SOPD Frequency Control 4 — Questions and Answers
Question 1: A control area's frequency bias (B) is set at -500 MW/0.1 Hz. If frequency drops by 0.2 Hz, how many MW should the area contribute to frequency response?
- 250 MW
- 500 MW
- 1000 MW (Correct answer)
- 2000 MW
Correct answer: 1000 MW
Frequency response = B × Δf in 0.1 Hz units = 500 MW/0.1 Hz × 2 (for 0.2 Hz) = 1000 MW.
Question 2: Which operating condition is considered a violation of good utility practice regarding frequency response?
- Operating generators at 95% of rated capacity
- Blocking or withdrawing governor response during normal operations to preserve unit life (Correct answer)
- Scheduling spinning reserves equal to the largest single contingency
- Using AGC to correct ACE within 10 minutes
Correct answer: Blocking or withdrawing governor response during normal operations to preserve unit life
Blocking governor response removes the unit's contribution to primary frequency response, undermining interconnection reliability and violating NERC BAL-003 obligations.
Question 3: What is 'tertiary frequency control' or 'economic dispatch' in relation to frequency management?
- The third stage of UFLS that activates at the lowest frequency threshold
- Longer-term redispatch of generation for economic optimization after frequency is restored (Correct answer)
- The third governor droop stage that activates during extreme frequency events
- Manual operator override of AGC during frequency emergencies
Correct answer: Longer-term redispatch of generation for economic optimization after frequency is restored
Tertiary control involves economic redispatch over longer timeframes (15 minutes to hours) to optimize generation after frequency and ACE have been restored by primary and secondary controls.
Question 4: During an over-frequency event caused by sudden large load loss, what is the appropriate operator action?
- Arm additional spinning reserves to prevent further frequency rise
- Reduce generation output or trip generation to rebalance load and generation (Correct answer)
- Increase tie-line exports to neighboring control areas immediately
- Activate over-frequency load shedding relays manually
Correct answer: Reduce generation output or trip generation to rebalance load and generation
Over-frequency from load loss requires reducing generation (or increasing load/exports) to rebalance the system and bring frequency back to 60 Hz.
Question 5: What is the function of the Time Error Correction (TEC) program coordinated by interconnection operators?
- To correct metering errors in frequency transducer readings
- To adjust scheduled frequency slightly above or below 60 Hz to compensate for accumulated clock error (Correct answer)
- To synchronize AGC software clocks across balancing authorities
- To calibrate under-frequency relay setpoints annually
Correct answer: To adjust scheduled frequency slightly above or below 60 Hz to compensate for accumulated clock error
Time Error Correction adjusts target frequency (e.g., 60.02 Hz or 59.98 Hz) to recover accumulated time error in electric clocks synchronized to power system frequency.
Question 6: A balancing authority loses its AGC system. What is the operator's primary obligation?
- Immediately declare a system emergency and shed all non-critical load
- Manually maintain ACE as close to zero as practical using available resources (Correct answer)
- Transfer operational control to the neighboring reliability coordinator
- Increase spinning reserves to 150% of the single largest contingency
Correct answer: Manually maintain ACE as close to zero as practical using available resources
Without AGC, operators must manually monitor and correct ACE to maintain frequency control obligations per NERC BAL-001 and BAL-002 standards.
Question 7: Which characteristic of a generating unit determines how quickly it can respond to a governor signal during a frequency event?
- The unit's voltage regulation (AVR) response speed
- The unit's ramp rate and governor time constant (Correct answer)
- The transformer turns ratio connecting the unit to the grid
- The exciter ceiling voltage of the generator
Correct answer: The unit's ramp rate and governor time constant
A unit's ramp rate (MW/minute capability) and governor time constant determine the speed and magnitude of its primary frequency response.
SOPD Frequency Control 4
A control area's frequency bias (B) is set at -500 MW/0.1 Hz.
If frequency drops by 0.2 Hz, how many MW should the area contribute to frequency response?