Phase angle regulating transformer protection using digital relays

Phase angle regulating transformers are dynamic changers, used to control the real power flow through interconnected power systems. This paper describes the specifics of an installed phase angle regulating (PAR) transformer, and protection techniques using modern digital relays. More specifically the paper is focused on issues applying current differential protection to a 120 MVA phase regulating transformer on 138 kV power system at CLECO´s Beaver Creek 138/34.5 kV substation in Pineville, Louisiana.