BEE Power Systems Engineering 4

Question 1

Which bus type in a power flow study has both voltage magnitude and angle specified as the slack (reference) bus?

Accepted Answer

Vδ bus (swing bus)

Answer

The slack (swing or Vδ) bus has fixed voltage magnitude and angle (usually 1.0∠0°) and absorbs the system's power imbalance.

Question 2

What is the main advantage of high-voltage DC (HVDC) transmission over AC transmission for very long distances?

Accepted Answer

No reactive power losses and no skin effect over long distances

Answer

HVDC has no reactive power losses, no charging current, no skin effect, and no stability limit over distance, making it efficient for bulk long-distance transmission.

Question 3

An underground cable has significantly higher capacitance per unit length than an overhead line. What operational problem does this create for long AC cables?

Accepted Answer

Excessive charging current that can exceed the cable's thermal rating

Answer

The high capacitance generates large charging currents that can occupy most of the cable's thermal capacity before any load current is even delivered.

Question 4

In a power system protection scheme, what is the purpose of a 'zone of protection'?

Accepted Answer

To identify the section of the system that a specific relay is responsible for isolating during faults

Answer

A protection zone defines the electrical boundary within which a relay detects faults and initiates breaker tripping to isolate only the faulted section.

Question 5

What is the purpose of a power system stabilizer (PSS) installed on a synchronous generator excitation system?

Accepted Answer

Damp low-frequency electromechanical oscillations to improve small-signal stability

Answer

A PSS adds a supplementary signal to the voltage regulator to provide damping torque, suppressing rotor oscillations (typically 0.1–2 Hz) that can destabilize interconnected systems.

BEE - Bachelor of Electrical Engineering Practice Test

BEE - Bachelor of Electrical Engineering Practice Test

BEE Power Systems Engineering 4