calculating power costs on a 45 and 15 KVA dry type distribution transformers due to no load losses
You have assumed each transformer is connected to a load and that load is at the rated VA of the transformer. This may not be true. If it is true then the efficiency figure can be used to calculate the approximate losses for a load that has a  power factor of unity. At very low power factors in the load this assumption may be a little inaccurate.

If the transformer Is not constantly delivering full VA the losses will be less. Consider the losses when the transformer is disconnected from a load. There will be minimal copper loss but there may be a slight increase in iron loss, but, overall I would suggest the no-load losses are significantly less. This must be factored in if the load is variable or intermittent.