Differential protection of single-core symmetrical phase shifting transformers

The development of the single-core symmetrical phase shifting transformer (PST) model and testing results of its selected differential protection is described in this paper. Generally, a PST is used for controlling the active power between the two systems being connected with one or more parallel transmission lines (paths). Most types of PSTs allow for changing of phase shift in a certain pre-defined range and thus the differential protection must on-line compensate for the phase angle shift introduced by a PST. Otherwise the error magnitude would be very high (even 1 pu) and problem with sensitivity and stabilization of protection can take place. An appropriate simulation model of the single-core symmetrical phase shifting transformer has been developed in MATLAB/Simulink environment. Next, the selected PST differential protection (proposed in the literature) was tested for various disturbances. The simulative testing results bring information about limitations of the selected algorithm and create basis for further research.