Load growth and power flow control with DSRs: Balanced vs unbalanced transmission networks

An important issue in today's power system is the need to analyze and determine the adequacy of transmission capacity. There is a need for approaches to increase transmission system capacity without construction of new transmission facilities, all while assuring secure operation of the grid. Distributed Series Reactors (DSRs) are a new smart grid technology that can be applied to control flows in transmission or distribution systems. DSRs can be used to balance phase flows in a single line as well as to control the distribution of flow in a meshed system. This paper investigates DSRs to control power flow to alleviate overloads due to increased power transfer. The IEEE 39 bus standard model is modified to a 3-phase unbalanced transmission model with 345 kV lines that accounts for tower geometry. Using the symmetrical components transformation, a balanced, 3-phase model is then derived from the unbalanced, 3-phase model. DSR designs based on the unbalanced, 3-phase model and the balanced, 3-phase model are compared and used to demonstrate the effectiveness of DSR control in handling load growth. Only unbalanced impedances are addressed i.e., non-transposed lines, but the effects of impedance unbalance are shown to be significant on the resulting DSR design.