Double-end grounding loop resistance tester without dismounting grounding wire

Abstract

The utility model relates to a double-end grounding loop resistance tester without dismounting a grounding wire, which comprises a test host and at least one clamp-type wireless current acquisition device, and the test host and the clamp-type wireless current acquisition device are in wireless communication connection through ZigBee. The test host comprises a power supply, a current source, a voltage collector, a current collector, a calculation controller and a man-machine interaction screen. The power supply adopts a 50AH power battery, and based on a constant-current and voltage-limiting output mode, the maximum output current is 500A; the current source adopts a large current source based on a phase-shifted full-bridge circuit, and is a direct current source integrating 200A, 300A, 400A and 500A multi-gear output current; the device has the advantages of being simple in structure, convenient to use, high in working efficiency, capable of achieving accurate measurement and high in safety coefficient.

Description

Technical Field

[0001] This utility model belongs to the technical field of circuit breaker circuit resistance testing equipment, specifically relating to a double-ended grounding circuit resistance tester that does not require removal of the grounding wire. Background Technology

[0002] GIS equipment has advantages such as small size, small footprint, and convenient maintenance, and is widely used in 110kV and above substations. The service life and operational reliability of GIS equipment are related to the degree of heat generated during operation, which largely depends on the quality of contact between the internal contacts. Increased contact resistance will increase conductor losses during energization, raising the temperature at the contact points. The magnitude of this resistance directly affects the current-carrying capacity during normal operation. Accurate measurement of the GIS conductive circuit resistance can effectively determine whether there are contact defects in the conductive circuit, helping to reduce the probability of GIS equipment failure, which is particularly important for the safe operation of the power system. When measuring the conductive circuit resistance at GIS substations, the DC voltage drop method is generally used. Power grid company anti-accident measures stipulate that the grounding switch lead conductor is prohibited from being directly connected to the casing. Therefore, currently, the grounding switch lead conductor is grounded through the grounding busbar to ensure... To ensure accurate and reliable measurement results, the DC voltage drop method requires disassembling the grounding busbar leads on the corresponding GIS equipment casing. The workload of removing the screws between the grounding switch leads and the grounding busbar is enormous. Furthermore, disassembling the grounding wire does not meet the on-site safety requirements. If the grounding busbar is not reset after the test, or if the screws are not tightened or the surface is not deoxidized, unreliable grounding will occur, posing a significant threat to the safe operation of the power grid. Additionally, the resistance measured by the DC voltage drop method is the resistance of the switch and the two grounding switches in the conductive circuit. Since the grounding switch does not need to be frequently opened and closed, oxide films and dirt can easily accumulate at the grounding switch outlet, causing poor contact and excessive contact resistance, which significantly affects the measurement of the switch circuit resistance. Therefore, it is essential to provide a simple, easy-to-use, efficient, accurate, and safe double-ended grounding circuit resistance tester that does not require disassembly of the grounding wire. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a double-ended grounding loop resistance tester that is simple in structure, easy to use, highly efficient, accurate in measurement, and has a high safety factor, without the need to remove the grounding wire.

[0004] The purpose of this utility model is achieved as follows: a double-ended grounding loop resistance tester that does not require removal of the grounding wire, comprising a test host and at least one clamp-on wireless current acquisition device, wherein the test host and the clamp-on wireless current acquisition device are connected by ZigBee wireless communication. The test host includes a power supply, a current source, a voltage acquisition device, a current acquisition device, a computing controller, and a human-machine interface screen; the power supply uses a 50AH power battery, based on a constant current and voltage limiting output mode, with a maximum output voltage of 15V and a maximum output current of 500A; the current source adopts a high current source based on a phase-shifted full-bridge circuit, integrating a DC current source with multiple output current levels of 200A, 300A, 400A, and 500A.

[0005] The test host also has reserved Bluetooth and Wi-Fi interfaces. The test host is given an excitation signal by a current source to test the current of each grounding node and calculates the loop resistance by a calculation controller.

[0006] Specifically, Bluetooth and Wi-Fi interfaces are reserved to enable intelligent, automated, and digital power testing operations; the computing controller is connected to the voltage acquisition unit, current acquisition unit, and current source respectively; the human-machine interface screen is connected to the computing controller; and the power supply provides power to the entire test host.

[0007] The phase-shifted full-bridge circuit includes four power switching transistors S1~S4, parasitic capacitances C1~C4 corresponding to the switching transistors, and a resonant inductor L. r Secondary-side synchronous rectifier switches QR1~QR4, filter inductor L f and filter capacitor C f The phase-shifted full-bridge circuit consists of two bridge arms: the bridge arm composed of S1 and S2 is the leading arm, and the bridge arm composed of S3 and S4 is the lagging arm.

[0008] The phase-shifted full-bridge circuit also includes a DC bus filter capacitor, a high-frequency transformer, an output filter inductor, and a DC blocking capacitor.

[0009] The primary-side switching transistor of the phase-shifted full-bridge circuit is model IPW60R041C6, and the secondary-side switching transistor is model IRFP4468. The primary-side switching transistor of the phase-shifted full-bridge circuit is driven by a UCC27714 bridge driver, and the secondary-side switching transistor is driven by a UCC27254 single-transistor driver chip. The sampling circuit of the phase-shifted full-bridge circuit uses ACPL-C790 optocouplers for both primary-side bus voltage sampling and output voltage sampling.

[0010] The clamp-on wireless current acquisition device is provided in units of 1 to 3. When measuring a single-phase GIS circuit, one clamp-on wireless current acquisition device is required. When measuring a three-phase common GIS circuit, for the measurement of the middle phase B, if the grounding busbar is connected to one or both of the adjacent phases, two clamp-on wireless current acquisition devices are required. If the grounding busbar is connected to the casing at the B phase outlet, three clamp-on wireless current acquisition devices are required.

[0011] The clamp-on wireless current acquisition device uses a Hall effect DC sensor to detect DC current; the Hall effect DC sensor uses a zero-flux closed-loop Hall current probe.

[0012] The zero-flux closed-loop Hall current probe includes a probe core, a Hall element, a coil, a drive circuit, and a control circuit. The left port of the drive circuit is connected to the Hall chip, the right port is connected to the coil, and the middle circuit is an amplification drive circuit.

[0013] The probe core is composed of two semi-circular rings made by stacking silicon steel sheets, with the rings interlocking in the middle.

[0014] The Hall element uses an indium antimonide HG362A chip and is placed in the air gap between two quarter-circular magnetic cores, with an angle difference of 90° from the jaw position.

[0015] The beneficial effects of this utility model are as follows: This utility model is a double-ended grounding loop resistance tester that does not require the removal of the grounding wire. In use, this utility model adopts a multi-level, constant current output, and lightweight high-current DC current source, which improves the reliability and efficiency of the test. This utility model uses a high-precision, wireless transmission, and highly adaptable clamp-on wireless current acquisition device to test the current value of the parallel branch shunt and feed it back to the calculation controller of the test host to calculate the actual value of the resistance of the GIS loop under test. It can realize the loop resistance test without removing the grounding bars on both sides, eliminating the risk of electric shock caused by removing the grounding bars, significantly improving the on-site work efficiency, and improving the test efficiency and accuracy. This utility model realizes the test of GIS conductive loop resistance without removing the grounding wire, which can protect the GIS equipment to the greatest extent, eliminate the safety risks and time costs caused by removing the grounding wire, effectively improve the reliability of power grid operation, and greatly improve the work efficiency of GIS loop resistance testing. It also increases the life of GIS equipment, reduces the GIS test and maintenance costs, and brings huge economic benefits. This utility model has the advantages of simple structure, convenient use, high work efficiency, accurate measurement, and high safety factor. Attached Figure Description

[0016] Figure 1 This is a schematic diagram showing the composition of the test host of this utility model and the connection structure between the test host and the clamp-type wireless current acquisition device.

[0017] Figure 2 This is the circuit diagram of the phase-shifted full-bridge circuit of this utility model.

[0018] Figure 3 This is a circuit diagram of the secondary-side RCD absorption circuit of this utility model.

[0019] Figure 4 This is a circuit diagram of the bus voltage sampling circuit of this utility model.

[0020] Figure 5 This is a circuit diagram of the bus voltage sampling and conditioning circuit of this utility model.

[0021] Figure 6 This is a temperature sampling circuit diagram of the present invention.

[0022] Figure 7 This is the temperature protection circuit diagram of this utility model.

[0023] Figure 8 This is a measurement diagram of a single-phase GIS branch circuit according to this utility model.

[0024] Figure 9 This is a measurement diagram of the two branch lines of the three-phase integrated GIS of this utility model.

[0025] Figure 10 This is a diagram of the two semi-circular toothed interlocking structures of this utility model. Detailed Implementation

[0026] This invention employs an adaptive high-current DC source as the test power supply. Under different opening and closing combinations of switches and disconnectors, it measures the current values ​​of each branch and the voltage difference in the conductive loop. The data is then imported into a measuring instrument for multi-port network data analysis and calculation. Based on Kirchhoff's current-voltage law, in the coupled topology model of GIS loop resistance and grounding resistance, and using excitation signals (i.e., high-current signals) at different ports, the current and voltage signals at other grounding terminals are tested, yielding the corresponding current-voltage matrix. Finally, the loop resistance of each part of the GIS is solved, realizing the calculation of the loop resistance value. This invention can maximize the protection of GIS equipment, extend its lifespan, eliminate the safety risks and time costs associated with dismantling grounding wires, reduce GIS testing and maintenance costs, effectively improve the reliability of power grid operation, greatly enhance the efficiency of GIS loop resistance testing, and bring significant economic benefits.

[0027] The present invention will be further described below with reference to the accompanying drawings. Example

[0028] like Figure 1-10As shown, a double-ended grounding loop resistance tester that does not require removing the grounding wire includes a test host and at least one clamp-on wireless current acquisition device. The test host and the clamp-on wireless current acquisition device are connected via ZigBee wireless communication. The test host includes a power supply, a current source, a voltage acquisition device, a current acquisition device, a computing controller, and a human-machine interface screen. The test host also has reserved Bluetooth and Wi-Fi interfaces. The test host receives an excitation signal from the current source to test the current at each grounding node, and analyzes and calculates the loop resistance through the computing controller. The clamp-on wireless current acquisition device uses a Hall effect DC sensor to detect the DC current. The Hall effect DC sensor is a zero-flux closed-loop Hall current probe, integrating a voltage probe and a current probe, which can reduce the complexity of on-site wiring. The use of wireless data transmission makes the on-site operation safer and more efficient.

[0029] The power supply uses a 50AH high-capacity power battery and is based on a constant current and voltage limiting output mode. The maximum output voltage is 15V and the maximum output current is 500A. It can ensure that the current flowing through the device under test is greater than 300A without disconnecting the grounding wire to shunt the current, which meets the test standard requirements. In addition, to meet the user's requirements for output time, all gears can continuously output for 60 seconds, which is very practical for some scenarios that require high current to burn off the oxide film.

[0030] Specifically, it is powered by a 50AH high-capacity power battery, and the total weight of the instrument is about 15kg. The maximum output voltage can reach 15V. Theoretically, if the output is 100A / 5s, it can continuously measure nearly 200 times, which fully meets the needs of field use. It can perform field measurements without connecting to a 220V AC power supply, making the instrument suitable for outdoor mobile operations. The main power supply supports multi-machine parallel operation and adopts a constant current and voltage limiting mode, and the output current can be adjusted arbitrarily.

[0031] The current source is a high current source based on a phase-shifted full-bridge circuit, integrating a DC current source with multiple output current levels of 200A, 300A, 400A and 500A.

[0032] Specifically, for ordinary GIS circuits and open-type switch measuring circuits, the current flowing through the device under test must be no less than 100A. For UHV main circuits or large-capacity equipment main circuits, the test current requirement is no less than 300A. Considering the grounding wire current shunting, the output current of the measuring instrument must be no less than 400-500A. In order to meet the different requirements of GIS or switch with different capacities for test current, the device integrates 200A, 300A, 400A and 500A output current ranges. It adopts a high current source based on a phase-shifted full-bridge circuit, and the maximum output current of the main power supply reaches 500A, ensuring that the current flowing through the device under test after three-phase shunting and grounding grid shunting meets the test standard requirements.

[0033] The clamp-on wireless current acquisition device is provided in units of 1 to 3. When measuring a single-phase GIS circuit, one clamp-on wireless current acquisition device is required. When measuring a three-phase common GIS circuit, for the measurement of the middle phase B, if the grounding busbar is connected to one or both of the adjacent phases, two clamp-on wireless current acquisition devices are required. If the grounding busbar is connected to the casing at the B phase outlet, three clamp-on wireless current acquisition devices are required.

[0034] Specifically, determining the number of clamp-on wireless current acquisition devices mainly requires determining the number of branch circuits in the measurement loop; each branch circuit requires one clamp-on wireless current acquisition device. Figure 8 The diagram shown illustrates a single-phase GIS circuit measurement. In this mode, only the grounding busbar forms a shunt branch, and there is only one branch. Therefore, only one clamp-on wireless current acquisition device is needed. The clamp-on wireless current acquisition device measures the shunt value of the parallel branch between the external grounding grid and the equipment casing of the main circuit using Hall effect sensors. Then, it uses a computing controller to calculate the actual resistance value of the measured main circuit. Taking the measurement of the GIS switch circuit resistance as an example (e.g.) Figure 8 As shown), the resistance of the main circuit under test is R. 开关 The total resistance of the parallel branches (ground grid and casing) is R2, and the shunt current is I2; V + V is the output voltage of the host. - I is the voltage difference between the two terminals. + R is the host output current; 开关 =(V + -V - ) / (I + -I2).

[0035] like Figure 9 The diagram shown is a three-phase common GIS circuit measurement diagram. For the measurement of the middle phase B, there are the current shunt circuits of the other two phases A and C, as well as the current shunt branch of the grounding bus. If the grounding bus is connected to one or two of the adjacent two phases, it is only necessary to clamp the clamp-on wireless current acquisition device between phases A and B and between phases B and C to find out the current shunt situation of all branches. In this case, only two clamp-on wireless current acquisition devices are needed.

[0036] If the grounding busbar is connected to the casing at the B-phase outlet, two clamp-on wireless current acquisition devices cannot calculate all the shunt currents. There is also a shunt branch of the grounding busbar, so another clamp-on wireless current acquisition device is needed. In summary, to ensure that it is applicable to most shunt situations, at least three clamp-on wireless current acquisition devices are needed.

[0037] For GIS equipment where the three-phase external grounding blocks A, B, and C are connected together (e.g., Figure 9As shown), two clamp-on wireless current acquisition devices are needed to measure the total shunt value of the parallel branches; taking the measurement of the resistance of phase B circuit as an example, the shunt current from phase B grounding busbar to phase A grounding busbar is I. 分1 The current diversion from phase B grounding busbar to phase C grounding busbar is I. 分2 Then R 开关 =(V + -V - ) / (I + -I 分1 -I 分2 ).

[0038] In summary, this utility model has the following advantages: ① Different test modes are adopted for different test environments, and one to three clamp-on wireless current acquisition devices can be selected to meet the requirements of single GIS loop resistance testing and collective GIS loop resistance testing; ② Based on the traditional back resistance meter, by adding one or more current acquisition devices to measure the ground grid shunt, and then subtracting the ground grid shunt from the total current, the actual current of the circuit under test can be accurately obtained, and the loop resistance of the switch or disconnector can be calculated according to Ohm's law; ③ Measuring the GIS loop resistance does not require disassembling the grounding busbar, saving time and effort, greatly improving on-site work efficiency, and eliminating the risk of electric shock caused by removing the grounding busbar. The device is small in size, light in weight, and portable, making it very suitable for on-site operations; ④ It effectively avoids the safety hazards caused by incomplete grounding, detects poor contact inside the GIS equipment, reduces the risk of excessive temperature rise or insufficient current carrying capacity during the operation of the GIS equipment, reduces the probability of accidents, extends equipment life, and has direct economic benefits.

[0039] This invention relates to a double-ended grounding loop resistance tester that does not require the removal of the grounding wire. In use, this invention employs a multi-level, constant current output, and lightweight high-current DC current source to improve testing reliability and efficiency. It utilizes a high-precision, wirelessly transmitted, and highly adaptable current acquisition module to measure the current value of the parallel branch shunt and feed it back to the test host's calculation controller to calculate the actual resistance value of the GIS loop under test. This allows for loop resistance testing without removing the grounding bars on both sides, eliminating the risk of electric shock caused by removing the grounding bars, significantly improving on-site work efficiency, and enhancing testing efficiency and accuracy. This invention has the advantages of simple structure, ease of use, high work efficiency, accurate measurement, and a high safety factor. Example

[0040] like Figure 1-10As shown, a double-ended grounding loop resistance tester that does not require removal of the grounding wire includes a test host and at least one clamp-on wireless current acquisition device. The test host and the clamp-on wireless current acquisition device are connected via ZigBee wireless communication. The test host includes a power supply, a current source, a voltage acquisition unit, a current acquisition unit, a computing controller, and a human-machine interface screen. The power supply uses a 50AH power battery and operates in a constant current-limiting voltage output mode, with a maximum output current of 500A. The current source is a high-current source based on a phase-shifted full-bridge circuit, integrating multiple output current levels of 200A, 300A, 400A, and 500A DC current sources.

[0041] Specifically, a high-power isolated DC-DC converter with a phase-shifted full-bridge DC-DC circuit was selected as the basic topology for the test power supply.

[0042] The phase-shifted full-bridge circuit includes four power switching transistors S1~S4, parasitic capacitances C1~C4 corresponding to the switching transistors, and a resonant inductor L. r Secondary-side synchronous rectifier switches QR1~QR4, filter inductor L f and filter capacitor C f The phase-shifted full-bridge circuit consists of two bridge arms: the bridge arm composed of S1 and S2 is the leading arm, and the bridge arm composed of S3 and S4 is the lagging arm.

[0043] Specifically, the basic structure of a phase-shifted full-bridge circuit is as follows: Figure 2 As shown, S1~S4 are four power switching transistors, C1~C4 are the parasitic capacitances of the corresponding switching transistors, and L r The inductor is a resonant inductor, including the transformer leakage inductance. QR1~QR4 are the secondary-side synchronous rectifier switching transistors, and L... f For the filter inductor, C f The filter capacitor is used. The phase-shifted full-bridge circuit consists of two bridge arms. The upper and lower power switches of each bridge arm are complementary and conduct. The drive signals of the corresponding switches in the two bridge arms are out of phase by one phase, i.e., the phase shift angle φ. The output voltage can be adjusted by adjusting the size of the phase shift angle. Since the drive signals of S1 and S2 lead the drive signals of S3 and S4, the bridge arm composed of S1 and S2 is called the leading arm, and the bridge arm composed of S3 and S4 is called the lagging arm. The phase-shift control realizes the soft switching of the switches by utilizing the resonance generated between the leakage inductance of the transformer and the junction capacitance of the power switches, which reduces the switching loss and is beneficial to improving the switching frequency, power density and overall efficiency of the converter.

[0044] The phase-shifted full-bridge circuit also includes a DC bus filter capacitor, a high-frequency transformer, an output filter inductor, and a DC blocking capacitor.

[0045] Specifically, the high-frequency transformer is the core of the full-bridge DC-DC converter; the secondary voltage waveform of the high-frequency transformer is a square wave, and filtering is necessary to obtain DC output. The operating frequency of the output filter inductor is twice the switching frequency, and its main function is to limit the output current ripple. Due to the high accuracy requirements of the output current source, the ripple is selected to be 5% of the maximum output current; the output filter capacitor C... f Four 35V / 4.7uF capacitors can be connected in parallel to meet the capacitance requirements while reducing ESR;

[0046] DC blocking capacitor: In practical applications of phase-shifted full-bridge circuits, if the characteristics of the switching transistors are inconsistent, a DC component will be generated on the primary side of the transformer. This DC component acts on the primary winding of the high-frequency transformer. Since the resistance of the transformer winding is very small, a large DC bias current will be generated in the transformer. Over time, this current will cause DC magnetization of the iron core until saturation, resulting in a "biased magnetization" problem. To solve this problem, a DC blocking capacitor C needs to be connected in series in the primary circuit of the transformer. b To suppress the DC component, increase the DC blocking capacitor C. b Afterwards, whether the converter's operation changes depends on the added C. b The value; based on the relationship between the rate of change of the primary inductor current and the rate of change of the secondary inductor current during the freewheeling phase, there are two operating modes, K p =U cbp1 / L p K s =NV o / L f , (L p For the original edge leakage, L f (for secondary-side filter inductance), when K p >K s When operating in mode 1, the primary and secondary sides are disconnected, and the circuit's operating mode is affected by C. b The impact; with C b As K increases, the range of zero-voltage turn-on achieved by the lagging arm increases, but the duty cycle loss also increases accordingly; when K p ≤K s When operating in mode 2, the primary and secondary sides are connected in series as a super-front arm commutator, the duty cycle loss reaches its maximum and no longer increases with C. b The value increases, and at this time the circuit's operation is not affected by C. b The impact.

[0047] In summary, while a smaller DC blocking capacitor can reduce duty cycle loss, it will increase the primary voltage of the transformer and the current in the clamping diode, thus increasing the difficulty of component selection and the power loss of the system. Therefore, the value of the DC blocking capacitor should not be too small; generally, it is advisable that its maximum voltage does not exceed 20% of the input voltage, i.e., V0. Cbp=20%V in .

[0048] The primary-side switching transistor of the phase-shifted full-bridge circuit is model IPW60R041C6, with a rated voltage of 600V, a rated current of 49A-77.5A, and an on-resistance of 40mΩ-77mΩ. The secondary-side switching transistor is model IRFP4468, with a rated voltage of 100V, a rated current of 195A, and an on-resistance of 2.6mΩ. The primary-side switching transistor of the phase-shifted full-bridge circuit is driven by a UCC27714 bridge driver, and the secondary-side switching transistor is driven by a UCC27254 single-transistor driver chip. The sampling circuit of the phase-shifted full-bridge circuit uses ACPL-C790 optocouplers for both primary-side bus voltage sampling and output voltage sampling.

[0049] Specifically, ① Main circuit: The DC bus voltage of the phase-shifted full-bridge circuit is designed to be up to 360V, the maximum primary current is 240(1+5%)A / 7.5=33.6A, the primary switching transistor is IPW60R041C6, its rated voltage is 600V, the rated current at 25℃ is 77.5A, the rated current at 100℃ is 49A, the on-resistance at 25℃ is 40mΩ, and the on-resistance at 100℃ is 77mΩ;

[0050] The rated voltage of the secondary-side switch is 360V / 7.5=48V. However, during commutation, the resonant inductor resonates with the junction capacitance of the secondary-side switch, causing the secondary-side switch to withstand a higher reverse voltage. An RCD snubber circuit can be used to partially suppress the resonant voltage and reduce the voltage drop across the switch. The rated voltage of the switch is selected to be 100V. The secondary-side RCD snubber circuit is as follows: Figure 3 As shown, the maximum current of the secondary switch is 252A. In practice, the current of a single 100V withstand voltage switch cannot meet the requirements. Multiple switches can be connected in parallel. The secondary switch selected is IRFP4468, which has a rated voltage of 100V, a rated current of 195A, and an on-resistance of 2.6mΩ.

[0051] ② Drive Circuit: The primary-side switching transistors can be driven using a bridge drive. The UCC27714 is selected as the primary-side full-bridge driver chip, and a high-speed optocoupler 6N137 is used for electrical isolation from the control system. The drive power supply uses a dedicated power supply module, specifically the F2415S-2W module. The 5V power supply for the optocoupler uses the LM1117F-5.0 power supply chip. Each secondary-side switching transistor uses three transistors in parallel, requiring a large drive current. Therefore, a single-transistor driver chip is selected, specifically the UCC27254. The UCC27254 is a dual low-voltage transistor driver, which can connect the two drives in parallel to improve the drive capability. Similarly, a high-speed optocoupler 6N137 is used to isolate the drive circuit from the control circuit. The drive power supply uses a similar circuit to the primary-side drive power supply.

[0052] ③ Sampling Circuit: The load of this system is a resistive load, and the output adopts a voltage-limited constant current mode. The output voltage and output current must be sampled for control. At the same time, the primary bus voltage and transformer primary current are sampled for protection control. The primary bus voltage sampling uses a high-precision optocoupler ACPL-C790. The sampling circuit is as follows: Figure 4 As shown, the corresponding conditioning circuit is as follows: Figure 5 As shown.

[0053] The primary-side current is sampled using series resistors, employing four 5mΩ constantan wires in parallel as sampling resistors. The current signal is converted to a voltage signal, amplified by a high-precision optocoupler, and then DC biased and filtered by a corresponding conditioning circuit. The output voltage is also sampled using an ACPL-C790, with current limiting and voltage division by resistors followed by optocoupler amplification, and then sent to the DSP for sampling via a conditioning circuit. For larger output currents, a shunt is used for sampling. The shunt signal is then amplified by the ACPL-C790 optocoupler and processed by the sampling conditioning circuit before being sent to the DSP. During normal operation, the primary-side switching transistors and secondary-side switching transistors are placed on a heatsink. At full power, these become two hot spots in the system. Additionally, the transformer and inductor core may also generate significant heat. To improve system reliability, thermistors are used to sample the temperature at these four points. The sampling circuit is as follows: Figure 6 As shown, ports R_Temp1+ and R_Temp1- are connected to the two ends of the thermistor, respectively.

[0054] ④ Protection Circuit: This includes input voltage overvoltage protection, primary-side current overcurrent protection, output voltage overvoltage protection, output current overcurrent protection, and overtemperature protection. The protection circuit compares the sampled and conditioned circuit with a standard threshold using a comparator LM393 to obtain the protection signal. Taking the overtemperature protection circuit as an example, its specific circuit is as follows: Figure 7 As shown, high and low temperature protection will be activated when the temperature sampling signal is higher than 2.69V or lower than 0.38V, with corresponding temperature ranges of -40℃ and +90℃.

[0055] When the system is protected, especially after hardware protection, a vicious cycle of protection failure followed by shutdown and then protection reactivation is not allowed. Therefore, a protection latch circuit is required. When hardware protection occurs, the system shuts down. The protection latch and protection encoding circuit first latches the protection signal to prevent the problem of protection failure and reactivation. At the same time, the signal is encoded and reported to the controller for identification. The protection event is reported through the human-machine interface screen.

[0056] ⑤ Communication circuit: The CAN communication circuit uses the SN65HVD230QDR chip, and a common-mode inductor is added to the output to suppress interference; a high-speed optocoupler 6N137 is used to isolate the RS232 transmit and receive signals.

[0057] The clamp-on wireless current acquisition device uses a Hall effect DC sensor to detect DC current; the Hall effect DC sensor uses a zero-flux closed-loop Hall current probe.

[0058] The zero-flux closed-loop Hall current probe includes a probe core, a Hall element, a coil, a drive circuit, and a control circuit. The left port of the drive circuit is connected to the Hall chip, the right port is connected to the coil, and the middle circuit is an amplification drive circuit. The amplification drive circuit uses an OPA551 operational amplifier with a maximum output current of 200mA and a sampling resistor of 33mΩ.

[0059] Specifically, ① Probe core: Select magnetic materials with high magnetic focusing ability, such as permalloy. The basic materials of permalloy are iron and nickel. In order to improve its performance, other elements such as copper and molybdenum are added. Adding these elements can not only improve the relative hardness of the material, but also reduce the eddy current after it is made into a stacked magnetic core, and increase the resistivity of the material.

[0060] As one feasible specific embodiment, the probe magnetic core is a core composed of two semi-circular rings formed by stacking silicon steel sheets, with the rings interlocking in the middle. The shape of the probe magnetic core is as follows: Figure 10 As shown, this magnetic core has a large diameter and a small cross-section, making it suitable for measuring the current of the object being measured in narrow or flat spaces. It uses a stacking method, with the two semicircular rings interlocking at the joint (referred to as the opening), which effectively avoids magnetic leakage, improves the magnetic induction intensity, and enhances the measurement accuracy.

[0061] ② Hall element: A high-sensitivity indium antimonide HG362A chip is used as the Hall element. It is placed in the air gap between two quarter-circular magnetic cores, with an angle difference of 90° from the jaw position. This mounting method can solve the accuracy problem caused by air gap leakage magnetic field through measurement algorithm correction. The Hall element is mounted in a single-in-line package and is powered by both voltage and power supply modes. The input impedance is 1250Ω, the output impedance is 2500Ω, the output voltage range is 78~102mV, and the offset voltage is -8~8mV.

[0062] ③ Coil: The working principle of a closed-loop Hall current sensor is magnetic balance. It uses the magnetic field generated by the secondary coil to balance the magnetic field generated by the measured current on the magnetic core. By detecting the signal of the secondary coil, the magnitude of the measured current can be indirectly obtained. The secondary coil, also known as the compensation coil, is a thin copper wire wound around an iron core and insulated from each other. In the current sensor, the secondary coil is connected to the load or compensation circuit. The quality of the secondary coil material directly affects the long-term stability of the current sensor. The main material of the secondary coil is copper, and it also contains a small amount of nickel, nickel-copper alloy, and polyurethane varnish. These trace elements can improve the performance of the material. In practical applications, the power loss should not be too large. If the power consumption is selected to be no more than 2W, the number of turns of the secondary coil can be calculated to be N=2000 turns.

[0063] ④ Driving circuit: The selected material is an SbAs Hall sensor, model HW302B sensor chip. The left port of the Hall chip driving circuit is connected to the Hall chip, the right port is connected to the coil, and the middle circuit is an amplification driving circuit. The amplifier is an operational amplifier with high current output capability, model OPA551, with a maximum output current of 200mA. The sampling resistor is 33mΩ. By sampling the voltage across this resistor, the current on the secondary coil can be calculated, and then the primary current can be calculated.

[0064] The closed-loop Hall current sensor uses feedback current I S The generated magnetic field is eliminated by the magnetic field generated by the current to be measured, thus maintaining the magnetic flux of the iron core in the air gap at zero. At this time, the potential difference across the Hall element is 0. Then, the feedback current is sampled through the sampling circuit, ultimately achieving indirect measurement of the current to be measured. The presence of R1 and R3 in the amplifier circuit and the negative feedback control chip ensures that I S Automatically adjust until the current difference between R2 and R4 is 0; I S The measurement is performed by sampling resistor R7. The feedback current passes through the sampling resistor and generates a voltage drop V0 across it, which can be used to calculate the measured current.

[0065] In summary, the innovations of this utility model include: ① Eliminating induced electricity and ensuring personal safety: Traditional testing methods require disconnecting the grounding copper busbar on one side of the circuit breaker under test when conducting loop resistance tests. However, since other equipment is energized, disconnecting the grounding copper busbar of one grounding switch can induce electricity in the circuit breaker under test through a single disconnecting switch, threatening the personal safety of personnel; ② Ensuring stable equipment operation: The application of double-ended grounding technology reduces the need for disassembling and assembling grounding busbars, avoiding the risk of personnel falling from heights, colliding with equipment, or being struck by tools during prolonged disassembly and assembly of grounding busbars, thus protecting both equipment and personal safety; ③ Saving operating time and improving work efficiency: In the circuit resistance test of (GIS) circuit breakers, the disassembly and assembly of the grounding copper busbar is time-consuming and laborious. Using this utility model can eliminate this operation, which will greatly reduce the labor intensity and improve work efficiency; ④ Wide range of applications, covering most GIS field measurements: There are two modes: traditional test mode and clamp meter direct test mode. The traditional back resistance meter mode requires disassembling one side of the grounding busbar on both sides of the switch under test to avoid the influence of ground grid current shunting; the clamp meter direct test mode uses a current sensor to directly obtain the actual current of the circuit under test. The clamp meter direct test mode can accurately detect the circuit resistance of the switch or disconnect device through Ohm's law. It can accurately measure the circuit resistance without disassembling the grounding busbar. The test process is simple and efficient; the clamp meter direct test mode can realize single-sided current shunting mode test and double-sided current shunting mode test.

[0066] This invention relates to a double-ended grounding loop resistance tester that does not require the removal of the grounding wire. In use, this invention employs a multi-level, constant current output, and lightweight high-current DC current source to improve testing reliability and efficiency. It utilizes a high-precision, wirelessly transmitted, and highly adaptable current acquisition module to measure the current value of the parallel branch shunt and feed it back to the test host's calculation controller to calculate the actual resistance value of the GIS loop under test. This allows for loop resistance testing without removing the grounding bars on both sides, eliminating the risk of electric shock caused by removing the grounding bars, significantly improving on-site work efficiency, and enhancing testing efficiency and accuracy. This invention has the advantages of simple structure, ease of use, high work efficiency, accurate measurement, and a high safety factor.

Claims

1. A dismounting-free grounding wire double-terminal grounding loop resistance tester, comprising a test host and at least one clamp-type wireless current collecting device, and ZigBee wireless communication connection between the test host and the clamp-type wireless current collecting device, characterized in that: The test host includes a power supply, a current source, a voltage acquisition unit, a current acquisition unit, a computing controller, and a human-machine interface screen. The power supply uses a 50AH power battery and is based on a constant current and voltage limiting output mode, with a maximum output current of 500A. The current source is a high current source based on a phase-shifted full-bridge circuit, integrating multiple output current levels of 200A, 300A, 400A, and 500A DC current sources.

2. The dual termination grounding circuit resistance tester of claim 1, wherein: The test host also has reserved Bluetooth and Wi-Fi interfaces. The test host is given an excitation signal by a current source to test the current of each grounding node and calculates the loop resistance by a calculation controller.

3. The dual termination grounding circuit resistance tester of claim 1, wherein: The phase-shifted full-bridge circuit comprises four power switching tubes S1-S4, parasitic capacitances C1-C4 corresponding to the switching tubes, a resonant inductor L r , auxiliary-side synchronous rectification switching tubes QR1-QR4, a filter inductor L f , and a filter capacitor C f ; the phase-shifted full-bridge circuit is composed of two bridge arms, comprising a leading arm bridge arm composed of S1 and S2 and a lagging arm bridge arm composed of S3 and S4.

4. The dual termination grounding circuit resistance tester of claim 3, wherein: The phase-shifted full-bridge circuit also includes a DC bus filter capacitor, a high-frequency transformer, an output filter inductor, and a DC blocking capacitor.

5. The dual termination grounding circuit resistance tester of claim 4, wherein: The primary-side switching transistor of the phase-shifted full-bridge circuit is model IPW60R041C6, and the secondary-side switching transistor is model IRFP4468. The primary-side switching transistor of the phase-shifted full-bridge circuit is driven by a UCC27714 bridge driver, and the secondary-side switching transistor is driven by a UCC27254 single-transistor driver chip. The sampling circuit of the phase-shifted full-bridge circuit uses ACPL-C790 optocouplers for both primary-side bus voltage sampling and output voltage sampling.

6. The dual termination grounding circuit resistance tester of claim 1, wherein: The clamp-on wireless current acquisition device is provided in units of 1 to 3. When measuring a single-phase GIS circuit, one clamp-on wireless current acquisition device is required. When measuring a three-phase common GIS circuit, for the measurement of the middle phase B, if the grounding busbar is connected to one or both of the adjacent phases, two clamp-on wireless current acquisition devices are required. If the grounding busbar is connected to the casing at the B phase outlet, three clamp-on wireless current acquisition devices are required.

7. The dual termination grounding circuit resistance tester of claim 6, wherein: The clamp-on wireless current acquisition device uses a Hall effect DC sensor to detect DC current; the Hall effect DC sensor uses a zero-flux closed-loop Hall current probe.

8. The dual termination grounding circuit resistance tester of claim 7, wherein: The zero-flux closed-loop Hall current probe includes a probe core, a Hall element, a coil, a drive circuit, and a control circuit. The left port of the drive circuit is connected to the Hall chip, the right port is connected to the coil, and the middle circuit is an amplification drive circuit, which uses an OPA551 operational amplifier.

9. The dual termination grounding circuit resistance tester of claim 8, wherein: The probe core is composed of two semi-circular rings made by stacking silicon steel sheets, with the rings interlocking in the middle.

10. The dual termination grounding circuit resistance tester of claim 9, wherein: The Hall element uses an indium antimonide HG362A chip and is placed in the air gap between two quarter-circular magnetic cores, with an angle difference of 90° from the jaw position.

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