Distribution transformers are an essential part of any power distribution system. In order to thoroughly simulate and analyze such a system, accurate models must be developed that make use of readily available field data. In addition, unbalanced loading situations, which are encountered frequently in distribution transformer utilization, must be handled properly. These requirements form the basis for the modeling of the open-wye/open-delta and open-delta/open-delta distribution transformer connections.

The Distribution Engineering Workstation (DEWorkstation), an Electric Power Research Institute (EPRI) software package, is the environment in which the open bank connections are modeled. In particular, a load flow analysis application, called Power Flow, provides the framework for all transformer connection modeling. This framework incorporates a method of tracing through the circuit to determine the voltages and currents on each side of the transformer connection. From theses parameters, the power rating of each set of paired windings can be determined.

The accuracy of the open bank models developed in DEWorkstation is confirmed through comparison with more rigorous open-wye/open-delta and open-delta/open-delta distribution transformer models. Making use of transformer bank loading results from software developed by Pennsylvania Power and Light (PP&L), the open-wye/open-delta and open-delta/open-delta transformer connections are validated. Other transformer connections that could be verified using the results from PP&L are also presented.