Phase-shifting transformer control and protection settings verification

San Diego Gas & Electric (SDG&E) initiated a project to add two parallel 400 MVA (+31.3° to −80.1°) phase-shifting transformers (PSTs) at a 230 kV interconnection substation. California ISO (CAISO) proposed the PST project to provide flow control between SDG&E and Comisión Federal de Electricidad (CFE) 230 kV systems during critical N-1 or N-1-1 500 kV line contingencies. With the need to integrate renewable generation, many utilities are using PSTs to manage the grid (e.g., American Electric Power [AEP] has eight PSTs in their system). SDG&E is presently reviewing the need for additional PST projects. The authors collaborated to address the unique challenges of parallel PST protection and control for this wide-ranging PST application, including implementation of CAISO control and automatic contingency-based tap-changer runback. This paper discusses SDG&E's process to execute the project, including settings development, simulation, lab and field testing, and in-service testing. The authors discuss oscillography analysis used during lab testing, energization, and loading to verify the overall design and programming.