SOPD Grid Reliability 3 — Questions and Answers
Question 1: What is the primary function of Automatic Generation Control (AGC) in maintaining grid reliability?
- It automatically disconnects overloaded transmission lines
- It continuously adjusts generator output to maintain area control error near zero and correct frequency (Correct answer)
- It monitors transformer tap positions to regulate voltage
- It calculates real-time contingency analysis for the control area
Correct answer: It continuously adjusts generator output to maintain area control error near zero and correct frequency
AGC automatically sends raise/lower signals to participating generators to balance generation with load and maintain the Area Control Error (ACE) near zero, supporting frequency regulation.
Question 2: During a widespread voltage collapse, which characteristic typically precedes the collapse?
- Frequency rises rapidly above 60.5 Hz
- Voltages decline progressively despite reactive power support, and reactive reserves are exhausted (Correct answer)
- Tie-line flows reverse direction simultaneously across the interconnection
- System frequency oscillates between 59 and 61 Hz for several minutes
Correct answer: Voltages decline progressively despite reactive power support, and reactive reserves are exhausted
Voltage collapse is preceded by declining voltages and depletion of reactive power reserves; once reactive reserves are exhausted, voltage can collapse rapidly and uncontrollably.
Question 3: What does the term 'islanding' refer to in power system operations?
- A grid section operating in isolation from the main interconnection (Correct answer)
- The process of energizing a dead bus for system restoration
- Intentional disconnection of generation from load for maintenance
- A technique for balancing reactive power across substations
Correct answer: A grid section operating in isolation from the main interconnection
Islanding occurs when a portion of the power system becomes electrically separated from the main grid and operates independently, which may be intentional (controlled) or unintentional.
Question 4: Under NERC Standard EOP-006, what is the primary goal of a Transmission Operator during system restoration?
- To restore load as rapidly as possible regardless of equipment status
- To restore the system in a manner that re-establishes the transmission network and supports generation pick-up safely (Correct answer)
- To notify all customers of estimated restoration times within 15 minutes
- To transfer all emergency load to neighboring control areas first
Correct answer: To restore the system in a manner that re-establishes the transmission network and supports generation pick-up safely
EOP-006 requires TOPs to follow restoration plans that safely re-energize transmission paths and coordinate generation pick-up to restore reliable system operation.
Question 5: Which scenario best describes an 'N-2 contingency' condition?
- Two generating units operating below rated output simultaneously
- The simultaneous or sequential loss of two bulk electric system elements (Correct answer)
- A transmission line operating at twice its emergency rating
- Two control areas experiencing frequency deviations at the same time
Correct answer: The simultaneous or sequential loss of two bulk electric system elements
N-2 contingency refers to the loss of two system elements (lines, generators, transformers) and is used to evaluate the system's ability to withstand more severe disturbances than the basic N-1 standard.
Question 6: A system operator sees that the Area Control Error (ACE) is persistently negative. What does this indicate?
- The control area is exporting more power than scheduled
- The control area is generating less than its load plus net scheduled interchange, causing it to draw unscheduled power from neighbors (Correct answer)
- Frequency in the control area is consistently above 60 Hz
- Reactive power consumption exceeds reactive generation within the area
Correct answer: The control area is generating less than its load plus net scheduled interchange, causing it to draw unscheduled power from neighbors
A persistently negative ACE means the area is importing more power than scheduled (under-generating relative to load), placing an unscheduled burden on neighboring areas.
Question 7: What is the significance of the 'must-run' designation for certain generating units?
- These units are required to run continuously at maximum output
- These units must operate to maintain reliability in specific locations regardless of economic dispatch order (Correct answer)
- These units are exempt from all NERC reliability standards
- These units cannot be taken out of service for maintenance during summer months
Correct answer: These units must operate to maintain reliability in specific locations regardless of economic dispatch order
Must-run units are committed for reliability reasons (voltage support, local capacity, stability) rather than economics, and they must operate even if they are not the lowest-cost resource.
SOPD Grid Reliability 3
What is the primary function of Automatic Generation Control (AGC) in maintaining grid reliability?