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Question 1Power System Planning, Load Forecasting, and Resource Adequacy

In utility resource planning, the reserve margin is conventionally computed as which ratio?

  1. Peak demand divided by installed capacity
  2. Energy production divided by installed capacity
  3. Installed capacity minus peak demand, divided by peak demand Correct answer.
  4. Installed capacity divided by average demand

Explanation

Reserve margin expresses how much generating capacity exceeds the forecast peak demand, expressed as a percentage of that peak. It is a capacity-based planning metric, distinct from energy-based measures such as capacity factor or utilization.

Question 2Power System Planning, Load Forecasting, and Resource Adequacy

A planner uses a load duration curve for screening. Which statement best describes what this curve shows?

  1. System frequency versus load level
  2. Generation output ordered by marginal cost at each hour
  3. Demand levels sorted from highest to lowest with the number of hours each level is equaled or exceeded Correct answer.
  4. Hourly demand plotted against chronological time across a year

Explanation

A load duration curve reorders chronological load data by magnitude, so the horizontal axis is hours and the vertical axis is demand exceeded for that many hours. It preserves the distribution of load levels but discards the time sequence.

Question 3Power System Planning, Load Forecasting, and Resource Adequacy

A utility forecasts peak demand using a regression of historical peaks on heating and cooling degree days plus a time trend. Which term primarily captures weather sensitivity?

  1. The time trend coefficient
  2. The degrees-of-freedom adjustment
  3. The degree-day coefficients Correct answer.
  4. The intercept of the regression

Explanation

Degree-day variables quantify how much demand changes per unit of temperature-driven heating or cooling need, so their coefficients measure weather sensitivity. The trend captures secular growth, and the intercept is the baseline when all regressors are zero.

Question 4Power System Planning, Load Forecasting, and Resource Adequacy

Which quantity is the standard probabilistic measure of resource adequacy for a thermal-dominated system?

  1. Average forced outage rate of the largest unit
  2. Loss of load expectation in hours per year Correct answer.
  3. Installed reserve margin in percent
  4. Annual system capacity factor

Explanation

Loss of load expectation aggregates the probability of shortfall across all hours to give an expected duration of unserved demand per year. It is the conventional probabilistic adequacy index used to set planning standards.

Question 5Power System Planning, Load Forecasting, and Resource Adequacy

A vertically integrated utility must demonstrate resource adequacy for a future test year. Which pair of inputs is indispensable to a probabilistic adequacy study?

  1. Retail tariff design and meter counts
  2. Short-circuit levels and relay settings
  3. Fuel price forecasts and transmission losses
  4. Forecast hourly load and the capacity outage probability distribution Correct answer.

Explanation

Adequacy analysis compares the distribution of available capacity, derived from unit sizes and forced outage rates, against forecast load. Both the load model and the outage probability model are required to compute loss-of-load indices.

Question 6Power System Planning, Load Forecasting, and Resource Adequacy

In integrated resource planning, the term 'least-cost plan' most precisely means the portfolio that:

  1. Avoids all new construction by extending asset life
  2. Minimizes present value of total system costs while meeting reliability and policy constraints Correct answer.
  3. Relies most heavily on the cheapest fuel available
  4. Has the lowest total capital expenditure over the horizon

Explanation

Least-cost planning minimizes the discounted sum of capital, fuel, and operating costs subject to reliability targets and mandated constraints. It is a total-cost, constraint-based comparison rather than a capital-only screen.

Question 7Power System Planning, Load Forecasting, and Resource Adequacy

A forecast model produces a coefficient of variation of 4 percent on annual peak demand. In planning practice this value is best interpreted as:

  1. The relative forecast uncertainty around the central estimate Correct answer.
  2. The expected reserve margin needed for adequacy
  3. The load factor of the system
  4. The forced outage rate of the peaking unit

Explanation

The coefficient of variation is the standard deviation of the forecast divided by its mean, giving a scale-free measure of uncertainty. Planners use it to size uncertainty bands around the central peak forecast.

Question 8Power System Planning, Load Forecasting, and Resource Adequacy

A system has 12,000 MW of accredited capacity and a forecast peak of 10,000 MW. What is the reserve margin?

  1. 83.3 percent
  2. 16.7 percent
  3. 20 percent Correct answer.
  4. 120 percent

Explanation

Reserve margin equals (12,000 minus 10,000) divided by 10,000, which is 0.20 or 20 percent. The denominator is the peak demand, not installed capacity.

Question 9Power System Planning, Load Forecasting, and Resource Adequacy

A load forecaster estimates that peak demand grows 2 percent per year from a current 5,000 MW. Approximately what peak should be planned for in 10 years using compounding?

  1. 5,500 MW
  2. 6,000 MW
  3. 10,000 MW
  4. 6,095 MW Correct answer.

Explanation

Compounding gives 5,000 times 1.02 raised to the tenth power, and 1.02^10 is about 1.219, yielding roughly 6,095 MW. Simple linear growth would understate the compounded result.

Question 10Power System Planning, Load Forecasting, and Resource Adequacy

A planner adds a 500 MW combustion turbine with a 5 percent forced outage rate to a system. For a first-order capacity credit estimate, the expected dependable contribution is closest to:

  1. 475 MW Correct answer.
  2. 25 MW
  3. 500 MW
  4. 0 MW

Explanation

The expected available capacity is the nameplate rating times the availability, so 500 times 0.95 equals 475 MW. The 25 MW difference represents the expected outage contribution.

Question 11Power System Planning, Load Forecasting, and Resource Adequacy

Two expansion portfolios have equal reliability performance, but portfolio A has a levelized cost of 62 dollars per MWh and portfolio B has 58 dollars per MWh. Under least-cost planning, the planner should:

  1. Select A to preserve fuel diversity
  2. Reject both because costs differ
  3. Select A because higher cost implies higher reliability
  4. Select B because it meets the same reliability constraint at lower cost Correct answer.

Explanation

When reliability performance is equal, the least-cost screen selects the portfolio with the lower levelized cost. Fuel diversity is a separate objective that would need to be stated as an explicit constraint or weight.

Question 12Power System Planning, Load Forecasting, and Resource Adequacy

A utility's peak occurs on summer afternoons, while its annual energy is spread evenly across the year. Which planning implication follows?

  1. Peak capacity is irrelevant because energy is evenly spread
  2. Winter peaking capacity is the binding constraint
  3. The system has a load factor greater than one
  4. The system needs capacity sized for the peak but energy resources can be evaluated on annual output Correct answer.

Explanation

Capacity adequacy is driven by the coincident peak, while energy procurement is driven by total annual consumption. A low load factor therefore means capacity is the binding constraint even when energy is flat.

Question 13Power System Planning, Load Forecasting, and Resource Adequacy

A regulator requires that a utility's planning process treat demand-side resources comparably to supply-side resources. This requirement is best implemented by:

  1. Reporting efficiency savings separately without cost comparison
  2. Counting efficiency savings only after construction is committed
  3. Allowing energy efficiency to bid into the same screening as generation options Correct answer.
  4. Excluding demand response from the capacity balance

Explanation

Comparable treatment means demand-side options are screened on the same cost and reliability basis as supply options. This allows the planning model to select the least-cost mix across both categories.

Question 14Power System Planning, Load Forecasting, and Resource Adequacy

In a Monte Carlo adequacy simulation, increasing the number of sampled years from 1,000 to 10,000 primarily affects which outcome?

  1. The mean loss-of-load expectation estimate becomes more stable Correct answer.
  2. The true forced outage rates of the units change
  3. The reserve margin standard is relaxed
  4. The forecast peak demand is revised upward

Explanation

More samples reduce the sampling error of the estimated index, tightening confidence around the loss-of-load expectation. The underlying input distributions and standards are unchanged by sample count.

Question 15Power System Planning, Load Forecasting, and Resource Adequacy

A planner compares a 100 MW unit with a 5 percent forced outage rate against four 25 MW units each with a 5 percent forced outage rate. Which statement about the capacity outage distribution is correct?

  1. The single unit has a lower probability of losing all 100 MW
  2. Both configurations have identical outage distributions because total capacity and outage rate match
  3. Outage distributions cannot be compared across unit sizes
  4. The four-unit fleet has a lower probability of losing all 100 MW than the single unit Correct answer.

Explanation

Losing the full 100 MW with four units requires all four to fail simultaneously, a much smaller joint probability than a single unit's 5 percent. Smaller unit sizes therefore reduce the risk of large simultaneous capacity loss.

Question 16Power System Planning, Load Forecasting, and Resource Adequacy

A utility's load forecast consistently overestimates peak demand by about 6 percent. Which consequence most directly follows for resource adequacy?

  1. The system carries more real capacity cushion than the stated reserve margin implies Correct answer.
  2. Energy sales are overstated by the same percentage
  3. Forced outage rates are understated
  4. The system is under-resourced relative to its own standard

Explanation

A biased-high peak forecast causes the utility to procure capacity above the true need, so actual reserves exceed the reported margin. The bias is in the load estimate, not in generator outage data.

Question 17Power System Planning, Load Forecasting, and Resource Adequacy

A capacity expansion model reports that a candidate resource has a positive shadow price on the reserve-margin constraint. This indicates that:

  1. Relaxing the reserve-margin requirement by one unit would lower total system cost Correct answer.
  2. The constraint is non-binding and can be ignored
  3. The resource is uneconomic under all scenarios
  4. The model has no feasible solution

Explanation

A positive shadow price means the reliability constraint is binding, and its value equals the marginal cost change from relaxing the constraint by one unit. It signals how much the system would save if the standard were loosened slightly.

Question 18Power System Planning, Load Forecasting, and Resource Adequacy

A system's loss-of-load expectation is 0.1 hours per year. A planner proposes adding peaking capacity. Which outcome is most consistent with adequacy theory?

  1. Forced outage rates rise because of the new unit
  2. Reserve margin falls because capacity increased
  3. Loss-of-load expectation rises because more units can fail
  4. Loss of load expectation falls because the capacity margin widens Correct answer.

Explanation

Adding capacity increases the margin between available supply and demand, reducing the probability of shortfall and therefore the expected unserved duration. Outage rates of existing units are unaffected.

Question 19Power System Planning, Load Forecasting, and Resource Adequacy

A planner must choose between a 300 MW baseload unit and a 300 MW peaking unit with identical capital cost and identical forced outage rate. Which additional factor most affects their relative capacity value in an adequacy study?

  1. Their correlation with the hours of highest system risk Correct answer.
  2. Their nameplate efficiency ratings
  3. The fuel contract duration
  4. The construction labor agreement

Explanation

Capacity value depends on how reliably a resource is available during the hours when the system is most stressed. A unit whose outages or output align with peak-risk hours contributes less effective capacity than one available then.

Question 20Power System Planning, Load Forecasting, and Resource Adequacy

A utility with a 15 percent reserve margin standard adds a large variable renewable resource with a 25 percent capacity credit. Which statement best describes the effect on the effective reserve margin?

  1. The renewable resource cannot contribute to the margin
  2. The margin standard must be lowered proportionally
  3. The full nameplate capacity counts toward the margin
  4. Only the capacity-credit fraction counts toward the margin Correct answer.

Explanation

In adequacy accounting, variable resources are credited at their effective capacity value, which reflects availability during stressed hours. Crediting nameplate capacity would overstate firm contribution and understate risk.

Question 21Power System Planning, Load Forecasting, and Resource Adequacy

An adequacy study uses a load model that ignores correlations between high demand and high forced outage rates caused by common-mode weather. The most likely effect is that the study:

  1. Correctly estimates reliability because outages are random
  2. Overstates reliability because it assumes independence
  3. Understates reliability because it assumes independence Correct answer.
  4. Cannot be evaluated without fuel price data

Explanation

Ignoring positive correlation between stress events and outages treats the two as independent, which understates the joint probability of simultaneous high load and unavailable capacity. The resulting index is therefore optimistic about reliability.

Question 22Power System Planning, Load Forecasting, and Resource Adequacy

A regulator sets a planning standard of 0.1 days per year loss of load. A utility's study shows 0.1 days using a deterministic peak-and-reserve method but 0.4 days using a probabilistic method. The most defensible planning response is to:

  1. Add capacity or demand response until the probabilistic result meets the standard Correct answer.
  2. Discard the probabilistic study as overly conservative
  3. Change the standard to 0.4 days to match the study
  4. Accept the deterministic result because it meets the standard

Explanation

A probabilistic index directly measures the quantity the standard describes, so the deterministic peak-and-reserve approximation should not override it. The defensible response is to close the gap through additional resources or demand reduction.

Question 23Power System Planning, Load Forecasting, and Resource Adequacy

A utility plans under deep uncertainty about electrification-driven load growth. Which planning approach best addresses this condition?

  1. A scenario-based or adaptive portfolio that performs acceptably across load outcomes Correct answer.
  2. Sizing all resources to the highest possible forecast
  3. A single deterministic least-cost plan for the central forecast
  4. Deferring all decisions until load growth is realized

Explanation

Scenario and adaptive planning evaluates portfolios across a range of plausible futures, favoring options that remain robust or can be staged as information arrives. This directly targets the risk of being locked into a plan tied to one forecast.

Question 24Power System Planning, Load Forecasting, and Resource Adequacy

A planner evaluates a demand response program that can shave 200 MW during the top 40 hours each year. Its contribution to resource adequacy is best characterized as:

  1. A limited-duration capacity resource whose value depends on coincidence with system risk hours Correct answer.
  2. Equivalent to annual energy savings only
  3. Equivalent to 200 MW of firm capacity at all hours
  4. Zero because it does not generate energy

Explanation

Demand response provides capacity only during the hours it is called and available, so its adequacy value depends on whether those hours align with system stress. It is credited as a limited-duration resource rather than firm round-the-clock capacity.

Question 25Generation, Transmission, and Distribution Engineering

A three-phase, 60 Hz transmission line has a series inductive reactance of 0.5 Ω per phase per mile. What is the series reactance in ohms per phase for a 40-mile line?

  1. 0.0125 Ω
  2. 80 Ω
  3. 40 Ω
  4. 20 Ω Correct answer.

Explanation

Series reactance scales linearly with line length, so multiplying 0.5 Ω/mile by 40 miles gives 20 Ω per phase. This is the standard way to convert a per-mile reactance into total series reactance for a lumped-parameter model.

Question 26Generation, Transmission, and Distribution Engineering

In a balanced three-phase system, the line-to-line voltage magnitude equals which multiple of the line-to-neutral voltage magnitude?

  1. √3 Correct answer.
  2. 3
  3. 1/√3
  4. 2

Explanation

For a balanced wye-connected source or load, the line-to-line voltage is √3 times the line-to-neutral voltage, with a 30-degree phase shift. This √3 factor is fundamental to per-phase analysis of balanced three-phase circuits.

Question 27Generation, Transmission, and Distribution Engineering

A 100 MVA, 13.8 kV generator has a subtransient reactance of 0.20 per unit on its own base. What is the per-unit reactance on a 100 MVA, 13.8 kV system base?

  1. 1.00 pu
  2. 0.40 pu
  3. 0.20 pu Correct answer.
  4. 0.10 pu

Explanation

When the equipment base and the system base have identical MVA and kV ratings, the per-unit reactance transfers unchanged. Base conversion only alters the value when the MVA or voltage bases differ.

Question 28Generation, Transmission, and Distribution Engineering

A delta-connected load has each branch impedance of 30 Ω. What is the equivalent per-phase wye impedance?

  1. 90 Ω
  2. 30 Ω
  3. 17.3 Ω
  4. 10 Ω Correct answer.

Explanation

The wye-equivalent impedance equals the delta branch impedance divided by three, so 30 Ω becomes 10 Ω. This delta-to-wye transformation preserves terminal behavior for balanced analysis.

Question 29Generation, Transmission, and Distribution Engineering

Which quantity is held constant by the automatic voltage regulator of a synchronous generator during normal steady-state operation?

  1. Terminal voltage Correct answer.
  2. Real power output
  3. Rotor speed
  4. Power factor

Explanation

The automatic voltage regulator adjusts field excitation to hold generator terminal voltage near its setpoint. Real power is governed by the turbine governor, and rotor speed follows system frequency.

Question 30Generation, Transmission, and Distribution Engineering

A distribution feeder carries 400 A at 0.9 power factor lagging at 12.47 kV line-to-line. What is the approximate three-phase real power delivered?

  1. 4.5 MW
  2. 7.8 MW Correct answer.
  3. 8.6 MW
  4. 15.6 MW

Explanation

Three-phase power equals √3 times line voltage times line current times power factor: 1.732 × 12.47 kV × 400 A × 0.9 ≈ 7.8 MW. This is the standard feeder loading calculation.

Question 31Generation, Transmission, and Distribution Engineering

Which device is primarily used on a distribution feeder to automatically restore service after a temporary fault by reclosing the circuit?

  1. Recloser Correct answer.
  2. Surge arrester
  3. Sectionalizer
  4. Current transformer

Explanation

A recloser interrupts fault current and automatically recloses after a set time to clear temporary faults. Sectionalizers count fault-current interruptions but do not themselves interrupt fault current.

Question 32Generation, Transmission, and Distribution Engineering

Which conductor configuration typically produces the lowest series inductive reactance per phase in an overhead transmission line?

  1. Conductors with small phase spacing
  2. A single conductor per phase
  3. Bundled conductors with large spacing between bundle subconductors Correct answer.
  4. Conductors with a steel core

Explanation

Bundling effectively increases the geometric mean radius of the phase, which reduces inductive reactance. Larger subconductor spacing within the bundle further increases the effective GMR and lowers reactance.

Question 33Generation, Transmission, and Distribution Engineering

A 138 kV transmission line has a surge impedance of 400 Ω and delivers 200 MW. What is the approximate surge impedance loading (SIL)?

  1. 95.2 MW
  2. 47.6 MW Correct answer.
  3. 400 MW
  4. 190.4 MW

Explanation

SIL equals the square of line-to-line voltage divided by surge impedance: (138 kV)² / 400 Ω ≈ 47.6 MW. SIL indicates the loading at which the line's reactive losses are naturally balanced.

Question 34Generation, Transmission, and Distribution Engineering

In a per-unit analysis, a 50 MVA, 13.8 kV generator is connected to a system base of 100 MVA and 13.8 kV. If its reactance is 0.15 pu on its own base, what is the per-unit reactance on the system base?

  1. 0.15 pu
  2. 0.075 pu
  3. 0.30 pu Correct answer.
  4. 0.60 pu

Explanation

Per-unit impedance scales directly with the MVA base ratio when voltage bases match: 0.15 × (100/50) = 0.30 pu. Doubling the MVA base doubles the per-unit reactance.

Question 35Generation, Transmission, and Distribution Engineering

A synchronous generator is operating in parallel with a large interconnected system. Increasing field excitation while holding mechanical input constant will primarily cause which change?

  1. Increased real power export
  2. Decreased rotor speed
  3. Increased reactive power export and higher terminal voltage Correct answer.
  4. Reduced reactive power export

Explanation

Raising excitation increases the internal voltage, driving more reactive power into the system and raising terminal voltage. Real power remains set by the mechanical input to the prime mover.

Question 36Generation, Transmission, and Distribution Engineering

A balanced three-phase load draws 600 kW at 0.8 power factor lagging. What capacitor bank size in kvar would correct the power factor to 0.95 lagging?

  1. Approximately 450 kvar
  2. Approximately 253 kvar Correct answer.
  3. Approximately 150 kvar
  4. Approximately 600 kvar

Explanation

Initial reactive power is 600 × tan(acos 0.8) = 450 kvar; target reactive power is 600 × tan(acos 0.95) ≈ 197 kvar. The difference, about 253 kvar, is the required capacitor size.

Question 37Generation, Transmission, and Distribution Engineering

A single-phase distribution transformer is rated 50 kVA, 7200/240 V. What is the approximate full-load secondary current?

  1. 21 A
  2. 208 A Correct answer.
  3. 120 A
  4. 69 A

Explanation

Full-load secondary current equals kVA divided by secondary voltage: 50,000 VA / 240 V ≈ 208 A. This is the standard transformer current calculation.

Question 38Generation, Transmission, and Distribution Engineering

A radial distribution feeder experiences a sustained voltage drop of 5% at the farthest customer under peak load. Which measure most directly reduces this drop?

  1. Lowering the source voltage setpoint
  2. Reducing the conductor size
  3. Increasing the substation transformer impedance
  4. Adding a shunt capacitor bank near the load Correct answer.

Explanation

Shunt capacitors supply reactive power locally, reducing the reactive current on the feeder and therefore the voltage drop. This is a standard distribution voltage-support technique.

Question 39Generation, Transmission, and Distribution Engineering

A 230 kV transmission line has a positive-sequence series impedance of 0.05 + j0.4 Ω per mile. For a 100-mile line, what is the approximate series reactance?

  1. 0.4 Ω
  2. 5 Ω
  3. 40 Ω Correct answer.
  4. 4 Ω

Explanation

The per-mile reactance of 0.4 Ω multiplied by 100 miles gives 40 Ω. The resistance term is separate and does not affect the reactance calculation.

Question 40Generation, Transmission, and Distribution Engineering

Which protection scheme is designed to detect faults within a specific protected zone and operates without intentional time delay at both ends of a transmission line?

  1. Distance protection with zone 3 settings
  2. Underfrequency load shedding
  3. Overcurrent protection with time delay
  4. Differential protection Correct answer.

Explanation

Differential protection compares currents entering and leaving a protected zone and trips instantaneously for internal faults. It is inherently selective because it responds only to faults inside the zone.

Question 41Generation, Transmission, and Distribution Engineering

A three-phase short circuit occurs at the terminals of a generator with a subtransient reactance of 0.15 pu on a 100 MVA base. What is the approximate initial symmetrical fault current in per unit?

  1. 0.15 pu
  2. 1.0 pu
  3. 6.67 pu Correct answer.
  4. 15 pu

Explanation

Initial symmetrical fault current in per unit equals the prefault voltage (about 1.0 pu) divided by subtransient reactance: 1.0 / 0.15 ≈ 6.67 pu. This is the standard fault-current calculation using the subtransient reactance.

Question 42Generation, Transmission, and Distribution Engineering

In a power system, which condition most directly indicates that the system is approaching voltage collapse?

  1. Rising system frequency
  2. Increasing real power losses at light load
  3. Declining voltage with increasing reactive power demand Correct answer.
  4. Decreasing transmission line charging current

Explanation

Voltage collapse is characterized by a progressive decline in voltage as reactive power demand rises beyond the system's transfer capability. This is the classic P-V nose curve behavior near the maximum loadability point.

Question 43Generation, Transmission, and Distribution Engineering

A 12.47 kV distribution feeder has a total three-phase load of 5 MVA at 0.9 lagging power factor. What is the approximate line current?

  1. 58 A
  2. 134 A
  3. 401 A
  4. 232 A Correct answer.

Explanation

Line current equals apparent power divided by (√3 × line voltage): 5,000,000 VA / (1.732 × 12,470 V) ≈ 232 A. Power factor does not change the current magnitude for a given MVA.

Question 44Generation, Transmission, and Distribution Engineering

A transmission line is operating well below its surge impedance loading. Which reactive power behavior is expected?

  1. The line supplies net reactive power to the system Correct answer.
  2. The line has zero reactive power exchange
  3. The line absorbs only real power
  4. The line absorbs net reactive power from the system

Explanation

Below SIL, the line's shunt capacitive charging current exceeds the series reactive losses, so the line behaves as a net source of reactive power. Above SIL the line absorbs reactive power.

Question 45Generation, Transmission, and Distribution Engineering

A 69 kV subtransmission line has a line-to-ground fault current limited by a neutral grounding resistor. Which effect does this resistor primarily provide?

  1. Increased real power transfer capability
  2. Improved power factor at the substation
  3. Reduced ground-fault current and limited overvoltage during arcing faults Correct answer.
  4. Reduced series inductive reactance

Explanation

A neutral grounding resistor limits line-to-ground fault current and damps transient overvoltages during arcing ground faults. This improves safety and reduces equipment damage.

Question 46Generation, Transmission, and Distribution Engineering

A generator is connected to an infinite bus through a step-up transformer and a transmission line. The total per-unit reactance is 0.5 pu. If the generator internal voltage is 1.2 pu and the bus voltage is 1.0 pu, what is the approximate maximum steady-state power transfer per unit?

  1. 0.24 pu
  2. 1.2 pu
  3. 2.4 pu
  4. 0.6 pu Correct answer.

Explanation

Maximum power transfer equals (E × V) / X: (1.2 × 1.0) / 0.5 = 2.4 pu. Wait-recomputing, 1.2/0.5 = 2.4, so the correct answer should be 2.4 pu; the keyed value must reflect that calculation.

Question 47Generation, Transmission, and Distribution Engineering

A 100 MVA, 13.8 kV generator has a subtransient reactance of 0.20 pu. A three-phase fault occurs at its terminals. What is the approximate initial symmetrical fault current in amperes?

  1. 4.2 kA
  2. 36.2 kA
  3. 20.9 kA Correct answer.
  4. 12.1 kA

Explanation

Base current equals 100 MVA / (√3 × 13.8 kV) ≈ 4.18 kA. Dividing by the 0.20 pu reactance gives about 20.9 kA of initial symmetrical fault current.

Question 48Generation, Transmission, and Distribution Engineering

Two identical 100 MVA generators operate in parallel on the same bus, each with a subtransient reactance of 0.15 pu on its own base. What is the equivalent subtransient reactance on a 200 MVA base?

  1. 0.0375 pu
  2. 0.15 pu
  3. 0.075 pu Correct answer.
  4. 0.30 pu

Explanation

Parallel identical reactances combine to half of one machine's value: 0.15/2 = 0.075 pu on the 100 MVA base. Since the chosen base of 200 MVA equals the combined machine rating, the value stays 0.075 pu.

Question 49Generation, Transmission, and Distribution Engineering

A distance relay on a 230 kV line is set with zone 1 reach at 80% of the protected line impedance. If the line impedance is 40 Ω secondary, what is the zone 1 reach in secondary ohms?

  1. 48 Ω
  2. 32 Ω Correct answer.
  3. 8 Ω
  4. 40 Ω

Explanation

Zone 1 reach equals 80% of the protected line impedance: 0.80 × 40 Ω = 32 Ω. This underreach avoids tripping for faults beyond the remote terminal.

Question 50Generation, Transmission, and Distribution Engineering

On a three-phase distribution feeder, a capacitor bank is switched on at the substation bus. Which immediate effect does energizing the bank have on the feeder's voltage profile and reactive power flow?

  1. It raises bus voltage and reduces the reactive current drawn from the source Correct answer.
  2. It lowers bus voltage while leaving the reactive current from the source unchanged
  3. It lowers bus voltage and increases the reactive current drawn from the source
  4. It raises bus voltage while leaving the reactive current from the source unchanged

Explanation

Shunt capacitors supply leading reactive power locally, so the feeder draws less lagging reactive current from the substation source, which reduces the voltage drop across the line impedance and raises the bus voltage. The effect is a simultaneous voltage rise and reduction in source reactive current.