Transmission 138 kV

Bath  designed the protective relay schemes and control circuits on four 138kV/12.5kV substations that are part of a 138kV transmission line loop that feeds two refineries. One of the four substations is completely new, while the other three were upgraded and retrofitted. All four of the substations are in-line substations, each with two 138kV line breakers and one 138kV bus-tie breaker. Each of the four substations contains two, 24/32/40 MVA; 138/12.5Kv rated step-down transformers and 15kV switchgear line-ups, to distribute power to the plants.

Bath performed all the design engineering for the 138kV breakers, the 138/12.5kV transformers, and the 15kV switchgear line-ups, including the protection and control circuits. Bath provided new, revised, and demolition drawings for all four substations. Bath also performed short circuit studies, power flow studies, and relay and fuse coordination studies for all the 138kV and 15kV equipment. The short circuit and load flow models contained 50 buses, 200 components, and 75 branches. Protective relays ranged from SEL 311L and ABB REL 356 microprocessor based current differential relays using fiber optic communication links to ABB CO-9 electromechanical relays.

Bath also supplied field supervision during installation and commissioning. All short-circuit, load flow, and relay coordination studies were performed with the aid of SKM PTW-32 power systems analysis software.