Q12 — Loss of 125VDC / EDG Starting
APE 58 AK3.01 (4.0)
Given:
• Unit 2 lost 2A 125 VDC bus
• Then SI actuation occurs
What is the effect on the 2A EDG?
• Unit 2 lost 2A 125 VDC bus
• Then SI actuation occurs
What is the effect on the 2A EDG?
A. EDG will NOT start, start circuit from DC power
B. EDG will NOT start, SEC has no power for diesel start relay
C. EDG will start, SSPS directly starts EDG with redundant DC
D. EDG will start, start circuit from vital instrument power
▶ Show Answer & Explanation
✓ A. Correct. EDG starting circuits are supplied from 125 VDC power. With no DC power, EDG cannot start automatically from SI/SEC or remotely.
✗ B. SEC relays are supplied by vital instrument power, not DC. But the EDG start circuit itself needs DC power, so the conclusion (EDG will not start) is correct but the reason is wrong.
✗ C. SSPS sends SI to SECs, SECs send start to EDG start circuitry which is DC powered. No redundant DC supply for the 2A EDG start circuit.
✗ D. EDG start circuit requires DC power, not vital instrument power.
Ref: NOS05EDG000-15 | LO: NOS05EDG000-15, Obj 14.c | Source: New | Cognitive: Fundamental/Memory
Connections
- Related systems: DC Power, EDGs
- Related exam: 2023 NRC Written Exam