SOPD Load Forecasting & Energy Scheduling 3 — Questions and Answers
Question 1: The 'unit commitment' problem in energy scheduling determines:
- Which generating units to start up or shut down over a planning horizon (Correct answer)
- The optimal voltage setpoint for each generator
- How to allocate frequency regulation capacity among units
- The order in which transmission lines are energized
Correct answer: Which generating units to start up or shut down over a planning horizon
Unit commitment solves which generators should be online or offline over a scheduling horizon, balancing startup costs, fuel costs, and reliability requirements.
Question 2: A system operator notices that actual load is tracking 8% above the day-ahead forecast on a summer afternoon. Which is the FIRST corrective action?
- Declare a system emergency and shed load
- Issue a real-time adjustment to dispatch additional committed reserves (Correct answer)
- Contact neighboring control areas to import emergency energy
- Reduce system voltage by 5% to lower load
Correct answer: Issue a real-time adjustment to dispatch additional committed reserves
Dispatching pre-committed reserves is the first response to a load-above-forecast condition before escalating to emergency procedures.
Question 3: Which statistical method is MOST commonly used to forecast short-term (next 24 hours) electric load?
- Monte Carlo simulation
- Regression analysis with weather and time variables (Correct answer)
- Markov chain modeling
- Fourier series decomposition only
Correct answer: Regression analysis with weather and time variables
Multiple linear regression combining weather variables (temperature, humidity) with time-of-day and day-of-week factors is the most widely used short-term forecasting method.
Question 4: During a cold snap, a load forecast model shows higher-than-expected morning load. This phenomenon is BEST described as:
- System inertia overshoot
- Morning pickup or cold load pickup (Correct answer)
- Voltage collapse precursor
- Frequency deviation demand response
Correct answer: Morning pickup or cold load pickup
Cold load pickup occurs when thermostatic loads that were off during an outage or overnight all energize simultaneously, causing a sharp demand surge.
Question 5: An interchange schedule between Control Area A and Control Area B is set at 500 MW export from A. If actual flow is 520 MW, the 20 MW difference is called:
- Inadvertent energy flow (Correct answer)
- Spinning reserve activation
- Emergency energy transfer
- Regulation service energy
Correct answer: Inadvertent energy flow
Inadvertent energy is the difference between scheduled and actual interchange flow, tracked and settled between control areas periodically.
Question 6: Which type of load forecasting error has the GREATEST potential to cause a reliability problem?
- A 2% underestimate on a mild spring day
- A 10% underestimate on the annual system peak day (Correct answer)
- A 5% overestimate on a weekend morning
- A 3% overestimate during light load conditions
Correct answer: A 10% underestimate on the annual system peak day
A significant underestimate on the peak demand day is most dangerous because adequate generation and reserves may not be committed when the system is most stressed.
Question 7: In energy markets, a 'day-ahead market' schedule becomes binding at:
- The time the bid is submitted to the market operator
- The close of the day-ahead market, typically the evening before operating day (Correct answer)
- The first 15-minute interval of the operating day
- After the real-time market clears for each operating hour
Correct answer: The close of the day-ahead market, typically the evening before operating day
Day-ahead market schedules are binding after the market closes, typically around 10 AM to noon the day before, establishing the energy schedule for the next operating day.
SOPD Load Forecasting & Energy Scheduling 3
The 'unit commitment' problem in energy scheduling determines: