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Exams > 2023 Q15 — Grid Disturbance / Unit Trip Effects on MVARs

2023 Q15 — Grid Disturbance / Unit Trip Effects on MVARs

⚠️ DRAFT
Q15 — Grid Disturbance / Unit Trip Effects on MVARs APE 77 AA2.05 (3.7)
Given:
• Both units at 100%
• Unit 1 350 MVARs OUT
• Unit 2 200 MVARs OUT
• Unit 1 trips

What is the effect on grid voltage and Unit 2 MVARs?
A. Grid voltage rise, MVARs rise
B. Grid voltage rise, MVARs lower
C. Grid voltage lower, MVARs lower
D. Grid voltage lower, MVARs rise
▶ Show Answer & Explanation
✓ D. Correct. Loss of a Salem unit causes 500KV switchyard voltage to lower (below 493 KV or by 2%). As grid voltage lowers, generating units share reactive load, Unit 2 MVARs rise to compensate for the lost reactive support.
✗ A. Grid voltage lowers on loss of a large generating unit, it does not rise.
✗ B. Grid voltage lowers, not rises. MVARs rise, not lower.
✗ C. Grid voltage correctly lowers, but MVARs rise not lower — remaining units compensate for lost reactive support.
Ref: S2.OP-AB.GRID-0001 (R23) | LO: NOS05ABGRID-13, Obj 3.b | Source: Modified - Salem 2022 NRC RO17 | Cognitive: Comprehension/Analysis

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