Power Flow Consideration of Impedance Correction for Phase Shifting Transformers

In high voltage electric grids, phase shifting transformers (PSTs) are devices in which the phase shift across the device can be varied to control the flow of real power. A consequence of this phase variation is that PST's series impedance often varies with the phase shift, sometimes substantially. In power system analysis applications this variation is often modeled using a piecewise-linear impedance correction table. This paper analyzes the influence of incorporating impedance correction tables on a power flow solution. The presented method is implemented in two different test systems. A two-bus test system shows various transformer correction tables can make different power flow solutions. A 37-bus test system demonstrates the influence of the impedance correction table on both normal operating condition and contingency scenarios. The results reveal that impedance correction tables have impacts on power flow solutions and may help alleviate the overloaded lines following a contingency.