Power System Operations Flashcards
7 cards from real SOPD practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Power System Operations flashcards as text
A 500 kV line trips unexpectedly and operators observe voltage dropping on adjacent buses. What is the most likely cause of the voltage depression?
Answer: Loss of reactive power support that the tripped line was providing through its charging current
Transmission lines generate reactive power through their shunt capacitance; losing a line removes this reactive support and depresses voltage.
Under what condition is a power system said to be operating in a 'voltage collapse' scenario?
Answer: When voltage instability leads to uncontrollable reduction in voltage despite increased reactive power injection
Voltage collapse occurs when the system can no longer supply adequate reactive power and voltage spirals downward beyond the point of recovery.
What is the primary benefit of operating generators in 'droop control' mode rather than isochronous control?
Answer: It enables stable load sharing among multiple generators without hunting or instability
Droop control provides inherent load sharing by causing each generator's output to increase proportionally as frequency falls, preventing instability from competing governors.
What does the term 'spinning reserve' mean in power system operations?
Answer: Unloaded generation capacity synchronized to the grid that can respond immediately to load changes
Spinning reserve is synchronized, partially loaded capacity that can increase output immediately without start-up delay.
Which protective relay function is specifically designed to detect loss of excitation in a synchronous generator?
Answer: Loss-of-field relay (impedance-based, ANSI 40)
The ANSI 40 (loss-of-field) relay uses impedance measurement to detect when a generator has lost its excitation and begins absorbing reactive power.
A power system operator must shed 1,000 MW of load to prevent cascading outages. Which approach is preferred to minimize customer impact?
Answer: Rotating or controlled load shedding distributed across multiple areas
Rotating load shedding distributes the interruption impact equitably and avoids prolonged outages in any single area.
What is the significance of the 'short-circuit level' (fault MVA) at a bus in system planning?
Answer: It indicates the magnitude of current during a bolted three-phase fault and drives equipment ratings
Fault MVA determines the interrupting duty required of breakers and the withstand ratings of equipment at that bus.