Scope: The generator differential protection contact-multiplication branch: RL5 GPRM and GPRR contacts in parallel feeding relay coil 30C between DC buses K801 and K802.. The drawing is a control (contact multiplication) schematic, not a power SLD; this branch is the only one with built-in redundancy and represents the 'GEN DIFF PROTN OPTD' function.
Boundary: Source K801 (DC+ bus), sink K802 (DC- return bus).. Coil 30C operates only when current flows from K801 through a closed contact and the coil to K802; the buses are the drawing's interface to the DC supply on sheet 008.
Can fail: other. Contacts (GPRM/GPRR) and the 30C relay coil are the devices that can fail to operate; wiring (K807) and the DC supply/return buses are treated as perfect connectors.
Success: any_path. 30C energises if either the GPRM or GPRR differential relay contact closes; any closed path from K801 through 30C to K802 operates the trip/CO2 multiplication.
Not modelled:
- Other branches (30A, 30B, 30D, 50ZX) and the 30C output contacts to 86A/CO2/annunciation: They are separate trip functions with independent initiating contacts, not redundant paths for the generator differential trip.
- DC supply source and MCB upstream of K801/K802 (sheet 008): Shown on another sheet; not on this drawing.
- Failure of the GPRM/GPRR relays themselves (sheets 044/045): Only their output contacts appear here.