An analytical module is given to measure and minimize the circulating current in paralleling transformers. The calculation of circulating current in transformer paralleling is made as an example. The circulating method and balanced VAR method are discussed and integrated into a tap changer control. This method is suitable for all applications including transformers with different capacities and number of transformers in parallel. The balanced VAR method extends the paralleling prerequisites to source side separation application where the master-slave method is not working. A voltage control device implemented with the method discussed is introduced， together with regional automatic voltage control（AVC） and substation automation（SA） integration.