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.
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.
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