Comparison of the ´Sen´ transformer with the unified power flow controller

The independent control of active and reactive power flow in a transmission line is necessary for the transfer of bulk power along a desired path in the most economical way. A ´Sen´ transformer (ST) uses transformer and tap changers that are traditionally used to build a voltage-regulating transformer (VRT) and a phase angle regulator (PAR). The ST regulates the voltage at a point in the transmission line as a VRT does. Additionally, the ST provides an independent and bidirectional active and reactive power (P and Q) flow control in the transmission line as a voltage-sourced converter (VSC)-based unified power flow controller (UPFC) does. Although both the ST and the PAR use a comparable number of components, the ST provides an area of controllability in the P-Q plane similar to a UPFC, while the PAR provides a linear P-Q characteristic. The technology of transformer and tap changer is proven to be reliable and cost-effective when compared with the emerging technology of VSC. The new ST is adequate to provide independent control of active and reactive power flow in most utility applications.