Transient stability assessment of power systems with phase shifting transformers

There is an number of Phase Shifting Transformers (PSTs) installed in power systems that needs to be taken into account when assessing a transient stability. A conventional method of transient stability analysis a digital simulation can easily satisfy demanded models complexity while direct methods require energy functions that adequately represent a post-fault system. We present two ways how to enter effects of phase angle regulator (PAR) that is a member of PSTs into a powers systems' energy function. Consequently several new energy functions are presented. Two cases were considered; first uses advantages of a reduced system and a second one a structure preserving framework. Two numerical examples validate the proposed energy functions by comparing critical clearing times obtained directly and by a step-by-step time-domain simulation.