Measuring device for opening arcing time of low-voltage circuit breaker and judging method thereof

Abstract

The invention discloses a low-voltage circuit breaker opening arcing time measuring device and a judging method thereof. The device comprises a low-voltage circuit breaker main line current measuring circuit which is composed of an enameled coil, a current limiting resistor, an anti-parallel voltage stabilizing diode set, an input resistor, a voltage sensor and a grounding resistor. The function is that an alternating current signal of a main circuit of the low-voltage circuit breaker is converted into an induced voltage of the enameled coil according to the electromagnetic induction principle; the induced voltage quality adjusting circuit is composed of a voltage follower, a reverse series voltage stabilizing diode group and an RC filter; and the induced voltage time sequence analysis processing and opening arcing time judgment module is composed of a differential circuit, an analog-to-digital converter, a digital signal processor, a display and a data memory. The device aims at improving the safety in the electric power operation process through a non-physical measurement mode, the method aims at improving the fault diagnosis accuracy and efficiency of the circuit breaker in the opening process, and efficient technical support is provided for equipment management and system maintenance of a low-voltage power distribution system.

Description

Technical Field

[0001] The present invention relates to a measuring device and a determination method for the arcing time of a low-voltage circuit breaker during opening based on the analysis of the characteristics of the main circuit current signal, and belongs to the technical field of the operation performance detection of low-voltage circuit breakers. Background Art

[0002] As an important electrical switching device for the operation of distribution network systems such as ring main units, switchgear, and pole-mounted switches, the opening and closing performance during the operation of a low-voltage circuit breaker will directly affect the reliability and stability of the power supply of the distribution network. During multiple opening and closing processes of the low-voltage circuit breaker, wear will occur between the moving contact and the static contact of the main circuit, and this wear degree will have a negative impact on the arcing time during opening and the arcing time during closing of the low-voltage circuit breaker, thereby affecting the opening and closing performance of the circuit breaker during operation. In view of this phenomenon, the operation performance quality of the moving and static contacts of the main circuit of the low-voltage circuit breaker can be determined by the arcing time during opening or the arcing time during closing, and effective technical support can be provided for the subsequent operation and maintenance of low-voltage circuit breaker equipment and the reliability of the power supply of the distribution network.

[0003] Although the arcing phenomenon between the moving and static contacts of a low-voltage circuit breaker is a high-temperature and high-brightness discharge phenomenon, since the opening and closing processes of the low-voltage circuit breaker are in a closed space, and this closed space is filled with media such as vacuum, sulfur hexafluoride, or oil, it is very difficult to determine the arcing time during opening of the low-voltage circuit breaker from the perspectives of image recognition, temperature measurement, etc.

[0004] Chinese Patent CN202010403998.5 discloses an arcing time measurement method based on the comparison of the no-load test and the load test of a circuit breaker. Based on the measurement data such as the opening control current curve, the contact voltage curve, the stroke curve, and the main circuit current curve of the circuit breaker, first, the position of the initial opening point of the stroke curve between the moving and static contacts of the circuit breaker is determined during the no-load test, and then the division ratio of this initial opening point position in the entire stroke between the moving and static contacts is applied to the load test process to determine the arcing time of the circuit breaker. However, with the multiple opening and closing operations of the moving and static contacts of the main circuit of the circuit breaker, and the structural accuracy aging of the attached mechanical action device, the length of the inherent stroke between the moving and static contacts of the circuit breaker changes, thereby affecting the reliability of the stroke curve data and the accuracy of the measurement of the arcing time of the circuit breaker.

[0005] Chinese Patent Application CN202310345705.6 discloses a method for measuring the opening and closing time of a circuit breaker based on the analysis of AC current harmonics and the discrimination of the mutation points of the fundamental DC current curve. The method includes collecting the current signal during the opening and closing process of the main circuit of the circuit breaker, as well as processes such as frequency decomposition, bandwidth range setting, filtering, and determination of the mutation moment of the fundamental current curve of the current signal, so as to determine the opening and closing moments and the starting moments of opening and closing of the circuit breaker. However, the effective collection of the current signal during the opening and closing process of the main circuit of the circuit breaker is a prerequisite for the effective implementation of this patent. Therefore, designing a safe and reasonable measuring device for the opening and closing current of the main line of a low-voltage circuit breaker and performing simple and effective analysis and processing on the measured current signal are essential conditions for realizing the determination of the opening and closing time of the circuit breaker.

[0006] In summary, these technologies for measuring the arc burning time or opening and closing time of low-voltage circuit breakers do not have strong practicality and applicability, and none of them can comprehensively consider the integration between the hardware measuring device and data information processing. Summary of the Invention

[0007] Object of the Invention: In order to overcome the deficiencies in the prior art, the present invention provides a measuring device and a determination method for the arc burning time of the opening of a low-voltage circuit breaker; based on the principle that an alternating magnetic field generates an induced voltage in an enameled coil, this device converts the current signal of the main line of the low-voltage circuit breaker into a voltage signal, having the safety of live operation with non-physical contact; this method, on the basis of measuring the current signal of the main line of the low-voltage circuit breaker, through reasonable circuit design, selection of component models and electrical parameters, converts this analog signal into a digital signal that can be recognized and received by a digital signal processor, thus laying a foundation for the analysis and processing of the induced voltage time series and the determination of the arc burning time of the opening of the low-voltage circuit breaker.

[0008] Technical Solution: To achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] A measuring device for the arc burning time of the opening of a low-voltage circuit breaker includes a measuring circuit for the current of the main line of the low-voltage circuit breaker, an adjustment circuit for the quality of the induced voltage, an analysis and processing module for the induced voltage time series, and a determination module for the arc burning time of the opening.

[0010] The measuring circuit for the current of the main line of the low-voltage circuit breaker includes an enameled coil arranged on the side of the main line of the low-voltage circuit breaker, which is used to convert the current signal of the main line of the low-voltage circuit breaker into the induced voltage of the enameled coil and perform overvoltage protection and measurement on the induced voltage; generally speaking, it is required that the enameled coil should be in close contact with the main line of the low-voltage circuit breaker, and its function is to improve the efficiency of converting the alternating current (which is also an alternating magnetic field) of the main line of the low-voltage circuit breaker into the induced voltage of the enameled coil.

[0011] The adjustment circuit for the induced voltage quality optimally adjusts the induced voltage, including voltage following, signal isolation, impedance matching, and RC filtering;

[0012] The induced voltage time series analysis and processing and opening arcing time determination module smooths the timing curve of the optimally adjusted induced voltage and extracts the core distortion value, and determines the opening arcing time length of the low-voltage circuit breaker according to the extracted core distortion value.

[0013] Specifically, in the measurement circuit of the main line current of the low-voltage circuit breaker, the induced current of the enameled coil is adjusted through a current-limiting resistor, and overvoltage protection in both the positive and negative directions is provided for the enameled coil through a reverse-parallel voltage-stabilizing diode group; the current-limiting resistor and the reverse-parallel voltage-stabilizing diode group jointly complete the preliminary adjustment and processing of the induced voltage to adapt to the voltage ranges of subsequent voltage followers, analog-to-digital converters, etc.; for example, the induced voltage of ±100V can be adjusted to ±5V or ±3V, etc., with the aim of controlling the voltage amplitude measured and output by the voltage sensor within the acceptable range of the voltage follower and the analog-to-digital converter.

[0014] Specifically, in the measurement circuit of the main line current of the low-voltage circuit breaker, the number of turns of the enameled coil and the resistance value of the current-limiting resistor are determined according to the current amplitude of the main line of the low-voltage circuit breaker to ensure the effectiveness and analyzability of the peak-to-peak value of the induced voltage in the enameled coil and limit the induced current in the enameled coil within a set range. Specifically, the number of turns N of the enameled coil is determined by the maximum current amplitude of the main line of the low-voltage circuit breaker and the principle of induced electromotive force; for example: when the measurement range is determined, this also indicates that the range of the induced voltage E of the enameled coil has been determined, and then the magnetic flux Φ generated by the maximum current of the main line of the low-voltage circuit breaker in the enameled coil and the formula are used to determine the number of turns N of the enameled coil; in the formula, dt represents the differential of time.

[0015] Specifically, in the measurement circuit of the main line current of the low-voltage circuit breaker, the reverse-parallel voltage-stabilizing diode group realizes overvoltage protection in both the positive and negative directions of the enameled coil by limiting the amplitude of the induced voltage in both the positive and negative directions. The induced voltage of the enameled coil is an alternating voltage in both the positive and negative directions, so the reverse-parallel voltage-stabilizing diode group can realize electrical safety protection for the components of the subsequent measurement circuit by limiting the amplitude of this alternating voltage in both the positive and negative directions.

[0016] Specifically, in the measurement circuit of the main line current of the low-voltage circuit breaker, the measurement and proportional conversion of the induced voltage are completed through a circuit composed of an input resistor, a voltage sensor, and a grounding resistor. The voltage sensor should have high measurement accuracy and can achieve different measurement transformation ratios by changing the resistance values of the input resistor and the grounding resistor. For example, by using the LV25-P type voltage sensor produced by LEM Company, an alternating voltage measurement accuracy of ±0.5% can be achieved. In particular, the measurement accuracy of the LV25-P type voltage sensor can be further corrected and improved through software program algorithms and hardware experimental tests.

[0017] Specifically, in the adjustment circuit of the induced voltage quality, the voltage follower is used to reduce the signal attenuation of the induced voltage during transmission and ensure that the induced voltage maintains effective driving ability during transmission. The circuit composed of a reverse series voltage stabilizing diode group and an RC filter is used to improve the signal response speed of the induced voltage and reduce the abnormal spike data distortion points and high-frequency noise of the induced voltage.

[0018] Specifically, in the adjustment circuit of the induced voltage quality, the voltage follower has excellent characteristics of low offset and high stability and can effectively transmit weak measurement voltage signals. For example: by using a bipolar OP07 type voltage follower (amplifier) with non-chopper-stabilized zero characteristics, a measurement voltage offset of up to 150 μV, a measurement voltage error of up to 2 μV / month, and a following ability for a measurement voltage range of ±22 V can be achieved. Moreover, according to the need to adjust the measurement voltage range, the voltage amplitude amplification or reduction ability of this voltage follower can be achieved by building an appropriate peripheral circuit and setting the resistance values.

[0019] Specifically, in the adjustment circuit of the induced voltage quality, in addition to having an overvoltage protection function, the reverse series voltage stabilizing diode group can also complete the fast level shift of the measurement voltage signal. For example, it can quickly achieve the processing and adjustment of the measurement voltage signal in the positive and negative directions.

[0020] Specifically, in the adjustment circuit of the induced voltage quality, the RC filter can filter out the high-frequency harmonics of the measurement voltage signal, thereby improving the response speed of the measurement voltage transmitted to the differential circuit and the analog-to-digital converter and eliminating individual induced voltage distortion data generated by the hardware circuit. In particular, the value of the RC filter is adjustable and can achieve the filtering function of induced voltage harmonics with different frequencies according to the adjustment and optimization needs of the hardware circuit.

[0021] Specifically, the induction voltage time series analysis and processing and opening arc time determination module is divided into two parts: hardware and software. The hardware part includes a differential circuit, an analog-to-digital converter, a digital signal processor, a display, and a memory. The software part is a software program running in the digital signal processor. The optimized adjusted induction voltage is converted from an analog signal to a digital signal through the differential circuit and the analog-to-digital converter. The digital signal processor processes the digital signal into a smooth time series curve by the polynomial fitting method, and completes the optimized setting of the polynomial order through error analysis and comparison, and determines the core abnormal value by the adjacent time series data slope mutation method and the set threshold. The role of the display is to complete the display of data information such as the induction voltage time series curve, the start / stop time of the low-voltage circuit breaker arc. The memory can complete the storage of information such as the original induction voltage data and the analysis process data.

[0022] Specifically, the optimized adjusted induction voltage needs to be transformed from analog to digital before analysis and processing. To improve the conversion speed, resolution, and accuracy of analog-to-digital conversion, a single-channel flash analog-to-digital converter (Flash ADC) can be used to achieve the preliminary processing of the induction voltage. For example, the LS08D1000 analog-to-digital converter independently developed and produced in China has the advantages of low power consumption (510mW), high speed (1GSPS), high resolution (8Bits), and low error rate (10 -13 ) and can convert an 800mV peak-to-peak analog voltage signal into a digital signal with high quality. In particular, the differential circuit and the domestic LS08D1000 analog-to-digital converter need to cooperate with each other to achieve high-quality analog-to-digital conversion. For example, by using the ultra-high-speed differential line driver LMH6555 and its peripheral auxiliary circuits, the advantages of weak analog signal recognition and strong anti-electromagnetic interference can be achieved.

[0023] Specifically, by calculating and analyzing the resistance values of the LV25-P type voltage sensor, the input resistance, and the grounding resistance, the electrical signal compatibility and matching between the LV25-P type voltage sensor, the bipolar OP07 type voltage follower, and the LS08D1000 analog-to-digital converter can be achieved. The following is an example of the configuration process:

[0024] (1) Assuming that the current amplitude of the enameled coil is ±10mA, when the external input resistance of the LV25-P type voltage sensor is 1500Ω, the voltage measurement range of the LV25-P type voltage sensor is ±10mA * 1500Ω = ±15V;

[0025] (2) Since the output current range of the LV25-P type voltage sensor is ±25 mA, when the grounding resistance of the LV25-P type voltage sensor is 10 Ω, its output voltage range is ±25 mA * 10 Ω = ±0.25 V, and this ±0.25 V voltage range fully meets the requirements of the 800 mV peak-to-peak input signal range of the LS08D1000 analog-to-digital converter;

[0026] (3) Based on the above steps (1) and (2), the input voltage / output voltage ratio of the LV25-P type voltage sensor can be calculated as 15 V / 0.25 V = 60, and this ratio is beneficial to the next-step analysis and processing of the induced voltage signal.

[0027] Specifically, in the induced voltage time series analysis and processing and opening arc time determination module, the adjacent time series data slope mutation method is used to determine the core anomaly value, and then the opening arc time length of the low-voltage circuit breaker is determined. Specifically: for the smoothed time series curve, the adjacent time series data slope mutation method and a set threshold are used to determine the core anomaly value, and the moment corresponding to the first core anomaly value is determined as the starting moment t1 of the opening arc of the low-voltage circuit breaker; after the starting moment t1, the zero-point constant value judgment method is used to determine the stopping moment t2 of the opening arc of the low-voltage circuit breaker; the difference between the starting moment t1 and the stopping moment t2 is determined as the opening arc time length of the low-voltage circuit breaker.

[0028] A method for determining the opening arc time of a low-voltage circuit breaker includes the following steps:

[0029] Step1: Install an enameled coil on the side of the main circuit of the low-voltage circuit breaker, convert the current signal of the main circuit of the low-voltage circuit breaker into the induced voltage of the enameled coil, and perform overvoltage protection and measurement on the induced voltage;

[0030] Step2: Perform optimization adjustments on the induced voltage, including voltage following, signal isolation, impedance matching, and RC filtering, to reduce the signal attenuation of the induced voltage during transmission, ensure that the induced voltage maintains an effective driving ability during transmission, improve the signal response speed of the induced voltage, reduce the abnormal spike data anomalies and high-frequency noise of the induced voltage, and obtain the optimized adjusted induced voltage;

[0031] Step3: Convert the optimized adjusted induced voltage from an analog signal to a digital signal, process the digital signal into a smooth time series curve by the polynomial fitting method, and complete the optimized setting of the polynomial order through error analysis and comparison;

[0032] Step 4: For the smoothed time series curve, use the adjacent time series data slope mutation method and set a threshold to determine the core outliers, and determine the starting moment t1 of the arc extinction during the opening of the low-voltage circuit breaker as the moment corresponding to the first core outlier;

[0033] Step 5: After the starting moment t1, use the zero-point constant value judgment method to determine the stopping moment t2 of the arc extinction during the opening of the low-voltage circuit breaker, that is, after the starting moment t1, determine the moment when the time series curve is first constant at zero as the stopping moment t2 of the arc extinction during the opening of the low-voltage circuit breaker;

[0034] Step 6: Determine the difference between the starting moment t1 and the stopping moment t2 as the arc extinction time length during the opening of the low-voltage circuit breaker.

[0035] In the above method for determining the arc extinction time during the opening of the low-voltage circuit breaker, the execution process of the software program for the induction voltage time series and the determination of the starting / stopping time of the arc extinction during the opening of the low-voltage circuit breaker can be completed using the Python computer language, and the hardware environment for running this software program uses the TMS320 series digital signal processors. The Python computer language has the advantages of readability, simplicity, and a rich function standard library, which can improve the quality and efficiency of software program writing; the TMS320 series digital signal processors have the advantages of fast calculation speed, high precision, stable operation, and low price; through the PySerial library and serial communication function, the software and hardware compatibility and operation efficiency between the Python computer language and the TMS320 series digital signal processors can be improved.

[0036] Beneficial effects: The measuring device and its determination method for the arc extinction time during the opening of the low-voltage circuit breaker provided by the present invention have the following advantages compared with the prior art: 1. The present invention utilizes the electromagnetic induction principle to realize the conversion of the alternating current in the main circuit of the low-voltage circuit breaker into the induction voltage of the enameled coil in a non-physical contact manner, improving the safety and convenience of the entire measuring device; 2. The present invention realizes the characteristics such as overvoltage protection, response speed, voltage stabilization ability, and filtering ability of the enameled coil induction voltage by designing mutually compatible and matching hardware circuits such as voltage sensors, voltage followers, and analog-to-digital converters; 3. The present invention adopts a method of comprehensive application of software and hardware to realize the smoothing processing of the induction voltage time series curve, and determines the arc extinction time during the opening of the low-voltage circuit breaker by extracting data outliers; 4. The present invention can improve the accuracy and efficiency of fault diagnosis during the opening of the low-voltage circuit breaker, providing efficient technical support for the system management and maintenance of low-voltage power distribution equipment. Description of the Drawings

[0037] Figure 1 It is a schematic diagram of the overall structure of the measuring device for the arc extinction time during the opening of the low-voltage circuit breaker;

[0038] Figure 2For different forms of the relative position between the enameled coil and the main circuit of the low-voltage circuit breaker during the actual measurement process;

[0039] Figure 3 For the overall electrical compatibility design of the measuring device for the arc extinguishing time of the low-voltage circuit breaker during opening;

[0040] Figure 4 For the calibration method to improve the measurement accuracy of the voltage sensor;

[0041] Figure 5 For the method of selecting the polynomial order during the smoothing process of the timing curve of the induced voltage;

[0042] Figure 6 For the determination method of the arc extinguishing time of the low-voltage circuit breaker during opening;

[0043] The figure includes: 1 - Main circuit of the low-voltage circuit breaker; 2 - Alternating current; 3 - Alternating magnetic field; 4 - Enameled coil; 5 - Current-limiting resistor 5; 6 - Reverse-parallel voltage-stabilizing diode group; 7 - Input resistor; 8 - Voltage sensor; 9 - Grounding resistor; 10 - Voltage follower; 11 - Reverse-series voltage-stabilizing diode group; 12 - RC filter. Specific implementation mode

[0044] To more clearly illustrate the measuring device for the arc extinguishing time of the low-voltage circuit breaker of the present invention and its determination method, the following will be comprehensively elaborated in the form of an illustration with drawings. It should be noted that: Without adopting new technologies, new methods or new theories, only by simply selecting components and adjusting electrical parameters for the structure shown in the drawings of the present invention, it is also possible to measure and determine the arc extinguishing time of other low-voltage switches.

[0045] As Figure 1 shown, for the overall structure of a measuring device for the arc extinguishing time of a low-voltage circuit breaker, it includes three main parts: the measuring circuit for the current of the main circuit of the low-voltage circuit breaker, the adjustment circuit for the quality of the induced voltage, and the module for analyzing and processing the time series of the induced voltage and determining the arc extinguishing time. The following will further explain the present invention from the perspectives of composition, installation, configuration, implementation, etc.

[0046] The first part: The measuring circuit for the current of the main circuit of the low-voltage circuit breaker

[0047] The measuring circuit for the main line current of the low-voltage circuit breaker includes an enameled coil arranged on the side of the main line of the low-voltage circuit breaker, which is used to convert the current signal of the main line of the low-voltage circuit breaker into the induced voltage of the enameled coil, and adjust the induced current of the enameled coil through a current-limiting resistor. The enameled coil is protected against overvoltage in both positive and negative directions by a reverse-parallel voltage stabilizing diode group; the current-limiting resistor and the reverse-parallel voltage stabilizing diode group jointly complete the preliminary adjustment and processing of the induced voltage; the measurement and proportional conversion of the induced voltage are completed through a circuit composed of an input resistor, a voltage sensor, and a grounding resistor.

[0048] In the measuring circuit for the main line current of the low-voltage circuit breaker: First, according to Ampere's rule, an alternating current will generate an alternating magnetic field around the main line of the low-voltage circuit breaker; then, according to the principle of electromagnetic induction, an induced voltage will occur in the enameled coil in the alternating magnetic field; finally, the current-limiting resistor is used to ensure that the induced current in the enameled coil is within a limited amplitude (safe amplitude).

[0049] To ensure that the amplitude of the induced voltage of the enameled coil is within a safe range, a reverse-parallel voltage stabilizing diode group is used to protect the induced constant voltage of the enameled coil against overvoltage; since the induced voltage of the enameled coil alternates in both positive and negative directions, a reverse-parallel voltage stabilizing diode group can complete the overvoltage protection function.

[0050] The method for determining the number of turns N of the enameled coil is as follows: When the measurement range is determined, this indicates that the range of the induced voltage E of the enameled coil has been determined, and then the magnetic flux Φ generated by the maximum alternating current in the enameled coil and the formula are used to determine the number of turns N of the enameled coil; where: dt represents the differential of time t, and time t is related to the frequency of the alternating current; under normal circumstances, the alternating current in China's power distribution network is 50Hz, then time t = 0.02s.

[0051] To maintain electrical compatibility with the subsequent circuit, the overvoltage protection amplitude (maximum value) of the reverse-parallel voltage stabilizing diode group is selected as ±10V, and the current limit of the enameled coil is set to ±10mA.

[0052] To improve the measurement accuracy of the induced voltage of the enameled coil, a LV25-P type voltage sensor produced by LEM Company is selected as the voltage sensor. The operating supply voltage of this sensor is ±15V, and it can achieve an alternating voltage measurement accuracy of ±0.5%.

[0053] Specifically, the process of high-precision measurement and proportional conversion of the induced voltage of the enameled coil composed of an input resistor, a voltage sensor, and a grounding resistor is as follows:

[0054] (1) Set the current limit of the enameled coil to ±10 mA. Then, when the external input resistance 7 of the LV25-P type voltage sensor is 1500 Ω, the voltage measurement range of the LV25-P type voltage sensor is ±10 mA * 1500 Ω = ±15 V;

[0055] (2) Since the output current range of the LV25-P type voltage sensor is ±25 mA, when the grounding resistance 9 of the LV25-P type voltage sensor is 10 Ω, its output voltage range is ±25 mA * 10 Ω = ±0.25 V. This ±0.25 V voltage range fully meets the amplitude requirements of the analog input signal for the analog-to-digital converter in the subsequent circuit;

[0056] (3) Based on the above steps (1) and (2), it can be calculated that the ratio of the input voltage to the output voltage of the LV25-P type voltage sensor is 15 V / 0.25 V = 60. This ratio is beneficial for the next step of data analysis and processing of the induced voltage signal.

[0057] Part Two: Adjustment Circuit for the Quality of the Induced Voltage

[0058] The adjustment circuit for the quality of the induced voltage performs optimized adjustments on the induced voltage, including voltage following, signal isolation, impedance matching, and RC filtering; it reduces the signal attenuation of the induced voltage during transmission through a voltage follower, and ensures that the induced voltage maintains an effective driving ability during transmission. It improves the signal response speed of the induced voltage and reduces the abnormal spike data distortion points and high-frequency noise of the induced voltage through a circuit composed of a reverse series voltage regulator diode group and an RC filter.

[0059] The function of the voltage follower is to improve the driving ability of the induced voltage signal so as to effectively transmit the induced voltage signal to the analog-to-digital converter. The voltage follower has excellent characteristics of low offset and high stability, and can achieve the effective transmission of weak induced voltage signals. For example: by using a bipolar OP07 type voltage follower (amplifier) with non-chopped zero stability characteristics, a measurement voltage offset of up to 150 μV, a measurement voltage error of up to 2 μV / month, and a following ability for a measurement voltage range of ±22 V can be achieved; and, according to the need for adjusting the measurement voltage range, the voltage amplitude of the voltage follower 10 can be amplified or reduced by appropriately setting the values of the peripheral resistors.

[0060] The reverse series voltage regulator diode group has two functions: one is overvoltage protection; the other is to quickly realize the processing and adjustment of the induced voltage signal in the positive and negative directions (signal level shift function).

[0061] The function of the RC filter is to improve the response speed of the induced voltage signal transmitted to the analog-to-digital converter and reduce the abnormal spike data outliers and high-frequency noise in the induced voltage time series; the resistance and capacitance in the RC filter have adjustable characteristics, aiming to achieve the filtering function of different induced voltage harmonic orders according to the adjustment and optimization needs of the hardware circuit.

[0062] Part Three: Induced Voltage Time Series Analysis and Processing and Tripping Arcing Time Determination Module

[0063] The induced voltage time series analysis and processing and tripping arcing time determination module smooths the timing curve of the optimized and adjusted induced voltage and extracts the core outliers, and determines the tripping arcing time length of the low-voltage circuit breaker according to the extracted core outliers; it includes a differential circuit, an analog-to-digital converter, a digital signal processor, a display, and a memory. The optimized and adjusted induced voltage is converted from an analog signal to a digital signal through the differential circuit and the analog-to-digital converter. The digital signal processor processes the digital signal into a smooth timing curve by the polynomial fitting method, and completes the optimized setting of the polynomial order through error analysis and comparison. The core outliers are determined by the adjacent time series data slope mutation method and the set threshold; the function of the display is to complete the display of data information such as the induced voltage timing curve and the tripping arcing start / stop moment of the low-voltage circuit breaker; the memory can complete the storage of information such as the original induced voltage data and the analysis process data.

[0064] In order to improve the conversion speed, resolution, and accuracy of the induced voltage analog / digital quantity, a single-channel flash analog-to-digital converter (Flash ADC) is used to achieve the preliminary processing of the induced voltage. For example: The domestically developed and produced LS08D1000 analog-to-digital converter has the advantages of low power consumption (510mW), high speed (1GSPS), high resolution (8Bits), and low error rate (10 -13 ) and can convert an 800mV peak-to-peak analog voltage signal into a digital signal with high quality.

[0065] The domestic LS08D1000 analog-to-digital converter needs to cooperate with the differential circuit to achieve high-quality conversion of analog / digital quantity. For example: By using the ultra-high-speed differential line driver LMH6555 and its peripheral auxiliary circuit, the advantages of weak analog signal recognition and strong anti-electromagnetic interference can be achieved.

[0066] Part Four: Two Different Installation Methods between the Enameled Coil and the Main Circuit of the Low-Voltage Circuit Breaker during the Actual Measurement Process

[0067] In the actual application process, due to the characteristics of the equipment structure, it is impossible for the enameled coil to only appear parallel to the main circuit of the low-voltage circuit breaker ( Figure 1As shown in the figure, the shape of the main circuit of the low-voltage circuit breaker may be curved, vertical, inclined, etc. Therefore, the enameled coil needs to change its shape to maintain close contact with the main circuit of the low-voltage circuit breaker. As Figure 2 shown, there are two different installation methods between the enameled coil and the main circuit of the low-voltage circuit breaker:

[0068] Installation method ①: When the low-voltage circuit breaker is installed at the upper end of the utility pole (commonly known as the pole-mounted switch), part of the edge of the enameled coil is in close contact with the main circuit of the low-voltage circuit breaker, aiming to increase the alternating magnetic flux Φ generated by the alternating current in the main circuit of the low-voltage circuit breaker in the enameled coil.

[0069] Installation method ②: When the low-voltage circuit breaker is installed inside the distribution cabinet or ring main unit (commonly known as the box-type substation switch), part of the edge of the enameled coil is installed close to the path of the main circuit of the low-voltage circuit breaker, and the purpose is also to increase the alternating magnetic flux Φ generated by the alternating current in the main circuit of the low-voltage circuit breaker in the enameled coil.

[0070] The enameled coil is generally cast with an insulating material with electrical insulation characteristics and flexibility, aiming to further improve the electrical insulation characteristics and shape adjustability of the enameled coil.

[0071] To improve the portability and ease of operation of the measurement circuit and its software and hardware system, an insulating blanket is used to tightly wrap part of the edge of the enameled coil and the main circuit of the low-voltage circuit breaker, and an insulating clip is used to improve the firmness of the insulating blanket's wrapping of the enameled coil and the main circuit of the low-voltage circuit breaker, thus realizing the above two installation methods ① and ② from the perspective of application practice.

[0072] Part Five: Overall Design of the Measuring Device for the Arcing Time of the Low-Voltage Circuit Breaker during Opening

[0073] As Figure 3 shown, for the overall electrical compatibility design of the measuring device for the arcing time of the low-voltage circuit breaker during opening, by means of calculating and selecting the number of turns of the enameled coil, overvoltage protection, measurement ratio, improving driving ability, etc., the entire electrical compatibility process of the designed measurement circuit is as follows:

[0074] (1) According to the amplitude of the alternating current in the main circuit of the low-voltage circuit breaker, calculate and select the number of turns N of the enameled coil so that the amplitude of the induced voltage of the entire enameled coil is within ±10V;

[0075] (2) Select a zener diode with a regulated voltage value of 10V and achieve ±10V overvoltage protection through a reverse parallel structure;

[0076] (3) By designing the resistance values of the input resistance and the grounding resistance, the measurement ratio of the LV25-P type voltage sensor is realized to be 60, its measurement range is ±15V, and the output range is ±0.25V;

[0077] (4) The voltage follower OP07 only improves the driving ability for the voltage uploaded by the LV25-P type voltage sensor, without amplifying or reducing its voltage amplitude (i.e., 1:1).

[0078] (5) The domestic LS08D1000 type analog-to-digital converter is selected, and the peak-to-peak voltage it can recognize and process is 800 mV (±0.4 V), meeting the requirement of ±0.25 V uploaded by the voltage follower OP07.

[0079] As Figure 4 shown, it is a calibration method to improve the measurement accuracy of the voltage sensor. Through error analysis and gain coefficient design, the measurement accuracy of the voltage sensor for the induced voltage of the enameled coil can be further improved on the basis of hardware measurement. The following is an example:

[0080] (1) When the voltage sensor is not powered on, if the software system of the digital signal processor receives a measurement value Z = -X = -20 (the measured voltage Y = 0 V), then the value -20 is the non-powered-on error value of the hardware measurement device.

[0081] (2) Power on the voltage sensor and actually measure the induced voltage of the enameled coil, and assume that the software system of the digital signal processor obtains a measurement value Z = 1020 at this time.

[0082] (3) In the above step (2), if the value of the measured voltage Y is known (Y = 0.2 V), then the gain coefficient K = (Z - 20) / Y = (1020 - 20) / 0.2 = 5000 can be calculated.

[0083] (4) According to the calculation and analysis results of the above steps (1) and (3), set the gain coefficient K = 5000.

[0084] (5) The high-precision induced voltage value measured by the software system of the digital signal processor is V = (Z - 20) / K.

[0085] It should be noted that: in the above calibration process to improve the measurement accuracy of the voltage sensor, the read value Z of the software system is a value after analog-to-digital conversion, and this value is not the actual measured induced voltage value. Generally, the larger the gain coefficient K, the higher its resolution, and the more it can improve the measurement accuracy of the voltage sensor for the induced voltage of the enameled coil.

[0086] As Figure 5As shown, it is a method for selecting the polynomial order in the process of smoothing the induction voltage time series curve. During the actual measurement process, considering factors such as hardware circuit interference and high-order harmonics of the alternating current in the main circuit of the low-voltage circuit breaker, the measured induction voltage time series curve will have local fluctuations, as shown in Figure 5 the original data curve in. Therefore, the method of polynomial fitting is used to smooth the measured induction voltage time series curve. For example: From Figure 5 the comparison of the results of smoothing the original data with the two polynomial orders shown, it can be seen that selecting the order of 7 can improve the consistency (lower error) before and after smoothing the induction voltage time series.

[0087] In particular, by selecting an appropriate polynomial order, the local small fluctuations of the induction voltage time series curve can be smoothed, but the curve with large local fluctuations will not be smoothed. Therefore, the smoothing process of the induction voltage time series curve will not have a negative impact on the subsequent determination of the arc ignition start time t1 and stop time t2 of the low-voltage circuit breaker.

[0088] Part Six: Implementation Process of the Test Device for the Arc Extinguishing Time of the Low-Voltage Circuit Breaker

[0089] Based on the measurement device for the arc extinguishing time of the low-voltage circuit breaker composed of the above three main parts, the method for determining the arc extinguishing time of the low-voltage circuit breaker is realized, including the following steps:

[0090] Step1. Install an enameled coil on the side of the main circuit of the low-voltage circuit breaker, convert the current signal of the main circuit of the low-voltage circuit breaker into the induction voltage of the enameled coil, and perform overvoltage protection and measurement on the induction voltage;

[0091] Step2. Perform optimization adjustments on the induction voltage, including voltage following, signal isolation, impedance matching, and RC filtering, to reduce the signal attenuation of the induction voltage during transmission, ensure that the induction voltage maintains effective driving ability during transmission, improve the signal response speed of the induction voltage, and reduce the abnormal spike data singularities and high-frequency noise of the induction voltage, so as to obtain the optimized adjusted induction voltage;

[0092] Step3. Convert the optimized adjusted induction voltage from an analog signal to a digital signal, process the digital signal into a smooth time series curve by the polynomial fitting method, and complete the optimized setting of the polynomial order through error analysis and comparison; the calculation formula for error analysis is Error=(D1-D2) / D1, where D1 represents the original data and D2 represents the fitted data;

[0093] Step 4: For the smoothed time series curve, the adjacent time series data slope mutation method and a set threshold are used to determine the core abnormal values, and the moment corresponding to the first core abnormal value is determined as the starting moment t1 of the arc burning during the opening of the low-voltage circuit breaker.

[0094] Step 5: After the starting moment t1, the zero-point constant value judgment method is used to determine the stopping moment t2 of the arc burning during the opening of the low-voltage circuit breaker, that is, after the starting moment t1, the first moment that remains constant at zero on the time series curve is determined as the stopping moment t2 of the arc burning during the opening of the low-voltage circuit breaker.

[0095] Step 6: The difference between the starting moment t1 and the stopping moment t2 is determined as the arc burning time length of the low-voltage circuit breaker during opening.

[0096] In the algorithm process of this judgment method, the software program execution process uses the Python computer language, and the hardware environment for running this software program is the TMS320 series digital signal processors. The Python computer language has the advantages of readability, simplicity, and a rich function standard library, which can improve the quality and efficiency of software program writing; the TMS320 series digital signal processors have the advantages of fast calculation speed, high precision, and stable operation; through the PySerial library and the serial port communication function, the software and hardware compatibility and operation efficiency between the Python computer language and the TMS320 series digital signal processors can be improved.

[0097] Part VII: Measurement Results of the Arc Burning Time during the Opening of the Low-voltage Circuit Breaker

[0098] As Figure 6 shown, it is the discrimination method for the arc burning time during the opening of the low-voltage circuit breaker. Figure 6 For the main circuit current curve 13 of the low-voltage circuit breaker shown in, its original data (before smoothing) is from the real physical data before and after the opening of a certain 10 kV distribution network low-voltage circuit breaker. After the current curve 13 is smoothed, it can be clearly discriminated the starting moment t1 of the arc burning corresponding to the first abnormal value point of the current curve, and the stopping moment t2 of the arc burning. The difference between the moment t2 and the moment t1 is the arc burning time of the low-voltage circuit breaker during opening.

[0099] The starting moment t1 is the moment when the closing signal 14 of the low-voltage circuit breaker changes from high level to low level, and the stopping moment t2 is the moment when the opening signal 15 of the low-voltage circuit breaker changes from low level to high level. High level represents the valid bit.

[0100] Furthermore, based on Ampere's rule and the principle of electromagnetic induction, the induced voltage curve of the enameled coil is exactly the same as the main circuit current curve 13 of the low-voltage circuit breaker in terms of frequency and shape, except for a certain difference in amplitude between the two. Therefore, it is entirely possible to analyze and process the induced voltage curve of the enameled coil and then accurately determine the arcing time during opening of the low-voltage circuit breaker. So, Figure 6 The example of determining the start / stop time of arcing during opening by analyzing the main circuit current curve 13 of the low-voltage circuit breaker does not conflict with determining the start / stop time of arcing during opening by analyzing the induced voltage curve of the enameled coil.

[0101] In particular, the determination of the first distortion point of the above-mentioned main circuit current curve 13 (or the induced voltage curve of the enameled coil) of the low-voltage circuit breaker is achieved by the sudden change of the slope between two adjacent data, and the sudden change amplitude of this slope is much larger than the sudden change amplitude of the slope before and after the peak point (maximum value) of the curve; the above-mentioned arcing stop moment during opening is the first moment when the curve is constant at zero.

[0102] Furthermore, the entire hardware measurement circuit system can be powered by a storage battery with 3.3V, 5V, and ±15V DC outputs, thereby improving the portability and diverse application scenarios of the entire measuring device.

[0103] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any form. Any technical solutions obtained by using equivalent replacements or equivalent transformations fall within the protection scope of the present invention.

Claims

1. A device for measuring the arcing time of a low voltage circuit breaker, characterized in that: It includes a measurement circuit for the main line current of a low-voltage circuit breaker, an adjustment circuit for the quality of an induced voltage, an induced voltage time series analysis and processing module, and a switch-off arcing time determination module; The measuring circuit of the main circuit current of the low-voltage circuit breaker comprises an enameled coil arranged on the side of the main circuit of the low-voltage circuit breaker, which is used to convert the current signal of the main circuit of the low-voltage circuit breaker into an induced voltage of the enameled coil, and to perform overvoltage protection and measurement on the induced voltage; The induced voltage quality adjustment circuit performs optimization adjustment on the induced voltage including voltage following, signal isolation, impedance matching, and RC filtering; The induced voltage time series analysis and processing and opening arcing time determination module smoothes the optimized and adjusted induced voltage time series curve and extracts the core distortion value, and determines the opening arcing time length of the low voltage circuit breaker according to the extracted core distortion value.

2. The device for measuring the arcing time of a low voltage circuit breaker according to claim 1, characterized in that: In the measurement circuit of the main line current of the low-voltage circuit breaker, the induced current of the enameled coil is adjusted by a current limiting resistor, and the enameled coil is protected from overvoltage in both positive and reverse directions by a reverse parallel zener diode group; the current limiting resistor and the reverse parallel zener diode group jointly complete the preliminary adjustment and processing of the induced voltage; and the measurement and proportional conversion of the induced voltage are completed by a circuit composed of an input resistor, a voltage sensor and a grounding resistor.

3. The device for measuring the arcing time of a low voltage circuit breaker according to claim 2, characterized in that: In the measurement circuit of the main line current of the low-voltage circuit breaker, the number of turns of the enameled coil and the resistance value of the current-limiting resistor are determined according to the current amplitude of the main line of the low-voltage circuit breaker, thereby ensuring the validity and analyzability of the peak-to-peak value of the induced voltage in the enameled coil and limiting the induced current of the enameled coil to be within a set range; the reverse parallel zener diode group realizes overvoltage protection of the enameled coil in both the forward and reverse directions by limiting the amplitude of the induced voltage in both the forward and reverse directions.

4. The device for measuring the arcing time of a low voltage circuit breaker according to claim 1, characterized in that: In the circuit for adjusting the quality of the induced voltage, the signal attenuation of the induced voltage during the transmission process is reduced by a voltage follower to ensure that the induced voltage maintains an effective driving capability during the transmission process. The circuit composed of a reverse series Zener diode group and an RC filter is used to improve the signal response speed of the induced voltage and reduce abnormal peak data distortion points and high-frequency noise of the induced voltage.

5. The device for measuring the arcing time of a low voltage circuit breaker according to claim 1, characterized in that: The induced voltage time series analysis and processing and trip arcing time determination module includes a differential circuit, an analog-to-digital converter, a digital signal processor, a display and a memory. The optimized and adjusted induced voltage is converted from an analog signal to a digital signal through the differential circuit and the analog-to-digital converter. The digital signal processor processes the digital signal into a smooth timing curve through a polynomial fitting method, and completes the optimization setting of the polynomial order through error analysis and comparison. The core distortion value is determined by using the slope mutation method of adjacent time series data and setting a threshold.

6. The device for measuring the arcing time of a low voltage circuit breaker according to claim 1 or 5, characterized in that: In the induced voltage time series analysis and processing and opening arcing time determination module, the adjacent time series data slope mutation method is used to determine the core distortion value, and then the opening arcing time length of the low-voltage circuit breaker is determined. Specifically, for the smoothed time series curve, the adjacent time series data slope mutation method and the set threshold are used to determine the core distortion value, and the time corresponding to the first core distortion value is determined as the starting time t1 of the opening arcing of the low-voltage circuit breaker; After the starting time t1, the zero-point constant value judgment method is used to determine the stop time t2 of the low-voltage circuit breaker opening arcing; the difference between the starting time t1 and the stop time t2 is determined as the opening arcing time length of the low-voltage circuit breaker.

7. A method for determining the arcing time of a low voltage circuit breaker, characterized in that: The steps include: Step 1. Install an enameled coil on the side of the main line of the low-voltage circuit breaker, convert the current signal of the main line of the low-voltage circuit breaker into the induced voltage of the enameled coil, and perform overvoltage protection and measurement on the induced voltage; Step 2, optimize and adjust the induced voltage including voltage following, signal isolation, impedance matching, and RC filtering to reduce the signal attenuation of the induced voltage during transmission, ensure that the induced voltage maintains effective driving capability during transmission, improve the signal response speed of the induced voltage, reduce abnormal peak data distortion points and high-frequency noise of the induced voltage, and obtain the optimized and adjusted induced voltage; Step 3, convert the optimized and adjusted induced voltage from an analog signal into a digital signal, process the digital signal into a smooth timing curve through a polynomial fitting method, and complete the optimization setting of the polynomial order through error analysis and comparison; Step 4: For the smoothed time series curve, the core distortion value is determined by using the slope mutation method of adjacent time series data and setting the threshold, and the time corresponding to the first core distortion value is determined as the starting time t1 of the arcing of the low-voltage circuit breaker; Step 5, after the starting time t1, the zero point constant value judgment method is used to determine the stop time t2 of the arcing of the low-voltage circuit breaker opening, that is, after the starting time t1, the first time on the timing curve that is constant at zero is determined as the stop time t2 of the arcing of the low-voltage circuit breaker opening; Step 6: Determine the difference between the start time t1 and the stop time t2 as the arcing time length of the low-voltage circuit breaker.

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