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NERC EXAM, TEST, PRACTICE EXAM AND STUDY
GUIDE LATEST 202 5 - 2026 ACTUAL EXAM 150
QUESTIONS AND CORRECT DETAILED ANSWERS
WITH RATIONALES (VERIFIED ANSWERS) |ALREADY
GRADED A+
What should a transmission operator do if an SOL or IROL is exceeded? - ANSWER-Inform its RC of the exceedance and the actions being taken to return the system to within limits. % drop in frequency results in a % drop in total load ( % drop in motor load). - ANSWER- 1%, 2%, 3% % decrease in voltage results in % decrease in load? - ANSWER-5%, 3 % % load shed will increase frequency Hz? - ANSWER-6% - 10%, 1 Hz Manual load shed greater than or equal to MW is reportable? - ANSWER- 100 MW Loss of Firm Load greater than or equal to MW is reportable? - ANSWER- 300 MW Two lines into a BA trip leaving that area islanded. What will likely be the impact to the BES? - ANSWER- interconnection frequency will increase Restore load in % blocks of total synchronized generation? Do you count available reserves? - ANSWER-5%, no What is the formula for calculating current (amps)? - ANSWER-I = MVA/(sqrt(3)*Vline) 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
What are Generator Shift Factors used for? - ANSWER-To the determine the amount of change in generator output needed to relieve an overload. What is the formula for GSFs. - ANSWER-Change in generator ouput = overload/(GSF1 - GSF2) (hint: always increase generators with negative SF and decrease those with positive SF) What is the percentage change of electrical loading on a line due to electrical power transfer from one area to another? - ANSWER-Power Transfer Distribution Factor (PTDF) What are Power Transfer Distribution Factors used for? - ANSWER-Used to determine the amount of interchange to curtail when a tie-line is overloaded. Used in the Transmission Loading Relief (TLR) process. What is the percentage of change in electrical loading on a line due to electrical power transfer from one area to another while considering outages? - ANSWER-Outage Transfer Distribution Factor (OTDF) (looks at contingencies) What is the percentage of power flow on a line that is redistributed to another line as a result of that line's outage? - ANSWER-Line Outage Distribution Factor (LODF) ACE calculating system must be available % of the calendar year? - ANSWER-99.5% Frequency metering must be within Hz accuracy and available % of the calendar year? - ANSWER-0.001 Hz, 99.95% If a BA denies a Reliability Adjustment Arranged Interchange due to reliability reasons, the BA must report it to the RC within minutes? - ANSWER-10 minutes 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
An RC must conduct ____ drills, exercises, or simulations of system emergencies each year. - ANSWER- 2 At least once every , the RC must request each TOP and GOP to participate in system emergency drills. - ANSWER-2 years Each RC, BA, and TOP must have an which describes how it will operate in the event its primary control center functionality is lost. - ANSWER-operating plan Cranking paths should be established and additional generation brought on-line to maintain the blackstart unit at % - % capacity. - ANSWER-25 % - 50 % During restoration, frequency should be maintained between Hz - Hz. - ANSWER-59.75 Hz - 61.00 Hz Generation used during restoration must be able to absorb MVARs due to ...? - ANSWER-MVAR production by lightly loaded transmission lines, AVRs operating in manual during restoration What are the 3 requirements of a blackstart unit? - ANSWER-reliable fuel supply, low station service load, ability to operate in isochronous mode What are the two switching strategies during restoration and what are their advantages and disadvantages? - ANSWER-open all breakers: simplest because all breakers at affected stations are opened, but have limited and critical dc battery power controlled breaker operation: opens only breakers necessary, but high need for field personnel and emphasis on isolation What two types of units are often used as blackstart resources? - ANSWER-simple cycle gas and hydro What are the main impacts of a Geomagnetic Disturbance? - ANSWER-transformer core saturation, transformer insulation and winding damage, protective device tripping, increased inductive load 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 happens to your frequency, ACE value, and Tie-line flow when you experience a loss of generation external to your area? - ANSWER-Frequency drops, No change in ACE, Tie-line flows increase out of your system What happens to your frequency, ACE value, and Tie-line flow when you experience a loss of generation inside your balancing area? - ANSWER-Frequency drops, ACE drops, Tie-flows increase into your area How is Frequency Response Obligation (FRO) calculated? - ANSWER-It is calculated based on the BA's annual percentage of generation and load in it's interconnection How is the FRO of a Frequency Response Sharing Group calculated? - ANSWER-FRO determined by adding individual FROs of each member How is the Frequency Response Measure (FRM) calculated? - ANSWER-It is the median of all frequency responses observed for frequency deviations events identifies by NERC for the previous year How should the Frequency Response Measure be set compared to the Frequency Response Obligation?
- ANSWER-Frequency Response Measure should be set equal to or more negative than Frequency Response Obligation Who determines your Frequency Bias Setting? - ANSWER-It is determined by NERC based on previous years Frequency Response Measure What is CPS 1 (Control Performance Standard)? - ANSWER-One minute clock average over a year and is based on ACE deviation in correlation to frequency deviation. CPS 1 has a 100% minimum compliance. Measures how well a BA balances load and generation to support the interconnection. What is BAAL (Balancing Authority ACE Limit)? - ANSWER-ACE does not exceed its BAAL for more than 30 consecutive minutes 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 is happening in an EEA2? - ANSWER-the BA or load serving entity is no longer able to provide its customers expected energy requirements and is designated an Energy Deficient Entity. Procedures have been implemented. Maintaining contingency reserves. Public appeals to reduce demand, voltage reduction, Interruption of non-firm end use loads, Demand-side management, Utility load conservation measures What is happening in an EEA3? - ANSWER-Firm load shed Where is voltage reduction implemented and why? - ANSWER-On the distribution side. Used to lower load when the transmission system is heavily loaded. When would voltage reduction take place on transmission system? - ANSWER-Only during restoration (+/- 10% nominal voltage) What are the AGC modes? - ANSWER-Tie-Line Bias, Flat Frequency, Flat Tie-Line What mode should AGC always be in unless its use becomes detrimental to reliable system operations? - ANSWER-Tie-Line Bias When would AGC be operated in Flat Frequency mode? - ANSWER-When tie-line metering is unavailable (still have tie-lines. not islanded. flat frequency is not the same as isochronous) When would AGC be operated in Flat Tie-Line mode? - ANSWER-When frequency metering is unavailable In an island situation what happens to AGC? - ANSWER-It should be suspended What does a generator governor do? - ANSWER-Arrests frequency but does not restore it 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.
