A grounding resistance detection device and method for a substation grounding grid

Abstract

The present invention relates to a grounding resistance detection device and method for a substation grounding grid, comprising a detection power supply, a grounding terminal, and a detection terminal; the detection power supply is sequentially connected to a first capacitor and a second capacitor through a first step-up transformer, the second capacitor is respectively connected to a spherical gap switch and a first current-limiting resistor, the spherical gap switch is connected to the grounding terminal, and the first current-limiting resistor is connected to the detection terminal; the second capacitor, the first current-limiting resistor, and the grounding grid to be tested form a capacitor discharge loop; the grounding resistance R of the grounding grid is R=Uc / Ic-R1, Uc and Ic are the discharge voltage and discharge current of the second capacitor, respectively, and R1 is the resistance value of the first current-limiting resistor. The first step-up transformer and the second capacitor form a high-voltage, high-current discharge mode to test the grounding resistance of the grounding grid, which conforms to the working state of the substation when it is struck by lightning or a high-voltage ground fault occurs, and the measurement is more reasonable. At the same time, the high-voltage, high-current discharge mode is less susceptible to interference generated by the magnetic field of electrical equipment in the substation.

Description

Technical Field

[0001] The present invention relates to the technical field of grounding detection, and in particular to a grounding resistance detection device and method for a substation grounding grid. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Substation grounding grids are designed to meet the requirements of equipment operation, safety, and protective grounding. They can quickly conduct fault short-circuit currents or lightning currents to the earth for discharge. Typically made of galvanized steel, these grids are buried during the initial construction of substations. Over time, these grids are subject to soil corrosion. As the substation operates, the material gradually thins or breaks, increasing grounding resistance. This reduces the ability to conduct short-circuit or lightning currents to the earth, posing a threat to personnel and equipment safety.

[0004] When a substation is struck by lightning or a high-voltage grounding fault occurs, high voltage and high current will directly enter the grounding grid. Traditional grounding resistance tests are carried out with low voltage (220V) and small current (about 10A), which is quite different from the actual working state of the grounding grid. At the same time, various types of electrical equipment in the substation have complex electromagnetic interference, which will interfere with the measurement results of grounding resistance and cause errors. Summary of the Invention

[0005] In order to solve at least one technical problem existing in the above-mentioned background technology, the present invention provides a grounding resistance detection device and method for a substation grounding grid. The method of high-voltage and high-current high-voltage capacitor discharge is used to test the grounding grid resistance, which is closer to the actual working state and the measurement is more reasonable.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A first aspect of the present invention provides a grounding resistance detection device for a substation grounding grid, comprising a detection power supply, a grounding terminal, and a detection terminal;

[0008] The detection power supply is connected to the first capacitor and the second capacitor in sequence through the first step-up transformer, the second capacitor is respectively connected to the ball gap switch and the first current limiting resistor, the ball gap switch is connected to the ground end, and the first current limiting resistor is connected to the detection end; the second capacitor, the first current limiting resistor and the grounding grid to be tested form a capacitor discharge loop; the grounding resistance of the grounding grid is R=Uc / Ic-R1, Uc and Ic are the discharge voltage and discharge current of the second capacitor respectively, and R1 is the resistance value of the first current limiting resistor.

[0009] The grounding end is the grounding nail driven into the ground, and the detection end is the location of the grounding grid to be tested.

[0010] A second current-limiting resistor is connected between the first step-up transformer and the first capacitor. The first capacitor is connected to the second capacitor through a second rectifier module and a third current-limiting resistor arranged in sequence. The first rectifier module is connected to the line between the first capacitor and the second rectifier module, and the first rectifier module is connected to the detection power supply.

[0011] The spherical gap switch includes an upper hemisphere and a lower hemisphere arranged in parallel with a gap therebetween. The upper hemisphere is connected to the second capacitor, and the lower hemisphere is connected to the ground end. A hole is provided in the middle of the lower hemisphere, and a needle electrode is connected to the hole through an insulating layer. The needle electrode is located in the center of the hole.

[0012] The ball gap switch is a discharge trigger switch for the capacitor discharge circuit, and discharge is achieved by generating a trigger signal through a signal generation circuit.

[0013] The signal generating circuit includes an inverter, the input port of the inverter is connected to the DC power supply through the fifth resistor and the fourth resistor in sequence, the inverter is connected to the fourth resistor through the third capacitor and the switch in sequence, and the inverter is also connected to the DC power supply through a diode.

[0014] The output port of the inverter is connected to the gate G of the IGBT. When the trigger signal is output, the collector C and emitter E of the IGBT are turned on, and the line between the fourth rectifier module and the fourth capacitor is connected to the detection power supply through the turned-on IGBT.

[0015] The detection power supply is connected to the fourth capacitor through the second step-up transformer, the sixth current-limiting resistor and the fourth rectifier module in sequence. The fourth capacitor is connected to the lower hemisphere of the spherical gap switch through the seventh resistor.

[0016] A second aspect of the present invention provides a method for detecting grounding resistance of a grounding grid using the above-mentioned device, comprising the following steps:

[0017] When the voltage of the first step-up transformer reaches the positive half cycle, the first capacitor is charged, and when the voltage of the first step-up transformer reaches the negative half cycle, the first capacitor and the first step-up transformer simultaneously charge the second capacitor;

[0018] After the second capacitor is charged and the ball gap switch is triggered to conduct, the second capacitor, the first current limiting resistor and the grounding grid to be measured form a conductive capacitor discharge loop, and the second capacitor discharges the capacitor discharge loop;

[0019] The discharge voltage Uc and the discharge current Ic of the second capacitor are obtained, and the grounding resistance R of the grounding grid is R=Uc / Ic-R1, where R1 is the resistance value of the first current limiting resistor R1.

[0020] Compared with the existing technology, one or more of the above technical solutions have the following beneficial effects:

[0021] The first step-up transformer and the second capacitor form a high-voltage, high-current discharge method to test the grounding resistance of the grounding grid. This is in line with the working state when the substation is struck by lightning or a high-voltage grounding fault occurs, and the measurement is more reasonable. At the same time, the high-voltage, high-current discharge method is less susceptible to interference from the magnetic field generated by electrical equipment in the substation. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0023] Figure 1 A schematic diagram of a charging and discharging circuit of a second capacitor C2 of a detection device provided by one or more embodiments of the present invention;

[0024] Figure 2 A circuit diagram for generating an initial trigger signal for a detection device provided by one or more embodiments of the present invention;

[0025] Figure 3 A schematic diagram of the ball gap switch structure of a detection device provided by one or more embodiments of the present invention;

[0026] Figure 4 A schematic diagram of a ball gap switch trigger circuit of a detection device provided by one or more embodiments of the present invention;

[0027] In the figure: 1. Needle electrode; 2. Insulation layer. DETAILED DESCRIPTION

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0029] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0030] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0031] As described in the background technology, when a substation is struck by lightning or a high-voltage grounding fault occurs, high voltage and high current will directly enter the grounding grid. Traditional grounding resistance tests are all carried out with low voltage (220V) and small current (about 10A). Various types of electrical equipment in the substation have complex electromagnetic interference, which will interfere with the measurement results of the grounding resistance and cause errors.

[0032] Therefore, the following embodiments provide a grounding resistance detection device and method for a substation grounding grid, so as to achieve the purpose of directly testing the grounding resistance using high voltage and high current.

[0033] Currently, primary equipment in substations typically operates at voltages of 10kV, 35kV, 110kV, 220kV, and above, and lightning strike voltages can reach thousands of kilovolts or more. When high-voltage equipment in a substation grounds or is struck by lightning, the grounding grid is responsible for directing the grounding or lightning current into the earth, preventing damage to personnel or equipment. Testing grounding grid resistance using high-voltage, high-current, high-voltage capacitor discharge is more realistic and provides more accurate measurements.

[0034] Example 1:

[0035] like Figure 1-4 As shown, the purpose of this embodiment is to provide a grounding resistance detection device for a substation grounding grid, including a detection power supply, a grounding terminal G1 and a detection terminal G2;

[0036] The detection power supply is connected to the first capacitor C1 and the second capacitor C2 in sequence through the first step-up transformer T1. The second capacitor C2 is respectively connected to the spherical gap switch Q and the first current-limiting resistor R1. The spherical gap switch Q is connected to the ground terminal G1, and the first current-limiting resistor R1 is connected to the detection terminal G2. The second capacitor C2, the first current-limiting resistor R1 and the grounding grid to be tested form a capacitor discharge loop. The grounding resistance of the grounding grid is R = Uc / Ic-R1, where Uc and Ic are the discharge voltage and discharge current of the second capacitor C2, respectively.

[0037] The grounding terminal G1 should be a grounding nail driven into the ground, and the detection terminal G2 is the location of the grounding grid to be tested.

[0038] A second current-limiting resistor R2 is connected between the first step-up transformer T1 and the first capacitor C1. The first capacitor C1 is connected to the second capacitor C2 through a second rectifier module D2 and a third current-limiting resistor R3 arranged in sequence. The first rectifier module D1 is connected to the line between the first capacitor C1 and the second rectifier module D2, and the first rectifier module D1 is connected to the detection power supply.

[0039] The spherical gap switch Q includes two metal hemispheres (upper hemisphere B1 and lower hemisphere B2) arranged in parallel with a gap. The upper hemisphere B1 is connected to the second capacitor C2, and the lower hemisphere is connected to the ground terminal G1. A hole is provided in the middle of the lower hemisphere B1, and the needle electrode 1 is connected to the hole through the insulating layer 2. The needle electrode 1 is located in the center of the hole.

[0040] The spherical gap switch Q is a discharge trigger switch of the capacitor discharge circuit, and discharge is achieved by generating a trigger signal through a signal generation circuit.

[0041] The signal generating circuit includes an inverter, the input port of the inverter is connected to the DC power supply +5V through the fifth resistor R5 and the fourth resistor R4 in sequence, the inverter is connected to the fourth resistor R4 through the third capacitor C3 and the switch in sequence, and the inverter is also connected to the DC power supply +5V through the diode D3.

[0042] The output port of the inverter is connected to the gate G of the IGBT. When the trigger signal is output, the collector C and emitter E of the IGBT are turned on, and the line between the fourth rectifier module D4 and the fourth capacitor C4 is connected to the detection power supply through the turned-on IGBT.

[0043] The detection power supply is connected to the fourth capacitor C4 through the second boost transformer T2, the sixth current limiting resistor R6 and the fourth rectifier module D4 in sequence. The fourth capacitor C4 is connected to the lower hemisphere B2 of the ball gap switch Q through the seventh resistor R7.

[0044] The output port of the inverter triggers a signal, the fourth capacitor C4 discharges, the gap between the needle electrode and the lower hemisphere B2 breaks down, and plasma is generated to distort the electric field between the upper and lower hemispheres of the spherical gap switch Q, thereby causing the two hemispheres to break down and trigger the spherical gap switch Q. At this time, the second capacitor C2 is connected to the ground terminal G1, and the second capacitor C2 discharges.

[0045] Specifically:

[0046] After the step-up transformer draws power from the substation maintenance power box, it charges the high-voltage capacitor through the charging circuit. After it is fully charged, the circuit is designed to control the discharge of the capacitor. The instantaneous voltage and current of the capacitor discharge are recorded to calculate the grounding resistance.

[0047] Main wiring diagram Figure 1As shown, the 220V voltage from the maintenance power supply box is connected to the step-up transformer T1. When the voltage of transformer T1 reaches the positive half cycle, it charges capacitor C1 through current-limiting resistor R2. During the negative half cycle, capacitor C1 and transformer T1 simultaneously charge C2 through current-limiting resistor R3, shortening the charging time. After the voltage of capacitor C2 is increased to a sufficiently high voltage (such as 30kV), the ball gap switch Q is triggered. After the ball gap switch Q is turned on, the left end of capacitor C2 is equivalent to being directly connected to G1, and the potential becomes ground. Then, the right end of capacitor C2 is at a negative high potential. In this way, capacitor C2, current-limiting resistor R1, and grounding grid R form a capacitor discharge loop.

[0048] Ground terminal G1 should be a grounding spike driven into the ground to an appropriate depth. G2 is connected to the ground terminal to be tested, and R is the ground resistance. Use an oscilloscope or data acquisition card to record the discharge voltage Uc and current Ic of capacitor C2. The resistance R can be measured based on the values ​​of the discharge voltage Uc and current Ic at the same moment. Ground resistance R = Uc / Ic - R1. Multiple measurements of Uc / Ic can be used to average the values ​​to minimize errors.

[0049] Component models and parameters should be selected based on actual site conditions. For example, transformer T1 can have a ratio of 220:21000 and a capacity of 1kVA. Rectifier stack D1 (first rectifier module D1) uses a 2CL130 / 0.5 model with a maximum reverse withstand voltage of 130kV and a maximum current of 0.5A. Rectifier stack D2 (second rectifier module D2) uses a 2CL70 / 0.1 model with a maximum reverse withstand voltage of 70kV and a maximum current of 0.1A. Current-limiting resistors R2 and R3 are both 2MΩ. Their function is to limit the charging current and prevent excessive power from flowing through the charging circuit. This allows for a lower-capacity transformer to reduce installation costs, but this also increases charging time. Capacitor C1 uses a 0.1uF electrolytic capacitor with a rated voltage of 30kV. C2 should be a larger capacity capacitor (high voltage capacitor). The larger the capacity, the longer the discharge time of C2. The easier it is to measure the voltage and current at the moment of discharge, and the more accurate the calculation results. After calculation, the pulse capacitor model HZ MJ50kv-2uF can be selected.

[0050] The initial trigger signal is generated by a signal generation circuit with the inverter 74LS14 as the main chip. Figure 2 As shown in the figure, when the manual switch is open, input port 1 of inverter 74LS14 is connected to the +5V DC power supply through resistors R4 and R5, resulting in a high level. When the switch is closed, input port 1 of inverter 74LS14 is grounded through a small resistor R5, resulting in a low level. When the switch is manually closed once, a step signal is generated at input port 1 of inverter 74LS14. After inversion by the inverter, this signal is generated as the initial trigger signal, which is output at output port 2. Figure 2The diode D3 and capacitor C3 play the role of protection and voltage regulation. The optional model of D3 is IS1500, and C3 can be a 0.1uF ordinary capacitor. The current limiting resistors R4 and R5 play the role of current limiting protection, and their resistance values ​​are 7.4kΩ and 100Ω respectively.

[0051] The main discharge circuit uses a spherical gap switch Q as the discharge trigger switch. Figure 3 As shown, the spherical gap switch Q consists of two metal hemispheres (upper hemisphere B1 and lower hemisphere B2), separated by a certain distance. Upper hemisphere B1 is connected to the left end of capacitor C2. When capacitor C2 is charged, upper hemisphere B1 is at a high voltage potential, while the lower hemisphere is connected to ground G1. Lower hemisphere B1 has a small hole with a diameter of approximately 1 mm in the center. An insulating layer 2 (e.g., polytetrafluoroethylene) secures a needle electrode 1 (e.g., a tungsten needle) within the hole, with the needle electrode 1 positioned in the center.

[0052] like Figure 4 As shown, the 220kV power supply is boosted by voltage regulator T2 and then flows through current-limiting resistor R6 and rectifier stack D4 to charge capacitor C4. Voltage regulator T2 can have a ratio of 220:3000 and a capacity of 0.5kVA. Current-limiting resistor R6 has a resistance of 1kΩ. Rectifier stack D4 can be a 2CL10 / 0.1 model. Capacitor C4 can be a 0.1uF electrolytic capacitor. Input port 2 of the inverter 74LS14 is connected to the gate G of the IGBT. When the switch is manually opened and closed, the input port 2 of the inverter 74LS14 outputs a trigger signal, the collector C and emitter E of the IGBT are turned on, the upper end of the charged capacitor C4 is grounded, and a negative high voltage is formed at the lower end. The lower end of the capacitor C4 is connected to the metal needle electrode of the lower hemisphere of the spherical gap switch through R7, so that a negative high voltage is also formed on the metal needle electrode. The gap between the metal needle electrode and the lower hemisphere B2 (grounded) is broken down, generating plasma that distorts the electric field between the upper and lower hemispheres of the spherical gap switch Q, thereby breaking down the two hemispheres and grounding the left end of the capacitor C2. Figure 1 The main circuit discharges.

[0053] It should be noted that the breakdown voltage of the spherical gap is related to the distance, and the appropriate spherical gap distance should be selected according to the voltage level of the capacitor discharge. According to references, it is generally believed that the electric field strength for air breakdown is E = 30kV / cm.

[0054] The above device uses a high-voltage, high-current discharge method to test the grounding grid resistance, which is closer to the actual working state of the grounding grid and the measurement is more reasonable. At the same time, the high-voltage, high-current discharge method is less susceptible to interference from the magnetic field generated by electrical equipment in the substation.

[0055] C2 in the above device is a high-voltage capacitor. After a long period of charging, the high-voltage capacitor stores electrical energy. Although the stored electrical energy is small, triggering the discharge of the high-voltage capacitor will generate a transient current in a very short time. This current meets the requirements of high voltage and large current, and is in line with the working state of the grounding network when the substation is struck by lightning or a high-voltage grounding fault occurs. A single capacitor is small in size, low in price, and easy to use.

[0056] Example 2:

[0057] The working method of the above-mentioned device for detecting the grounding resistance of the grounding grid includes the following steps:

[0058] When the voltage of the first step-up transformer reaches the positive half cycle, the first capacitor is charged, and when the voltage of the first step-up transformer reaches the negative half cycle, the first capacitor and the first step-up transformer simultaneously charge the second capacitor;

[0059] After the second capacitor is charged and the ball gap switch is triggered to turn on, the second capacitor, the first current limiting resistor R1 and the grounding grid to be tested form a capacitor discharge loop;

[0060] The discharge voltage Uc and the discharge current Ic of the second capacitor are obtained, and the grounding resistance R of the grounding grid is R=Uc / Ic-R1.

[0061] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A grounding resistance detection device for a substation grounding grid, characterized by: Including detection power supply, ground terminal and detection terminal; The detection power supply is connected to the first capacitor and the second capacitor in sequence through the first step-up transformer. The second capacitor is respectively connected to the ball gap switch and the first current limiting resistor. The ball gap switch is connected to the ground terminal. The first current limiting resistor is connected to the detection terminal. The second capacitor, the first current limiting resistor and the grounding grid to be tested form a capacitor discharge loop. The grounding resistance of the grounding grid is R=Uc / Ic-R1, where Uc and Ic are the discharge voltage and discharge current of the second capacitor, respectively, and R1 is the resistance value of the first current limiting resistor. A second current-limiting resistor is connected between the first step-up transformer and the first capacitor, and the first capacitor is connected to the second capacitor via a second rectifier module and a third current-limiting resistor arranged in sequence; The ball gap switch is a discharge trigger switch of the capacitor discharge circuit, and discharge is achieved by generating a trigger signal through a signal generation circuit; The second capacitor should be a larger capacity capacitor, a high voltage capacitor; When the transformer voltage reaches the positive half cycle, it charges the first capacitor through the second current limiting resistor. When it reaches the negative half cycle, the first capacitor and the first step-up transformer simultaneously charge the second capacitor through the third current limiting resistor. The signal generating circuit includes an inverter, wherein an input port of the inverter is connected to a DC power supply via a fifth resistor and a fourth resistor in sequence, the inverter is connected to the fourth resistor via a third capacitor and a switch in sequence, and the inverter is further connected to the DC power supply via a diode; The output port of the inverter triggers a signal, the fourth capacitor discharges, the gap between the needle electrode and the lower hemisphere breaks down, and plasma is generated to distort the electric field between the upper and lower hemispheres of the spherical gap switch, causing the two hemispheres to break down and trigger the spherical gap switch. At this time, the second capacitor is connected to the ground terminal and the second capacitor discharges.

2. The grounding resistance detection device for a substation grounding grid according to claim 1, characterized in that: The grounding end is a grounding nail driven into the ground, and the detection end is a position of the grounding grid to be detected.

3. The grounding resistance detection device for a substation grounding grid according to claim 1, characterized in that: The line between the first capacitor and the second rectifier module is connected to the first rectifier module, and the first rectifier module is connected to a detection power supply.

4. The grounding resistance detection device for a substation grounding grid according to claim 1, wherein: The spherical gap switch includes an upper hemisphere and a lower hemisphere arranged in parallel with a gap therebetween. The upper hemisphere is connected to the second capacitor, and the lower hemisphere is connected to the ground end. A hole is provided in the middle of the lower hemisphere, and a needle electrode is connected in the hole through an insulating layer. The needle electrode is located in the center of the hole.

5. The grounding resistance detection device for a substation grounding grid according to claim 1, characterized in that: The output port of the inverter is connected to the gate G of the IGBT. When a trigger signal is output, the collector C and emitter E of the IGBT are turned on, and the line between the fourth rectifier module and the fourth capacitor is connected to the detection power supply through the turned-on IGBT.

6. The grounding resistance detection device for a substation grounding grid according to claim 5, characterized in that: The detection power supply is connected to the fourth capacitor through the second step-up transformer, the sixth current-limiting resistor and the fourth rectifier module in sequence, and the fourth capacitor is connected to the lower hemisphere of the spherical gap switch through the seventh resistor.

7. A method for detecting grounding resistance of a grounding grid based on the device according to any one of claims 1 to 6, comprising the following steps: When the voltage of the first step-up transformer reaches the positive half cycle, the first capacitor is charged, and when the voltage of the first step-up transformer reaches the negative half cycle, the first capacitor and the first step-up transformer simultaneously charge the second capacitor; After the second capacitor is fully charged, the ball gap switch is triggered to conduct, and the second capacitor, the first current limiting resistor, and the grounding grid to be measured form a conductive capacitor discharge loop, and the second capacitor discharges the capacitor discharge loop; The discharge voltage Uc and the discharge current Ic of the second capacitor are obtained, and the grounding resistance R of the grounding grid is R=Uc / Ic-R1, where R1 is the resistance value of the first current limiting resistor.

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