Specific implementation plan
 The present invention will be further described in detail below in conjunction with the drawings.
 See figure 1 , The overall structure of the system hardware of the present invention includes a self-integrating Rogowski coil, signal conditioning circuit (high frequency), A/D conversion circuit, trigger detection circuit, power frequency current transformer, signal conditioning circuit (power frequency), zero-crossing comparison circuit , Data acquisition control circuit, data storage module and data processing module.
 The high-frequency signal output by the Rogowski coil is processed by the signal conditioning circuit (high frequency) and the trigger detection circuit to generate a pre-trigger signal, which is sent to the data acquisition control circuit to start high-frequency signal acquisition; in the control of the data acquisition control module Under the A/D conversion circuit, the conditioned signal is converted into a digital quantity and recorded in the data storage module for use by the subsequent data processing module; the digital acquisition control circuit sends out an internal trigger signal after completing the data acquisition. Start the phase angle calculation and spectrum analysis tasks of the data processing module;
 The output signal of the power frequency current sensor is converted into an analog voltage signal through the power frequency signal conditioning circuit and input to the zero-crossing comparison circuit. After being processed by the zero comparison circuit, the power-frequency current zero-crossing signal is generated, which is input to the data in the form of pulse trigger Acquisition control circuit and data processing module are used to start the timer/counter in the data acquisition control circuit and data processing module respectively;
 The data processing module uses its internal timer/counter pulse counting method to measure the time difference between the power frequency current zero-crossing signal output by the zero-crossing comparison circuit and the internal trigger signal output by the data acquisition control circuit, so as to calculate the time difference when the high-frequency current occurs. The phase angle of the power frequency current in the protection circuit. The data processing module performs spectrum analysis on the waveform data of the high-frequency current signal stored in the data storage module, and judges whether it is based on the spectrum characteristics of the high-frequency current, the phase angle of the protected circuit current when it appears, and the regularity of its occurrence. The high-frequency current caused by the arc fault is recorded by the arc fault counter; when this regular high-frequency current signal is detected in more than 10 consecutive power frequency current cycles, it is judged that there is a protected circuit An arc fault occurs.
 See figure 2 The Rogowski coil used in the present invention is a non-magnetic air-core coil (its dimensions are: inner diameter a=40mm, outer diameter b=80mm, height h=24mm, number of turns N=36 turns, and it is wound with Φ=0.5mm copper wire System), the protected wire loop passes through the Rogowski coil, and the current in the wire is coupled to the magnetic field to generate an induced current in the secondary side of the Rogowski coil. This current passes through the coil sampling resistor (R f =0.5Ω) converted to voltage. The Rogowski coil current sensor is in a self-integrating working state, and its upper limit cut-off frequency is about 45.5MHz.
 The arc fault detection method based on the time-frequency characteristics of the high-frequency component of the current proposed by the present invention has the following technical characteristics:
 1. The arc fault detection method based on the time-frequency characteristics of the current high-frequency component detects the transient high-frequency current in the protected circuit. For the transient high-frequency current caused by the arc fault, the frequency is only related to the circuit characteristic parameters, and its frequency It is much higher than the harmonic frequency detected by the general power frequency current sensor in the power grid.
 2. This detection method judges the periodic appearance of the high frequency components of the current caused by the arc fault to distinguish it from the general arc (single occurrence) caused by the normal operation of switching appliances, plug insertion and unplugging, etc.; due to arc faults The transient high-frequency current of the protected circuit has a high frequency (>0.5MHz). Through digital filtering and spectrum judgment of the high-frequency current, the high-frequency current caused by the arc fault can be compared with the high-frequency current caused by the application of ordinary power electronic loads. High frequency components (generally less than 100kHz) are distinguished to reduce misjudgment;
 3. As the core current sensor of the present invention, the Rogowski coil is characterized in that: the Rogowski coil itself has no direct electrical connection with the current circuit under test, but is coupled through an electromagnetic field, so it has good electrical insulation with the main circuit; because there is no iron core Saturation problem, wide measurement range, the same winding, the current measurement range can be from a few amperes to hundreds of kiloamps; wide frequency range, generally can be designed from 0.1 to 100MHz or more; measurement accuracy is high, can be designed to be better than 0.1% , Generally between 0.5% and 1%.
 4. Calculate the high-frequency current by counting the time interval between the two pulse signals of the power-frequency current zero-crossing signal output by the zero-crossing comparator circuit and the internal trigger signal output by the data acquisition control circuit in a power-frequency half-wave period The phase angle of the power frequency current in the protected circuit at the moment of occurrence, analyze whether it appears periodically, and combine the data processing module to analyze the correlation analysis of the spectral characteristics of the high-frequency current signals collected in different power frequency half-wave cycles as the judgment Whether high frequency current is the criterion caused by arc fault.
 Based on the above characteristics, the phase angle calculation of the load current of the protected circuit loop and the spectrum analysis of the current high-frequency component when the current high-frequency component appears include the following steps:
 1. The load circuit current of the protected circuit is converted into a voltage signal by the sampling resistance of the Rogowski coil, and then input into the A/D conversion circuit and the trigger detection circuit through the high-frequency signal conditioning circuit. When the trigger detection circuit judges that the high-frequency current exceeds the set threshold (It can be set according to 10%-15% of the peak-to-peak value of the actual measured signal, which is set to 1V in this experimental device). A pre-trigger signal is issued, which starts the data acquisition control module for data acquisition and storage; in the data acquisition control module Under control, the adjusted high-frequency current signal is converted into a digital quantity through the A/D conversion circuit, and stored in the data storage module;
 The output signal of the power frequency current sensor passes through the power frequency signal conditioning circuit and enters the zero-crossing comparison circuit. When the zero-crossing comparison circuit detects the zero-crossing of the power-frequency current, it sends out a power-frequency current zero-crossing signal, which is input to the data acquisition control module. And data processing module;
 2. When the data processing module detects the power frequency current zero-crossing signal output by the zero-crossing comparison circuit, it starts the internal timer/counter and records the current value of the internal timer/counter; if the data acquisition control is detected during the timer/counter counting process The internal trigger signal sent by the circuit will record the current value of the timer/counter again; find the difference between the two counts, and calculate the time interval and the corresponding power frequency current phase according to its operating frequency;
 After the calculation of the phase is completed, the data processing module uses the waveform data recorded in the data storage module to calculate the characteristic frequency value sequence of the high-frequency current and its average relative error with the reference value sequence (the calculation result of the high-frequency current in the last power frequency half wave), If the calculation result of the average relative error between the high-frequency current characteristic frequency value and the reference value is greater than 5%, the arc fault counter is reset; otherwise, the arc fault counter is incremented by 1, and the current characteristic frequency value sequence of the high-frequency current is stored as a reference for subsequent comparison Value, turn off the internal timer/counter;
 3. Repeat the above process. In each half-wave period of the power frequency, calculate the phase angle and spectral characteristic parameters of the high-frequency current, and compare them with the previous half-wave period. If it is within the set error range (phase If the error is less than π/50, the average relative error of frequency is less than 5%), then counting is performed. When high-frequency current is detected continuously for 10 power frequency cycles (the count value exceeds 20), it is judged that an arc fault has occurred, and an arc fault alarm signal is issued.
 The implementation of the technical solution for measuring and analyzing the high frequency components of the current in the primary loop includes the following steps:
 1. Select the Rogowski coil parameters suitable for high-frequency current measurement, and design the self-integrating Rogowski coil to measure the high-frequency component of the current in the primary loop. The equivalent circuit of the lumped parameter of the Rogowski coil is as figure 2 As shown, where M, L 0 , R 0 , C 0 , R f They respectively represent the mutual inductance of the coil and the primary current-carrying conductor, the equivalent self-inductance of the coil, the equivalent internal resistance of the coil, the equivalent capacitance of the coil, and the coil termination resistance. When measuring high-frequency current signals, the voltage output from the self-integrating Rogowski coil is approximately linear with the high-frequency current in the primary loop, i 1 (t)≈-L 0 u 0 (t)/MR f. The transfer impedance of a self-integrating Rogowski coil is defined as the ratio of the output voltage of the coil to the high-frequency current of the primary loop. This value can be obtained by numerical calculation or calibrated by a standard signal source.
 2. The voltage signal output by the Rogowski coil is filtered by a high-pass (lower-limit cut-off frequency of 100kHz) filter to remove low-frequency interference, and then amplitude adjusted by an operational amplifier with a bandwidth of 50MHz to make it in the high-speed A/D circuit and trigger Within the analog input level range of the control circuit.
 3. Using a high-speed comparator (signal propagation delay time <7ns), set the arc fault transient high-frequency current comparison threshold (set according to 10%-15% of the measured high-frequency signal peak-to-peak value). By setting the threshold, other low-energy radio frequency interference can be filtered out from the hardware, and the storage effectiveness of the storage module for the output results of the high-speed A/D converter can be improved. When the input signal meets the trigger condition (exceeds the threshold), a pre-trigger signal is issued.
 4. The high-speed A/D conversion module uses a high-speed device with a sampling rate of 100MSPS, and its sampling clock is provided by the CPLD circuit of the data acquisition control module; the data acquisition control module and the data storage module form a high-speed FIFO (first in, first out) memory for storage The collected signal waveform, the storage capacity of the data storage module is determined by the A/D sampling rate and the total sampling time (for example, the sampling rate is 100MSPS, the sampling time is 0.080ms, and it can be designed as 16KB);
 When the data acquisition control module receives the pre-trigger signal within 5ms-10ms after the power frequency current zero-crossing signal, the data acquisition control module determines that the pre-trigger signal is valid, starts A/D sampling, and according to the state of the A/D converter output Signal, when the conversion is completed, the data is taken out and sent to the data storage module. When the data acquisition buffer is full, the data acquisition control module sends an internal trigger signal to the data processing module to start the data processing task, and the concatenated data storage module is in a write operation invalid state before the data processing module takes the data.
 5. The data processing module uses DSP as the core. When receiving the internal trigger signal sent by the data acquisition control module, the data processing module performs processing tasks such as power frequency current phase calculation and high frequency current spectrum analysis in an interrupt response mode, and reads The data in the data storage module is processed to determine whether an arc fault occurs, and when the processing is completed, the write operation of the data storage module is reset to be valid to wait for rewriting high-frequency data.
 6. In each power frequency half-wave period, if there is a high-frequency current, the high-frequency current signal is sampled, stored, analyzed and processed, and compared with the analysis result of the last half-wave period. Within a certain error range (phase error <5%), it will be accumulated. When the high-frequency current is continuously detected in 20 power frequency half-wave cycles, it is judged that an arc fault has occurred, and an arc fault alarm signal is issued.
 Such as image 3 As shown, the software flow of the interrupt response process of the data processing module is as follows:
 (1) The data processing module receives the internal trigger signal from the data acquisition control module, enters interrupt processing, and then goes to step (2);
 (2) Using the difference between the current value of the timer/counter and the previous recorded value, calculate the time interval T between the current occurrence of the high-frequency current and the current zero-crossing time, and then go to step (3);
 (3) Calculate the time interval T and the reference value T between the current occurrence of high-frequency current and the current zero-crossing time ref Error|T-T ref |, if the calculation result is less than 0.2ms (equivalent to the phase error of the power frequency current
 (4) Read the high-frequency current waveform data in the data storage module to the memory variable X[n] inside the DSP, and then go to step (5);
 (5) Perform FFT (Fast Fourier Transform) transformation on the waveform data in X[n] to obtain the frequency domain data of the signal (corresponding relationship between power density and frequency), store it in the memory variable Y[n], and then Step (6);
 (6) Use mathematical morphological filtering method to smooth the frequency domain data in variable Y[n], store the result in variable Z[n], and then go to step (7);
 (7) Compare and search in the variable Z[n], obtain the frequency point corresponding to the power density represented by Z[n] and the peak power density on the frequency curve in turn, store the variable F[N], and then go to Step (8);
 (8) Sort these frequencies according to the signal power density value "from large to small", and take out the first M frequency points F corresponding to the largest power density in sequence. 1 , F 2 ……F M As the characteristic frequency value of this measurement signal, (M is a constant, generally an integer between 3 and 7 can be selected), and then go to step (9);
 (9) Calculate the signal characteristic frequency F[M] and the reference characteristic frequency F obtained by this measurement ref [M] average relative error If the calculation result is less than 0.05, go to step (11), otherwise go to step (10);
 (10) Clear the arc fault counter, Flag=0, then go to step (14)
 (11) Set the arc fault counter, Flag=Flag+1, then go to step (12)
 (12) Determine the arc fault count value, if Flag<20, go to step (14), otherwise go to step (13);
 (13) Send out an arc fault alarm signal, and then go to step (14);
 (14) Save the time interval T between the current occurrence of high-frequency current and the current zero-crossing time as the reference value T ref , Then go to step (15);
 (15) Save the characteristic frequency F[M] of the current high-frequency current as the reference value F ref [M], then go to step (16);
 (16) Exit interrupt processing.