Power grid fault identification and protection method and system

Abstract

The invention belongs to the field of power grid fault identification, and particularly relates to a power grid fault identification and protection method and system. Preliminarily judging that the power grid has a fault risk under the condition that any phase current meets a first fault criterion and any line voltage meets a second fault criterion; if the power grid is preliminarily judged to have the fault risk, starting fault judgment, and determining whether the power grid has a fault according to a fault judgment result; the first fault criterion comprises that the current value of any phase of current in the three-phase current is larger than the value of the moment before the set time length, and the absolute value of the difference between the variable quantity in the current set time length and the variable quantity in the previous set time length is larger than a first current threshold value; the second fault criterion comprises that the current value of any line voltage in the three-line voltage is smaller than the value of the moment before the set time length, and the absolute value of the difference between the variable quantity in the current set time length and the variable quantity in the previous set time length is greater than the first voltage threshold value; the set duration is smaller than the period of the phase current and the period of the line voltage.

Description

Technical Field

[0001] This invention belongs to the field of power grid fault identification, and specifically relates to a method and system for identifying and protecting against power grid faults. Background Technology

[0002] The phenomenon of short-term, significant voltage fluctuations or even brief power outages lasting several seconds in the power grid due to lightning strikes, short circuits, power failures, and other internal and external factors is called "voltage dips." Voltage dips are mostly caused by power grid faults. Traditional medium-voltage power supply system protection schemes have a detection time of approximately 60ms when a fault occurs, and the system voltage can only recover after the protection reliably clears the fault. The voltage dip during this process lasts at least 120ms. This means that traditional medium-voltage power supply system protection schemes require a considerable amount of time to complete the entire process of fault identification and protection. This approach can easily lead to the tripping or damage of sensitive loads used in production enterprises (such as numerous contactors, frequency converters, PLCs, and various digital devices), potentially causing production interruptions, significant economic losses to the enterprise, and even affecting the safe and stable operation of the power grid.

[0003] With the development of power grid fault identification technology, some optimized protection schemes for medium-voltage power supply systems have been proposed. These protection schemes can achieve rapid fault identification (i.e., complete fault identification in a short time, such as within 10ms to 20ms, which greatly shortens the detection time compared to 60ms), but in practical applications, protection malfunctions often occur. Summary of the Invention

[0004] The purpose of this invention is to provide a method and system for identifying and protecting against power grid faults, which solves the problem that fault protection often fails to activate when quickly identifying power grid faults in the prior art.

[0005] To achieve the above objectives, the present invention provides a method for identifying power grid faults, the method comprising:

[0006] If any phase current in the three-phase current of the power grid satisfies the first fault criterion and any line voltage in the power grid satisfies the second fault criterion, it is preliminarily determined that the power grid has a risk of fault existence; if it is preliminarily determined that the power grid has a risk of fault existence, fault judgment is initiated, and the existence of fault in the power grid is determined based on the fault judgment result.

[0007] The first fault criterion includes: the current value of any phase current in the three-phase current of the power grid is larger than the value at a time before the set time period, and the absolute value of the difference between the change in the current set time period and the change in the previous set time period is greater than the first current threshold.

[0008] The second fault criterion includes: the current value of any of the three line voltages of the power grid is smaller than the value at a time before the set time period, and the absolute value of the difference between the change in the current set time period and the change in the previous set time period is greater than the first voltage threshold.

[0009] The set duration is less than both the period of the phase current and the period of the line voltage.

[0010] Beneficial Effects: This invention provides a novel method for identifying power grid faults, which achieves accurate fault identification through a two-stage judgment process. The first stage is a qualitative judgment, that is, a preliminary assessment of whether the power grid poses a risk of fault. The second stage is a quantitative judgment, that is, based on the assessment of the risk of fault, the final judgment is made on whether a fault actually exists in the power grid. The qualitative judgment stage employs two different fault criteria, combining two different dimensions to measure the fault. One is based on a sudden change in phase current, and the other is based on a sudden change in line voltage. If only one fault criterion is met, it is insufficient to indicate a risk, thus filtering out some power grid fluctuations caused by a single abnormal change in current or voltage. Only when both fault criteria are met is the risk of a power grid fault identified. However, this stage only provides a preliminary conclusion that the power grid may have a fault, and this possibility needs to be discussed in two actual scenarios: one where the power grid actually has a fault, and the other where the power grid does not actually have a fault. Based on this preliminary conclusion, further assessment is needed. Therefore, after determining that there is a risk of grid fault, a quantitative assessment is then conducted to definitively determine the fault (i.e., initiating fault assessment). Since some abnormal situations not caused by grid faults have already been screened out based on risk assessment before initiating fault assessment, fault assessment only needs to assess the remaining abnormal situations. The fault characteristics of these abnormal situations are very similar to those of grid faults. Therefore, conducting fault assessment at this time can effectively reduce the risk of misjudgment.

[0011] Furthermore, the fault diagnosis method includes:

[0012] The three-point algorithm is used to calculate the current amplitude of the phase current that satisfies the first fault criterion and the voltage amplitude of the line voltage that satisfies the second fault criterion.

[0013] If the calculated current amplitude is greater than the second current threshold and the calculated voltage amplitude is less than the second voltage threshold, then the power grid is determined to have a fault; otherwise, the power grid is determined not to have a fault.

[0014] Furthermore, the three-point algorithm includes a first improved three-point algorithm;

[0015] When the sudden change in current is less than or equal to the current threshold, the method for calculating the current amplitude of the phase current that satisfies the first fault criterion using the first improved three-point algorithm includes:

[0016] ;

[0017] When the voltage surge value is less than or equal to the voltage threshold value, the method for calculating the voltage amplitude of the line voltage that satisfies the second fault criterion using the first improved three-point algorithm includes:

[0018] ;

[0019] in, This represents the current amplitude of the phase current that satisfies the first fault criterion. This represents the voltage amplitude of the line voltage that satisfies the second fault criterion. , , These represent the current current sampling point, the current sampling point with a set number of sampling intervals before the current sampling point, and the current sampling point with twice the set number of sampling intervals before the current sampling point, respectively. , , These represent the current voltage sampling point, the voltage sampling point at a predetermined sampling interval before the current sampling point, and the voltage sampling point at twice the predetermined sampling interval before the current sampling point, respectively; the predetermined number is greater than or equal to 1, and N is the number of periodic sampling points.

[0020] Furthermore, the three-point algorithm includes a second improved three-point algorithm;

[0021] When the sudden change in current exceeds the current threshold, the method for calculating the current amplitude of the phase current satisfying the first fault criterion using the second improved three-point algorithm includes:

[0022] ;

[0023] When the voltage surge value exceeds the voltage threshold value, the methods for calculating the voltage amplitude of the line voltage that satisfies the second fault criterion using the second improved three-point algorithm include:

[0024] ;

[0025] in, This represents the current amplitude of the phase current that satisfies the first fault criterion. This represents the voltage amplitude of the line voltage that satisfies the second fault criterion. , , These represent the current current sampling point, the current sampling point with a set number of sampling intervals before the current sampling point, and the current sampling point with twice the set number of sampling intervals before the current sampling point, respectively. , , These represent the current voltage sampling point, the voltage sampling point at a predetermined sampling interval before the current sampling point, and the voltage sampling point at twice the predetermined sampling interval before the current sampling point, respectively; the predetermined number is greater than or equal to 1.

[0026] Furthermore, the set duration is taken as the sampling period of the three-phase current and the line voltage of the power grid.

[0027] The present invention also provides a power grid fault identification system, including a processor for executing a computer program to implement the steps of the power grid fault identification method described above.

[0028] The power grid fault identification system can achieve the same beneficial effects as the power grid fault identification method described above.

[0029] To achieve the above objectives, the present invention also provides a method for protecting against power grid faults. The method includes: under the condition that any phase current in the three-phase current of the power grid satisfies a first fault criterion and any line voltage in the line voltage of the power grid satisfies a second fault criterion, it is initially determined that the power grid has a risk of fault existence; if it is initially determined that the power grid has a risk of fault existence, fault judgment is initiated, and the presence of a fault in the power grid is determined based on the fault judgment result.

[0030] If a fault is confirmed in the power grid, current limiting is applied to the power grid to achieve fault protection; if the fault disappears after current limiting, current limiting is stopped and power supply is restored; if the fault does not disappear after current limiting, fault isolation is performed.

[0031] The first fault criterion includes: the current value of any phase current in the three-phase current of the power grid is larger than the value at a time before the set time period, and the absolute value of the difference between the change in the current set time period and the change in the previous set time period is greater than the first current threshold.

[0032] The second fault criterion includes: the current value of any of the three line voltages of the power grid is smaller than the value at a time before the set time period, and the absolute value of the difference between the change in the current set time period and the change in the previous set time period is greater than the first voltage threshold.

[0033] The set duration is less than both the period of the phase current and the period of the line voltage.

[0034] Furthermore, the method for determining whether the fault has disappeared after current limiting includes: if the situation after current limiting simultaneously meets the conditions that the maximum phase current is less than the current limiting setting and the maximum phase current after current limiting by the first set multiple, and the minimum line voltage is greater than the line voltage rating by the second set multiple, then it is determined that the fault has disappeared after current limiting; otherwise, it is determined that the fault has not disappeared after current limiting; both the first set multiple and the second set multiple are less than 1.

[0035] Furthermore, the fault diagnosis method includes:

[0036] The three-point algorithm is used to calculate the current amplitude of the phase current that satisfies the first fault criterion and the voltage amplitude of the line voltage that satisfies the second fault criterion.

[0037] If the calculated current amplitude is greater than the second current threshold and the calculated voltage amplitude is less than the second voltage threshold, then the power grid is determined to have a fault; otherwise, the power grid is determined not to have a fault.

[0038] Furthermore, the three-point algorithm includes a first improved three-point algorithm;

[0039] When the sudden change in current is less than or equal to the current threshold, the method for calculating the current amplitude of the phase current that satisfies the first fault criterion using the first improved three-point algorithm includes:

[0040] ;

[0041] When the voltage surge value is less than or equal to the voltage threshold value, the method for calculating the voltage amplitude of the line voltage that satisfies the second fault criterion using the first improved three-point algorithm includes:

[0042] ;

[0043] in, This represents the current amplitude of the phase current that satisfies the first fault criterion. This represents the voltage amplitude of the line voltage that satisfies the second fault criterion. , , These represent the current current sampling point, the current sampling point with a set number of sampling intervals before the current sampling point, and the current sampling point with twice the set number of sampling intervals before the current sampling point, respectively. , , These represent the current voltage sampling point, the voltage sampling point at a predetermined sampling interval before the current sampling point, and the voltage sampling point at twice the predetermined sampling interval before the current sampling point, respectively; the predetermined number is greater than or equal to 1, and N is the number of periodic sampling points.

[0044] Furthermore, the three-point algorithm includes a second improved three-point algorithm;

[0045] When the sudden change in current exceeds the current threshold, the method for calculating the current amplitude of the phase current satisfying the first fault criterion using the second improved three-point algorithm includes:

[0046] ;

[0047] When the voltage surge value exceeds the voltage threshold value, the methods for calculating the voltage amplitude of the line voltage that satisfies the second fault criterion using the second improved three-point algorithm include:

[0048] ;

[0049] in, This represents the current amplitude of the phase current that satisfies the first fault criterion. This represents the voltage amplitude of the line voltage that satisfies the second fault criterion. , , These represent the current current sampling point, the current sampling point with a set number of sampling intervals before the current sampling point, and the current sampling point with twice the set number of sampling intervals before the current sampling point, respectively. , , These represent the current voltage sampling point, the voltage sampling point at a predetermined sampling interval before the current sampling point, and the voltage sampling point at twice the predetermined sampling interval before the current sampling point, respectively; the predetermined number is greater than or equal to 1.

[0050] Furthermore, the set duration is taken as the sampling period of the three-phase current and line voltage of the power grid. Beneficial effects: This invention also provides a novel method for protecting against power grid faults. This method, while achieving the same beneficial effects as the aforementioned power grid fault identification method, provides accurate fault protection for the power grid.

[0051] The present invention also provides a power grid fault protection system, including a processor for executing a computer program to implement the steps of the power grid fault protection method described above.

[0052] The power grid fault protection system can achieve the same beneficial effects as the power grid fault protection methods described above. Attached Figure Description

[0053] Figure 1 This is an architecture diagram of the bus voltage maintenance system in an embodiment of the power grid fault identification method of the present invention;

[0054] Figure 2 This is a topology example diagram illustrating the normal operation of the bus voltage maintenance system in an embodiment of the power grid fault identification method of the present invention.

[0055] Figure 3 This is a flowchart of the fault identification and voltage maintenance process in the embodiment of the power grid fault identification method of the present invention;

[0056] Figure 4 This is a topology example diagram of the bus voltage maintenance system in a fault protection state in an embodiment of the power grid fault identification method of the present invention. Detailed Implementation

[0057] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0058] Implementation methods for power grid fault identification

[0059] This embodiment presents a technical solution for identifying power grid faults. The main concept of this solution is to combine two abnormal conditions—current surges and voltage surges—to provide important criteria for judging the fault risk of the power grid. Furthermore, the existence of fault risk in the power grid is used as the basic condition for initiating fault determination, ultimately achieving fault identification.

[0060] Traditional power grid fault identification techniques typically utilize the phenomenon of abnormally large currents that occur during power grid faults (i.e., short-circuit faults). This is because the impedance at the short-circuit fault point drops sharply, causing the current to surge instantaneously to several times or even tens of times its normal value; in other words, the current undergoes a sudden change during a power grid fault. The basic principle of fault identification is: if the sudden change in current exceeds a set threshold, a power grid fault is identified, and fault protection is activated. However, practical applications and research have revealed that relying solely on sudden current changes cannot accurately reflect actual power grid faults. While sudden current changes are a typical manifestation of abnormal power grid operation, they can be caused by various factors such as power supply fluctuations, load changes, capacitor operation, equipment malfunction, grounding faults, or system oscillations. These situations are not directly equivalent to faults. Using only "sudden current change" as a fault criterion can easily lead to misjudgments and erroneous protection activation, thus affecting the stable operation of the entire power grid.

[0061] The topology of the power grid bus voltage maintenance system is as follows: Figure 1 As shown. The main components of this system are: protection devices, general switches, fast switches, and current-limiting reactors. Figure 2 The diagram shows the normal operating state of the system (this is the typical state). In this state, both the ordinary switch and the fast switch are closed. The current-limiting reactor is bypassed by the fast switch and is in the off state. The system supplies power to the next level through the loop formed by the ordinary switch, the fast switch, and the circuit. The protection device collects the operating status of this bay, such as voltage, current, and switch position, to determine the real-time operating status of the system.

[0062] In this embodiment, the following two situations may occur simultaneously when a power grid fault actually occurs:

[0063] A) The sudden increase in current exceeds the threshold range, that is, the current undergoes an excessive sudden change (excessive means increasing over time).

[0064] B) A sudden increase in current (i.e., an excessive current surge) will generate a larger voltage drop on components such as lines and transformers (i.e., ΔV = I × R, where R is the line resistance; this relationship shows that the current I and the voltage drop ΔV are numerically proportional), thus causing a sudden voltage drop. That is, the sudden decrease in voltage exceeds the threshold range, which is also called a short-term voltage surge (short-term means decreasing over time).

[0065] Apart from combinations A) and B), other combinations of current and voltage surges cannot accurately reflect power grid faults. This implementation method, based on the analysis of combinations A) and B), sets corresponding criteria for current and voltage surges respectively. Then, based on these two different criteria, it determines whether to initiate fault identification. Initiating fault identification represents a preliminary judgment that a fault may exist (i.e., risk). If, based on these two criteria, it is ultimately determined not to initiate fault identification, then it can be directly considered that there is no possibility of a fault, i.e., no fault risk.

[0066] In this embodiment, if any phase current in the three-phase current of the power grid satisfies the first fault criterion and any line voltage in the line voltage of the power grid satisfies the second fault criterion, it is initially determined that the power grid has a risk of fault existence; if it is initially determined that the power grid has a risk of fault existence, fault judgment is initiated, and the existence of fault in the power grid is determined based on the fault judgment result.

[0067] The aforementioned first fault criterion includes: the current value of any phase current in the three-phase current of the power grid is larger than the value at a time before the set time period, and the absolute value of the difference between the change in the current set time period and the change in the previous set time period is greater than the first current threshold.

[0068] The second fault criterion mentioned above includes: the current value of any of the three line voltages of the power grid is smaller than the value at a time before the set time period, and the absolute value of the difference between the change in the current set time period and the change in the previous set time period is greater than the first voltage threshold.

[0069] The set duration is shorter than both the phase current period and the line voltage period.

[0070] Specifically, the criteria set for the situations reflected in A) and B) above are as follows:

[0071] 1) A first fault criterion is established for the situation described in A). The first fault criterion is: the current value of any phase current in the three phases is larger than the value at a time before a set time period (since the object being detected is a sudden change, the change is extremely rapid, so the set time period should be a relatively short time period), and the absolute value of the difference between the change in the current set time period and the change in the previous set time period is greater than the first current threshold.

[0072] In this embodiment, the set duration is taken as the sampling period of the three-phase current and line voltage of the power grid. In other embodiments, the set duration can also be flexibly set according to actual needs.

[0073] In a specific embodiment, the expression for the first fault criterion is as follows:

[0074] (1)

[0075] in, This refers to the current sampling point time. The sampling period; Indicates the time of the previous sampling point; This indicates the time of the sampling point two steps prior to the previous one; It can represent the sampled value of the current in any one of the three phases A, B, and C. The range of values ​​for is {a, b, c}; when When =a, This represents the sampled value of the A-phase current; when When =b, This represents the sampled value of the B-phase current; when When =c, This represents the sampled value of the C-phase current; This is the rated current.

[0076] Specifically, the upper part of equation (1) Its meaning is: the current of a certain phase in the current segment for a set duration (i.e., to The change within the sampling period is greater than the previous set time period (i.e., to The change within the sampling period and The superposition of the phase current. The change in the phase current over the previous set time period is a known quantity, and Since the summation amount is a constant, it is also a constant. In this embodiment, this summation amount is selected as the first current threshold. Therefore, when the following conditions are met... This condition means that the sudden change in the phase current exceeds the first current threshold.

[0077] The lower half of equation (1) Its meaning is: the current of a certain phase at the current sampling point (i.e., The sampled value at time (i.e., the current value of the phase current) is greater than the current at the previous sampling point (i.e., the value of the phase current at time ... The sampled value at time (i.e., the set duration) (The value at a previous moment). This expression describes the phase current at... Time to The changes during this period show an upward trend. Therefore, if the following conditions are met... This indicates that the sudden change in the phase current is a sudden increase, rather than a sudden decrease.

[0078] If the current of a certain phase satisfies equation (1), it means that the current of that phase satisfies the condition represented by A), that is, the current of that phase undergoes a sudden change and the sudden change is a sudden increase, that is, the current of that phase undergoes an excessive sudden change. This conclusion can reflect the grid fault based on the current dimension.

[0079] 2) A second fault criterion is provided for the situation described in B). The second fault criterion is: the current value of any of the three line voltages (i.e., AB line voltage, BC line voltage, and CA line voltage) is smaller than the value at a time before the set time period, and the absolute value of the difference between the change in the current set time period and the change in the previous set time period is greater than the first voltage threshold.

[0080] In a specific embodiment, the expression for the second fault criterion is as follows:

[0081] (2)

[0082] in, It can represent the sampled value of the voltage of any one of the lines AB, BC, and CA. The range of values ​​for is {a, b, c}; when When =a, This represents the sampled value of the line voltage (AB); when When =b, This represents the sampled value of the BC line voltage; when When =c, This represents the sampled value of the CA line voltage; This is the rated line voltage; the meanings of other parameters have been explained and will not be repeated here.

[0083] The upper part of equation (2) Its meaning is: the set duration of a certain line voltage in the current segment (i.e. to The change within the sampling period is greater than the previous set time period (i.e., to The change within the sampling period and The superposition of quantities. Similar to the sudden change in current, the change in line voltage during the previous sampling period is a known quantity, and Since the summation amount is a constant, it is also a constant. In this embodiment, this summation amount is selected as the second voltage threshold. Therefore, when the following conditions are met... This condition means that the sudden change in the line voltage exceeds the second voltage threshold.

[0084] The lower half of equation (2) Its meaning is: the line voltage at the current sampling point (i.e., The sampled value at time (i.e., the current value of the line voltage) is less than the line voltage at the previous sampling point (i.e., the value at which the line voltage was measured). The sampled value at time (i.e., the value at a time before the set duration of the line voltage). This expression describes the line voltage at... Time to The change during this time period shows a downward trend. Therefore, if the following conditions are met... This indicates that the sudden change in the line voltage is a sudden decrease, rather than a sudden increase.

[0085] If a line voltage meets the second fault criterion, it means that the line voltage meets the condition represented by B), that is, the line voltage undergoes a sudden change and the change is a sudden decrease, that is, the line voltage experiences a shortfall. This conclusion can reflect power grid faults based on the voltage dimension.

[0086] In this embodiment, by combining the first fault criterion and the second fault criterion, a preliminary judgment can be made as to whether a fault exists in the power grid, thus determining whether to initiate fault identification. In fact, when both the first and second fault criterions are met simultaneously, it means that the fault conditions reflected in A) and B) are simultaneously satisfied. In this case, a preliminary judgment can be made that there is a fault risk (i.e., there is a possibility of a fault). If there is no fault risk, i.e., the first and second fault criterions are not met simultaneously, the power grid can be considered fault-free at present. This method is equivalent to first characterizing the fault, that is, first filtering out some abnormal situations that do not meet the fault conditions at all. The remaining situations are risk situations, and the fault can be further determined based on these risk situations (i.e., the final determination of whether a fault exists).

[0087] In this embodiment, after initially determining that the power grid has a risk of failure, a fault diagnosis is initiated. For example... Figure 3 As shown, the fault judgment method includes: calculating the current amplitude of the phase current that meets the first fault criterion and the voltage amplitude of the line voltage that meets the second fault criterion using a three-point algorithm.

[0088] If the calculated current amplitude is greater than the second current threshold and the calculated voltage amplitude is less than the second voltage threshold, then the power grid is determined to have a fault; otherwise, the power grid is determined not to have a fault.

[0089] In this embodiment, the above three-point algorithm includes the first improved three-point algorithm;

[0090] When the sudden change in current (i.e., the change in current within a certain time window) is less than or equal to the current threshold (in which case the current amplitude is relatively stable), the current amplitude of the phase current that satisfies the first fault criterion is calculated using the first improved three-point algorithm. The calculation method includes:

[0091] (3)

[0092] When the voltage surge value (i.e., the change in voltage within a certain time window) is less than or equal to the voltage threshold value (in which case the voltage amplitude is relatively stable), the voltage amplitude of the line voltage that satisfies the second fault criterion is calculated using the first improved three-point algorithm. The calculation method includes:

[0093] (4)

[0094] in, This represents the calculated current amplitude (i.e., the current amplitude of the phase current that satisfies the first fault criterion). This represents the calculated voltage amplitude (i.e., the voltage amplitude of the line voltage that satisfies the second fault criterion). , , These represent the current current sampling point, the current current sampling point - M (i.e., the sampling point with a set number of sampling intervals before the current sampling point), and the current current sampling point - M*2 (i.e., the current sampling point with twice the set number of sampling intervals before the current sampling point), respectively. , , These represent the current voltage sampling point, the current voltage sampling point - M (i.e., the sampling point with a set number of sampling intervals before the current voltage sampling point), and the current voltage sampling point - M*2 (i.e., the voltage sampling point with twice the set number of sampling intervals before the current voltage sampling point); M represents the set number, which actually means the number of current or voltage sampling points to be pushed forward (the set number is greater than or equal to 1, i.e., M≥1). To improve the accuracy of the criterion (i.e., the criterion determined based on the calculation results), the number of sampling points for discrimination can be flexibly set; N is the number of periodic sampling points. In this embodiment, the above three-point algorithm includes the second improved three-point algorithm;

[0095] When the sudden change in current exceeds the current threshold (in which case the sudden change in current amplitude is large), the current amplitude of the phase current satisfying the first fault criterion is calculated using the second improved three-point algorithm. The calculation method includes:

[0096] (5)

[0097] When the voltage surge value exceeds the voltage threshold value (in which case the voltage amplitude surge is large), the voltage amplitude of the line voltage satisfying the second fault criterion is calculated using the second improved three-point algorithm. The calculation method includes:

[0098] (6)

[0099] The meanings of the parameters in the above formula have been explained and will not be repeated here.

[0100] It is important to note that compared to the ordinary three-point algorithm, the two improved three-point algorithms described above significantly improve the accuracy and reliability of amplitude calculations. However, each of the first and second improved three-point algorithms has its own advantages. The first improved three-point algorithm has a relatively simple calculation formula and a faster calculation speed; while the second improved three-point algorithm has a more complex calculation formula, it has stronger noise reduction capabilities and higher accuracy. These respective advantages make them suitable for different scenarios. When the abrupt changes in current or voltage amplitude are large, the accuracy of the first improved three-point algorithm is significantly affected by noise interference, while the second improved three-point algorithm has stronger noise reduction capabilities for abrupt changes. In this scenario, the second improved three-point algorithm should be used. Conversely, when the abrupt changes in current or voltage amplitude are small, and fast calculation is usually desired, the first improved three-point algorithm is more suitable. In this embodiment, the relationship between the current surge value and the current threshold value determines whether a large current surge has occurred; similarly, the relationship between the voltage surge value and the voltage threshold value determines whether a large voltage surge has occurred. That is, the current threshold value and the voltage threshold value are the standards for measuring whether current and voltage surges have occurred. In one embodiment, the current threshold value is set to 1. Therefore, as long as the current surge value does not exceed 1, it indicates a small current surge. For example, if the current surges from 0 to 0.8 (surge value 0.8, 0.8 < 1), the first improved three-point algorithm is used. Similarly, in this embodiment, if the current surge value exceeds 1, it indicates a large current surge. For example, if the current surges from 0 to 1.2 (surge value 1.2, 1.2 > 1), the second improved three-point algorithm is used.

[0101] Specifically, after calculating the current and voltage amplitudes, it is necessary to determine whether a fault exists in the power grid based on the comparison results. All possible comparison results and their corresponding fault determination results are shown below:

[0102] ① If the current amplitude calculated by the three-point algorithm is greater than the second current threshold, and the voltage amplitude calculated by the three-point algorithm is greater than the second voltage threshold, then it is determined that there is no fault in the power grid;

[0103] ② If the current amplitude calculated by the three-point algorithm is greater than the second current threshold, and the voltage amplitude calculated by the three-point algorithm is less than the second voltage threshold, then it is determined that there is a fault in the power grid;

[0104] ③ If the current amplitude calculated by the three-point algorithm is less than the second current threshold, and the voltage amplitude calculated by the three-point algorithm is greater than the second voltage threshold, then it is determined that there is no fault in the power grid;

[0105] ④ If the current amplitude calculated by the three-point algorithm is less than the second current threshold, and the voltage amplitude calculated by the three-point algorithm is less than the second voltage threshold, then it is determined that there is no fault in the power grid.

[0106] In summary, only fault determination in case ② indicates a fault in the power grid. That is, if the current amplitude calculated using the three-point algorithm is greater than the second current threshold, and the voltage amplitude calculated using the three-point algorithm is less than the second voltage threshold, then a fault in the power grid can be definitively determined. In other cases, no fault is considered to exist. This method is equivalent to quantitatively determining the existence of a fault based on the initially assessed risk situation (i.e., situations where a fault is possible, which could be a confirmed fault or a misjudgment requiring further clarification). The absolute basis for determining a fault is the calculated electrical parameter amplitude. Fault determination based on amplitude has high accuracy and reliability, but it involves a large computational load. The initial risk assessment stage can filter out situations where no fault is possible, thus significantly reducing the computational load and improving efficiency.

[0107] Implementation of Power Grid Fault Identification System

[0108] This embodiment provides a technical solution for a power grid fault identification system. The system includes a processor containing executable program instructions, which are used to implement the power grid fault identification method as described in the above-described embodiment.

[0109] Since the specific working method and working principle of the power grid fault identification system in this embodiment have been described in detail in the above-described power grid fault identification method embodiments, they will not be repeated here.

[0110] Implementation methods for power grid fault protection

[0111] This embodiment provides a technical solution for a power grid fault protection method. This solution protects the power grid from faults based on fault identification using a power grid fault identification method.

[0112] In this embodiment, if any phase current in the three-phase current of the power grid satisfies the first fault criterion and any line voltage in the line voltage of the power grid satisfies the second fault criterion, it is initially determined that the power grid has a risk of fault existence; if it is initially determined that the power grid has a risk of fault existence, fault judgment is initiated, and the existence of fault in the power grid is determined based on the fault judgment result.

[0113] If a fault is confirmed in the power grid, current limiting is applied to the power grid to achieve fault protection; if the fault disappears after current limiting, current limiting is stopped and power supply is restored; if the fault does not disappear after current limiting, fault isolation is performed.

[0114] The aforementioned first fault criterion includes: the current value of any phase current in the three-phase current of the power grid is larger than the value at a time before the set time period, and the absolute value of the difference between the change in the current set time period and the change in the previous set time period is greater than the first current threshold.

[0115] The second fault criterion mentioned above includes: the current value of any of the three line voltages of the power grid is smaller than the value at a time before the set time period, and the absolute value of the difference between the change in the current set time period and the change in the previous set time period is greater than the first voltage threshold.

[0116] The set duration is shorter than both the phase current period and the line voltage period.

[0117] In this embodiment, rapid current limiting is implemented on the power grid when a fault is detected. The specific method of rapid current limiting is as follows: the ordinary switch remains closed, the fast-acting switch is immediately tripped, and a current-limiting reactor is engaged to maintain bus voltage stability. The topology of the bus voltage maintenance system when a fault occurs and the current-limiting reactor is engaged is as follows: Figure 4 As shown.

[0118] Current-limiting reactors are used to quickly limit short-circuit current for short-term fault protection. Therefore, after the current-limiting reactor is activated, it is necessary to determine whether the fault has disappeared and to identify the fault type based on the determination result. If the fault disappears, it indicates that the fault type is a temporary fault that can be quickly recovered; if the fault does not disappear, it indicates that the fault type is a permanent fault that is difficult to recover from. In this embodiment, corresponding handling methods are provided for temporary and permanent faults respectively. After determining the fault type, it is only necessary to select the corresponding handling measure.

[0119] In this embodiment, the method for determining whether the fault has disappeared after current limiting includes: if the situation after current limiting simultaneously satisfies the conditions that the maximum phase current is less than the current limiting setting and the maximum phase current after current limiting by a first set multiple, and the minimum line voltage is greater than the line voltage rating by a second set multiple, then it is determined that the fault has disappeared after current limiting; otherwise, it is determined that the fault has not disappeared after current limiting; both the first set multiple and the second set multiple are less than 1.

[0120] In a specific embodiment, the criteria for determining whether the fault has disappeared are expressed as follows:

[0121] (7)

[0122] in, This is the maximum phase current; To limit the current setting; To determine the maximum phase current after the fast switching tripping action, the first set multiple is 0.5. Minimum line voltage; The line voltage is the rated value, and the second setting multiple is 0.9.

[0123] If all three conditions in equation (7) are met simultaneously, the fault is determined to have disappeared; otherwise, the fault is determined to have not disappeared.

[0124] In this embodiment, if the fault is determined to have disappeared, that is, if the fault is determined to be temporary, the corresponding handling measures are: close the fast switch, remove the current-limiting reactor, and restore normal power supply.

[0125] If the fault is determined to be permanent, the corresponding handling measure is to disconnect the ordinary switch to isolate the fault.

[0126] In this embodiment, the fault determination method includes:

[0127] The three-point algorithm is used to calculate the current amplitude of the phase current that satisfies the first fault criterion and the voltage amplitude of the line voltage that satisfies the second fault criterion.

[0128] If the calculated current amplitude is greater than the second current threshold and the calculated voltage amplitude is less than the second voltage threshold, then the power grid is determined to have a fault; otherwise, the power grid is determined not to have a fault.

[0129] In this embodiment, the above three-point algorithm includes the first improved three-point algorithm;

[0130] When the sudden change in current is less than or equal to the current threshold, the current amplitude of the phase current satisfying the first fault criterion is calculated using the first improved three-point algorithm. The calculation method includes:

[0131]

[0132] When the voltage surge value is less than or equal to the voltage threshold value, the voltage amplitude of the line voltage satisfying the second fault criterion is calculated using the first improved three-point algorithm. The calculation method includes:

[0133]

[0134] in, This represents the current amplitude of the phase current that satisfies the first fault criterion. This represents the voltage amplitude of the line voltage that satisfies the second fault criterion. , , These represent the current current sampling point, the current sampling point with a set number of sampling intervals before the current sampling point, and the current sampling point with twice the set number of sampling intervals before the current sampling point, respectively. , , These represent the current voltage sampling point, the voltage sampling point at a predetermined sampling interval before the current sampling point, and the voltage sampling point at twice the predetermined sampling interval before the current sampling point, respectively; the predetermined number is greater than or equal to 1.

[0135] In this embodiment, the above three-point algorithm includes the second improved three-point algorithm;

[0136] When the sudden change in current exceeds the current threshold, the current amplitude of the phase current satisfying the first fault criterion is calculated using the second improved three-point algorithm. The calculation method includes:

[0137]

[0138] When the voltage surge value exceeds the voltage threshold value, the voltage amplitude of the line voltage satisfying the second fault criterion is calculated using the second improved three-point algorithm. The calculation method includes:

[0139]

[0140] in, This represents the current amplitude of the phase current that satisfies the first fault criterion. This represents the voltage amplitude of the line voltage that satisfies the second fault criterion. , , These represent the current current sampling point, the current sampling point with a set number of sampling intervals before the current sampling point, and the current sampling point with twice the set number of sampling intervals before the current sampling point, respectively. , , These represent the current voltage sampling point, the voltage sampling point at a predetermined sampling interval before the current sampling point, and the voltage sampling point at twice the predetermined sampling interval before the current sampling point, respectively; the predetermined number is greater than or equal to 1.

[0141] In this embodiment, the set duration is taken as the sampling period of the three-phase current and the line voltage of the power grid.

[0142] Implementation of power grid fault protection systems

[0143] This embodiment provides a technical solution for a power grid fault protection system. The system includes a processor containing executable program instructions, which are used to implement the power grid fault protection method as described in the above-described power grid fault protection method embodiment.

[0144] Since the specific working mode and working principle of the power grid fault protection system in this embodiment have been described in detail in the above-described power grid fault protection method embodiments, they will not be repeated here.

[0145] It should be understood that the above-described specific embodiments of the present invention are merely illustrative or explanatory of the principles of the present invention, and do not constitute a limitation thereof.

Claims

1. A method of identifying a power grid fault, characterized in that, Under the condition that any one of the three-phase currents of the power grid satisfies a first fault criterion and any one of the line voltages of the power grid satisfies a second fault criterion, it is preliminarily determined that the power grid has a risk of existing a fault; If it is preliminarily determined that the power grid has a risk of existing a fault, a fault judgment is started, and whether the power grid has a fault is determined according to a fault judgment result; The first fault criterion comprises that a current value of any one of the three-phase currents of the power grid at a current time is larger than a value at a time before a set time length, and an absolute value of a difference between a variation amount in a current segment of the set time length and a variation amount in a previous segment of the set time length is greater than a first current threshold value; The second fault criterion comprises that a voltage value of any one of the line voltages of the power grid at the current time is smaller than a value at the time before the set time length, and an absolute value of a difference between a variation amount in the current segment of the set time length and the variation amount in the previous segment of the set time length is greater than a first voltage threshold value; The set time length is smaller than a period of the phase current and smaller than a period of the line voltage.

2. The method of identifying a power grid fault according to claim 1, characterized in that, The fault judgment comprises: The current amplitude of the phase current satisfying the first fault criterion and the voltage amplitude of the line voltage satisfying the second fault criterion are calculated by a three-point algorithm respectively; If the calculated current amplitude is greater than a second current threshold value and the calculated voltage amplitude is smaller than a second voltage threshold value, it is determined that the power grid has a fault; otherwise, it is determined that the power grid does not have a fault.

3. The method of identifying a power grid fault according to claim 2, characterized in that, The three-point algorithm comprises a first improved three-point algorithm; In a case where the current mutation value is less than or equal to a current threshold value, the current amplitude of the phase current satisfying the first fault criterion is calculated by the first improved three-point algorithm, and the calculation manner comprises: ； In a case where the voltage mutation value is less than or equal to a voltage threshold value, the voltage amplitude of the line voltage satisfying the second fault criterion is calculated by the first improved three-point algorithm, and the calculation manner comprises: ； wherein, denotes the current amplitude of the phase current satisfying the first fault criterion; denotes the voltage amplitude of the line voltage satisfying the second fault criterion; denote the current sample point at present, the current sample point before a set number of sampling intervals, and the current sample point before two times the set number of sampling intervals, respectively; denote the voltage sample point at present, the voltage sample point before a set number of sampling intervals, and the voltage sample point before two times the set number of sampling intervals, respectively; the set number is greater than or equal to 1, and N is the number of period sampling points.​​​​ 4. The method of identifying power grid faults according to claim 2, characterized in that, The three-point algorithm comprises a second improved three-point algorithm; In a case where the current mutation value is greater than the current threshold value, the current amplitude of the phase current satisfying the first fault criterion is calculated by the second improved three-point algorithm, and the calculation manner comprises: ； In a case where the voltage mutation value is greater than the voltage threshold value, the voltage amplitude of the line voltage satisfying the second fault criterion is calculated by the second improved three-point algorithm, and the calculation manner comprises: ； wherein, denotes a current amplitude of the phase current satisfying the first fault criterion; denotes a voltage amplitude of the line voltage satisfying the second fault criterion; , , denote a current sample point of the current, a current sample point of the current before a set number of sampling intervals, and a current sample point of the current before two times the set number of sampling intervals, respectively; , , denote a voltage sample point of the voltage, a voltage sample point of the voltage before a set number of sampling intervals, and a voltage sample point of the voltage before two times the set number of sampling intervals, respectively; the set number is greater than or equal to 1.

5. The method of identifying power grid faults of claim 1, wherein, The set time length is a sampling period of the three-phase current of the power grid and a sampling period of the line voltage of the power grid.

6. A system for identifying power grid faults, comprising a processor, characterized in that The processor is configured to execute a computer program to implement steps of the power grid fault identification method in any one of claims 1-5.

7. A method of protection against power grid faults, characterized in that, Under the condition that any one of the three-phase currents of the power grid satisfies a first fault criterion and any one of the line voltages of the power grid satisfies a second fault criterion, it is preliminarily determined that the power grid has a risk of existing a fault; If it is preliminarily determined that the power grid has a risk of existing a fault, a fault judgment is started, and whether the power grid has a fault is determined according to a fault judgment result; In a case where it is determined that the power grid has a fault, current limiting is performed on the power grid to achieve fault protection; if it is determined that the fault disappears after the current limiting, the current limiting is stopped and power supply is restored; If it is determined that the fault does not disappear after the current limiting, fault isolation is performed; The first fault criterion comprises: any phase current of the three-phase current of the power grid currently increases compared with the value at a time point before a set time length, and the absolute value of the difference between the change amount in the current time length and the change amount in the previous time length is greater than a first current threshold value; The second fault criterion comprises: any line voltage of the three-line voltage of the power grid currently decreases compared with the value at a time point before a set time length, and the absolute value of the difference between the change amount in the current time length and the change amount in the previous time length is greater than a first voltage threshold value; The set time length is smaller than the period of the phase current and the period of the line voltage.

8. The method of protecting against power grid failure of claim 7, wherein, The manner of determining whether the fault disappears after current limiting comprises: if the conditions of the maximum phase current after current limiting being less than the limited current constant value and the first set multiple of the maximum phase current after current limiting, and the minimum line voltage being greater than the second set multiple of the line voltage rated value are simultaneously met, it is determined that the fault disappears after current limiting; otherwise, it is determined that the fault does not disappear after current limiting; the first set multiple and the second set multiple are both less than 1.

9. The method of protecting against power grid failure of claim 7, wherein, The manner of fault judgment comprises: The current amplitude of the phase current meeting the first fault criterion and the voltage amplitude of the line voltage meeting the second fault criterion are calculated by a three-point algorithm respectively; If the calculated current amplitude is greater than a second current threshold value, and the calculated voltage amplitude is less than a second voltage threshold value, it is determined that the power grid has a fault; otherwise, it is determined that the power grid does not have a fault.

10. The method of protecting against power grid failure of claim 9, wherein, The three-point algorithm comprises a first improved three-point algorithm; In the case that the current mutation value is less than or equal to a current threshold value, the manner of calculating the current amplitude of the phase current meeting the first fault criterion by the first improved three-point algorithm comprises: ； In the case that the voltage mutation value is less than or equal to a voltage threshold value, the manner of calculating the voltage amplitude of the line voltage meeting the second fault criterion by the first improved three-point algorithm comprises: ； wherein, denotes a current amplitude of the phase current satisfying the first fault criterion; denotes a voltage amplitude of the line voltage satisfying the second fault criterion; , , denote a current sample point of the current sample point, a current sample point of the current sample point before a set number of sampling intervals, and a current sample point of the current sample point before twice the set number of sampling intervals, respectively; , , denote a voltage sample point of the current sample point, a voltage sample point of the current sample point before a set number of sampling intervals, and a voltage sample point of the current sample point before twice the set number of sampling intervals, respectively; the set number is greater than or equal to 1, and N is a number of period sampling points.

11. The method of protecting against power grid failure of claim 9, wherein, The three-point algorithm comprises a second improved three-point algorithm; In the case that the current mutation value is greater than the current threshold value, the manner of calculating the current amplitude of the phase current meeting the first fault criterion by the second improved three-point algorithm comprises: ； In the case that the voltage mutation value is greater than the voltage threshold value, the manner of calculating the voltage amplitude of the line voltage meeting the second fault criterion by the second improved three-point algorithm comprises: ； wherein, denotes a current amplitude of the phase current satisfying the first fault criterion; denotes a voltage amplitude of the line voltage satisfying the second fault criterion; , , denote a current sample point of the current, a current sample point of the current before a set number of sampling intervals, and a current sample point of the current before twice the set number of sampling intervals, respectively; , , denote a voltage sample point of the voltage, a voltage sample point of the voltage before a set number of sampling intervals, and a voltage sample point of the voltage before twice the set number of sampling intervals, respectively; the set number is greater than or equal to 1.

12. The method of protecting against power grid failure of claim 7, wherein, The set time length takes the sampling period of the three-phase current of the power grid and the sampling period of the line voltage of the power grid.

13. A system for protection of power grid faults, comprising a processor, characterized in that The processor is configured to execute a computer program to implement the steps of the power grid fault protection method according to any one of claims 7-12.

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