Demagnetization device and method for weak current sensor

Abstract

The invention belongs to the technical field of electrical measurement, and particularly discloses a demagnetization device and method for a weak current sensor. The device is characterized in that a demagnetization starting unit is used for extracting current frequency domain data in a tth time period, acquiring all-even-order harmonics in the tth time period, comparing the all-even-order harmonics in the tth time period with an all-even-order harmonic component threshold, and judging whether to start the demagnetization unit by combining the state of a weak current sensor in a (t-1) th time period; the demagnetization unit is used for providing demagnetization current for demagnetization according to the all-even harmonic and the demagnetization times; and the demagnetization detection unit is used for carrying out full-frequency-domain current detection according to the current deviation between the measured current and the current during normal operation, and if demagnetization is not thorough, the demagnetization unit is driven to carry out multiple times of demagnetization. The method improves the resolution and accuracy of weak current detection, and guarantees the safe and stable operation of a power grid system.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrical measurement, and more particularly relates to a demagnetization device and method for a weak current sensor. BACKGROUND

[0002] As one of the information quantities of power grid electricity detection, the implementation of comprehensive and accurate measurement of current plays a crucial role in the power grid system. Through the measurement and accurate detection of the current, problems can be found in time, and safety hazards can be eliminated.

[0003] The magnetic modulation type current sensor is widely used in the field of weak current detection due to its high stability and low noise characteristics. Therefore, it is often applied to the ultra-high voltage direct current transmission system and installed in the converter transformer, lightning arrester and other structures for measuring leakage current. The patent document (CN109870632A- separable ampere level alternating current and microampere level direct current self-calibration type current transformer) provides a non-contact sensor for measuring weak current signals, and the resolution of the measurement reaches the microampere level, which can realize accurate measurement of mA level alternating current microampere direct current mixed signals. However, when the ultra-high voltage direct current transmission system is subjected to short circuit, lightning strike, pulse and surge and other transient large impacts, the magnetic modulator contains residual magnetism, which will cause inaccurate measurement of the magnetic modulator, and even may cause abnormal work. Therefore, there is an urgent need for a demagnetization device and method for a weak current sensor to further improve the resolution and accuracy of current detection and lay a foundation for the safe and stable operation of the smart grid. SUMMARY

[0004] In view of the defects of the prior art, the purpose of the present application is to provide a demagnetization device and method for a weak current sensor, which aims to solve the problem that when the ultra-high voltage direct current transmission system is subjected to short circuit, lightning strike, pulse and surge and other transient large impacts, the magnetic modulator contains residual magnetism, which will cause inaccurate measurement of the magnetic modulation type current sensor.

[0005] The first aspect of the present application relates to a demagnetization device for a weak current sensor, comprising: a demagnetization starting unit, a demagnetization unit and a demagnetization detection unit; The demagnetization starting unit is used to obtain the current measurement data of the weak current sensor, extract the current frequency domain data in the tth time period, obtain the full even harmonic in the tth time period, compare the full even harmonic in the tth time period with the full even harmonic component threshold, and combine the t-1th time period weak current sensor state. When it is judged that the tth time period is abnormal from the weak current sensor state and turns to normal, the demagnetization unit is started; The demagnetization unit is used to provide demagnetization current according to the full even harmonic in the tth time period and the demagnetization number for demagnetization; The demagnetization detection unit is used to detect the current deviation between the measured current and the normal operation current, and if the demagnetization is not complete, the demagnetization unit is driven to demagnetize multiple times.

[0006] In some embodiments, the demagnetization start unit is set to represents that the weak current sensor state is normal in the t-1 time period, represents that the weak current sensor state is abnormal in the t-1 time period, and when , if , then , if , then , when , if , then , if , then , , until , update ; wherein is the full even harmonic component threshold value; , are the abnormality counters of the system in the t-step time period and the t-1 step time period, respectively; is the full even harmonic in the t time period; p is the total number of steps of the set one-time demagnetization operation.

[0007] In some embodiments, the demagnetization current in the demagnetization unit is:

[0008] wherein is the proportional coefficient, is the number of demagnetizations, is the full even harmonic current measured when the weak current sensor is in normal operation and there is no residual magnetism; is the full even harmonic in the t time period; is the full even harmonic measured by the weak current sensor after the first demagnetization step.

[0009] In some embodiments, the current deviation in the demagnetization detection unit is:

[0010] wherein is the harmonic value of the measured current, is the current in normal operation Second harmonic value m Represents the highest harmonic of the measured current; setting This is the allowable value for demagnetization testing. If the measured current deviates from the normal operating current by no more than [percentage missing], [the value is missing]. If the measured current demagnetizes completely, it is considered demagnetization is complete; if the measured current deviates from the normal operating current by more than [a certain amount], it is considered demagnetization is complete. If so, it indicates that the demagnetization was incomplete.

[0011] In some embodiments, the demagnetizing unit includes a demagnetizing winding and a demagnetizing power supply; the demagnetizing winding is uniformly wound around a magnet on a weak current sensor; both ends of the demagnetizing winding are connected to the demagnetizing power supply.

[0012] In some implementations, the demagnetizing unit is used to set the scaling factor, the number of demagnetizing steps, the frequency of the demagnetizing power supply, and the time interval between each demagnetizing step according to actual needs.

[0013] The second aspect of this application relates to a demagnetizing method for a weak current sensor, comprising the following steps: Step 1: Based on the current measurement data of the weak current sensor, extract the current frequency domain data in the t-th time period, obtain the even harmonics in the t-th time period, compare the even harmonics in the t-th time period with the threshold of the even harmonic components, and combine the state of the weak current sensor in the (t-1)-th time period. When it is determined that the state of the weak current sensor changes from abnormal to normal in the t-th time period, proceed to Step 2. Step 2: Set the proportional coefficient, number of demagnetization steps, frequency of the demagnetization power supply, and time interval between each demagnetization step. Provide the first demagnetization current based on the even harmonics and number of demagnetization steps in the t-th time period to perform demagnetization. Step 3: After completing the first step of the first demagnetization operation, calculate the demagnetizing current and time required for the second step of demagnetization based on the all-even harmonic current after the first step. Continue this process until the next step... Demagnetization is complete; the first demagnetization step is finished. Step 4: Calculate the current deviation between the measured current and the normal operating current, and perform full-frequency domain current detection. If demagnetization is incomplete, proceed to Step 2 until demagnetization is complete.

[0014] In some implementations, in step one, setting This indicates that the weak current sensor is functioning normally during the (t-1)th time period. This indicates that the weak current sensor is in an abnormal state during the (t-1)th time period. At that time, if Then let , ;like Then let , ;when At that time, if Then let , ;like Then let , until ,renew ;exist After changing from 0 to 1, the demagnetization operation is initiated. in, The threshold value for all even harmonic components; , These are the values ​​of the system's anomaly counter during the t-th and t-1-th time intervals, respectively. The t-th time interval contains all even harmonics; p This represents the total number of steps in one demagnetization operation.

[0015] In some implementations, the demagnetizing current is:

[0016] in, This is the proportionality coefficient. The number of times the magnetization is performed. The measured even-order harmonic current is the current of a weak current sensor under normal operation and without residual magnetism. The t-th time interval contains all even harmonics; For the first After demagnetization, the weak current sensor measures the even-order harmonic current.

[0017] In some implementations, the current deviation in step four is:

[0018] in, For measuring current Second harmonic value Current during normal operation Second harmonic value m Represents the highest harmonic of the measured current; setting This is the allowable value for demagnetization testing. If the measured current deviates from the normal operating current by no more than [percentage missing], [the value is missing]. If the measured current demagnetizes completely, it is considered demagnetization is complete; if the measured current deviates from the normal operating current by more than [a certain amount], it is considered demagnetization is complete. If so, it indicates that the demagnetization was incomplete.

[0019] Overall, the technical solutions conceived in this application have the following beneficial effects compared with the prior art: The application provides a demagnetization device and method of a weak current sensor, and a demagnetization unit is introduced on the basis of a magnetic modulation type weak current sensor, so that the influence of residual magnetism on the magnetic modulation type weak current sensor after the magnetic modulation type weak current sensor encounters transient impact such as lightning, surge and short circuit and cannot work normally is greatly improved, the resolution and accuracy of weak current detection are further improved, and the safe and stable operation of a power grid system is ensured. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 Fig. 1 is a structural schematic diagram of a demagnetization device of a weak current sensor provided by an embodiment of the application.

[0021] Figure 2 Fig. 2 is a flowchart of a demagnetization method of a weak current sensor provided by an embodiment of the application.

[0022] In all the drawings, the same reference signs are used to represent the same elements or structures, in which: 1 is a sensor excitation source; 2 is a ring-shaped magnetic core; 3 is a sensor output module; 4 is an external demagnetization power supply; 5 is a demagnetization starting unit; 6 is a demagnetization detection unit; and 7 is a demagnetization unit. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the application more clear, the application is further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the application and should not be used to limit the application.

[0024] In the application, the term "and / or" is used to describe the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B can mean that A exists alone, A and B exist together, and B exists alone. In the application, the symbol " / " represents the relationship of or, for example, A / B represents A or B.

[0025] In the application, the terms "first" and "second" are used to distinguish different objects, rather than to describe the specific order of the objects.

[0026] In the embodiments of the application, the words such as "exemplary" or "for example" are used to mean by way of example, illustration or description. Any embodiment or design scheme described as "exemplary" or "for example" in the embodiments of the application should not be interpreted as more preferred or more advantageous than other embodiments or design schemes. Rather, the words such as "exemplary" or "for example" are intended to present the relevant concept in a specific manner.

[0027] In the description of the embodiments of the application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0028] The application provides a demagnetization device and method of a weak current sensor. On the basis of a magnetic modulation type weak current sensor, a demagnetization unit is introduced, which greatly improves the influence of remanence on the magnetic modulation type weak current sensor after the sensor encounters transient impacts such as lightning, surges and short circuits, so that the weak current sensor cannot work normally, and further improves the resolution and accuracy of weak current detection, lays a foundation for advanced applications of smart grids, and ensures safe and stable operation of the system.

[0029] The embodiments of the application are described below with reference to the accompanying drawings.

[0030] In one aspect, as Figure 1 shown, the application provides a demagnetization device of a weak current sensor, comprising: a demagnetization starting unit, a demagnetization unit and a demagnetization detection unit; Among them, the weak current sensor includes a sensor excitation source 1, a ring-shaped magnetic core 2 and a sensor output module 3; The demagnetization starting unit 5 is used to obtain the weak current sensor measurement current data based on the weak current sensor measurement current data, extract the current frequency domain data in the first t time period by using Fourier analysis , so as to obtain all even harmonics ; wherein, represents the time period, is the number of harmonics; Set represents that the state of the weak current sensor in the t-1 time period is normal, represents that the state of the weak current sensor in the t-1 time period is abnormal, and the state is determined according to the state flag bit of the previous time period ; When , let , ; if , let , ; wherein, is the threshold of all even harmonic components; , are respectively the abnormal counter values of the system in the t step time period and the t-1 step time period; specifically, can be represented as:

[0031] When , let , ; if , let , , until , update , specifically, can be expressed as:

[0032] In After changing from 0 to 1, the demagnetization unit starts, and the demagnetization signal is transmitted to the demagnetization unit; The demagnetization unit 7 includes a demagnetization winding Uniformly wound on the magnet on the weak current sensor, the two ends of the demagnetization winding are connected with the external demagnetization power supply 4 respectively; the external demagnetization power supply 4 is an alternating current source, which can provide a demagnetization current with a frequency of According to the law of electromagnetic induction, the magnetic field strength is equal to the ratio of magnetic flux and length:

[0033] Magnetic flux The number of turns of the demagnetization coil , demagnetization current And the shape of the coil, which can be expressed as:

[0034] Operation:

[0035] In the case of fixed vacuum permeability , relative permeability , demagnetization coil turns And the length of the demagnetization coil By constantly changing the size of the demagnetization current , realize demagnetization, and the demagnetization current Mainly determined by the full even harmonic And the number of demagnetization times, the size of the demagnetization current The time of demagnetization is set as follows:

[0036] Among them, The proportionality coefficient, The number of demagnetization, The full even harmonic current measured under the condition that the sensor is running normally and there is no residual magnetism, The full even harmonic current measured by the sensor after the first demagnetization Step; Demagnetization detection unit 6: after the first demagnetization of the demagnetization unit is completed, the completion signal is sent to the demagnetization detection unit, and the residual magnetism detection is carried out. The residual magnetism can be reflected by measuring the current deviation from the normal running current, and the difference between the two is , using full frequency domain current detection, specifically as follows:

[0037] Wherein, 20 here represents 1st harmonic (power frequency) to 20th harmonic; The current measured by the current sensor The current measured by the current sensor The current measured by the current sensor The current measured by the current sensor If the measured current deviates from the normal operation current by no more than , that is, , then it is determined that demagnetization is complete; if the measured current deviates from the normal operation current by more than , that is,

[0038] The second aspect, as shown in Figure 2 , the application provides a demagnetization method of a weak current sensor, comprising: Step S1: the demagnetization unit receives the signal of the demagnetization starting unit, and starts to prepare for demagnetization; Step S2: the demagnetization power supply is started, and the proportionality coefficient , the demagnetization step number , the frequency of the demagnetization power supply , and the time interval between each demagnetization step are set; Step S3: demagnetization starts, and the demagnetization coil completes the first step of demagnetization program according to the set settings, and the demagnetization current of the first step is usually the largest; Step S4: after completing the first step of demagnetization operation, the demagnetization coil enters the demagnetization time interval period, during which no demagnetization current is generated; at the same time, the demagnetization unit analyzes and calculates the output current of the sensor at this time to obtain the full even harmonic current after the first step of demagnetization, and calculates the demagnetization current and demagnetization time required for the second step of demagnetization; Step S5: the second step of demagnetization is performed, and then step S402 is repeated to calculate the demagnetization current and demagnetization time required for the third step of demagnetization; Step S6: in this way, until the step of demagnetization is completed, and the first demagnetization is ended; the demagnetization unit sends the first demagnetization signal to the demagnetization detection unit; Step S7: the demagnetization detection unit analyzes and calculates the output current of the sensor at this time to obtain the harmonic value , and compares the deviation with the measured current under the normal and error-free condition; If the measured current deviates from the normal operation current by no more than , that is, , it is determined that demagnetization is complete; if the measured current deviates from the normal operation current by more than , that is, , the demagnetization detection unit sends a demagnetization signal to the demagnetization unit again, and step S2 is repeated until demagnetization is complete.

[0039] In some specific manners, the proportional coefficient , the demagnetization step number , the frequency of the demagnetization power supply , and the time interval between each demagnetization step may be set according to actual needs to ensure correct demagnetization.

[0040] On the other hand, the application provides a demagnetization device and method for a weak current sensor, which selects the leakage current data of a 800kV ultra-high voltage direct current transmission system converter transformer valve side bushing to the ground, performs demagnetization operation after artificial setting of lightning and the like, and ensures the accuracy of the measurement of the weak current sensor, and the specific steps are as follows: Step S1: According to the analysis result of the leakage current in the normal operation condition, the leakage current measured by the weak current sensor is subjected to Fourier analysis, and the data is shown in Table 1: Table 1

[0041] The full even harmonic of the leakage current in the normal operation condition is obtained:

[0042] In the t time period, an artificial fault is set, a 1S long direct current grounding fault is set in the system, the leakage current at this time is measured, and Fourier analysis is also performed, and the result is shown in Table 2: Table 2

[0043] According to the data result of Table 2, the full even harmonic of the t time period is obtained:

[0044] The full even harmonic component threshold is set to 20mA, the set , and , therefore, ​This indicates that the system has entered an abnormal state; repeat the above operation to measure the leakage current in time period t+1, and perform the Fourier analysis in step 1 as well. The results are shown in Table 3: Table 3

[0045] Based on the data in Table 3, the fully even harmonics in the (t+1)th time interval are obtained. :

[0046] Comparison ,therefore , Analyzing the leakage current data for the next time period again, the following calculations were performed: ,at this time, , The value changing from 0 to 1 triggers the demagnetization unit to start. Step S2: Start the external demagnetizing power supply and set the proportional coefficient of the external demagnetizing power supply. =0.02, number of demagnetization steps The frequency of the demagnetizing power supply Hz and the time interval between each demagnetization step Perform the first demagnetization operation and calculate the demagnetization current:

[0047] Table 4 shows the leakage current data measured by the weak current sensor after the first step of demagnetization: Table 4

[0048] Based on the results of step 1 demagnetization, The full even harmonic current measured by the sensor after the first demagnetization step: Calculate the demagnetizing current in step 2:

[0049] Perform step 2 demagnetization, and so on. After step 2 demagnetization is completed, perform step 3 demagnetization, and so on until step 30 demagnetization is completed. Step S3: After demagnetization in step 30, the first demagnetization procedure is complete, the demagnetization detection unit is activated, and the demagnetization detection allowable value is set. The leakage current measured after the first demagnetization The data is shown in Table 5: Table 5

[0050] Perform full-frequency domain current detection:

[0051] , demagnetization end, weak current sensor residual magnetism is cleared.

[0052] The application provides a demagnetization device and method of a weak current sensor. On the basis of a magnetic modulation type weak current sensor, a demagnetization unit is introduced, which greatly improves the influence of residual magnetism on the magnetic modulation type weak current sensor after the sensor encounters transient impacts such as lightning, surges and short circuits, and further improves the resolution and accuracy of weak current detection, thereby ensuring the safe and stable operation of a power grid system.

[0053] It should be understood that expressions such as "include" and "may include" used in the present application indicate the presence of disclosed functions, operations or constituent elements, and do not limit one or more additional functions, operations and constituent elements. In the present application, terms such as "include" and / or "have" can be interpreted to mean that a specific characteristic, number, operation, constituent element, component or combination thereof is present, but cannot be interpreted to exclude the presence or addition of one or more other characteristics, numbers, operations, constituent elements, components or combinations thereof.

[0054] In the description of the embodiments of the present application, it should be noted that, unless otherwise explicitly specified and limited, the term "connection" should be understood broadly, for example, "connection" can be detachable connection, or can be non-detachable connection; can be direct connection, or can be indirect connection through an intermediate medium.

[0055] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A demagnetizing device for a weak current sensor, characterized in that, include: Demagnetization start unit, demagnetization unit, and demagnetization detection unit; The demagnetizing start unit is used to extract the current frequency domain data in the t-th time period from the current data measured by the weak current sensor, obtain the even harmonics in the t-th time period, compare the even harmonics in the t-th time period with the threshold of the even harmonic components, and combine the state of the weak current sensor in the (t-1)-th time period. When it is determined that the state of the weak current sensor changes from abnormal to normal in the t-th time period, the demagnetizing unit is started. The demagnetizing unit is used to provide demagnetizing current according to the even harmonics and the number of demagnetizations in the t-th time period, so as to perform demagnetization; The demagnetization detection unit is used to perform full-frequency domain current detection based on the current deviation between the current measured by the weak current sensor and the current under normal operating conditions. If the demagnetization is not complete, the demagnetization unit is driven to perform demagnetization multiple times.

2. The demagnetizing device according to claim 1, characterized in that, Setting in the demagnetization start unit This indicates that the weak current sensor is functioning normally during the (t-1)th time period. This indicates that the weak current sensor is in an abnormal state during the (t-1)th time period. At that time, if Then let , ;like Then let , ;when At that time, if Then let , ;like Then let , until ,renew ; in, The threshold value for all even harmonic components; , These are the values ​​of the system's anomaly counter during the t-th and t-1-th time intervals, respectively. The t-th time interval contains all even harmonics; p This represents the total number of steps in one demagnetization operation.

3. The demagnetizing device according to claim 1, characterized in that, The demagnetizing current in the demagnetizing unit is: in, This is the proportionality coefficient. The number of times the magnetization is performed. The measured even-order harmonic current is the current of a weak current sensor under normal operation and without residual magnetism. The t-th time interval contains all even harmonics; For the first After demagnetization, the weak current sensor measures the even-order harmonic current.

4. The demagnetizing device according to any one of claims 1 to 3, characterized in that, The current deviation in the demagnetization detection unit is: in, For measuring current Second harmonic value Current during normal operation Second harmonic value m Represents the highest harmonic of the measured current; setting This is the allowable value for demagnetization detection. If the current deviation between the measured current and the current under normal operating conditions does not exceed... If the measured current demagnetizes completely, it is considered demagnetization is complete; if the measured current deviates from the normal operating current by more than [a certain amount], it is considered demagnetization is complete. If so, it indicates that the demagnetization was incomplete.

5. The demagnetizing device according to claim 1, characterized in that, The demagnetizing unit includes a demagnetizing winding and a demagnetizing power supply; the demagnetizing winding is evenly wound on the magnet of the weak current sensor; the two ends of the demagnetizing winding are respectively connected to the demagnetizing power supply.

6. The demagnetizing device according to claim 5, characterized in that, The demagnetizing unit is used to set the proportional coefficient, number of demagnetizing steps, frequency of the demagnetizing power supply, and time interval between each demagnetizing step according to actual needs.

7. A method for demagnetizing a weak current sensor, characterized in that, Includes the following steps: Step 1: Based on the current measurement data of the weak current sensor, extract the current frequency domain data in the t-th time period, obtain the even harmonics in the t-th time period, compare the even harmonics in the t-th time period with the threshold of the even harmonic components, and combine the state of the weak current sensor in the (t-1)-th time period. When it is determined that the state of the weak current sensor changes from abnormal to normal in the t-th time period, proceed to Step 2. Step 2: Set the proportional coefficient, number of demagnetization steps, frequency of the demagnetization power supply, and time interval between each demagnetization step. Provide the first demagnetization current based on the even harmonics and number of demagnetization steps in the t-th time period to perform demagnetization. Step 3: After completing the first step of the first demagnetization operation, calculate the demagnetizing current and time required for the second step of demagnetization based on the all-even harmonic current after the first step. Continue this process until the next step... Demagnetization is complete; the first demagnetization step is finished. Step 4: Calculate the current deviation between the measured current and the normal operating current, and perform full-frequency domain current detection. If demagnetization is incomplete, proceed to Step 2 until demagnetization is complete.

8. The demagnetizing method according to claim 7, characterized in that, In step one, set This indicates that the weak current sensor is functioning normally during the (t-1)th time period. This indicates that the weak current sensor is in an abnormal state during the (t-1)th time period. At that time, if Then let , ;like Then let , ;when At that time, if Then let , ;like Then let , until ,renew ;exist After changing from 0 to 1, the demagnetization operation is initiated. in, The threshold value for all even harmonic components; , These are the values ​​of the system's anomaly counter during the t-th and t-1-th time intervals, respectively. The t-th time interval contains all even harmonics; p This represents the total number of steps in one demagnetization operation.

9. The demagnetizing method according to claim 7 or 8, characterized in that, The demagnetizing current is: in, This is the proportionality coefficient. The number of times the magnetization is performed. The measured even-order harmonic current is the current of a weak current sensor under normal operation and without residual magnetism. The t-th time interval contains all even harmonics; For the first After demagnetization, the weak current sensor measures the even-order harmonic current.

10. The demagnetization method according to claim 7, characterized in that, The current deviation in step four is: in, For measuring current Second harmonic value Current during normal operation Second harmonic value m Represents the highest harmonic of the measured current; setting This is the allowable value for demagnetization testing. If the measured current deviates from the normal operating current by no more than [percentage missing], [the value is missing]. If the measured current demagnetizes completely, it is considered demagnetization is complete; if the measured current deviates from the normal operating current by more than [a certain amount], it is considered demagnetization is complete. If so, it indicates that the demagnetization was incomplete.

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