Phase asymmetry principle line selection method

Abstract

The invention discloses a line selection method based on a phase asymmetry principle, and the method comprises the steps: achieving the recognition of a fault line through employing the phase asymmetry and symmetric difference characteristics of a fault line and a sound line, and a non-fault phase of the fault line in a three-phase current break variable during a single-phase grounding fault; according to the invention, the fault line identification is realized by using the current break variable characteristic difference during the single-phase earth fault; the fault phase current abrupt change of the fault line is the sum of ground capacitance current of the whole network, and the three-phase current abrupt change presents significant phase asymmetry; the three-phase current break variables of the sound line, the non-fault phase of the fault line and the line behind the fault point are the ground capacitance current break variables of each phase, and the amplitude and the waveform are basically consistent and are symmetrical; the transient-steady state data window is combined with the sampling value redundancy selection design, so that the method has the advantages of quick response, high action speed, simple calculation and high reliability, and the defect of zero-sequence electric quantity measurement accuracy is avoided.

Description

Technical Field

[0001] This invention relates to the field of single-phase grounding fault detection technology, and in particular to a line selection method based on the principle of phase asymmetry. Background Technology

[0002] The ΔI_PAM (ΔI_PhaseAsymmetryMethod) principle of phase asymmetry in three-phase current surges differs from any other principle scheme. It uses the phase asymmetry between the three-phase current surges caused by a single-phase ground fault as the criterion. In other words, it adopts the very significant phase asymmetry between the sum of the total network capacitive current flowing into the grounded phase of the faulted line and the capacitive current of the ungrounded phase and the current of the faulted phase. Theoretically, it avoids the drawbacks of the accuracy of zero-sequence electrical quantity measurement. Obviously, its relay characteristics are superior in terms of operation performance. The detection and line selection protection of single-phase grounding faults in low-current grounding systems has always been one of the difficulties in fault handling in the power distribution field. Traditional methods rely on the accuracy of zero-sequence electrical quantity measurement, which is easily affected by interference. Summary of the Invention

[0003] Therefore, the technical problem to be solved by this invention is: single-phase grounding fault detection and line selection protection in low-current grounding systems.

[0004] The above-mentioned technical problems are solved by the following technical solution: This invention proposes a line selection method based on the principle of phase asymmetry, which includes using the phase asymmetry and symmetry differences in the three-phase current changes between the faulty line and the healthy line, and between the non-faulty phase of the faulty line, during a single-phase ground fault to identify the faulty line.

[0005] In a preferred embodiment of the phase asymmetry principle line selection method of the present invention: the three-phase current sampling values ​​of each line of the distribution network are collected; the three-phase current mutation amount of each line is calculated; and the maximum, intermediate and minimum values ​​of the three-phase mutation amount amplitude of each sampling point are determined according to the three-phase current mutation amount.

[0006] In a preferred embodiment of the line selection method based on the phase asymmetry principle described in this invention: if the sudden change in the three-phase current of a certain line exhibits phase asymmetry characteristics and meets the preset criterion conditions, then the line is determined to be a single-phase ground fault line; if the sudden change in the three-phase current of a certain line exhibits relative symmetry characteristics, then the line is determined to be a healthy line.

[0007] In a preferred embodiment of the phase asymmetry principle-based line selection method of the present invention: the criterion includes an instantaneous asymmetry criterion for a single sampling point, and the instantaneous asymmetry criterion formula includes maxΔi p (k)≥Δi set ;maxΔi p (k)≥k1×minΔi p(k); maxΔi p (k)-midΔi p (k)≥k2×(midΔi p (k)-minΔi p (k);midΔi p (k)≤k3×minΔi p (k); in, , , Sampling points The maximum, median, and minimum values ​​of the three-phase current surge; This is the minimum setpoint for the phase current sudden change; , , This is the asymmetric coefficient.

[0008] In a preferred embodiment of the phase asymmetry principle line selection method of the present invention: the criterion further includes a global asymmetry criterion for the data window, wherein the global asymmetry criterion must satisfy: maxΔi p ≥k1×minΔi p; Where, maxΔi p The maximum periodic mutation value selected from the phase with the largest mutation value within the data window; minΔi p This represents the maximum periodic mutation value selected from the phase with the minimum mutation value within the data window.

[0009] In a preferred embodiment of the phase asymmetry principle line selection method described in this invention: the calculation of the three-phase current mutation amount of each line is specifically performed using the periodic mutation amount calculation formula: Δip(k)=|ip(k)-ip(kN)|-|ip(kN)-ip(k-2N)|; in, for Xiangzai Periodic mutation amount at a point Choose any one of the three phases A, B, and C; for Xiangzai Current sampling value at the point; This represents the number of sampling points for one power frequency cycle.

[0010] In a preferred embodiment of the phase asymmetry principle line selection method described in this invention: after the starting element captures the moment of the ground fault, a transient data window or a steady-state data window is extracted; within the data window, the number of sampling points that satisfy the instantaneous asymmetry criterion is counted; when the number of sampling points that satisfy the instantaneous asymmetry criterion exceeds a set threshold, and simultaneously satisfies the overall asymmetry criterion, it is identified as a single-phase ground fault.

[0011] In a preferred embodiment of the phase asymmetry principle-based line selection method of the present invention: the minimum constant value of the phase current sudden change is: The value range is 0.002. ~1.000 ,in This refers to the secondary rated current of the current transformer.

[0012] In a preferred embodiment of the phase asymmetry principle-based line selection method described in this invention: the asymmetry coefficient The asymmetry coefficient is used to describe the degree of asymmetry between the maximum and minimum values, with a typical value of 3.00; The asymmetry coefficient is used to describe the asymmetry between the maximum and median values, with a typical value of 4.00; Used to describe the asymmetry between the median and minimum values, with a typical value of 1.50.

[0013] In a preferred embodiment of the phase asymmetry principle line selection method described in this invention: the number of sampling points of the data window satisfy ,in The number of sampling points for one power frequency cycle; capable of identifying single-phase ground faults within 35ms.

[0014] The beneficial effects of this invention are as follows: fault line identification is achieved by utilizing the difference in current mutation characteristics during a single-phase ground fault; the current mutation of the faulty phase of the faulty line is the sum of the ground capacitance current of the entire network, and the three-phase current mutations show significant phase asymmetry; the three-phase current mutations of the healthy line, the non-faulty phase of the faulty line, and the line after the fault point are the phase-to-ground capacitance current mutations of each phase, with amplitudes and waveforms basically consistent, showing relative symmetry; the use of a metastable data window combined with a sampling value redundancy selection design has the advantages of rapid response, fast action speed, simple calculation, and high reliability, while avoiding the drawbacks of measuring the accuracy of zero-sequence electrical quantities. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments of the present invention will be briefly described below. Obviously, the drawings described below only relate to some embodiments of the present invention and are not intended to limit the present invention. Wherein: Figure 1 A flowchart of the present invention is shown. Detailed Implementation

[0016] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0017] The terminology used in this invention is that which is currently widely used in the art in consideration of the function of the invention; however, these terms may vary according to the intent of those skilled in the art, precedent, or new technology in the art. Furthermore, specific terms may be chosen by the applicant, and in such cases, their detailed meanings will be described in the detailed description of the invention. Therefore, the terms used in this specification should not be construed as simple names, but rather based on their meanings and the overall description of the invention.

[0018] See Figure 1 This embodiment provides a line selection method based on the principle of phase asymmetry, which includes using the phase asymmetry and symmetry differences in the three-phase current changes between the faulty line and the healthy line, and between the non-faulty phase of the faulty line, during a single-phase ground fault to identify the faulty line. When a single-phase ground fault occurs, the sudden change in the fault phase current of the faulted line is the sum of the ground capacitance current of the entire network. The sudden change in the three-phase current shows significant phase asymmetry. The sudden changes in the three-phase current of the healthy line, the non-faulted phase of the faulted line, and the line after the fault point are the sudden changes in the ground capacitance current of each phase. The amplitude and waveform are basically consistent, showing relative symmetry.

[0019] Collect the three-phase current sampling values ​​of each line in the distribution network; calculate the three-phase current mutation of each line; and determine the maximum, median, and minimum values ​​of the three-phase current mutation amplitude at each sampling point based on the three-phase current mutation. The expression for the current in a certain phase at the beginning of the line before the fault is: Where n is the line number, p is any one of the three phases A, B, and C, Cnp is the phase-to-ground capacitance of a certain phase of the line, and it is assumed that the phase-to-ground capacitance of each phase of a certain line is equal (CnA=CnB=CnC=Cn), uN is the neutral point voltage (i.e., the neutral point zero-sequence voltage), ep is the phase potential of a certain phase of the power supply, and inpL is the load current of a certain phase of the line.

[0020] If the sudden changes in the three-phase current of a certain line exhibit phase asymmetry and meet the preset criteria, then the line is determined to be a single-phase ground fault line; if the sudden changes in the three-phase current of a certain line exhibit relative symmetry, then the line is determined to be a healthy line. In the healthy line and the line after the fault point, the amplitude and waveform of the sudden changes in the three-phase current are basically the same. In the fault line, only the sudden changes in the current of the two healthy phases are basically the same, while the sudden changes in the current of the fault phase are significantly different because they include the current at the fault point.

[0021] The criterion conditions include an instantaneous asymmetric criterion for a single sampling point, and the instantaneous asymmetric criterion formula includes maxΔi. p (k)≥Δi set ;maxΔi p (k)≥k1×minΔi p (k); maxΔi p (k)-midΔi p (k)≥k2×(midΔi p (k)-minΔi p (k)); midΔi p (k)≤k3×minΔi p (k); in, , , Sampling points The maximum, median, and minimum values ​​of the three-phase current surge; This is the minimum setpoint for the phase current sudden change; , , This is the asymmetric coefficient.

[0022] Minimum set value of phase current change The value range is 0.002. ~1.000 ,in This refers to the secondary rated current of the current transformer.

[0023] asymmetric coefficient Used to describe the asymmetry between the maximum and minimum values, with a typical value of 3.00; asymmetry coefficient. Used to describe the asymmetry between the maximum and median values, with a typical value of 4.00; asymmetry coefficient. Used to describe the asymmetry between the median and minimum values, with a typical value of 1.50.

[0024] The criteria also include a global asymmetry criterion for data windows, which must satisfy the following: maxΔi p ≥k1×minΔi p; Where, maxΔi p The maximum periodic mutation value selected from the phase with the largest mutation value within the data window; minΔi p This represents the maximum periodic mutation value selected from the phase with the minimum mutation value within the data window.

[0025] When the starting element accurately captures the moment of a single-phase ground fault, and within the set transient data window sampling points, the number of sampling points that meet the first four criteria formulas in the above formula exceeds the set number, then combined with the last criterion formula in the above formula, a single-phase ground fault can be identified within 35ms. Similarly, this algorithm can also be used to calculate and identify single-phase ground faults using steady-state data windows.

[0026] The new algorithm is characterized by its use of a metastable data window and a redundant sampling value selection algorithm, which has significant advantages such as rapid algorithm response, fast action speed, simple calculation, and high reliability. In actual power systems, various factors such as the characteristics of electrical equipment, load influence, transient processes, and measurement links can all have an impact, so these factors must be fully considered during product design. Among these, the main adverse factors include: unbalanced load fluctuations, transient harmonics, current transformer accuracy, and the accuracy of low-end measurements in the product.

[0027] In the above formula, the three-phase current abrupt change of each line is calculated using the periodic abrupt change calculation formula: ; ; ; ; ; Δip(k)=|ip(k)-ip(kN)|-|ip(kN)-ip(k-2N)|; in, for Xiangzai Periodic mutation amount at a point Choose any one of the three phases A, B, and C; for Xiangzai Current sampling value at the point; The number of sampling points for one power frequency cycle is denoted as m; m is the number of sampling points for the transient data window, and m≤N, for example, m=N / 2; it can complete the identification of single-phase grounding faults within 35ms.

[0028] After the starting element detects the ground fault, it captures a transient data window or a steady-state data window. Within the data window, it counts the number of sampling points that meet the instantaneous asymmetry criterion. When the number of sampling points that meet the instantaneous asymmetry criterion exceeds the set threshold and also meets the overall asymmetry criterion, it is identified as a single-phase ground fault.

[0029] Set a transient data window (number of sampling points m≤N, where N is the number of sampling points per cycle, e.g., m=N / 2), and calculate the cycle change of the current change in each phase within the window (the formula includes the definition of parameters such as Δip(k) and maxΔip(k)). Valid sampling points are screened by combining multiple criteria: including the minimum value of mutation, the asymmetry between the maximum and minimum values, and the ratio of the differences among the three. After the number of sampling points that meet the criteria reaches the standard, the fault identification is completed by combining the final criteria. Detection can be achieved within 35ms under transient data window, and steady-state data window application is also supported.

[0030] Finally, it should be noted that the methods and devices described in detail above are merely embodiments, and those skilled in the art can modify these embodiments in different ways as long as they do not depart from the scope of the present invention.

Claims

1. A line selection method based on the principle of phase asymmetry, characterized in that: include, The fault line can be identified by utilizing the phase asymmetry and symmetry differences in the three-phase current changes between the faulty line and the healthy line, and between the non-faulty phase of the faulty line during a single-phase ground fault.

2. The line selection method based on the phase asymmetry principle according to claim 1, characterized in that: Collect the three-phase current sampling values ​​of each line in the distribution network; calculate the three-phase current mutation amount of each line; and determine the maximum, median, and minimum values ​​of the three-phase current mutation amount amplitude at each sampling point based on the three-phase current mutation amount.

3. The line selection method based on the phase asymmetry principle according to claim 2, characterized in that: If the sudden change in the three-phase current of a certain line exhibits phase asymmetry and meets the preset criterion conditions, then the line is determined to be a single-phase ground fault line. If the sudden changes in the three-phase current of a certain line exhibit a relatively symmetrical characteristic, then the line is determined to be a healthy line.

4. The line selection method based on the phase asymmetry principle according to claim 3, characterized in that: The criterion includes an instantaneous asymmetric criterion for a single sampling point, and the instantaneous asymmetric criterion formula includes maxΔi. p (k)≥Δi set ;maxΔi p (k)≥k1×minΔi p (k); maxΔi p (k)-midΔi p (k)≥k2×(midΔi p (k)-minΔi p (k);midΔi p (k)≤k3×minΔi p (k); in, , , Sampling points The maximum, median, and minimum values ​​of the three-phase current surge; This is the minimum setpoint for the phase current sudden change; , , This is the asymmetric coefficient.

5. The line selection method based on the phase asymmetry principle according to claim 4, characterized in that: The calculation of the three-phase current mutation in each line is specifically performed using the periodic mutation calculation formula: Δip(k) = |ip(k) - ip(kN)| - |ip(kN) - ip(k-2N)|; in, for Xiangzai Periodic mutation amount at a point Choose any one of the three phases A, B, and C; for Xiangzai Current sampling value at the point; This represents the number of sampling points for one power frequency cycle.

6. The line selection method based on the phase asymmetry principle according to claim 5, characterized in that: The criteria also include a global asymmetry criterion for the data window, which must satisfy the following: maxΔi p ≥k1×minΔi p; Where, maxΔi p The maximum periodic mutation value selected from the phase with the largest mutation value within the data window; minΔi p This represents the maximum periodic mutation value selected from the phase with the minimum mutation value within the data window.

7. The line selection method based on the phase asymmetry principle according to claim 6, characterized in that: After the starting element detects the ground fault, it captures a transient data window or a steady-state data window. Within the data window, it counts the number of sampling points that meet the instantaneous asymmetry criterion. When the number of sampling points that meet the instantaneous asymmetry criterion exceeds the set threshold and also meets the overall asymmetry criterion, it is identified as a single-phase ground fault.

8. The line selection method based on the phase asymmetry principle according to claim 7, characterized in that: The minimum constant value of the phase current change The value range is 0.

002. ~1.000 ,in This refers to the secondary rated current of the current transformer.

9. The line selection method based on the phase asymmetry principle according to claim 8, characterized in that: The asymmetry coefficient The asymmetry coefficient is used to describe the degree of asymmetry between the maximum and minimum values, with a typical value of 3.00; The asymmetry coefficient is used to describe the asymmetry between the maximum and median values, with a typical value of 4.00; Used to describe the asymmetry between the median and minimum values, with a typical value of 1.

50.

10. The line selection method based on the phase asymmetry principle according to claim 9, characterized in that: The number of sampling points of the data window satisfy ,in The number of sampling points for one power frequency cycle; capable of identifying single-phase ground faults within 35ms.

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