NCEES Electrical Engineering PE Exam 1 — Questions and Answers
Question 1: On the NCEES PE Electrical exam, what does the 'power factor' of an AC circuit represent?
- The ratio of reactive power to apparent power
- The ratio of real power to apparent power (cos θ) (Correct answer)
- The efficiency of the electrical generator
- The ratio of voltage to current magnitude
Correct answer: The ratio of real power to apparent power (cos θ)
Power factor (PF = cos θ = P/S) is the ratio of real (useful) power consumed to the apparent (total) power supplied, ranging from 0 to 1.
Question 2: In the NCEES PE Electrical exam, what is the purpose of a 'per-unit system' in power systems analysis?
- To normalize quantities to a common base, simplifying calculations across transformers and voltage levels (Correct answer)
- To measure power in SI units only
- To convert three-phase to single-phase equivalents
- To eliminate reactive power from calculations
Correct answer: To normalize quantities to a common base, simplifying calculations across transformers and voltage levels
The per-unit system normalizes voltages, currents, powers, and impedances to a chosen base, eliminating transformer turns ratios and simplifying multi-voltage-level system analysis.
Question 3: For the NCEES PE Electrical exam, which protection device operates based on time-current characteristics to interrupt overcurrents?
- Surge arrester
- Overcurrent relay (inverse time) (Correct answer)
- Capacitor bank
- Voltage regulator
Correct answer: Overcurrent relay (inverse time)
Inverse-time overcurrent relays trip faster as current magnitude increases, providing coordination with downstream devices and protecting against sustained overloads and faults.
Question 4: On the NCEES PE Electrical exam, what is the 'synchronous reactance' of a synchronous generator?
- The resistance of the generator windings at DC
- The effective internal reactance that determines voltage regulation and fault current (Correct answer)
- The reactance of the transmission line connected to the generator
- The magnetic reluctance of the rotor core
Correct answer: The effective internal reactance that determines voltage regulation and fault current
Synchronous reactance (Xs) is the per-phase internal impedance of a synchronous machine, governing its voltage regulation, stability, and contribution to fault currents.
Question 5: In the NCEES PE Electrical exam, what does 'short-circuit MVA' (fault MVA) represent?
- The rated power of circuit breakers in MVA
- The magnitude of power available during a three-phase fault at a bus (Correct answer)
- The motor starting apparent power
- The transformer inrush current in MVA
Correct answer: The magnitude of power available during a three-phase fault at a bus
Short-circuit MVA at a bus represents the severity of a three-phase fault, calculated as the product of the prefault voltage and the available fault current, used for equipment ratings.
Question 6: For the NCEES PE Electrical exam, which transformer connection is most commonly used to supply a four-wire distribution system from a three-phase source?
- Delta-Delta
- Wye-Delta
- Delta-Wye with grounded neutral (Correct answer)
- Open-Delta
Correct answer: Delta-Wye with grounded neutral
The delta-wye (Δ-Y) transformer with a grounded wye secondary is standard for distribution because it provides a neutral conductor for single-phase loads and grounding.
NCEES Electrical Engineering PE Exam 1
On the NCEES PE Electrical exam, what does the 'power factor' of an AC circuit represent?