Insulation monitoring method and equipment for low-voltage power grid

Abstract

The invention discloses a low-voltage power grid insulation monitoring method and low-voltage power grid insulation monitoring equipment, a PT opening triangular part and a zero-sequence current transformer are specially configured for a 400V low-voltage power grid, and two paths of analog signals of zero-sequence voltage and zero-sequence current of the power grid are synchronously collected; the analog signals are transmitted to an acquisition processing circuit module, and are converted into zero-sequence voltage and zero-sequence current digital signals carrying vector phase angle digital quantity information through low-voltage filtering and analog-to-digital conversion processing; then the digital signal is transmitted to an MCU microcontroller module, calculation and separation are carried out through a built-in data analysis processing sub-module, and values of a resistive component and a capacitive component of the zero-sequence current are obtained; and judging whether the line has an insulation hidden danger or capacitive capacitance interference based on the two component values. Zero-sequence electric signals can be collected at high precision, distributed capacitance interference is weakened, and accurate detection and early warning of early-stage potential insulation hidden dangers in a low-voltage power grid are achieved.

Description

Technical Field

[0001] This application relates to power system insulation monitoring technology, specifically to a low-voltage power grid insulation monitoring method and a low-voltage power grid insulation monitoring device. Background Technology

[0002] In existing technologies, the detection of electrical insulation hazards in three-phase four-wire low-voltage power grids mainly relies on residual current protection technology. While residual current protection, as a mandatory standard configuration for personal safety protection in low-voltage TN systems, effectively prevents electric shock accidents and electrical fires, it is essentially an isolated parameter in the electrical field. It lacks a corresponding concept of residual voltage, cannot obtain information related to resistive and capacitive insulation in the three-phase circuit through phase angle relationships, struggles to effectively identify and separate capacitive interference, and cannot perform refined analysis of the development status of insulation hazards.

[0003] Zero-sequence voltage and zero-sequence current, as paired electrical parameters, are crucial for assessing the insulation status of a power grid. In medium- and high-voltage power grid systems, voltage transformers typically convert high voltage to low voltage signals, and three-phase PTs connected in an open delta configuration are used to acquire the zero-sequence voltage, while a zero-sequence current transformer is used to acquire the zero-sequence current. However, for 400V / 380V low-voltage power grid systems, due to economic and functional limitations, existing technologies generally use direct measurement of three-phase voltage and current to obtain signals, without dedicated hardware acquisition devices such as open delta PT components and zero-sequence current transformers. Zero-sequence voltage and current parameters are often indirectly calculated using digital algorithms such as the symmetrical component method of three-phase voltage and phase current. Furthermore, the zero-sequence current generated by grounding faults is relatively large, allowing protection mechanisms to be triggered without additional hardware. This algorithm has significant accuracy deficiencies. In particular, during the operation of low-voltage power grids, the interference of ground distributed capacitive current (capacitive component) can severely mask the relatively weak early and middle stage potential resistive insulation hazard signals, making it difficult for existing technologies to effectively identify and separate resistive and capacitive components, and lacking the ability to accurately identify capacitive interference. At the same time, existing technologies have not established a multi-level low-threshold monitoring mechanism, cannot carry out abrupt change monitoring based on baseline values, are difficult to capture early and middle stage weak insulation hazard signals, and are even less able to track the growth trend of hazards.

[0004] Meanwhile, zero-sequence current protection in low-voltage TN systems has a sensitivity only in the ampere range. It must avoid the influence of normal unbalanced current and capacitive current, failing to meet the milliampere-level rapid disconnection requirements necessary for personal safety. Furthermore, its application is limited to upstream locations such as transformers and busbar sections, making real-time monitoring of early-stage potential insulation hazards in branch lines impossible. Therefore, existing low-voltage power grid insulation detection technologies lack high-precision hardware acquisition methods for zero-sequence voltage and current, are severely affected by distributed capacitive current, and cannot effectively identify and separate capacitive interference. The lack of multi-level low-threshold monitoring, baseline comparison, and abrupt change monitoring mechanisms results in the inability to accurately detect early-stage potential insulation hazards or effectively monitor their growth trends. This leads to long-term undetected insulation safety hazards in the power supply system, making it difficult for maintenance personnel to take targeted intervention measures before accidents occur, increasing the risk of safety accidents caused by insulation hazards. Summary of the Invention

[0005] The purpose of this application is to provide a low-voltage power grid insulation monitoring method and a low-voltage power grid insulation monitoring device, which can acquire zero-sequence voltage and zero-sequence current signals with high precision, reduce distributed capacitance interference, and achieve accurate detection and early warning of potential insulation hazards in the early and middle stages.

[0006] This application provides a method for monitoring the insulation of a low-voltage power grid, including: A PT open delta component and a zero-sequence current transformer are specially set up for the 400V low-voltage power grid to simultaneously collect the zero-sequence voltage analog signal and the zero-sequence current analog signal of the low-voltage power grid. The zero-sequence voltage analog signal and the zero-sequence current analog signal are transmitted to the acquisition and processing circuit module. The acquisition and processing circuit module performs low-voltage filtering and analog-to-digital conversion to convert the analog signals into zero-sequence voltage digital signals and zero-sequence current digital signals containing vector phase angle digital information. The zero-sequence voltage digital signal and the zero-sequence current digital signal are transmitted to the MCU microcontroller module. The data analysis and processing submodule of the MCU microcontroller module calculates and separates them to obtain the values ​​of the resistive component and the capacitive component of the zero-sequence current. Based on the values ​​of the resistive and capacitive components of the zero-sequence current, it is determined whether there are potential insulation hazards or capacitive interference in the low-voltage power grid lines.

[0007] Furthermore, this application also proposes that the primary side of the PT open delta component is distributed and connected to the three-phase voltages A, B, and C of the low-voltage power grid, and the secondary side of the PT open delta component does not have a lead-out port corresponding to the phase voltage, but only a zero-sequence voltage output port is set at the opening of the PT open delta component, and a zero-sequence voltage analog signal is output through the zero-sequence voltage output port.

[0008] Furthermore, this application also proposes that the PT ratio in the PT open delta component adopts a reverse amplification setting to convert the millivolt-level zero-sequence voltage vector value in the low-voltage power grid into a large voltage vector value, and the PT ratio includes 1:5.

[0009] Furthermore, this application also proposes to set up a zero-sequence voltage sampling and processing sub-unit in the acquisition and processing circuit module, and to set up a separate signal amplification sub-circuit in the zero-sequence voltage sampling and processing sub-unit to amplify and process the weak zero-sequence voltage analog signal at the millivolt level in the low-voltage power grid through the signal amplification sub-circuit.

[0010] Furthermore, this application also proposes to set up an energy metering chip in the acquisition and processing circuit module, so as to improve the calculation accuracy of the zero-sequence voltage analog signal and the zero-sequence current analog signal, while reducing the software program workload of the MCU microcontroller module.

[0011] Furthermore, this application also proposes that the data analysis and processing submodule of the MCU microcontroller module calculates and separates the values ​​of the zero-sequence current resistive component and the zero-sequence current capacitive component, including: using the phase characteristics that the zero-sequence current resistive component is in phase with the zero-sequence voltage and the zero-sequence current capacitive component leads the zero-sequence voltage by 90 degrees, vector separation is performed on the zero-sequence voltage digital signal and the zero-sequence current digital signal to obtain the effective values ​​of the zero-sequence current resistive component and the zero-sequence current capacitive component.

[0012] Furthermore, this application also proposes that, after obtaining the values ​​of the resistive component and the capacitive component of the zero-sequence current, the data analysis and processing submodule of the MCU microcontroller module further includes: integrating the zero-sequence voltage digital signal and the zero-sequence current digital signal with respect to time to obtain the zero-sequence voltage time integration parameter and the zero-sequence current time integration parameter for each time period.

[0013] Furthermore, this application proposes to further analyze and process the zero-sequence voltage time integral parameters and zero-sequence current time integral parameters to obtain the zero-sequence current resistive component time integral parameters and the zero-sequence current capacitive component time integral parameters, and combine the integral parameters to more accurately determine the potential insulation hazard status of low-voltage power grid lines.

[0014] Furthermore, this application also proposes that the data analysis and processing submodule of the MCU microcontroller module calculates the electrical parameters of each electrical circuit in the low-voltage power grid based on the zero-sequence voltage digital signal and the zero-sequence current digital signal. The electrical parameters include the effective values ​​of voltage and current, fundamental parameters, harmonic parameters, as well as frequency, phase angle, active power, reactive power, apparent power, active energy, reactive energy, apparent energy, and power factor.

[0015] Furthermore, this application also proposes a method for judging potential insulation hazards in low-voltage power grid lines based on the numerical value of the zero-sequence current resistive component, including: setting multi-level low-threshold early warning standards for the zero-sequence current resistive component, wherein the thresholds of the multi-level low-threshold early warning standards are all lower than the upper limit of the alarm threshold specified by the residual current type electrical fire monitoring detector; monitoring whether the absolute value of the zero-sequence current resistive component reaches the multi-level low-threshold early warning standards, and simultaneously monitoring the growth trend of the zero-sequence current resistive component. If the absolute value meets the standard or shows a monotonically increasing trend, it is determined that there are early to mid-stage potential insulation hazards in the low-voltage power grid line.

[0016] Furthermore, this application also proposes a method for judging capacitive interference in low-voltage power grid lines based on the numerical values ​​of the zero-sequence current capacitive component, including: recording the numerical sequence of the zero-sequence current capacitive component during normal operation of the low-voltage power grid line as the baseline value of capacitive capacitance; monitoring whether the real-time value of the zero-sequence current capacitive component undergoes a sudden change that is not caused by line modification; if a sudden change occurs, it is determined that there is capacitive interference or anomaly in the low-voltage power grid line due to drastic changes in distributed parameters.

[0017] Furthermore, this application also proposes a low-voltage power grid insulation monitoring device, comprising: The PT open delta component is used to acquire the zero-sequence voltage analog signal of a 400V low-voltage power grid; Zero-sequence current transformer is used to synchronously acquire the zero-sequence current analog signal of a 400V low-voltage power grid. The acquisition and processing circuit module communicates with the PT open delta component and the zero-sequence current transformer to perform low-voltage filtering and analog-to-digital conversion on the zero-sequence voltage analog signal and the zero-sequence current analog signal, and outputs zero-sequence voltage digital signal and zero-sequence current digital signal containing vector phase angle digital information. The MCU microcontroller module communicates with the data acquisition and processing circuit module. The MCU microcontroller module has a built-in data analysis and processing submodule, and is externally connected to a human-machine interface module and a communication module. The MCU microcontroller module runs the steps of the low-voltage power grid insulation monitoring method described above through the data analysis and processing submodule to complete the judgment of low-voltage power grid insulation hazards.

[0018] Furthermore, this application also proposes that the MCU microcontroller module transmits the detection values, insulation hazard analysis results, and early warning information to the human-machine interface module for local display; the MCU microcontroller module transmits the above data information to the communication module for external remote communication, and the communication module includes at least one communication method among 4G and Bluetooth.

[0019] Compared with existing technologies, the low-voltage power grid insulation monitoring method and equipment provided in this application acquire zero-sequence voltage and current signals by specially setting up a PT open delta component and a zero-sequence current transformer, and process them to separate resistive and capacitive components. On this basis, by setting multiple low thresholds and establishing baseline values ​​for insulation parameters, the growth trend and abrupt change monitoring characteristics of insulation parameters can be accurately identified. It can acquire zero-sequence voltage and zero-sequence current signals with high precision, reduce distributed capacitance interference, and achieve accurate detection and early warning of potential insulation hazards in the early and middle stages. Attached Figure Description

[0020] Figure 1 This is a schematic flowchart of a low-voltage power grid insulation monitoring method provided in an embodiment of this application; Figure 2 This is a schematic diagram of the structure of a low-voltage power grid insulation monitoring device provided in an embodiment of this application. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this application clearer, specific embodiments of this application will be described in further detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely for explaining this application and not for limiting it. It should also be noted that, for ease of description, only the parts relevant to this application are shown in the drawings, not all of them. Before discussing exemplary embodiments in more detail, it should be mentioned that some exemplary embodiments are described as processes or methods depicted as flowcharts. Although the flowcharts describe operations (or steps) as being processed sequentially, many of these operations can be performed in parallel, concurrently, or simultaneously. Furthermore, the order of the operations can be rearranged. A process can be terminated when its operation is completed, but it may also have additional steps not included in the drawings. A process can correspond to a method, function, procedure, subroutine, subroutine, etc.

[0022] The terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such use of data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and the number of objects is not limited; for example, a first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0023] Existing insulation detection technologies for three-phase four-wire low-voltage power grids primarily rely on residual current protection, but these methods cannot precisely analyze the state of insulation defects through phase relationships. Current technologies often employ digital algorithms to calculate zero-sequence voltage and current, resulting in large accuracy errors. They struggle to identify weak early-stage resistive insulation defects and are susceptible to interference from distributed capacitance currents. Consequently, early-stage potential insulation defects in low-voltage power grids are difficult to detect accurately and effectively, posing safety risks to the power supply system.

[0024] like Figure 1 As shown, this application proposes a low-voltage power grid insulation monitoring method, including: setting up a PT open delta component and a zero-sequence current transformer specifically for a 400V low-voltage power grid to simultaneously acquire the zero-sequence voltage analog signal and the zero-sequence current analog signal of the low-voltage power grid; transmitting the zero-sequence voltage analog signal and the zero-sequence current analog signal to an acquisition and processing circuit module, where the acquisition and processing circuit module performs low-voltage filtering and analog-to-digital conversion processing to convert the analog signal into a zero-sequence voltage digital signal and a zero-sequence current digital signal containing vector phase angle digital information; transmitting the zero-sequence voltage digital signal and the zero-sequence current digital signal to an MCU microcontroller module, where the data analysis and processing submodule of the MCU microcontroller module calculates and separates the values ​​of the zero-sequence current resistive component and the zero-sequence current capacitive component; and based on the values ​​of the zero-sequence current resistive component and the zero-sequence current capacitive component, determining whether there are potential insulation hazards or capacitive interference in the low-voltage power grid line.

[0025] The low-voltage power grid insulation monitoring method in this embodiment firstly sets up a PT open-delta component and a zero-sequence current transformer specifically for 400V low-voltage power grids to synchronously acquire the zero-sequence voltage and zero-sequence current analog signals of the low-voltage power grid. Specifically, the PT open-delta component can be composed of three single-phase voltage transformers, with their primary sides connected to the three-phase lines of the low-voltage power grid, and their secondary sides forming an open delta connection through a specific connection method, from which the zero-sequence voltage analog signal is led out. The zero-sequence current transformer can be a ring transformer, fitted around the three-phase conductors or the three-phase and neutral wires in a three-phase four-wire system of the low-voltage power grid, to sense and output the zero-sequence current analog signal. Thus, real-time, synchronous analog acquisition of zero-sequence voltage and zero-sequence current in the low-voltage power grid is achieved.

[0026] Subsequently, the acquired zero-sequence voltage and zero-sequence current analog signals are transmitted to the acquisition and processing circuit module. This module performs low-voltage filtering and analog-to-digital conversion on the analog signals, converting them into zero-sequence voltage and zero-sequence current digital signals containing vector phase angle digital information. For example, the acquisition and processing circuit module may include an analog filter to remove high-frequency noise and interference from the analog signal. Then, the filtered analog signal is converted into a digital signal by an analog-to-digital converter (ADC). This ADC samples the analog signal at a certain sampling frequency and converts it into a digital quantity with a certain number of quantization bits, thus preserving the amplitude and phase information of the original analog signal.

[0027] In some implementations, the converted zero-sequence voltage and zero-sequence current digital signals are transmitted to an MCU microcontroller module. This MCU module has a built-in data analysis and processing submodule that performs calculations and separations on the digital signals to obtain the values ​​of the resistive and capacitive components of the zero-sequence current. Specifically, the data analysis and processing submodule can perform Fourier transforms or correlation operations on the input digital signals to extract the fundamental components of the zero-sequence voltage and zero-sequence current and their phase angles. Based on this phase angle information, for example by decomposing the zero-sequence current vector into two directions in phase and orthogonal to the zero-sequence voltage, the effective values ​​of the resistive and capacitive components of the zero-sequence current can be calculated.

[0028] Finally, based on the obtained values ​​of the zero-sequence current resistive and capacitive components, it is determined whether there are potential insulation defects or capacitive interference in the low-voltage power grid lines. For example, the calculated zero-sequence current resistive component can be compared with a preset fixed threshold; if its value exceeds the threshold, a potential insulation defect is identified. Simultaneously, the zero-sequence current capacitive component can be compared with a reference value during normal operation; if its value deviates significantly, capacitive interference or anomalies are identified.

[0029] This embodiment achieves high-precision hardware acquisition of zero-sequence voltage and current in a 400V low-voltage power grid by specially configuring a PT open delta component and a zero-sequence current transformer. Through refined digital processing and vector separation of the acquired signals, the resistive and capacitive components of the zero-sequence current can be accurately obtained. Therefore, this method overcomes the limitations of traditional digital algorithms, such as insufficient accuracy and susceptibility to distributed capacitance current interference. It can effectively identify weak early-stage resistive insulation defects in low-voltage power grids and determine capacitive capacitance interference, thereby achieving accurate monitoring of the insulation status of low-voltage power grids and early warning of potential defects.

[0030] In some possible embodiments, the primary side of the PT open delta component is connected to the three-phase voltages A, B, and C of the low-voltage power grid. The secondary side of the PT open delta component does not have output ports corresponding to the phase voltages. Instead, a zero-sequence voltage output port is set at the opening of the PT open delta component, and the zero-sequence voltage analog signal is output through the zero-sequence voltage output port.

[0031] Specifically, the primary side of the PT open delta component is distributed and connected to the A, B, and C phase voltages of the low-voltage power grid. This means that the primary winding of the PT open delta component is electrically connected to the three-phase lines (A phase, B phase, and C phase) of the low-voltage power grid respectively. This connection method ensures that the PT open delta component can fully sense the changes in the voltage of each phase in the low-voltage power grid, laying the foundation for the accurate extraction of the subsequent zero-sequence voltage.

[0032] The secondary side of the open delta-type PT component does not have output ports corresponding to the phase voltages, meaning that the secondary winding of this component is designed not to provide separate A-phase, B-phase, and C-phase voltage output terminals. This design eliminates the redundant phase voltage outputs that traditional PTs may provide, allowing the component's function to focus more on the extraction of zero-sequence voltage, avoiding the wiring complexity or potential signal interference that may be caused by redundant ports.

[0033] Setting a zero-sequence voltage output port only at the opening of the PT open delta component means that after the secondary winding of the PT open delta component is connected in an open delta configuration, only a single output port is led out at both ends of the opening. This opening is precisely the point where the zero-sequence voltage is concentrated. By setting a dedicated output port at this location, it is ensured that the output signal is a pure zero-sequence voltage signal synthesized internally.

[0034] Outputting the zero-sequence voltage analog signal through the zero-sequence voltage output port means that this dedicated port directly provides the zero-sequence voltage analog signal for subsequent processing. This direct output method simplifies the signal transmission path from the PT to the acquisition and processing circuit module, reduces intermediate links, and thus improves signal transmission efficiency and reliability.

[0035] In some possible embodiments, it is proposed that the PT ratio in the PT open delta component adopts a reverse amplification setting to convert the millivolt-level zero-sequence voltage vector value in the low-voltage power grid into a large voltage vector value, wherein the PT ratio includes 1:5.

[0036] Specifically, traditional voltage transformers (PTs) are typically used to step down high voltages to low voltages for measurement. However, in this case, to address the weak zero-sequence voltage signal in low-voltage power grids, the PT open-delta component is designed with inverse amplification capabilities. This means that the voltage amplitude output from its secondary side will be greater than the zero-sequence voltage amplitude input from the primary side, thus achieving preliminary amplification of the weak zero-sequence voltage signal. This setup helps improve the signal-to-noise ratio, providing a clearer and easier-to-process input for subsequent signal processing. Under normal conditions or during early insulation degradation, the amplitude of the zero-sequence voltage in low-voltage power grids is typically only in the millivolt range. This weak signal is easily attenuated or overwhelmed by noise during transmission and processing. Through the inverse amplification setting, the PT open-delta component can amplify these millivolt-level zero-sequence voltage signals to volt levels or higher, creating a "large voltage vector value" that allows the acquisition and processing circuit module to effectively identify and process them. This conversion not only amplifies the signal but also preserves its original vector phase angle information, ensuring the accuracy of subsequent data analysis. The PT transformation ratio is 1:5, which is a specific reverse amplification ratio. This means that when the primary side of the PT open delta component senses 1 unit of zero-sequence voltage, its secondary side will output 5 units of zero-sequence voltage. For example, if the zero-sequence voltage on the primary side is 10 millivolts, the secondary side will output 50 millivolts. This specific transformation ratio is optimized based on the actual zero-sequence voltage range of the low-voltage power grid and the input requirements of the subsequent acquisition and processing circuit modules, aiming to provide sufficient amplification while avoiding signal saturation or distortion.

[0037] In some possible embodiments, a zero-sequence voltage sampling and processing subunit is proposed within the acquisition and processing circuit module. This subunit has a separate signal amplification subcircuit to amplify the weak millivolt-level zero-sequence voltage analog signal from the low-voltage power grid. Specifically, the zero-sequence voltage sampling and processing subunit is dedicated to processing the zero-sequence voltage analog signal. Its function is to physically or logically isolate the processing path of the zero-sequence voltage signal from the processing paths of other signals (such as zero-sequence current signals), ensuring that the zero-sequence voltage signal is not interfered with by other signals during processing and that it can be optimized for its characteristics. This subunit can be an independent circuit board area or a specific functional module within an integrated circuit, designed to provide a dedicated and optimized processing environment for the weak zero-sequence voltage signal. Within the zero-sequence voltage sampling and processing subunit, a separate signal amplification subcircuit is provided. This signal amplification subcircuit is specifically designed for amplifying the zero-sequence voltage analog signal. This can be achieved using high-precision, low-noise operational amplifiers or instrumentation amplifiers, with precise resistor network configuration to achieve stable and linear amplification of millivolt-level signals. For example, multi-stage amplifier circuits can be used to progressively increase the signal amplitude while effectively suppressing noise. The signal amplification sub-circuit amplifies the weak millivolt-level zero-sequence voltage analog signal from the low-voltage power grid. This amplification aims to increase the amplitude of the weak zero-sequence voltage analog signal to the optimal input range of the analog-to-digital converter (ADC) in the acquisition and processing circuit module, thereby fully utilizing the quantization accuracy of the ADC. Through amplification, the effective components of the signal are enhanced, while the influence of noise is relatively reduced, significantly improving the signal-to-noise ratio and providing high-quality input for subsequent digital signal processing.

[0038] To address this, this application further proposes performing low-voltage filtering and analog-to-digital conversion on the zero-sequence voltage analog signal and the zero-sequence current analog signal in the acquisition and processing circuit module, and then transmitting the converted digital signal to the MCU microcontroller module for data analysis. However, when achieving high-precision measurement and complex calculations, traditional analog-to-digital conversion and preliminary processing may face insufficient accuracy or significantly increase the software workload of the MCU microcontroller module, thereby affecting the system's real-time performance or placing higher demands on the MCU's performance.

[0039] To address the aforementioned issues, this application proposes that an energy metering chip be incorporated into the acquisition and processing circuit module. This energy metering chip improves the calculation accuracy of the zero-sequence voltage analog signal and the zero-sequence current analog signal, while simultaneously reducing the software workload of the MCU microcontroller module.

[0040] Specifically, the acquisition and processing circuit module is mainly responsible for receiving analog signals from the open delta component of the PT and the zero-sequence current transformer, and preprocessing and digitizing them. Its core function is to convert continuously changing analog signals into discrete digital signals for subsequent processing by the microcontroller. In this embodiment, this module serves as the carrier of the energy metering chip, and its signal processing capabilities are enhanced by integrating this chip.

[0041] The aforementioned energy metering chip is an integrated circuit specifically designed for the accurate measurement of energy parameters. These chips typically integrate a high-resolution analog-to-digital converter (ADC), a digital signal processor (DSP), and dedicated algorithms for calculating parameters such as voltage, current, power, and energy. They can digitize input analog signals at high sampling rates and with high precision, and perform preliminary numerical processing and calibration. Typical implementations include using a multi-channel synchronous sampling ADC to ensure the time synchronization of zero-sequence voltage and current analog signals; built-in hardware multipliers and accumulators for efficient power and energy calculations; and support for various communication interfaces (such as SPI and I2C) for data exchange with external MCU microcontroller modules. For example, a metering chip with high dynamic range and low power consumption can be selected, which may include temperature compensation circuitry and a reference voltage source to ensure measurement stability under different environmental conditions. Its core function is to provide measurement accuracy far exceeding that of general-purpose ADCs and to undertake some complex computational tasks, thereby reducing the burden on the MCU microcontroller module.

[0042] The improvement in the calculation accuracy of the zero-sequence voltage and zero-sequence current analog signals refers to the accuracy from analog signals to the final digital quantization result. The power metering chip, through its internal high-resolution ADC (e.g., 24-bit or higher) and optimized sampling algorithms, can more precisely capture minute changes in the zero-sequence voltage and zero-sequence current analog signals, reducing quantization errors and noise interference. Furthermore, the chip's internal digital signal processing unit can execute more complex filtering, calibration, and compensation algorithms, further improving the accuracy of the measurement results and ensuring more reliable subsequent analysis of the resistive and capacitive components of the zero-sequence current.

[0043] The reduction in software workload for the MCU microcontroller module refers to the fact that in traditional solutions, the MCU microcontroller module is responsible for data acquisition, filtering, calibration after analog-to-digital conversion, as well as the calculation of complex electrical parameters (such as RMS value, phase angle, power, etc.). With the introduction of an energy metering chip, these computationally intensive tasks (such as RMS value calculation, phase difference calculation, and even preliminary resistive / capacitive component separation) can be completed by the metering chip's hardware accelerator or built-in DSP. The MCU microcontroller module only needs to read the high-precision data already processed by the metering chip through a simple communication interface, thereby significantly simplifying the MCU's software programming complexity, reducing its CPU utilization, and allowing it to focus on higher-level logic judgments and system management tasks, improving the overall system's response speed and efficiency.

[0044] In some possible embodiments, the data analysis and processing submodule of the MCU microcontroller module is proposed to calculate and separate the values ​​of the zero-sequence current resistive component and the zero-sequence current capacitive component, including: using the phase characteristics that the zero-sequence current resistive component is in phase with the zero-sequence voltage and the zero-sequence current capacitive component leads the zero-sequence voltage by 90 degrees, vector separation is performed on the zero-sequence voltage digital signal and the zero-sequence current digital signal to obtain the effective values ​​of the zero-sequence current resistive component and the zero-sequence current capacitive component.

[0045] Specifically, in AC circuits, the current and voltage of a purely resistive load are in phase, while the current of a purely capacitive load leads the voltage by 90 degrees. In the zero-sequence loop of a low-voltage power grid, the resistive component of the zero-sequence current mainly originates from leakage current caused by insulation degradation, and its phase is basically consistent with the phase of the zero-sequence voltage. The capacitive component of the zero-sequence current mainly originates from the charging and discharging current of the grid-to-ground distributed capacitance, and its phase typically leads the zero-sequence voltage by 90 degrees. After receiving the zero-sequence voltage and zero-sequence current digital signals after analog-to-digital conversion, the data analysis and processing submodule of the MCU microcontroller module first performs precise phase analysis on these two digital signals. This can be achieved through digital signal processing algorithms, such as obtaining the amplitude and phase of the fundamental component of the signal through Fast Fourier Transform (FFT), or determining the instantaneous phase of the signal using methods based on zero-crossing detection and peak detection.

[0046] After acquiring the phase information of the zero-sequence voltage digital signal and the zero-sequence current digital signal, the data analysis and processing submodule will perform vector separation using the aforementioned inherent phase characteristics. Vector separation refers to decomposing a composite zero-sequence current vector into a resistive component that is in phase with the zero-sequence voltage and a capacitive component that leads the zero-sequence voltage by 90 degrees. This vector separation method based on phase characteristics can accurately distinguish between the resistive component representing insulation leakage and the capacitive component representing capacitor charging and discharging in the zero-sequence current.

[0047] After vector separation, the data analysis and processing submodule further calculates the effective values ​​of the separated zero-sequence current resistive and capacitive components. The effective value (RMS value) is an important parameter of alternating current (AC), reflecting its actual heating effect and is the most commonly used current and voltage measurement indicator in power systems. The effective value is typically calculated by squaring, averaging, and then taking the square root of the separated digital signal over one or more cycles.

[0048] In some possible embodiments, the data analysis and processing submodule of the MCU microcontroller module, after obtaining the values ​​of the resistive component of the zero-sequence current and the capacitive component of the zero-sequence current, further includes: integrating the zero-sequence voltage digital signal and the zero-sequence current digital signal with respect to time to obtain the zero-sequence voltage time integration parameter and the zero-sequence current time integration parameter for each time period.

[0049] Specifically, the data analysis and processing submodule of the MCU microcontroller module is a core component, responsible for executing complex algorithms and data operations. Its functions extend beyond vector separation of the zero-sequence voltage and zero-sequence current digital signals to obtain resistive and capacitive components; it also includes further mathematical processing of these digital signals, such as time integration. This submodule typically consists of a high-performance processor, memory, and corresponding firmware, capable of efficiently processing large amounts of real-time sampled data and executing preset analysis logic. Integrating the zero-sequence voltage and zero-sequence current digital signals over time refers to the process of summing or averaging continuously sampled zero-sequence voltage and zero-sequence current digital signals over a certain time period. Its purpose is to convert instantaneously changing signals into parameters that reflect their cumulative effect over a period of time. Specific implementation methods can include discrete integration, where the current sampled value is summed with the integral value from the previous moment within each sampling period, and multiplied by the sampling time interval to obtain the integral value for that time period; or sliding window integration, where all sampling points within a preset time window are integrated, and the window slides forward as time progresses, continuously updating the integration result; or periodic integration, which, considering the periodicity of AC signals, integrates over one or more complete periods to eliminate the influence of periodic fluctuations and obtain a more stable average trend. Through this integration process, instantaneous fluctuations and noise in the signal can be effectively smoothed, and the average characteristics or cumulative effects of the signal over a longer time scale can be extracted. Thus, the time integral parameters of zero-sequence voltage and zero-sequence current for each time period are obtained. These parameters are values ​​obtained after time integration processing, representing the cumulative amount or average trend of the zero-sequence voltage and zero-sequence current digital signals within a specific time period. These integral parameters are no longer instantaneous values, but comprehensive indicators with a time dimension; for example, they can be the average value or effective value integral of the zero-sequence voltage within a certain time period, or the accumulated charge of the zero-sequence current, etc.

[0050] In some possible embodiments, it is proposed to further analyze and process the zero-sequence voltage time integral parameter and the zero-sequence current time integral parameter to obtain the zero-sequence current resistive component time integral parameter and the zero-sequence current capacitive component time integral parameter, and combine the integral parameters to further determine the potential insulation hazard status of the low-voltage power grid line.

[0051] Specifically, "further analysis and processing" here refers to conducting deeper and more refined data mining and pattern recognition based on the already obtained zero-sequence voltage time integral parameters and zero-sequence current time integral parameters. This may include, but is not limited to: performing trend analysis on the integral parameters, such as calculating their rate of change and acceleration; performing correlation analysis to assess the mutual influence between the two; or using statistical methods, such as mean, variance, and standard deviation, to extract more stable features. Furthermore, signal processing techniques such as Fourier transform and wavelet analysis can be used to extract frequency domain or time-frequency domain features from the integral parameters, thereby revealing insulation degradation patterns hidden in the data.

[0052] Based on the above re-analysis, the time-integral parameters of the resistive and capacitive components of the zero-sequence current are obtained. This step aims to further decompose the time-integrated zero-sequence current parameters into resistive and capacitive components. This can be achieved through a method similar to vector separation of instantaneous zero-sequence current, but the object of operation is the integral parameter. For example, vector decomposition can be performed using the phase relationship between the time-integral parameters of the zero-sequence voltage and the zero-sequence current, projecting the time-integral parameter of the zero-sequence current onto two directions that are in phase and orthogonal to the time-integral parameter of the zero-sequence voltage, respectively obtaining the time-integral parameters of the resistive and capacitive components. This separation helps to distinguish the effects of changes in insulation resistance and distributed capacitance on the zero-sequence current at the integration level.

[0053] Subsequently, the potential insulation defects of the low-voltage power grid line are further assessed by combining the integral parameters. "Combining the integral parameters" means using the time integral parameters of the zero-sequence current resistive component and the zero-sequence current capacitive component obtained above, as well as possibly including the time integral parameters of the zero-sequence voltage and zero-sequence current, as a comprehensive judgment criterion. By analyzing these integral parameters in multiple dimensions and across multiple time scales, a more comprehensive insulation condition assessment model can be established. For example, composite thresholds based on these integral parameters can be set, or machine learning algorithms can be used to train historical data to identify different types of insulation degradation patterns.

[0054] In some possible embodiments, it is proposed that the electrical parameters of each electrical circuit in the low-voltage power grid be calculated based on the zero-sequence voltage digital signal and the zero-sequence current digital signal in the data analysis and processing submodule of the MCU microcontroller module. The electrical parameters include the effective values ​​of voltage and current, fundamental parameters, harmonic parameters, as well as frequency, phase angle, active power, reactive power, apparent power, active energy, reactive energy, apparent energy, and power factor.

[0055] Specifically, the data analysis and processing submodule of the MCU microcontroller module is configured not only to process the zero-sequence component but also to provide a more comprehensive assessment of the overall operating status of the power grid. This submodule can utilize digital signal processing (DSP) algorithms, such as Fast Fourier Transform (FFT), Discrete Fourier Transform (DFT), or sliding window algorithms, to perform real-time or near-real-time analysis of the obtained zero-sequence voltage and current digital signals, as well as phase voltage and current digital signals that may be acquired through other channels. These algorithms can extract frequency domain features from the time-domain signals, thereby calculating various electrical parameters.

[0056] When calculating the electrical parameters, the effective values ​​of voltage and current can be obtained by squaring the digital signal over one or more cycles, taking the average value, and then taking the square root. The fundamental and harmonic parameters can be calculated by using FFT or DFT algorithms to decompose the time-domain signal into a superposition of different frequency components. The component corresponding to the grid fundamental frequency is the fundamental wave, and the remaining frequency components are harmonics. Their amplitudes and phase angles are then calculated separately. Frequency can be determined by detecting the zero-crossing points of the signal or by analyzing the dominant frequency component using FFT, for example, by calculating the number of zero-crossing points per unit time. The phase angle can be obtained by comparing the zero-crossing time differences of different signals (such as voltage and current) or by obtaining the phase information of each component through FFT analysis. Active power, reactive power, and apparent power can be calculated based on the effective values ​​of voltage and current and their phase angles, or by using the average value of instantaneous power. Active energy, reactive energy, and apparent energy are obtained by time integration of the corresponding power, which typically requires the MCU microcontroller module to continuously monitor the power and accumulate the power values ​​over a specific time period. The power factor is calculated as the ratio of active power to apparent power.

[0057] In some possible embodiments, a method for determining potential insulation hazards in low-voltage power grid lines based on the numerical value of the zero-sequence current resistive component is proposed. Specifically, this method includes: setting multi-level low-threshold early warning standards for the zero-sequence current resistive component, where the threshold values ​​of all multi-level low-threshold early warning standards are lower than the upper limit of the alarm threshold specified by the residual current type electrical fire monitoring detector; monitoring whether the absolute value of the zero-sequence current resistive component reaches the multi-level low-threshold early warning standards, and simultaneously monitoring the growth trend of the zero-sequence current resistive component. If the absolute value meets the standard or shows a monotonically increasing trend, it is determined that the low-voltage power grid line has early to mid-stage potential insulation hazards.

[0058] Specifically, for the resistive component of the zero-sequence current, a series of progressive warning thresholds can be set. For example, they can be set as I_R1, I_R2, I_R3, etc., where I_R1 < I_R2 < I_R3. These thresholds should be determined comprehensively based on factors such as the actual operation experience of the low-voltage power grid, equipment type, environmental conditions, and the aging characteristics of insulation materials. By setting multi-level thresholds, refined hierarchical warning for the degree of insulation deterioration can be achieved, reflecting everything from slight deterioration to severe deterioration. At the same time, the values of these multi-level low-threshold warning standards are all set to be lower than the upper limit of the alarm threshold specified by conventional residual current type electrical fire monitoring detectors. This means that even if the resistive component of the zero-sequence current has not reached the dangerous level that may cause a fire, as long as it reaches the lower warning threshold set by this method, the system can issue a warning, thus achieving earlier detection of insulation hidden dangers.

[0059] During the monitoring process, the data analysis and processing sub-module of the MCU microcontroller module continuously and real-time obtains the absolute value of the calculated resistive component of the zero-sequence current. Subsequently, this absolute value is compared level by level with the pre-set multi-level low-threshold warning standards. Once the absolute value of the resistive component of the zero-sequence current reaches or exceeds any warning threshold, the system will trigger the corresponding warning mechanism. In addition, in addition to monitoring the instantaneous absolute value of the resistive component of the zero-sequence current, the data analysis and processing sub-module of the MCU microcontroller module also stores and analyzes the historical data of this component to evaluate its trend over time. This can be achieved by calculating the average growth rate, slope over a period of time or using statistical methods such as moving average. For example, a time window can be set to observe the change amount or change rate of the resistive component of the zero-sequence current within this window. When the absolute value of the resistive component of the zero-sequence current reaches any level of the pre-set multi-level low-threshold warning standards, or even if its absolute value has not reached the highest warning threshold, but through trend monitoring, it is found that it shows a continuous and non-accidental monotonically increasing trend, the system determines that there are medium-early potential insulation hidden dangers in the low-voltage power grid line. This judgment mechanism combines instantaneous state and dynamic changes, and can capture the early signals of insulation deterioration more comprehensively and sensitively.

[0060] In some possible embodiments, a method for judging the capacitive capacitance interference of the low-voltage power grid line based on the value of the capacitive component of the zero-sequence current is proposed, including: recording the numerical sequence of the capacitive component of the zero-sequence current when the low-voltage power grid line is operating normally as the capacitive capacitance baseline value; monitoring whether there is a mutation in the real-time value of the capacitive component of the zero-sequence current that is not caused by line modification. If a mutation occurs, it is determined that there is capacitive capacitance interference or abnormality with a sharp change in distribution parameters in the low-voltage power grid line.

[0061] This involves recording the numerical sequence of the zero-sequence current capacitive component during normal operation of the low-voltage power grid line, serving as a baseline value for capacitive capacitance. The aim is to establish a reference benchmark reflecting the characteristics of the zero-sequence current capacitive component under normal operating conditions. Specifically, the values ​​of the zero-sequence current capacitive component can be continuously or periodically collected and stored during the initial operation of the low-voltage power grid line or when it is confirmed to be in a healthy state. These values ​​can form a time series, and their normal fluctuation range and typical characteristics can be characterized using statistical methods (e.g., calculating the mean, standard deviation, trend line, or constructing confidence intervals). This baseline value can effectively eliminate the conventional influence of the line's inherent distributed capacitance, normal load changes, and environmental factors on the zero-sequence current capacitive component, providing an accurate reference for subsequent anomaly detection.

[0062] The monitoring process involves dynamically comparing and analyzing the real-time values ​​of the zero-sequence current capacitive component against a pre-established baseline value. A "sudden change" refers to a significant and sustained change in the real-time value of the zero-sequence current capacitive component within a short period, where the magnitude or rate of change exceeds the normal fluctuation range, and this change is not caused by known, planned line modifications or equipment connections. Sudden changes can be detected using various algorithms, such as methods based on statistical control charts (e.g., Shewhart charts, CUSUM charts), or by comparing the deviation and rate of change between the real-time value and the baseline value with a preset threshold. Excluding changes "not caused by line modifications" is to avoid misjudging normal system configuration changes as faults, thereby improving the accuracy of the judgment.

[0063] If a sudden change occurs, it is determined that the low-voltage power grid line has capacitive capacitance interference or anomalies due to drastic changes in distributed parameters. When a sudden change occurs in the real-time value of the zero-sequence current capacitive component that is not caused by line modification, it indicates that the capacitive characteristics of the low-voltage power grid line have changed significantly. This change usually indicates the presence of new capacitive loads in the line, deterioration of insulation performance, cable dampness, abnormal increase in ground capacitance due to equipment failure, or other forms of capacitive capacitance interference. Through this judgment, capacitive anomalies that may affect the stable operation and insulation status of the power grid can be identified in a timely manner, providing a basis for taking further investigation and maintenance measures.

[0064] Traditional insulation detection technologies for three-phase four-wire low-voltage power grids primarily rely on residual current protection, but these methods cannot accurately analyze the state of insulation defects through phase relationships. Existing technologies often employ digital algorithms to calculate zero-sequence voltage and current, resulting in large accuracy errors. They struggle to identify weak early-stage resistive insulation defects and are susceptible to interference from distributed capacitance currents. Consequently, early-stage potential insulation defects in low-voltage power grids are difficult to detect accurately and effectively, posing safety risks to the power supply system.

[0065] like Figure 2 As shown in the illustration, this application also discloses a low-voltage power grid insulation monitoring device, comprising: The PT open delta component is used to acquire the zero-sequence voltage analog signal of a 400V low-voltage power grid; Zero-sequence current transformer is used to synchronously acquire the zero-sequence current analog signal of a 400V low-voltage power grid. The acquisition and processing circuit module is communicatively connected to the PT open delta component and the zero-sequence current transformer. It performs low-voltage filtering and analog-to-digital conversion on the zero-sequence voltage analog signal and the zero-sequence current analog signal, and outputs zero-sequence voltage digital signal and zero-sequence current digital signal containing vector phase angle digital information. The MCU microcontroller module is communicatively connected to the data acquisition and processing circuit module. The MCU microcontroller module has a built-in data analysis and processing submodule and is externally connected to a human-machine interface module and a communication module. The MCU microcontroller module implements the steps of the above method through the data analysis and processing submodule to complete the judgment of insulation hazards in the low-voltage power grid.

[0066] The innovation of this embodiment lies in combining the PT open delta component with the zero-sequence current transformer in a hardware synchronous acquisition method, thereby breaking through the technical bottleneck of the lack of zero-sequence voltage hardware acquisition device in 400V low-voltage power grids and realizing high-precision capture of weak zero-sequence voltage analog signals; at the same time, the data analysis and processing submodule is used to perform resistive / capacitive component vector separation of the zero-sequence current, effectively eliminating the interference of distributed capacitance current, and achieving the effect of accurately identifying early and middle resistive insulation hazards and monitoring the development trend of hazards.

[0067] Specifically, the PT open-delta component, specially configured for 400V low-voltage power grids, has its primary side connected to the three-phase voltages A, B, and C, while the secondary side only has a zero-sequence voltage output port at the open end, directly outputting the zero-sequence voltage analog signal, avoiding calculation errors caused by three-phase voltage imbalance in traditional digital algorithms. The zero-sequence current transformer synchronously acquires the zero-sequence current analog signal around the three-phase conductors and the neutral wire, ensuring timing consistency with the zero-sequence voltage signal. The acquisition and processing circuit module eliminates high-frequency noise through low-voltage filtering and uses high-precision analog-to-digital conversion to retain vector phase angle information, converting the millivolt-level weak signal into a precise digital quantity. The data analysis and processing submodule of the MCU microcontroller module performs vector decomposition on the digital signal based on the phase characteristics of the zero-sequence current resistive component being in phase with the zero-sequence voltage and the capacitive component leading by 90 degrees, separating the effective values ​​of the resistive and capacitive components.

[0068] Based on this, the device monitors the absolute value and growth trend of the resistive component of zero-sequence current through a multi-level low-threshold early warning mechanism, achieving early warning of potential insulation hazards at the milliampere level. Simultaneously, it records the numerical sequence of capacitive components as a baseline, comparing abrupt changes in real time to identify abnormal distribution parameters. The human-machine interface module provides local data display, and the communication module supports 4G or Bluetooth remote transmission, enabling maintenance personnel to obtain insulation status analysis results promptly. In summary, this embodiment, through hardware-level synchronous acquisition and vector separation technology, fundamentally solves the problems of insufficient accuracy of zero-sequence parameters and capacitive interference in existing technologies, providing reliable technical support for the early detection and trend prediction of insulation hazards in low-voltage power grids.

[0069] In some possible embodiments, the aforementioned MCU microcontroller module transmits the detection values, insulation hazard analysis results, and early warning information to the human-machine interface module for local display; the MCU microcontroller module transmits the aforementioned data information to the communication module for external remote communication, and the communication module includes at least one communication method among 4G and Bluetooth.

[0070] Specifically, the MCU (Microcontroller Unit) module is the core control unit of the entire monitoring equipment, responsible for executing various steps in the low-voltage power grid insulation monitoring method and performing data processing and logical judgments. The Human-Machine Interface (HMI) module is the interface between the equipment and the user, typically including a display screen, buttons, and indicator lights. The HMI module transmits the detection values ​​calculated by the MCU (e.g., zero-sequence voltage digital signal, zero-sequence current digital signal, zero-sequence current resistive component, and zero-sequence current capacitive component values), insulation hazard analysis results (e.g., whether potential insulation hazards exist, hazard level, etc.), and early warning information (e.g., reaching multi-level low-threshold early warning standards, sudden changes in capacitive capacitance interference, etc.) to the HMI module for local display. This aims to provide on-site operators with intuitive and real-time equipment operating status and insulation monitoring results. The HMI module can use various forms such as an LCD, OLED, or touchscreen, and the displayed content can include real-time data curves, alarm lists, historical records, and system setting menus. Data transmission between the MCU and the HMI module can use serial communication protocols such as SPI, I2C, and UART, or high-speed data transmission via a parallel bus. The MCU microcontroller module formats the data to be displayed according to its internal algorithm and user configuration, and writes the data into the display buffer through the display driver chip, and finally displays it on the screen.

[0071] Simultaneously, the MCU microcontroller module transmits the aforementioned data to the communication module, enabling remote communication. Remote communication refers to sending the device's internal monitoring data and analysis results to a remote monitoring center, cloud platform, or mobile terminal, achieving remote monitoring, data storage, and management. The communication module is the hardware unit that implements this function, responsible for converting the data processed by the MCU microcontroller module into a signal format suitable for long-distance transmission. The MCU microcontroller module and the communication module typically exchange data using interfaces such as UART, SPI, and I2C. Internally, the communication module encapsulates the data into corresponding network protocol packets (such as TCP / IP, MQTT, etc.) according to its supported communication methods. The transmitted data can be used to build historical databases, perform big data analysis, and realize fault prediction and equipment maintenance planning. Meanwhile, remote users can view the device status in real time, receive alarm information, and perform remote control through a mobile app or web interface.

[0072] To adapt to different application scenarios and network environments, the communication module includes at least one communication method: 4G and Bluetooth. It is suitable for devices deployed in areas with Wi-Fi coverage, offering advantages such as high transmission speed and relatively low cost. The communication module can integrate a chip to connect to a local router via TCP / IP protocol, thereby accessing the Internet. 4G is suitable for devices deployed in areas with mobile cellular network coverage, eliminating the need for a local LAN and offering advantages such as wide coverage and high mobility. The communication module can integrate a 4G module to access the operator's network via a SIM card, enabling wide area network communication. Bluetooth is suitable for short-range wireless communication between the device and nearby mobile terminals (such as smartphones and tablets), commonly used for on-site debugging, parameter configuration, or temporary data download. The communication module can integrate a Bluetooth chip for point-to-point communication with paired devices via the Bluetooth protocol. In practical applications, the communication module can support multiple communication methods simultaneously; for example, prioritizing data transmission and automatically switching to 4G when unavailable, or using Bluetooth for local maintenance.

[0073] Using the above methods, the low-voltage power grid insulation monitoring system of this industrial facility can accurately collect zero-sequence voltage and zero-sequence current, effectively separate resistive and capacitive components, and, based on multi-level low threshold and trend analysis, accurately judge and warn of potential insulation hazards in the early and middle stages. At the same time, it can identify capacitive interference, significantly improve the operational safety and reliability of the low-voltage power grid, and make up for the shortcomings of existing technologies in low-voltage power grid insulation monitoring.

[0074] The above description is merely a preferred embodiment and the technical principles employed in this application. This application is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions that can be made by those skilled in the art will not depart from the scope of protection of this application. Therefore, although this application has been described in detail through the above embodiments, this application is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of this application. The scope of this application is determined by the scope of the claims.

Claims

1. A method for monitoring insulation in a low-voltage power grid, characterized in that, Includes the following steps: The zero-sequence voltage analog signal is acquired by a PT open delta component configured in the 400V low-voltage power grid, and the zero-sequence current analog signal is acquired simultaneously by a zero-sequence current transformer configured in the 400V low-voltage power grid. The zero-sequence voltage analog signal and the zero-sequence current analog signal are subjected to low-voltage filtering by the acquisition and processing circuit module, and then converted into zero-sequence voltage digital signal and zero-sequence current digital signal containing vector phase angle digital information. The zero-sequence voltage digital signal and the zero-sequence current digital signal are calculated and separated by the data analysis and processing submodule in the MCU microcontroller module to obtain the values ​​of the resistive component and the capacitive component of the zero-sequence current. Based on the values ​​of the zero-sequence current resistive component and the zero-sequence current capacitive component, determine whether the low-voltage power grid line has potential insulation defects or capacitive interference, including: A multi-level low-threshold early warning standard is set for the zero-sequence current resistive component. The absolute value of the zero-sequence current resistive component is monitored to see if it reaches the multi-level low-threshold early warning standard, while simultaneously monitoring the growth trend of the zero-sequence current resistive component. If the absolute value meets the standard or shows a monotonically increasing trend, it is determined that the 400V low-voltage power grid has an early-middle potential insulation hazard. The thresholds of the multi-level low-threshold early warning standard are all lower than the upper limit of the alarm threshold specified by the residual current type electrical fire monitoring detector; or... The numerical sequence of the zero-sequence current capacitive component is recorded during normal operation of the 400V low-voltage power grid as the baseline value of capacitive capacitance. The real-time value of the zero-sequence current capacitive component is monitored for any sudden change relative to the baseline value of capacitive capacitance. If a sudden change occurs, it is determined that there is capacitive capacitance interference in the low-voltage power grid line.

2. The low-voltage power grid insulation monitoring method according to claim 1, characterized in that, The primary side of the PT open delta component is connected to the three-phase voltages A, B, and C of the low-voltage power grid. The secondary side of the PT open delta component does not have output ports corresponding to the phase voltages. Instead, a zero-sequence voltage output port is set at the opening of the PT open delta component, through which the zero-sequence voltage analog signal is output.

3. The low-voltage power grid insulation monitoring method according to claim 2, characterized in that, The PT ratio in the PT open delta component adopts a reverse amplification setting to convert the millivolt-level zero-sequence voltage vector value in the low-voltage power grid into a large voltage vector value. The PT ratio includes 1:

5.

4. The low-voltage power grid insulation monitoring method according to claim 1, characterized in that, The acquisition and processing circuit module includes a zero-sequence voltage sampling and processing subunit, which has a separate signal amplification subcircuit. The signal amplification subcircuit amplifies the weak zero-sequence voltage analog signal at the millivolt level in the low-voltage power grid.

5. The low-voltage power grid insulation monitoring method according to claim 1, characterized in that, The data acquisition and processing circuit module is equipped with an energy metering chip, which improves the calculation accuracy of the zero-sequence voltage analog signal and the zero-sequence current analog signal, while reducing the software workload of the MCU microcontroller module.

6. The low-voltage power grid insulation monitoring method according to claim 1, characterized in that, The data analysis and processing submodule of the MCU microcontroller module calculates and separates the values ​​of the zero-sequence current resistive component and the zero-sequence current capacitive component, including: using the phase characteristics that the zero-sequence current resistive component is in phase with the zero-sequence voltage and the zero-sequence current capacitive component leads the zero-sequence voltage by 90 degrees, vector separation is performed on the zero-sequence voltage digital signal and the zero-sequence current digital signal to obtain the effective values ​​of the zero-sequence current resistive component and the zero-sequence current capacitive component.

7. The low-voltage power grid insulation monitoring method according to claim 1, characterized in that, After obtaining the values ​​of the resistive component and the capacitive component of the zero-sequence current, the data analysis and processing submodule of the MCU microcontroller module further includes: integrating the zero-sequence voltage digital signal and the zero-sequence current digital signal with respect to time to obtain the zero-sequence voltage time integration parameter and the zero-sequence current time integration parameter for each time period.

8. The low-voltage power grid insulation monitoring method according to claim 7, characterized in that, Based on the time integral parameters of the zero-sequence voltage and the time integral parameters of the zero-sequence current, further analysis and processing are performed to obtain the time integral parameters of the resistive component of the zero-sequence current and the time integral parameters of the capacitive component of the zero-sequence current. Combined with the integral parameters, the potential insulation hazard status of the low-voltage power grid line is further determined.

9. A low-voltage power grid insulation monitoring device, characterized in that, include: The PT open delta component is used to acquire the zero-sequence voltage analog signal of a 400V low-voltage power grid; Zero-sequence current transformer is used to synchronously acquire the zero-sequence current analog signal of a 400V low-voltage power grid. The acquisition and processing circuit module is communicatively connected to the PT open delta component and the zero-sequence current transformer. It performs low-voltage filtering and analog-to-digital conversion on the zero-sequence voltage analog signal and the zero-sequence current analog signal, and outputs zero-sequence voltage digital signal and zero-sequence current digital signal containing vector phase angle digital information. The MCU microcontroller module is communicatively connected to the acquisition and processing circuit module. The MCU microcontroller module has a built-in data analysis and processing sub-module and is externally connected to a human-machine interface module and a communication module. The data analysis and processing submodule is used to calculate and separate the zero-sequence voltage digital signal and the zero-sequence current digital signal to obtain the values ​​of the zero-sequence current resistive component and the zero-sequence current capacitive component. The data analysis and processing submodule is further used to determine, based on the values ​​of the zero-sequence current resistive component and the zero-sequence current capacitive component, whether the low-voltage power grid line has potential insulation defects or capacitive interference, including: A multi-level low-threshold early warning standard is set for the zero-sequence current resistive component. The absolute value of the zero-sequence current resistive component is monitored to see if it reaches the multi-level low-threshold early warning standard, while simultaneously monitoring the growth trend of the zero-sequence current resistive component. If the absolute value meets the standard or shows a monotonically increasing trend, it is determined that the 400V low-voltage power grid has an early-middle potential insulation hazard. The thresholds of the multi-level low-threshold early warning standard are all lower than the upper limit of the alarm threshold specified by the residual current type electrical fire monitoring detector; or... The numerical sequence of the zero-sequence current capacitive component is recorded during normal operation of the 400V low-voltage power grid as the baseline value of capacitive capacitance. The real-time value of the zero-sequence current capacitive component is monitored for any sudden change relative to the baseline value of capacitive capacitance. If a sudden change occurs, it is determined that there is capacitive capacitance interference in the low-voltage power grid line.

10. The low-voltage power grid insulation monitoring device according to claim 9, characterized in that, The MCU microcontroller module transmits the detection values, insulation hazard analysis results, and early warning information to the human-machine interface module for local display; the MCU microcontroller module also transmits the aforementioned data information to the communication module for external remote communication.

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