When existing recommendations for PST protection can let you down

The paper will present implemented protection scheme on two, symmetrical, double core design Phase Shifting Transformers (PST) [6], each rated at 600MVA, 400kV, 866A, 50Hz, ±40° with in total 64 tap positions (32 advance and 32 retard). Thus, every individual tap introduce phase angle shift of 1,25°. The used PST protection scheme follows the protection recommendations published by IEEE [1]. It shall be noted that this IEEE recommendation is mainly based on information available in reference [2]. However during execution of this project new challenges were faced due to following reasons: • Slightly different construction of PST • Numerical differential relays are used instead of electro-mechanical ones originally suggested in [1,2] Due to these differences this paper will: • Indicate at which statements IEEE publication [1] is wrong due to slightly different PST design • Provide design and setting guidelines for 87P and 87S functions when modern numerical transformer differential protection is used