BEE Bachelor of Electrical Engineering Power Systems Engineering Questions and Answers Flashcards

What is the main advantage of HVDC transmission over HVAC for very long distance bulk power transfer?

Answer: Lower transmission losses due to absence of reactive power losses

HVDC eliminates reactive power losses and has lower resistive losses per unit length, making it more efficient for long-distance transmission.

A power system has a total spinning reserve of 500 MW. If the largest online generating unit is rated at 600 MW, what reliability concern exists?

Answer: The system cannot cover the loss of its largest unit

Spinning reserve of 500 MW is insufficient to cover the 600 MW loss from the largest unit trip, violating the N-1 contingency criterion.

In symmetrical component analysis, the zero-sequence impedance of a delta-connected transformer winding is considered to be what?

Answer: Infinite, since zero-sequence currents cannot flow in a delta winding

A delta winding presents infinite impedance to external zero-sequence currents because there is no neutral return path.

What is the typical per-unit reactance range for a large power transformer used in a 500 kV transmission system?

Answer: 0.08 to 0.15 per unit

Large EHV power transformers typically have leakage reactance in the range of 0.08 to 0.15 per unit on their own MVA base.

During a load flow analysis using the Newton-Raphson method, PQ buses have which quantities specified?

Answer: Real power and reactive power

At PQ (load) buses, both real power P and reactive power Q are specified, while voltage magnitude and angle are calculated.

What phenomenon causes voltage collapse in a heavily loaded power system?

Answer: Inability of the system to meet reactive power demand as load increases beyond the nose curve limit

Voltage collapse occurs when the system cannot supply sufficient reactive power to maintain voltage as load approaches the maximum power transfer point on the PV curve.