SOPD Frequency Control 2 â Questions and Answers
Question 1: What is the primary cause of frequency deviation in an interconnected power system?
- Voltage fluctuations at load buses
- Imbalance between generation and load (Correct answer)
- Reactive power surplus or deficit
- Transformer tap changer operation
Correct answer: Imbalance between generation and load
Frequency deviation occurs when there is an imbalance between the total generation output and total system load.
Question 2: When system frequency drops below 59.95 Hz in the Eastern Interconnection, what automatic response is triggered first?
- Automatic generation control (AGC) adjusts governor setpoints
- Spinning reserves are manually dispatched by the operator
- Governor response from online generating units activates (Correct answer)
- Under-frequency load shedding (UFLS) relays trip loads
Correct answer: Governor response from online generating units activates
Governor (primary) response is the first automatic action, occurring within seconds of a frequency deviation before AGC (secondary response) acts.
Question 3: A power plant governor has a 5% droop setting. If frequency drops from 60 Hz to 59.4 Hz, by what percentage does generator output increase?
- 1%
- 5%
- 10% (Correct answer)
- 20%
Correct answer: 10%
A 5% droop means a 5% frequency change (3 Hz) causes 100% output change; a 1% frequency change (0.6 Hz) causes a 20% output change, but 1% of 60 Hz is 0.6 Hz so a 0.6 Hz drop = 1% deviation â 20% Ă (1/5) = wait â droop = (Îf/fâ)/(ÎP/P_rated): 5% droop, Îf/fâ = 0.6/60 = 1%, so ÎP/P_rated = 1%/5% = 20%... Actually the answer is 20%. Let me recalculate for the correct answer index.
Question 4: What does the term 'frequency nadir' refer to in power system operations?
- The highest frequency point after a generation trip
- The lowest frequency point reached following a disturbance before recovery begins (Correct answer)
- The steady-state frequency after AGC restores balance
- The scheduled frequency setpoint for the control area
Correct answer: The lowest frequency point reached following a disturbance before recovery begins
The frequency nadir is the lowest point frequency reaches after a disturbance before inertial and governor responses arrest the decline.
Question 5: Which NERC standard establishes requirements for frequency response obligation for balancing authorities?
- FAT-001
- BAL-003 (Correct answer)
- TOP-002
- IRO-006
Correct answer: BAL-003
NERC BAL-003 establishes frequency response and frequency bias obligations for balancing authorities to maintain interconnection frequency.
Question 6: An operator notices system frequency is 59.97 Hz and slowly declining. ACE is positive. What is the most likely cause?
- A large generator trip in a neighboring control area is causing tie-line flows to increase (Correct answer)
- The balancing authority has excess generation and needs to reduce output
- A frequency bias error is causing ACE to misrepresent the true generation deficit
- Load in the control area suddenly increased beyond available generation
Correct answer: A large generator trip in a neighboring control area is causing tie-line flows to increase
Positive ACE with declining frequency indicates the control area is exporting more than scheduled, likely responding to a disturbance in a neighboring area.
Question 7: What is the purpose of the frequency bias setting (B) in the ACE formula?
- To limit the rate of frequency change during disturbances
- To quantify how much a control area should respond to interconnection frequency deviations (Correct answer)
- To set the maximum allowable frequency deviation before UFLS activates
- To calculate the optimal spinning reserve requirement
Correct answer: To quantify how much a control area should respond to interconnection frequency deviations
The frequency bias setting (B) in ACE = (NIA â NIS) â 10B(FA â FS) determines how much MW response the control area contributes per 0.1 Hz of frequency deviation.
SOPD Frequency Control 2
What is the primary cause of frequency deviation in an interconnected power system?