Short-circuit fault judgment method and system for electrical fireproof current-limiting protector

Abstract

The invention discloses a short-circuit fault judgment method and system for an electrical fireproof current-limiting protector. The method comprises the following steps: acquiring a real-time current signal in a protected line; performing zero-cross detection on the real-time current signal to determine a phase index of the sampling point in the alternating current period; based on the phase index, a corresponding dynamic current protection threshold is obtained from a pre-generated dynamic threshold table, and the dynamic threshold table is adaptively updated according to the actual load working condition; and comparing the real-time current signal with the dynamic current protection threshold, and if the real-time current signal exceeds the dynamic current protection threshold, determining that a short-circuit fault occurs. Compared with the prior art, the method has the advantages that the phase synchronization of zero-cross detection and the dynamic threshold table capable of being learned online are combined, so that rapid, accurate and self-adaptive detection and protection on the short-circuit fault under the complex and changeable load working conditions are realized.

Description

Technical Field

[0001] This invention relates to the field of electrical safety protection technology, and in particular to a method and system for judging short-circuit faults in electrical fire-prevention current-limiting protectors. Background Technology

[0002] With the continuous improvement of building electrification and the penetration rate of new energy sources, the loads connected to the end of the power distribution system are becoming increasingly complex, including various nonlinear sources such as LED lighting, variable frequency air conditioners, charging piles, distributed photovoltaics, and energy storage inverters. The connection of such loads causes the current waveform to evolve from the traditional power frequency sine wave to a complex form containing a large number of harmonics and intermittent impacts, making the system operating conditions increasingly demanding. In this context, aging insulation, loose joints, and animal chewing can all easily cause short circuit faults. The huge energy released instantaneously by a short circuit can cause the cable temperature to rise sharply, igniting surrounding combustibles and becoming the initial ignition source for electrical fires. Therefore, the sensitivity, response speed, and robustness of the detection algorithm of current-limiting protectors directly determine whether the fault current can be quickly cut off in the early stage of a fire, thereby suppressing the generation of electric arcs and preventing the spread of fire.

[0003] Currently, common short-circuit fault detection schemes mainly include the following categories: First, the static threshold comparison method, which multiplies the rated current by a fixed coefficient as the action threshold. This method cannot adapt to load fluctuations, and the action time varies greatly under different load conditions, resulting in insufficient protection accuracy. Second, the current change rate detection method (di / dt), which can detect sudden current changes, but is susceptible to high-frequency interference and false alarms in situations with waveform distortion and rich harmonics. Third, detection methods based on fast Fourier transform or full waveform analysis have high computational complexity, requiring a long time for the microprocessor to complete the calculation, and are prone to missing the microsecond-level current limiting time window. In addition, during the system power-on initialization phase, due to the lack of historical current data reference, the protector is in a blind start state. If a short circuit occurs at this time, the detection algorithm will delay action due to the lack of a reference, forming a protection blind zone.

[0004] A search revealed that Chinese Patent Publication No. CN106159876A discloses an electrical fire-prevention current-limiting protector and a fault current detection method. This method detects sudden current changes, identifies the stable point of the change, and uses the current value and phase information at that point to predict the peak value of the abnormal current. The predicted peak value is then compared with a preset fixed threshold. If it exceeds the threshold, it is judged as a short circuit and current-limiting protection is executed. However, this method still relies on a static fixed threshold and cannot be adaptively adjusted according to the actual load conditions. In situations with large load fluctuations or nonlinear loads, it is prone to misjudgment or protection delay.

[0005] Therefore, how to achieve fast, accurate, and adaptive detection and protection of short-circuit faults under complex and ever-changing load conditions is a core technical problem that needs to be solved. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects of the prior art and provide a short-circuit fault judgment method and system for electrical fire protection current limiting protectors.

[0007] The objective of this invention can be achieved through the following technical solutions: According to a first aspect of the present invention, a method for determining short-circuit faults in an electrical fire-resistant current-limiting protector is provided, comprising: Collect real-time current signals of the protected line; Zero-crossing detection is performed on the real-time current signal to determine the phase index of the sampling point in the AC cycle; Based on the phase index, the corresponding dynamic current protection threshold is obtained from the pre-generated dynamic threshold table, which is adaptively updated according to the actual load conditions. The real-time current signal is compared with the dynamic current protection threshold. If the real-time current signal exceeds the dynamic current protection threshold, a short-circuit fault is determined to have occurred.

[0008] As a preferred technical solution, if the real-time current signal does not exceed the dynamic current protection threshold, further auxiliary judgment is performed, specifically including: The rate of change of the real-time current signal within a preset time window is calculated. If the rate of change exceeds a preset rate of change threshold, a short-circuit fault is determined to have occurred.

[0009] As a preferred technical solution, the process of calculating the rate of change specifically includes: Maintain a sliding window containing a fixed number of historical current sample values; Each time a new sample value is acquired, the difference between it and the previous sample value is calculated, and the sum of differences is updated. The differential sum reflects the rate of change of current within the preset time window.

[0010] As a preferred technical solution, the construction process of the dynamic threshold table includes: Based on the rated frequency and rated current of the power grid, calculate the initial expected current value for the phase index that is uniformly distributed within the AC cycle; Based on the initial expected current value, the initial dynamic threshold boundary corresponding to each phase point is determined to form an initial dynamic threshold table.

[0011] As a preferred technical solution, the construction process of the dynamic threshold table includes: Based on the rated frequency and rated current of the power grid, calculate the initial expected current value for the phase index that is uniformly distributed within the AC cycle; Based on the initial expected current value, the initial dynamic threshold boundary corresponding to each phase point is determined to form an initial dynamic threshold table.

[0012] As a preferred technical solution, the filtering algorithm is a first-order low-pass filtering algorithm, and the adaptively updated smoothing coefficient is adjustable.

[0013] As a preferred technical solution, the zero-crossing detection includes: Identify valid zero-crossing events using the hysteresis comparison method; After a preset number of valid zero-crossing events are continuously identified, the system is determined to enter the zero-crossing synchronization state and short-circuit fault judgment is initiated based on the dynamic threshold table.

[0014] As a preferred technical solution, the method further includes a backup judgment mode: During the system power-on initialization phase or when phase loss of synchronization is detected, the real-time current signal is compared with a fixed static protection threshold based on the rated current to determine short-circuit faults.

[0015] As a preferred technical solution, after determining that a short circuit fault has occurred, a protection action is performed, and the online learning and updating of the dynamic threshold table is stopped.

[0016] According to a second aspect of the present invention, a short-circuit fault detection system for implementing the method is provided, the system comprising: The signal acquisition module is used to acquire real-time current signals in the protected line; The zero-crossing detection module is used to perform zero-crossing detection on the real-time current signal to determine the phase index of the sampling point in the AC cycle; The dynamic threshold management module is used to pre-generate and adaptively update the dynamic threshold table according to the actual load conditions, and obtain the corresponding dynamic current protection threshold from the dynamic threshold table based on the phase index. The fault determination module is used to compare the real-time current signal with the dynamic current protection threshold. If the real-time current signal exceeds the dynamic current protection threshold, a short circuit fault is determined to have occurred. The protection execution module is used to perform current limiting protection actions when a short-circuit fault is detected.

[0017] Compared with the prior art, the present invention has the following advantages: 1. This invention constructs an adaptively updatable dynamic threshold table and combines it with accurate zero-crossing detection to obtain a real-time phase index, thereby achieving real-time tracking and matching of protection thresholds to actual load conditions. This improves the accuracy and reliability of the criteria while ensuring detection speed.

[0018] 2. This invention adopts a dual judgment mechanism of dynamic threshold as the main judgment and current change rate as the auxiliary judgment. It can quickly respond to typical short circuits with amplitude exceeding the limit, and can also effectively identify early short circuits with drastic changes or faults with special waveforms. This reduces the risk of false alarms or missed alarms caused by a single criterion and improves the reliability of fault identification.

[0019] 3. The zero-crossing detection of this invention adopts a hysteresis comparison and continuous confirmation mechanism, and serves as a synchronization reference for dynamic threshold applications. It can effectively filter out false zero-crossing signals caused by noise or harmonics, ensure the accuracy of phase synchronization, avoid protection failure or malfunction caused by synchronization errors, and effectively enhance the anti-interference capability of the system.

[0020] 4. This invention designs a backup mechanism that includes dynamic threshold mode and static threshold mode. When the system is powered on and initialized or when the phase is out of sync, it can automatically degrade to static threshold protection, ensuring that there is no protection blind spot under any operating condition, and improving the overall robustness and safety of the system.

[0021] 5. The dynamic threshold table of the present invention has online self-learning capability and is updated smoothly through filtering algorithm, so that the protection threshold can slowly and stably track the long-term changes of the load, avoiding malfunctions caused by parameter jumps. Attached Figure Description

[0022] Figure 1 This is a flowchart of the method of the present invention; Figure 2 This is a flowchart illustrating the construction process of the dynamic threshold table of the present invention. Figure 3 This is a flowchart illustrating the real-time updating of the dynamic threshold table in this invention. Figure 4 This is a flowchart of the sliding window difference calculation of the present invention; Figure 5 This is a system architecture diagram of the present invention; Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0024] Example 1: like Figure 1 As shown, the present invention provides a short-circuit fault judgment method for electrical fire-resistant current-limiting protectors, specifically including: Step S1: System initialization and parameter pre-calculation After the system is powered on, the angular frequency of the sine waveform is calculated based on the preset peak rated current and the nominal frequency of the power grid. A complete sinusoidal period from 0 to 2π is uniformly divided into N phase points, preferably N=200, and the expected current value and the slope of the rate of change of current are calculated for each phase point. like Figure 2 As shown, based on the expected current value, the slope of the current change rate, and the dynamic factor, the initial dynamic current protection threshold (including the upper and lower boundaries) is calculated for each phase point, forming an initial dynamic threshold table; Initialize the data buffer: clear the sliding window storing historical current sample values, reset the differential accumulator, and set the window not full flag; Set the system to its initial state: set the working mode to static threshold mode, clear the zero-crossing synchronization counter, and clear the fault counter.

[0025] Step S2: Real-time current signal acquisition and timestamp recording The real-time current signal I_now in the power grid line is acquired at a fixed sampling frequency, and the current high-precision timer timestamp is recorded. Step S3: Zero-crossing detection The hysteresis comparison method is used to compare the signs of the current sampled value I_now with the previous sampled value I_prev. If the signs are opposite, it is marked as a suspected zero crossing. Calculate |I_now - I_prev|, and only if this value is greater than the preset hysteresis threshold is it confirmed as a valid zero-crossing event; Record the timestamps of valid zero-crossing points and update the zero-crossing counter; When at least four stable and equally spaced valid zero-crossing points are detected consecutively, the system is determined to have entered the zero-crossing synchronization state, and the current power grid frequency and phase reference are calculated and updated.

[0026] Step S4: Selecting the working mode and obtaining the protection threshold If the system is in zero-crossing synchronization state, it enters dynamic threshold mode. Based on the current timestamp and phase reference, it calculates the precise phase index of the current sampling point and obtains the corresponding dynamic current protection threshold from the dynamic threshold table. If the system is not synchronized (during initialization or phase loss), it enters static threshold mode and uses a fixed static protection threshold based on the rated current.

[0027] Step S5: Short Circuit Fault Main Judgment The absolute value of the real-time current signal, |I_now|, is compared with the protection threshold obtained in step S4. If |I_now| is greater than this threshold, then the main fault flag is set. Step S6: Short Circuit Fault Auxiliary Judgment like Figure 4 As shown, I_now is stored in a circular buffer, and if the window is full, the oldest value is removed. Calculate the current difference: diff_new = I_now - I_prev; If the window is full, subtract the difference diff_old corresponding to the oldest value from the accumulated sum, and then add diff_new; otherwise, simply accumulate diff_new.

[0028] If the absolute value of the difference sum |diff_sum| exceeds the preset rate of change threshold, then the auxiliary fault flag is set.

[0029] Step S7: Normal state handling and adaptive learning.

[0030] If neither step S5 nor S6 determines a fault, the system is in a normal state. In this state, if phase synchronization is effective, an adaptive update of the dynamic threshold table is initiated, and the update process is as follows: Figure 3 As shown: Obtain the current phase index, use a filtering algorithm (such as first-order low-pass filtering), smoothly update the expected current value of the phase point according to the current actual current value, and recalculate the dynamic current protection threshold of the point accordingly, so as to realize online learning of the threshold table.

[0031] Step S8: Short circuit fault handling.

[0032] Once a short-circuit fault is determined through step S5 or S6, protection actions are immediately executed, including: outputting a control signal to drive a high-speed switching device to disconnect the protected circuit, triggering an audible and visual alarm, and simultaneously stopping the online learning and updating of the dynamic threshold table.

[0033] The method of this invention acquires real-time current signals and performs zero-crossing detection to determine the phase. Based on this phase, an adaptive protection threshold is obtained from a dynamically updated threshold table. By comparing the real-time current with the dynamic threshold, a short-circuit fault can be quickly and accurately determined, achieving microsecond-level fast protection and reliable load-adaptive judgment.

[0034] Example 2: like Figure 5 As shown, the present invention provides a hardware system for implementing the above method, the system mainly comprising: Signal acquisition module 1: Responsible for acquiring line current information with high fidelity, including: Current sensing unit: It adopts a high linearity current transformer or open-loop Hall current sensor, which is connected in series with the protected live wire or neutral wire to convert the large current signal on the primary side into a small current or voltage signal that is indirectly and safely isolated from it. Signal conditioning unit: An amplification and filtering circuit consisting of operational amplifiers, resistors, and capacitors amplifies the weak signal output by the sensor to the range of the microcontroller's ADC, and suppresses high-frequency noise and glitches through a low-pass filter to ensure the quality of the input signal.

[0035] Zero-crossing detection module 2: This module, with a processor (MCU) at its core, is responsible for determining the current phase reference. Its function is implemented through software. The continuous current sampling values ​​sent by the signal acquisition module are compared in real time to determine the sign change; The system performs amplitude verification (hysteresis comparison) on suspected zero-crossing events, eliminates noise interference, counts and verifies the interval time of continuous and stable zero-crossing points, and finally determines whether the system has achieved reliable phase synchronization with the power grid, and outputs the phase synchronization status flag and the calculated accurate phase index.

[0036] Dynamic Threshold Management Module 3: This module is a software logic module that runs within the core processing module and includes: Storage unit: Used to store a dynamic threshold table containing dynamic thresholds for 200 phase points; Calculation and Update Unit: During initialization, the initial threshold table is pre-calculated and filled according to the rated parameters. During normal system operation, the first-order low-pass filter algorithm is called based on the phase index provided by the zero-crossing detection module to smooth the expected current value of the corresponding phase point and dynamically recalculate and update the protection threshold in the threshold table so that the threshold characteristics are consistent with the actual load conditions.

[0037] Fault diagnosis module 4: This module is a software logic module that executes the core judgment and decision-making processes, including: Threshold comparison unit: Receives the current dynamic threshold or static threshold from the dynamic threshold management module, quickly compares it with the real-time current value sent by the signal acquisition module, and performs the main judgment; Change rate calculation unit: Maintains a software sliding window to calculate and update the current difference accumulation in real time to assess the degree of current change and perform auxiliary judgment; Logic decision unit: It combines the results of the main judgment and the auxiliary judgment, and uses OR logic to make a judgment. As long as any condition is met, it immediately outputs a short circuit fault judgment signal.

[0038] Protection Execution Module 5: This module receives instructions from the fault judgment module and performs physical current limiting actions, including: The drive unit typically consists of a high-speed optocoupler isolator and a MOSFET gate driver. When a fault signal is received, the optocoupler quickly turns on, and the driver outputs a large current to pull down the gate voltage of the power MOSFET at an extremely fast speed. Power switching unit: It adopts a power MOSFET with low on-resistance and high switching speed, which is connected in series in the main power supply circuit. Under the action of the drive unit, the MOSFET switches from on to off within a few microseconds, cutting off the short-circuit current. Status indication and alarm unit: Includes LED indicator lights and piezoelectric buzzers to provide intuitive visual and audible alarm signals when a fault occurs.

[0039] System workflow: The signal acquisition module converts the line current into a clean voltage signal and digitizes it; the zero-crossing detection module analyzes the digital signal and establishes phase synchronization; the dynamic threshold management module provides adaptive protection thresholds based on the synchronization status and phase information; the fault judgment module compares the real-time current with the threshold and the rate of change to make a fault judgment; once a short circuit is determined, the protection execution module immediately acts, cuts off the circuit and alarms.

[0040] The system of this invention includes a signal acquisition module, a zero-crossing detection module, a dynamic threshold management module, a fault judgment module, and a protection execution module connected in sequence. The modules work together to complete the entire process from current sensing, phase synchronization, threshold adaptive management, fault comprehensive decision-making to rapid physical current limiting, providing hardware support for fast, accurate and adaptive short-circuit detection and current limiting protection.

[0041] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for judging short-circuit faults in electrical fire-resistant current-limiting protectors, characterized in that, include: Collect real-time current signals from the protected circuit; Zero-crossing detection is performed on the real-time current signal to determine the phase index of the sampling point in the AC cycle; Based on the phase index, the corresponding dynamic current protection threshold is obtained from the pre-generated dynamic threshold table, which is adaptively updated according to the actual load conditions. The real-time current signal is compared with the dynamic current protection threshold. If the real-time current signal exceeds the dynamic current protection threshold, a short-circuit fault is determined to have occurred.

2. The short-circuit fault judgment method for an electrical fire-resistant current-limiting protector according to claim 1, characterized in that, If the real-time current signal does not exceed the dynamic current protection threshold, further auxiliary judgment is performed, specifically including: The rate of change of the real-time current signal within a preset time window is calculated. If the rate of change exceeds a preset rate of change threshold, a short-circuit fault is determined to have occurred.

3. The short-circuit fault judgment method for an electrical fire-resistant current-limiting protector according to claim 2, characterized in that, The process of calculating the rate of change specifically includes: Maintain a sliding window containing a fixed number of historical current sample values; Each time a new sample value is acquired, the difference between it and the previous sample value is calculated, and the sum of differences is updated. The differential sum reflects the rate of change of current within the preset time window.

4. The short-circuit fault judgment method for an electrical fire-resistant current-limiting protector according to claim 1, characterized in that, The process of constructing the dynamic threshold table includes: Based on the rated frequency and rated current of the power grid, calculate the initial expected current value for the phase index that is uniformly distributed within the AC cycle; Based on the initial expected current value, the initial dynamic threshold boundary corresponding to each phase point is determined to form an initial dynamic threshold table.

5. The short-circuit fault judgment method for an electrical fire-resistant current-limiting protector according to claim 1, characterized in that, The adaptive update of the dynamic threshold table includes: When the system is in normal non-short-circuit operation and zero-crossing synchronization is effective, obtain the current phase index; Based on the real-time current signal at the current moment, a filtering algorithm is used to smoothly update the expected current value corresponding to the current phase index; Based on the updated expected current value, the dynamic current protection threshold for the corresponding phase point in the dynamic threshold table is recalculated and updated.

6. The short-circuit fault judgment method for an electrical fire-resistant current-limiting protector according to claim 5, characterized in that, The filtering algorithm is a first-order low-pass filtering algorithm, and the adaptively updated smoothing coefficient is adjustable.

7. The short-circuit fault judgment method for an electrical fire-resistant current-limiting protector according to claim 1, characterized in that, The zero-crossing detection includes: Valid zero-crossing events are identified using the hysteresis comparison method. After a preset number of valid zero-crossing events are continuously identified, the system is determined to enter the zero-crossing synchronization state and short-circuit fault judgment is initiated based on the dynamic threshold table.

8. The short-circuit fault judgment method for an electrical fire-resistant current-limiting protector according to claim 1, characterized in that, The method also includes a backup judgment mode: During the system power-on initialization phase or when phase loss of synchronization is detected, the real-time current signal is compared with a fixed static protection threshold based on the rated current to determine short-circuit faults.

9. A short-circuit fault judgment method for an electrical fire-resistant current-limiting protector according to claim 1, characterized in that, Upon determining that a short-circuit fault has occurred, protective actions are executed, and online learning and updating of the dynamic threshold table are stopped.

10. A short-circuit fault detection system for implementing the method as described in any one of claims 1-9, characterized in that, include: The signal acquisition module is used to acquire real-time current signals in the protected line; The zero-crossing detection module is used to perform zero-crossing detection on the real-time current signal to determine the phase index of the sampling point in the AC cycle; The dynamic threshold management module is used to pre-generate and adaptively update the dynamic threshold table according to the actual load conditions, and obtain the corresponding dynamic current protection threshold from the dynamic threshold table based on the phase index. The fault determination module is used to compare the real-time current signal with the dynamic current protection threshold. If the real-time current signal exceeds the dynamic current protection threshold, a short circuit fault is determined to have occurred. The protection execution module is used to perform current limiting protection actions when a short-circuit fault is detected.

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