A Study on Internal Fault Simulation Methods for 345kV Autotransformers

In order to improve the reliability of protection systems, performance verification tests of protection relays are essential. KEPCO applies pre-defined test procedures using RTDS for this purpose[13]. For transformer protection relays, performance verification under internal winding fault conditions is necessary. RSCAD/RTDS offers internal fault models not available in similar programs, but it has limitations in representing the actual short-circuit characteristics of three-winding transformers. In contrast, transient analysis programs like PSCAD or EMTP can simulate faults without requiring expensive equipment like RTDS and effectively express the actual short-circuit characteristics of transformers. However, they lack internal fault models. This paper proposes a method to address the limitations of three-winding transformers in RTDS. Additionally, it presents techniques to implement transformer internal faults in ATP-EMTP equivalent to those in RTDS, along with comparative verification cases using the RTDS model.