Power transformer testing intervals for spare transformers

[Charlie.A]

Was wondering what best practices are used when considering a stored power transformers that has never been in service and is approximately 17 years old. An example of type of transformer would be that of a 40MVA, sealed unit with fins installed, filled with oil with a N2 blanket. Looking for info. on recommended testing intervals and necessary tests to perform on STORED never in service unit. Thank you.
Charlie.A

 

[thermionic1]

#1 - Are heaters connected and operating in the control cabinet?
#2 - Are you experiencing N2 loss beyond what is expected?
#3 - How does the oil quality look?
#4 - Does visual inspection reveal any rusting, leaking? Do fans rotate freely?

Our local utilities check on these things annually. Some may consider a Doble test on the bushings every 5 years. It's presumed that if the unit was to be utilized, a full battery of tests would be performed. SFRA would be appropriate before and after moving the unit in a fully assembled state.