BEE Power System 4

Question 1

What is corona discharge in transmission lines, and what is its primary cause?

Accepted Answer

Ionization of air around conductors when electric field stress exceeds air's dielectric strength

Answer

When the electric field gradient at the conductor surface exceeds approximately 30 kV/cm (peak), air molecules ionize producing visible glow, hissing, and power loss.

Question 2

The symmetrical components method decomposes an unbalanced three-phase phasor set into:

Accepted Answer

Positive, negative, and zero sequence components

Answer

Fortescue's theorem shows any unbalanced three-phase system equals the superposition of positive-sequence, negative-sequence, and zero-sequence balanced phasor sets.

Question 3

A 345-kV transmission line uses bundled conductors primarily to:

Accepted Answer

Reduce line inductance and increase current-carrying capacity while reducing corona

Answer

Bundling reduces the conductor's geometric mean radius effect on inductance, lowers surface electric field gradient to reduce corona, and increases thermal rating.

Question 4

What is the purpose of a Buchholz relay in a power transformer?

Accepted Answer

To detect internal faults by sensing gas and oil surge inside the conservator tank

Answer

A Buchholz relay detects gas generated by incipient internal faults (arcing or overheating) and oil surges from sudden severe faults, triggering alarms or trips.

Question 5

In power system economic dispatch, the criterion for optimal allocation of load among generators is:

Accepted Answer

Incremental cost of generation is equal across all committed units

Answer

The equal incremental cost criterion (lambda dispatch) minimizes total fuel cost by equating the marginal (incremental) cost λ across all generating units.

BEE - Bachelor of Electrical Engineering Practice Test

BEE - Bachelor of Electrical Engineering Practice Test

BEE Power System 4