Direct-current residual current detection device

Abstract

The invention provides a direct-current residual current detection device. The direct-current residual current detection device comprises an amplification ring, a shielding ring, a sensor and a signal processing module, a to-be-detected magnetic field is amplified through the amplification ring, a stray magnetic field is shielded through the shielding ring, a magnetic field intensity signal generated by residual current of a to-be-detected double-core wire is detected through the sensor and converted into a voltage signal to be sent to the signal processing unit to be processed so as to output direct-current residual current, and the direct-current residual current can be monitored in real time through one-time installation. The device does not need to change the original circuit, can overcome the problem that the DC residual current detection is liable to be interfered by a stray magnetic field, and guarantees the detection precision and stability of the DC residual current under the condition of magnetic field interference.

Description

Technical Field

[0001] The present invention relates to the technical field of residual current detection, and particularly relates to a DC residual current detection device. Background Art

[0002] With the rapid development of new energy power, DC distributed power sources such as photovoltaic and wind power, and DC loads such as new energy vehicle charging piles are connected to the power grid. The new AC-DC power grid is booming, and the subsequent residual current detection technology urgently needs to be innovated. Residual current refers to the current whose vector sum of currents in each phase (including the neutral line) in a low-voltage distribution line is not zero. When faults such as short circuits, overloads, and poor grounding occur in the power system or the operating state of equipment is unstable, residual current will be generated. Severe residual current will endanger personal safety, cause equipment damage, lead to unstable operation of the power system and energy waste.

[0003] In related technologies, the power system improves the safety of the AC power supply system by adding an overcurrent protection module or a leakage protection module; in addition, due to the complex and diverse forms of residual current caused by lack of maintenance of electrical equipment, aging of insulation, non-standard distribution installation, or overloaded distribution lines, the detection results of the device for real-time detection of residual current are inaccurate, and the detected residual current is less than the actual value, resulting in false alarms, and there are major safety hazards in the power supply system.

[0004] There is also a TMR current sensor made by a tunneling magnetoresistive sensor TMR. However, when the measured current is direct current, the induced magnetic field will be affected by stray magnetic fields such as geomagnetism, thereby affecting the accuracy of the TMR current sensor when measuring current. Summary of the Invention

[0005] The present invention provides a DC residual current detection device, and its purpose is to ensure the detection accuracy of residual current.

[0006] In order to achieve the above purpose, the present invention provides a DC residual current detection device, including:

[0007] An amplification loop for amplifying the magnetic field to be measured, a shielding loop for shielding stray magnetic fields, a sensor for detecting the magnetic field intensity signal generated by the residual current of the double-core wire to be measured, and a signal processing module for outputting DC residual current;

[0008] The outer diameter of the amplification loop is smaller than the inner diameter of the shielding loop;

[0009] The amplification loop and the shielding loop form a concentric double magnetic ring. The amplification loop is arranged inside the shielding loop, and the double-core wire to be measured vertically passes through the center of the concentric double magnetic ring;

[0010] An amplification loop air gap is provided on the amplification loop, and the sensor is arranged at the amplification loop air gap of the amplification loop;

[0011] The output end of the sensor is electrically connected to the input end of the signal processing module.

[0012] Furthermore, the sensor is a TMR linear magnetic field sensor.

[0013] Furthermore, the signal processing module includes:

[0014] A power supply unit, a zero-adjusting unit, an amplifying unit, a filtering unit, a display unit, and a processing unit;

[0015] The input end of the power supply unit is connected to the mains end, and the output end of the power supply unit is respectively connected to the power supply ends of the zero-adjusting unit, the amplifying unit, the filtering unit, and the processing unit;

[0016] The output end of the zero-adjusting unit is connected to the zero-adjusting end of the amplifying unit, the input end of the amplifying unit is connected to the output end of the sensor, the output end of the amplifying unit is connected to the input end of the filtering unit, the output end of the filtering unit is respectively connected to the first input end of the display unit and the input end of the processing unit, and the output end of the processing unit is connected to the second input end of the display unit.

[0017] Furthermore, the size of the amplification loop is determined by the amplification factor.

[0018] Furthermore, the process of determining the size of the amplification loop by the amplification factor includes:

[0019] Based on the residual current detection model without an amplification loop established at the target point to be measured, the magnetic induction intensity at the target point to be measured is obtained;

[0020] Based on the residual current detection model with an amplification loop established at the target point to be measured, the magnetic induction intensity at the point to be measured at the air gap of the amplification loop is obtained;

[0021] According to the magnetic induction intensity at the target point to be measured and the magnetic induction intensity at the point to be measured at the air gap of the amplification loop, an amplification factor expression of the amplification loop is obtained;

[0022] According to the amplification factor expression of the amplification loop, the key variables affecting the amplification factor of the amplification loop are determined;

[0023] Using simulation software to establish a simulation model of the double-core wire to be measured and an amplification loop model;

[0024] Matching the parameters of the double-core wire to be measured with the actual working conditions and setting the specific values of the key variables affecting the amplification factor of the amplification loop to simulate the simulation model and the amplification loop model, and obtaining the size of the amplification loop.

[0025] Furthermore, the size of the shielding loop is determined by the shielding effectiveness.

[0026] Furthermore, the process of determining the size of the shielding ring based on the shielding effectiveness includes:

[0027] Based on the established external magnetic field shielding model of the shielding ring, an expression for the shielding effectiveness of the shielding ring is obtained;

[0028] According to the shielding effectiveness expression of the shielding ring, the factors affecting the shielding effectiveness of the shielding ring are determined;

[0029] According to the size of the amplification ring, the shielding effectiveness expression of the shielding ring is simplified to obtain the key factors affecting the shielding effectiveness;

[0030] Using simulation software, a shielding ring model is established and a static magnetic field is applied along the X-axis as the stray magnetic field;

[0031] The parametric scanning method is used to set the specific values of the key factors affecting the shielding effectiveness to simulate the shielding ring, and the size of the shielding ring is obtained.

[0032] Furthermore, there is a gap between the inner diameter of the shielding ring and the outer diameter of the amplification ring.

[0033] The above solution of the present invention has the following beneficial effects:

[0034] The DC residual current detection device provided by the present invention includes an amplification ring, a shielding ring, a sensor, and a signal processing module; compared with the prior art, the present invention amplifies the magnetic field to be measured through the amplification ring, shields the stray magnetic field through the shielding ring, detects the magnetic field intensity signal generated by the residual current of the double-core wire to be measured through the sensor and converts it into a voltage signal and sends it to the signal processing unit for processing to output the DC residual current. It can monitor the DC residual current in real time with one installation, and using this device does not require changing the original circuit wiring, and can also overcome the problem that DC residual current detection is easily interfered by stray magnetic fields, and ensure the detection accuracy and stability of DC residual current in the face of magnetic field interference.

[0035] Other beneficial effects of the present invention will be described in detail in the subsequent specific implementation part. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic structural diagram of an embodiment of the present invention;

[0037] Figure 2 It is a structural diagram of the signal processing module in an embodiment of the present invention;

[0038] Figure 3 It is a circuit schematic diagram of the signal processing module in an embodiment of the present invention;

[0039] Figure 4 It is a schematic diagram of the magnetic field generated by an energized DC double-core wire at any point P in space;

[0040] Figure 5 Schematic diagram of the amplified magnetic field of the amplification loop;

[0041] Figure 6 Schematic diagram of the shielding of the shielding loop in the embodiment of the present invention;

[0042] Figure 7 Schematic diagram of the response characteristics of the concentric double magnetic rings in the embodiment of the present invention.

[0043] Explanation of the reference numerals in the drawings:

[0044] 1 - Amplification loop, 2 - Shielding loop, 3 - Sensor. Specific implementation manners

[0045] To make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the drawings and specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0046] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention. In addition, the terms "first", "second", "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0047] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installed", "connected", "connected" should be understood in a broad sense. For example, it can be a locking connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0048] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0049] The present invention provides a DC residual current detection device for existing problems.

[0050] As Figure 1As shown in the figure, an embodiment of the present invention provides a DC residual current detection device, including:

[0051] An amplification loop 1 for amplifying the magnetic field to be measured, a shielding loop 2 for shielding stray magnetic fields, a sensor 3 for detecting the magnetic field intensity signal generated by the residual current of the double-core wire to be measured, and a signal processing module for outputting DC residual current;

[0052] The amplification loop 1 and the shielding loop 2 form a concentric double magnetic ring. The amplification loop 1 is arranged inside the shielding loop 2, and the double-core wire to be measured vertically passes through the center of the concentric double magnetic ring;

[0053] An amplification loop air gap is provided on the amplification loop 1, and the sensor 3 is arranged at the amplification loop air gap of the amplification loop 1;

[0054] The output end of the sensor 3 is electrically connected to the input end of the signal processing module.

[0055] Most preferably, the sensor 3 is a TMR linear magnetic field sensor.

[0056] It should be noted that the linear magnetic field sensor (TMR, Tunneling Magnetoresistance) is a magnetic sensor based on the tunneling magnetoresistance effect. By using the tunnel structure in the micro-nano structure, high-sensitivity and low-power magnetic field measurement are realized under the action of an external magnetic field; it has high sensitivity, can accurately measure tiny magnetic fields, is suitable for occasions requiring high-precision magnetic field measurement, has low power consumption, can save energy and extend the service life of the device, and maintains stable performance in a wide temperature range, suitable for application requirements under various environmental conditions.

[0057] Most preferably, as Figure 2 shown, the signal processing module includes:

[0058] A power supply unit, a zero adjustment unit, an amplification unit, a filtering unit, a display unit, and a processing unit;

[0059] The input end of the power supply unit is connected to the mains end, and the output end of the power supply unit is respectively connected to the power supply ends of the zero adjustment unit, the amplification unit, the filtering unit, and the processing unit;

[0060] The output end of the zero adjustment unit is connected to the zero adjustment end of the amplification unit. The input end of the amplification unit is connected to the output end of the sensor. The output end of the amplification unit is connected to the input end of the filtering unit. The output end of the filtering unit is respectively connected to the first input end of the display unit and the input end of the processing unit. The output end of the processing unit is connected to the second input end of the display unit.

[0061] In the embodiment of the present invention, the circuit diagram of the signal processing module is as Figure 3 shown, and it is composed of Figure 3It can be seen that the power supply unit includes a power interface composed of a socket, a first inductor L1, a fifth capacitor C5, and a sixth capacitor C6, a DC-DC conversion circuit composed of a conversion chip, a second inductor L2, a third inductor L3, a third capacitor C3, and a fourth capacitor C4, a decoupling capacitor circuit composed of a seventh capacitor C7, an eighth capacitor C8, a ninth capacitor C9, a tenth capacitor C10, an eleventh capacitor C11, and a twelfth capacitor C12, and a single-chip microcomputer power supply circuit composed of a buck chip, a thirteenth capacitor C13, a fourteenth capacitor C14, a fifteenth capacitor C15, a sixteenth capacitor C16, a seventeenth capacitor C17, and an eighteenth capacitor C18;

[0062] The first pin of the socket is respectively connected to the positive electrode of the sixth capacitor C6 and the first end of the first inductor L1, and the second end of the first inductor L1 is respectively connected to the positive electrode of the fifth capacitor C5 and the second pin of the conversion chip;

[0063] The second pin of the socket is respectively connected to the negative electrode of the sixth capacitor C6 and the negative electrode of the fifth capacitor C5 and grounded;

[0064] The first pin of the conversion chip is grounded;

[0065] The sixth pin of the conversion chip is connected to the first end of the second inductor L2, and the second end of the second inductor L2 is respectively connected to the positive electrode of the third capacitor C3, the positive electrode of the seventh capacitor C7, the positive electrode of the eighth capacitor C8, the positive electrode of the ninth capacitor C9, the first end of the tenth capacitor C10, the first end of the eleventh capacitor C11, the first end of the twelfth capacitor C12, the first pin of the buck chip, the positive power supply end of the amplification unit, the positive power supply end of the zero adjustment unit, and the positive power supply end of the filtering unit;

[0066] The seventh pin of the conversion chip is respectively connected to the negative electrode of the third capacitor C3 and the positive electrode of the fourth capacitor C4 and grounded;

[0067] The eighth pin of the conversion chip is connected to the first end of the third inductor L3, and the second end of the third inductor L3 is respectively connected to the negative electrode of the fourth capacitor C4, the negative electrode of the seventh capacitor C7, the negative electrode of the eighth capacitor C8, the negative electrode of the ninth capacitor C9, the second end of the tenth capacitor C10, the second end of the eleventh capacitor C11, the second end of the twelfth capacitor C12, the negative power supply end of the amplification unit, the negative power supply end of the zero adjustment unit, and the negative power supply end of the filtering unit;

[0068] The third pin of the buck chip is connected to the positive electrode of the thirteenth capacitor C13, and the negative electrode of the thirteenth capacitor C13 is connected to the negative electrode of the fourteenth capacitor C14 and grounded;

[0069] The second pin of the step-down chip is respectively connected to the positive electrode of the fourteenth capacitor C14, the first power supply terminal of the processing unit, the first end of the eighteenth capacitor C18, the first end of the seventeenth capacitor C17, the first end of the sixteenth capacitor C16, the first end of the fifteenth capacitor C15, and the second power supply terminal of the processing unit;

[0070] The second end of the fifteenth capacitor C15 is respectively connected to the second ends of the sixteenth capacitor C16, the seventeenth capacitor C17, and the eighteenth capacitor C18 and grounded.

[0071] In the embodiment of the present invention, the power supply unit further includes a power supply indicator light, which is composed of a first light-emitting diode LED1, a second light-emitting diode LED2, a seventh resistor R7, and an eighth resistor R8; the anode of the first light-emitting diode LED1 is connected to the second end of the second inductor L2, the cathode of the first light-emitting diode is connected to the first end of the seventh resistor R7, the second end of the seventh resistor R7 is grounded, the anode of the second light-emitting diode LED2 is grounded, the cathode of the second light-emitting diode LED2 is connected to the first end of the eighth resistor R8, and the second end of the eighth resistor R8 is connected to the second end of the third inductor L3.

[0072] In the embodiment of the present invention, it can be seen that the amplification unit includes an amplifier. The first pin of the amplifier is connected to the eighth pin through the first resistor R1. The second pin and the third pin of the amplifier are both connected to the output end of the sensor through the input interface. The fourth pin of the amplifier is connected to the second end of the third inductor L3. The fifth pin of the amplifier is connected to the output end of the zero-adjustment unit. The sixth pin of the amplifier is connected to the input end of the filtering unit. The seventh pin of the amplifier is connected to the second end of the second inductor L2. Figure 3 It can be seen that the zero-adjustment unit includes a first operational amplifier chip, a second resistor R2, and a third resistor R3;

[0073] In the embodiment of the present invention, it can be seen that the filtering unit includes a second operational amplifier chip, a first capacitor C1, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, and a second capacitor C2; Figure 3 The first pin of the first operational amplifier chip is respectively connected to the first ends of the second resistor R2 and the third resistor R3. The third end of the second resistor R2 is respectively connected to the second end of the third inductor L3 and the second pin of the first operational amplifier chip. The third end of the third resistor R3 is respectively connected to the second end of the second inductor L2 and the fifth pin of the first operational amplifier chip. The third pin and the fourth pin of the first operational amplifier chip are both connected to the fifth pin of the amplifier.

[0074] The first pin of the first operational amplifier chip is respectively connected to the first ends of the second resistor R2 and the third resistor R3. The third end of the second resistor R2 is respectively connected to the second end of the third inductor L3 and the second pin of the first operational amplifier chip. The third end of the third resistor R3 is respectively connected to the second end of the second inductor L2 and the fifth pin of the first operational amplifier chip. The third pin and the fourth pin of the first operational amplifier chip are both connected to the fifth pin of the amplifier.

[0075] In the embodiment of the present invention, it can be seen that the filtering unit includes a second operational amplifier chip, a first capacitor C1, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, and a second capacitor C2; Figure 3 It can be seen that the filtering unit includes a second operational amplifier chip, a first capacitor C1, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, and a second capacitor C2;

[0076] The first pin of the second operational amplifier chip is grounded. The third pin of the second operational amplifier chip is respectively connected to the second end of the fourth resistor R4 and the first end of the second capacitor C2. The first end of the fourth resistor R4 is respectively connected to the first end of the sixth resistor R6, the first end of the first capacitor C1, and the second end of the fifth resistor R5. The first end of the fifth resistor R5 is connected to the sixth pin of the amplifier. The second end of the first capacitor C1 is grounded. The second end of the sixth resistor R6 is respectively connected to the second end of the second capacitor C2 and the fourth pin of the second operational amplifier chip. The fourth pin of the second operational amplifier chip is respectively connected to the first input end of the display unit and the input end of the processing unit through the output interface J1. The second pin of the second operational amplifier chip is connected to the second end of the third inductor L3. The fifth pin of the second operational amplifier chip is connected to the second end of the second inductor L2.

[0077] It should be noted that the processing unit in the embodiment of the present invention is composed of a single-chip microcomputer processing chip and its peripheral circuits, and is used to calculate the DC residual current by using the voltage signal output by the filtering unit.

[0078] It should be noted that the display unit in the embodiment of the present invention is an oscilloscope, and is used to display the voltage waveform output by the filtering unit or the waveform of the DC residual current.

[0079] Specifically, the size of the amplification loop 1 is determined by the amplification factor, and the process includes:

[0080] Based on the residual current detection model without the amplification loop 1 established at the target measurement point, the magnetic induction intensity at the target measurement point is obtained;

[0081] Based on the residual current detection model with the amplification loop 1 established at the target measurement point, the magnetic induction intensity at the measurement point at the air gap of the amplification loop 1 is obtained;

[0082] According to the magnetic induction intensity at the target measurement point and the magnetic induction intensity at the measurement point at the air gap of the amplification loop 1, the amplification factor expression of the amplification loop 1 is obtained;

[0083] According to the amplification factor expression of the amplification loop 1, the key variables affecting the amplification factor of the amplification loop 1 are determined;

[0084] Use simulation software to establish a simulation model of the double-core wire to be measured and a model of the amplification loop 1;

[0085] Match the parameters of the double-core wire to be measured with the actual working conditions and set the specific values of the key variables affecting the amplification factor of the amplification loop 1 to simulate the simulation model and the model of the amplification loop 1, and obtain the size of the amplification loop 1.

[0086] Specifically, the process of obtaining the magnetic induction intensity at the target measurement point based on the residual current detection model without the amplification loop 1 established at the target measurement point is as follows:

[0087] Figure 4 Shown is a schematic diagram of the magnetic field generated by a live DC twin-core wire at any point P in space. When opposite-direction currents I1 and I2 are applied to the twin-core wire under test, the difference I between I1 and I2 Δ is the residual current. It is stipulated that the straight line where the center connection of the two wires lies is the y-axis, and the x-axis is perpendicular to the y-axis. The residual current detection model without amplification loop 1 established at the target point to be measured by combining the superposition theorem and the Biot-Savart law is as follows:

[0088]

[0089] where μ0 is the magnetic permeability of vacuum, with a magnitude of 4π×10-7 (H / m);

[0090] The magnetic field components of B1 and B2 along the x-axis and y-axis can be obtained as follows:

[0091]

[0092] The relationship between the magnetic induction intensity generated by the residual current and each magnetic field component is as follows:

[0093]

[0094] Substitute B 1x 、B 1y 、B 2x 、B 2y to obtain:

[0095]

[0096] When point P is on the perpendicular bisector of the centers of the two wires, θ1 and θ2 are equal, and I1 and I2 are equal. The magnetic induction intensity at the target point to be measured is obtained as:

[0097]

[0098] where I1 and I2 are the distances from point P to the twin-core wire respectively; θ1 and θ2 are the angles between the lines connecting point P to the centers of the twin-core wire and the x-axis respectively; B1 and B2 are the magnitudes of the magnetic induction intensities generated by the twin-core wire at point P respectively; B 1x 、B 2x are the magnetic field components of B1 and B2 on the x-axis respectively; B 1y 、B 2y are the magnetic field components of B1 and B2 on the y-axis respectively.

[0099] Specifically, based on the residual current detection model with amplification loop 1 established at the target point to be measured, the process of obtaining the magnetic induction intensity at the point to be measured at the air gap of amplification loop 1 is as follows:

[0100] First, according to as Figure 5The structural schematic diagram of the amplification loop 1 is shown. The DC twin-core wire passes through the center of the amplification loop 1, and the currents are I1 and I2 respectively; R1 is the outer diameter of the amplification loop 1; r1 is the inner diameter of the amplification loop 1; r is the average radius of the amplification loop 1; d is the air-gap width of the amplification loop 1, and the TMR linear magnetic field sensor is placed at the center of the air gap; μ1 is the relative magnetic permeability of the amplification loop 1. The remaining current detection model with the amplification loop 1 established at the target measurement point by Ampere's circuital law is as follows:

[0101]

[0102] According to the magnetic circuit law, the magnetic flux density remains unchanged in a closed magnetic circuit, that is:

[0103] B d = B1

[0104] μ0H d = μ1H1

[0105] where B1 is the magnetic induction intensity of a magnetic path inside the magnetic ring; B d is the magnetic induction intensity at the TMR sensor. Substituting the remaining current detection model with the amplification loop 1, we can get:

[0106]

[0107] Since the relative magnetic permeability of the magnetic flux concentrating ring material is generally 1000 - 12000, which is much larger than the relative magnetic permeability μ0 of vacuum, the magnetic induction intensity at the measurement point in the air gap of the amplification loop 1 is obtained as:

[0108]

[0109] In the formula, Hd is the magnetic field intensity in the air gap; H1 is the magnetic field intensity inside the amplification loop 1; N is the number of turns of the coil, which is taken as 1 in the embodiment of the present invention.

[0110] Specifically, according to the magnetic induction intensity at the target measurement point and the magnetic induction intensity at the measurement point in the air gap of the amplification loop 1, the amplification factor expression of the amplification loop 1 is obtained as:

[0111]

[0112] where A represents the amplification factor of the amplification loop 1.

[0113] From the above formula, it can be seen that the amplification loop 1 can effectively amplify the magnetic field to be measured and improve the sensitivity of the TMR sensor detection.

[0114] According to the amplification factor expression of the amplification loop 1, the amplification factor is proportional to the average radius r of the amplification loop 1 and inversely proportional to the air-gap width d. It can be determined that the key variables affecting the amplification factor of the amplification loop 1 are the average radius and the air-gap width of the amplification loop 1.

[0115] Specifically, a simulation model of the double-core wire to be measured and a model of the amplification loop 1 are established using simulation software; the parameters of the double-core wire to be measured are matched with the actual working conditions, and specific values of the key variables affecting the amplification factor of the amplification loop 1 are set to simulate the simulation model and the amplification loop 1 model, and the process of obtaining the size of the amplification loop 1 is as follows:

[0116] Iterations are performed on r1, R1, and d in Matlab to calculate the corresponding amplification factors. Considering that the double-core wire needs to pass through the center of the amplification loop 1, r1 is set to be not less than 2 mm. Since the overall size of the current sensor should not be too large, the outer radius R1 of the amplification loop 1 (R1 = r1 + m) is set to be not greater than 20 mm. The relative permeability μ1 of the amplification loop 1 is taken as 4000, and some of the data in the iteration are shown in Table 1:

[0117] Table 1 Influence of the size parameters of the amplification loop 1 on the amplification factor

[0118]

[0119] By analyzing the data, it can be concluded that both the increase in the size of the amplification loop 1 and the decrease in the air-gap width can effectively improve the amplification factor; under comprehensive consideration, in the embodiments of the present invention, r1 is finally determined to be 5 mm, R1 is 8 mm, and d is 3 mm. At this time, the amplification factor A is 13.61; when measuring with the TMR2003 sensor chip with a sensitivity of 6 mV / V / Oe, the overall sensitivity of the detection device will reach 82 mV / V / Oe.

[0120] Specifically, the size of the shielding loop 2 is determined by the shielding effectiveness, and the process includes:

[0121] Based on the established shielding external magnetic field model of the shielding loop 2, the shielding effectiveness expression of the shielding loop 2 is obtained;

[0122] According to the shielding effectiveness expression of the shielding loop 2, the factors affecting the shielding effectiveness of the shielding loop 2 are determined;

[0123] According to the size of the amplification loop 1, the shielding effectiveness expression of the shielding loop 2 is simplified to obtain the key factors affecting the shielding effectiveness;

[0124] Using simulation software to establish a model of the shielding loop 2 and applying a static magnetic field along the X-axis as the stray magnetic field;

[0125] The parametric scanning method is used to set specific values of the key factors affecting the shielding effectiveness to simulate the shielding loop 2, and the size of the shielding loop 2 is obtained.

[0126] Since the shielding ring 2 is made of a material with high magnetic permeability, when placed in an external magnetic field, it will absorb most of the external magnetic flux and conduct it into the material, thus greatly weakening the interference of the external magnetic field on the internal current measurement and achieving the purpose of shielding the external magnetic field. The shielding effectiveness SE is an important parameter to measure the performance of the device in shielding the external magnetic field. The larger the SE, the better the shielding effect.

[0127] Specifically, based on the established model of the shielding ring 2 for shielding the external magnetic field, the process of obtaining the expression of the shielding effectiveness of the shielding ring 2 is as follows:

[0128] First, according to Figure 6 the structure diagram of the shielding ring 2 and the magnetic field superposition theorem as shown, assuming that the magnetic field intensity of the stray magnetic field such as the geomagnetic field is H0 and it is uniformly incident in the horizontal direction, and the magnetic field intensity at the position of the TMR sensor is H d , then the shielding effectiveness SE expressed in decibels (dB) can be calculated by the following formula:

[0129]

[0130] The magnetic flux of the external magnetic field flowing into the shielding ring 2 is:

[0131] Φ0 = μ0H0πR2h

[0132] In the formula, μ0 = 4π×10 -7 H / m; h is the axial height of the shielding ring 2;

[0133] The magnetic flux flowing through the shielding wall is:

[0134] Φ2 = μ2H2·2mh = 2μ2H2mh

[0135] In the formula, μ2 is the relative magnetic permeability of the material of the shielding ring 2; H2 is the magnetic field intensity inside the wall of the shielding ring 2;

[0136] The magnetic flux passing through the shielding ring 2 and entering the shielded cavity is:

[0137] Φ S = μ0H S1 πr2h

[0138] In the formula, H S1 is the magnetic field intensity inside the cavity of the shielding ring 2 after shielding;

[0139] Obviously, there is:

[0140] Φ0 = Φ2 + Φ S

[0141] That is

[0142] μ0H0πR2h = 2μ2H2mh + μ0H S1 πr2h

[0143] The magnetic resistance on the inner wall of the upper half of the magnetic focusing ring obtained from magnetic circuit calculation is:

[0144]

[0145] Where l is the magnetic circuit length; μ is the magnetic permeability of the medium; C is the cross-sectional area of the magnetic circuit;

[0146] Then the magnetic potential drop on it is:

[0147]

[0148] Next, calculate the magnetic potential drop of the shielded cavity part. The magnetic resistance of the upper half of the cavity is:

[0149]

[0150] Then the magnetic potential drop of the cavity part is:

[0151]

[0152] Since the calculation of the magnetic potential drop is independent of the magnetic circuit path, then U M = U T , that is:

[0153]

[0154] Combined with the formula μ0H0πR2h = 2μ2H2mh + μ0H S1 πr2h and We can obtain H0 and H S1 Satisfy:

[0155]

[0156] Next, conduct a mathematical derivation of the magnetic field intensity at the TMR sensor;

[0157] Since the proportional relationship between H0 and H S1 has been calculated in the above formula, next, only the proportional relationship between H S1 and H d needs to be obtained to calculate the shielding coefficient of the concentric double magnetic ring structure.

[0158] Assume that there is no magnetic leakage in the air gap. In the embodiment of the present invention, the amplification ring 1 is simplified to a closed magnetic ring for mathematical derivation; it should be noted that at this time, the magnetic field H S1 shielded by the shielding ring 2 flowing into the amplification ring 1 is:

[0159] Φ S1 = μ0H S1 πR1h

[0160] Finally, the obtained H1 and H S1The proportional relationship satisfies:

[0161]

[0162] In the formula, H1 is the magnetic field strength inside the wall of the amplification ring 1;

[0163] Combined with the formula μ0H d = μ1H1 and obtain H S1 and H d The proportional relationship satisfies:

[0164]

[0165] Combined with the formula and the above formula, the shielding effectiveness expression of the shielding ring 2 is obtained as:

[0166]

[0167] According to the shielding effectiveness expression of the shielding ring 2, the factors affecting the shielding effectiveness of the shielding ring 2 are determined to be the inner diameter, outer diameter and relative magnetic permeability of the concentric double magnetic ring.

[0168] Specifically, the process of simplifying the shielding effectiveness expression of the shielding ring 2 according to the size of the amplification ring 1 to obtain the key factors affecting the shielding effectiveness is as follows:

[0169] Since the size of the amplification ring 1 has been determined, the shielding effectiveness expression of the shielding ring 2 is simplified according to the size of the amplification ring 1 to obtain:

[0170]

[0171] Based on the above formula, the key factors affecting the shielding effectiveness can be determined to be the inner diameter and outer diameter of the shielding ring 2.

[0172] Specifically, use the simulation software to establish the model of the shielding ring 2 and apply a static magnetic field along the X-axis as the stray magnetic field; use the parametric scanning method to set the specific values of the key factors affecting the shielding effectiveness to simulate the shielding ring 2 to obtain the size of the shielding ring 2, and the process is as follows:

[0173] Take the relative permeability μ2 of the shielding ring 2 as 1000, calculate the change of shielding effectiveness under different inner radii and thicknesses, and it can be obtained that the influence of the thickness m on the shielding effectiveness is more significant than the inner diameter r2 of the shielding ring 2. When m exceeds 1 mm, the SE value exceeds 60 dB, indicating that the concentric double magnetic ring has excellent anti-interference performance under this condition; further observation shows that when m exceeds 5 mm, continuing to increase the value of m has limited effect on improving the shielding effectiveness, which may be due to magnetic saturation effect or saturation of magnetic field distribution. Therefore, from the perspective of optimizing anti-interference ability and cost-effectiveness, in the embodiment of the present invention, r2 is taken as 15 mm and m is taken as 5 mm. At this time, the shielding effectiveness SE is 71.47 dB, and the shielding ring 2 can shield 99.9% of the external interference magnetic field.

[0174] So far, the specific dimensions of the concentric double magnetic ring designed in the embodiment of the present invention are: the inner diameter of the amplification ring 1 is 10 mm, the outer diameter is 16 mm, and the air gap width is 3 mm; the inner diameter of the shielding ring 2 is 30 mm, and the outer diameter is 40 mm.

[0175] Specifically, there is a gap between the inner diameter of the shielding ring 2 and the outer diameter of the amplification ring 1.

[0176] In order to verify whether the dimensions of the amplification ring 1 and the shielding ring 2 are correct in the embodiment of the present invention, a concentric double magnetic ring simulation model is established in the ANSYS Maxwell simulation software. The materials of the amplification ring 1 and the shielding ring 2 are ferrite, and the relative permeability and size parameters are consistent with the previous derivation. A static magnetic field H0 with a magnitude of 0.5 Oe is set to be incident along the normal direction of the concentric double magnetic ring to simulate the interference of stray magnetic fields such as geomagnetism on the residual current detection, and the relative error ε between the theoretical value and the simulation value of SE is calculated. SE , and the expression is:

[0177]

[0178] The results are shown in Table 2:

[0179] Table 2 Relative error of SE of current sensor

[0180] SE theoretical value / dB SE simulation value / dB <![CDATA[ε SE / %]]> 71.47 70.79 0.96

[0181] It can be seen from Table 2 that the design results of the embodiment of the present invention are basically consistent with the simulation results, which proves that the designed dimensions of the shielding ring 2 can effectively suppress external stray magnetic field interference.

[0182] Next, verify the measurement of the residual current by the concentric double magnetic ring structure:

[0183] A DC double-core wire model is established at the center of the concentric double magnetic ring. The wire material is copper, and currents in opposite directions are respectively passed through. The current difference is the residual current I. Δ。Control the residual current to vary between 20 mA and 200 mA, and record the magnetic induction intensity at the position of the TMR linear magnetic field sensor when the residual current increases positively as B d+ and the magnetic induction intensity when the residual current decreases reversely as B d- ; At the same time, to verify the relative error ε A of the magnification, the embodiment of the present invention measures the magnetic induction intensity B at the same position without the concentric double magnetic rings. By comparing B with B d+ , B d- values, the simulation value of the magnification A can be calculated. The calculation process of ε A is the same as the calculation expression of the relative error between the SE theoretical value and the simulation value. The finally drawn response characteristics of the concentric double magnetic rings are as Figure 7 shown. Observing Figure 7 the following conclusions can be drawn:

[0184] 1) Both the B d+ and B d- curves show good linear relationships, proving that the concentric double magnetic ring structure has a high linearity in response to the induced magnetic field, and this method can be applied to current measurement;

[0185] 2) In the figure, the B d+ and B d- curves almost coincide, indicating that regardless of whether the residual current increases or decreases, the concentric double magnetic ring structure can maintain the same response characteristics and ensure the measurement accuracy;

[0186] 3) At different residual currents, ε A is less than 1%, so the theoretical derivation of the magnification in the embodiment of the present invention is basically correct. It should be noted that ε A is overall less than 0, indicating that A 理论值 is less than A 仿真值 , which may be due to the average radius in the expression of the magnification of the amplification ring 1 being less than the actual distance from the wire to the measurement point, resulting in a smaller theoretical calculation;

[0187] 4) As the residual current increases, ε A slightly increases, and it is speculated that the error comes from the magnetic leakage phenomenon of the air gap;

[0188] Generally speaking, the simulation results of the concentric double magnetic ring structure in the embodiment of the present invention are consistent with the mathematical model, and the errors of both the magnification and the shielding effectiveness are within 1%; during the simulation process, the current sensor of this structure shows good response characteristics and meets the requirements of detection sensitivity and anti-external magnetic interference.

[0189] The DC residual current detection device provided by the embodiment of the present invention includes an amplification loop, a shielding loop, a sensor, and a signal processing module. Compared with the prior art, in the embodiment of the present invention, the magnetic field to be measured is amplified by the amplification loop, the stray magnetic field is shielded by the shielding loop, the magnetic field intensity signal generated by the residual current of the double-core wire to be measured is detected by the sensor and converted into a voltage signal and sent to the signal processing unit for processing to output the DC residual current. The DC residual current can be monitored in real time with one installation, and the original circuit does not need to be changed when using this device. Moreover, the problem that the DC residual current detection is vulnerable to stray magnetic field interference can be overcome, and the detection accuracy and stability of the DC residual current can be ensured in the face of magnetic field interference.

[0190] The above is the preferred embodiment of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A DC residual current detection device, characterized in that, Including: An amplification loop for amplifying the magnetic field to be measured, a shielding loop for shielding stray magnetic fields, a sensor for detecting the magnetic field intensity signal generated by the residual current of the double-core wire to be measured, and a signal processing module for outputting a DC residual current; The outer diameter of the amplification loop is smaller than the inner diameter of the shielding loop; The amplification loop and the shielding loop form a concentric double magnetic ring. The amplification loop is arranged inside the shielding loop, and the double-core wire to be measured vertically passes through the center of the concentric double magnetic ring; An air gap of the amplification loop is provided on the amplification loop, and the sensor is arranged at the air gap of the amplification loop; The output end of the sensor is electrically connected to the input end of the signal processing module.

2. The DC residual current detection device according to claim 1, characterized in that The sensor is a TMR linear magnetic field sensor.

3. The DC residual current detection device according to claim 2, wherein The signal processing module includes: A power supply unit, a zero adjustment unit, an amplification unit, a filtering unit, a display unit, and a processing unit; The input end of the power supply unit is connected to the mains power supply end, and the output end of the power supply unit is respectively connected to the power supply end of the zero adjustment unit, the power supply end of the amplification unit, the power supply end of the filtering unit, and the power supply end of the processing unit; The output end of the zero adjustment unit is connected to the zero adjustment end of the amplification unit. The input end of the amplification unit is connected to the output end of the sensor. The output end of the amplification unit is connected to the input end of the filtering unit. The output end of the filtering unit is respectively connected to the first input end of the display unit and the input end of the processing unit. The output end of the processing unit is connected to the second input end of the display unit.

4. The DC residual current detection device according to claim 3, characterized in that, The size of the amplification loop is determined by the amplification factor.

5. The DC residual current detection device according to claim 4, characterized in that, The process of determining the size of the amplification loop by the amplification factor includes: Based on the residual current detection model without an amplification loop established at the target measurement point, the magnetic induction intensity at the target measurement point is obtained; Based on the residual current detection model with an amplification loop established at the target measurement point, the magnetic induction intensity at the measurement point at the air gap of the amplification loop is obtained; According to the magnetic induction intensity at the target measurement point and the magnetic induction intensity at the measurement point at the air gap of the amplification loop, an amplification factor expression of the amplification loop is obtained; According to the amplification factor expression of the amplification loop, the key variables affecting the amplification factor of the amplification loop are determined; Using simulation software to establish a simulation model of the double-core wire to be measured and an amplification loop model; Matching the parameters of the double-core wire to be measured with the actual working conditions and setting specific values of the key variables affecting the amplification factor of the amplification loop to simulate the simulation model and the amplification loop model to obtain the size of the amplification loop.

6. The DC residual current detection device according to claim 5, characterized in that, The size of the shielding loop is determined by the shielding effectiveness.

7. The DC residual current detection device according to claim 6, characterized in that, The process of determining the size of the shielding loop by the shielding effectiveness includes: Based on the established shielding loop model for shielding external magnetic fields, a shielding effectiveness expression of the shielding loop is obtained; According to the shielding effectiveness expression of the shielding loop, the factors affecting the shielding effectiveness of the shielding loop are determined; Simplifying the shielding effectiveness expression of the shielding loop according to the size of the amplification loop to obtain the key factors affecting the shielding effectiveness; Using simulation software to establish a shielding loop model and applying a static magnetic field along the X-axis as a stray magnetic field; Using the parametric scanning method to set specific values of the key factors affecting the shielding effectiveness to simulate the shielding loop to obtain the size of the shielding loop.

8. The DC residual current detection device according to claim 7, characterized in that, There is a gap between the inner diameter of the shielding ring and the outer diameter of the amplifying ring.

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