The iron core of the transformer is the mechanical skeleton of the whole transformer, and it is also an important part of the magnetic circuit for the transformer. Therefore, checking the iron core is an important link to ensure the operation of the transformer. There are eight steps to check the iron core:
1. Check whether the outer surface of the iron core is smooth, whether there is short circuit or discoloration between the pieces, whether there is any burn marks of discharge, whether there is any peeling off of the insulating film, whether there is any grease and debris on the top of the upper iron yoke and the bottom of the lower iron yoke, wipe it with clean white cloth or foam plastic, and if there is any warped or irregular place on the laminated iron, beat with wooden mais or copper mais to flatten it.
The iron core shall be flat, the insulating paint film shall not fall off, the lamination shall be tight, the silicon steel sheet on the side shall not be warped or wavy, the surface of each part of the iron core shall be free of oil dirt and impurities, there shall be no short circuit and lap between the pieces, and the joint clearance shall meet the requirements.
2. Check the tightness and insulation status of the upper and lower clamping parts of the iron core, square iron and winding platen, and check whether there are creepage burns and discharge traces of the insulating platen.
In order to facilitate the monitoring of the insulation status of the iron core in operation, a small sleeve can be installed on the cover of the transformer box during overhaul to lead out the iron core grounding wire (piece).
(1) Good insulation shall be maintained between the iron core and the upper and lower clamping parts, square iron, press plate and sole plate;
(2) There should be an obvious uniform gap between the steel platen and the iron core: the insulation platen should be kept intact, without damage and crack, and have appropriate tightness:
(3) steel platen shall not form a closed loop, and there should be a little ground;
(4) After opening the connecting piece between the upper clamp and the iron core and the connecting piece between the steel platen and the upper clamp, the insulation resistance between the iron core and the upper and lower clamp and the steel platen and the iron core is measured, and there should be no obvious change compared with previous tests.
3. Check the contact between pressure nails and insulation pads. Use a dedicated wrench to tighten the fastening bolts at the upper and lower clamps, square iron, and pressure nails one by one. Ensure that the positive and reverse pressure nails and locking nuts on the clamps are not loose, that they are in good contact with the insulation washer, and that there is no burn mark.
4. Tighten the core bolts of the upper and lower iron cores with a special wrench, check and measure the insulation condition. The insulation resistance of the core bolts is not significantly changed compared with previous tests.
5. Check the oil circuit between the iron core and the iron core and the clamp. The oil circuit should be unblocked, and the oil channel pads should not fall off or be blocked, and should be arranged neatly.
6. Check the connection and insulation status of the earthing piece of the iron core. Only one point of earthing is allowed in the iron core.
7. Check that the pull plate and steel strip of the non-porous structure iron core should be tight and have sufficient mechanical strength. They should be well insulated and do not form a loop and do not contact the iron core
8. Check the electric field shielding insulation and grounding of the iron core. The insulation is good and the grounding is reliable.
