Q19 — 4KV SPT Failure and Bus Transfer
062 AC Dist-A1.03 (2.5)
Given:
- Unit 2 is MODE 3
- 2A 4KV Vital Bus is powered from 23 SPT
- 2B and 2C 4KV Vital Busses are powered from 24 SPT
Subsequently
- The 23 SPT fails to 0 VAC
Which ONE of the following completes the statement below?
The 23 SPT Supply Breaker to 2A 4KV Vital Bus will FIRST open when 23 SPT Voltage lowers to less than a MAXIMUM of _(1)_ % of normal voltage.
After the electrical transient is complete, 2A 4KV Vital Bus will be powered by _(2)_.
- Unit 2 is MODE 3
- 2A 4KV Vital Bus is powered from 23 SPT
- 2B and 2C 4KV Vital Busses are powered from 24 SPT
Subsequently
- The 23 SPT fails to 0 VAC
Which ONE of the following completes the statement below?
The 23 SPT Supply Breaker to 2A 4KV Vital Bus will FIRST open when 23 SPT Voltage lowers to less than a MAXIMUM of _(1)_ % of normal voltage.
After the electrical transient is complete, 2A 4KV Vital Bus will be powered by _(2)_.
A. (1) 70 (2) EDG 2A
B. (1) 35 (2) EDG 2A
C. (1) 70 (2) 24 SPT
D. (1) 35 (2) 24 SPT
▶ Show Answer & Explanation
✓ C. Correct. For Part 1, the 23 SPT Supply Breaker to 2A 4KV Vital Bus will FIRST open when 23 SPT Voltage lowers to less than a MAXIMUM of 70% of normal voltage. For Part 2, after the electrical transient is complete, 2A 4KV Vital Bus will be powered by 24 SPT.
✗ A. Part 1 is correct. For Part 2, EDG 2A can power the 2A 4KV Vital bus. The candidate could incorrectly conclude that when 23ASD breaker opens, EDG 2A will power the 2A 4KV Bus.
✗ B. For Part 1, 35% of bus normal voltage is permissive setpoint which allows breaker 24ASD to close to power the 2A 4KV Vital Bus. The candidate could incorrectly conclude that the 23 SPT Supply Breaker will FIRST open when voltage lowers to less than 35% of normal. For Part 2, EDG 2A can power the 2A 4KV Vital bus. The candidate could incorrectly conclude that EDG 2A will power the bus.
✗ D. For Part 1, 35% of bus normal voltage is permissive setpoint which allows breaker 24ASD to close to power the 2A 4KV Vital Bus. The candidate could incorrectly conclude that the 23 SPT Supply Breaker will FIRST open at 35%. Part 2 is correct.
Ref: NOS054KVAC0-08 (4160 Electrical System) | LO: NOS054KVAC0-08 — State the setpoints, coincidence, blocks and permissives for automatic actuations associated with the 4160 Electrical System | Source: Bank | Cognitive: Higher (Analysis)
Connections
- Related systems: 4KV
- Related exam: 2018 NRC Written Exam