Introduction Single-phase grounding faults are the most common faults affecting the reliability of power supply in medium and low voltage power grids. With the further deepening of power grid transformation and the promulgation of relevant regulations by the State Power Corporation, the adoption of arc suppression coil grounding systems is the future development trend in substation design and transformation. The measurement and control system is required to perform routine power monitoring and capacitance current measurement under normal conditions, and to quickly control the arc suppression coil for compensation and collect relevant power data to accurately analyze the faulty line after a single-phase grounding fault occurs. This article briefly introduces the neutral point grounding system via arc suppression coil, and mainly elaborates on how to quickly build a power measurement and control system using the LabVIEW development tool. [b]Neutral Point Grounding System via Arc Suppression Coil[/b] [b]1. Introduction[/b] With the expansion of the distribution network and the extensive use of underground cables, the grounding current is very large when a single-phase grounding fault occurs. If the grounding arc cannot be reliably extinguished, it will quickly develop into a phase-to-phase short circuit, causing line tripping and power outage. If the grounding arc develops into intermittent extinguishing and reignition, it will cause arc grounding overvoltage, endangering the insulation of electrical equipment. Installing an arc suppression coil at the neutral point of the power grid is an effective measure to reduce grounding current and suppress arcing grounding overvoltage. This is clearly stipulated in the power industry standard DL/T620-1997 "Overvoltage Protection and Insulation Coordination of AC Electrical Installations". To ensure power supply reliability, a neutral point grounded system with an arc suppression coil is allowed to continue operating for two hours during a single-phase grounding fault. During this time, the fault persists and may further expand, causing damage to transmission and transformation equipment. In actual operation, the faulty line should be located and eliminated quickly while ensuring uninterrupted power supply as much as possible. Therefore, the research and development of low-current grounding fault location devices is of great significance for ensuring the reliability of power supply in medium and low voltage power grids, preventing the development and expansion of accidents, and reducing the probability of faults. Our company's adjustable-capacity automatic tuning arc suppression coil grounding device is an intelligent complete set of electrical equipment for automatically compensating for single-phase grounding fault current in 6-35kV voltage level distribution networks. This device adopts advanced thyristor technology and the NI PX platform, which can accurately measure the ground capacitive reactance of the power grid line, quickly and automatically compensate for single-phase grounding current, with good compensation effect and high operational reliability. Furthermore, it can quickly select the faulty line after a fault occurs, greatly improving the power supply reliability of the power grid. It is an indispensable electrical device for distribution networks. [b]2. Working Principle[/b] When a single-phase ground fault occurs in a neutral-point ungrounded power grid, as shown in Figure 1. If there is no arc suppression coil, the current through the grounding point is [align=center] [/align] If an arc suppression coil is installed at the neutral point of the power grid, the current through the grounding point is When a single-phase ground fault occurs in the power grid, if the inductive reactance of the arc suppression coil is less than and close to the ground capacitive reactance of the line, the capacitive current of the grounding will be completely compensated by the inductive current provided by the arc suppression coil, and the grounding arc will be easily extinguished. However, during normal grid operation, the inductive reactance of the arc suppression coil can cause a very high potential at the neutral point of the grid. The usual solution is to connect a damping resistor box in series in the line to limit the neutral point voltage, and then short-circuit the resistor during a ground fault. However, this also leads to reduced device reliability and increased operation and maintenance workload. Therefore, the ideal arc suppression coil should have the following characteristics: when a single-phase ground fault occurs in the grid, the inductive reactance of the arc suppression coil, under overcompensation, approaches the line's capacitive reactance to ground; while during normal grid operation, the inductive reactance of the arc suppression coil automatically moves away from this resonant point. Figure 1 shows a single-phase ground fault circuit diagram. The grounding device developed by our company can automatically track changes in grid parameters and adjust the capacitive load on the secondary side of the arc suppression coil to change its primary equivalent inductive reactance, achieving dynamic tuning. Under normal grid operation, it changes the tap of the arc suppression coil. When the neutral point displacement voltage is less than 10% of the rated system phase voltage, it simultaneously measures and records the neutral point current Io and neutral point voltage Uo for each tap, and then identifies the two taps with the highest voltage. The neutral point current Io and neutral point voltage Uo are then used to... By analyzing the changing data, the capacitive current of the power grid can be calculated: Where: Ic is the calculated capacitive current; Uo1 and Uo2 are the neutral point voltages at the two maximum levels, respectively; Io1 and Io2 are the neutral point currents corresponding to Uo1 and Uo2, respectively. Practice has shown that, under the condition that the system parameters are measured correctly, the error of the system capacitive current calculated using the above formula is small, and a satisfactory result can be obtained by averaging. Currently, domestic fault location devices mainly use steady-state analysis, transient analysis, and signal injection methods for fault location. Steady-state analysis methods include zero-sequence current amplitude-phase ratio method, zero-sequence power direction method, and zero-sequence current harmonic direction method; transient analysis methods include the first half-wave principle method and wavelet analysis method. In recent years, due to the increased use of neutral point grounding via arc suppression coils in my country's power distribution networks and power supply systems of large industrial and mining enterprises, residual current increment criterion has been added to fault location devices to complement the use of automatic tuning arc suppression coils for fault location. Our company's adjustable-capacity automatic tuning arc suppression coil grounding device combines the advantages of several line selection methods and uses comprehensive criteria to achieve high-accuracy line selection. **[b]Building an Arc Suppression Coil Measurement and Control System using LabVIEW[/b]** 1. Choosing LabVIEW and NI PXI In today's rapidly evolving world, how can we keep pace with technological advancements? How can we reliably and quickly transform new technologies into productive forces? The answer lies in freeing engineers from complex hardware design and tedious text programming, allowing them to focus their limited energy on成果转化 (technology transfer/commercialization). Using LabVIEW, system control and result display can be performed in an interactive graphical front panel. Data can also be displayed on web pages or linked to other applications or existing code through ActiveX, dynamic link libraries, and databases. Simultaneously, various hardware devices can be used to collect data. After data collection, LabVIEW's powerful built-in test analysis and display functions can be used to transform raw data into meaningful results. LabVIEW's development speed is 4 to 10 times faster than traditional text programming, and it is intuitive and easy to learn. Utilizing LabVIEW's modular and hierarchical structure, the entire system can be quickly prototyped, designed, and run. LabVIEW uses a dataflow programming model, making it easy to create flowcharts that can execute multiple tasks simultaneously. Therefore, LabVIEW is a multi-tasking system capable of running multiple programs concurrently. The NI PXI-8145T includes an embedded processor running a real-time operating system. LabVIEW RT applications can be developed in a Windows environment, then downloaded and installed to control independent hardware alongside the real-time operating system. Even if the host computer suddenly stops working, the LabVIEW embedded application can continue to run. M-series cards can fully utilize Hyper-Threading and multi-threading technologies, and can all use LabVIEW RT modules and NI-DAQmx to create reliable, deterministic, independent programs without user intervention. For measurement and control devices in arc suppression coil grounding systems, the requirements are numerous, including dozens of analog signals and more than ten input/output channels. Data analysis is labor-intensive and requires high accuracy. Furthermore, reliable operation and strong anti-interference capabilities are required in power systems, and the development cycle is relatively tight. Using traditional self-made signal conditioning boards, sample-and-hold boards, digital I/O boards, and control systems such as DSPs is not only time-consuming and labor-intensive, but may also result in poor anti-interference capabilities, numerous program vulnerabilities, and a large maintenance workload, causing unnecessary trouble for future technical training and upgrades. In summary, using the LabVIEW development platform and RT embedded processor in conjunction with an advanced data acquisition card is our best choice. 2. The primary equipment in the system hardware design includes: dry-type grounding transformers (providing the neutral point and station service transformer), arc suppression coils (providing inductive current compensation for the grid's capacitive current to ground), trigger boards with patented zero-crossing triggering technology, high-power, high-performance thyristor components, self-healing low-voltage parallel capacitors, voltage transformers, current transformers (including zero-sequence current transformers), and fuses. The signal conditioning board is used for signal preprocessing of the analog quantities to be acquired. Analog quantities include neutral point voltage, neutral point current, and zero-sequence current of each line. Preprocessing includes converting large signals into small signals within the allowable range of the NI M-series data acquisition card, and filtering. The digital I/O board provides corresponding digital trigger signals to the data acquisition card, trigger signals to the trigger board to control the thyristor switching, and alarm and trip signals. The NI PXI-1031 four-slot power supply chassis, PXI-6221 data acquisition card, PXI-8145 RT controller, and PXI-8423 dual-port RS-485 serial card form the core of the measurement and control system. The touchscreen provides the human-machine interface. The Siemens TP170A touchscreen supports the Modbus protocol and connects to the RS-232 communication port of the PXI-8145 RT via a 232 twisted-pair cable. A touchscreen user interface was created using Siemens touchscreen configuration software, and a multi-threaded Modbus communication application was created using LabVIEW 7.1 to enable data exchange between the PXI-8145 RT slave station and the touchscreen master station. This allows users to easily monitor field data, modify operating parameters, query data records, and control operating modes. A computer with the LabVIEW application installed is connected to the PXI-8145 RT controller via Ethernet or a RS-232 twisted-pair cable. This is primarily used for power plant automation, enabling remote data monitoring, recording, operation, querying, and printing. 3. System Software Design: To ensure real-time program operation, a Timed Loop is primarily used, which completes tasks within a user-specified timeframe. Furthermore, Invoke Nodes are used to dynamically control VI operation and event structures. More importantly, a multi-threaded programming approach is employed, enabling a multi-tasking system with multiple programs running simultaneously. The program mainly includes: data acquisition and analysis, Modbus touchscreen communication, shunting measurement and control, shunting compensation and fault location, routine operation and control, TCP/IP communication services, and host computer monitoring, etc. LabVIEW's powerful data acquisition and analysis functions make the analysis of large amounts of data extremely convenient and accurate, greatly reducing workload. Appropriate use of the For loop structure can significantly simplify certain calculations, such as active power, harmonic phase, and transient analysis. More significantly, LabVIEW's powerful toolkit support makes system construction simpler. Various calculation modules, such as the FFT calculation module, are readily available, making power flow calculations in power systems much simpler. Figure 3 shows the upper-level computer monitoring system screen provided by our company for a power plant in Northwest China. This monitoring system is entirely written in LabVIEW 7.1, uses RS-232 communication for polling, and realizes data monitoring, parameter setting, operating mode setting, various fault indication alarms, automatic data report generation, report printing, and line selection result display for six sets of arc suppression coil controllers in the field. It has been successfully applied in the field. Primary equipment includes: dry-type grounding transformers (for artificial neutral point and station service transformers) manufactured by our company, arc suppression coils (for providing inductive current to compensate for the capacitive current of the power grid to ground), trigger boards with national patented zero-crossing triggering technology, high-power high-performance thyristor components, self-healing low-voltage parallel capacitors, voltage transformers, current transformers (including zero-sequence current transformers), and fuses. The signal conditioning board is used for signal preprocessing of the analog quantities to be acquired. Analog quantities include neutral point voltage, neutral point current, and zero-sequence current of each line. Preprocessing includes converting large signals into small signals within the allowable range of the NI M-series data acquisition card, and filtering. The digital I/O board provides corresponding digital trigger signals to the data acquisition card, trigger signals to the trigger board to control the thyristor switching, and alarm and trip signals. The NI PXI-1031 four-slot power supply chassis, PXI-6221 data acquisition card, PXI-8145 RT controller, and PXI-8423 dual-port RS-485 serial card form the core of the measurement and control system. The touchscreen provides the human-machine interface. The Siemens TP170A touchscreen supports the Modbus protocol and connects to the RS-232 communication port of the PXI-8145 RT via a 232 twisted-pair cable. A touchscreen user interface was created using Siemens touchscreen configuration software, and a multi-threaded Modbus communication application was created using LabVIEW 7.1 to enable data exchange between the PXI-8145 RT slave station and the touchscreen master station. This allows users to easily monitor field data, modify operating parameters, query data records, and control operating modes. A computer with the LabVIEW application installed is connected to the PXI-8145 RT controller via Ethernet or a RS-232 twisted-pair cable. This is primarily used for power plant automation, enabling remote data monitoring, recording, operation, querying, and printing. 3. System Software Design: To ensure real-time program operation, a Timed Loop is primarily used, which completes tasks within a user-specified timeframe. Furthermore, Invoke Nodes are used to dynamically control VI operation and event structures. More importantly, a multi-threaded programming approach is employed, enabling a multi-tasking system with multiple programs running simultaneously. The program mainly includes: data acquisition and analysis, Modbus touchscreen communication, shunting measurement and control, shunting compensation and fault location, routine operation and control, TCP/IP communication services, and host computer monitoring, etc. LabVIEW's powerful data acquisition and analysis functions make large-scale data analysis extremely convenient and accurate, greatly reducing workload. Appropriate use of the For loop structure can significantly simplify certain calculations, such as active power, harmonic phase, and transient analysis. More significantly, LabVIEW's powerful toolkit support makes system construction simpler. Various calculation modules, such as the FFT module, are readily available, making power flow calculations in power systems much simpler. Figure 3 shows the upper-level computer monitoring system screen provided by our company for a power plant in Northwest China. This monitoring system is entirely written in LabVIEW 7.1, uses RS-232 communication for polling, and realizes data monitoring, parameter setting, operating mode setting, various fault indication alarms, automatic data report generation, report printing, and line selection result display for six sets of arc suppression coil controllers in the field. It has been successfully applied in the field. Edited by: He Shiping