Dual-feature zero line falling detection method for three-phase four-wire intelligent electric energy meter

Abstract

The invention relates to the technical field of null line falling detection, in particular to a dual-feature null line falling detection method for a three-phase four-wire intelligent electric energy meter. Comprising the following steps: setting an initial threshold, and calculating the initial threshold as Un * (1 + / -epsilon%) according to rated voltage Un provided by different markets and deviation + / -epsilon% allowed by a power grid; acquiring voltage signals in real time, acquiring L1 phase voltage, L2 phase voltage and L3 phase voltage according to the EMU metering chip, and calculating an average value and a voltage standard deviation of each phase voltage; calculating a dynamic threshold value; a threshold value is set, and after a target threshold value is obtained through calculation, a voltage comparator threshold value is set through a DAC module; calculating the harmonic content of the voltage; verifying voltage harmonic analysis; zero line falling judgment is carried out; after the null line is dropped, null line dropping alarm is carried out; through the process, the accuracy of judgment can be greatly improved, the problem of high false alarm rate caused by dependence of a single feature is avoided, and the reliability and the accuracy are improved.

Description

Technical Field

[0001] This invention relates to the field of neutral wire failure detection technology, and in particular to a dual-feature neutral wire failure detection method for three-phase four-wire smart energy meters. Background Technology

[0002] In modern power systems, three-phase four-wire power supply is widely used in industrial, commercial, and some residential electricity applications. The reliable operation of the three-phase four-wire meter is crucial for monitoring and measuring electrical parameters in this system. The neutral wire plays a vital role in stabilizing the neutral point potential and ensuring voltage balance across all phases. A neutral wire disconnection fault can trigger a series of serious problems. When the neutral wire of a three-phase four-wire meter is disconnected and the load is unbalanced, the neutral point will drift, causing the phase voltages to become unstable at their rated values. Some phase voltages may rise significantly, far exceeding the withstand voltage range of the electrical equipment, easily causing insulation breakdown, equipment damage, or even fires and other safety accidents. Conversely, some phase voltages may drop significantly, preventing the equipment from starting or operating stably.

[0003] Regarding the accuracy of electricity metering, a broken neutral wire can severely interfere with the metering accuracy of three-phase four-wire meters. Meters calculate energy consumption based on three-phase voltage and current. Voltage anomalies caused by a broken neutral wire distort the data collected by the meter, leading to metering deviations and inaccurate billing. For the safety and protection of the power system, timely and accurate detection of broken neutral wire faults is fundamental to ensuring the safe operation of the power grid. Currently, the smart meter industry commonly uses two methods for detecting broken neutral wires: one is a hardware-based detection method that relies on a circuit to form a loop, using a bias voltage injected into the neutral wire circuit to determine the fault; the other is a software algorithm-based detection method based on voltage difference, phase analysis, and imbalance methods.

[0004] However, in the existing judgment methods mentioned above, the reference threshold for the voltage comparator on the circuit is a fixed value, which does not take into account the voltage fluctuations of the power grid in different market areas, which may lead to missed detections. Furthermore, the software judgment relies on a single feature, resulting in a high false alarm rate. It cannot cope with complex fault scenarios such as voltage fluctuations and load changes, and may result in misjudgments or missed detections, leading to low accuracy, real-time performance and reliability of neutral wire detection. Summary of the Invention

[0005] The purpose of this invention is to provide a dual-feature neutral wire detection method for three-phase four-wire smart energy meters. This method addresses the technical problems of existing circuit-sampling voltage comparators using fixed reference thresholds, which fail to account for voltage fluctuations in different market regions, leading to missed alarms. Furthermore, the software's reliance on a single feature results in a high false alarm rate, making it unable to handle complex fault scenarios such as voltage fluctuations and load changes, resulting in misjudgments or missed detections. The method aims to solve these problems.

[0006] To achieve the above objectives, the present invention employs a dual-feature neutral wire detection method for three-phase four-wire smart energy meters, comprising the following steps: Set an initial threshold, and calculate the initial threshold as Un*(1±ε%) based on the rated voltage Un provided by different markets and the allowable deviation ±ε% of the power grid. Real-time acquisition of voltage signals; obtaining the L1 phase voltage, L2 phase voltage, and L3 phase voltage from the EMU metering chip; calculating the average value and standard deviation of each phase voltage. Calculate the dynamic threshold; Set the threshold: After calculating the target threshold, set the voltage comparator threshold through the DAC module. Calculate voltage harmonic content; Verification of voltage harmonic analysis; Perform a zero-wire detection; An alarm will be triggered after the neutral wire is lost.

[0007] In the step of calculating the dynamic threshold: If it is determined that the average voltage Uagv fluctuates within a continuous time T1, it indicates that the power grid is currently unstable and the threshold should be appropriately relaxed to Un*(1±(ε+2)%). Once the power grid stabilizes, if it is determined that there is a deviation between the average voltage Uagv and the rated voltage Un within a continuous time T2, the threshold is updated to Uagv*(1±ε%). Set the upper limit of the fault threshold to 1.2Un. If the voltage is determined to be greater than the upper limit of the fault threshold within a continuous time T3, the neutral wire alarm will be forcibly triggered and dynamic threshold adjustment will no longer be performed.

[0008] In the step of calculating voltage harmonic content: The voltage value is collected by the EMU metering chip, and it is determined whether the voltage value is greater than the minimum start-up voltage. Perform a Fast Fourier Transform on the voltage values ​​collected multiple times; The content of each harmonic and the total harmonic distortion rate are calculated based on the extracted fundamental and harmonic RMS values.

[0009] In the steps of verifying voltage harmonic analysis: If it is determined that the harmonic content of each phase voltage is more than twice the harmonic content under normal grid conditions and the amplitude deviation of each phase harmonic voltage is less than 5%, then a potential neutral wire drop event may occur.

[0010] In the step of determining if the neutral wire has dropped: Read and judge the output value of each phase voltage comparator. If an abnormal return is found in a certain phase, mark that phase as suspicious. After obtaining the status of all phases, a three-phase linkage judgment is performed. That is, if any one phase is abnormal but not all three phases are abnormal, and the total power outage is excluded, it is considered that the neutral wire may have been lost. Further confirmation of the neutral wire failure was made based on voltage harmonic analysis.

[0011] Among the steps for triggering a neutral wire failure alarm after a neutral wire failure occurs: Record the neutral wire failure event, including the time of occurrence and the voltage values ​​of each phase at the time of the abnormality; The relay will trip and the alarm light will flash.

[0012] This invention discloses a dual-feature neutral wire loss detection method for three-phase four-wire smart energy meters. The method involves setting an initial threshold, calculated as Un*(1±ε%) based on the rated voltage Un provided by different markets and the allowable deviation ±ε% of the power grid; real-time acquisition of voltage signals, obtaining the L1, L2, and L3 phase voltages from the EMU metering chip, and calculating the average value and standard deviation of each phase voltage; calculating a dynamic threshold; setting the threshold by setting the voltage comparator threshold through a DAC module after obtaining the calculated target threshold; calculating the voltage harmonic content; verifying voltage harmonic analysis; performing neutral wire loss judgment; and triggering a neutral wire loss alarm upon occurrence of a neutral wire loss. By adding a voltage comparator to the three-phase energy meter circuit, the system can quickly respond to voltage surges, meeting the timeliness requirements of some customers and improving the real-time performance of fault diagnosis. Secondly, the addition of a dynamic threshold calculation function based on the grid status allows for adjustment of the comparator threshold, avoiding misjudgments caused by significant differences in voltage fluctuation ranges across different regions compared to the traditional fixed threshold method, thus improving the adaptability of the energy meter. Finally, by combining the abnormal monitoring of the voltage comparator with the characteristic analysis of voltage harmonic content, the two work together to significantly improve the accuracy of the judgment, avoiding the problem of high false alarm rates caused by reliance on a single feature, and improving reliability and accuracy. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 This is a circuit diagram of the dual-feature neutral wire detection method for three-phase four-wire smart energy meters according to the present invention.

[0015] Figure 2 This is a flowchart of the dual-feature neutral wire detection method for three-phase four-wire smart energy meters according to the present invention.

[0016] Figure 3 This is a flowchart of the steps of the dual-feature neutral wire detection method for three-phase four-wire smart energy meters of the present invention.

[0017] Figure 4 This is a flowchart of steps S300 of the present invention.

[0018] Figure 5 This is a flowchart of steps S500 of the present invention.

[0019] Figure 6 This is a flowchart of steps S700 of the present invention.

[0020] Figure 7 This is a flowchart of steps S800 of the present invention. Detailed Implementation

[0021] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application.

[0022] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0023] It should be understood that although the terms first, second, third, etc., may be used in this application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0024] Please see Figures 1-7 This invention provides a dual-feature neutral wire dropping detection method for three-phase four-wire smart energy meters, comprising the following steps: S100: Set the initial threshold. Calculate the initial threshold as Un*(1±ε%) based on the rated voltage Un provided by different markets and the allowable deviation ±ε% of the power grid. S200: Real-time acquisition of voltage signals, obtaining L1 phase voltage, L2 phase voltage and L3 phase voltage based on EMU metering chip, and calculating the average value and standard deviation of each phase voltage; S300: Calculates dynamic threshold; S400: Set the threshold value. After calculating the target threshold, the voltage comparator threshold is set through the DAC module. S500: Calculates voltage harmonic content; S600: Verify voltage harmonic analysis. If it is determined that the harmonic content of each phase voltage is more than twice the harmonic content under normal grid conditions and the amplitude deviation of each phase harmonic voltage is less than 5%, then mark that a neutral wire drop event may occur. S700: Performs neutral wire detection; S800: After a neutral wire failure occurs, a neutral wire failure alarm will be triggered.

[0025] In this embodiment, an initial threshold is set, calculated as Un*(1±ε%) based on the rated voltage Un provided by different markets and the allowable deviation ±ε% of the power grid; voltage signals are acquired in real time, and the L1, L2, and L3 phase voltages are obtained from the EMU metering chip, calculating the average value and standard deviation of each phase voltage; dynamic thresholds are calculated; thresholds are set, and the calculated target threshold is set through the DAC module to set the voltage comparator threshold; voltage harmonic content is calculated; voltage harmonic analysis is verified; neutral wire drop detection is performed; and a neutral wire drop alarm is triggered after a neutral wire drop occurs; in the above process, the voltage is measured by the three-phase energy meter. Adding a voltage comparator to the circuit can quickly respond to voltage surges, meeting the timeliness requirements of some customers and improving the real-time performance of fault diagnosis. Secondly, the addition of a dynamic threshold calculation function based on the grid status can adjust the comparator threshold, which avoids misjudgment caused by large differences in voltage fluctuation range in different regions compared to the traditional fixed threshold method, thus improving the adaptability of the energy meter. Finally, by combining the abnormal monitoring of the voltage comparator with the characteristic analysis of voltage harmonic content, the two can significantly improve the accuracy of judgment, thus avoiding the problem of high false alarm rate caused by reliance on a single feature, and improving reliability and accuracy. The system includes several mechanisms: voltage signal monitoring, which assesses the stability of the average voltage over a continuous time period. If the average voltage is unstable, the threshold is updated based on the calculated grid instability threshold. If the average voltage is stable but deviates from the rated voltage, the threshold is updated based on the calculated voltage deviation threshold. Otherwise, the threshold is not updated. The system also monitors the voltage comparator output, reading and judging the output values ​​of each phase. If an abnormality is detected in a phase, that phase is marked as suspicious. After obtaining the status of all phases, a three-phase linkage judgment is performed. If any one phase is abnormal, but not all three phases are abnormal, it is considered a possible neutral wire drop, and voltage harmonic analysis is performed. During voltage harmonic analysis, after judging a voltage surge, the system analyzes whether the harmonic content of each phase exceeds twice the harmonic content under normal grid conditions and whether the amplitude deviation of the harmonic voltage in each phase is less than 5%. If the judgment is correct, the neutral wire drop event is recorded, a neutral wire drop alarm is triggered, and abnormality recording and fault handling are performed. Finally, a voltage upper limit warning is issued. If the voltage is judged to be greater than the overvoltage threshold, the abnormal judgment mechanism of monitoring the voltage comparator output and voltage harmonic analysis is directly used to trigger the neutral wire drop alarm, without further dynamic threshold adjustment.

[0026] Furthermore, in the step of calculating the dynamic threshold: S301: If it is determined that the average voltage Uagv fluctuates within a continuous time T1, it indicates that the power grid is currently unstable and the threshold should be appropriately relaxed to Un*(1±(ε+2)%). S302: After the power grid stabilizes, if it is determined that there is a deviation between the average voltage Uagv and the rated voltage Un within the continuous time T2, the threshold is updated to Uagv*(1±ε%). S303: Set the upper limit of the fault threshold to 1.2Un. If the voltage is determined to be greater than the upper limit of the fault threshold within a continuous time T3, the neutral wire alarm will be forcibly triggered and dynamic threshold adjustment will no longer be performed.

[0027] In this implementation, firstly, if it is determined that the average voltage Uagv fluctuates within a continuous time T1, it indicates that the power grid is currently unstable and the threshold needs to be appropriately relaxed to Un*(1±(ε+2)%). Secondly, after the power grid stabilizes, if it is determined that there is a deviation between the average voltage Uagv and the rated voltage Un within a continuous time T2, the threshold is updated to Uagv*(1±ε%). Finally, the upper limit of the fault threshold is set to 1.2Un. If it is determined that the voltage is greater than the upper limit of the fault threshold within a continuous time T3, the neutral wire alarm is forcibly triggered, and dynamic threshold adjustment is no longer performed.

[0028] Furthermore, in the step of calculating the voltage harmonic content: S501: Collects voltage values ​​from the EMU metering chip and determines whether the voltage value is greater than the minimum start-up voltage; S502: Performs Fast Fourier Transform on the voltage values ​​acquired multiple times; S503: Calculate the content of each harmonic and the total harmonic distortion rate based on the extracted fundamental and harmonic RMS values.

[0029] In this embodiment, firstly, the voltage value is collected by the EMU metering chip, and it is determined whether the voltage value is greater than the minimum start-up voltage; secondly, the voltage values ​​collected multiple times are processed by Fast Fourier Transform (FFT); finally, the harmonic content of each harmonic and the total harmonic distortion (THD) are calculated based on the extracted fundamental and harmonic RMS values.

[0030] Furthermore, in the step of determining if the neutral wire has dropped: S701: Read and judge the output value of each phase voltage comparator. If an abnormal return is found in a certain phase, mark that phase as suspicious. S702: After obtaining the status of all phases, a three-phase linkage judgment is performed. That is, if any one phase is abnormal but not all three phases are abnormal, and the total power outage is excluded, it is considered that the neutral wire may have been lost. S703: Further confirmation of the neutral wire failure based on voltage harmonic analysis.

[0031] In this embodiment, firstly, the output values ​​of the voltage comparators for each phase are read and judged. If an abnormal return is read for a certain phase, the phase is marked as suspicious. After obtaining the status of all phases, a three-phase linkage judgment is performed. That is, if any one phase is abnormal and not all three phases are abnormal, and the total power outage is excluded, it is considered that the neutral wire may have been dropped. Finally, the voltage harmonic analysis in the S600 method step is used to further confirm that the neutral wire has been dropped.

[0032] Furthermore, in the steps of triggering a neutral wire failure alarm after a neutral wire failure occurs: S801: Records neutral wire failure events, including the time of occurrence and the voltage values ​​of each phase at the time of the abnormality; S802: Triggers the relay circuit breaker and causes the alarm light to flash.

[0033] In this embodiment, firstly, the neutral wire loss event is recorded, including the time of occurrence and the voltage values ​​of each phase when the abnormality occurs; then, the relay is tripped and the alarm light flashes.

[0034] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein.

[0035] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope.

Claims

1. A dual-feature neutral wire detection method for three-phase four-wire smart energy meters, characterized in that, Includes the following steps: Set an initial threshold, and calculate the initial threshold as Un*(1±ε%) based on the rated voltage Un provided by different markets and the allowable deviation ±ε% of the power grid. Real-time acquisition of voltage signals; obtaining the L1 phase voltage, L2 phase voltage, and L3 phase voltage from the EMU metering chip; calculating the average value and standard deviation of each phase voltage. Calculate the dynamic threshold; Set the threshold: After calculating the target threshold, set the voltage comparator threshold through the DAC module. Calculate voltage harmonic content; Verification of voltage harmonic analysis; Perform a zero-wire detection; An alarm will be triggered after the neutral wire is lost.

2. The dual-feature neutral wire detection method for three-phase four-wire smart energy meters as described in claim 1, characterized in that, In the step of calculating the dynamic threshold: If it is determined that the average voltage Uagv fluctuates within a continuous time T1, it indicates that the power grid is currently unstable and the threshold should be appropriately relaxed to Un*(1±(ε+2)%). Once the power grid stabilizes, if it is determined that there is a deviation between the average voltage Uagv and the rated voltage Un within a continuous time T2, the threshold is updated to Uagv*(1±ε%). Set the upper limit of the fault threshold to 1.2Un. If the voltage is determined to be greater than the upper limit of the fault threshold within a continuous time T3, the neutral wire alarm will be forcibly triggered and dynamic threshold adjustment will no longer be performed.

3. The dual-feature neutral wire detection method for three-phase four-wire smart energy meters as described in claim 1, characterized in that, In the steps of calculating voltage harmonic content: The voltage value is collected by the EMU metering chip, and it is determined whether the voltage value is greater than the minimum start-up voltage. Perform a Fast Fourier Transform on the voltage values ​​collected multiple times; The content of each harmonic and the total harmonic distortion rate are calculated based on the extracted fundamental and harmonic RMS values.

4. The dual-feature neutral wire detection method for three-phase four-wire smart energy meters as described in claim 1, characterized in that, In the steps of verifying voltage harmonic analysis: If it is determined that the harmonic content of each phase voltage is more than twice the harmonic content under normal grid conditions and the amplitude deviation of each phase harmonic voltage is less than 5%, then a potential neutral wire drop event may occur.

5. The dual-feature neutral wire detection method for three-phase four-wire smart energy meters as described in claim 1, characterized in that, In the steps of determining if the neutral wire is missing: Read and judge the output value of each phase voltage comparator. If an abnormal return is found in a certain phase, mark that phase as suspicious. After obtaining the status of all phases, a three-phase linkage judgment is performed. That is, if any one phase is abnormal but not all three phases are abnormal, and the total power outage is excluded, it is considered that the neutral wire may have been lost. Further confirmation of the neutral wire failure was made based on voltage harmonic analysis.

6. The dual-feature neutral wire detection method for three-phase four-wire smart energy meters as described in claim 1, characterized in that, In the steps of triggering a neutral wire failure alarm after a neutral wire failure occurs: Record the neutral wire failure event, including the time of occurrence and the voltage values ​​of each phase at the time of the abnormality; The relay will trip and the alarm light will flash.

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