Method and device for identifying the faulty phase of a low voltage power grid leakage fault

Abstract

The application discloses a method and device for identifying the phase of a low-voltage power grid electric leakage fault, and the method comprises the following steps: collecting a bus zero-sequence voltage signal, a bus three-phase voltage signal and a low-voltage power grid insulation resistance value in real time; when the zero-sequence voltage value exceeds a set zero-sequence voltage starting value and the low-voltage power grid insulation resistance value is smaller than a set minimum action resistance value, a single-phase or two-phase electric leakage fault is determined; whether the phase difference of the three-phase voltage and the zero-sequence voltage signal after the electric leakage fault occurs meets criterion 1 is calculated according to the three-phase voltage and the zero-sequence voltage signal; whether the three-phase voltage and the zero-sequence voltage signal after the electric leakage fault occurs meets criterion 2 is identified according to the three-phase voltage and the zero-sequence voltage signal; when a certain phase or a certain two phases simultaneously meet the above two criteria after the electric leakage fault occurs, the certain phase or the certain two phases are determined as the electric leakage grounding fault phase. The application avoids complicated mathematical analysis and operation, has good practicability, and effectively ensures the safe and reliable operation of the low-voltage power grid.

Description

Technical Field

[0001] This invention relates to a method and apparatus for phase identification of leakage faults in low-voltage power grids, belonging to the field of electrical safety technology. Background Technology

[0002] In my country's industrial and mining low-voltage power supply systems (380V-1140V), the neutral points of power transformers mostly adopt non-effective grounding. The most frequent longitudinal and lateral electrical faults in these systems are single-phase or two-phase grounding leakage faults, which are major contributing factors to electric shock injuries, phase-to-phase short circuits, electrical fires, and explosions of gas, coal dust, and particulate matter. For power supply safety, regardless of the grounding method used, my country's industrial and mining low-voltage power supply systems are equipped with leakage protection devices that can automatically disconnect leakage feeders or selective leakage protection devices. Currently, the various types of leakage protection devices used in my country's industrial and mining low-voltage power grids can only identify feeder lines with single-phase or two-phase grounding leakage faults, but cannot accurately determine the faulty phase. This increases the time required for on-site technicians to troubleshoot and reduces the economic efficiency of mines.

[0003] In existing technologies, the faulty phase is usually determined by the change in the three-phase voltage to ground during a single-phase leakage or by a phase-sensitive comparison method. However, as the load size and leakage resistance of the low-voltage power grid change, the reliability, sensitivity, and anti-interference capabilities of these methods are poor, resulting in a high false fault rate. Furthermore, these methods can only identify single-phase grounding leakage faults and cannot identify two-phase grounding leakage faults, thus creating a dead zone.

[0004] Therefore, developing a new method for identifying leakage faults that is accurate, has a fast response time, and strong anti-interference ability is of great significance for ensuring the continuity, reliability, and safety of power supply in mines and improving mine production efficiency. Summary of the Invention

[0005] To address the aforementioned problems, this invention proposes a method and apparatus for identifying phase leakage faults in low-voltage power grids, which can quickly and accurately identify single-phase or two-phase grounding leakage faults.

[0006] The technical solution adopted by this invention to solve its technical problem is as follows:

[0007] In a first aspect, the present invention provides a method for phase identification of leakage faults in a low-voltage power grid, comprising the following steps:

[0008] Real-time acquisition of bus zero-sequence voltage signal, bus three-phase voltage signal and insulation resistance value of low-voltage power grid;

[0009] When the zero-sequence voltage value exceeds the set zero-sequence voltage start value and the low-voltage grid insulation resistance value is less than the set minimum operating resistance value, it is determined to be a single-phase or two-phase grounding leakage fault.

[0010] The phase difference between the three-phase voltage and the zero-sequence voltage signal is calculated based on the leakage fault and whether it meets the criterion 1. The criterion 1 is: the phase difference between the three-phase voltage and the zero-sequence voltage signal is φ, and its operating range is 20°≤φ≤140°.

[0011] Based on the three-phase voltage and zero-sequence voltage signal after the leakage fault occurs, it is determined whether the three-phase voltage and zero-sequence voltage signal meet the criteria 2. The criteria 2 is: the phase relationship between the three-phase voltage and zero-sequence voltage signal conforms to the zero-sequence fundamental frequency harmonic phase discrimination method.

[0012] When a leakage fault occurs, if one or two phases simultaneously meet the above two criteria, the one or two phases are determined to be the leakage ground fault phase.

[0013] As one possible implementation of this embodiment, the zero-sequence fundamental frequency doubling phase discrimination method is as follows:

[0014] The zero-sequence fundamental frequency harmonic phase discrimination rule for single-phase grounding leakage fault lines is set as follows: 1) Simultaneously harmonic the fundamental zero-sequence voltage and zero-sequence current signals to any frequency U between 50Hz and 250Hz. 0B Signals and I 0B Signal; 2) Zero-sequence voltage signal U 0B The falling edge must be located at the zero-sequence current signal I. 0B Between the rising and falling edges, and the zero-sequence voltage signal U 0B The pulse width must be greater than the zero-sequence current signal I. 0B The pulse width; the zero-sequence current and zero-sequence voltage signals of each branch are judged according to the above two zero-sequence fundamental frequency doubling phase discrimination rules.

[0015] As one possible implementation of this embodiment, when the zero-sequence voltage value exceeds the set zero-sequence voltage start-up value and the low-voltage grid insulation resistance value is less than the set minimum operating resistance value, that is, when conditions 1 and 2 are simultaneously satisfied:

[0016] Condition 1: U Q >k R U bmax

[0017] Condition 2: U JY <U lmin

[0018] Among them, U Q U is the zero-sequence voltage value. JY This represents the insulation resistance value of the low-voltage power grid; kR U bmax U is the zero-sequence voltage start-up value. bmax k represents the effective value of the maximum unbalanced zero-sequence voltage during normal operation of a low-voltage power grid. R U is the reliability coefficient; lmin This is the minimum operating resistance value.

[0019] As one possible implementation of this embodiment, the formula for calculating the phase difference between the three-phase voltage and the zero-sequence voltage signal is as follows:

[0020]

[0021]

[0022]

[0023] Where, φ A φ B φ C These are the phase differences between the three-phase voltage and the zero-sequence voltage signal, respectively.

[0024] The phase relationship between the three-phase voltage and the zero-sequence voltage signal is as follows:

[0025]

[0026]

[0027]

[0028]

[0029] U0>U A

[0030] U0>U B ………(3)

[0031] U0>U C

[0032] T U01 <T A1 ,T U02 <T A2

[0033] T U01 <T B1 ,T U02 <T B2 ………(4)

[0034] T U01 <T C1 ,T U02 <T C2

[0035] Where U0 is the pulse width of the zero-sequence voltage signal on the bus after a leakage fault occurs, U A U is the pulse width of phase A voltage after a leakage fault occurs. B U is the pulse width of phase B voltage after a leakage fault occurs. C The pulse width of phase C voltage after a leakage fault occurs;

[0036] T U01 T is the time it takes for the zero-sequence voltage signal to change from a low level to a high level. U02 T is the time it takes for the zero-sequence voltage signal to change from a high level to a low level. A1 T is the time it takes for the phase A voltage signal to change from a low level to a high level. A2 T is the time it takes for the phase A voltage signal to change from a high level to a low level. B1 T is the time it takes for the phase B voltage signal to change from a low level to a high level. B2 T is the time it takes for the phase B voltage signal to change from a high level to a low level. C1 T is the time it takes for the C-phase voltage signal to change from a low level to a high level. C2 This is the time it takes for the C-phase voltage signal to change from a low level to a high level.

[0037] As one possible implementation of this embodiment, the reliability coefficient of the set zero-sequence voltage start-up value is in the range of 2-4.5.

[0038] As one possible implementation of this embodiment, the set minimum operating resistance value ranges from 3.5kΩ to 20kΩ.

[0039] As one possible implementation of this embodiment, the phase difference φ is preferably 90°. 0 .

[0040] As one possible implementation of this embodiment, the method further includes:

[0041] After a leakage fault occurs, the acquired zero-sequence voltage signal is subjected to low-pass filtering, phase shifting, feedback, zero-crossing detection, opto-isolation, and shaping to form a zero-sequence voltage square wave signal with a pulse width of 180 degrees. The acquired three-phase voltage signals are subjected to low-pass filtering, amplitude discrimination, opto-isolation, and shaping to form a three-phase voltage square wave signal with a pulse width varying between 0 and 180 degrees.

[0042] Secondly, an embodiment of the present invention provides a device for phase identification of leakage faults in a low-voltage power grid, comprising:

[0043] The data acquisition module is used to acquire the zero-sequence voltage signal of the busbar, the three-phase voltage signal of the busbar, and the insulation resistance value of the low-voltage power grid in real time.

[0044] The fault determination module is used to determine a single-phase or two-phase grounding leakage fault when the zero-sequence voltage value exceeds the set zero-sequence voltage start value and the low-voltage grid insulation resistance value is less than the set minimum operating resistance value.

[0045] The phase difference judgment module is used to calculate whether the phase difference between the three-phase voltage and the zero-sequence voltage signal meets criterion 1 based on the three-phase voltage and the zero-sequence voltage signal after the leakage fault occurs. Criterion 1 is: the phase difference between the three-phase voltage and the zero-sequence voltage signal is φ, and its operating range is 20°≤φ≤140°.

[0046] The phase relationship judgment module is used to identify whether the three-phase voltage and zero-sequence voltage signal meet criterion 2 after the occurrence of leakage fault. Criterion 2 is: the phase relationship between the three-phase voltage and zero-sequence voltage signal meets the zero-sequence fundamental frequency harmonic phase discrimination method.

[0047] The fault phase identification module is used to determine whether a certain phase or two phases are the leakage ground fault phases when a leakage fault occurs and one or two phases simultaneously meet the above two criteria.

[0048] As one possible implementation of this embodiment, the zero-sequence fundamental frequency doubling phase discrimination method is as follows:

[0049] The zero-sequence fundamental frequency harmonic phase discrimination rule for single-phase grounding leakage fault lines is set as follows: 1) Simultaneously harmonic the fundamental zero-sequence voltage and zero-sequence current signals to any frequency U between 50Hz and 250Hz. 0B Signals and I 0B Signal; 2) Zero-sequence voltage signal U 0B The falling edge must be located at the zero-sequence current signal I. 0B Between the rising and falling edges, and the zero-sequence voltage signal U 0B The pulse width must be greater than the zero-sequence current signal I. 0B The pulse width; the zero-sequence current and zero-sequence voltage signals of each branch are judged according to the above two zero-sequence fundamental frequency doubling phase discrimination rules.

[0050] As one possible implementation of this embodiment, when the zero-sequence voltage value exceeds the set zero-sequence voltage start-up value and the low-voltage grid insulation resistance value is less than the set minimum operating resistance value, that is, when conditions 1 and 2 are simultaneously satisfied:

[0051] Condition 1: U Q >k R U bmax

[0052] Condition 2: U JY <U lmin

[0053] Among them, UQ U is the zero-sequence voltage value. JY This represents the insulation resistance value of the low-voltage power grid; k R U bmax U is the zero-sequence voltage start-up value. bmax k represents the effective value of the maximum unbalanced zero-sequence voltage during normal operation of a low-voltage power grid. R U is the reliability coefficient; lmin This is the minimum operating resistance value.

[0054] As one possible implementation of this embodiment, the formula for calculating the phase difference between the three-phase voltage and the zero-sequence voltage signal is as follows:

[0055]

[0056]

[0057]

[0058] Where, φ A φ B φ C These are the phase differences between the three-phase voltage and the zero-sequence voltage signal, respectively.

[0059] The phase relationship between the three-phase voltage and the zero-sequence voltage signal is as follows:

[0060]

[0061]

[0062]

[0063]

[0064] U0>U A

[0065] U0>U B ………(3)

[0066] U0>U C

[0067] T U01 <T A1 ,T U02 <T A2

[0068] T U01 <T B1 ,T U02 <T B2 ………(4)

[0069] T U01 <TC1 ,T U02 <T C2

[0070] Where U0 is the pulse width of the zero-sequence voltage signal on the bus after a leakage fault occurs, U A U is the pulse width of phase A voltage after a leakage fault occurs. B U is the pulse width of phase B voltage after a leakage fault occurs. C The pulse width of phase C voltage after a leakage fault occurs;

[0071] T U01 T is the time it takes for the zero-sequence voltage signal to change from a low level to a high level. U02 T is the time it takes for the zero-sequence voltage signal to change from a high level to a low level. A1 T is the time it takes for the phase A voltage signal to change from a low level to a high level. A2 T is the time it takes for the phase A voltage signal to change from a high level to a low level. B1 T is the time it takes for the phase B voltage signal to change from a low level to a high level. B2 T is the time it takes for the phase B voltage signal to change from a high level to a low level. C1 T is the time it takes for the C-phase voltage signal to change from a low level to a high level. C2 This is the time it takes for the C-phase voltage signal to change from a low level to a high level.

[0072] As one possible implementation of this embodiment, the reliability coefficient of the set zero-sequence voltage start-up value is in the range of 2-4.5.

[0073] As one possible implementation of this embodiment, the set minimum operating resistance value ranges from 3.5kΩ to 20kΩ.

[0074] As one possible implementation of this embodiment, the phase difference φ is preferably 90°. 0 .

[0075] As one possible implementation of this embodiment, the apparatus further includes:

[0076] The data processing module is used to perform low-pass filtering, phase shifting, feedback, zero-crossing detection, opto-isolation, and shaping on the acquired zero-sequence voltage signal after a leakage fault occurs, forming a zero-sequence voltage square wave signal with a pulse width of 180 degrees. It also performs low-pass filtering, amplitude discrimination, opto-isolation, and shaping on the acquired three-phase voltage signals, forming a three-phase voltage square wave signal with a pulse width varying between 0 and 180 degrees.

[0077] As one possible implementation of this embodiment

[0078] The technical solutions of the embodiments of the present invention can have the following beneficial effects:

[0079] This invention comprehensively identifies leakage faults by analyzing the phase relationship between the zero-sequence voltage and the three-phase bus voltage, as well as the phase difference between the zero-sequence voltage and the three-phase bus voltage. This method is unaffected by the type of neutral grounding, operating mode, load changes, or leakage grounding resistance of the low-voltage power grid. Furthermore, the method is simple and efficient, avoiding tedious mathematical analysis and calculations, and is highly practical, effectively ensuring the safe and reliable operation of the low-voltage power grid.

[0080] Compared with existing phase-sensitive comparison direction methods and three-phase voltage effective value comparison methods with the same function, this invention is more reliable, has a higher phase selection accuracy, and a faster discrimination speed. It can not only accurately identify the phase of a single-phase leakage fault, but also accurately identify the phase of a two-phase grounding leakage fault, and there is no "dead zone" in the phase selection protection range.

[0081] This invention can be implemented not only with complex programmable logic devices such as CPLD or FPGA, but also with single-chip microcomputer systems and DSP systems, thereby realizing the ability to process multiple signals in parallel and greatly improving the speed and accuracy of fault phase identification in a low-voltage power grid leakage fault phase identification and protection device. Attached Figure Description

[0082] Figure 1 This is a flowchart illustrating a method for phase identification of leakage faults in a low-voltage power grid according to an exemplary embodiment;

[0083] Figure 2 This is a structural diagram of a device for phase identification of leakage faults in a low-voltage power grid, according to an exemplary embodiment.

[0084] Figure 3 This is a flowchart of phase identification of low-voltage power grid leakage faults using the device described in this invention. Detailed Implementation

[0085] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0086] To clearly illustrate the technical features of this solution, the invention will be described in detail below through specific embodiments and in conjunction with the accompanying drawings. The following disclosure provides many different embodiments or examples for implementing different structures of the invention. To simplify the disclosure of the invention, components and arrangements of specific examples are described below. Furthermore, reference numerals and / or letters may be repeated in different examples. This repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. It should be noted that the components illustrated in the drawings are not necessarily drawn to scale. Descriptions of well-known components, processing techniques, and processes are omitted in this invention to avoid unnecessarily limiting the invention.

[0087] like Figure 1 As shown in the figure, an embodiment of the present invention provides a method for phase identification of leakage faults in a low-voltage power grid, comprising the following steps:

[0088] Real-time acquisition of bus zero-sequence voltage signal, bus three-phase voltage signal and insulation resistance value of low-voltage power grid;

[0089] When the zero-sequence voltage value exceeds the set zero-sequence voltage start value and the low-voltage grid insulation resistance value is less than the set minimum operating resistance value, it is determined to be a single-phase or two-phase grounding leakage fault.

[0090] The phase difference between the three-phase voltage and the zero-sequence voltage signal is calculated based on the leakage fault and whether it meets the criterion 1. The criterion 1 is: the phase difference between the three-phase voltage and the zero-sequence voltage signal is φ, and its operating range is 20°≤φ≤140°.

[0091] Based on the three-phase voltage and zero-sequence voltage signal after the leakage fault occurs, it is determined whether the three-phase voltage and zero-sequence voltage signal meet the criteria 2. The criteria 2 is: the phase relationship between the three-phase voltage and zero-sequence voltage signal conforms to the zero-sequence fundamental frequency harmonic phase discrimination method.

[0092] When a leakage fault occurs, if one or two phases simultaneously meet the above two criteria, the one or two phases are determined to be the leakage ground fault phase.

[0093] As one possible implementation of this embodiment, the zero-sequence fundamental frequency doubling phase discrimination method is as follows:

[0094] The zero-sequence fundamental frequency harmonic phase discrimination rule for single-phase grounding leakage fault lines is set as follows: 1) Simultaneously harmonic the fundamental zero-sequence voltage and zero-sequence current signals to any frequency U between 50Hz and 250Hz. 0B Signals and I 0B Signal; 2) Zero-sequence voltage signal U 0B The falling edge must be located at the zero-sequence current signal I. 0BBetween the rising and falling edges, and the zero-sequence voltage signal U 0B The pulse width must be greater than the zero-sequence current signal I. 0B The pulse width; the zero-sequence current and zero-sequence voltage signals of each branch are judged according to the above two zero-sequence fundamental frequency doubling phase discrimination rules.

[0095] As one possible implementation of this embodiment, when the zero-sequence voltage value exceeds the set zero-sequence voltage start-up value and the low-voltage grid insulation resistance value is less than the set minimum operating resistance value, that is, when conditions 1 and 2 are simultaneously satisfied:

[0096] Condition 1: U Q >k R U bmax

[0097] Condition 2: U JY <U lmin

[0098] Among them, U Q U is the zero-sequence voltage value. JY This represents the insulation resistance value of the low-voltage power grid; k R U bmax U is the zero-sequence voltage start-up value. bmax k represents the effective value of the maximum unbalanced zero-sequence voltage during normal operation of a low-voltage power grid. R U is the reliability coefficient; lmin This is the minimum operating resistance value.

[0099] As one possible implementation of this embodiment, the formula for calculating the phase difference between the three-phase voltage and the zero-sequence voltage signal is as follows:

[0100]

[0101]

[0102]

[0103] Where, φ A φ B φ C These are the phase differences between the three-phase voltage and the zero-sequence voltage signal, respectively.

[0104] The phase relationship between the three-phase voltage and the zero-sequence voltage signal is as follows:

[0105]

[0106]

[0107]

[0108]

[0109] U0>U A

[0110] U0>U B ………(3)

[0111] U0>U C

[0112] T U01 <T A1 ,T U02 <T A2

[0113] T U01 <T B1 ,T U02 <T B2 ………(4)

[0114] T U01 <T C1 ,T U02 <T C2

[0115] Where U0 is the pulse width of the zero-sequence voltage signal on the bus after a leakage fault occurs, U A U is the pulse width of phase A voltage after a leakage fault occurs. B U is the pulse width of phase B voltage after a leakage fault occurs. C The pulse width of phase C voltage after a leakage fault occurs;

[0116] T U01 T is the time it takes for the zero-sequence voltage signal to change from a low level to a high level. U02 T is the time it takes for the zero-sequence voltage signal to change from a high level to a low level. A1 T is the time it takes for the phase A voltage signal to change from a low level to a high level. A2 T is the time it takes for the phase A voltage signal to change from a high level to a low level. B1 T is the time it takes for the phase B voltage signal to change from a low level to a high level. B2 T is the time it takes for the phase B voltage signal to change from a high level to a low level. C1 T is the time it takes for the C-phase voltage signal to change from a low level to a high level. C2 This is the time it takes for the C-phase voltage signal to change from a low level to a high level.

[0117] As one possible implementation of this embodiment, the reliability coefficient of the set zero-sequence voltage start-up value is in the range of 2-4.5.

[0118] As one possible implementation of this embodiment, the set minimum operating resistance value ranges from 3.5kΩ to 20kΩ.

[0119] As one possible implementation of this embodiment, the phase difference φ is preferably 90°.

[0120] As one possible implementation of this embodiment, the method further includes:

[0121] After a leakage fault occurs, the acquired zero-sequence voltage signal is subjected to low-pass filtering, phase shifting, feedback, zero-crossing detection, opto-isolation, and shaping to form a zero-sequence voltage square wave signal with a pulse width of 180 degrees. The acquired three-phase voltage signals are subjected to low-pass filtering, amplitude discrimination, opto-isolation, and shaping to form a three-phase voltage square wave signal with a pulse width varying between 0 and 180 degrees.

[0122] This invention directly performs frequency multiplication on the three-phase voltage and zero-sequence voltage signals, and then uses the multiplied signal as the identification of leakage fault phases. This reduces the selection time for single-phase or two-phase grounding leakage faults to ≤20ms, meeting the leakage fault protection action time requirement (≤30ms) specified in the MT189-88 standard. This successfully solves the technical problem that leakage fault phases in low-voltage power grids in industrial and mining areas cannot be quickly and accurately identified.

[0123] like Figure 2 As shown in the figure, an embodiment of the present invention provides a device for phase identification of leakage faults in a low-voltage power grid, comprising:

[0124] The data acquisition module is used to acquire the zero-sequence voltage signal of the busbar, the three-phase voltage signal of the busbar, and the insulation resistance value of the low-voltage power grid in real time.

[0125] The fault determination module is used to determine a single-phase or two-phase grounding leakage fault when the zero-sequence voltage value exceeds the set zero-sequence voltage start value and the low-voltage grid insulation resistance value is less than the set minimum operating resistance value.

[0126] The phase difference judgment module is used to calculate whether the phase difference between the three-phase voltage and the zero-sequence voltage signal meets criterion 1 based on the three-phase voltage and the zero-sequence voltage signal after the leakage fault occurs. Criterion 1 is: the phase difference between the three-phase voltage and the zero-sequence voltage signal is φ, and its operating range is 20°≤φ≤140°.

[0127] The phase relationship judgment module is used to identify whether the three-phase voltage and zero-sequence voltage signal meet criterion 2 after the occurrence of leakage fault. Criterion 2 is: the phase relationship between the three-phase voltage and zero-sequence voltage signal meets the zero-sequence fundamental frequency harmonic phase discrimination method.

[0128] The fault phase identification module is used to determine whether a certain phase or two phases are the leakage ground fault phases when a leakage fault occurs and one or two phases simultaneously meet the above two criteria.

[0129] As one possible implementation of this embodiment, the data acquisition module includes:

[0130] Zero-sequence voltage acquisition module, used to acquire the zero-sequence voltage signal of the bus in a low-voltage power grid;

[0131] The three-phase voltage acquisition module is used to acquire the three-phase voltage signal of the low-voltage power grid.

[0132] The low-voltage power grid insulation resistance value acquisition module is used to acquire the three-phase-to-ground insulation resistance value of the low-voltage power grid.

[0133] As one possible implementation of this embodiment, the apparatus further includes:

[0134] The data processing module is used to perform low-pass filtering, phase shifting, feedback, zero-crossing detection, opto-isolation, and shaping on the acquired zero-sequence voltage signal after a leakage fault occurs, forming a zero-sequence voltage square wave signal with a pulse width of 180 degrees. It also performs low-pass filtering, amplitude discrimination, opto-isolation, and shaping on the acquired three-phase voltage signals, forming a three-phase voltage square wave signal with a pulse width varying between 0 and 180 degrees.

[0135] This invention directly performs frequency multiplication on the three-phase voltage and zero-sequence voltage signals, and then uses the multiplied signal as the identification of leakage fault phases. This reduces the selection time for single-phase or two-phase grounding leakage faults to ≤20ms, meeting the leakage fault protection action time requirement (≤30ms) specified in the MT189-88 standard. This successfully solves the technical problem that leakage fault phases in low-voltage power grids in industrial and mining areas cannot be quickly and accurately identified.

[0136] like Figure 3 As shown, the process of identifying low-voltage power grid leakage faults using the device for phase identification of low-voltage power grid leakage faults according to the present invention is as follows:

[0137] (1) Real-time acquisition of bus zero-sequence voltage signal, bus three-phase voltage signal and insulation resistance value of low-voltage power grid in low-voltage power grid;

[0138] When a single-phase or two-phase grounding leakage fault occurs in a low-voltage power grid, the low-voltage system will generate a zero-sequence voltage. The magnitude of the zero-sequence voltage and the three-phase insulation resistance value is used to determine whether a grounding leakage fault has occurred.

[0139] (2) Detect the zero-sequence voltage value and minimum operating voltage value of the bus in the low-voltage power grid. When the zero-sequence voltage value exceeds the set zero-sequence voltage start-up value and the insulation resistance value of the low-voltage power grid is less than the set minimum operating resistance value, that is, when conditions 1 and 2 are met simultaneously, it is considered that a single-phase or two-phase grounding leakage fault has occurred in the low-voltage power grid, and proceed to steps (3) and (4); where UQ U is the zero-sequence voltage value. JY This refers to the insulation resistance value of the low-voltage power grid.

[0140] Condition 1: U Q >k R U bmax

[0141] Condition 2: U JY <U lmin

[0142] Where, k R U bmax U is the zero-sequence voltage start-up value. bmax k represents the effective value of the maximum unbalanced zero-sequence voltage during normal operation of a low-voltage power grid. R The reliability coefficient ranges from 2 to 4.5, with 3.5 being preferred.

[0143] Among them, U lmin The minimum operating resistance value is 3.5kΩ-20kΩ, preferably 11kΩ;

[0144] (3) After the leakage fault occurs, the zero-sequence voltage and three-phase voltage signals of the bus in the low-voltage power grid are collected, and the three-phase voltage and zero-sequence voltage signals are used to identify the single-phase or two-phase grounding leakage fault according to the following two criteria.

[0145] Criterion 1: The phase difference between the three-phase voltage and the zero-sequence voltage signal is φ, and its value range is 20°≤φ≤140°;

[0146] Criterion 2: The phase relationship between the three-phase voltage and the zero-sequence voltage signal conforms to the zero-sequence fundamental frequency harmonic phase discrimination method;

[0147] After a leakage fault occurs, the time it takes for the bus zero-sequence voltage and three-phase voltage signals to change from low to high level is first collected, and then the time it takes for the bus zero-sequence voltage and three-phase voltage signals to change from high to low level is collected.

[0148] The phase difference between the three-phase voltage and the bus zero-sequence voltage signal after a leakage fault occurs is calculated using the following formula:

[0149]

[0150]

[0151]

[0152] Where, φ A φ B φ C These are the phase differences between the three-phase voltage and the zero-sequence voltage signal, respectively.

[0153] φ A φ B φ C The phase value range is 20°≤φ≤140°. In the preferred embodiment of this application, the phase difference φ value is selected as 90°.

[0154] The phase relationship between the three-phase voltage and the bus zero-sequence voltage signal after a leakage fault occurs is calculated using the following formula:

[0155]

[0156]

[0157]

[0158]

[0159] U0>U A

[0160] U0>U B ………(3)

[0161] U0>U C

[0162] T U01 <T A1 ,T U02 <T A2

[0163] T U01 <T B1 ,T U02 <T B2 ………(4)

[0164] T U01 <T C1 ,T U02 <T C2

[0165] Where U0 is the pulse width of the zero-sequence voltage signal on the bus after a leakage fault occurs, U A U is the pulse width of phase A voltage after a leakage fault occurs. B U is the pulse width of phase B voltage after a leakage fault occurs. C The pulse width of phase C voltage after a leakage fault occurs;

[0166] T U01 T is the time it takes for the zero-sequence voltage signal to change from a low level to a high level. U02 T is the time it takes for the zero-sequence voltage signal to change from a high level to a low level. A1 T is the time it takes for the phase A voltage signal to change from a low level to a high level. A2T is the time it takes for the phase A voltage signal to change from a high level to a low level. B1 T is the time it takes for the phase B voltage signal to change from a low level to a high level. B2 T is the time it takes for the phase B voltage signal to change from a high level to a low level. C1 T is the time it takes for the C-phase voltage signal to change from a low level to a high level. C2 The time it takes for the C-phase voltage signal to change from a low level to a high level.

[0167] After a leakage fault occurs, the phase difference between the three-phase voltage and the zero-sequence voltage signal is calculated according to the above formula (1) to see if it meets the criterion 1;

[0168] After a leakage fault occurs, the three-phase voltage and zero-sequence voltage signal are compared according to the above formulas (2), (3), and (4) to determine whether the three-phase voltage and zero-sequence voltage signal meet criterion 2.

[0169] When a leakage fault occurs, if one or two phases simultaneously meet the above two criteria, the one or two phases are determined to be the leakage ground fault phase.

[0170] Compared with existing phase-sensitive comparison direction methods and three-phase voltage effective value comparison methods with the same function, this invention is more reliable, has a higher phase selection accuracy, and a faster discrimination speed. It can not only accurately identify the phase of a single-phase leakage fault, but also accurately identify the phase of a two-phase grounding leakage fault, and there is no "dead zone" in the phase selection protection range.

[0171] This invention can be implemented not only with complex programmable logic devices such as CPLD or FPGA, but also with single-chip microcomputer systems and DSP systems, thereby realizing the ability to process multiple signals in parallel and greatly improving the speed and accuracy of fault phase identification in a low-voltage power grid leakage fault phase identification and protection device.

[0172] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A method for identifying a fault phase of a low voltage power grid leakage fault, characterized in that, The method comprises the following steps: Real-time acquisition of bus zero sequence voltage signals, bus three-phase voltage signals and insulation resistance values of the low-voltage power grid; When the zero sequence voltage value exceeds a set zero sequence voltage starting value and the insulation resistance value of the low-voltage power grid is less than a set minimum action resistance value, a single-phase or two-phase ground leakage fault is determined; According to the phase difference between the three-phase voltage and the zero-sequence voltage signal after the occurrence of the electric leakage fault, whether the phase difference between the three-phase voltage and the zero-sequence voltage signal meets criterion 1 is calculated, the criterion 1 is that the phase difference between the three-phase voltage and the zero-sequence voltage signal is φ, and the action region is 20 o ≤ φ ≤ 140 o ; After the leakage fault occurs, whether the three-phase voltage and zero sequence voltage signals meet criterion 2 is identified according to the three-phase voltage and zero sequence voltage signals, wherein the criterion 2 is that the phase relationship of the three-phase voltage and zero sequence voltage signals meets a zero sequence fundamental frequency phase discrimination method; The zero sequence fundamental frequency multiplication phase discrimination method is: setting the zero sequence fundamental frequency multiplication phase discrimination rule of single-phase ground leakage fault line: 1) simultaneously multiplying the fundamental frequency zero sequence voltage and zero sequence current signals to an arbitrary frequency between 50HZ and 250HZ U 0B signal and I 0B signal; 2) the falling edge of the zero sequence voltage signal U 0B must be located between the rising edge and the falling edge of the zero sequence current signal I 0B , and the pulse width of the zero sequence voltage signal U 0B must be greater than the pulse width of the zero sequence current signal I 0B ; the zero sequence current and zero sequence voltage signals of each branch are discriminated according to the above two zero sequence fundamental frequency multiplication phase discrimination rules; When a certain phase or certain two phases simultaneously meet criterion 1 and criterion 2 after the leakage fault occurs, the certain phase or certain two phases are determined as leakage ground fault phases; When the zero sequence voltage value exceeds a set zero sequence voltage starting value and the insulation resistance value of the low-voltage power grid is less than a set minimum action resistance value, i.e. when condition 1 and condition 2 are simultaneously met: Condition 1 : U Q > k R U bmax Condition 2: U JY <U lmin wherein U Q is the zero sequence voltage value, U JY is the insulation resistance value of the low voltage network; k R U bmax is the zero sequence voltage starting value, U bmax is the maximum unbalanced zero sequence voltage effective value during normal operation of the low voltage network, k R is the reliability factor; U lmin is the minimum operating resistance value; The calculation formula of the phase difference between the three-phase voltage and zero sequence voltage signals is: φ A =|T U01 -T A1 |﹡ ; φ B =|T U01 -T B1 |﹡ ; …… (1) φ C =|T U01 -T C1 |﹡ ; wherein φ A , φ B , and φ C are the phase differences between the three-phase voltage and the zero-sequence voltage signals, respectively. The phase relationship of the three-phase voltage and zero sequence voltage signals is as follows: U0 = |T U01 - T UO2 | * T U A =|T A1 -T A2 |﹡ U B =|T B1 -T B2 |﹡ ………(2) U C =|T C1 -T C2 |﹡ U0 > U A U0 > U B ……… (3) U0 > U C T U01 <T A1 , T U02 <T A2 T U01 <T B1 , T U02 <T B2 ………(4) T U01 <T C1 , T U02 <T C2 Wherein, U0 is the pulse width of the bus zero sequence voltage signal after the occurrence of the leakage fault, U A is the pulse width of the A-phase voltage after the occurrence of the leakage fault, U B is the pulse width of the B-phase voltage after the occurrence of the leakage fault, U C is the pulse width of the C-phase voltage after the occurrence of the leakage fault; T U01 is the time for the zero sequence voltage signal to change from a low level to a high level state, T U02 is the time for the zero sequence voltage signal to change from a high level to a low level state, T A1 is the time for the A phase voltage signal to change from a low level to a high level state, T A2 is the time for the A phase voltage signal to change from a high level to a low level state, T B1 is the time for the B phase voltage signal to change from a low level to a high level state, T B2 is the time for the B phase voltage signal to change from a high level to a low level state, T C1 is the time for the C phase voltage signal to change from a low level to a high level state, T C2 is the time for the C phase voltage signal to change from a high level to a low level state.

2. The method for identifying a fault phase of a low voltage power grid leakage according to claim 1, characterized in that, The reliable coefficient of the set zero sequence voltage starting value is in the range of 2-4.5, and the set minimum action resistance value is in the range of 3.5kΩ-20kΩ.

3. The method for identifying a faulty phase of a low voltage power grid leakage according to claim 1 or 2, characterized in that The method comprises the following steps: After the leakage fault occurs, the collected zero sequence voltage signals are subjected to low-pass filtering, phase shifting, feedback, zero-crossing detection, photoelectric isolation and shaping processing to form zero sequence voltage square wave signals with a pulse width of 180 degrees, and the collected three-phase voltage signals are subjected to low-pass filtering, amplitude discrimination, photoelectric isolation and shaping processing to form three-phase voltage square wave signals with a pulse width varying between 0 and 180 degrees.

4. A device for identifying the faulty phase of a low voltage power grid earth fault, characterized in that, The method comprises the following steps: A data acquisition module is configured to acquire bus zero sequence voltage signals, bus three-phase voltage signals and insulation resistance values of the low-voltage power grid in real time; A fault determination module is configured to determine a single-phase or two-phase ground leakage fault when the zero sequence voltage value exceeds a set zero sequence voltage starting value and the insulation resistance value of the low-voltage power grid is less than a set minimum action resistance value; The phase difference judging module is configured to calculate whether the phase difference between the three-phase voltage and the zero sequence voltage signal meets criterion 1 according to the three-phase voltage and the zero sequence voltage signal after the electric leakage fault occurs, wherein the criterion 1 is that the phase difference between the three-phase voltage and the zero sequence voltage signal is φ, and the action region of the criterion 1 is 20 o ≤ φ ≤ 140 o . The phase relationship judging module is used for judging whether the three-phase voltage and zero sequence voltage signals conform to criterion 2 according to the three-phase voltage and zero sequence voltage signals after the electric leakage fault occurs, the criterion 2 being that the phase relationship of the three-phase voltage and zero sequence voltage signals conforms to a zero sequence fundamental wave frequency multiplication phase distinguishing method; the zero sequence fundamental wave frequency multiplication phase distinguishing method being that a zero sequence fundamental wave frequency multiplication phase distinguishing rule of a single-phase grounding electric leakage fault line is set, 1) simultaneously multiplying the fundamental wave zero sequence voltage and zero sequence current signals to an arbitrary frequency between 50HZ and 250HZ U 0B signal and I 0B signal; 2) the falling edge of the zero sequence voltage signal U 0B must be located between the rising edge and the falling edge of the zero sequence current signal I 0B , and the pulse width of the zero sequence voltage signal U 0B must be greater than the pulse width of the zero sequence current signal I 0B ; the zero sequence current and zero sequence voltage signals of each branch are distinguished according to the above two zero sequence fundamental wave frequency multiplication phase distinguishing rules; A fault phase determination module is configured to determine a certain phase or certain two phases as leakage ground fault phases when the certain phase or certain two phases simultaneously meet criterion 1 and criterion 2 after the leakage fault occurs; When the zero sequence voltage value exceeds a set zero sequence voltage starting value and the insulation resistance value of the low-voltage power grid is less than a set minimum action resistance value, i.e. when condition 1 and condition 2 are simultaneously met: Condition 1 : U Q > k R U bmax Condition 2: U JY <U lmin wherein, U Q is the zero sequence voltage value, U JY is the low voltage network insulation resistance value; k R U bmax is the zero sequence voltage starting value, U bmax is the maximum unbalanced zero sequence voltage effective value during normal operation of the low voltage network, k R is the reliability factor; U lmin is the minimum operating resistance value; The calculation formula of the phase difference between the three-phase voltage and zero sequence voltage signals is: φ A =|T U01 -T A1 |﹡ ; φ B =|T U01 -T B1 |﹡ ;... (1) φ C =|T U01 -T C1 |﹡ ; wherein φ A , φ B , and φ C are the phase differences between the three-phase voltage and the zero-sequence voltage signals, respectively. The phase relationship of the three-phase voltage and zero sequence voltage signals is as follows: U0 = |T U01 - T UO2 | * |T U A =|T A1 -T A2 |﹡ U B =|T B1 -T B2 |﹡ ………(2) U C =|T C1 -T C2 |﹡ U0 > U A U0 > U B ……… (3) U0 > U C T U01 <T A1 , T U02 <T A2 T U01 <T B1 , T U02 <T B2 ……… (4) T U01 <T C1 , T U02 <T C2 Wherein, U0 is the pulse width of the bus zero sequence voltage signal after the occurrence of the electric leakage fault, U A is the pulse width of the A-phase voltage after the occurrence of the electric leakage fault, U B is the pulse width of the B-phase voltage after the occurrence of the electric leakage fault, U C is the pulse width of the C-phase voltage after the occurrence of the electric leakage fault; T U01 time for the zero sequence voltage signal to change from a low to a high state, T U02 time for the zero sequence voltage signal to change from a high to a low state, T A1 time for the A phase voltage signal to change from a low to a high state, T A2 time for the A phase voltage signal to change from a high to a low state, T B1 time for the B phase voltage signal to change from a low to a high state, T B2 time for the B phase voltage signal to change from a high to a low state, T C1 time for the C phase voltage signal to change from a low to a high state, T C2 time for the C phase voltage signal to change from a high to a low state.

5. The device for identifying the faulty phase of a low voltage power grid leakage according to claim 4, characterized in that, The reliable coefficient of the set zero sequence voltage starting value is in the range of 2-4.5, and the set minimum action resistance value is in the range of 3.5kΩ-20kΩ.

6. The device for identifying the faulty phase of a low voltage network leakage according to claim 4 or 5, characterized in that it further comprises The method comprises the following steps: A data processing module is configured to, after the leakage fault occurs, subject the collected zero sequence voltage signals to low-pass filtering, phase shifting, feedback, zero-crossing detection, photoelectric isolation and shaping processing to form zero sequence voltage square wave signals with a pulse width of 180 degrees, and subject the collected three-phase voltage signals to low-pass filtering, amplitude discrimination, photoelectric isolation and shaping processing to form three-phase voltage square wave signals with a pulse width varying between 0 and 180 degrees.

Images