Application of phase shifting transformers in the tie-lines of interconnected power systems

Unscheduled power flows (also known as loop flows) are an increasing problem in the Central and Eastern European (CEE) region. These flows can negatively affect the secure operation of interconnected power systems and limit their cross-border trade capacity. Transmission system operators can prevent unscheduled flows entering their systems by installing phase shifting transformers (PSTs) in their tie-lines. This paper presents selected results of a study on the possibilities for cross-border active power flow control using PSTs installed in the tie-lines on Polish–German and Czech–German interfaces. The interactions between these devices are also demonstrated. One of the most frequently used designs of PST is shown as well. The problem is discussed of unscheduled flows in the CEE region as well as the active power flow control method using PSTs.