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Application of Electromagnetic Core in Fault Indicator Collection Unit

Application of Electromagnetic Core in Fault Indicator Collection Unit

2021-10-21

1. The principle of collecting electricity from the acquisition unit


The fault indicator acquisition unit current induction takes electricity using the electromagnetic induction principle of "moving electricity to generate magnetism, and moving magnetism to generate electricity". The alternating current on the wire is generated on the secondary coil through the permalloy core electromagnetic coupling. Voltage and current realize the transmission of electric power and achieve the purpose of getting 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 magnetic 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 magnetoresistance Φr, magnetic space radiation (magnetic leakage ΦL), etc. 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 magnetic resistance Φr and the leakage magnetic ΦL, the greater the output power of the secondary side.


Since the permalloy magnetic core collection unit needs to meet the requirements of live installation and disassembly, the magnetic core needs to adopt a cutting and buckling 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, there will be an air gap due to the cutting gap. Compared with the original toroidal core, its magnetic resistance 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 magnetic ΦL, the greater the output power of the secondary side.


In order to reduce the magnetic circuit loss and increase the output power level of the secondary side under the same wire current, it is necessary to use magnetic core materials with high permeability and high saturation magnetic flux density Bs value, so that the selection of magnetic core materials tends to be high-end . Through our various experiments, the materials that meet the power requirements of the fault indicator collection unit are: Permalloy 1L85, iron-based nanocrystalline 1K107.


Physical properties / magnetic properties of magnetic materials:


2. The relationship between magnetic flux and power/relational calculation between theoretical formulas:


(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


in:


μ: 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 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 greater the primary 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 magnetic resistance loss and magnetic leakage loss, that is, to improve the magnetic permeability, optimize the effective magnetic circuit length of the magnetic core, and adopt excellent technology guarantee The cut surface of the magnetic core fits tightly. In our actual processing practice, the permeability of the 1K107 iron-based nanocrystalline core after cutting can reach more than 15,000, and the permeability of the 1J85 permalloy core after cutting can reach more than 12,000. What is the magnetic permeability of the permalloy core after cutting? It will be broken down in the next episode.


3. Analysis of the reason for the burnt out of the power coil


Since the power coil works under power frequency conditions, the core loss caused by the eddy current of the magnetic core will not be too large under the condition of reasonable design of the magnetic core, so the permalloy core magnetic core will not be burned, and burned on site The situation is mainly caused by improper design of the secondary winding.


When the working current of the primary side of the fault indicator rises, the output current of the secondary side also rises accordingly, that is, I1:I2 =N1:N2 is satisfied. Therefore, it is necessary to consider the winding copper wire according to the possible continuous large current on the primary side wire. The wire diameter and the current density on the winding should not be too large, otherwise high heat will be generated on the winding and cause the coil to burn out.


4. Example application


Both 1J85 (0.2mm permalloy) and 1K107 (0.025mm iron-based nanocrystalline) are ultra-high permeability soft magnetic materials. Under power frequency conditions, the eddy current loss is almost negligible. In power-taking applications, its excellent magnetic properties are unmatched by other permalloy core magnetic materials. The price of the magnetic core between 1J85 and 1K107 is about 2:1. In mass applications, the magnetic performance advantage of 1K107 and the price advantage are outstanding.


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