Generator Step Up Transformer Storage Condition

I'll take a wild guess.

Store the transformer in the same manner it was when it arrived, and before it was hooked up.

Open the transformers up and pour out all the electrons inside. Seal the wires with neutron sealer so that no more electrons can go back into the transformer.

As an additional precaution, you can spray the transformers with clear anti-static coating, so stray electrons can't see them.

If this fails, consult the OEM.

Thanks Lyn. . . .

I appreciate your comments.

Parameters i.e insulation, oil etc

You asked the OEM and they gave you an answer. Follow their advice. If you do not understand their advice you should ask them for an explanation. I suspect their "charged condition" refers to these transformers remaining sealed and charged with the anhydrous coolant they come with but that is just a guess on my part.

When they say "charged condition" I suspect that they mean air tight with a nitrogen gas blanket over the top oil. Periodically sample the oil and the nitrogen and have the samples analyzed to determine if oxygen is somehow bleeding into the tank.

It's going to cost you a few bottles of nitrogen and a pressure gauge but if the pressure starts falling you should investigate. Kept free of outside air the interior of the tank will not degrade unless there were impurities in the oil prior to mothballing. DGA (Dissolved Gas Analysis) is your friend.

The OEM is right.

We have stored transformers for years in energised condition with regular tests for dielectric strength and water content of the oil. Maintain the breather as usual and check for leaks regularly.

The no load losses are much cheaper than repairs to a deteriorated transformer.

can you not calculate the no load losses, then compare the losses to the cost of replacing/repairing the transformer?

That way you will see which one is the correct course of action to take.

and while you are at it.. don't forget to include how long it will take to replace the transformer IF it fails while switched off. Not every transformer supplier has a spare on the shelf.