Power System Protection Design and Validation for a Modular Controllable Transformer (MCT)

In recent years, distributed energy resources (DERs) have been increasingly integrated into power systems that affect grid management and operations. Since the operating conditions of DERs vary greatly and are more intermittent than those of conventional energy systems, power systems are experiencing greater stability problems. Modular controllable transformers (MCTs) have been proposed as an optimum solution to address these issues. MCTs are specialized transformers that utilize fractionally rated power converters and perform several grid support functions in addition to isolation and voltage conversion. Protection requirements for MCT have not yet been defined in the standards. This paper aims to improve the performance and protection of MCTs by proposing and validating their protection schemes. These protection schemes include differential protection, overcurrent relay, and under and overvoltage relay. These protection schemes have been implemented, and simulation results that validate their effectiveness are presented in this paper.