Leakage Selection Criterion, Comprehensive Discrimination Method and Device for Leakage Fault in Low-Voltage Power Grid

Abstract

The present invention discloses a leakage fault selection criterion, a comprehensive discrimination method and device for a low-voltage power grid. The comprehensive discrimination method includes the following steps: acquiring in real time a DC detection signal, a zero-sequence voltage and zero-sequence current signals of each branch that reflect the insulation level of the low-voltage power grid; comprehensively determining the leakage fault of the low-voltage power grid by using a variety of leakage fault selection criteria for the low-voltage power grid; sending out a leakage fault signal according to the determined leakage fault type, and quickly cutting off the corresponding fault line through a tripping circuit. The present invention combines a variety of leakage fault selection criteria for comprehensive discrimination of leakage faults in a low-voltage power grid, which not only adapts to the determination of various leakage faults in a low-voltage power grid, but also improves the accuracy of discrimination of leakage faults in a low-voltage power grid. The present invention realizes the compatibility between horizontal selective protection and vertical selective protection, and solves the technical problem of frequent overstepping tripping of the total leakage detection protection.

Description

Technical Field

[0001] The invention relates to a leakage selection criterion and a comprehensive judgment method and device for a low-voltage power grid leakage fault, belonging to the technical field of leakage fault judgment. Background Art

[0002] In my country, the neutral point of the 380V~1140V low-voltage power supply system in underground mines widely adopts the non-effective grounding method. The most common longitudinal and transverse electrical faults in the low-voltage power grid in the mine are leakage faults, accounting for more than 80% of all electrical faults. Leakage not only causes personal electric shock, gas and coal dust explosions and early explosion of electric detonators, but also the long-term existence of leakage current may further deteriorate the insulation of electrical equipment, thereby causing phase short circuits, electrical fires and other electrical accidents that endanger the safety of mines. In order to ensure the safety of personal electric shock and reduce the probability of gas and coal dust explosions caused by leakage, according to the relevant safety regulations of my country: the main switch of the low-voltage power grid in the mine and the branch switches must be equipped with a total leakage protection device that can automatically cut off the fault line and a selective leakage protection device, and the action time is 200ms and 30ms respectively. When a leakage fault occurs in the low-voltage power grid, the power supply of the faulty part must be cut off immediately, and the power supply of the non-faulty part must not be cut off, so as to reduce the scope of power outage and ensure the safe and continuous power supply of the low-voltage power grid in the mine. For a long time, various types of total leakage protection devices and selective leakage protection devices have been widely used in my country's underground low-voltage power grids in mines. Since these total leakage protection devices (the working principle is basically the additional DC detection type) and selective leakage protection devices (the working principle is basically the zero-sequence current amplitude method or the zero-sequence power direction method) are all composed of a single detection principle, decades of actual operation have shown that their protection performance and application effects are generally not ideal.

[0003] The shortcomings of the total leakage protection device are as follows: (1) The action is non-selective, that is, when leakage occurs at any point in the power grid, the entire power grid will be shut down, expanding the scope of the power outage. (2) The nature of the fault is not clear enough. When the backup protection of the total leakage protection device is activated, it is impossible to specify whether a single-phase concentrated leakage fault has occurred in a branch, or a single-phase concentrated leakage fault has occurred within the bus range, or a three-phase dispersed leakage fault has occurred in the power grid, which is not conducive to the determination and analysis of the nature of the leakage fault and makes it difficult to eliminate the leakage fault. (3) It cannot be used in conjunction with the lateral selective leakage protection device. When a single-phase concentrated leakage fault occurs in a branch, it will frequently cause the total leakage protection device to trip. (4) The action time is long, and it is impossible to ensure that the personal electric shock is less than 30mA·S as required by the safety system, which increases the risk of personal electric shock and has poor protection safety.

[0004] The disadvantages of the selective leakage protection device are as follows: (1) The action resistance value is unstable. When the load parameters change or the insulation resistance decreases, it is easy to fail to operate or operate prematurely. (2) There is a protection dead zone, which cannot protect three-phase dispersed leakage faults, and the protection is not comprehensive. (3) When a lateral leakage fault occurs, the probability of misselection, omission, and misselection is very high, that is, the selectivity and accuracy of the selective leakage protection are on average below 50%. (4) It cannot be used in conjunction with the total leakage protection device. When a single-phase concentrated leakage fault occurs in the branch, it will frequently cause the total leakage protection to trip. This phenomenon has caused an embarrassing situation in which only one of the two protection devices can be selected in engineering applications. (5) It cannot work in a system with a zero-sequence reactor compensation circuit in the low-voltage power grid. Selective leakage protection can only be achieved under the premise of abolishing the existing zero-sequence reactor compensation function of the underground low-voltage power grid, so that the capacitive current of the low-voltage power grid cannot be compensated and suppressed, thereby increasing the risk of personal electric shock and ignition of gas explosions, making the safety problem in the mine more prominent.

[0005] Therefore, developing a new comprehensive leakage selection and identification method that not only has clear leakage fault properties and longitudinal and transverse selectivity protection functions, but also can realize accurate leakage selection in low-voltage power grids with zero-sequence reactor compensation circuits has always been a technical problem that needs to be solved urgently in production sites. Summary of the invention

[0006] In order to solve the above problems, the present invention proposes a leakage selection criterion and a comprehensive judgment method and device for low-voltage power grid leakage faults, which can quickly and accurately judge the type of leakage faults.

[0007] The technical solution adopted by the present invention to solve the technical problem is:

[0008] In the first aspect, an embodiment of the present invention provides a leakage selection criterion for a low-voltage power grid leakage fault. If the zero-sequence voltage signal of the low-voltage power grid and the zero-sequence current signal of the branch conform to the zero-sequence fundamental frequency double phase discrimination principle, and the DC detection signal reflecting the insulation level of the low-voltage power grid is less than or equal to the set minimum allowable value, then it is determined that a single-phase concentrated leakage fault has occurred in the branch.

[0009] As a possible implementation of this embodiment, the specific determination condition of the single-phase concentrated leakage fault is:

[0010] U JY ≤UR min ………(1)

[0011] Among them, U JY It is a DC detection signal that reflects the insulation level of the low-voltage power grid during normal operation; UR min is the minimum allowed value;

[0012] 00 <U 0W <180 0 ………(5)

[0013] Among them, U 0W is the pulse width of the positive half-wave of the zero-sequence voltage signal U0;

[0014]

[0015] Among them, I 01W 、I 02W ……I 0nW are the pulse widths of the positive half-waves of the zero-sequence current signals I 01 、I 02 ……I 0n of each branch;

[0016]

[0017] Among them, T U01 、T U02 are respectively the time when the positive half-wave waveform of the zero-sequence voltage signal U0 changes from a low level to a high level and the time when it changes from a high level to a low level within the first power frequency cycle. I 01F 、I 01S are respectively the time when the positive half-wave waveform of the first zero-sequence current signal I 01 changes from a low level to a high level and the time when it changes from a high level to a low level within the first power frequency cycle. I 02F 、I 02S are respectively the time when the positive half-wave waveform of the second zero-sequence current signal I 02 changes from a low level to a high level and the time when it changes from a high level to a low level within the first power frequency cycle. I 0nF 、I 0nS are respectively the time when the positive half-wave waveform of the nth zero-sequence current signal I 0n changes from a low level to a high level and the time when it changes from a high level to a low level within the first power frequency cycle.

[0018] In a second aspect, a leakage fault selection criterion for a low-voltage power grid provided by an embodiment of the present invention is that when a DC detection signal reflecting the insulation level of the low-voltage power grid is less than or equal to a set minimum allowable value, if there is a bus zero-sequence voltage signal in the low-voltage power grid and there is no branch zero-sequence current signal, or, there are a zero-sequence voltage signal and a branch zero-sequence current signal in the low-voltage power grid but they do not conform to the zero-sequence fundamental frequency doubling phase discrimination principle, it is determined that a single-phase concentrated leakage fault occurs within the bus range.

[0019] As a possible implementation manner of this embodiment, the specific determination condition for a single-phase concentrated leakage fault occurring within the bus range is:

[0020] U JY ≤UR min ………(1)

[0021] Among them, U JY is the DC detection signal reflecting the insulation level of the low-voltage power grid during normal operation; UR min is the minimum allowable value;

[0022] 0 0 <U 0W <180 0 ………(5)

[0023] Among them, U 0W is the pulse width of the positive half-wave of the zero-sequence voltage signal U0;

[0024] At the same time, there is no zero-sequence current signal on the branch of the low-voltage power grid.

[0025] As a possible implementation of this embodiment, the specific determination condition for a single-phase concentrated leakage fault occurring within the bus range is:

[0026] U JY ≤UR min ………(1)

[0027] Among them, U JY is the DC detection signal reflecting the insulation level of the low-voltage power grid during normal operation; UR min is the minimum allowable value;

[0028] 0 0 <U 0W <180 0 ………(5)

[0029] Among them, U 0W is the pulse width of the positive half-wave of the zero-sequence voltage signal U0;

[0030]

[0031] Among them, I 01W 、I 02W ……I 0nW are the pulse widths of the positive half-waves of the zero-sequence current signals I 01 、I 02 ……I 0n ;

[0032] At the same time, the zero-sequence voltage signal of the low-voltage power grid and the zero-sequence current signal of the branch do not conform to the zero-sequence fundamental frequency double-frequency phase discrimination principle.

[0033] Thirdly, a leakage fault selection criterion for a low-voltage power grid provided by an embodiment of the present invention. If there is no zero-sequence voltage signal and branch zero-sequence current signal in the low-voltage power grid, and the leakage fault lasts for a certain period of time, it is determined as a three-phase dispersed leakage fault.

[0034] As a possible implementation manner of this embodiment, the specific determination condition for the leakage fault lasting for a certain period of time is:

[0035] (U JY ≤UR min )≥T SX ………(2)

[0036] Wherein, U JY is a DC detection signal reflecting the insulation level of the low-voltage power grid during normal operation; UR min is the minimum allowable value; T SX is the duration of the leakage fault.

[0037] Fourthly, a leakage fault selection criterion for a low-voltage power grid provided by an embodiment of the present invention. If a single-phase concentrated leakage fault as described above occurs in the low-voltage power grid, or a single-phase concentrated leakage fault occurs within the range of the bus as described above, or a three-phase dispersed leakage fault as described above occurs, and any one of the above leakage faults lasts for a certain period of time, it is determined as the total backup protection.

[0038] As a possible implementation manner of this embodiment, the specific determination condition for the leakage fault lasting for a certain period of time is:

[0039] (U JY ≤UR min )≥T ZH ………(3)

[0040] Wherein, U JY is a DC detection signal reflecting the insulation level of the low-voltage power grid during normal operation; UR min is the minimum allowable value, T ZH is the duration of the leakage fault.

[0041] As a possible implementation manner of this embodiment,

[0042]

[0043] Wherein, T is the sampling period.

[0044] As a possible implementation manner of this embodiment, the zero-sequence fundamental frequency doubling phase discrimination principle is: 1) Simultaneously double the fundamental frequency zero-sequence voltage and zero-sequence current signals to any frequency U 0B signal and I 0B signal between 50HZ and 250HZ; 2) The zero-sequence voltage signal U0B The falling edge of 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 .

[0045] Fifthly, a comprehensive discrimination method for leakage faults in a low-voltage power grid provided by an embodiment of the present invention includes the following steps:

[0046] Acquire in real time the DC detection signal, zero-sequence voltage, and zero-sequence current signals of each branch that reflect the insulation level of the low-voltage power grid;

[0047] Comprehensively determine the leakage faults in the low-voltage power grid by using the above-mentioned multiple leakage selection criteria for leakage faults in the low-voltage power grid;

[0048] Send out a leakage fault signal according to the determined leakage fault type, and quickly cut off the corresponding fault line through a tripping circuit.

[0049] Sixthly, a comprehensive discrimination device for leakage faults in a low-voltage power grid provided by an embodiment of the present invention includes:

[0050] A data acquisition module for acquiring in real time the DC detection signal, zero-sequence voltage, and zero-sequence current signals of each branch that reflect the insulation level of the low-voltage power grid;

[0051] A fault determination module for detecting in real time the numerical change of the DC detection signal U that reflects the insulation level of the low-voltage power grid. When the DC detection signal U JY is less than or equal to the set minimum allowable value, perform a comprehensive discrimination of the nature of the leakage fault; JY

[0052] A fault type comprehensive determination module for comprehensively determining the leakage faults in the low-voltage power grid by using multiple leakage selection criteria for leakage faults in the low-voltage power grid;

[0053] A fault alarm processing module for sending out a leakage fault signal according to the determined leakage fault type, and quickly cutting off the corresponding fault line through a tripping circuit.

[0054] As a possible implementation manner of this embodiment, the fault type comprehensive determination module includes:

[0055] A single-phase concentrated leakage fault determination module for determining whether a single-phase concentrated leakage fault occurs in a branch;

[0056] A bus single-phase concentrated leakage fault determination module for determining whether a single-phase concentrated leakage fault occurs within the bus range;

[0057] ​A three-phase dispersed leakage fault determination module is used to determine whether a three-phase dispersed leakage fault occurs in a low-voltage power grid;

[0058] A total backup protection determination module is used to determine whether it is a total backup protection.

[0059] As a possible implementation manner of this embodiment, the specific process for the single-phase concentrated leakage fault determination module to determine whether a single-phase concentrated leakage fault occurs in a branch is as follows: If the zero-sequence voltage signal of the low-voltage power grid and the zero-sequence current signal of the branch conform to the zero-sequence fundamental frequency multiple-phase discrimination principle, and the DC detection signal reflecting the insulation level of the low-voltage power grid is less than or equal to the set minimum allowable value, it is determined that a single-phase concentrated leakage fault occurs in this branch.

[0060] As a possible implementation manner of this embodiment, the bus single-phase concentrated leakage fault determination module is used to determine whether a single-phase concentrated leakage fault occurs within the bus range. The specific process is as follows: When the DC detection signal reflecting the insulation level of the low-voltage power grid is less than or equal to the set minimum allowable value, if the low-voltage power grid has a bus zero-sequence voltage signal and no branch zero-sequence current signal, or, the low-voltage power grid has a zero-sequence voltage signal and a branch zero-sequence current signal but does not conform to the zero-sequence fundamental frequency multiple-phase discrimination principle, it is determined that a single-phase concentrated leakage fault occurs within the bus range.

[0061] As a possible implementation manner of this embodiment, the specific process for the three-phase dispersed leakage fault determination module to determine whether a three-phase dispersed leakage fault occurs in the low-voltage power grid is as follows: If the low-voltage power grid has no zero-sequence voltage signal and no branch zero-sequence current signal, and the leakage fault lasts for a certain period of time, it is determined as a three-phase dispersed leakage fault.

[0062] As a possible implementation manner of this embodiment, the specific process for the total backup protection determination module to determine whether it is a total backup protection is as follows: If a single-phase concentrated leakage fault occurs in the low-voltage power grid, or a single-phase concentrated leakage fault occurs within the bus range, or a three-phase dispersed leakage fault occurs, and any of the above leakage faults lasts for a certain period of time, it is determined as a total backup protection.

[0063] The technical solution of the embodiment of the present invention can have the following beneficial effects:

[0064] The present invention provides four leakage fault selection criteria for low-voltage power grids, namely single-phase concentrated leakage fault determination, bus single-phase concentrated leakage fault determination, three-phase dispersed leakage fault determination, and total backup protection determination, and combines the four selection criteria for comprehensive discrimination of low-voltage power grid leakage faults, which not only adapts to the determination of various low-voltage power grid leakage faults, but also improves the accuracy of low-voltage power grid leakage fault discrimination.

[0065] The comprehensive discrimination method for leakage faults in a low-voltage power grid of the present invention not only has clear leakage fault properties and comprehensive protection functions, but also has the protection functions for single-phase concentrated leakage faults in branches, single-phase concentrated leakage faults within the range of the bus, three-phase dispersed leakage faults, and total backup protection functions.

[0066] The comprehensive discrimination method for leakage faults in a low-voltage power grid of the present invention has comprehensive leakage fault protection, and the protection range covers the entire low-voltage power supply unit without any dead zone of action. No matter where the concentrated or dispersed leakage fault occurs within the power supply unit, it can trigger a protection trip.

[0067] The comprehensive discrimination method for leakage faults in a low-voltage power grid of the present invention has high safety for leakage fault protection. It can accurately select the leakage in the circuit state where the low-voltage power grid has a zero-sequence reactor compensation (regardless of whether the zero-sequence reactor is in an under-compensated or over-compensated state). By applying the zero-sequence fundamental frequency doubling phase discrimination method, the discrimination time for single-phase concentrated leakage faults in branches ≤ 20ms, and the discrimination time for single-phase concentrated leakage faults in the bus ≤ 30ms. No matter where a personal electric shock accident occurs in the low-voltage power grid, it can ensure that the personal electric shock current does not exceed the safety value of 30mA·S.

[0068] The comprehensive discrimination method for leakage faults in a low-voltage power grid of the present invention has a stable action value, is easy to set, and can reflect the change of the insulation level of the low-voltage power grid to the ground in real time and accurately; it has high sensitivity and can quickly and reliably act when the zero-sequence current of the fault branch ≤ 10mA, and has a strong response ability to critical leakage faults; the line selection accuracy is high, and the corresponding line can be cut off according to the different nature of the leakage fault. The power outage range during leakage faults is small, improving the reliability of power supply.

[0069] The comprehensive discrimination method for leakage faults in a low-voltage power grid of the present invention realizes the compatibility between transverse selective protection and longitudinal selective protection, and solves the technical problem of frequent overstepping tripping of the total leakage detection protection. Brief Description of the Drawings

[0070] Figure 1 is a flowchart of a comprehensive discrimination method for leakage faults in a low-voltage power grid shown according to an exemplary embodiment;

[0071] Figure 2 is a structural diagram of a comprehensive discrimination device for leakage faults in a low-voltage power grid shown according to an exemplary embodiment;

[0072] Figure 3 is a flowchart of comprehensively discriminating leakage faults in a low-voltage power grid by using the device of the present invention. Detailed Embodiments

[0073] The following further describes the present invention in conjunction with the drawings and embodiments:

[0074] To clearly illustrate the technical features of this solution, the present invention will be elaborated in detail below through specific embodiments and in conjunction with its accompanying drawings. The following disclosure provides many different embodiments or examples for implementing different structures of the present invention. To simplify the disclosure of the present invention, the components and settings of specific examples are described below. In addition, the present invention may repeat reference numerals and / or letters in different examples. This repetition is for the purpose of simplification and clarity, and does not itself indicate the relationship between the various embodiments and / or settings discussed. It should be noted that the components illustrated in the drawings are not necessarily drawn to scale. The present invention omits the description of well-known components and processing technologies and processes to avoid unnecessarily limiting the present invention.

[0075] As Figure 1 shown, a comprehensive discrimination method for leakage faults in a low-voltage power grid provided by an embodiment of the present invention includes the following steps:

[0076] Real-time collect and obtain DC detection signals, zero-sequence voltages, and zero-sequence current signals of each branch that reflect the insulation level of the low-voltage power grid;

[0077] Use multiple leakage selection criteria for leakage faults in the low-voltage power grid to comprehensively determine the leakage faults in the low-voltage power grid;

[0078] According to the determined leakage fault type, send out a leakage fault signal and quickly cut off the corresponding fault line through a tripping circuit.

[0079] The multiple leakage selection criteria for leakage faults in the low-voltage power grid include at least any one or more of the following four.

[0080] As a possible implementation manner of this embodiment, the first leakage selection criterion for leakage faults in the low-voltage power grid: If the zero-sequence voltage signal of the low-voltage power grid and the zero-sequence current signal of the branch conform to the zero-sequence fundamental frequency multiple-phase discrimination principle, and the DC detection signal reflecting the insulation level of the low-voltage power grid is less than or equal to the set minimum allowable value, then it is determined that a single-phase concentrated leakage fault has occurred in this branch.

[0081] As a possible implementation manner of this embodiment, the specific determination conditions for the single-phase concentrated leakage fault are:

[0082] U JY ≤UR min ………(1)

[0083] Among them, U JY is the DC detection signal reflecting the insulation level of the low-voltage power grid during normal operation; UR min is the minimum allowable value;

[0084] 0 0 <U 0W <1800 ………(5)

[0085] Among them, U 0W is the pulse width of the positive half-wave of the zero-sequence voltage signal U0;

[0086]

[0087] Among them, I 01W 、I 02W ……I 0nW are the pulse widths of the positive half-waves of the zero-sequence current signals I 01 、I 02 ……I 0n respectively;

[0088]

[0089] Among them, T U01 、T U02 are respectively the time when the positive half-wave waveform of the zero-sequence voltage signal U0 changes from low level to high level and the time when it changes from high level to low level within the first power frequency cycle. I 01F 、I 01S are respectively the time when the positive half-wave waveform of the first path zero-sequence current signal I 01 changes from low level to high level and the time when it changes from high level to low level within the first power frequency cycle. I 02F 、I 02S are respectively the time when the positive half-wave waveform of the second path zero-sequence current signal I 02 changes from low level to high level and the time when it changes from high level to low level within the first power frequency cycle. I 0nF 、I 0nS are respectively the time when the positive half-wave waveform of the nth path zero-sequence current signal I 0n changes from low level to high level and the time when it changes from high level to low level within the first power frequency cycle.

[0090] As a possible implementation manner of this embodiment,

[0091]

[0092]

[0093] Among them, T is the sampling period.

[0094] Conditions for discriminating single-phase concentrated leakage faults in branch circuits: When a single-phase concentrated leakage fault occurs in a certain branch of the low-voltage power grid, there is a bus zero-sequence voltage signal, zero-sequence current signals in each branch, and the zero-sequence current signal and zero-sequence voltage signal of the branch with the leakage fault conform to the zero-sequence fundamental harmonic multiple-frequency phase discrimination method. At the same time, there is also an insulation resistance value detection signal. Only when all these three conditions are met is it determined that a single-phase concentrated leakage fault has occurred in a certain branch.

[0095] As a possible implementation of this embodiment, the second leakage selection criterion for low-voltage power grid leakage faults: When the DC detection signal reflecting the insulation level of the low-voltage power grid is less than or equal to the set minimum allowable value, if there is a bus zero-sequence voltage signal in the low-voltage power grid and no zero-sequence current signal in the branches, or if there are zero-sequence voltage signals and zero-sequence current signals in the branches of the low-voltage power grid but they do not conform to the zero-sequence fundamental harmonic multiple-frequency phase discrimination principle, it is determined that a single-phase concentrated leakage fault has occurred within the range of the bus.

[0096] As a possible implementation of this embodiment, the specific determination conditions for a single-phase concentrated leakage fault occurring within the range of the bus are:

[0097] U JY ≤UR min ………(1)

[0098] Among them, U JY is the DC detection signal reflecting the insulation level of the low-voltage power grid during normal operation; UR min is the minimum allowable value;

[0099] 0 0 <U 0W <180 0 ………(5)

[0100] Among them, U 0W is the pulse width of the positive half-wave of the zero-sequence voltage signal U0;

[0101] At the same time, there is no zero-sequence current signal on the branches of the low-voltage power grid.

[0102] As a possible implementation of this embodiment, the specific determination conditions for a single-phase concentrated leakage fault occurring within the range of the bus are:

[0103] U JY ≤UR min ………(1)

[0104] Among them, U JY is the DC detection signal reflecting the insulation level of the low-voltage power grid during normal operation; UR min is the minimum allowable value;

[0105] 0 0 <U0W <180 0 ………(5)

[0106] Among them, U 0W is the pulse width of the positive half - wave of the zero - sequence voltage signal U0;

[0107]

[0108] Among them, I 01W 、I 02W ……I 0nW are the pulse widths of the positive half - waves of the zero - sequence current signals I 01 、I 02 ……I 0n of each branch;

[0109] Meanwhile, the zero - sequence voltage signal of the low - voltage power grid does not conform to the zero - sequence fundamental - frequency multiple - phase discrimination principle with the zero - sequence current signal of the branch.

[0110] Conditions for judging single - phase concentrated leakage faults within the bus range: When a single - phase concentrated leakage fault occurs at a certain place within the low - voltage power grid bus range, there are two situations for judging the bus leakage fault: 1) There is a zero - sequence voltage signal of the bus, no zero - sequence current signal of the branch, and at the same time, there is an insulation resistance value detection signal, then it is judged as a bus leakage fault; 2) There is a zero - sequence voltage signal of the bus, there is a zero - sequence current signal of the branch, but the zero - sequence current of each branch does not conform to the zero - sequence fundamental - frequency multiple - phase discrimination method with the zero - sequence voltage signal, and at the same time, there is an insulation resistance value detection signal. In this case, it is also judged as a bus leakage fault.

[0111] As a possible implementation manner of this embodiment, for the third leakage - fault selection - leakage criterion of the low - voltage power grid, if there is no zero - sequence voltage signal and zero - sequence current signal in the low - voltage power grid, and the leakage fault lasts for a certain period of time, it is determined as a three - phase dispersed leakage fault.

[0112] As a possible implementation manner of this embodiment, the specific determination condition for the leakage fault lasting for a certain period of time is:

[0113] (U JY ≤UR min )≥T SX ………(2)

[0114] Among them, U JY is the DC detection signal reflecting the insulation level of the low - voltage power grid during normal operation; UR min is the minimum allowable value; T SX is the duration of the leakage fault.

[0115] Conditions for judging three-phase dispersed leakage faults: When the insulation values of the three phases to the ground in a low-voltage power grid uniformly drop to the minimum allowable value specified in the national standard (for example, in a 380V power grid, when the insulation resistance value of each phase to the ground is less than or equal to 10.5KΩ, it is judged that a three-phase leakage fault has occurred), it is determined that a three-phase dispersed leakage fault has occurred in the low-voltage power grid. When a three-phase leakage fault occurs in the low-voltage power grid, because the insulation values of the three phases to the ground drop uniformly, there is no zero-sequence voltage signal in the system, and there is no zero-sequence current signal in each branch, only the insulation resistance value detection signal.

[0116] As a possible implementation of this embodiment, the leakage fault selection criterion for the fourth type of low-voltage power grid leakage fault: If a single-phase concentrated leakage fault as described above occurs in the low-voltage power grid, or a single-phase concentrated leakage fault occurs within the range of the bus as described above, or a three-phase dispersed leakage fault as described above occurs, and any of the above leakage faults persists for a certain period of time, it is determined as the total backup protection.

[0117] As a possible implementation of this embodiment, the specific determination condition for the leakage fault persisting for a certain period of time is:

[0118] (U JY ≤UR min )≥T ZH ………(3)

[0119] Wherein, U JY is the DC detection signal reflecting the insulation level of the low-voltage power grid during normal operation; UR min is the minimum allowable value, and T ZH is the duration of the leakage fault.

[0120] The conditions for judging the total backup protection are divided into the following three cases:

[0121] First, a single-phase concentrated leakage fault occurs in a certain branch, but due to a fault in the circuit breaker of this branch or other reasons, the faulty branch cannot be disconnected, resulting in the continuous existence of the leakage fault. At this time, the total backup protection tripping circuit should operate after a delay of 180 - 250ms from the start of the leakage fault, and disconnect the main power supply incoming switch.

[0122] Second, a single-phase leakage fault occurs within the range of the bus. Due to a problem in the bus tripping circuit or other reasons, the main power supply incoming switch is not quickly disconnected, resulting in the continuous existence of the bus leakage fault. At this time, the total backup protection tripping circuit should operate after a delay of 180 - 250ms from the start of the leakage fault, and disconnect the main power supply incoming switch.

[0123] Thirdly, a three-phase leakage fault occurs in the low-voltage power grid. Due to problems in the three-phase leakage tripping circuit or other reasons, the main power supply incoming switch is not quickly disconnected, resulting in the continuous existence of the three-phase leakage fault. At this time, after a delay of 180 - 250 ms from the start of the leakage fault, the total backup protection tripping circuit should operate to disconnect the main power supply incoming switch.

[0124] As a possible implementation manner of this embodiment, the zero-sequence fundamental frequency doubling phase discrimination principle is as follows: 1) Simultaneously double the fundamental frequency zero-sequence voltage and zero-sequence current signals to any frequency U 0B signal and I 0B signal between 50HZ and 250HZ; 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 .

[0125] The present invention provides four kinds of leakage fault selection criteria for low-voltage power grid leakage faults, namely single-phase concentrated leakage fault determination, bus single-phase concentrated leakage fault determination, three-phase dispersed leakage fault determination, and total backup protection determination. By combining these four selection criteria for comprehensive discrimination of low-voltage power grid leakage faults, it not only adapts to the determination of various low-voltage power grid leakage faults, but also improves the accuracy of low-voltage power grid leakage fault discrimination. The present invention realizes the compatibility between horizontal selective protection and vertical selective protection, and solves the technical problem of frequent overstep tripping of the total leakage detection protection.

[0126] As Figure 2 shown, a comprehensive discrimination device for low-voltage power grid leakage faults provided by an embodiment of the present invention includes:

[0127] A data acquisition module for real-time acquisition of DC detection signals, zero-sequence voltages, and zero-sequence current signals of each branch that reflect the insulation level of the low-voltage power grid;

[0128] A fault determination module for real-time detection of the numerical change of the DC detection signal U JY that reflects the insulation level of the low-voltage power grid. When the DC detection signal U JY is less than or equal to the set minimum allowable value, a comprehensive discrimination of the nature of the leakage fault is performed;

[0129] A fault type comprehensive discrimination module for determining the type of low-voltage power grid leakage fault by using various selection criteria for low-voltage power grid leakage faults;

[0130] A fault alarm processing module for sending out a leakage fault signal according to the determined type of leakage fault and quickly cutting off the corresponding fault line through a tripping circuit.

[0131] As a possible implementation manner of this embodiment, the comprehensive fault type discrimination module includes:

[0132] A single-phase concentrated leakage fault determination module, configured to determine whether a single-phase concentrated leakage fault occurs in a branch;

[0133] A bus single-phase concentrated leakage fault determination module, configured to determine whether a single-phase concentrated leakage fault occurs within the range of the bus;

[0134] A three-phase scattered leakage fault determination module, configured to determine whether a three-phase scattered leakage fault occurs in a low-voltage power grid;

[0135] A total backup protection determination module, configured to determine whether it is a total backup protection.

[0136] As Figure 3 shown, the specific process of comprehensively discriminating the leakage fault of the low-voltage power grid by using the device of the present invention is as follows.

[0137] Step 1: Real-time collect and obtain the insulation value, zero-sequence voltage, and zero-sequence current signals of each branch that reflect the insulation level of the low-voltage power grid.

[0138] Step 2: After data processing, the insulation value signal that reflects the insulation level of the low-voltage power grid collected forms a DC detection signal U JY that reflects the insulation level of the low-voltage power grid. The zero-sequence voltage obtained by sampling forms a zero-sequence voltage signal U0 after data processing. The zero-sequence currents of each branch (for example, there are n branches) obtained by sampling form zero-sequence current signals after data processing, which are respectively denoted as I 01 、I 02 ……I 0n . The acquisition process of the insulation resistance value signal is as follows: When a leakage fault occurs in a branch or a bus, for example, the time when the leakage fault occurs is defined as 0 ms. Starting from the moment when the leakage fault occurs, it takes about 20 - 30 ms for the insulation resistance value detection circuit to extract the insulation detection signal, that is, the time to obtain the insulation detection signal is greater than the time to determine the leakage fault.

[0139] Step 3: By detecting the numerical change of the DC detection signal U JY that reflects the insulation level of the low-voltage power grid in real time through Step 2, when the DC detection signal U JY is less than or equal to the set minimum allowable value, that is, when Condition 1 is satisfied, it is considered that a leakage fault has occurred;

[0140] Condition 1: U JY ≤UR min ………(1)

[0141] Condition 2: (UJY ≤UR min )≥T SX ………(2)

[0142] Condition 3: (U JY ≤UR min )≥T ZH ………(3)

[0143] Wherein, U JY is a DC detection signal reflecting the insulation level of the low-voltage power grid during normal operation; UR min is the minimum allowable value. In the case of a 380V low-voltage power grid, UR min has a value range of 2.8 - 4.2 kΩ, preferably 3.5 kΩ; in the case of a 660V low-voltage power grid, UR min has a value range of 8.8 - 13.3 kΩ, preferably 11 kΩ; in the case of a 1140V low-voltage power grid, UR min has a value range of 16 - 24 kΩ, preferably 20 kΩ; T SX is the duration of the leakage fault, T SX is the third criterion threshold, and its value range is 60 ms to 100 ms, preferably 80 ms, T ZH is the duration of the leakage fault, T ZH is the fourth criterion threshold, and its value range is 180 ms to 250 ms, preferably 200 ms.

[0144] Step 4: Calculate the pulse widths of the zero-sequence voltage and the first positive half-wave waveforms of the zero-sequence currents of each branch in the first power frequency cycle after the occurrence of the leakage fault according to the following formula by using the zero-sequence voltage and the zero-sequence currents of each branch collected in real time in Step 2:

[0145] Condition 4:

[0146]

[0147] Condition 5:

[0148] 0 0 <U 0W <180 0 ………(5)

[0149] Condition 6:

[0150]

[0151] Wherein, T is the sampling period, U 0W is the pulse width of the positive half-wave of the zero-sequence voltage signal U0, I 01W 、I 02W ……I 0nW are the zero-sequence current signals of each branch01 , I 02 ……I 0n The pulse width of the positive half cycle;

[0152] Through step 2, the zero-sequence voltage and the zero-sequence current of each branch collected in real time are used to determine whether the zero-sequence current and the zero-sequence voltage signal of each branch in the first power frequency cycle after the occurrence of the leakage fault satisfy the zero-sequence fundamental frequency double-frequency phase discrimination method according to the following conditions:

[0153] Condition 7:

[0154]

[0155] Among them, T U01 , T U02 are respectively the time when the waveform of the positive half cycle of the zero-sequence voltage signal U0 changes from the low level to the high level and the time when it changes from the high level to the low level in the first power frequency cycle, I 01F , I 01S are respectively the time when the waveform of the positive half cycle of the first-way zero-sequence current signal I 01 changes from the low level to the high level and the time when it changes from the high level to the low level in the first power frequency cycle, I 02F , I 02S are respectively the time when the waveform of the positive half cycle of the second-way zero-sequence current signal I 02 changes from the low level to the high level and the time when it changes from the high level to the low level in the first power frequency cycle, I 0nF , I 0nS are respectively the time when the waveform of the positive half cycle of the nth-way zero-sequence current signal I 0n changes from the low level to the high level and the time when it changes from the high level to the low level in the first power frequency cycle;

[0156] The four comprehensive leakage selection and discrimination criteria are as follows:

[0157] Criterion 1: There are zero-sequence voltage and branch zero-sequence current signals, and the branch zero-sequence current signal satisfies the zero-sequence fundamental frequency double-frequency phase discrimination method, then it is determined that the nature of the leakage fault is a single-phase concentrated leakage fault in the branch;

[0158] Criterion 2: There is zero-sequence voltage, no branch zero-sequence current signal, or there is a branch zero-sequence current signal but it does not satisfy the zero-sequence fundamental frequency double-frequency phase discrimination method, then it is determined that the nature of the leakage fault is a single-phase concentrated leakage fault in the bus range;

[0159] Criterion 3: There is no zero-sequence voltage and branch zero-sequence current signal, and the duration of the leakage fault ≥ T SX , then it is determined that the nature of the leakage fault is a three-phase dispersed leakage fault;

[0160] Criterion 4: There is a branch leakage, or bus leakage, or three-phase dispersed leakage fault, and the duration of the leakage fault ≥ T ZH , then it is determined that the total backup protection has occurred.

[0161] The process of comprehensively selecting and discriminating leakage according to the criterion is as follows:

[0162] After the leakage fault occurs, when the zero-sequence current signal of a certain branch satisfies Criterion 1, that is, satisfies the above Conditions 1, 5, 6, and 7 at the same time, it is determined that a single-phase concentrated leakage fault has occurred in a certain branch;

[0163] After the leakage fault occurs, when it satisfies Criterion 2, that is, satisfies the above Conditions 1 and 5 at the same time but does not satisfy Condition 6, or satisfies the above Conditions 1, 5, and 6 at the same time but does not satisfy Condition 7, it is determined that a single-phase concentrated leakage fault has occurred within the bus range;

[0164] After the leakage fault occurs, when it satisfies Criterion 3, that is, satisfies Condition 2 but does not satisfy Conditions 5 and 6, it is determined that a three-phase dispersed leakage fault has occurred;

[0165] After the leakage fault occurs, when it satisfies Criterion 4, that is, satisfies Criterion 1 and Condition 3 at the same time, or satisfies Criterion 2 and Condition 3 at the same time, or satisfies Criterion 3 and Condition 3 at the same time, it is determined as the total backup protection.

[0166] Step 5: According to the comprehensive leakage selection and discrimination method, determine the nature of the leakage fault, send out the leakage fault signal, perform Chinese display of fault information, fault information storage, network communication, indicate and memorize the fault line through a light-emitting diode and give an audible alarm, and at the same time, quickly cut off the corresponding fault line through the tripping circuit to prevent the accident from expanding.

[0167] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: It is still possible to modify the specific implementation manners of the present invention or make equivalent replacements, and any modification or equivalent replacement that does 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 leakage selection criterion for low-voltage power grid leakage faults, characterized in that, If a single-phase concentrated leakage fault occurs in the low-voltage power grid, or a single-phase concentrated leakage fault occurs within the range of the low-voltage power grid bus, or a three-phase dispersed leakage fault occurs in the low-voltage power grid, and any of the above leakage faults persists for a certain period of time, it is determined as the total backup protection; The determination process for a single-phase concentrated leakage fault in the low-voltage power grid is as follows: If the zero-sequence voltage signal of the low-voltage power grid and the zero-sequence current signal of the branch conform to the zero-sequence fundamental frequency multiple-phase discrimination principle, and the DC detection signal reflecting the insulation level of the low-voltage power grid is less than or equal to the set minimum allowable value, it is determined that a single-phase concentrated leakage fault has occurred in this branch; The determination process for a single-phase concentrated leakage fault within the range of the bus is as follows: When the DC detection signal reflecting the insulation level of the low-voltage power grid is less than or equal to the set minimum allowable value, if the low-voltage power grid has a bus zero-sequence voltage signal and no branch zero-sequence current signal, or, the low-voltage power grid has a zero-sequence voltage signal and a branch zero-sequence current signal but does not conform to the zero-sequence fundamental frequency multiple-phase discrimination principle, it is determined that a single-phase concentrated leakage fault has occurred within the range of the bus; The determination process for a three-phase dispersed leakage fault in the low-voltage power grid is as follows: If the low-voltage power grid has no zero-sequence voltage signal and branch zero-sequence current signal, and the leakage fault persists for a certain period of time, it is determined as a three-phase dispersed leakage fault.

2. The leakage selection criterion for low-voltage power grid leakage faults according to claim 1, characterized in that, The specific determination conditions for the single-phase concentrated leakage fault are: U JY ≤UR min ………(1) Among them, U JY is a DC detection signal reflecting the insulation level of the low-voltage power grid during normal operation; UR min is the minimum allowable value; 0 0 ＜U 0W ＜180 0 ………(5) Among them, U 0W is the pulse width of the positive half cycle of the zero-sequence voltage signal U0; Among them, I 01W , I 02W ……I 0nW are the zero-sequence current signals of each branch I 01 , I 02 ……I 0n the pulse widths of the positive half-cycles; Among them, T U01 and T U02 are respectively the time when the waveform of the positive half-cycle of the zero-sequence voltage signal U0 changes from a low level to a high level and the time when it changes from a high level to a low level within the first power frequency cycle. T I01F and T I01S are respectively the time when the waveform of the positive half-cycle of the first zero-sequence current signal I 01 changes from a low level to a high level and the time when it changes from a high level to a low level within the first power frequency cycle. T I02F and T I02S are respectively the time when the waveform of the positive half-cycle of the second zero-sequence current signal I 02 changes from a low level to a high level and the time when it changes from a high level to a low level within the first power frequency cycle. T I0nF and T I0nS are respectively the time when the waveform of the positive half-cycle of the nth zero-sequence current signal I 0n changes from a low level to a high level and the time when it changes from a high level to a low level.

3. The leakage selection criterion for low-voltage power grid leakage faults according to claim 1, characterized in that, The specific determination conditions for the single-phase concentrated leakage fault occurring within the range of the bus are: U JY ≤UR min ………(1) Among them, U JY is the DC detection signal reflecting the insulation level of the low-voltage power grid during normal operation; UR min is the minimum allowable value; 0 0 ＜U 0W ＜180 0 ………(5) Among them, U 0W is the pulse width of the positive half cycle of the zero-sequence voltage signal U0; At the same time, there is no zero-sequence current signal on the branch of the low-voltage power grid.

4. The leakage selection criterion for low-voltage power grid leakage faults according to claim 1, characterized in that, The specific determination conditions for the single-phase concentrated leakage fault occurring within the range of the bus are: U JY ≤UR min ………(1) Among them, U JY is a DC detection signal that reflects the insulation level of the low-voltage power grid during normal operation; UR min is the minimum allowable value; 0 0 ＜U 0W ＜180 0 ………(5) Among them, U 0W is the pulse width of the positive half-wave of the zero-sequence voltage signal U0; Among them, I 01W , I 02W ……I 0nW are the zero-sequence current signals of each branch I 01 , I 02 ……I 0n pulse widths of the positive half cycles; At the same time, the zero-sequence voltage signal of the low-voltage power grid and the zero-sequence current signal of the branch do not conform to the zero-sequence fundamental frequency multiple-phase discrimination principle.

5. The leakage selection criterion for low-voltage power grid leakage faults according to claim 2 or 4, characterized in that, Wherein, T is the sampling period.

6. A comprehensive discrimination method for low-voltage power grid leakage faults, characterized in that, It includes the following steps: Real-time collect and obtain the DC detection signal, zero-sequence voltage, and zero-sequence current signals of each branch that reflect the insulation level of the low-voltage power grid; Use the leakage selection criterion for the low-voltage power grid leakage fault described in Claim 1 to comprehensively determine the low-voltage power grid leakage fault; Send a leakage fault signal according to the determined leakage fault type, and quickly cut off the corresponding fault line through the tripping circuit.

7. An integrated discrimination device for leakage faults in a low-voltage power grid, characterized in that, It includes: A data acquisition module for real-time collecting and obtaining the DC detection signal, zero-sequence voltage, and zero-sequence current signals of each branch that reflect the insulation level of the low-voltage power grid; A fault determination module, which is used to detect in real time the numerical change of the DC detection signal U that reflects the insulation level of the low-voltage power grid. When the DC detection signal U JY is less than or equal to the set minimum allowable value, a comprehensive discrimination of the nature of the leakage fault is carried out; JY ​ A fault type comprehensive determination module for comprehensively determining the low-voltage power grid leakage fault by using multiple leakage selection criteria for the low-voltage power grid leakage fault; A fault alarm processing module for sending a leakage fault signal according to the determined leakage fault type and quickly cutting off the corresponding fault line through the tripping circuit; The fault type comprehensive determination module includes: A single-phase concentrated leakage fault determination module for determining whether a single-phase concentrated leakage fault has occurred in the branch; A bus single-phase concentrated leakage fault determination module for determining whether a single-phase concentrated leakage fault has occurred within the range of the bus; A three-phase dispersed leakage fault determination module for determining whether a three-phase dispersed leakage fault has occurred in the low-voltage power grid; A total backup protection determination module for determining whether it is the total backup protection; The specific process of the single-phase concentrated leakage fault determination module for determining whether a single-phase concentrated leakage fault occurs in a branch is as follows: If the zero-sequence voltage signal of the low-voltage power grid and the zero-sequence current signal of the branch conform to the zero-sequence fundamental frequency multiple-phase discrimination principle, and the DC detection signal reflecting the insulation level of the low-voltage power grid is less than or equal to the set minimum allowable value, then it is determined that a single-phase concentrated leakage fault occurs in this branch; The specific process of the bus single-phase concentrated leakage fault determination module for determining whether a single-phase concentrated leakage fault occurs within the bus range is as follows: When the DC detection signal reflecting the insulation level of the low-voltage power grid is less than or equal to the set minimum allowable value, if the low-voltage power grid has a bus zero-sequence voltage signal and no branch zero-sequence current signal, or, the low-voltage power grid has a zero-sequence voltage signal and a branch zero-sequence current signal but does not conform to the zero-sequence fundamental frequency multiple-phase discrimination principle, then it is determined that a single-phase concentrated leakage fault occurs within the bus range; The specific process of the three-phase dispersed leakage fault determination module for determining whether a three-phase dispersed leakage fault occurs in the low-voltage power grid is as follows: If the low-voltage power grid has no zero-sequence voltage signal and no branch zero-sequence current signal, and the leakage fault lasts for a certain period of time, then it is determined as a three-phase dispersed leakage fault; The specific process of the total backup protection determination module for determining whether it is a total backup protection is as follows: If a single-phase concentrated leakage fault occurs in the low-voltage power grid, or a single-phase concentrated leakage fault occurs within the bus range, or a three-phase dispersed leakage fault occurs, and any of the above leakage faults lasts for a certain period of time, then it is determined as a total backup protection.

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