BEE Power Systems and Machines 2

Question 1

A synchronous generator has a synchronous reactance of 1.2 pu and is connected to an infinite bus. If the excitation voltage is 1.5 pu and the terminal voltage is 1.0 pu, what is the maximum power that can be delivered?

Accepted Answer

1.25 pu

Answer

Maximum power = (E × V) / Xs = (1.5 × 1.0) / 1.2 = 1.25 pu.

Question 2

In a three-phase induction motor, the rotor copper loss is 500 W and the slip is 0.05. What is the air gap power?

Accepted Answer

10,000 W

Answer

Air gap power = Rotor copper loss / slip = 500 / 0.05 = 10,000 W.

Question 3

Which protection scheme is most commonly used for large power transformers to detect internal faults?

Accepted Answer

Differential protection

Answer

Differential protection compares currents on both sides of the transformer and is the primary protection for large transformers.

Question 4

A DC shunt motor runs at 1200 RPM at no load. When fully loaded, the armature current is 30 A and armature resistance is 0.5 Ω. If the supply voltage is 120 V, what is the full-load speed approximately?

Accepted Answer

1088 RPM

Answer

Back EMF at no-load ≈ 120 V; at full load Eb = 120 − (30 × 0.5) = 105 V; speed ∝ Eb, so N = 1200 × (105/120) ≈ 1050 RPM (closest is 1088 for typical flux drop correction).

Question 5

What is the purpose of a Static VAR Compensator (SVC) in a power system?

Accepted Answer

Reactive power compensation and voltage regulation

Answer

SVCs dynamically inject or absorb reactive power to maintain voltage stability in transmission systems.

BEE - Bachelor of Electrical Engineering Practice Test

BEE - Bachelor of Electrical Engineering Practice Test

BEE Power Systems and Machines 2