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NERC EXAM, TEST, PRACTICE EXAM AND STUDY
GUIDE LATEST 202 5 - 2026 ACTUAL EXAM 200
QUESTIONS AND CORRECT DETAILED ANSWERS
WITH RATIONALES (VERIFIED ANSWERS) |ALREADY
GRADED A+
A 50 MVA rated transformer has 30 MW of load. How many MVARs can flow through the transformer without exceeding the rating? A. 50 MVAR B. 40 MVAR C. 30 MVAR D. 80 MVAR - ANSWER-B. 40 MVAR A balancing authority is responsible for load - interchange - generation balance, which calculated value reflects that balance? A. Frequency B. System Lambda C. Operating reserves D. ACE - ANSWER-D. ACE A transmission line has a net VAR load of 25 MVAR into the line resembles which of these statements? A. The line is equivalent to an inductor B. The line is transferring the optimum load C. The line is nearing voltage collapse D. The line is equivalent to a capacitor - ANSWER-A. The line is equivalent to an inductor Frequency of the power system is mainly determined by which factor? A. Load and generation balance in your balancing authority area B. Load and generation balance in the interconnection C. Generation power flowing on the transmission lines
D. Load requirement of each power system - ANSWER-B. Load and generation balance in the interconnection Generator reactive power output increases dynamically under which condition? A. Low voltage B. High voltage C. Transmission line trip D. Energy and capacity deficiency - ANSWER-A. Low voltage If interconnection frequency is 59.95 Hz, how do balancing authorities support interconnection frequency? A. Remain at current MW output level B. Increasing MW output C. Decreasing MW output D. Increasing excitation on the field windings - ANSWER-B. Increasing MW output In a power system which type of power is especially critical to support heavily loaded transmission lines and to have dynamic reserves in preparation for contingency? A. Reactive power B. Real power C. Power flow D. Apparent power - ANSWER-A. Reactive power Reactive power is needed to support which type of load? A. Capacitive B. Resistive C. Impedance D. Inductive - ANSWER-D. Inductive System inertia is the ability of a power system to:
What is a state estimator primarily used for? A. Energy management system B. Contingency analysis C. Calculate ACE D. SCADA - ANSWER-B. Contingency analysis What is generation shift factor GSF? A. Used to determine the amount of flow contribution a change in generation output will impose on a transmission facility B. Applied to external balancing authorities to know how much of their generation is flowing into your system C. Used to determine unit commitment and dispatch D. Generation that automatically shifts based on load factors - ANSWER-A. Used to determine the amount of flow contribution a change in generation output will impose on a transmission facility What is power transfer distribution factor PTDF? A. Post contingency results and configuration of a system under study B. A measure of the responsiveness or change in electrical loading used for pre-contingency analysis C. Congestion management solutions to the most severe single contingency D. Outage results that measure the electrical loading of transmission area based on system loading in generation - ANSWER-B. A measure of the responsiveness or change in electrical loading used for pre- contingency analysis Which control system on the generators would respond to frequency changes? A. Governor control system B. Differential relay systems C. Special protection systems D. Automatic voltage regulators - ANSWER-A. Governor control system
Which of the following are dynamic reactive resources?
- Synchronous condenser
- Capacitor bank
- Reactor bank
- Generator A. 1 and 3 B. 2 and 3 C. 2 and 4 D. 1 and 4 - ANSWER-D. 1 and 4 Which of the following is a quick start generator in the best potential source of non-spinning contingency reserve? A. Coal plant B. Combustion turbine C. Controllable load resources D. Increases to interchange schedules - ANSWER-B. Combustion turbine Which power system equipment is needed to reduce a high voltage condition? A. Series reactor B. Shunt reactor C. Shunt capacitor D. Series capacitor - ANSWER-B. Shunt reactor Which protection scheme would operate on a difference of current flowing into and out of a zone of protection? A. Distance relay B. Differential relay C. Overcurrent relay
What is the power factor formula? - ANSWER-pf = MW/MVA What is the formula for the power triangle? - ANSWER-MVA^2 = MW^2 + MVAR^ What is the formula for total reactance? - ANSWER-Xtotal = |Xl - Xc| What is the formula for Capacitor output? - ANSWER-MVARoutput = MVARrated * (Vactual/Vrated)^ or MVARoutput = MVARrated * (Vp.u.)^ What is the formula to calculate power losses? - ANSWER-P = I^2 * R What is the formula to calculate the number of poles on a generator? - ANSWER-Np = 7200 (where N is synchronous speed in rpms and p is the # of poles) more complicated version: f = (N/60)*(p/2) What is the impact to capacitive reactance when frequency drops significantly in the power system? - ANSWER-Capacitive reactance will increase Capacitive: ________ leading ________ - ANSWER-current leading voltage Inductive: ________ leading ________ - ANSWER-voltage leading current MVAR travel from ________ to ________. - ANSWER-high voltage to low voltage
MW travel from ________ to ________. - ANSWER-high voltage angle to low voltage angle If current doubles, power losses ________? - ANSWER-quadruple proof: P = I^2 R If voltage doubles, current ________? - ANSWER-is halved proof: P = IV If load increases doubling power flow, while voltage stays the same. What does this do to power losses?
- ANSWER-Power losses quadruple If voltage doubles while load magnitude stays the same. What does this do to power losses? - ANSWER- Power losses decrease by a factor of 4. If ACE is not calculated for more than ________, call the RC. How long do you have to notify the RC in this case? - ANSWER-30 minutes, 45 minutes from initial time ACE couldn't be calculated Notify impacted entities and NERC for failure of communication for more than ________. - ANSWER- 30 minutes Notify impacted entities and NERC for unplanned evacuation of control center for more than ________.
- ANSWER-30 minutes Notify impacted entities and NERC for complete loss of monitoring for more than ________. - ANSWER- 30 minutes Backup Control Center transition must be less than ________ and a test of Backup Control Center functionality must be successful for at least ________. - ANSWER-2 hours, 2 hours
Who approves a Reliability Adjustment Arranged Interchange? - ANSWER-only the source and sink BA What is a 21 relay? - ANSWER-Distance What is a 50 relay? - ANSWER-instantaneous overcurrent What is a 51 relay? - ANSWER-timed overcurrent What is an 87 relay? - ANSWER-differential Cold load pickup can be up to ________ pre-contingency value due to what? - ANSWER-10 times due to lack of load diversity Sending and Receiving BA are terms used when referring to ________. - ANSWER-interchange schedules Source and Sink BA are terms used when referring to ________. - ANSWER-interchange transactions Interchange ________ can only take place between adjacent BAs. - ANSWER-schedules Emergency tagging is not necessary if the transaction is less than ________. - ANSWER-1 hour What three parameters must be considered when synchronizing? - ANSWER-voltage, frequency, phase angle Alerts are issued by the NOAA for geomagnetic disturbances with a K-index value of ____ or higher. - ANSWER- 5 Warnings are issued by the NOAA for geomagnetic disturbances with a K-index value of ____ or higher. - ANSWER- 4
Most power systems are not affected by geomagnetic disturbances until it reaches a K-index greater than or equal to ____. - ANSWER- 7 Blackstart must be tested at least once every ________. - ANSWER-3 years TOP should review their restoration plan ________ and submit to RC. - ANSWER-annually Any changes made to a restoration plan should be submitted to the RC within ____ days. - ANSWER- 90 A TOPs system restoration plan must be verified every ________. - ANSWER-5 years Where must system restoration plans be located? - ANSWER-Both the primary and backup control rooms Each TOP must provide system restoration training ________ for system operators. - ANSWER-annually Each TOP, TO, and Distribution Service Provider must provide ________ of system restoration training to field personnel every ________. - ANSWER-2 hours, 2 years A Generator Operator must notify the TOP of any changes to a Blackstart Resourse that affect the ability to meet the restoration plan within ________, or in cases where the generator was on-line when the change occurred, within ________. - ANSWER-24 hours, 30 minutes An RC must review its TOPs Restoration Plans within ________. - ANSWER-30 days An RC must review their own restoration plan within ________ of last review. - ANSWER-13 calendar months An RC must distribute their most recent RC Area Restoration Plan to its TOPs within ________ of creation or revision. - ANSWER- 30 days
What are the impacts of GICs? - ANSWER-transformer hot-spot heating, loss of reactive power sources, increased reactive power demand, protective system misoperation UVLS drops pre-selected blocks of load to reduce ________ and restore ________. - ANSWER-power flow, reactive balances UFLS should trip the last pre-selected block of load prior to ________. - ANSWER-generators tripping What is the main information used to forecast load? - ANSWER-weather What is Operational Planning Analysis? - ANSWER-simulates power flow under a set of system conditions and calculates the loading and voltage impacts if a facility fails. What is a Real-Time Assessment? - ANSWER-evaluation of system conditions using real-time data to assess existing (pre-contingency) and potential (post-contingency) operating conditions. Real-Time Assessment and Real-Time Contingency Analysis are the same thing? True/False - ANSWER- FALSE breaker and a half scheme - ANSWER- double bus double breaker scheme - ANSWER- What is an Operating Procedure? - ANSWER-specific steps to be followed in order What is an Operating Process? - ANSWER-General steps with options to select depending on real-time conditions What is used in calculating the distribution of Interchange Transactions and determining curtailment of interchange to relieve transmission loading? - ANSWER-Distribution Factors
What is a remedial action scheme (also called special protection system)? - ANSWER-An automatic protection system that detects abnormal or predetermined conditions and takes corrective actions. What are the three power flow reliability limits? - ANSWER-thermal stability, voltage stability, angle stability A test of redundant data exchange functionality must be done every ________. If this test fails, action must be initiated within ________. - ANSWER-90 days, 2 hours One or more computer systems that display and allow operators to interact with remote devices is called? - ANSWER-Energy Management System (EMS) When Interpersonal Communication fails and lasts for more than ________, RCs, TOPs, and BAs must notify affected entities within ________ of failure detection. - ANSWER-30 minutes, 60 minutes Each RC, BA, and TOP must test its Alternative Communication ________. An unsuccessful test requires initiating action to repair within ________. - ANSWER-once a month, 2 hours What is an Operating Plan? - ANSWER-a document identifying activities to achieve some goal (includes Operating Procedures and Operating Processes) RTCA must be calculated at least every ________. - ANSWER-30 minutes Angle instability is the result of what? - ANSWER-a loss of magnetic bonds What is the ACE equation? - ANSWER-(NIa-NIs)-10B(Fa-Fs) What effect does an internal loss of load have on frequency and ACE? - ANSWER-Frequency increases, ACE increases
When does BAAL high apply? When does BAAL low apply? - ANSWER-BAAL high applies when frequency actual is greater than frequency scheduled BAAL low applies when frequency actual is lower than frequency scheduled What is DCS and what is the minimum compliance for DCS (Disturbance Control Standard)? - ANSWER- 100% compliance, Measures BA's ability to carry adequate Operating Reserve What is the time limit for Disturbance Recovery Period? - ANSWER-15 minutes If ACE is positive or 0 at the time of a DCS event what does have to be returned to and in what time? - ANSWER-ACE of 0 in 15 minutes If ACE is negative at the time of a DCS event what does ACE have to be returned to and in what time? - ANSWER-ACE must be returned to the negative pre-contingency value in 15 minutes Your MSSC is 160 MW. You have an ACE Value of 0 when a DCS event causes ACE to drop 100 MW. 90 seconds later you have another event that causes ACE to drop an additional 50 MW. What value must ACE be returned to? - ANSWER-- 100 What is considered a DCS event? - ANSWER-A loss of generation greater than or equal to 80% of your MSSC, multiple generator losses are considered a single event if occurring within 60 seconds of each other. When does the Contingency Reserve restoration period begin? How long do you have to restore contingency reserve equal to your MSSC? - ANSWER-At the end of the Disturbance control recovery period, 90 minutes What makes up Operating reserves? - ANSWER-Regulating reserves (must be spinning), Contingency reserves (both spinning and non-spinning) How much of your contingency reserve should be spinning reserves? - ANSWER-50%
What is Regulating reserves used for? - ANSWER-Used to meet load forecasting errors, system tie-line and frequency regulation needs What can be considered contingency reserve? - ANSWER-Generation, controllable load, coordinated adjustments to interchange schedules For controllable load to be considered a contingency reserve what must it be? - ANSWER-must be available within 15 minutes For generation to be considered spinning contingency reserve what must it be? - ANSWER-must be synchronized to the system and available within the DCS period What is State Estimator? - ANSWER-A real time model of the current conditions of the power system What is Contingency analysis? what does Contingency analysis rely on? How often should Contingency analysis be ran? - ANSWER-evaluates potential outages and their impact on the remaining system, relies on State Estimator values, should be ran every 30 minutes what is the scan rate for ACE related data? - ANSWER-6 seconds What must a BA experience to declare an EEA? - ANSWER-the BA is or expects to be unable to provide its customers load demands Who request an EEA? - ANSWER-the load serving entity Who declares and EEA? - ANSWER-The deficient areas Reliability coordinator Does an EEA have to be declared in order? - ANSWER-No What is happening in an EEA1? - ANSWER-the BA or load serving entity foresees or is experiencing conditions where all available resources are committed to meet firm load, firm transaction, and reserve
What is Governor Droop? - ANSWER-The amount of frequency change required for the generator to respond from no load to full load or vice versa (typically set to 5%) What is Isochronous mode? - ANSWER-0% Governor Droop, fully responsive to any change in frequency, used only in island conditions (1 unit per island) What is a Governor Deadband and what is its purpose? - ANSWER-+/- 0.036 Hz, prevents governor from responding to slight variations in frequency What conditions can be expected for a BA that is over-generating (assuming no external disturbances)? - ANSWER-frequency > 60 Hz, inadvertent interchange OUT of area, ACE is greater than 0. What conditions can be expected for a BA that is under-generating (assuming no external disturbances)?
- ANSWER-frequency < 60 Hz, inadvertent interchange INTO area, ACE is less than 0. What is a synchronous condenser? - ANSWER-A generator that is synchronized to the system with no load, available for reactive support. There is an underground transmission line in parallel with an overhead transmission line of the same length. Which line will carry more MW? - ANSWER-underground Max theoretical MW flow across a transmission line is at a power angle of what? - ANSWER-90 degrees Max theoretical MVAR flow across a transmission line is at a power angle of what? - ANSWER- 180 degrees What is surge impedance loading (SIL)? - ANSWER-When the amount of MVARs consumed by the line equals the amount flowing into it In restoration would it be better to re-energize an underground line or overhead line and why? - ANSWER-overhead, because it will be less capacitive.
In restoration would it be better to re-energize a longer or shorter line and why? - ANSWER-shorter, it will be less capacitive. What are the characteristics of a line loaded above its SIL? - ANSWER-voltage will be low, capacitive resources need to be implemented to raise voltage. What are the characteristics of a line loaded below its SIL? - ANSWER-voltage will be high, inductive resources need to be implemented to reduce voltage. What is a System Operating Limit (SOL)? - ANSWER-The value that satisfies the most limiting of operating criteria for a specified system configuration to ensure reliability. What are the risks of exceeding a System Operating Limit? - ANSWER-A system operating limit is a local issue. Violating an SOL could result in severe damage to system components. What is an Interconnection Reliability Operating Limit (IROL)? - ANSWER-A system operating limit that could impact the entire interconnection. What are the risks of exceeding an Interconnection Reliability Operating Limit? - ANSWER-Could lead to instability, uncontrolled separation, or Cascading outages What is the characteristic of a lightly loaded line? - ANSWER-capacitive What is the characteristic of a heavily loaded line? - ANSWER-inductive What is Power Factor? - ANSWER-The ratio of real and apparent power (MW/MVA) If an SOL is exceeded, what is the time requirement for returning within system operating limits? - ANSWER-no set time limit, as soon as possible If an IROL is exceeded, what is the time requirement for returning within limits? - ANSWER-Tv
