SOPD Emergency Response & System Restoration Procedures 2 — Questions and Answers
Question 1: During a widespread blackout, what is the correct sequence for restoring the transmission system?
- Energize load first, then generation
- Restore generation, establish transmission backbone, then pick up load (Correct answer)
- Pick up load incrementally before establishing transmission paths
- Restore all feeders simultaneously to reduce restoration time
Correct answer: Restore generation, establish transmission backbone, then pick up load
The standard black start sequence establishes generation and transmission backbone first before incrementally picking up customer load to avoid overloads.
Question 2: A synchronizing check relay (25) prevents closing a breaker when:
- The bus voltage is below nominal
- The frequency difference between two systems exceeds the relay's set threshold (Correct answer)
- The line current exceeds the relay's rating
- The power factor is lagging
Correct answer: The frequency difference between two systems exceeds the relay's set threshold
A sync-check relay monitors voltage magnitude, angle, and frequency difference, blocking closure when the differential exceeds its permitted threshold to prevent a damaging out-of-phase close.
Question 3: What is 'islanding' in power system context during an emergency?
- Isolating a single generator from the grid for maintenance
- A portion of the system operating isolated from the main grid, potentially with uncontrolled frequency (Correct answer)
- Separating load shed blocks by geographic region
- Routing power around a faulted transmission line
Correct answer: A portion of the system operating isolated from the main grid, potentially with uncontrolled frequency
Islanding occurs when a section of the power grid continues to operate independently after separation from the main grid, which can create unsafe frequency and voltage conditions.
Question 4: Under NERC EOP-005, what must operators verify before energizing a transmission line during restoration?
- Only that the line current rating is not exceeded
- That protection systems are in service and the line is clear of work tags (Correct answer)
- That the line has been de-energized for at least one hour
- That neighboring control areas have approved the energization
Correct answer: That protection systems are in service and the line is clear of work tags
EOP-005 requires operators to confirm protection systems are in service and the element is free of clearances/tags before energizing during system restoration.
Question 5: When frequency drops below the first stage of an Under-Frequency Load Shedding (UFLS) scheme, the scheme automatically:
- Trips generating units to reduce instability
- Disconnects a pre-set block of customer load to arrest the frequency decline (Correct answer)
- Opens all transmission tie lines to neighboring areas
- Activates spinning reserves and waits 10 minutes before shedding load
Correct answer: Disconnects a pre-set block of customer load to arrest the frequency decline
UFLS automatically trips pre-programmed load blocks to reduce demand and arrest frequency decline when it falls below defined thresholds.
Question 6: A system operator notices bus voltage is 8% below scheduled level during an emergency. The FIRST corrective action should be:
- Shed industrial load immediately
- Request neighboring areas to reduce their exports
- Raise generation reactive output (MVAr) and check capacitor bank status (Correct answer)
- Trip the lowest-priority transmission line
Correct answer: Raise generation reactive output (MVAr) and check capacitor bank status
Low voltage is primarily corrected by increasing reactive power supply — raising generator excitation or switching in capacitor banks — before resorting to load shedding.
Question 7: During black start restoration, why is it important to control the rate of load pickup?
- To prevent the transmission line from overheating too quickly
- To avoid excessive frequency dips that could trip the black start unit off-line (Correct answer)
- To allow protection relay settings to be recalculated
- To ensure billing meters are reset before load is added
Correct answer: To avoid excessive frequency dips that could trip the black start unit off-line
Adding load too fast causes frequency to dip; if the dip is large enough it can trip the black start generator on under-frequency, losing the restoration anchor.
SOPD Emergency Response & System Restoration Procedures 2
During a widespread blackout, what is the correct sequence for restoring the transmission system?