SOPD Frequency Control 5 — Questions and Answers
Question 1: What is the primary difference between 'spinning reserve' and 'non-spinning reserve' in frequency control?
- Spinning reserve is on synchronous units already online; non-spinning reserve requires unit startup (Correct answer)
- Spinning reserve responds in 30 minutes; non-spinning reserve responds in 10 minutes
- Spinning reserve is used only for over-frequency events; non-spinning for under-frequency
- Spinning reserve is thermal generation only; non-spinning includes hydro and wind
Correct answer: Spinning reserve is on synchronous units already online; non-spinning reserve requires unit startup
Spinning reserve is unloaded capacity on already-synchronized online units; non-spinning (supplemental) reserve requires starting offline units, taking longer to deploy.
Question 2: How does increased penetration of inverter-based resources (IBR) such as solar PV affect system frequency dynamics?
- IBR improves frequency response by providing faster governor action than synchronous generators
- IBR reduces system inertia if it displaces synchronous generation, making frequency more sensitive to disturbances (Correct answer)
- IBR automatically provides frequency response through built-in under-frequency protection relays
- IBR has no effect on frequency dynamics because it operates at unity power factor
Correct answer: IBR reduces system inertia if it displaces synchronous generation, making frequency more sensitive to disturbances
Inverter-based resources do not inherently provide synchronous inertia, so high IBR penetration that displaces synchronous generators reduces total system inertia.
Question 3: What is 'Control Performance Standard 1' (CPS1) as defined by NERC?
- A limit on the maximum rate of frequency change (ROCOF) during contingency events
- A statistical measure of how well a balancing authority's ACE correlates with interconnection frequency error over time (Correct answer)
- A requirement to maintain frequency within ±0.5 Hz of 60 Hz at all times
- A standard for the minimum spinning reserve a balancing authority must carry
Correct answer: A statistical measure of how well a balancing authority's ACE correlates with interconnection frequency error over time
CPS1 measures the one-minute average of ACE × frequency error over a year; a score ≥100% indicates the area is helping (not hurting) interconnection frequency control.
Question 4: During a frequency emergency, a system operator issues an 'Energy Emergency Alert' (EEA). What level indicates the operator has shed firm load?
- EEA Level 1
- EEA Level 2
- EEA Level 3 (Correct answer)
- EEA Level 4
Correct answer: EEA Level 3
EEA Level 3 indicates the operator has exhausted all other resources and is implementing firm load shedding to maintain system reliability.
Question 5: What is the effect of a 'flat frequency response' characteristic (infinite droop or blocked governor) on interconnection frequency control?
- It improves frequency stability by preventing oscillations between generators
- It reduces the unit's contribution to primary response, increasing frequency deviation for all interconnected areas (Correct answer)
- It allows the unit to provide more reactive power during voltage events
- It speeds up AGC response by removing governor deadband interference
Correct answer: It reduces the unit's contribution to primary response, increasing frequency deviation for all interconnected areas
A unit with blocked governors or infinite droop provides no primary frequency response, meaning other units must compensate and frequency deviations will be larger.
Question 6: A frequency disturbance causes frequency to drop to 59.3 Hz in the Western Interconnection. Which action would MOST quickly arrest further frequency decline?
- Committing additional fast-start combustion turbines (20-minute startup)
- Dispatching demand response programs with 10-minute notification
- Governor response from already-online generators with headroom (Correct answer)
- Purchasing emergency energy from neighboring interconnections via DC ties
Correct answer: Governor response from already-online generators with headroom
Governor primary response from online generators acts within seconds, far faster than starting offline units, activating demand response, or arranging emergency interchange.
Question 7: What condition is described when two synchronous areas are interconnected and one experiences a sudden generation loss causing frequency to drop in both areas?
- Islanding — each area separates and responds independently
- Interconnection frequency response — all synchronous generators in both areas contribute proportionally to governor droop (Correct answer)
- Resonance — the two areas' natural frequencies interact destructively
- Voltage collapse — reactive power transfer limits prevent real power support
Correct answer: Interconnection frequency response — all synchronous generators in both areas contribute proportionally to governor droop
In a synchronous interconnection, a frequency disturbance in one area is shared across all connected areas, with every online governor contributing to primary response proportional to its droop setting.
SOPD Frequency Control 5
What is the primary difference between 'spinning reserve' and 'non-spinning reserve' in frequency control?