Scope: The 735 to 315 kV transformation inside the red dashed study boundary: BUS 735, both transformer bays (HV disconnectors, breakers and CTs, TR-01 and TR-02), the four 315 kV bays, and BUS 315-A and BUS 315-B.. The drawing's dashed boundary note says this is the study boundary and that items outside it are out of scope.
Boundary: Source = 735 kV lines feeding BUS 735 (treated as perfect). Sink = a virtual '315 kV network' node fed by both BUS 315-A and BUS 315-B.. These are the points where power enters and leaves the dashed study boundary. Both buses leave the sheet 'to 315 kV network', so delivery through either bus counts as success.
Can fail: breaker, disconnector, ct, transformer, busbar. These are the in-boundary primary equipment items in series in the power path; any one of them failing open or faulting interrupts its branch. The source (735 kV lines) and the virtual sink are boundary terminals and are treated as perfect.
Success: any_path. Note 1: everything is normally closed, and the station supplies the 315 kV network if at least one intact path connects BUS 735 to either 315 kV bus. Each 1650 MVA transformer is assumed able to carry the station load alone (capacity is not checked).
Not modelled:
- Protection, control and auxiliary systems (relays, DC supply, trip circuits): Not shown on the drawing (Note 4); CTs are modelled only as series primary elements.
- Capacity and N-1 loading limits of the transformers and buses: An any-path RBD is connectivity only; the transformer ratings and the 315 kV load are not given.
- Fault propagation and breaker failure to clear (a bus fault taking out adjacent equipment): An RBD treats failures as independent opens; protection coordination is not on the sheet.
- Common-cause failures and maintenance outages: No data on the drawing; all blocks are treated as independent.
- Junction points at the transformer LV leads: These are connection dots, not equipment; they are treated as perfect.