NERC TO Exam Prep Free practice test →

Free NERC TO Practice Questions

10 free, exam-style Transmission Operator Certification (NERC TO) practice questions with answers and explanations. No signup required. Work through them below, then take the full free NERC TO practice test to study every exam domain.

Question 1

While operating within all facility ratings, a Transmission Operator's contingency analysis shows that the loss of a single 345 kV line would cause voltage to collapse across a wide area, risking cascading outages. How should this limit be classified, and what time constraint applies to operating beyond it?

  1. An IROL; operation beyond it must not exceed its IROL Tv, which is 30 minutes or less
  2. An SOL; operation beyond it is permitted for up to 60 minutes before mitigation
  3. A facility rating; it remains valid until the next operations-planning study refresh
  4. A stability limit; it may be exceeded as long as area voltage stays above 90 percent
Show answer & explanation

Correct answer: A - An IROL; operation beyond it must not exceed its IROL Tv, which is 30 minutes or less

Question 2

System voltage at a 230 kV bus is sagging below the acceptable range as load increases. The operator must restore voltage while preserving the system's ability to ride through the next contingency. Which action is the MOST appropriate FIRST step?

  1. Drive nearby generators to maximum reactive output to raise voltage immediately
  2. Switch in a shunt capacitor bank to supply reactive power locally at the bus
  3. Lower generator excitation to reduce reactive output across the surrounding area
  4. Switch in a shunt reactor at the affected bus to correct the declining voltage
Show answer & explanation

Correct answer: B - Switch in a shunt capacitor bank to supply reactive power locally at the bus

Question 3

A transmission line is carrying 60 MW of real power and 80 MVAR of reactive power. What is the approximate apparent power loading on the line, and what is the power factor?

  1. 140 MVA at a power factor of 0.43
  2. 70 MVA at a power factor of 0.86
  3. 100 MVA at a power factor of 0.60
  4. 100 MVA at a power factor of 0.80
Show answer & explanation

Correct answer: C - 100 MVA at a power factor of 0.60

Question 4

A Transmission Operator's real-time contingency analysis tool has been unavailable for 25 minutes due to an EMS failure, and a state estimator solution has not converged. Regarding the Real-time Assessment requirement, what is the operator's obligation?

  1. The assessment interval relaxes to once per hour whenever the automated analysis tools are offline
  2. The 30-minute assessment requirement is suspended until the contingency analysis tool is restored
  3. A Real-time Assessment is still required every 30 minutes, by alternative methods if needed
  4. The Reliability Coordinator assumes the assessment duty for the area until the tools are recovered
Show answer & explanation

Correct answer: C - A Real-time Assessment is still required every 30 minutes, by alternative methods if needed

Question 5

A Reliability Coordinator notifies its Balancing Authorities and Transmission Operators that an energy deficient Balancing Authority has exhausted all available generation and is now implementing load management procedures, but firm load has not yet been interrupted. Which Energy Emergency Alert level does this describe?

  1. EEA 1
  2. EEA 2
  3. EEA 3
  4. EEA 0
Show answer & explanation

Correct answer: B - EEA 2

Question 6

During a switching operation, a Transmission Operator issues an oral Operating Instruction to a field operator. The field operator repeats the instruction back, but not word-for-word. To correctly complete three-part communication, what must the issuing operator do?

  1. Confirm the response was correct, or reissue the instruction if it was not
  2. Require the field operator to repeat the instruction again, this time verbatim
  3. Treat the exchange as complete, because the repeat-back itself closes the loop
  4. Hold the instruction until the Reliability Coordinator independently verifies it
Show answer & explanation

Correct answer: A - Confirm the response was correct, or reissue the instruction if it was not

Question 7

Following a major disturbance, a portion of the transmission system has separated into an electrical island that is now energized by a blackstart unit. As the operator restores load and ties, why must load be picked up in measured increments rather than all at once?

  1. Large load steps would hold the island's generators below their minimum stable operating points
  2. Rapid load pickup would absorb reactive power and overvoltage the island's lightly loaded long lines
  3. Restoration procedures require the island to be resynchronized to the grid before any load is added
  4. A load step beyond available generation depresses frequency and can collapse the island
Show answer & explanation

Correct answer: D - A load step beyond available generation depresses frequency and can collapse the island

Question 8

A Balancing Authority's frequency is below 60 Hz and its Area Control Error (ACE) is negative. Assuming a typical tie-line bias control setup, what does this combination most directly indicate?

  1. Scheduled interchange exceeds actual interchange, so no generation change is warranted
  2. The Balancing Authority is over-generating and should back down its generation
  3. The Balancing Authority is under-generating and should increase its generation
  4. A neighbor lost generation, so this Balancing Authority should hold output steady
Show answer & explanation

Correct answer: C - The Balancing Authority is under-generating and should increase its generation

Question 9

A protective relay scheme operates and trips a 500 kV line for a fault located outside its intended zone of protection, on an adjacent healthy line. This is an example of what, and what is the primary reliability concern?

  1. A selectivity miss with no real reliability impact, since the original fault is still cleared in time
  2. An overtrip from lost protection security, removing a healthy element and worsening the event
  3. A correct dependability action that speeds fault clearing and thereby improves overall reliability
  4. A routine high-speed reclosing operation that will restore the tripped line automatically in seconds
Show answer & explanation

Correct answer: B - An overtrip from lost protection security, removing a healthy element and worsening the event

Question 10

A geomagnetic disturbance (GMD) forecast indicates elevated geomagnetically induced current (GIC) activity over the next 24 hours. As part of emergency preparedness, which transmission concern should the operator anticipate FIRST?

  1. Line charging on the lightly loaded circuits drives a sustained and damaging rise in system voltage
  2. The induced currents push a broadly uniform increase in operating frequency across the interconnection
  3. Dielectric stress from the induced current sharply reduces the loading capability of underground cables
  4. Transformer half-cycle saturation heats units and raises reactive absorption, depressing voltage
Show answer & explanation

Correct answer: D - Transformer half-cycle saturation heats units and raises reactive absorption, depressing voltage

Ready for the real thing?

Practice hundreds more NERC TO questions with instant scoring, weak-area drills, and full exam simulations.

Start the free practice test See pricing