Evaluation of load division among transformers of different capacities in the grounded wye-delta and open wye-open delta banks under balanced loading and various power factor conditions

This paper evaluates the load division among transformers of different capacities in the grounded wye-delta and open wye-open delta banks under balanced loading and various power factor conditions. In some contingency cases two or three singlephase transformers of different kVA ratings are connected as a three-phase transformer bank to provide three-phase service for critical customers. In these cases, the load division among transformers becomes unequal and results in an unbalanced distribution system. The results of this study corroborate power company experience. Even when both three-phase sources and loads of the bank are balanced, the load division among transformers is unequal if transformers of different capacities are used in a bank, or an open wye-open delta connection is adopted.