The unbalanced load cost on transformer losses at a distribution system

Small differences in transformer losses are not important when a transformer is analyzed alone but they are significant when the population of transformers present in an electricity distribution system are considered. Based on those facts, it was analyzed the effects of the unbalanced loads connected to the secondary of transformer in the transformer load losses. The load losses are calculated based on distribution transformers load measurement in the field, and on the values of standards ABNT-NBR54401999. The measured power of transformers were 30, 45 and 75 kVA, the most common rated power for transformers in a Brazilian distribution system. Such measurements statistically represent the population of three-phase transformers from a power utility with 15% of deviation from the most probable value. Analysis is also carried out comparing the ideal case ofperfect balanced loads with the real case. Finally, it is obtained the total annual cost caused by unbalanced loads in their transformers for a power utility.