13.8 kV utility substation
13.8 kV distribution substation single-line diagram with 138 kV grid input, 15 MVA step-down transformer, and three feeder breakers per IEEE 315.
For the power systems engineer
Scenario
A power systems engineer documents a distribution substation design for a utility interconnection application or a facility's electrical permit drawings. The single-line diagram is the first deliverable in any power system project — required by IEEE, NFPA 70E, and utility interconnection standards before detailed engineering begins.
Annotation key
utility = utility [label: "..."]— utility supply source (three-phase symbol)[type: transformer, kva:..., primary:..., secondary:...]— step-down transformer with rated kVA and voltage levels[type: bus, voltage:...]— horizontal bus bar at the specified voltage level[type: breaker, amps:...]— rated circuit breaker[type: load, label:...]— load or feeder destination->— directed power path from source to load
How to read
The 138 kV grid source feeds the high-voltage bus, which connects to the primary of the 15 MVA step-down transformer. The transformer secondary feeds the 13.8 kV medium-voltage bus. Three 1200 A circuit breakers fan out from the MV bus to three distribution feeders — each breaker isolates its feeder independently.