SOPD Grid Reliability 5 — Questions and Answers
Question 1: What is 'cascading failure' in the context of power grid reliability?
- Scheduled sequential outages for maintenance along a transmission corridor
- A sequence of dependent failures where each outage increases stress on remaining elements, potentially leading to widespread blackout (Correct answer)
- Multiple generators tripping simultaneously due to a common control system fault
- The planned reduction of power imports from neighboring regions during summer peak
Correct answer: A sequence of dependent failures where each outage increases stress on remaining elements, potentially leading to widespread blackout
Cascading failure occurs when the loss of one element increases loading on others, causing additional trips in a self-reinforcing sequence that can collapse a large portion of the grid.
Question 2: Under NERC's FAC-001 and FAC-002 standards, what must a Transmission Owner do before connecting a new facility to the BES?
- Obtain a certificate of public convenience from FERC
- Perform facilities connection requirements studies and obtain approval from the Transmission Planner/Operator (Correct answer)
- Notify all retail customers within 50 miles of the new facility
- Complete a 90-day trial period at reduced capacity before full energization
Correct answer: Perform facilities connection requirements studies and obtain approval from the Transmission Planner/Operator
FAC-001/002 require interconnection studies to ensure a new facility will not adversely affect bulk electric system reliability before it is connected.
Question 3: What is the role of the Wide-Area Measurement System (WAMS) and Phasor Measurement Units (PMUs) in grid reliability?
- They replace SCADA systems for all real-time monitoring functions
- They provide time-synchronized, high-resolution measurements of voltage angle and magnitude across the grid, improving situational awareness (Correct answer)
- They automatically control generator output based on system frequency
- They are used exclusively for post-event analysis after major disturbances
Correct answer: They provide time-synchronized, high-resolution measurements of voltage angle and magnitude across the grid, improving situational awareness
PMUs provide GPS time-stamped phasor data at high sampling rates (30+ per second), giving operators and reliability coordinators enhanced visibility into dynamic system conditions across wide areas.
Question 4: A system operator receives a Reliability Coordinator instruction to reduce inter-area flow on a specific path. What is the operator's obligation?
- Evaluate the instruction and implement it only if local conditions allow
- Implement the RC's instruction immediately, as the RC has the highest reliability authority (Correct answer)
- Consult with neighboring TOPs before taking any action
- Request written confirmation from FERC before complying
Correct answer: Implement the RC's instruction immediately, as the RC has the highest reliability authority
NERC standards require that Transmission Operators comply with Reliability Coordinator directives immediately; the RC has the highest authority and widest view of system conditions.
Question 5: What is 'reactive power compensation' and why is it critical to transmission system reliability?
- It is the process of adjusting real power flows to prevent thermal overloads
- It involves supplying or absorbing reactive power (Mvars) to maintain acceptable voltage profiles across the transmission system (Correct answer)
- It refers to the financial compensation paid to generators for providing ancillary services
- It is a protection scheme that prevents reverse power flow in transmission lines
Correct answer: It involves supplying or absorbing reactive power (Mvars) to maintain acceptable voltage profiles across the transmission system
Reactive power compensation — through capacitor banks, reactors, SVCs, or generators — is essential to maintain voltage within acceptable limits, since reactive power cannot be efficiently transported over long distances.
Question 6: In restoration operations, what is the correct sequence for reenergizing a transmission line after a fault?
- Close the sending-end breaker first, then check for voltage at the receiving end, then close the receiving-end breaker
- Verify relay targets are cleared, check for trapped charge, confirm protection is armed, then energize from the appropriate end per restoration plan (Correct answer)
- Simply close both breakers simultaneously to minimize restoration time
- Reduce all adjacent line flows to zero before reenergizing the faulted line
Correct answer: Verify relay targets are cleared, check for trapped charge, confirm protection is armed, then energize from the appropriate end per restoration plan
Safe line restoration requires clearing relay targets, verifying protection readiness, and following the restoration plan sequence to prevent re-faulting or switching surges from damaging equipment.
Question 7: What is 'transfer capability' in transmission system operations, and how does it relate to reliability?
- The maximum amount of electric power that can be transferred reliably over a transmission path while satisfying all applicable reliability constraints (Correct answer)
- The number of switchable elements available in a substation for load transfer
- The capacity of a transformer to step voltage up or down during peak demand
- The amount of power a generator can transfer to the grid before its step-up transformer saturates
Correct answer: The maximum amount of electric power that can be transferred reliably over a transmission path while satisfying all applicable reliability constraints
Transfer capability defines the power flow limit on a transmission path that, if exceeded, could violate thermal, voltage, or stability constraints under normal or contingency conditions.
SOPD Grid Reliability 5
What is 'cascading failure' in the context of power grid reliability?