Comparison of operational characteristics between a Sen Transformer and a phase angle regulator

Sen Transformer (ST) emulates an impedance in series with the transmission line and, in turn, allows the active and reactive power flows to change independently, meaning as desired. Traditionally, power flow control has been attempted with the use of a phase angle regulator (PAR), which can only regulate the phase angle of the line voltage and, in turn, allows the active and reactive power flows to change simultaneously, meaning both powers either increase or decrease; therefore, the line cannot be optimized for the highest amount of active power flow that generates the most revenue at the lowest amount of reactive power flow. In addition, for a desired amount of active power flow enhancement, the ST uses a much lower overall reactive power than what is needed in the case of a PAR; ST creates lower losses in the line; the rating of the ST is lower than that of the PAR. Moreover, the ST can enhance the power flow up to the line's thermal limit, which may be unattainable with the PAR due to its operating limitations.