Phase-shifting transformer with fixed phase between terminal voltage and voltage boost: tool for transient stability margin enhancement

摘要

The development of power electronics has enabled rapid and nearly continuous control of phase-shifting transformers (PSTs). As a consequence, new possibilities for solving problems concerning not only steady-state but also dynamic conditions in power systems are offered by electronically controlled PSTs. In the paper, the basic operating principles of a PST with fixed phase between terminal voltage and voltage boost (FP-PST) are presented. A mathematical model of a FP-PST is introduced, which is a representation of a longitudinal transmission system with a FP-PST included. It is shown that the location and the orientation of a FP-PST have a crucial impact on the behaviour of the power system. For the chosen test system, by applying the mathematical model, the most suitable location and orientation of a FP-PST were determined to solve problems concerning the first swing stability. On the same basis, appropriate FP-PST control is introduced to ensure the maximal stability margin for given FP-PST dimensions, small back swing and effective damping of subsequent swings. Modelling of the test system and FP-PST and dynamic simulation were performed in the stability mode of the NETOMAC program system. The minimal dimensions of a FP-PST were determined to ensure that the system remains stable after a fault followed by line tripping. Finally, the results of the dynamic simulation are presented.