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We have isolation transformers used in our noise test room. Basically, the just provide isolation so that during noise tests, the noise waveforms (impulse, surge spikes) from the tester is isolated from the auxiliary equipment or equipments that are not under test.

Unfortunately, they were soaked after flood. I have never been in this situation before so I am not really sure as to what I should do.

Right now, I am thinking of:

  1. Making sure the transformer is dry (how to do this specifically, I am not yet sure. Can I use temperature oven for example? If yes, at what temp/duration? I will try to find the manual (if it has) of the transformer if it has specs on its max temp)
  2. Visually checking the inside of transformer. Check for corrosion. Check for contaminants and if insulation is visually ok.
  3. Electrically check the isolation. I am thinking of dielectric withstand test between a primary and secondary wire. I am still unsure about applied voltage (how many kV) and trip current (1mA? 10 mA) that is needed.
  4. I can also use a resistance check if the resistance between primary and secondary is still very high. But I think if it passed dielectric withstand test, doing a resistance check is no longer necessary.
  5. Assuming dielectric withstand test is ok, what about the transformer characteristic? I assume that isolation transformer has 1:1 ratio turns for example. Can I for example use a variable transformer to input say, 10Vrms to check if same waveform of same magnitude is present in the secondary side, just to check if it is still working as intended?

Any suggestion or correction is highly appreciated as I've never done such debugging before.

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  • \$\begingroup\$ Step 5 is unnecessary; if the transformer is still alive at all, its properties will be fine. Is the transformer potted? If so, the chances of survival will be much higher. \$\endgroup\$
    – Jonathan S.
    Commented Nov 3, 2022 at 23:48
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    \$\begingroup\$ Bake the items at around 60C for a few hours to evaporate any moisture. The insulation materials in most transformers are good for well in excess of 60C, but there maybe plastics and wiring that wont like much more. \$\endgroup\$
    – Kartman
    Commented Nov 4, 2022 at 0:54
  • \$\begingroup\$ Not sure baking will drive the water out. You could just end up with hot water between the coils. I would consider "sucking" the water out with desiccant. You probably don't have any on-hand, but you can Amazon some overnight. Get a large quantity, and seal the transformers up in an airtight plastic bag with a few pounds of desiccant, leave for a week or so. Do the oven thing until you get the desiccant. Suggest you hi-pot these after service to make sure all is well... \$\endgroup\$
    – Kyle B
    Commented Nov 4, 2022 at 1:01
  • \$\begingroup\$ Floodwater contaminants might leave a film that may compromise the isolation. Wash the transformer with clean water (no soap) perhaps under a spray nozzle. (don't pressure wash. Use something like a tooth brush as well. Then go through the drying processes mentioned in other comments. If you use desiccant in an air tight plastic bag, get the bag that can be evacuated. Water does eventually evaporate on its own even at room temperature. Baking at 60C will increase the vapour pressure and speed up the drying time. \$\endgroup\$
    – user319836
    Commented Nov 4, 2022 at 2:24
  • \$\begingroup\$ wash with tap water, then follow with distilled water before baking \$\endgroup\$
    – jsotola
    Commented Nov 4, 2022 at 2:53

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Making sure the transformer is dry (how to do this specifically, I am not yet sure. Can I use temperature oven for example? If yes, at what temp/duration? I will try to find the manual (if it has) of the transformer if it has specs on its max temp)

A good way might be too also put a very low pressure or close to vacuum on it to get rid of the volatiles and to put mild heat to boil them off. Make sure the insulation is not made of PVC.

Checking continuity is good to make sure that there is no brakes and insulation, but it won't test to break down of insulation, that can only be done by applying high voltage. A high pot tester might work

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