Generation, Transmission and Distribution of Electrical Power: 25 flashcards
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1. What is the fundamental energy conversion in a generator?
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Mechanical energy is converted into electrical energy using electromagnetic induction.
2. Why are power plants located near fuel or water sources rather than near cities?
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Generation is sited where fuel or water is available; transmission then carries power to distant consumers.
3. What is the main purpose of the transmission system?
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To carry bulk electrical power over long distances at high voltage.
4. Why does raising transmission voltage reduce line losses?
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For constant power, higher voltage means lower current, and $I^2R$ loss depends on current squared.
5. If transmission voltage is doubled for the same power, what happens to resistive line loss?
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The current halves, so the $I^2R$ loss drops to one quarter.
6. Name four typical transmission voltages used in practice.
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132 kV, 220 kV, 400 kV, and 765 kV.
7. What does a step-up transformer do at the sending end of a transmission line?
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It raises the generator voltage to the transmission voltage.
8. What does a step-down transformer at a substation do?
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It reduces transmission voltage to sub-transmission or primary distribution voltage (e.g., 33 kV or 11 kV).
9. What voltage does a distribution transformer supply to consumers?
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400 V three-phase or 230 V single-phase.
10. Why are transmission networks usually meshed?
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To provide multiple paths for power flow, improving reliability and stability.
11. Why are distribution networks mostly radial?
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They are designed for reach and service to many small loads, often with a single path.
12. What is primary distribution voltage typically?
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11 kV or 33 kV.
13. What is secondary distribution voltage typically?
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400 V three-phase / 230 V single-phase.
14. Why is three-phase AC standard for generation, transmission, and distribution?
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It saves conductor material, enables self-starting induction motors, and provides two voltage levels from one supply.
15. In a star connection, what is the relationship between line voltage and phase voltage?
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$V_L = \sqrt{3}V_{ph}$ and $I_L = I_{ph}$.
16. In a delta connection, what is the relationship between line current and phase current?
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$I_L = \sqrt{3}I_{ph}$ and $V_L = V_{ph}$.
17. How is overall system efficiency calculated across stages?
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It is the product of the efficiencies of each stage.
18. What are the two main types of transformer losses?
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Core (iron) losses and copper ($I^2R$) losses.
19. Why are protection zones designed around voltage levels?
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A fault at a higher voltage (e.g., feeder) affects many consumers, while a lower-voltage fault affects few, so protection must isolate appropriately.
20. What type of conductors are used for transmission lines?
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ACSR (Aluminium Conductor Steel Reinforced) conductors on tall towers with large clearances.
21. What is a single-line diagram used for?
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To represent the three-phase power system compactly for analysis.
22. What is the function of a tap changer on a transformer?
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To compensate for voltage variation along feeders by adjusting the transformer turns ratio.
23. What is the key difference in purpose between transmission and distribution?
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Transmission transfers bulk power over long distances; distribution delivers power to individual consumers.
24. Why can't generators directly produce 400 kV?
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Generators produce moderate voltages (11–25 kV); transformers are needed to step up to transmission voltage economically.
25. What is the trade-off of using very high transmission voltages?
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Higher voltages require taller towers, larger clearances, and more expensive transformers, so the choice is an economic balance.
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