Principles and Practice of Engineering (PE) – Power Systems
Examination Questions And Correct Answers (Verified
Answers) Plus Rationales 2025/2026 Q&A | Instant
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1. Which of the following is the primary purpose of a step-up transformer in a
power system?
A. Reduce voltage for residential use
B. Reduce current to minimize losses
C. Increase voltage for transmission
D. Isolate the generator from the load
Step-up transformers increase voltage to reduce current for long-distance
transmission, minimizing I²R losses.
2. What is the typical per-unit value of a fully rated generator voltage?
A. 0.95 pu
B. 1.05 pu
C. 1.0 pu
D. 1.1 pu
The per-unit system normalizes quantities; a fully rated generator operates at
1.0 pu voltage under nominal conditions.
3. Which factor primarily determines the short-circuit current in a
transmission system?
A. Transformer impedance
B. Line impedance
C. Both transformer and line impedance
D. Generator rating only
Short-circuit current depends on all impedances between the source and the
fault location.
,4. A synchronous generator operating at 60 Hz is connected to a 3-phase
system. What is the rotor speed for a 4-pole machine?
A. 900 rpm
B. 1800 rpm
C. 1200 rpm
D. 3600 rpm
120⋅𝑓 120⋅60
Rotor speed 𝑁𝑠 = = = 1800rpm.
𝑃 4
5. In a three-phase, balanced wye system, the line voltage is 13.8 kV. What is
the phase voltage?
A. 13.8 kV
B. 23.9 kV
C. 7.97 kV
D. 11.0 kV
𝑉𝑙𝑖𝑛𝑒 13.8
Phase voltage 𝑉𝑝ℎ𝑎𝑠𝑒 = = ≈ 7.97kV.
√3 1.732
6. Which type of fault has the highest magnitude of short-circuit current?
A. Line-to-line
B. Line-to-ground
C. Three-phase
D. Double line-to-ground
Three-phase faults involve all phases and produce the maximum symmetrical
short-circuit current.
7. The primary purpose of a circuit breaker is to:
A. Limit voltage fluctuations
B. Provide continuous power
C. Interrupt fault currents
D. Step up voltage
Circuit breakers protect equipment by interrupting currents during faults.
, 8. What is the X/R ratio of a transmission line used for?
A. To size transformers
B. To calculate DC offset in short-circuit current
C. To determine reactive power flow
D. To measure voltage drop
The X/R ratio indicates the inductive to resistive proportion, affecting DC offset
and asymmetrical current.
9. Which of the following is a disadvantage of a high-voltage DC (HVDC)
system compared to AC transmission?
A. Lower transmission losses
B. Longer distance capability
C. Complex conversion equipment
D. Improved stability
HVDC requires rectifiers and inverters, increasing system complexity.
10. A delta-wye transformer has a primary line voltage of 69 kV and
secondary line voltage of 13.8 kV. The turns ratio is:
A. 5:1
B. 10:1
C. 5:1 (line-to-line)
D. 1:5
𝑉𝑝𝑟𝑖𝑚𝑎𝑟𝑦 69
Turns ratio for line-to-line voltage 𝑁 = = ≈ 5.
𝑉𝑠𝑒𝑐𝑜𝑛𝑑𝑎𝑟𝑦 13.8
11. Which type of relay operates by sensing the current magnitude and time
delay?
A. Distance relay
B. Differential relay
C. Inverse-time overcurrent relay
D. Directional relay
Examination Questions And Correct Answers (Verified
Answers) Plus Rationales 2025/2026 Q&A | Instant
Download Pdf
1. Which of the following is the primary purpose of a step-up transformer in a
power system?
A. Reduce voltage for residential use
B. Reduce current to minimize losses
C. Increase voltage for transmission
D. Isolate the generator from the load
Step-up transformers increase voltage to reduce current for long-distance
transmission, minimizing I²R losses.
2. What is the typical per-unit value of a fully rated generator voltage?
A. 0.95 pu
B. 1.05 pu
C. 1.0 pu
D. 1.1 pu
The per-unit system normalizes quantities; a fully rated generator operates at
1.0 pu voltage under nominal conditions.
3. Which factor primarily determines the short-circuit current in a
transmission system?
A. Transformer impedance
B. Line impedance
C. Both transformer and line impedance
D. Generator rating only
Short-circuit current depends on all impedances between the source and the
fault location.
,4. A synchronous generator operating at 60 Hz is connected to a 3-phase
system. What is the rotor speed for a 4-pole machine?
A. 900 rpm
B. 1800 rpm
C. 1200 rpm
D. 3600 rpm
120⋅𝑓 120⋅60
Rotor speed 𝑁𝑠 = = = 1800rpm.
𝑃 4
5. In a three-phase, balanced wye system, the line voltage is 13.8 kV. What is
the phase voltage?
A. 13.8 kV
B. 23.9 kV
C. 7.97 kV
D. 11.0 kV
𝑉𝑙𝑖𝑛𝑒 13.8
Phase voltage 𝑉𝑝ℎ𝑎𝑠𝑒 = = ≈ 7.97kV.
√3 1.732
6. Which type of fault has the highest magnitude of short-circuit current?
A. Line-to-line
B. Line-to-ground
C. Three-phase
D. Double line-to-ground
Three-phase faults involve all phases and produce the maximum symmetrical
short-circuit current.
7. The primary purpose of a circuit breaker is to:
A. Limit voltage fluctuations
B. Provide continuous power
C. Interrupt fault currents
D. Step up voltage
Circuit breakers protect equipment by interrupting currents during faults.
, 8. What is the X/R ratio of a transmission line used for?
A. To size transformers
B. To calculate DC offset in short-circuit current
C. To determine reactive power flow
D. To measure voltage drop
The X/R ratio indicates the inductive to resistive proportion, affecting DC offset
and asymmetrical current.
9. Which of the following is a disadvantage of a high-voltage DC (HVDC)
system compared to AC transmission?
A. Lower transmission losses
B. Longer distance capability
C. Complex conversion equipment
D. Improved stability
HVDC requires rectifiers and inverters, increasing system complexity.
10. A delta-wye transformer has a primary line voltage of 69 kV and
secondary line voltage of 13.8 kV. The turns ratio is:
A. 5:1
B. 10:1
C. 5:1 (line-to-line)
D. 1:5
𝑉𝑝𝑟𝑖𝑚𝑎𝑟𝑦 69
Turns ratio for line-to-line voltage 𝑁 = = ≈ 5.
𝑉𝑠𝑒𝑐𝑜𝑛𝑑𝑎𝑟𝑦 13.8
11. Which type of relay operates by sensing the current magnitude and time
delay?
A. Distance relay
B. Differential relay
C. Inverse-time overcurrent relay
D. Directional relay
