SOPD Load Dispatching 5 — Questions and Answers
Question 1: What is 'inadvertent interchange' and how does it affect a control area?
- Unintended power exchange across tie lines that accumulates over time, requiring payback to affected areas (Correct answer)
- A sudden loss of generation that causes unplanned power flow reversals
- Scheduled but uncompleted energy transactions that are billed at penalty rates
- Reactive power that unintentionally flows through a neighboring utility's system
Correct answer: Unintended power exchange across tie lines that accumulates over time, requiring payback to affected areas
Inadvertent interchange is the unplanned difference between actual and scheduled tie-line flows that accumulates over time and is tracked for eventual repayment.
Question 2: How does governor droop affect a generator's response to a system frequency drop?
- The governor automatically increases the generator's MW output as frequency decreases, with the amount proportional to the droop setting (Correct answer)
- The generator trips offline if frequency drops below its droop threshold
- Droop causes the generator to hold constant MW output regardless of frequency change
- The governor increases excitation to compensate for reactive power loss during frequency drops
Correct answer: The governor automatically increases the generator's MW output as frequency decreases, with the amount proportional to the droop setting
Governor droop is a proportional control where a decrease in system frequency causes the governor to open fuel/steam valves and increase generator MW output automatically.
Question 3: What is the role of 'supplemental reserve' (also called 'non-spinning reserve') in load dispatching?
- Generation capacity that is off-line but can be synchronized and delivering power within 10 to 30 minutes (Correct answer)
- Spinning generators held at minimum load to respond within seconds
- Transmission capacity kept available for emergency power rerouting
- Customer load blocks enrolled in interruptible programs available within 1 minute
Correct answer: Generation capacity that is off-line but can be synchronized and delivering power within 10 to 30 minutes
Non-spinning (supplemental) reserve is off-line generation that can be started and loaded within a specified time (typically 10–30 minutes) to replace capacity following a contingency.
Question 4: A dispatcher is coordinating a 'hot start' of a steam unit. Compared to a 'cold start,' what is the key difference?
- A hot start requires less time and fuel because the unit's boiler and turbine are still warm from recent operation (Correct answer)
- A hot start uses higher steam pressure to bring the unit online more efficiently
- A hot start means the unit was never fully shut down and can deliver power immediately
- A hot start requires additional operator steps to safely purge the boiler before ignition
Correct answer: A hot start requires less time and fuel because the unit's boiler and turbine are still warm from recent operation
A hot start is faster and cheaper because residual heat in the boiler and turbine reduces the warm-up time and fuel required to bring the unit to synchronization.
Question 5: Which condition would most likely trigger a dispatcher to implement 'emergency energy' procedures?
- Spinning reserve has been depleted following multiple generator trips and the system cannot meet load from committed resources alone (Correct answer)
- A single generator trips and ACE briefly goes negative for 30 seconds
- A tie line trips but adequate reserve remains available in the control area
- Load increases by 2% over the forecast for the peak hour of the day
Correct answer: Spinning reserve has been depleted following multiple generator trips and the system cannot meet load from committed resources alone
Emergency energy procedures are invoked when normal reserve resources are exhausted and the system cannot maintain reliability without external emergency assistance.
Question 6: What is the function of 'load shedding' as a last-resort tool in dispatch operations?
- Deliberately disconnecting blocks of load to prevent total system collapse when generation is critically insufficient (Correct answer)
- Temporarily reducing generator output to protect equipment from overheating
- Transferring load between substations to balance distribution feeders
- Activating demand response contracts to reduce peak pricing periods
Correct answer: Deliberately disconnecting blocks of load to prevent total system collapse when generation is critically insufficient
Load shedding involves intentionally de-energizing portions of the system to reduce total demand and prevent a widespread blackout when generation cannot meet load.
Question 7: In the context of load dispatching, what does 'reactive power management' primarily influence?
- Voltage levels across the transmission system, which affect both system stability and thermal loading of lines (Correct answer)
- Real power (MW) balance between generation and load throughout the grid
- System frequency by adjusting the power factor of large industrial customers
- The economic dispatch order of generators based on their efficiency curves
Correct answer: Voltage levels across the transmission system, which affect both system stability and thermal loading of lines
Reactive power (MVAR) management controls voltage profiles across the network; insufficient reactive support leads to voltage collapse, while excess can cause overvoltages.
SOPD Load Dispatching 5
What is 'inadvertent interchange' and how does it affect a control area?