A method and device for selecting a low-voltage circuit grounding line and confirming a grounding point range

Abstract

The present invention discloses a method for selecting a grounding line and confirming a grounding point range in a low-voltage circuit, which relates to the field of power grid protection technology and includes the following steps: obtaining impedance parameters of the circuit power supply, equipment, and cable; connecting impedances in series in the circuit according to the measured parameters to make the three-phase impedances equal; installing a high-frequency current generating module and a grounding capacitor at the end of the circuit; creating a grounding impedance matching table for each device and important node according to the measured impedance parameters; the high-frequency current generating module alternately generates AC and DC currents and measures the neutral point and capacitor currents; and determining the grounding phase and grounding range by calculating the impedance based on the measured values. The present invention installs a high-frequency current generating module and a grounding capacitor at the end of the circuit. The high-frequency current generating module is activated when a fault occurs. During phase selection, each module generates high-frequency current in a sequential cycle, enters the fault phase selection and fault location logic, and can achieve accurate fault location, quickly select the grounded phase, locate the grounding point range, and improve the operational reliability of the low-voltage system.

Description

Technical Field

[0001] The present invention relates to the field of low-voltage circuit grounding point search, and in particular to a method and device for low-voltage circuit grounding line selection and grounding point range confirmation. Background Art

[0002] Grounding faults in substation low-voltage systems often cause voltage fluctuations, switch tripping, equipment power outages, and protective equipment malfunction or refusal to operate, significantly impacting power system reliability. Currently, methods such as the pull-through method are often used to locate the grounding point in substation neutral-grounded low-voltage systems. This requires disconnecting the circuit, posing a significant risk to the safe and stable operation of the power system. Furthermore, grounding faults are often intermittent and temporary, depending on weather conditions, and can only be pinpointed to a specific branch, making it impossible to accurately locate the fault point using grounding finder equipment.

[0003] When a low-voltage system is short-circuited, the operating circuit must be disconnected when searching for the grounding point by the pulling-line method. The use of grounding search instruments has a time lag and can only locate a certain branch, resulting in problems with timeliness and accuracy. Summary of the Invention

[0004] In order to solve the deficiencies of the above-mentioned prior art, the present invention provides a low-voltage circuit grounding line selection and grounding point range confirmation method and device, which can quickly select the grounding phase, locate the grounding point range, and improve the operational reliability of the low-voltage system.

[0005] The technical solution proposed by the present invention is:

[0006] A method for selecting a low-voltage circuit grounding line and confirming a grounding point range includes the following steps:

[0007] Obtain loop power, equipment and cable impedance parameters;

[0008] Connect impedances in series in the loop according to the measured parameters to make the three-phase impedances equal;

[0009] Install a high-frequency current generating module and a grounding capacitor at the end of the loop;

[0010] Prepare ground impedance matching tables for each device and important nodes based on measured impedance parameters;

[0011] The high-frequency current generation module generates AC and DC alternately and measures the neutral point and capacitor currents;

[0012] Calculate the impedance based on the measured value to determine the grounding phase and determine the grounding range.

[0013] As a further technical solution of the present invention, impedances are connected in series in the loop according to the measurement parameters so that the three-phase impedances are equal and at least one compensation impedance is zero.

[0014] As a further technical solution of the present invention, a high-frequency current generating module and a grounding capacitor are installed at the tail end of the loop. Specifically, the high-frequency current generating module arranged at the tail end of the loop is started when a fault occurs. When selecting a phase, the high-frequency current generating module generates high-frequency current in a sequential cycle. After the fault phase is determined, only the fault phase module emits high-frequency current to determine the fault range.

[0015] As a further technical solution of the present invention, the measurement of neutral point and capacitor current is specifically as follows: when the neutral point current mutation amount is greater than a set value, the fault phase selection and fault location logic is entered.

[0016] As a further technical solution of the present invention, the grounding phase is determined based on the measured value to determine the grounding range, and the phase selection method is as follows: if the current generated by the three-phase ABC high-frequency current at the neutral point grounding point is the same, it is determined to be an N line fault; when the current of the N line high-frequency current generating module is generated, the N line grounding current is compared with the capacitor current. If the capacitor current is smaller, the grounding point is determined to be at the end of the line, otherwise multiple grounding of the N line occurs; if the N neutral point grounding current is unequal when the ABC three-phase high-frequency current generating modules generate current, the neutral point current size is compared when the three-phase high-frequency current is generated, and the phase with the smaller current is the fault phase; after determining the grounded phase, the system calculates the measured impedance and determines the fault range based on the measured impedance comparison impedance matching table.

[0017] The present invention also provides a low-voltage circuit grounding line selection and grounding point range confirmation device, comprising:

[0018] A high-frequency current generator, a current measuring element, an adjustable compensation resistor, a grounding capacitor, a memory, a control unit, and an alarm module. The current measuring element is installed at the neutral point grounding wire and the capacitor. The adjustable compensation resistor is connected in series on the three-phase circuit. The high-frequency current generator is set at the tail end of the ABCN circuit, and the tail end of the ABCN circuit is grounded through the grounding capacitor.

[0019] The output end of the control unit is connected to a high-frequency current generator, the output end of the current measuring element is connected to the control unit, and the control unit is connected to a memory and an alarm module.

[0020] As a further technical solution of the present invention, the current frequency of the high-frequency current generator is greater than 5000 Hz.

[0021] As a further technical solution of the present invention, the measurement accuracy of the current measuring element is at the milliampere level.

[0022] As a further technical solution of the present invention, the memory and the control unit use anti-interference devices.

[0023] The beneficial effects of the present invention are:

[0024] The present invention installs a high-frequency current generating module and a grounding capacitor at the end of the loop. The high-frequency current generating module activates when a fault occurs. During phase selection, each module sequentially generates high-frequency current. Once the faulty phase is determined, only the faulty phase module generates high-frequency current to determine the fault range. By measuring the neutral point and capacitor current in real time, the fault phase selection and fault location logic is activated when the neutral point current suddenly changes beyond a set value. This enables accurate fault location, rapid selection of the grounded phase, and localization of the grounding point, improving the operational reliability of the low-voltage system. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a flow chart of a method for selecting a low-voltage circuit grounding line and confirming a grounding point range proposed by the present invention;

[0026] Figure 2 This is a specific flow chart of the low-voltage circuit grounding line selection and grounding point range confirmation method proposed by the present invention;

[0027] Figure 3 This is a structural diagram of a low-voltage circuit grounding line selection and grounding point range confirmation device proposed by the present invention;

[0028] Figure 4 The present invention proposes an equivalent circuit diagram for low-voltage loop grounding line selection and grounding point range confirmation.

[0029] As shown in the figure:

[0030] 201 - high-frequency current generator, 202 - current measuring element, 203 - adjustable compensation resistor, 204 - grounding capacitor, 205 - memory, 206 - control unit, 207 - alarm module. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the concept, specific structure and technical effects of the present invention in conjunction with the embodiments and drawings to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0032] See also Figure 1 A method for selecting a low-voltage circuit grounding line and confirming a grounding point range comprises the following steps:

[0033] Step 101, obtaining loop power supply, device and cable impedance parameters;

[0034] Step 102: Connect impedances in series in the loop according to the measured parameters to make the three-phase impedances equal;

[0035] Step 103: Install a high-frequency current generating module and a grounding capacitor at the end of the loop;

[0036] Step 104: Create a ground impedance matching table for each device and important node based on the measured impedance parameters;

[0037] Step 105: The high-frequency current generating module generates AC and DC alternately and measures the neutral point and capacitor currents.

[0038] Step 106: Calculate the impedance based on the measured value to determine the grounded phase and determine the grounding range.

[0039] In step 101, the impedance of each device, terminal, inter-screen cable, power winding, grounding resistance and other components in the current generator to the current phase loop is measured respectively. In order to obtain a more accurate grounding point, as many points as possible should be measured to obtain the impedance parameters of the loop power supply, equipment and cable.

[0040] See also Figure 2 In the embodiment of the present invention, impedances are connected in series in the loop according to the measurement parameters so that the three-phase impedances are equal and at least one compensation impedance is zero.

[0041] Among them, a high-frequency current generating module and a grounding capacitor are installed at the end of the loop. The high-frequency current generating module is started when a fault occurs. When selecting the phase, each module generates high-frequency current in a cycle in sequence. After the fault phase is determined, only the fault phase module emits high-frequency current to determine the fault range.

[0042] Determine whether grounding is present and complete fault line selection. After line selection is complete, high-frequency AC and DC are alternately generated with a 2-second cycle, and the neutral point and capacitance currents are measured. After the grounding line is selected, the high-frequency current continues for 2 seconds, then enters the 2-second DC generation phase, and then alternates. Based on the two high-frequency current and DC measurement values, the grounding impedance and the impedance between the grounding point and the high-frequency current generator are calculated.

[0043] The high-frequency current generation module generates AC and DC alternately and measures the neutral point and capacitor currents. When the neutral point current mutation is greater than the set value, the fault phase selection and fault location logic is entered.

[0044] Create a grounding impedance matching table for each device and important node based on the measured impedance parameters; based on the impedance measured at different distances and locations on site, match the measured impedance when a fault occurs to determine the approximate grounding range.

[0045] The grounding resistance and the impedance between the grounding point and the high-frequency current generating device are calculated based on the current and output voltage measured when AC and DC are generated.

[0046] The grounded phase is determined based on the measured calculated value to determine the grounding range. The grounding resistance and the current between the grounding point and the high-frequency current generating device are calculated based on the current and output voltage measured when AC and DC are generated. The specific phase selection method is as follows: if the current generated by the three-phase ABC high-frequency current at the neutral point grounding point is the same, it is determined to be an N-line fault; when the current of the N-line high-frequency current generating module is generated, the N-line grounding current is compared with the capacitor current. If the capacitor current is smaller, the grounding point is determined to be at the end of the line, otherwise multiple grounding of the N line occurs; if the N neutral point grounding current is unequal when the ABC three-phase high-frequency current generating modules generate current, the neutral point current is compared when the three-phase high-frequency current is generated, and the phase with the smaller current is the fault phase; after determining the grounded phase, the system calculates the measured impedance and determines the fault range by comparing the measured impedance with the impedance matching table.

[0047] The specific test process of the present invention is as follows: when it is detected that the neutral point grounding current △I0 is less than the set value, continue to detect; when it is detected that the neutral point grounding current △I0 is greater than or equal to the set value, determine whether the high-frequency current generators on the ABC loops generate high-frequency currents when I0 are equal; if not, compare the magnitudes of I0 when the currents of the three phases ABC are generated, determine that the phase with the minimum current is the grounded phase, perform impedance calculation, and determine the grounding range by comparing the impedance with the impedance table;

[0048] When the high-frequency current generator on the ABC loop generates high-frequency current and I0 is equal, it is determined that the N-line high-frequency current generator generates high-frequency current, and it is determined whether the capacitor current is greater than the neutral point grounding current. If the capacitor current is greater than the neutral point grounding current, it is multi-point grounding of the N line. If the capacitor current is less than or equal to the neutral point grounding current, it is multi-point grounding of the N line tail end.

[0049] See also Figure 3 The present invention also provides a low-voltage circuit grounding line selection and grounding point range confirmation device, comprising:

[0050] A high-frequency current generator 201, a current measuring element 202, an adjustable compensation resistor 203, a grounding capacitor 204, a memory 205, a control unit 206, and an alarm module 207. The current measuring element 202 is installed at the neutral point grounding wire and capacitor. The adjustable compensation resistor 203 is connected in series on the three-phase circuit. The high-frequency current generator 201 is set at the end of the ABCN circuit, and the end of the ABCN circuit is grounded through the grounding capacitor 204.

[0051] The output end of the control unit 206 is connected to the high-frequency current generator 201 , the output end of the current measuring element 202 is connected to the control unit 206 , and the control unit 206 is connected to the memory 205 and the alarm module 207 .

[0052] The high-frequency current generator has a current frequency greater than 5000 Hz. The current measuring element is installed at the neutral grounding wire and capacitor, with milliampere-level measurement accuracy. Adjustable compensating resistors ensure that the three-phase operating impedances are equal, with at least one resistor having zero impedance.

[0053] See also Figure 4 , is the circuit equivalent principle diagram of the present invention, wherein Z1-Z3 are the power supply equivalent impedance, K is the grounding point, Za1-Zc2 are the equipment equivalent impedance, Zp1-Zp3 are the compensation impedance, I0 is the neutral point current, P1-P4 are the high-frequency current generating modules, C1 is the grounding capacitor, and I2 is the capacitor current.

[0054] The grounding capacitor specification ensures that the high-frequency current carrying capacity is at least an order of magnitude greater than the power-frequency current. The memory and control unit use conventional anti-interference devices and have an anti-interference structure that is not affected by the high-frequency current generated by the high-frequency current generator.

[0055] The alarm module can generate alarms for ground faults in different phases and ranges. It can use audible and visual alarms, or set different alarm lights for different phases. The alarm lights indicate the faulty phase and range, making it easier for maintenance personnel to identify and perform maintenance.

[0056] The present invention has been described in detail above. However, the present invention is not limited to the above-described embodiments. Various modifications may be made within the scope of knowledge of those skilled in the art without departing from the spirit of the present invention. Many other changes and modifications may be made without departing from the spirit and scope of the present invention. It should be understood that the present invention is not limited to the specific embodiments, and the scope of the present invention is defined by the appended claims.

Claims

1. A method for selecting a low-voltage circuit grounding line and confirming a grounding point range, characterized in that: The following steps are involved: Obtain loop power, equipment and cable impedance parameters; Connect impedances in series in the loop according to the measured parameters to make the three-phase impedances equal; Install a high-frequency current generating module and a grounding capacitor at the end of the loop; Prepare ground impedance matching tables for each device and important nodes based on measured impedance parameters; The high-frequency current generation module generates AC and DC alternately and measures the neutral point and capacitor currents; Calculate the impedance based on the measured value to determine the grounding phase and determine the grounding range; The measurement of the neutral point and capacitor current is specifically as follows: when the neutral point current mutation amount is greater than the set value, the fault phase selection and fault location logic is entered; The grounding phase is determined based on the measured value to determine the grounding range. The phase selection method is as follows: if the currents generated by the three-phase A, B, C, and C high-frequency currents at the neutral point grounding point are the same, it is determined that there is an N line fault; when the N line high-frequency current generating module generates current, the N line grounding current is compared with the capacitor current. If the capacitor current is smaller, the grounding point is determined to be at the end of the line, otherwise multiple grounding of the N line occurs; if the N neutral point grounding currents are unequal when the three-phase A, B, and C high-frequency current generating modules generate currents, the neutral point currents of the three phases are compared when the high-frequency currents are generated, and the phase with the smaller current is the fault phase; After determining the grounded phase, the system calculates the measured impedance and determines the fault range based on the measured impedance comparison with the impedance matching table.

2. A method for selecting a low-voltage circuit grounding line and confirming a grounding point range according to claim 1, characterized in that: The impedances are connected in series in the loop according to the measured parameters so that the three-phase impedances are equal and at least one compensation impedance is zero.

3. A method for selecting a low-voltage circuit grounding line and confirming a grounding point range according to claim 1, characterized in that: The high-frequency current generating module and the grounding capacitor are installed at the tail end of the loop. Specifically, the high-frequency current generating module arranged at the tail end of the loop is started when a fault occurs. When selecting a phase, the high-frequency current generating module generates high-frequency current in a sequential cycle. After the fault phase is determined, only the fault phase module emits high-frequency current to determine the fault range.

4. A low-voltage circuit grounding line selection and grounding point range confirmation device, using a low-voltage circuit grounding line selection and grounding point range confirmation method according to any one of claims 1 to 3, characterized in that: include: A high-frequency current generator, a current measuring element, an adjustable compensation resistor, a grounding capacitor, a memory, a control unit, and an alarm module. The current measuring element is installed at the neutral point grounding wire and the capacitor. The adjustable compensation resistor is connected in series on the three-phase circuit. The high-frequency current generator is set at the tail end of the ABCN circuit, and the tail end of the ABCN circuit is grounded through the grounding capacitor. The output end of the control unit is connected to a high-frequency current generator, the output end of the current measuring element is connected to the control unit, and the control unit is connected to a memory and an alarm module.

5. A low-voltage circuit grounding line selection and grounding point range confirmation device according to claim 4, characterized in that: The current frequency of the high-frequency current generator is greater than 5000 Hz.

6. A low-voltage circuit grounding line selection and grounding point range confirmation device according to claim 4, characterized in that: The measurement accuracy of the current measuring element is at the milliampere level.

7. A low-voltage circuit grounding line selection and grounding point range confirmation device according to claim 4, characterized in that: The memory and control unit use anti-interference devices.

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