This Guide provides protection methods for different types of Phase Shifting Transformers (PST) and discusses the interaction between protection and operating conditions of PSTs. Models representing PSTs to determine short circuit currents for relaying functions are presented. Sizing and location issues of protection current transformers employed in the protection of PSTs are included. This Guide provides examples of appropriate relay applications and settings. Purpose The purpose of this guide is to provide protection engineers with information that helps them to properly apply relays and other devices to protect phase-shifting transformers.