Any site that makes use out of transformers has to be cared for correctly and consistently. You can get both things when a professional transformer maintenance company is hired. They can perform many services so that you don't have to.
On-Site Care Program
Since transformers are typically large and bulky, taking these devices off your worksite and then transporting them to another site for repair and maintenance is pretty unrealistic. It's just best to hire a transformer maintenance company that has an on-site care program.