Method and device for fault detection and protection of low-voltage distribution line

Abstract

The invention belongs to the technical field of electric power safety, and particularly relates to a low-voltage distribution line fault detection and protection method and device. According to the method, a host computer and a slave computer are installed at the two ends of a monitored line respectively, the host computer and the slave computer synchronously collect and calculate line electrical parameters including current of each phase, current on a neutral line N, residual current, voltage of each phase, total harmonic content of the voltage of each phase and power of each phase, and the host computer and the slave computer interact information through wireless or optical fiber communication. And the host carries out fault logic judgment alarm or protection tripping, and records an SOE event report at the same time. The fault logic judgment rule comprises faults such as abnormal current, abnormal voltage, abnormal power, normal operation, electric leakage or parallel arc, poor contact or series arc, line aging and the like. According to the invention, the electrical parameters of the operation of the low-voltage distribution line can be monitored in real time, the fault type can be accurately judged, fault alarm or protection tripping can be carried out in time, and the safety and reliability of the low-voltage distribution line are improved.

Description

Technical Field

[0001] This invention belongs to the field of power safety technology, specifically relating to a method and device for fault detection and protection of low-voltage power distribution lines. Background Technology

[0002] With the continuous growth of the industrial economy, low-voltage power distribution lines (specifically referring to voltage levels of 400V and below) are an important component, and their safety and reliability play a crucial role in ensuring the safety and reliability of electricity supply for users. However, in actual operation, low-voltage power distribution lines are highly susceptible to various factors, such as aging lines, poor contact, and leakage, which can lead to various faults. These faults not only affect the normal operation of the power supply but may also induce serious safety accidents such as electrical fires. Therefore, ensuring the safe and stable operation of low-voltage power distribution lines is of paramount importance.

[0003] Traditional fault detection methods for low-voltage power distribution lines have significant drawbacks. On the one hand, they rely heavily on manual inspections, which are inefficient and prone to overlooking potential hazards, making them unsuitable for meeting increasingly complex power supply demands. On the other hand, traditional methods often monitor single-end electrical quantities (current, voltage), making it difficult to distinguish between faults with increased contact resistance (such as poor conductor contact or series arcing) and faults with decreased leakage resistance (such as leakage or parallel arcing). Furthermore, a single monitoring point cannot effectively identify whether anomalies have occurred at the end of the line, has insufficient sensitivity for detecting and protecting against series and parallel arcing faults, and cannot simultaneously assess voltage distortion and abnormal power loss characteristics. These methods suffer from slow response times and poor accuracy in fault detection and protection, are not precise enough for certain fault types, cannot promptly detect potential faults, cannot simultaneously detect both series and parallel arcing, and can even be detected as faults during the normal operation of nonlinear loads such as power electronics and arcing, easily leading to misjudgments.

[0004] In summary, there is an urgent need for an efficient and accurate method and device for fault detection and protection of low-voltage power distribution lines, in order to improve the safety and reliability of low-voltage power distribution lines and ensure the stable operation of low-voltage power distribution systems and the safety of electricity use. Summary of the Invention

[0005] The purpose of this invention is to provide a method and apparatus for fault detection and protection of low-voltage power distribution lines, which solves the problems of slow response speed, poor accuracy, and inability to simultaneously detect series arcs, parallel arcs, and power anomalies in existing low-voltage power distribution line fault detection and protection methods.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for fault detection and protection of low-voltage power distribution lines, characterized by comprising the following steps:

[0008] (1) Install the master and slave devices at the power supply end and load end of the monitored line respectively, and set the current difference set value. Voltage difference set value Power difference set value and voltage waveform distortion set value ;

[0009] (2) Both the master and slave are electrical parameter measuring devices. They synchronously collect and calculate the electrical parameters of the line, and the slave transmits the synchronized electrical parameters to the master.

[0010] (3) The host performs fault logic judgment based on the electrical parameters collected by the slave and the electrical parameters collected and calculated by itself. When a fault is detected, the alarm indicator light is lit or the protection trip is performed, and the SOE event report is recorded at the same time.

[0011] Furthermore, in step (2), the host and slave synchronously collect and calculate the electrical parameters of the line, including the current of each phase, the current on the neutral line N, the residual current, the voltage of each phase, the total harmonic content of the voltage of each phase, and the power of each phase.

[0012] Furthermore, the fault logic judgment in step (3) includes the following rules:

[0013] Abnormal voltage detection: Compare the effective voltage values ​​of the master and slave devices. If the difference is greater than the set voltage difference setting... If so, then an abnormal voltage is considered to exist;

[0014] Voltage distortion judgment: Compare the total harmonic content of the master and slave voltages. If the total harmonic content of the slave voltage is greater than the set voltage waveform distortion value... If the total harmonic content of the slave voltage is greater than the total harmonic content of the master voltage, then voltage distortion is considered to exist.

[0015] Abnormal current detection: Compare the effective current values ​​of the master and slave devices. If the difference is greater than the set current difference value... If so, it is considered that there is an abnormal current.

[0016] Furthermore, in the fault logic judgment of step (3), a series arc fault is determined to have occurred when the following five conditions are met simultaneously:

[0017] a) There is a voltage difference between the master and slave devices. ,and > ;

[0018] b) The slave voltage exhibits voltage distortion, and > ;

[0019] c) The host voltage also exhibits voltage distortion, and > ;

[0020] d) Arc fault current exists ,and >2.5A, where A represents the current unit ampere;

[0021] e) The fault time is greater than or equal to the alarm delay time setting, i.e. ≥ ;

[0022] in: ;

[0023] : Effective value of host voltage;

[0024] Slave voltage RMS value;

[0025] The maximum voltage drop generated by the load current flowing through the line during normal operation;

[0026] Total harmonic content of the host voltage;

[0027] Total harmonic content of slave voltage;

[0028] The current during a series arc fault. =0.5( + ) ;

[0029] : Effective value of host current;

[0030] Slave current RMS value;

[0031] Time of occurrence of series arc fault;

[0032] : Set value for the delay time of series arc alarm.

[0033] Furthermore, in the fault logic judgment of step (3), a parallel arc fault is determined to have occurred when the following two conditions are met simultaneously:

[0034] a) Parallel arc fault current exists ,and >2.5A;

[0035] b) The fault time is greater than or equal to the alarm delay time setting, i.e. ≥ ;

[0036] in:

[0037] Arc current during a parallel arc fault. = = - ;

[0038] The effective value difference between the master and slave currents;

[0039] : Effective value of host current;

[0040] Slave current RMS value;

[0041] Time of occurrence of parallel arc fault;

[0042] Parallel arc alarm delay time setting.

[0043] Furthermore, in step (3), a power anomaly is determined to have occurred when both of the following conditions are met simultaneously:

[0044] a) There is a power difference ,and > ;

[0045] b) The fault time is greater than or equal to the alarm delay time setting, i.e. ≥ .

[0046] in:

[0047] This indicates the power loss difference between the master and slave devices. ;

[0048] Average power of the host computer;

[0049] Average power of slave devices;

[0050] : Time of occurrence of abnormal power;

[0051] Abnormal power alarm delay time setting.

[0052] Furthermore, the communication method between the host and the slave is wireless or fiber optic communication, and the host synchronously collects electrical parameters with the slave through wireless or fiber optic communication.

[0053] Synchronous acquisition implementation: When the voltage crosses zero, the master sends a synchronization command to the slave and performs acquisition and calculation on the sampling sequence at the next voltage crossing. When the slave receives the synchronization command from the master and the most recent voltage crossing occurs, it performs acquisition and calculation on the current sampling sequence.

[0054] A device for fault detection and protection of low-voltage power distribution lines, comprising:

[0055] The host is used to collect electrical parameters at the power supply end of the monitored line and compare them with the electrical parameters transmitted from the load end to perform fault logic judgment.

[0056] The slave device is used to collect electrical parameters at the load end of the monitored line;

[0057] The communication module in the master and slave devices is used to support data communication and command synchronization between the master and slave devices;

[0058] The host integrates a computing unit, which is used to calculate and compare slave data with host data to identify fault types.

[0059] The host also contains an alarm and protection unit, which is used to trigger an alarm or perform a protection trip action based on the fault type judgment result of the computing unit, and at the same time record the SOE event report.

[0060] The beneficial effects of this invention are as follows:

[0061] 1. Real-time monitoring: By installing a master and slave device at each end of the monitored and protected line, electrical parameters at both ends of the line can be collected synchronously in real time, ensuring timely detection and location of the fault in the first instance. This real-time capability significantly improves the response speed for identifying faulty lines and reduces potential safety hazards.

[0062] 2. Multi-dimensional Collaborative Detection: This invention overcomes the limitations of traditional single-end detection methods, which are prone to false alarms and misjudgments. It innovatively constructs a master-slave dual-machine collaborative detection and protection system. By synchronously collecting and calculating electrical parameters such as three-phase voltage, current, power, and voltage distortion, it forms a four-dimensional criterion matrix including current difference, voltage difference, power difference, and voltage distortion, effectively improving the dimensionality and accuracy of fault feature extraction. Therefore, this invention can simultaneously detect and protect against series arcing, parallel arcing, and power anomaly faults, overcoming the influence of nonlinear loads and load fluctuations, ensuring stable operation even in complex power environments. This superiority allows the system to maintain efficient fault detection and protection capabilities when facing variable power loads.

[0063] 3. Differentiated Fault Identification Mechanism: A smart diagnostic model based on criterion combination features is established to address the complex operating conditions of low-voltage power distribution systems. Parallel arcs are accurately identified using current difference criteria, series arcs are accurately identified using voltage difference and voltage distortion criteria, and power difference criteria are used to identify power anomalies, achieving feature decoupling and accurate identification of various faults.

[0064] 4. Accurate Judgment: By analyzing electrical parameters such as current difference, voltage difference, power difference, and voltage distortion between the master and slave devices, this invention can adaptively identify various load types, including resistive, inductive, power electronic, and arc loads, accurately determining the type of fault in the line, such as leakage, parallel arcing, poor contact, series arcing, and line aging. This precise fault identification capability significantly improves the accuracy of fault detection and protection, reducing the possibility of false alarms and missed alarms.

[0065] 5. Timely Protection: When a fault is detected, the main unit can quickly issue an alarm or trip the protection circuit, promptly cutting off the faulty circuit to prevent further escalation and ensuring the safe operation of low-voltage power distribution lines. This rapid protection mechanism not only reduces the risk of equipment damage but also effectively prevents electrical fires and other safety accidents caused by faults, improving users' electrical safety.

[0066] 6. Intelligent Analysis: This invention combines advanced data processing algorithms to intelligently analyze collected electrical parameters, identify potential line fault trends, provide early warnings, and assist maintenance personnel in preventative maintenance. This proactive management approach can effectively extend the service life of low-voltage power distribution lines and reduce maintenance costs. Attached Figure Description

[0067] Figure 1 This is a schematic diagram of the low-voltage power distribution line fault detection and protection of the present invention;

[0068] Figure 2 This is the logic judgment diagram for series arc fault detection and protection of low-voltage power distribution lines in this invention;

[0069] Figure 3 This is the logic judgment diagram for parallel arc fault detection and protection of low-voltage power distribution lines in this invention;

[0070] Figure 4 This is the logic judgment diagram for low-voltage power distribution line fault detection and protection power abnormality fault in this invention;

[0071] Figure 5 This is a schematic diagram illustrating the implementation of the low-voltage power distribution line fault detection and protection method of the present invention. Detailed Implementation

[0072] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0073] like Figure 1 As shown in the diagram, the dashed box represents a section of the monitored line. There is no load or power supply connected within the dashed box. The left side of the dashed box is the power supply end, where the main unit is installed; the right side is the load end, where the slave unit is installed. Within the dashed box, 'r' represents the series contact resistance (reflecting poor conductor contact, series arcing, etc., generally small), and 'R' represents the parallel leakage resistance (reflecting leakage current, parallel arcing, etc., generally large). In a three-phase AC power system, ABC is typically used to represent the three phase wires (also called live wires); N represents the neutral wire (also called the neutral line); and E represents the protective earth wire (or protective earth wire), also called the ground wire. Figure 1 In this diagram, ABCNE represents information collected by the host, and A'B'C'N'E' represents information collected by the slave. Specific detection and protection methods are as follows.

[0074] 1. Equipment installation and electrical parameter acquisition and calculation

[0075] At both ends of the monitored line (power supply end and load end), a master unit and a slave unit are installed respectively. The master unit and slave unit synchronously collect the line's electrical parameters (current per phase, current on the neutral line N, residual current, voltage per phase, total harmonic content of voltage per phase, power per phase, etc.), and calculate the synchronously collected electrical parameters to obtain the following electrical parameters:

[0076] 1) Acquisition of host electrical parameters:

[0077] , , , , , , , ;

[0078] , , ;

[0079] , , ;

[0080] in:

[0081] Phase A voltage acquired by the host computer;

[0082] Phase B voltage acquired by the host computer;

[0083] : The C-phase voltage acquired by the host;

[0084] The current of phase A collected by the host computer;

[0085] : The B-phase current collected by the host;

[0086] : The C-phase current collected by the host;

[0087] : Neutral current collected by the host;

[0088] The residual current collected by the host computer;

[0089] The main unit calculates the power of phase A based on the collected phase A voltage and phase A current;

[0090] The main unit calculates the B-phase power based on the collected B-phase voltage and B-phase current.

[0091] The host calculates the C-phase power based on the collected C-phase voltage and C-phase current;

[0092] The host calculates the total harmonic content based on the collected A-phase voltage;

[0093] The host calculates the total harmonic content based on the collected B-phase voltage.

[0094] The host calculates the total harmonic content based on the collected C-phase voltage.

[0095] 2) Acquisition of electrical parameters from slave device:

[0096] , , , , , , , ;

[0097] , , ;

[0098] , , ;

[0099] in:

[0100] Phase A voltage acquired by the slave device;

[0101] Phase B voltage acquired by the slave device;

[0102] : The C-phase voltage acquired by the slave device;

[0103] Phase A current collected by the slave device;

[0104] Phase B current acquired by the slave device;

[0105] : The C-phase current collected by the slave device;

[0106] : Neutral current collected by the slave device;

[0107] The residual current collected by the slave device;

[0108] The power of phase A calculated by the slave device based on the collected phase A voltage and phase A current;

[0109] The slave device calculates the phase B power based on the collected phase B voltage and phase B current;

[0110] The C-phase power calculated by the slave device based on the collected C-phase voltage and C-phase current;

[0111] The total harmonic content is calculated by the slave device based on the collected phase A voltage.

[0112] The total harmonic content is calculated by the slave device based on the collected B-phase voltage.

[0113] The total harmonic content is calculated by the slave device based on the collected C-phase voltage.

[0114] 3) Calculation and meaning of electrical parameter formulas

[0115] The following electrical parameter formulas are general explanations for low-voltage distribution lines and do not refer to any specific phase. Each of the three phases (A, B, and C) can be calculated using these formulas.

[0116] In a power system, the following basic formulas can be derived from the formulas for calculating the effective values ​​of voltage and current.

[0117] The host calculates the effective value of the host voltage within one cycle based on the voltage sampling value. As shown in equation (1). Similarly, the slave device calculates the effective value of the slave device within one cycle based on the voltage sampling value. As shown in equation (2).

[0118] (1)

[0119] (2)

[0120] Where n: the nth voltage sample of the master and slave devices;

[0121] N: Number of sampling points in one power frequency cycle;

[0122] : Represents the voltage value at the i-th sampling point of the host;

[0123] : Represents the voltage value at the i-th sampling point of the slave device;

[0124] This indicates that the effective value is obtained by taking the square root of the average of the sum of the squares of the voltage values ​​at N sampling points within one power frequency cycle.

[0125] This indicates that the effective value is obtained by taking the square root of the average of the sum of the squares of the voltage values ​​of N sampling points within one power frequency cycle.

[0126] In power systems, the fundamental frequency calculation of voltage refers to the effective value of the fundamental frequency of the main engine voltage within one power frequency cycle. As shown in equation (3), the fundamental effective value of the slave voltage As shown in equation (4), the total harmonic content of the host voltage is... As shown in equation (5), the total harmonic content of the slave voltage As shown in equation (6).

[0127] (3)

[0128] (4)

[0129] (5)

[0130] (6)

[0131] in:

[0132] N: Number of sampling points in one power frequency cycle;

[0133] : Represents the voltage value of the host at the i-th sampling point;

[0134] : Represents the voltage value of the slave device at the i-th sampling point;

[0135] : Used to extract the fundamental component of a signal, corresponding to the cosine component of the fundamental wave;

[0136] : Used to extract the fundamental component of a signal, corresponding to the sinusoidal component of the fundamental wave;

[0137] : Represents the fundamental effective value of the obtained host voltage;

[0138] : Represents the fundamental effective value of the slave voltage obtained;

[0139] This represents the total effective value of the host voltage, including the fundamental frequency and all harmonic components.

[0140] : Represents the total effective value of the slave voltage, including the fundamental frequency and all harmonic components;

[0141] Total harmonic content of the host voltage;

[0142] Total harmonic content of slave voltage.

[0143] In a power system, the main unit calculates the effective value of the main unit current over one cycle based on the current sampling values. As shown in equation (7). Similarly, the slave device calculates the effective value of the slave current within one cycle based on the current sampling value. As shown in equation (8).

[0144] (7)

[0145] (8)

[0146] in:

[0147] n: The nth current sample of the master and slave devices;

[0148] N: Number of sampling points in one power frequency cycle;

[0149] : Represents the current value at the i-th sampling point of the host;

[0150] : Represents the current value at the i-th sampling point of the slave device;

[0151] This indicates that the effective value is obtained by taking the square root of the average of the sum of the squares of the current values ​​at N sampling points within one power frequency cycle.

[0152] This indicates that the effective value is obtained by taking the square root of the sum of the squares of the current values ​​at N sampling points within one power frequency cycle.

[0153] In a power system, the main unit can calculate the average power based on the collected current and voltage samples. As shown in equation (9). Similarly, the slave device calculates the average power based on the collected current and voltage samples. As shown in equation (10).

[0154] (9)

[0155] (10)

[0156] in:

[0157] n: The nth sampling point of the master and slave devices;

[0158] N: Number of sampling points in one power frequency cycle;

[0159] : Represents the voltage value at the i-th sampling point of the host;

[0160] : Represents the current value at the i-th sampling point of the host;

[0161] : Represents the voltage value at the i-th sampling point of the slave device;

[0162] : Represents the current value at the i-th sampling point of the slave device;

[0163] The average power of the main unit is calculated over one power frequency cycle. It is determined by the voltage... and current The product of the sampled values ​​is summed and then divided by the number of sample points N to obtain the result.

[0164] The average power calculated by the slave device over one power frequency cycle. It is obtained by adjusting the voltage... and current The product of the sampled values ​​is summed and then divided by the number of sample points N to obtain the result.

[0165] 2. Criteria for Determining Abnormal Electrical Parameters

[0166] 1) Basic rules: During normal operation, the current at both ends of the master and slave are equal, the voltage difference is not large, and the power difference between the two ends is small.

[0167] If the voltage difference between the two ends is large and the voltage distortion is large, it generally reflects poor contact or series arc in the line, which is called the abnormal voltage criterion.

[0168] If the currents at both ends are not equal, it generally reflects the presence of leakage or parallel arcs in the circuit, which is called the abnormal current criterion.

[0169] If the power difference between the two ends is large, it generally reflects aging of the line, leakage, or poor contact, which is called the abnormal power criterion.

[0170] 2) Abnormal Voltage Criteria: The host computer determines the abnormal voltage based on the effective voltage value it collects. As shown in equation (1), the effective value of the voltage transmitted from the slave device As shown in equation (2), the comparison yields... ,like Greater than the preset value If equation (11) holds, then an abnormal voltage drop is considered to exist; otherwise, no abnormal voltage drop exists.

[0171] (1)

[0172] (2)

[0173] (11)

[0174] in:

[0175] This indicates that the effective value is obtained by taking the square root of the average of the sum of the squares of the voltage values ​​at N sampling points within one power frequency cycle.

[0176] This indicates that the effective value is obtained by taking the square root of the average of the sum of the squares of the voltage values ​​at N sampling points within one power frequency cycle.

[0177] The maximum voltage drop generated by the load current flowing through the line during normal operation can be calculated using the basic formula (12);

[0178] (12)

[0179] in: The current flowing through the conductor (A); The resistivity of the conductor material at 0°C (mm²Ω / m); The temperature coefficient of resistance (1 / °C); The actual temperature of the conductor (°C); The length of the conductor is (m). This represents the cross-sectional area of ​​the conductor (m²).

[0180] This is the voltage difference calculated over one power frequency cycle. It represents the difference between the effective value of the master voltage and the effective value of the slave voltage over one power frequency cycle, minus the maximum voltage drop during normal operation. The value obtained later;

[0181] : A preset value used to determine if there is an abnormal voltage.

[0182] 3) Criteria for abnormal voltage distortion: According to the aforementioned formulas (5) and (6), if formulas (13) and (14) are satisfied at the same time, then it is considered that there is abnormal voltage distortion in the monitored line.

[0183] (5)

[0184] (6)

[0185] (13)

[0186] (14)

[0187] in:

[0188] Total harmonic content of the host voltage;

[0189] Total harmonic content of the slave voltage;

[0190] : Indicates the preset value for voltage waveform distortion.

[0191] 4) Abnormal Current Criteria: The host computer determines the abnormal current based on the effective value of the current it collects. As shown in equation (7), the effective value of the current transmitted from the slave device As shown in equation (8), the comparison yields... ,like Greater than the preset value If equation (15) holds, then an abnormal current is considered to exist; otherwise, no abnormal current exists.

[0192] (7)

[0193] (8)

[0194] (15)

[0195] in:

[0196] This represents the difference between the effective value of the master current and the effective value of the slave current within one power frequency cycle.

[0197] This indicates that the effective value is obtained by taking the square root of the average of the sum of the squares of the current values ​​at N sampling points within one power frequency cycle.

[0198] This indicates that the effective value is obtained by taking the square root of the average of the sum of the squares of the current values ​​at N sampling points within one power frequency cycle.

[0199] : A preset value used to determine whether there is abnormal current.

[0200] 5) Abnormal power criterion: The host calculates the average power based on the current and voltage samples it collects. As shown in equation (9), the average power transmitted from the slave device is calculated based on the current and voltage sampling values. By comparing the power loss data as shown in equation (10), it can be determined whether there is abnormal power loss in the tested line. If the power loss on the monitored line... Greater than the preset value If equation (16) holds, then abnormal power loss is considered to exist; otherwise, abnormal power loss does not exist.

[0201] (9)

[0202] (10)

[0203] (16)

[0204] in:

[0205] The average power of the main unit is calculated over one power frequency cycle. It is determined by the voltage... and current The product of the sampled values ​​is summed and then divided by the number of sample points N to obtain the result.

[0206] The average power calculated by the slave device over one power frequency cycle. It is obtained by adjusting the voltage... and current The product of the sampled values ​​is summed and then divided by the number of sample points N to obtain the result.

[0207] This represents the power loss difference between the master and slave devices, calculated as the average power of the master device minus the average power of the slave device.

[0208] : A preset value used to determine if there is a power anomaly.

[0209] 3. Information exchange and electrical parameter sampling synchronization between the master and slave devices.

[0210] The master and slave devices exchange information via wireless or fiber optic communication. The slave device sends the electrical parameter information it has collected and calculated to the master device via wireless or fiber optic communication. After receiving the information, the master device performs calculations on the electrical parameter information it has collected and calculated. Finally, the master device performs fault logic judgment based on the calculation results, and then performs subsequent actions such as illuminating alarm indicator lights or tripping protection circuit breakers, and recording SOE event reports.

[0211] When the voltage crosses zero, the master sends a synchronization command to the slave and collects and calculates the sampling sequence for the next voltage crossing. When the slave receives the synchronization command from the master and the voltage crosses zero for the most recent time, it collects and calculates the current sampling sequence. At this time, the data collected by both ends are synchronized.

[0212] 4. Fault logic judgment

[0213] Low-voltage power distribution line faults are mainly classified into series arc faults, parallel arc faults, and power abnormality faults, which are explained below.

[0214] 1) Logic judgment of series arc fault:

[0215] The series arc fault judgment logic of the present invention is as follows: Figure 2 As shown, where:

[0216] : Difference between the effective values ​​of the master and slave voltages minus The value after;

[0217] ;

[0218] : Effective value of host voltage;

[0219] Slave voltage RMS value;

[0220] The maximum voltage drop generated by the load current flowing through the line during normal operation;

[0221] Voltage limit is a settable value.

[0222] Total harmonic content of the host voltage;

[0223] Total harmonic content of the slave voltage;

[0224] Voltage waveform distortion limit is a settable value that can be set.

[0225] The current during a series arc fault. =0.5( + ) ;

[0226] : Effective value of host current;

[0227] Slave current RMS value;

[0228] Time of occurrence of series arc fault;

[0229] : Set value for the delay time of series arc alarm.

[0230] A series arc fault is determined to have occurred only if the following five conditions are met simultaneously. At the same time, the main unit will illuminate the alarm indicator or trip the protection circuit breaker, and record the SOE event report.

[0231] a) There is a voltage difference between the master and slave devices. ,and > ;

[0232] b) The slave voltage exhibits voltage distortion, and > ;

[0233] c) The host voltage must also exhibit voltage distortion, and > ;

[0234] d) Arc fault current exists ,and >2.5A;

[0235] e) The fault time is greater than or equal to the alarm delay time setting, i.e. ≥ .

[0236] Only when all five conditions above are met can it be determined that the series arc occurred on the circuit being detected and protected.

[0237] 2) Parallel arc fault logic judgment:

[0238] The parallel arc fault judgment logic of the present invention is as follows: Figure 3 As shown, where:

[0239] Arc current during a parallel arc fault = = - ;

[0240] : Difference between the effective values ​​of the master and slave currents;

[0241] : Effective value of host current;

[0242] : Effective value of slave current;

[0243] Time of occurrence of parallel arc fault;

[0244] Parallel arc alarm delay time setting.

[0245] A parallel arc fault can be determined to have occurred when the following two conditions are met. At the same time, the main unit will light up the alarm indicator or trip the protection circuit breaker, and record the SOE event report.

[0246] a) Parallel arc fault current exists ,and >2.5A;

[0247] b) The fault time is greater than or equal to the alarm delay time setting, i.e. ≥ .

[0248] Only when both of the above conditions are met can it be determined that the parallel arc occurred on the circuit being detected and protected.

[0249] 3) Power anomaly fault diagnosis:

[0250] The power anomaly fault logic judgment of the present invention is as follows: Figure 4 As shown, where:

[0251] : Indicates the power loss difference between the master and slave devices. ;

[0252] Average power of the host computer;

[0253] Average power of slave devices;

[0254] Abnormal power limit is a settable value;

[0255] : Time of abnormal power occurrence;

[0256] : Abnormal power alarm delay time setting.

[0257] A power anomaly can only be determined when the following two conditions are met, and the host will illuminate the alarm indicator and record the SOE event report.

[0258] a) There is a power difference ,and > ;

[0259] b) The fault time is greater than or equal to the alarm delay time setting, i.e. ≥ .

[0260] Only when both of the above conditions are met can it be determined that the power anomaly occurred on the line being detected and protected.

[0261] Example 1: A device for fault detection and protection of low-voltage power distribution lines, comprising:

[0262] The host is used to collect electrical parameters at the power supply end of the monitored line and compare them with the electrical parameters transmitted from the load end to perform fault logic judgment.

[0263] The slave device is used to collect electrical parameters at the load end of the monitored line;

[0264] The communication module in the master and slave devices is used to support data communication and command synchronization between the master and slave devices;

[0265] The host integrates a computing unit, which is used to calculate and compare slave data with host data to identify fault types.

[0266] The host also includes an alarm and protection unit, which is used to trigger an alarm or perform a protection trip action based on the fault type judgment result of the computing unit, and simultaneously record SOE event reports.

[0267] Example 2: Operational Case of Fault Detection and Protection Device for Low-Voltage Power Distribution Lines

[0268] 1. Equipment installation and commissioning

[0269] 1) such as Figure 5As shown, low-voltage power distribution line fault detection and protection devices are installed at both ends of the monitored low-voltage three-phase power distribution line to ensure that the devices are securely installed and correctly wired.

[0270] 2) Debug and set the fault detection and protection devices for the low-voltage power distribution lines at both ends. Voltage difference set value Power difference set value Voltage waveform distortion setpoint Series arc alarm delay time setting value Parallel arc alarm delay time setting Abnormal power alarm delay time setting wait.

[0271] 3) Test whether the wireless or fiber optic communication between the two low-voltage power distribution line fault detection and protection devices is normal to ensure that the information can be transmitted accurately.

[0272] 2. Data Acquisition, Calculation, and Transmission

[0273] 1) The fault detection and protection devices at both ends of the low-voltage distribution line collect and calculate the line electrical parameters in real time (current per phase, current on the neutral line N, residual current, voltage per phase, total harmonic content of voltage per phase, power per phase, etc.).

[0274] 2) The slave device will send the synchronously collected information to the host device via wireless or fiber optic cable.

[0275] 3. Fault Diagnosis and Handling

[0276] 1) After receiving the information sent by the slave device, the master device calculates the current difference, voltage difference, power difference, and total voltage harmonic content between the master and slave devices by combining the electrical parameter information it has collected.

[0277] 2) Compare the calculated current difference, voltage difference, power difference, and total voltage harmonic content with the set values ​​respectively. , , , Compare them.

[0278] If the current difference, voltage difference, power difference, and total voltage harmonic content at the master and slave ends are all less than the set value, then the line is judged to be operating normally.

[0279] If the voltage difference between the master and slave terminals is greater than a fixed value If voltage distortion is also present, it is determined that there is a series arc fault in the line. The host will light up the alarm indicator or trip the protection circuit breaker, and record the SOE event report.

[0280] If the current difference between the master and slave terminals is greater than a fixed value If a parallel arc fault is detected in the line, the host will illuminate the alarm indicator or trip the protection circuit breaker, and record the SOE event report.

[0281] If the power difference between the master and slave ends is greater than a fixed value If the signal is detected, it indicates that there is an abnormal power fault in the line, the host will issue an alarm, and at the same time record the SOE event report.

[0282] This embodiment also includes

[0283] 4. Maintenance and Management

[0284] 1) Regularly inspect and maintain the fault detection and protection devices for low-voltage power distribution lines to ensure that the devices operate normally.

[0285] 2) Analyze the fault records, summarize the patterns and causes of fault occurrence, and take corresponding improvement measures to improve the reliability of low-voltage power distribution lines.

[0286] Example 3: Power Anomaly Loss Classification

[0287] In the existing invention method, an alarm indicator light will illuminate when abnormal power loss occurs. Furthermore, different threshold values ​​can be set to correspond to different fault levels, and different indicator lights will be illuminated accordingly, facilitating user judgment and handling.

[0288] Under normal circumstances, a three-level, three-color method can be used to classify faults into three levels: red, orange, and blue. Red corresponds to critical alarms; orange represents important alarms; and blue represents general alarms, which facilitates users in handling faults in a tiered manner.

[0289] Example 4: Adaptive Adjustment Algorithm

[0290] An adaptive adjustment algorithm is designed to adaptively match the setpoint with the corresponding delay alarm and protection trip time based on the severity of the fault in the low-voltage power distribution line.

[0291] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for fault detection and protection of a low voltage distribution line, characterized in that, The method comprises the following steps: (1) install master and slave at power end and load end of monitored line respectively, set current difference limit value , voltage difference limit value , power difference limit value and voltage waveform distortion limit value ; (2) The host and the slave are both electrical parameter measuring devices, and the line electrical parameters are synchronously collected and calculated, and the slave transmits the synchronized electrical parameters to the host; (3) The host performs fault logic judgment according to the electrical parameters collected by the slave and combined with the electrical parameters collected and calculated by the host, and the alarm indicator is lighted or the protection tripping is performed when the fault is detected, and the SOE event report is recorded at the same time.

2. The method for low voltage distribution line fault detection and protection according to claim 1, characterized in that, The step (2) of synchronously collecting and calculating the line electrical parameters by the host and the slave includes the current of each phase, the current on the neutral line N, the residual current, the voltage of each phase, the total harmonic content of the voltage of each phase and the power of each phase.

3. The method for low voltage distribution line fault detection and protection according to claim 1, wherein, The fault logic judgment in the step (3) includes the following rules: Abnormal voltage determination: compare the effective values of the voltages of the master and slave, and if the difference is greater than a set voltage difference determination value, then it is considered that there is an abnormal voltage ; Voltage distortion judgment: compare the total harmonic content of the host and slave voltage, if the total harmonic content of the slave voltage is greater than the set voltage waveform distortion limit, and at the same time the total harmonic content of the slave voltage is greater than the total harmonic content of the host voltage, it is considered that there is voltage distortion; , and at the same time the total harmonic content of the slave voltage is greater than the total harmonic content of the host voltage, it is considered that there is voltage distortion; Abnormal current determination: compare the current effective values of the master and slave, if the difference is greater than the set current difference threshold value, then consider that there is an abnormal current. Abnormal current determination: compare the current effective values of the master and slave, if the difference is greater than the set current difference threshold value, then consider that there is an abnormal current.

4. The method for low voltage distribution line fault detection and protection according to claim 3, characterized in that: In the fault logic judgment of the step (3), when the following five conditions are met at the same time, it is judged that the series arc fault occurs: a) master-slave voltage difference , and > ; b) the voltage distortion exists from the machine voltage, and ;​ c) the host voltage also has voltage distortion, and ;​ d) an arc fault current is present , and > 2.5 A, A denoting the unit of current, ampere; e) the failure time is greater than or equal to the alarm delay time constant, i.e. ≥ ; wherein: ; : Host voltage effective value; : From machine voltage effective value; : maximum voltage drop produced by the line flowing load current during normal operation; : total harmonic content of the host voltage; : From the total harmonic content of the machine voltage; : current at the occurrence of a series arc fault, = 0.5( + ) ; : host current effective value; : From the machine current effective value; : time to series arc fault occurrence; : Series arc alarm delay time constant.

5. The method for low voltage distribution line fault detection and protection according to claim 3, wherein: In the fault logic judgment of the step (3), when the following two conditions are met at the same time, it is judged that the parallel arc fault occurs: a) a parallel arc fault current is present , and > 2.5 A; b) the failure time is greater than or equal to the alarm delay time constant, i.e. ≥ ; In the step (3), when the following two conditions are met at the same time, it is judged that the power abnormality occurs: : arc current at occurrence of a parallel arc fault, = arc current at occurrence of a series arc fault, = arc current at occurrence of a series arc fault, - arc current at occurrence of a parallel arc fault, ; : Master-slave current effective value difference; : host current effective value; : From the machine current effective value; : time to parallel arc fault occurrence; : Parallel arc alarm delay time constant.

6. The method for low voltage distribution line fault detection and protection according to claim 3, wherein: In the step (3), when the following two conditions are met at the same time, it is judged that the power abnormality occurs: a) presence of power difference , and > ; b) the failure time is greater than or equal to the alarm delay time constant, i.e. ≥ . The communication mode between the host and the slave is wireless or optical fiber communication, and the host performs synchronous collection of electrical parameters with the slave through wireless or optical fiber communication; : represents a difference in power loss between the master and the slave, ; : average power of the host; : average power from slave : Abnormal power time occurs; : Abnormal power alarm delay time constant value.

7. The method of low voltage distribution line fault detection and protection according to any one of claims 1 to 6, characterized in that: The implementation of synchronous collection: the host sends a synchronization instruction to the slave at the voltage zero crossing, and collects and calculates the sampling sequence at the next voltage zero crossing, and when the slave receives the synchronization instruction sent by the host, the current sampling sequence is collected and calculated at the nearest voltage zero crossing. It comprises:

8. An apparatus for fault detection and protection of a low voltage distribution line, characterized by The host is used for collecting electrical parameters at the power supply end of the monitored line, and performing data comparison and fault logic judgment with the electrical parameters collected and transmitted from the load end; The slave is used for collecting electrical parameters at the load end of the monitored line; The communication module in the host and the slave is used for supporting data communication and instruction synchronization between the host and the slave; The calculation unit integrated in the host is used for comparing the slave data and the host data in the host, and identifying the fault type; The alarm and protection unit in the host is used for triggering the alarm or performing the protection tripping action based on the fault type judgment result of the calculation unit, and recording the SOE event report at the same time. ​

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