Wonder the make? Not Reyrolle of course.
I chap I talked to years ago in France said that a country he worked for bought 5 transformers from the Far East.
They were cheaper than 3 or 4 Reyrolle ones.
Most of them only lasted a few years.
The problem he said was that the cooling or oil circulation system was useless on them.
If they had bought Reyrolle ones they would have had years of service. But the bean counters went for cheap.
Odd it seems that there is no backup system at Heathrow.
Allan C.