From what i've read the utility routes power around hot transformers if that "hot transformer" is warmer than it should be, that is if they calculate it is cost effective for them to do so.
every 10C increase in temperature cuts the life of the insulation and oil in half. but the document i read didn't mention how many degrees Celsius a "hot transformer" is.
Power transformers are a potential 100 year investment considering the average age is about 30-40 years far as i recall, and the reliability keeps getting better, not worse, as the reasons for why the oil breaks down are better understood. pretty sure one of my neighbors' house is still running on a 70+ year old pig pole on a 7,200 v line to ground power line.
I do not mean to sound like an industry whore but they know what they are doing. catastrophic failures are not common.
however where they seem to be making their money is lack of maintenance on overhead lines, also, fees.. they keep rising. and the ownership of the present system is changing hands too fast to guarantee transparency in my opinion.
there is a movement to create a local utility in my town and i'm not sure i want to know who is behind this plan. seems to me the reliability and price is good enough.
the present utility has been trying to find land to build a fourth substation but the city won't let them. so instead they spent a bunch of money subsidizing more energy efficient utilities such as heat pump hot water heaters, heat pumps instead of resistive heat, natural gas instead of electric heat.. their campaign was actually sucessfull enough they may not need to build a 4th substation for another 20 years.
however... they could just buy land to re route the existing substations.. and.. wait for it.. hook up the cooling fans on the existing three substations, then they would have a much longer term solution. honestly i don't understand all the friction in the system to pursuing logical activities. --and neighter does the person who told me they don't even have the existing three substations running at capacity nor do they have the cooling fans plugged in.. which I, having lived here 27 years can verify i have never seen them turn on.
on ships, dry transformers. resin encapsulated, probably filled with fire retarders which are usually also very toxic unfortunatly, very expensive, also much larger due to the air cooling requirement so they run just as hot but at a lower flux density, lower current density also due to lack of cooling capacity, however they run just as warm. lots of ships might have older dry transformers (cellulose, and , epoxy insulation) with 150C temperature rises.