Which two would cause a swell? (Choose two.)

Question

Options

• AGround fault interrupt
• BSudden load reductions
• CSingle-phase fault in a three-phase system
• DAutomatic transfer switch (ATS) transfer to secondary power

• A
  4% (2)
• B
  84% (38)
• C
  2% (1)
• D
  9% (4)

Explanation

Sudden load reductions (B) cause a voltage swell because when a large load abruptly disconnects, the supply system continues pushing energy into the circuit with less demand to absorb it, driving voltage temporarily above normal levels (typically 1.1 to 1.8 per unit). Note that since the question says "Choose two," the second correct answer is likely C: a single-phase fault in a three-phase system causes a swell on the unfaulted phases because the loss of balance shifts the neutral point, increasing voltage on the healthy conductors. A ground fault interrupt (A) is a protective device that responds to faults by interrupting current - it causes an outage, not a voltage rise. An ATS transfer to secondary power (D) produces a momentary interruption during the switching window, not an overvoltage condition.

Memory tip: Think "swell = less load or lost phase." Anything that suddenly removes demand (load dropout) or unbalances a three-phase system (single-phase fault) leaves excess voltage with nowhere to go - that's your swell.

No community discussion yet for this question.