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Exams > 2019 Q21 — 4KV SPT Breaker Spurious Open

2019 Q21 — 4KV SPT Breaker Spurious Open

⚠️ DRAFT
Q21 — 4KV SPT Breaker Spurious Open 062 A.C. Electrical Distribution-K3.01 (3.5)
Given:
• Unit 2 is MODE 3
• 2A 4KV Vital Bus is powered from 23 SPT
• 2B and 2C 4KV Vital Buses are powered from 24 SPT

Subsequently
• 23ASD (23 SPT Supply Breaker to 2A 4KV Vital Bus) SPURIOUSLY opens

Which ONE of the following completes the statement below?

After the electrical transient is complete, the 2A 4KV Vital Bus will be ___
A. de-energized
B. powered from 2A EDG with the blackout loads loaded by the 2A SEC
C. powered from the 24 SPT and the 2A EDG will NOT start
D. powered from the 24 SPT and the 2A EDG will start and remained unloaded
▶ Show Answer & Explanation
✓ B. Correct. With 23 SPT at normal voltage when 23ASD spuriously opens, the 23SPT transfer relay remains energized and an AUTOMATIC transfer of the 2A 4KV Vital Bus to the 24 SPT will not occur. Consequently, the 2A 4KV Bus will de-energize and the 2A EDG will start and power the bus in accordance with the 2A SEC operating in Mode II*.
✗ A. Incorrect but plausible. Since the 23SPT transfer relay remains energized, the operator may incorrectly determine that the 24 SPT and 2A EDG transfer scheme is defeated causing the 2A 4KV Bus to remain de-energized.
✗ C. Incorrect but plausible. This is the expected result if the 23 SPT transfer relay had de-energized.
✗ D. Incorrect but plausible. This would be partially correct if the 23 SPT transfer relay had de-energized.
Ref: NOS054KVAC0-08 (4160 ELECTRIC SYSTEM) | LO: Given a 4160 Electrical System failure, predict the effect on off-site power sources and Emergency Diesel Generators | Source: Bank | Cognitive: Higher

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