[frankharv]

I worked in a machine shop of a large shipyard and 20 years ago they had CNC Winders for rebuilding armatures for Navy ships.

They replaced older versions that were NC winders.

So this "hand wound" story is just that.

Windings going into Oil Tank? I think you mean varnish tank... After the rotating assembly is balanced they go into a protective coating tank that is a varnish.

[ggm]

Afaik utility scale Transformers operate in cooling tanks. Maybe that's what they meant about "afterward" "oil" covers many things. I believe the constant cycling and thermal load can make heinous PCBs.

[Animats]

It's liquid cooling. Even ordinary pole transformers are immersed in oil.[1] As transformers get larger, cooling fins appear, then active pumped cooling.

It's the usual cube-square scaling problem. Heat generation increases with the volume, while heat dissipation increases more slowly, with the surface area. For small animals, life is a struggle to keep warm. For large animals, life is a struggle to cool off.

[1] https://en.wikipedia.org/wiki/Distribution_transformer