Transformer core structureThe iron core is composed of silicon steel sheets. In order to reduce eddy current, there is a certain insulation resistance between the sheets (generally only a few ohms to tens of ohms). Due to the great capacitance between the sheets, it can be regarded as a path in the alternating electric field. Therefore, only one point of grounding in the iron core can clamp the potential of the whole stack of iron cores at the ground potential.The iron core is the main part of the magnetic circuit in the transformer. It is usually made of hot-rolled or cold-rolled silicon steel sheets with high silicon content and coated with insulating paint. The iron core and the coil wound on it form a complete electromagnetic induction system. The transmission power of power transformer depends on the material and cross-sectional area of iron core.
Key points of transformer installation protection(1) An iron yoke clamp grounding lead shall be set separately. Because if the iron core touches the upper clamp, resulting in multi-point grounding fault, the grounding current only flows inside the iron core clamp, and there is no current in the iron core grounding outgoing line, which will lead to the staff mistakenly believing that the iron core has not failed; After setting, no matter where the iron core touches the clamp, it will form a loop through two external grounding leads, so that the grounding current can be correctly detected externally.(2) The iron core grounding strip is placed in the middle of the cross section of the yoke. In this way, no matter where the insulating bolt of the iron yoke strap is and where the fault grounding point is, the maximum induced voltage of the circuit is only 1 / 4 of the turn voltage, and the maximum grounding current is only about a few amps, which is much smaller than when the iron core grounding strip is placed in other positions.
(3) If it is really necessary to place the iron core grounding strip at other positions due to inconvenient on-site installation, the insulating bolt and grounding strip of the iron yoke strap shall also be placed diagonally, so as to prevent large current.Iron core protective grounding in power transformerWhen the transformer works, an uneven electric field will be generated around the winding, and the suspension induced voltage will be generated on the iron core and other metal components. When the voltage difference between the suspension potentials exceeds the insulation voltage, internal discharge or ground discharge will occur. Therefore, a reliable grounding must be made at a certain point on the transformer core to discharge the suspended induced voltage of the core and protect the transformer.
Power transformer core materialSilicon steel lamination is generally used as the core material of power transformerSilicon steel has high permeability, so it is widely used in the manufacture of motors and transformers. Because the whole ferromagnetic material will produce large eddy current when working, which is unfavorable for the transformer. To reduce the eddy current (eddy current has skin effect), it is necessary to make ferromagnetic materials into thin sheets and then stack them into the required cross-sectional area.
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