Dry transformers are damp, cores are damp, coils are damp: encapsulated (epoxy and DuPont Nomex insulated paper), and open (you can see the wire cake). The former is generally not a big problem after the water, the latter is easy to be affected with moisture, but it is better to deal with.
1, first of all, with a 2500V shaking meter (mehmmeter) shake the high and low coil respectively to the ground (core) and the insulation resistance between the high and low voltage coil is what? And write it down, that's how you do it. If there are 100-200 - m Ω (generally more than 200 m Ω, can be directly hung net) you use 5000 v, the shaking table test again if there are so many, can be affected with damp be affected with damp is not too serious. The transformer can be no-load for a period of time (at this time, the core is heated, the coil is not heated), the safest way is to energize from low voltage, and the natural moisture will evaporate.
2, the core insulation is low to a certain extent, will cause the core may be multi-point grounding, which will generate circulation between the core and the structural parts, increase the loss, serious case may burn insulation, burn off the grounding piece. If the core insulation to the ground is not less than 10 megohm is qualified, generally not less than 2 megohm is also able to run, if you are not assured, you can use the kind of heating lamp to bake.
3. If it is an open dry transformer, or the insulation resistance is low, do not energize first. It depends on what conditions you have on the transformer site. If there is a drying room, it is simple, directly go into the baking (the temperature increases slowly, up to 105 degrees, and it should be possible to maintain 4 hours. But be sure to remove the control line of the thermometer and any heat-resistant material.) If there is no drying room and other conditions, you can only use a high-power fan blowing (it is best to filter the hot air blowing - it depends on what conditions can be provided on the scene).
4, insulation resistance can return to more than 200 m Ω, transformer can no-load running, it is best to 24 hours, and the load.
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