Power Systems Engineering Flashcards
7 cards from real BEE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Power Systems Engineering flashcards as text
In an economic dispatch problem, what condition must be satisfied for optimal allocation of real power generation among multiple units?
Answer: The incremental cost (λ) of each online unit must be equal
Economic dispatch requires that the incremental fuel cost (∂F/∂P) be equal for all online generators, ensuring no cost savings are possible by shifting load between units.
What is the purpose of a tap-changer on a power transformer in a transmission substation?
Answer: Regulate the secondary voltage by adjusting the turns ratio while energized
An on-load tap-changer (OLTC) adjusts the transformer turns ratio in small steps while the transformer is energized, maintaining secondary voltage within acceptable limits.
In a radial distribution system, what is the primary disadvantage compared to a looped or meshed network?
Answer: A single fault isolates all downstream customers, resulting in longer outages
Radial feeders have a single supply path, so any fault or equipment failure between the source and load causes a complete outage for all downstream customers.
Which characteristic of a synchronous generator determines its ability to supply reactive power to the system and support voltage?
Answer: Excitation (field current) level
Increasing field excitation causes the generator to become over-excited, supplying reactive power (capacitive) to the system and boosting bus voltage.
What is the 'skin effect' in conductors carrying AC current, and how does it affect transmission line design?
Answer: Concentration of current toward the conductor surface, increasing effective resistance at higher frequencies
At AC (60 Hz), current density is highest at the conductor surface and decreases inward, raising effective resistance above the DC value and motivating stranded ACSR conductor designs.
In power systems, what is the difference between a 'bolted fault' and an 'arcing fault'?
Answer: A bolted fault has zero impedance at the fault point producing maximum current; an arcing fault has arc impedance that limits current
A bolted (solid) fault assumes zero fault impedance, giving the highest possible short-circuit current; arcing faults have arc resistance that reduces fault current below the bolted level.
A 60 Hz power system experiences a sudden loss of a large generating unit. Which control mechanism acts first to arrest the frequency decline?
Answer: Governor response providing primary frequency control within seconds
Governor (primary) response acts within 5–30 seconds using droop control to automatically increase output on remaining units and arrest frequency decline before AGC intervenes.