BEE Power System 5

Question 1

In a high-voltage DC (HVDC) transmission system, what type of converter is used at the rectifier station?

Accepted Answer

Thyristor-based line-commutated converter (LCC) or voltage-source converter (VSC)

Answer

HVDC systems use LCC (thyristor bridge) for classical HVDC or VSC (IGBT-based) for modern HVDC, both converting AC to controlled DC for long-distance transmission.

Question 2

What does the X/R ratio of a power system bus indicate?

Accepted Answer

The relative magnitudes of system reactance to resistance, affecting fault current angle and protection

Answer

A high X/R ratio means fault currents are nearly purely reactive, which affects DC offset in fault current and the design of protective relay settings.

Question 3

What is the primary function of an underfrequency load shedding (UFLS) scheme?

Accepted Answer

To automatically drop blocks of load to arrest frequency decline and prevent system collapse

Answer

UFLS automatically disconnects prescheduled load blocks when frequency falls below set thresholds, restoring generation-load balance before frequency collapses.

Question 4

The Gauss-Seidel load flow method converges slowly because:

Accepted Answer

It updates bus voltages sequentially using the latest available values, leading to linear convergence

Answer

Sequential updating of bus voltages one at a time gives only linear (first-order) convergence, requiring many iterations compared to Newton-Raphson's quadratic convergence.

Question 5

A distance relay measures which quantity to determine if a fault is within its protective zone?

Accepted Answer

Apparent impedance seen at the relay location

Answer

A distance relay computes Z = V/I at its terminal; if the calculated impedance falls within the relay's impedance zone on the R-X diagram, it operates.

BEE - Bachelor of Electrical Engineering Practice Test

BEE - Bachelor of Electrical Engineering Practice Test

BEE Power System 5