The application of the electromagnetic core of the fault indicator acquisition unit and the cause of the burning of the electric coil -
1. The power acquisition principle of the acquisition unit The fault indicator current induction acquisition unit uses the electromagnetic induction principle of 'dynamic electricity generates magnetism, and dynamic magnetism generates electricity', and the alternating current on the wire is electromagnetically coupled through the permalloy core. The method generates voltage and current on the secondary coil, realizes the transmission of electric power, and achieves the purpose of taking electricity from the wire. As shown in the figure, when the primary current flows through the primary winding N1, an alternating magnetic flux Φ1 is generated in the core magnet, and the alternating magnetic flux Φ1 passes through the magnetic circuit of the magnetic core to generate an induced voltage value U on the secondary winding. Compared with other electromagnetic mutual inductance transformations, the primary winding here is a cable or wire, and the number of turns is 1 turn. When the alternating magnetic flux Φ1 forms a closed loop in the magnetic core, it will be hindered by the reluctance Φr, magnetic space radiation (flux leakage ΦL), etc., and part of the magnetic flux will be lost, only the part of the magnetic flux passing through the secondary winding Φ2 can effectively transfer electric energy to the secondary side, that is, Φ1=ΦL+Φr+Φ2. It can be seen that under the same working conditions, the smaller the reluctance Φr and the magnetic flux leakage ΦL, the greater the output power of the secondary side will be. Since the permalloy magnetic core acquisition unit needs to meet the requirements of live installation and disassembly, the magnetic core needs to adopt the cutting and fastening mode, that is, the magnetic core needs to be cut into two halves during production, and then closed to form a ring magnetic circuit during installation. When the magnetic circuit is closed, an air gap will be generated due to the cutting gap. Compared with the original ring core, its reluctance Φr and magnetic flux leakage ΦL are greatly increased. Under the same working conditions, the better the cutting process, the smaller the air gap, and the magnetic The smaller the resistance Φr and the leakage flux ΦL, the larger the output power of the secondary side will be. In order to reduce the magnetic circuit loss and increase the output power level of the secondary side under the same conductor current, it is necessary to use a magnetic core material with a high magnetic permeability and a high saturation magnetic flux density Bs value, so that the selection of the magnetic core material tends to be high-end. . After our multi-party experiments, the materials that meet the power-taking requirements of the fault indicator acquisition unit are: permalloy 1L85, iron-based nanocrystalline 1K107. Physical properties/magnetic properties of magnetic materials: 2. The relationship between magnetic flux and power/theoretical formula Correlation calculation between: (1)Φ1=B*Ae (2)B=μ*H (3)μ=AL*Le/0.4*π* N²*Ae(N²=1)(4) H=0.40π* N*I/Le Among them: μ: magnetic permeability B: magnetic flux density Ae: core cross-sectional area H: magnetic field strength AL: inductance coefficient Le: equivalent magnetic circuit length It can be seen that: at the same primary side current, The higher the magnetic permeability μ, the shorter the equivalent magnetic path length Le of the magnetic core, the larger the cross-sectional area Ae of the magnetic core, and the larger the primary side magnetic flux Φ1. In order to minimize the loss of Φr and ΦL after the magnetic flux on the primary side is transferred to the secondary side, it is necessary to reduce the reluctance loss and leakage loss, that is, to increase the magnetic permeability, optimize the effective magnetic path length of the magnetic core and adopt excellent process guarantee The cut face of the core fits snugly. In our actual processing practice, the magnetic permeability of the 1K107 iron-based nanocrystalline magnetic core after cutting can reach more than 15,000, and the magnetic permeability of the 1J85 permalloy magnetic core after cutting can reach more than 12,000. What is the magnetic permeability of permalloy iron core after cutting? Waiting for the next episode to break down. 3. Analysis of the cause of the burnout of the power-taking coil Since the power-taking coil works under power frequency conditions, the iron loss caused by the eddy current of the magnetic core will not be too large under the condition of a reasonable design of the magnetic core, so the permalloy magnetic core will not In the case of burning, the burning situation on site is mainly caused by the improper design of the secondary winding. When the working current on the primary side of the fault indicator rises, the output current on the secondary side will also rise accordingly, that is, I1:I2 =N1:N2 is satisfied, so it is necessary to consider the copper wire of the winding according to the possible continuous maximum current on the primary side wire Wire diameter, the value of the current density on the winding should not be too large, otherwise high heat will be generated on the winding, causing the coil to burn out. 4. Example application 1J85 (0.2mm permalloy) and 1K107 (0.025mm iron-based nanocrystalline) are soft magnetic materials with ultra-high magnetic permeability. Under power frequency conditions, eddy current loss is almost negligible. In the current fault indication In the power-taking application of the collector unit, its excellent magnetic properties are unmatched by other permalloy core magnetic materials. The magnetic core price between 1J85 and 1K107 is about 2:1. Under the application of large quantities, the magnetic performance advantage of 1K107 is outstanding, and the price advantage is outstanding.