The Introduction to the main functions of transformer iron core.

The function of the iron core: It is the main magnetic circuit of the transformer. The material of the iron core: 0.35~0.5mm thick silicon steel sheet iron core composition: The power transformer mainly uses a core-type structure iron core to form a closed magnetic circuit in the transformer. It is also the skeleton of the installation coil. It is an extremely important component for the electromagnetic function and mechanical strength of the transformer. The iron core is the magnetic circuit part of the transformer, which consists of an iron core column (windings on the column) and an iron yoke (connecting the iron core to form a closed magnetic circuit). In order to reduce eddy current and hysteresis losses and improve the magnetic conductivity of the magnetic circuit, the iron core is made of 0.35mm~0.5mm thick silicon steel sheets coated with insulating paint and then intertwined. The cross-section of the iron core of a small transformer is rectangular or square, and the cross-section of the iron core of a large transformer is stepped, which is to make full use of space.

1) Multi-point grounding failure of the iron core: the insulating cardboard between the pad foot of the lower clamp of the iron core and the rail falls off or is damaged, causing the laminations at the pad foot to collide and cause grounding; due to the wear of the submersible pump shaft, metal powder enters the oil tank and accumulates at the bottom of the oil tank, forming a bridge under the action of electromagnetic force, connecting the lower iron pulley with the pad foot or the bottom of the box, forming multi-point grounding; the thermometer seat cover on the tank cover is too long, and collides with the upper clamp or the iron choke and the edge of the side column, forming a new grounding address; the wooden pad between the lower clamp and the iron choke step is damp or the surface is not clean, and there is a lot of oil mud attached to it, so that its insulation resistance value drops to zero, forming multi-point grounding; nails, welding rod heads and other metal foreign objects fall into the oil tank, causing the iron core laminations to communicate with the box body, forming grounding; after the transformer is installed, the positioning pins on the top cover of the oil tank used for transportation are not turned over or removed, forming multi-point grounding. 2) Core overheating fault There are many reasons for the overheating of the transformer core, such as winding short circuit overload operation, poor and abnormal grounding of the core itself, short circuit between core pieces or partial short circuit of the core, grounding of the iron choke screw, core leakage, partial short circuit of the core, high power supply voltage, and blockage of the core cooling oil channel. In addition to the above, poor oil circulation or low oil volume in the box, oil degradation, large burrs around the core laminations, and uneven gaps when stacking the core pieces may all cause core overheating. The parts of the core partial overheating fault are basically on the core and the clamps. If the transformer in operation has overheating of the core, especially partial overheating, characteristic gases H2, CH4, C2H2, and C2H6 will be generated. Chromatographic analysis found that the content of dissolved gas components in the oil exceeded the standard.

Transformer core inspection Use a clean, lint-free white cloth to wipe the oil and impurities on the surface of the core 2) If the silicon steel sheet has curling, warping, etc., it should be carefully repaired with a wooden hammer. 3) Check that the oil channel gaskets of the core are arranged neatly, and there should be no looseness when tapping the oil channel gaskets; check that there should be no foreign matter in the oil channel of the core. Check that there should be an obvious uniform gap between the pressure plate and the upper iron yoke; check that the grounding plate bolts of the steel pressure plate are not loose. The insulating pressure plate should remain intact, without damage and cracks, and have appropriate tightness. 5) Use a 1000V insulation resistance meter to measure the insulation resistance between the core and the through-core screw and the steel pull belt. There is no obvious change compared with previous tests. Open the connecting piece between the upper clamp and the core and the connecting piece between the steel pressure plate and the upper clamp, and use a 2V insulation resistance meter to measure the insulation resistance of the core to the clamp and the ground. It should be no less than 100M ohms. After the measurement, reset the connecting piece to ensure it is reliable. 7) Use a wrench and a torque wrench to tighten the fasteners of the upper and lower clamps, upper beams, side beams, pads, pressure nails, and through-core screws of the core one by one. 8) Check the condition of the core electrical shielding. Use a 1000V insulation meter to measure the insulation resistance of the core electrical shielding to the ground. The insulation resistance should be greater than 100M ohms. ) Check the connection and insulation condition of the core grounding plate. The core is only allowed to be grounded at one point. The grounding plate is generally made of copper sheets with a thickness of 0.5mm and a width of not less than 30mm. It is inserted between 3~4 level cores. For large transformers, the insertion depth is not less than 80mm. The exposed part should be wrapped with insulation to prevent short-circuit the core.