SOPD Load Dispatching 3 — Questions and Answers
Question 1: What is 'load forecasting' and why is it critical for a power dispatcher?
- Predicting future demand to schedule generation and maintain reliability (Correct answer)
- Monitoring current load levels on transmission lines
- Calculating post-contingency power flows in real time
- Estimating reactive power needs for voltage support
Correct answer: Predicting future demand to schedule generation and maintain reliability
Load forecasting predicts future electricity demand, enabling dispatchers to schedule adequate generation resources and maintain system reliability.
Question 2: A unit commitment decision involves which of the following?
- Determining which generating units to start up or shut down over a planning horizon (Correct answer)
- Balancing reactive power across transmission buses in real time
- Selecting which tie lines to open during an emergency
- Assigning frequency regulation duty to specific generators
Correct answer: Determining which generating units to start up or shut down over a planning horizon
Unit commitment determines the on/off status of generating units over a scheduling period to meet forecasted demand at minimum cost while respecting operational constraints.
Question 3: During peak load periods, a dispatcher must manage 'demand response' resources. What does activating these resources accomplish?
- Reduces load from enrolled customers to balance supply and demand (Correct answer)
- Increases voltage on heavily loaded transmission corridors
- Restores tripped generation units to service faster
- Transfers load between control areas via tie lines
Correct answer: Reduces load from enrolled customers to balance supply and demand
Demand response activation reduces electricity consumption from participating customers, effectively lowering system load to balance it against available generation.
Question 4: What is 'interchange scheduling' in the context of load dispatching?
- Planning and coordinating power transfers between neighboring control areas (Correct answer)
- Scheduling maintenance outages for transformers and lines
- Assigning generation units to specific transmission paths
- Distributing reactive power among substations in a region
Correct answer: Planning and coordinating power transfers between neighboring control areas
Interchange scheduling involves coordinating planned power transfers over tie lines between adjacent control areas to meet load and economic objectives.
Question 5: A 'must-run' unit is dispatched even when it is uneconomical. Which situation most commonly justifies this?
- The unit provides critical voltage support or reliability in a constrained area (Correct answer)
- The unit has the lowest heat rate of all available generators
- The dispatcher wants to test the unit's governor response
- The unit's fuel contract requires a minimum monthly output
Correct answer: The unit provides critical voltage support or reliability in a constrained area
Must-run status is typically assigned when a unit is required for local voltage support, area stability, or to prevent thermal overloads in a transmission-constrained region.
Question 6: What is the function of 'automatic generation control' (AGC) in load dispatching?
- Automatically adjusts generator output to maintain frequency and scheduled tie-line flows (Correct answer)
- Automatically trips generators when frequency exceeds 60.5 Hz
- Continuously adjusts transformer tap positions to regulate voltage
- Automatically switches capacitor banks to correct power factor
Correct answer: Automatically adjusts generator output to maintain frequency and scheduled tie-line flows
AGC sends real-time raise/lower signals to generators to keep system frequency at 60 Hz and net area interchange at scheduled values, reducing ACE to zero.
Question 7: What does 'ramp rate' limit on a generating unit constrain?
- How quickly a generator can increase or decrease its MW output per minute (Correct answer)
- The maximum temperature the boiler can reach during full load
- The minimum number of minutes the unit must remain on before shutdown
- The maximum voltage the generator's exciter can produce
Correct answer: How quickly a generator can increase or decrease its MW output per minute
Ramp rate is the maximum rate of MW output change per minute for a generator, which dispatchers must respect when issuing raise or lower signals.
SOPD Load Dispatching 3
What is 'load forecasting' and why is it critical for a power dispatcher?