Dry transformer maintenance plan

Most important are the visual inspection and bolt tightening. I generally run a megger test between primary and secondary windings as well, because where I live, humidity is the killer. I will usually douse exposed metals with a moisture displacing electrical spray (especially exposed core laminations- I have seen significant separation of laminations due to moisture ingress and subsequent corrosion...) I have to admit, I have never had to take a dry transformer out of service due to degraded performance or anticipated failure- most of those I have had to replace have been killed by lightning...

In-service monitoring also proves critical- an overloaded transformer will let you know it is overworked through loud complaining and excessive heat- add more capacity before it cooks itself!

u should do turn ratio too.

but all producers ( Siemens, ABB, Sunbelt, another two - do not remember names) suggest only cleaning and bolts tightening. I do not fully happy with this short maintenance, but what will we get from having turn ratio ? and if do it - how offen ? how really effective this test for finding trouble within dry trafo ?