What are energy efficient (TP1) transformers?

"There is a growing movement in the electrical industry towards energy efficient products in all sectors including dry type transformers. In addition to the benefits to the environment, energy efficient transformers can realize substantial savings in operating costs thereby having a direct impact on the initial investment evaluated over a period of time. The specification covering energy efficiency in transformers, is the NEMA Standards Publication, TP-1-1996, ""Guide for Determining Energy Efficiency for Distribution Transformers"". This specification has carefully considered the total owning cost unique for industrial or commercial installations where the load factor is an integral part of the efficiency rating. "