As electric power distribution systems continue to grow in size and complexity. Reducing losses can result in substantial savings for utility. Other benefits from loss reduction include released system capacity, and possible deferral of capital expenditures for system improvements and expansion. While losses in distribution lines are due to copper losses, transformer losses occur due to both copper and core losses. An increase in loading will result in an increase of current flow and correspondingly greater amount of loss in the transformer. Moreover, an unbalance in the system load will increase transformer losses. The harmonic currents will cause a small increase in copper losses; however, the high frequency harmonic voltage can cause large core losses. Frequently, utilities are forced to use an oversized transformer to compensate when a large harmonic presence is indicated. A MATLAB model for the three-phase distribution transformer was built to calculate transformer efficiency at different loading conditions. Distribution transformers can be more efficient and economical providing that the right technology is considered. Electricity distribution companies could use the total owning cost method to make transformer purchasing decisions. This method allows the total losses over the whole life cycle to be taken into account.