Q17 — MVAR Loading / Voltage Regulator
APE 77 G2.1.27 (3.9)
Given:
• Both Units 1 and 2 are at 100% power with Voltage Regulators in AUTO.
• Unit 1 reactive load is 250 MVARs OUT.
• Unit 2 reactive load is 250 MVARs OUT.
• The 500 KV Ring Bus is closed.
Subsequently, Unit 2 trips.
Which ONE of the following completes both statements?
1. Unit 1 Main Generator Reactive (MVAR) loading will _(1)_.
2. Generator field current will _(2)_.
• Both Units 1 and 2 are at 100% power with Voltage Regulators in AUTO.
• Unit 1 reactive load is 250 MVARs OUT.
• Unit 2 reactive load is 250 MVARs OUT.
• The 500 KV Ring Bus is closed.
Subsequently, Unit 2 trips.
Which ONE of the following completes both statements?
1. Unit 1 Main Generator Reactive (MVAR) loading will _(1)_.
2. Generator field current will _(2)_.
A. _(1)_ rise by less than 250 MVAR
_(2)_ rise
_(2)_ rise
B. _(1)_ rise by less than 250 MVAR
_(2)_ lower
_(2)_ lower
C. _(1)_ rise 250 MVAR
_(2)_ rise
_(2)_ rise
D. _(1)_ rise 250 MVAR
_(2)_ lower
_(2)_ lower
▶ Show Answer & Explanation
✓ A. Correct. The reactive load that was being supplied by the tripped unit will be shared amongst the generators connected to the grid, therefore the reactive load increase on the operating unit will be less than 250 MVAR. The increased reactive loading on the operating unit will result in a sensed drop in terminal voltage and the voltage regulator will increase the generator field current to return the terminal voltage to setpoint.
✗ B. Incorrect. First part is correct. Second part is incorrect. Lowering the voltage regulator amps output will lower MVARs. Plausible because the operator may incorrectly understand the correct operation of the voltage regulator in response to changes in terminal voltage and MVARs.
✗ C. Incorrect. First part is incorrect. Second part is correct. Plausible because the applicant may believe that when Unit 2 trips, Unit 1 will pick up the full 250 MVARs based on Unit 1 being in close proximity to Unit 2 as opposed to other generator units located so far away from the island.
✗ D. Incorrect. First part is incorrect. Second part is incorrect. Plausible because the applicant may believe that when Unit 2 trips, Unit 1 will pick up the full 250 MVARs based on Unit 1 being in close proximity to Unit 2 as opposed to other generator units located so far away from the island. For Part 2, lowering the voltage regulator amps output will lower MVARs. Plausible because the operator may incorrectly understand the correct operation of the voltage regulator in response to changes in terminal voltage and MVARs.
Ref: NOS05EXCTR2-12 | LO: NOS05EXCTR2-12, Obj 6 — Describe the function and operating characteristics for the following Unit 2 Main Generator Exciter and Voltage Regulator components: Voltage Regulator | Source: Bank — Byron 2019 NRC RO15 (October exam) | Cognitive: Comprehension/Analysis
Connections
- Related systems: Main Turbine, 500KV
- Related exam: 2022 NRC Written Exam