SOPD Power Grid Operations & Management 2 — Questions and Answers
Question 1: What is the primary purpose of automatic generation control (AGC) in power grid operations?
- Manually dispatch generators to meet load
- Automatically adjust generator output to maintain system frequency and scheduled tie-line flows (Correct answer)
- Monitor transmission line temperatures
- Control reactive power output of capacitor banks
Correct answer: Automatically adjust generator output to maintain system frequency and scheduled tie-line flows
AGC automatically adjusts generator MW output to correct Area Control Error (ACE), maintaining frequency at 60 Hz and keeping net interchange on schedule.
Question 2: During a voltage collapse scenario, which corrective action should a system operator take FIRST?
- Trip generation units to reduce system load
- Shed load in the affected area to arrest voltage decline
- Energize shunt capacitor banks and request reactive support from neighboring areas (Correct answer)
- Open all tie-lines to islanded operation
Correct answer: Energize shunt capacitor banks and request reactive support from neighboring areas
Energizing capacitors and obtaining reactive support restores reactive power margin and arrests voltage decline before more drastic actions are required.
Question 3: A transmission line's thermal limit is reached at 115°C conductor temperature. What does this limit protect against?
- Insulation breakdown in underground cables only
- Excessive sag that could reduce ground clearance below safe minimums (Correct answer)
- Ferroresonance in nearby transformers
- Voltage instability on adjacent buses
Correct answer: Excessive sag that could reduce ground clearance below safe minimums
High conductor temperatures cause thermal elongation and increased sag, reducing ground clearance and creating a safety hazard.
Question 4: What does the term 'N-1 reliability criterion' require of a transmission system?
- The system must survive the simultaneous loss of any two elements
- The system must remain stable and within thermal limits following the loss of any single element (Correct answer)
- One backup generator must always be online for every operating unit
- No more than one switching operation may occur per hour
Correct answer: The system must remain stable and within thermal limits following the loss of any single element
The N-1 criterion requires that the bulk power system remain secure and within all limits after the sudden, unplanned loss of any single contingency element.
Question 5: When a large generating unit trips offline unexpectedly, what is the immediate grid response?
- System frequency rises as remaining generators speed up
- System frequency declines as load exceeds available generation (Correct answer)
- Voltage across the grid immediately drops to zero
- All tie-line flows reverse direction
Correct answer: System frequency declines as load exceeds available generation
Losing a large generator creates a power deficit; system frequency begins to drop until governor response and AGC restore the balance.
Question 6: What is 'spinning reserve' in power system operations?
- Generation capacity already synchronized to the grid and available to increase output within 10 minutes (Correct answer)
- Offline generation that can start and reach full load within 30 minutes
- Reserve capacity held by batteries only
- Reactive power surplus maintained by capacitor banks
Correct answer: Generation capacity already synchronized to the grid and available to increase output within 10 minutes
Spinning reserve is synchronized, unloaded generating capacity that can be rapidly called upon to arrest frequency decline following a contingency.
Question 7: A dispatcher observes that the Area Control Error (ACE) is persistently negative. What does this indicate?
- The area is exporting more power than scheduled
- The area is generating less than needed, causing underfrequency or excess imports (Correct answer)
- Voltage levels across the area are above normal limits
- All generators in the area are at maximum output
Correct answer: The area is generating less than needed, causing underfrequency or excess imports
Negative ACE means the area is under-generating relative to its scheduled net interchange and frequency contribution, requiring an increase in generation.
SOPD Power Grid Operations & Management 2
What is the primary purpose of automatic generation control (AGC) in power grid operations?