  The smart transformer (ST) implemented using power electronics converters,
has the capability of independent voltage control and reactive power isolation
between its primary and secondary terminals. This capability provides a
flexibility in the power system to support the voltage at the primary side and
control the demand at the secondary side. Using this flexibility, the system
power flow could, for example, be optimized for lower costs. This paper
proposes an ST model suitable for OPF analysis. The effects of using multiple
STs at different penetration levels, on the daily generation costs in an IEEE
39 bus test system are presented.
