CN114397494A - Residual current fault detection method and system - Google Patents
Residual current fault detection method and system Download PDFInfo
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- CN114397494A CN114397494A CN202111478531.8A CN202111478531A CN114397494A CN 114397494 A CN114397494 A CN 114397494A CN 202111478531 A CN202111478531 A CN 202111478531A CN 114397494 A CN114397494 A CN 114397494A
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
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Abstract
The application relates to a residual current fault detection method, which comprises the following steps: acquiring a bus unipolar current signal; filtering and characteristic reconstruction are carried out on the bus unipolar current signal by adopting a preset wavelet parameter to obtain a wavelet analysis signal; analyzing the change rate of the wavelet analysis signal, and extracting the period change of the wavelet analysis signal; comparing the period variation with a preset threshold value to obtain a residual current fault result; the preset wavelet parameters and the preset threshold are obtained through residual current simulation analysis. According to the scheme, the hardware design that the existing residual current protector needs to acquire signals from two ends of the bus is simplified, the hardware volume of the traditional direct current residual current protector is greatly reduced, and the accuracy of residual current fault detection is improved by applying a signal processing means to bus unipolar signals to realize detection.
Description
Technical Field
The application relates to the technical field of electric shock protection, in particular to a residual current fault detection method and system.
Background
With the improvement of the economic and technological levels, the rapid development of the power industry brings great convenience to the life of people. However, as the power consumption and the intensity of the electric equipment are remarkably increased, fire accidents and personal electric shock accidents are frequently caused. On the one hand, the reason for this is that the overload operation of the equipment generates a large amount of heat, which causes fire when short circuit occurs; on the other hand, when the equipment runs, the circuit is damaged, and the insulating sheath falls off to cause electric leakage on the electric equipment or the circuit, so that residual current existing in the system is caused. Therefore, it is necessary to detect the change of the residual current in the line to determine whether an electric shock or other ground leakage accident occurs.
At present, in order to deal with such accidents, a current method is to adopt a leakage protector to detect leakage current in a line and disconnect the threatening leakage line in time so as to protect the safety of the line, equipment and personnel of a power system. However, most of the existing residual current protectors are directed at an alternating current system, and cannot effectively protect residual current faults in the direct current system. And as the power consumption and the intensity of the electric equipment are obviously increased, the current level in the direct current system is increased, and the accuracy of the residual current detection is gradually reduced.
Disclosure of Invention
Accordingly, it is desirable to provide a method and a system for detecting a residual current fault, which can accurately determine whether a residual current fault occurs.
A method of residual current fault detection, the method comprising:
acquiring a bus unipolar current signal;
filtering and characteristic reconstruction are carried out on the bus unipolar current signal by adopting a preset wavelet parameter to obtain a wavelet analysis signal;
analyzing the change rate of the wavelet analysis signal, and extracting the period change of the wavelet analysis signal;
comparing the period variation with a preset threshold value to obtain a residual current fault result;
and obtaining the preset wavelet parameters and the preset threshold value through residual current simulation analysis.
In one embodiment, the process of obtaining the preset wavelet parameter and the preset threshold through residual current simulation analysis includes:
acquiring a bus unipolar current signal comprising simulated residual current; the simulation residual current is obtained by simulation under different bus voltage levels, bus current levels and residual current levels;
judging to obtain more than two simulation residual current fault results according to the bus unipolar current signals including the simulation residual current, more than two wavelet parameters and a threshold;
according to more than two simulated residual current fault results, counting to obtain the residual current fault accuracy rate corresponding to each wavelet parameter and the threshold value;
and selecting the wavelet parameter and the threshold with the highest residual current fault accuracy as a preset wavelet parameter and a preset threshold.
In one embodiment, the preset wavelet parameters include a preset wavelet basis, a preset decomposition layer number and a preset frequency band, and the filtering and feature reconstruction of the bus unipolar current signal using the preset wavelet parameters to obtain a wavelet analysis signal includes:
filtering the bus unipolar current signal to obtain a filtered bus unipolar current signal;
performing wavelet transformation on the filtered bus unipolar current signal by adopting the preset wavelet basis and the preset decomposition layer number, and extracting a decomposed low-frequency band wavelet coefficient according to the preset frequency band;
and performing characteristic construction on the low-frequency-band wavelet coefficient to obtain a wavelet analysis signal.
In one embodiment, the acquiring the bus unipolar current signal includes:
and sampling according to the sampling frequency and the time window to obtain the bus unipolar current signal.
In one embodiment, the period variation includes a first period variation and a second period variation, and the performing rate analysis on the wavelet analysis signal to extract the period variation of the wavelet analysis signal includes:
obtaining the amplitude variation and the maximum amplitude of the wavelet analysis signal corresponding to the current time window;
taking the amplitude variation as a first period variation of the current period; and taking the difference value of the maximum amplitude value and the maximum amplitude value of the wavelet analysis signal corresponding to the previous time window as the second period variable quantity of the current period.
In one embodiment, the step of comparing the period variation with a preset threshold to obtain a residual current fault result includes:
when the first period variable quantity of the current period is smaller than the preset pulse threshold value, the residual current fault result is no fault;
and when the variable quantity of the first period of the current period is larger than the preset pulse threshold value, obtaining a residual current fault result according to the variable quantity of the second period after the current period and the preset attenuation threshold value.
In one embodiment, the obtaining a residual current fault result according to a second period variation after the current period and the preset attenuation threshold includes:
when the variation of a second period of a preset number of continuous periods after the current period is smaller than the preset attenuation threshold, the residual current fault result is a fault; otherwise, the residual current fault result is no fault.
In one embodiment, a residual current fault detection system is provided, and the system comprises a current acquisition device and an upper computer, wherein the current acquisition device is connected with the anode/cathode of a bus and is also connected with the upper computer;
the current acquisition device is used for acquiring a bus unipolar current signal;
the upper computer is used for filtering and characteristic reconstruction of the bus unipolar current signal by adopting preset wavelet parameters to obtain a wavelet analysis signal; the wavelet analysis module is also used for analyzing the change rate of the wavelet analysis signal and extracting the period change of the wavelet analysis signal; and the residual current fault detection circuit is also used for comparing the period variation with a preset threshold value to obtain a residual current fault result.
In one embodiment, the residual current fault detection system further comprises a residual current simulation device, and the residual current simulation device is connected with the current collection device;
the residual current simulation device is used for simulating to obtain simulated residual currents under different bus voltage levels, bus current levels and residual current levels;
the current acquisition device is also used for acquiring a bus unipolar current signal comprising the simulated residual current;
the upper computer is also used for judging to obtain more than two simulated residual current fault results according to the bus unipolar current signals comprising the simulated residual currents, and more than two wavelet parameters and threshold values; according to more than two simulated residual current fault results, counting to obtain the residual current fault accuracy rate corresponding to each wavelet parameter and the threshold value; and selecting the wavelet parameter and the threshold with the highest residual current fault accuracy as a preset wavelet parameter and a preset threshold.
In one embodiment, the residual current simulation device comprises a direct current power supply module, a variable resistor R1, a variable resistor R2, a resistor R +, a resistor R-, a timing switch-on module and a current detection module, wherein the variable resistor R1 is connected between positive and negative output ends of the direct current power supply module, one end of the resistor R + is connected with a positive output end of the direct current power supply module, one end of the resistor R-is connected with a negative output end of the direct current power supply module, one end of the variable resistor R2 is connected with the other end of the resistor R + after being connected in series with the timing switch-on module, the other end of the variable resistor R2 is connected with the other end of the resistor R-, and the current detection module is connected with two ends of the variable resistor R2 after being connected in series with the timing switch-on module;
when the timing conducting module is conducted, the resistance values of the variable resistor R1 and the variable resistor R2 are adjusted, and simulation residual currents under different bus voltage levels, bus current levels and residual current levels are obtained through simulation.
According to the method and the system for detecting the residual current faults, the unipolar bus current signals are obtained, wavelet transformation analysis is carried out, the period variation of the wavelet analysis signals is extracted, and then the wavelet analysis signals are compared with the preset threshold value to judge whether the residual current faults occur, so that the hardware design that the existing residual current protector needs to obtain signals from the two ends of the bus is simplified, the hardware size of the traditional direct current residual current protector is greatly reduced, and the accuracy of the residual current detection is improved by applying a signal processing means to the unipolar bus signals to realize the detection.
Drawings
FIG. 1 is a schematic flow chart of a method for residual current fault detection in one embodiment;
FIG. 2 is a current waveform diagram of a residual current fault of 80mA when the bus voltage is 200V and no load occurs;
FIG. 3 is a current waveform diagram of a residual current fault of 80mA when the bus voltage is 200V and the bus current is 5A;
FIG. 4 is a current waveform diagram of a 300mA residual current fault occurring when the bus voltage is 200V and the bus current is 10A;
FIG. 5 is a graph showing the variation trend of the residual current with the bus current of 0-10A when the bus voltage is 200V and 400V and the residual current is 300 mA;
FIG. 6 is a schematic flow chart of a method for detecting residual current faults in another embodiment;
FIG. 7 is a signal diagram of wavelet analysis of unipolar bus current signals with 80mA residual current fault at bus voltage of 200V and bus current of 5A;
FIG. 8 is a signal diagram of wavelet analysis of a unipolar current signal of a bus with a residual current fault of 80mA at a bus voltage of 400V and a bus current of 5A;
FIG. 9 is a signal diagram of wavelet analysis of a unipolar current signal of a bus with a residual current fault of 80mA at a bus voltage of 400V and a bus current of 10A;
FIG. 10 is a schematic flow chart of a method for detecting residual current faults in another embodiment;
FIG. 11 is a schematic flow chart of a method for residual current fault detection in another embodiment;
FIG. 12 is a schematic flow chart of a method for residual current fault detection in another embodiment;
FIG. 13 is a schematic diagram of an embodiment of a residual current simulation apparatus;
FIG. 14 is a current waveform diagram of a simulation residual current of 80mA when the bus voltage is 200V and the bus current is 10A;
FIG. 15 is a current waveform diagram of a simulation residual current of 300mA when the bus voltage is 200V and the bus current is 10A;
FIG. 16 is a current waveform diagram of a simulation residual current of 300mA when the bus voltage is 400V and the bus current is 10A;
FIG. 17 is a current waveform diagram of a simulated residual current of 80mA when the bus voltage is 400V and the bus current is 20A;
FIG. 18 is a current waveform diagram of a simulation residual current of 300mA when the bus voltage is 400V and the bus current is 20A;
FIG. 19 is a graph showing the variation trend of the residual current with the bus current 0-20A when the bus voltage is 200V and the residual current is 300 mA.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the description of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.
It will be understood that, as used herein, the terms "first," "second," and the like may be used herein to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish one element from another. For example, a first resistance may be referred to as a second resistance, and similarly, a second resistance may be referred to as a first resistance, without departing from the scope of the present application. The first resistance and the second resistance are both resistances, but they are not the same resistance.
It is to be understood that "connection" in the following embodiments is to be understood as "electrical connection", "communication connection", and the like if the connected circuits, modules, units, and the like have communication of electrical signals or data with each other.
As used herein, the singular forms "a", "an" and "the" may include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises/comprising," "includes" or "including," etc., specify the presence of stated features, integers, steps, operations, components, parts, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, components, parts, or combinations thereof.
At present, a plurality of hardware such as a direct current bridge, a hall sensor, a magnetic modulation sensor and the like are mainly adopted to be respectively connected with a positive pole and a negative pole of a bus, a current value obtained after current phases of the positive pole and the negative pole of the bus are offset is calculated to obtain residual current, and then the fault or accident condition is obtained by judging the change of the residual current. The method has high requirements on hardware, and as the power consumption and the intensity of electric equipment are obviously increased, when the level of the bus current in the direct current system is increased, the weak amplitude of the residual current is larger relative to the difference value of the bus current, and the detection accuracy is gradually reduced.
Aiming at the situation, the application provides a method and a system for detecting the residual current fault based on a bus current signal analysis visual angle, but in a direct current system with a larger bus current grade, the obvious change degree of the direct current bus current is weakened, and huge obstruction is caused to the effective detection of the direct current residual current. Therefore, the method and the device have the advantages that the evolution rule of the direct current residual current under the condition of the voltage and current change trend of the direct current system is synchronously and effectively determined, and the direct current residual current protection under the condition of influence of various direct current system electric quantities is guided.
In one embodiment, as shown in fig. 1, there is provided a residual current fault detection method, including:
step 102: and acquiring a bus unipolar current signal.
Specifically, the bus unipolar current signal is a current signal obtained by connecting only the positive electrode or the negative electrode of the bus, and it is understood that the bus unipolar current signal may be a bus positive current signal or a bus negative current signal. In one embodiment, step 102 obtains the bus unipolar current signal, which includes sampling the bus unipolar current signal at a sampling frequency and a time window. Specifically, the values of the sampling frequency f and the time window T are not fixed, and can be set according to the actual bus current signal condition, for example, the following explanation takes the sampling frequency f as 1MHz and the time window T as 8ms as an example. In one embodiment, the sampling frequency f and the time window T may also be obtained by residual current simulation analysis.
The method for identifying the residual current faults by measuring and analyzing the bus current is feasible by simulating the real residual current fault current generated in the direct current system. As shown in fig. 2, when the bus voltage is 200V and a residual current fault of 80mA occurs during no-load, the bus current changes significantly during the fault, and the average value of the changed dc residual current is 84.7148 mA.
However, after the load is increased, as shown in fig. 3, when the bus current rises to 5A, the connected residual current branch circuit remains unchanged (the average value is 79.7468mA), and it can be seen from the fact that the real residual current fault current occurs in the dc system, the bus current does not change significantly before and after the residual current fault occurs, which increases the difficulty in accurately detecting the dc residual current. That is, when the bus current becomes large, the dc residual current fault occurring in the line cannot be effectively detected by simply depending on the bus current variation. By increasing the residual current to about 300mA (average value of 299.082mA), the bus current in fig. 3 is changed to a certain extent corresponding to 5A. However, as shown in fig. 4, after the system bus current is further increased to 10A, it can be seen that a real residual current fault current occurs in the dc system, and the change of the bus current before and after the residual current fault occurs is reduced.
Therefore, according to the research on the residual current rule under the conditions of various bus currents and voltage grades in the actual direct current power supply system, as shown in fig. 5, the conditions of 200V bus voltage and 300mA residual current are kept unchanged, the bus current is changed from 0-10A, the residual current shown by the dotted line shows a descending trend, and the direct current residual current amplitude is correspondingly reduced due to the fact that the line partial pressure is large when the bus current is increased. Then, the voltage of the bus is increased to 400V, the residual current shown by the solid line also keeps descending, but the amplitude of the residual current is increased when the voltage is increased. Aiming at the situation, the scheme considers that a wavelet transformation method is adopted to analyze the bus current and identify the residual current faults in the bus current.
Step 104: and filtering and characteristic reconstruction are carried out on the bus unipolar current signal by adopting a preset wavelet parameter to obtain a wavelet analysis signal.
The wavelet transform is a time-scale analysis method, is very suitable for processing non-stationary signals, can change the size of a time window and a frequency window, and analyzes the signals in a multi-resolution mode on a time domain and a frequency domain. Specifically, solving the wavelet transformation result of the residual current signal according to the following formula for the bus unipolar current signal f (t):
wherein WT (a, tau) is the result of wavelet transform, Ψ (t) is the wavelet basis, a represents the scale parameter, τ represents the translation parameter, scale a controls the expansion and contraction of the wavelet, and translation τ controls the translation of the wavelet.
Specifically, firstly, filtering the acquired bus unipolar current signal to obtain a filtered bus unipolar current signal, then performing wavelet transform on the filtered bus unipolar current signal by adopting a preset wavelet basis and a preset decomposition layer number, and extracting a decomposed low-frequency band wavelet coefficient according to a frequency band. And finally, performing characteristic construction on the low-frequency-band wavelet coefficient to obtain a wavelet analysis signal.
Step 106: and analyzing the change rate of the wavelet analysis signal, and extracting to obtain the period change of the wavelet analysis signal.
The period variation includes a first period variation and a second period variation. Specifically, the amplitude variation and the maximum amplitude of the wavelet analysis signal corresponding to the current time window are taken. Then the amplitude variation is used as the first period variation of the current period; and taking the difference value of the maximum amplitude value and the maximum amplitude value of the wavelet analysis signal corresponding to the previous time window as the second period variable quantity of the current period.
Step 108: and comparing the period variation with a preset threshold value to obtain a residual current fault result.
The preset threshold value comprises a preset pulse threshold value and a preset attenuation threshold value. Specifically, when the first period variation of the current period is smaller than the preset pulse threshold, the residual current fault result is no fault. And when the variable quantity of the first period of the current period is larger than the preset pulse threshold value, obtaining a residual current fault result according to the variable quantity of the second period after the current period and the preset attenuation threshold value.
The preset wavelet parameters and the preset threshold are obtained through residual current simulation analysis. Specifically, the simulation analysis process comprises the steps of firstly generating bus unipolar current signals under different bus voltage levels, bus current levels and residual current levels by adopting a residual current simulation model, and judging to obtain more than two simulation residual current fault results according to the bus unipolar current signals including simulation residual currents, more than two wavelet parameters and more than two wavelet thresholds. And then according to more than two simulated residual current fault results, counting to obtain the residual current fault accuracy rate corresponding to each wavelet parameter and the threshold value. And finally, selecting the wavelet parameter and the threshold with the highest residual current fault accuracy as a preset wavelet parameter and a preset threshold.
According to the method and the system for detecting the residual current faults, the unipolar bus current signals are obtained, wavelet transformation analysis is carried out, the period variation of the wavelet analysis signals is extracted, and then the wavelet analysis signals are compared with the preset threshold value to judge whether the residual current faults occur, so that the hardware design that the existing residual current protector needs to obtain signals from the two ends of the bus is simplified, the hardware size of the traditional direct current residual current protector is greatly reduced, and the accuracy of the residual current detection is improved by applying a signal processing means to the unipolar bus signals to realize the detection.
In one embodiment, as shown in fig. 6, the process of obtaining the preset wavelet parameter and the preset threshold value through residual current simulation analysis includes:
step 202: and acquiring a bus unipolar current signal comprising the simulated residual current.
And the simulation residual current is obtained by simulating under different bus voltage levels, bus current levels and residual current levels. Specifically, the bus voltage level, the bus current level and the residual current level can be set according to actual conditions, for example, the bus voltage can be changed within the range of 0-1000V, the bus current can be changed within the range of 0-20A, and the residual current can be changed within the range of 0-300 MA. In addition, the mode obtained by simulating the residual current is not fixed, and may be generated by a residual current simulation model, or may be another mode recognized by those skilled in the art. Through the combination of various voltage and current grades, the effectiveness of residual current fault characteristics used by the detection method is guaranteed from a physical simulation level, and the effective application range of the detection method in various system voltage grade, current grade and residual current grade forms is expanded.
Step 204: and judging to obtain more than two simulated residual current fault results according to the bus unipolar current signals including the simulated residual current, more than two wavelet parameters and a threshold value.
The wavelet parameters include parameters necessary for realizing wavelet transformation process, such as wavelet base, decomposition layer number and frequency band. The wavelet bases can be 15 common wavelet bases including spline wavelets, Daubechies wavelets, reverseBior wavelets and the like. The number of decomposition layers is used to divide the frequency range of the target signal, and may be an integer of 1 to 10.
Wherein the threshold comprises a pulse threshold and a decay threshold. The pulse threshold is used for judging whether a wavelet analysis result has a pulse, and if the pulse exists, the direct current residual current fault is considered to possibly occur. And the attenuation threshold is used for judging whether continuous attenuation occurs after the wavelet analysis result has pulses, and if the continuous attenuation occurs, the occurrence of residual current faults is confirmed. In one embodiment, the bus current evolution law when the residual current fault occurs is also obtained through residual current simulation analysis. Specifically, when the dc residual current is 80mA, wavelet transform is performed on the bus unipolar current signal measured under the conditions that the bus voltage is 200V and the bus current is 5A, and the obtained wavelet analysis signal is as shown in fig. 7. The voltage level is raised to 400V, the system current 5A is kept unchanged, and the wavelet transformation graph of the collected bus unipolar current signal is shown in FIG. 8. The system current level is increased to 10A, the system voltage is kept unchanged at 400V, and the wavelet transformation graph of the collected bus unipolar current signal is shown in FIG. 9. Therefore, when the residual current fault occurs, the wavelet analysis signal of the bus current generates a pulse with a larger amplitude, and the fault phenomenon of the residual current in the direct current power supply system is accurately indicated. Meanwhile, in the continuous occurrence process of the direct current residual current phenomenon, the amplitude of the wavelet analysis signal is always in a smaller amplitude state, and therefore the amplitude is extracted as a basis for detecting the direct current residual current fault.
Specifically, the optional wavelet parameters and the threshold are respectively used for judging whether the bus unipolar current signals including the simulated residual current have residual current faults or not, and more than two simulated residual current fault results are obtained. The process of determining whether there is a residual current fault is similar to the above steps 102 to 108, and is not described herein.
Step 206: and according to more than two simulated residual current fault results, counting to obtain the residual current fault accuracy rate corresponding to each wavelet parameter and the threshold value.
It can be understood that the bus unipolar current signals including the simulated residual current are all samples with residual current faults, and the residual current fault accuracy corresponding to each wavelet parameter and the threshold can be obtained by counting the detection rate of the simulated residual current fault result corresponding to each wavelet parameter and the threshold.
In another embodiment, in addition to the bus unipolar current signals including the simulated residual current, the bus unipolar current signals without the residual current fault can be used to detect each wavelet parameter and the threshold value, so as to obtain the corresponding residual current fault accuracy. The wavelet parameters and the threshold value are detected by adding the bus unipolar current signals without residual current faults, so that the final detection method has higher identification capability.
Step 208: and selecting the wavelet parameter and the threshold with the highest residual current fault accuracy as a preset wavelet parameter and a preset threshold.
Specifically, the wavelet parameter and the threshold with the highest residual current fault accuracy are selected as the preset wavelet parameter and the preset threshold, so that the highest residual current fault identification accuracy of the final detection method in the actual power grid operation process can be ensured.
In an embodiment, the preset wavelet parameters include a preset wavelet basis, a preset decomposition layer number, and a preset frequency band, and as shown in fig. 10, step 104 performs filtering and feature reconstruction on the bus unipolar current signal and the preset wavelet parameters to obtain a wavelet analysis signal, including:
step 302: and filtering the bus unipolar current signal to obtain a filtered bus unipolar current signal.
Specifically, the obtained bus unipolar current signal is filtered to obtain a high-frequency component and a low-frequency component. And taking the low-frequency component as a filtered bus unipolar current signal. For example, when the sampling frequency f is 1mHz, the bus unipolar current signal after filtering is a bus unipolar current signal of 0-500 kHz.
Step 304: and performing wavelet transformation on the filtered bus unipolar current signal by adopting a preset wavelet basis and a preset decomposition layer number, and extracting a decomposed low-frequency band wavelet coefficient according to a preset frequency band.
Specifically, according to the result of simulation analysis of the residual current, in this embodiment, a rbio3.1 wavelet is selected as a preset wavelet base, 2 layers of decomposition are selected for the preset decomposition layer number, and wavelet transformation is performed on the filtered bus unipolar current signal. And then selecting the wavelet coefficient of the low frequency band after wavelet transformation as the high frequency band component h20 of the second layer as the basis of subsequent characteristic construction, namely selecting the wavelet coefficient of which the characteristic frequency band is 125 kHz-250 kHz.
Step 306: and performing characteristic construction on the low-frequency-band wavelet coefficient to obtain a wavelet analysis signal.
Specifically, the wavelet coefficient with the characteristic frequency band of 125 kHz-250 kHz is subjected to characteristic construction to obtain a wavelet analysis result. Wherein the characteristic form is a square sum calculation mode.
In one embodiment, the period variation includes a first period variation and a second period variation, and as shown in fig. 11, the performing a rate analysis on the wavelet analysis signal in step 106 to extract the period variation of the wavelet analysis signal includes:
step 402: and (4) taking the amplitude variation and the maximum amplitude of the wavelet analysis signal corresponding to the current time window.
The amplitude variation is a difference between the maximum amplitude and the minimum amplitude, and the time window T is 8ms as an example. Specifically, the wavelet analysis signal is obtained by performing wavelet transformation on a bus unipolar current signal after being subjected to time window cutting, and is specifically a continuous signal. Therefore, the amplitude variation and the maximum amplitude of the wavelet analysis signal corresponding to the current time window are correspondingly calculated.
Step 404: taking the amplitude variation as the first period variation of the current period; and taking the difference value of the maximum amplitude value and the maximum amplitude value of the wavelet analysis signal corresponding to the previous time window as the second period variable quantity of the current period.
Specifically, the wavelet analysis signal for each time window length is taken as one cycle. Then, the variation of the amplitude thereof can be used as the variation of the first period of the current period, and the variation of the wavelet analysis signal in the current period can be characterized. Further, the difference between the maximum amplitude of the wavelet analysis signal in the current period and the maximum amplitude of the wavelet analysis signal in the previous period is used as the second period variation of the current period, so that the variation of the wavelet analysis signal in the current period relative to the wavelet analysis signal in the previous period can be represented.
In one embodiment, the preset threshold includes a preset pulse threshold and a preset attenuation threshold, as shown in fig. 12, the comparing step 108 of the period variation with the preset threshold to obtain the residual current fault result includes:
step 502: and when the variable quantity of the first period of the current period is smaller than the preset pulse threshold value, the residual current fault result is no fault.
Specifically, when the variation of the first period of the current period is smaller than the preset pulse threshold, it indicates that no sudden change occurs in the wavelet analysis signal in the current period, and the occurrence of no residual current fault can be analyzed. The preset pulse threshold value is obtained by analyzing after residual current simulation, and can be adjusted according to conditions in the subsequent actual detection process.
Step 504: and when the variable quantity of the first period of the current period is larger than the preset pulse threshold value, obtaining a residual current fault result according to the variable quantity of the second period after the current period and the preset attenuation threshold value.
Specifically, when the first period variation of the current period is greater than the preset pulse threshold, it indicates that a pulse signal condition occurs in the wavelet analysis signal in the current period, and a residual current fault may occur. According to the obtained evolution rule, the finally determined residual current fault result is obtained by continuously comparing the second period variable quantity after the current period with a preset attenuation threshold value. The means for comparing the second period variation with the preset attenuation threshold may be that the second period variation having a preset ratio among the second period variations of the consecutive preset number after the current period is smaller than the preset attenuation threshold; or the variation of the second cycle of the continuous preset number after the current cycle is smaller than the preset attenuation threshold; the method can also be in other forms according to the evolution law of the bus unipolar current signals under the residual current faults.
In one embodiment, the obtaining the residual current fault result according to the second period variation after the current period and the preset attenuation threshold in step 504 includes: when the variation of a second period continuously preset number of periods after the current period is smaller than a preset attenuation threshold value, the residual current fault result is a fault; otherwise, the residual current fault result is no fault.
Specifically, according to the evolution law obtained above, after a bus unipolar current signal after a residual current fault is indicated by a large-amplitude pulse, a small-amplitude state which can be maintained in the process of continuous occurrence is maintained. Therefore, when the variation of the second cycle of the continuous preset number of cycles after the current cycle is smaller than the preset attenuation threshold, the residual current fault result is a fault. The preset number can be set according to actual conditions, for example, in this embodiment, the preset number is 5.
In this embodiment, through looking over the pulse point of the wavelet analysis waveform of bus unipolar current signal, can confirm this point moment for the time point of circuit production direct current residual current, then through the reduction residual current characteristic trend that takes place constantly to make accurate judgement to the fault situation, greatly reduced traditional direct current residual current protector from this and measured the hardware volume.
It should be understood that, although the steps in the flowcharts related to the embodiments as described above are sequentially displayed as indicated by arrows, the steps are not necessarily performed sequentially as indicated by the arrows. The steps are not performed in the exact order shown and described, and may be performed in other orders, unless explicitly stated otherwise. Moreover, at least a part of the steps in the flowcharts related to the embodiments described above may include multiple steps or multiple stages, which are not necessarily performed at the same time, but may be performed at different times, and the execution order of the steps or stages is not necessarily sequential, but may be rotated or alternated with other steps or at least a part of the steps or stages in other steps.
Based on the same inventive concept, the embodiment of the application also provides a residual current fault detection system for realizing the residual current fault detection method. The implementation scheme for solving the problem provided by the system is similar to the implementation scheme recorded in the method, so that specific limitations in one or more embodiments of the residual current fault detection system provided below can be referred to the limitations on the residual current fault detection method in the foregoing, and details are not described herein again.
In one embodiment, the system comprises a current acquisition device and an upper computer, wherein the current acquisition device is connected with the anode/cathode of a bus, and the current acquisition device is also connected with the upper computer. The current acquisition device is used for acquiring a bus unipolar current signal; the upper computer is used for filtering and characteristic reconstruction of the bus unipolar current signal to obtain a wavelet analysis signal; the system is also used for analyzing the change rate of the wavelet analysis signal and extracting the period change of the wavelet analysis signal; and the method is also used for comparing the period variation with a preset threshold value to obtain a residual current fault result.
Specifically, the bus unipolar current signal is a current signal obtained by connecting only the bus positive electrode or the bus negative electrode. In one embodiment, the bus unipolar current signal is sampled at a sampling frequency and in a time window. Specifically, the values of the sampling frequency f and the time window T are not fixed, and may be set according to the actual bus current signal condition, for example, the sampling frequency f is 1MHz, and the time window T is 8 ms.
Furthermore, by simulating real residual current fault current generated in the direct current system, the method for identifying the residual current fault by measuring and analyzing the bus current is feasible. However, after the bus current of the system is further increased, the change of the bus current before and after the occurrence of the residual current fault is found to be reduced, so that the scheme considers that the bus current is analyzed by adopting a wavelet transformation method, and the residual current fault is identified.
Specifically, firstly, filtering the acquired bus unipolar current signal to obtain a filtered bus unipolar current signal, then performing wavelet transform on the filtered bus unipolar current signal by adopting a preset wavelet basis and a preset decomposition layer number, and extracting a decomposed low-frequency band wavelet coefficient according to a frequency band. And finally, performing characteristic construction on the low-frequency-band wavelet coefficient to obtain a wavelet analysis signal.
Specifically, the period variation includes a first period variation and a second period variation. And (4) taking the amplitude variation and the maximum amplitude of the wavelet analysis signal corresponding to the current time window. Then the amplitude variation is used as the first period variation of the current period; and taking the difference value of the maximum amplitude value and the maximum amplitude value of the wavelet analysis signal corresponding to the previous time window as the second period variable quantity of the current period.
In one embodiment, the residual current fault detection system further comprises a residual current simulation device, wherein the residual current simulation device is connected with the current collection device; the residual current simulation device is used for simulating to obtain simulated residual currents under different bus voltage levels, bus current levels and residual current levels; the current acquisition device is also used for acquiring a bus unipolar current signal comprising the simulated residual current; the upper computer is also used for judging more than two simulated residual current fault results according to the bus unipolar current signals comprising the simulated residual current, more than two wavelet parameters and more than two threshold values; according to more than two simulated residual current fault results, counting to obtain the residual current fault accuracy rate corresponding to each wavelet parameter and the threshold value; and selecting the wavelet parameter and the threshold with the highest residual current fault accuracy as a preset wavelet parameter and a preset threshold.
In one embodiment, as shown in fig. 13, the residual current simulation apparatus includes a dc power supply module, a variable resistor R1, a variable resistor R2, a resistor R +, a resistor R-, a timing switch-on module, and a current detection module, where the variable resistor R1 is connected between positive and negative output terminals of the dc power supply module, one end of the resistor R + is connected to a positive output terminal of the dc power supply module, one end of the resistor R-is connected to a negative output terminal of the dc power supply module, one end of the variable resistor R2 is connected to the timing switch-on module in series and then connected to the other end of the resistor R +, the other end of the resistor R-is connected to the other end of the resistor R-, and the current detection module is connected to two ends of the variable resistor R2 and the timing switch-on module in series; when the timing conduction module is conducted, the resistance values of the variable resistor R1 and the variable resistor R2 are adjusted, and simulation residual currents under different bus voltage levels, bus current levels and residual current levels are obtained through simulation.
Specifically, the resistor R + and the resistor R-respectively represent line resistances of the positive electrode and the negative electrode of the direct current bus. The variable resistor R1 can control the current of the loop bus, and the variable resistor R2 can control the current difference generated at the two ends of the bus, thereby achieving the purpose of simulating the generation of direct current residual current. The point A IPV2 and the point B IPV3 are detectable current points, when the time-lapse conducting module is conducted in an experiment, the variable resistor R2 is connected, the current values of the two points A, B are detected, the sum of the current values of the two points A, B is not zero, namely, the direct current residual current is generated in a line, and the required detected direct current residual current is A, B. Because the current at A, B is directly measured and then summed to obtain the residual current which is inaccurate, the current which is simulated and measured at the IPV4 of the variable resistor R2 is used as the final direct current residual current amplitude.
The timer conducting module comprises a timer and a switching element, the timer is connected with a control part of the switching element, and a controlled part of the switching element is connected with the variable resistor R2 in series. When the controlled part of the switch element is conducted, the variable resistor R2 is connected into the bus loop, so that the current difference generated at the two ends of the bus simulates to generate direct current residual current, and the magnitude of the direct current residual current generated by simulation can be changed by adjusting the resistance value of the variable resistor R2. The switching element may be a relay. The timer is used for outputting a conducting signal to the control part of the switching element after timing, and conducting the variable resistor R2, thereby realizing the purpose of increasing the residual current on the bus unipolar current signal at a specific moment.
As shown in fig. 14, the resistances of the variable resistor R1 and the variable resistor R2 of the simulation model are set, and an 80mA residual current fault occurs when the simulated bus voltage is 200V and the bus current is 10A. The direct current residual current is generated when the timing reaches 0.5s, the direct current residual current changes obviously, but the amplitude of the residual current is much smaller than that of the bus current, so that the change cannot be observed in the bus current in the whole time period, and the existence of the weak direct current residual current phenomenon is also verified in the simulation process, so that the necessity of accurately detecting the fault condition is verified. Further, the voltage and the current of the bus are kept unchanged, the residual current branch fault simulator is adjusted to increase the residual current to about 300mA, and the direct current residual current obtained through simulation is shown in fig. 15. Keeping the direct current residual current and the bus current unchanged, adjusting the bus voltage to be increased to about 400V, and obtaining the direct current residual current through simulation as shown in FIG. 16. It can be seen from the figure that the increased residual current makes the change of the bus current relatively obvious, and the influence of the amplitude of the direct current residual current is larger than the influence of the bus voltage on the current form. Under the support of the direct current residual current simulation device, the direct current residual current fault condition under the condition of larger bus current can be realized. Considering the bus voltage of 400V and the bus current of 20A, respectively, the bus current waveforms under the conditions of 80mA and 300mA dc residual current generation are shown in fig. 17 and 18. It can be clearly seen that the weak direct current residual current phenomenon frequently occurs under the condition of significantly increased bus current, and an effective weak direct current residual current detection method is urgently needed.
Further, the conditions of 200V system voltage and 300mA residual current are kept unchanged, the system current is changed within the range of 0-20A, and the residual current of the direct current system is in a descending rule trend as shown in fig. 19. The fact that the bus current is large as the types and the quantity of the load access are increased, the direct current residual current can show a decreasing trend along with the increase of the bus current, and the correctness of the obtained direct current residual current change trend under the previous experimental analysis condition is verified. Meanwhile, the simulation range of the direct current residual current can realize the influence of system voltage and current level outside the range of the experimental condition on the form and the characteristic of the direct current residual current.
The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present application. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present application shall be subject to the appended claims.
Claims (10)
1. A method of residual current fault detection, the method comprising:
acquiring a bus unipolar current signal;
filtering and characteristic reconstruction are carried out on the bus unipolar current signal by adopting a preset wavelet parameter to obtain a wavelet analysis signal;
analyzing the change rate of the wavelet analysis signal, and extracting the period change of the wavelet analysis signal;
comparing the period variation with a preset threshold value to obtain a residual current fault result;
and obtaining the preset wavelet parameters and the preset threshold value through residual current simulation analysis.
2. The method for detecting the residual current fault according to claim 1, wherein the process of obtaining the preset wavelet parameter and the preset threshold value through residual current simulation analysis comprises:
acquiring a bus unipolar current signal comprising simulated residual current; the simulation residual current is obtained by simulation under different bus voltage levels, bus current levels and residual current levels;
judging to obtain more than two simulation residual current fault results according to the bus unipolar current signals including the simulation residual current, more than two wavelet parameters and a threshold;
according to more than two simulated residual current fault results, counting to obtain the residual current fault accuracy rate corresponding to each wavelet parameter and the threshold value;
and selecting the wavelet parameter and the threshold with the highest residual current fault accuracy as a preset wavelet parameter and a preset threshold.
3. The method according to claim 1, wherein the preset wavelet parameters include a preset wavelet basis, a preset number of decomposition layers and a preset frequency band, and the filtering and feature reconstruction of the bus unipolar current signal using the preset wavelet parameters to obtain a wavelet analysis signal comprises:
filtering the bus unipolar current signal to obtain a filtered bus unipolar current signal;
performing wavelet transformation on the filtered bus unipolar current signal by adopting the preset wavelet basis and the preset decomposition layer number, and extracting a decomposed low-frequency band wavelet coefficient according to the preset frequency band;
and performing characteristic construction on the low-frequency-band wavelet coefficient to obtain a wavelet analysis signal.
4. The method of claim 1, wherein said obtaining a bus unipolar current signal comprises:
and sampling according to the sampling frequency and the time window to obtain the bus unipolar current signal.
5. The method of claim 4, wherein the period variation includes a first period variation and a second period variation, and the performing the rate of change analysis on the wavelet analysis signal to extract the period variation of the wavelet analysis signal comprises:
obtaining the amplitude variation and the maximum amplitude of the wavelet analysis signal corresponding to the current time window;
taking the amplitude variation as a first period variation of the current period;
and taking the difference value of the maximum amplitude value and the maximum amplitude value of the wavelet analysis signal corresponding to the previous time window as the second period variable quantity of the current period.
6. The method of claim 5, wherein the preset threshold comprises a preset pulse threshold and a preset attenuation threshold, and the comparing the periodic variation with the preset threshold to obtain the residual current fault result comprises:
when the first period variable quantity of the current period is smaller than the preset pulse threshold value, the residual current fault result is no fault;
and when the variable quantity of the first period of the current period is larger than the preset pulse threshold value, obtaining a residual current fault result according to the variable quantity of the second period after the current period and the preset attenuation threshold value.
7. The method of claim 6, wherein obtaining the residual current fault result according to the second period variation after the current period and the preset attenuation threshold comprises:
when the variation of a second period of a preset number of continuous periods after the current period is smaller than the preset attenuation threshold, the residual current fault result is a fault; otherwise, the residual current fault result is no fault.
8. The residual current fault detection system is characterized by comprising a current acquisition device and an upper computer, wherein the current acquisition device is connected with the anode/cathode of a bus and is also connected with the upper computer;
the current acquisition device is used for acquiring a bus unipolar current signal;
the upper computer is used for filtering and characteristic reconstruction of the bus unipolar current signal by adopting preset wavelet parameters to obtain a wavelet analysis signal; the wavelet analysis module is also used for analyzing the change rate of the wavelet analysis signal and extracting the period change of the wavelet analysis signal; the device is also used for comparing the period variation with a preset threshold value to obtain a residual current fault result; and obtaining the preset wavelet parameters and the preset threshold value through residual current simulation analysis.
9. The residual current fault detection system according to claim 8, further comprising a residual current simulation device, wherein the residual current simulation device is connected to the current collection device;
the residual current simulation device is used for simulating to obtain simulated residual currents under different bus voltage levels, bus current levels and residual current levels;
the current acquisition device is also used for acquiring a bus unipolar current signal comprising the simulated residual current;
the upper computer is also used for judging to obtain more than two simulated residual current fault results according to the bus unipolar current signals comprising the simulated residual currents, and more than two wavelet parameters and threshold values; according to more than two simulated residual current fault results, counting to obtain the residual current fault accuracy rate corresponding to each wavelet parameter and the threshold value; and selecting the wavelet parameter and the threshold with the highest residual current fault accuracy as a preset wavelet parameter and a preset threshold.
10. The residual current fault detection system according to claim 9, wherein the residual current simulation device comprises a dc power supply module, a variable resistor R1, a variable resistor R2, a resistor R +, a resistor R-, a timing conducting module and a current detection module, the variable resistor R1 is connected between positive and negative output terminals of the dc power supply module, one end of the resistor R + is connected to a positive output terminal of the dc power supply module, one end of the resistor R-is connected to a negative output terminal of the dc power supply module, one end of the variable resistor R2 is connected to the timing conducting module in series and then is connected to the other end of the resistor R +, the other end is connected to the other end of the resistor R-, and the current detection module is connected to both ends of the variable resistor R2 and the timing conducting module in series;
when the timing conducting module is conducted, the resistance values of the variable resistor R1 and the variable resistor R2 are adjusted, and simulation residual currents under different bus voltage levels, bus current levels and residual current levels are obtained through simulation.
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| CN116451044A (en) * | 2023-06-13 | 2023-07-18 | 深圳市超卓实业有限公司 | Machine adds equipment trouble early warning system based on data analysis |
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| CN116226776A (en) * | 2023-04-25 | 2023-06-06 | 广东电网有限责任公司云浮供电局 | Machine learning-based photovoltaic system abnormal residual current detection method |
| CN116451044A (en) * | 2023-06-13 | 2023-07-18 | 深圳市超卓实业有限公司 | Machine adds equipment trouble early warning system based on data analysis |
| CN116451044B (en) * | 2023-06-13 | 2023-08-18 | 深圳市超卓实业有限公司 | Machine adds equipment trouble early warning system based on data analysis |
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