the extracted fundamental phase θ1 of the voltage at the beginning of the fault phase line and the fundamental phase θ2 of the voltage at the end of the fault phase line, and judge the nature of the grounding fault according to the polarity of the phase difference Δθ to achieve accurate identification of the fault nature.

[0011] Furthermore, the calculation formula of the full-phase fast Fourier transform algorithm taking into account frequency shift compensation in S3 is:

[0012]

[0013] k0=Nf0 / f s

[0014] k=0,1,2,...,N-1

[0015] Among them, f0 and θ0 are the signal frequency and initial phase respectively, f s is the sampling frequency, N is the number of sampling points, k0 is the actual frequency position of the signal, Y(k) is the full-phase FFT spectrum of the input signal, and θ is the phase value identified by the full-phase fast Fourier transform algorithm.

[0016] Further, the S4 includes:

[0017] S41. Subtract the fundamental phase θ1 of the voltage at the beginning of the fault phase line from the fundamental phase θ2 of the voltage at the end of the fault phase line to obtain the phase difference Δθ between the voltage at the beginning and the end of the line. The calculation formula is:

[0018] Δθ=θ 1- θ2

[0019] S42. When the polarity of the phase difference Δθ is negative, that is, the terminal voltage leads the first-end voltage, the fault nature is judged to be a permanent fault; when the polarity of the phase difference Δθ is positive, that is, the terminal voltage lags behind the first-end voltage, the fault nature is judged to be a transient fault.

[0020] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects: the method of the present invention can accurately identify the nature of the grounding fault of the UHV transmission line with a fast grounding switch, and provide an indication for whether to perform a reclosing operation after the fault. It has the advantages of simple judgment criteria, high sensitivity, and strong resistance to transition resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A flow chart of a method for identifying the nature of a ground fault in an ultra-high voltage AC transmission line based on a phase difference polarity relationship provided in an embodiment of the present invention;

[0022] Figure 2 This is a diagram showing the instantaneous ground fault identification effect in an embodiment of the present invention;

[0023] Figure 3 This is a diagram showing the effect of permanent ground fault identification in an embodiment of the present invention. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0025] The embodiment of the present invention provides a method for identifying the nature of a ground fault in an ultra-high voltage AC transmission line based on a phase difference polarity relationship. Figure 1 As shown, the proposed method specifically includes:

[0026] S1. After the UHV AC transmission line protection detects a single-phase ground fault, it disconnects the circuit breakers at both ends of the faulty phase;

[0027] S2: The fast grounding switch of the fault phase is closed. After the grounding arc is extinguished, the fast grounding switch is opened.

[0028] S3: Using the full-phase fast Fourier transform algorithm taking into account frequency shift compensation, the fundamental phase of the voltage at the head end of the fault phase line is extracted and recorded as θ1, and the fundamental phase of the voltage at the end of the line is extracted and recorded as θ2;

[0029] Specifically, the calculation formula of the full-phase fast Fourier transform algorithm is:

[0030]

[0031] k0=Nf0 / f s

[0032] k=0,1,2,...,N-1

[0033] Among them, f0 and θ0 are the signal frequency and initial phase respectively, f s is the sampling frequency, N is the number of sampling points, k0 is the actual frequency position of the signal, Y(k) is the full-phase FFT spectrum of the input signal, and θ is the phase value identified by the full-phase fast Fourier transform algorithm.

[0034] S4: Calculate the voltage phase difference Δθ between the beginning and the end of the line according to the extracted fundamental phase θ1 of the voltage at the beginning of the fault phase line and the fundamental phase θ2 of the voltage at the end of the fault phase line, and judge the nature of the grounding fault according to the polarity of the phase difference Δθ to achieve accurate identification of the fault nature.

[0035] Specifically, step S4 includes:

[0036] S41. The phase difference Δθ is obtained by subtracting the voltage phase at the end of the line from the voltage phase at the beginning of the line. The calculation formula is:

[0037] Δθ=θ 1- θ2

[0038] S42. When the polarity of the phase difference Δθ is negative, that is, the terminal voltage leads the first-end voltage, the fault nature is judged to be a permanent fault; when the polarity of the phase difference Δθ is positive, that is, the terminal voltage lags behind the first-end voltage, the fault nature is judged to be a transient fault.

[0039] The effectiveness of the proposed modeling method is verified by simulation.

[0040] Taking a certain section of an actual 1000kV UHV AC double-circuit transmission line as an example, a simulation model was established using PSCAD / EMTDC. A ground fault was set at 0.15s, and the fault transition resistance was as high as 500 ohms. The circuit breakers at both ends of the fault phase were tripped at 0.35s. The full-phase fast Fourier transform algorithm with frequency shift compensation was used to extract the fundamental phase of the voltage at the beginning and end of the fault phase line. The phase difference Δθ between the beginning and end of the line voltage was calculated, and the phase difference change waveform of the instantaneous ground fault was obtained as follows: Figure 2 As shown, its polarity is positive, and the fault can be correctly identified as a transient fault; the phase difference change waveform of the permanent grounding fault is as follows Figure 3 As shown, its polarity is negative, and the fault can be correctly identified as a permanent fault, which verifies the effectiveness of the proposed ground fault property identification method.

[0041] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for identifying the nature of ground faults in ultra-high voltage AC transmission lines based on phase difference polarity relationship, characterized in that: include: S1. After the UHV AC transmission line protection detects a single-phase ground fault, it disconnects the circuit breakers at both ends of the faulty phase; S2: The fast grounding switch of the fault phase is closed. After the grounding arc is extinguished, the fast grounding switch is opened. S3: using the full-phase fast Fourier transform algorithm taking into account frequency shift compensation, extract the fundamental phase of the voltage at the head end of the fault phase line, recorded as θ1, and extract the fundamental phase of the voltage at the end of the fault phase line, recorded as θ2; S4: Calculate the voltage phase difference Δθ between the beginning and the end of the line according to the extracted fundamental phase θ1 of the voltage at the beginning of the fault phase line and the fundamental phase θ2 of the voltage at the end of the fault phase line, and judge the nature of the grounding fault according to the polarity of the phase difference Δθ to achieve accurate identification of the fault nature.

2. The method for identifying the nature of ground faults in ultra-high voltage AC transmission lines based on phase difference polarity relationship according to claim 1, characterized in that: The calculation formula of the full-phase fast Fourier transform algorithm taking into account frequency shift compensation in S3 is: k0=Nf0 / f s k=0,1,2,...,N-1 Among them, f0 and θ0 are the signal frequency and initial phase respectively, f s is the sampling frequency, N is the number of sampling points, k0 is the actual frequency position of the signal, Y(k) is the full-phase FFT spectrum of the input signal, and θ is the phase value identified by the full-phase fast Fourier transform algorithm.

3. The method for identifying the nature of ground faults in ultra-high voltage AC transmission lines based on phase difference polarity relationship according to claim 1, characterized in that: The S4 includes: S41. Subtract the fundamental phase θ1 of the voltage at the beginning of the fault phase line from the fundamental phase θ2 of the voltage at the end of the fault phase line to obtain the phase difference Δθ between the voltage at the beginning and the end of the line. The calculation formula is: Δθ=θ 1- θ2 S42. When the polarity of the phase difference Δθ is negative, that is, the terminal voltage leads the first-end voltage, the fault nature is judged to be a permanent fault; when the polarity of the phase difference Δθ is positive, that is, the terminal voltage lags behind the first-end voltage, the fault nature is judged to be a transient fault.

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