Power Transmission — Flashcards & Quiz

Q1: Why is electrical power transmitted at high voltage over long distances?

Power loss in transmission lines is P = I²R, where I is current and R is line resistance. For a given power P = VI, higher voltage V means lower current I. Reducing current dramatically reduces power loss. Transmitting at 500 kV instead of 25 kV reduces current by factor of 20, reducing power loss by factor of 400.

Q2: Describe the stages of electrical power distribution from power station to home.

Power is generated at 10-25 kV. Step-up transformers increase voltage to 500 kV for long-distance transmission (minimizing losses). Regional substations step down to 66 kV. Local substations step down to 11 kV. Finally, pole transformers step down to 230 V for homes. Each step balances efficiency, safety, and cost.

Q3: How do transmission line losses depend on current and resistance?

Power loss is Ploss = I²R, where I is current in the line and R is line resistance. Doubling current quadruples power loss. Resistance R = ρL/A increases with length L and decreases with cross-sectional area A. Thicker conductors and shorter distances reduce losses, but are expensive. High-voltage transmission is more cost-effective.

Q1: Transmitting electrical power at high voltage reduces power loss in transmission lines because power loss is proportional to current squared.

Answer: TRUE

TRUE. Power loss in lines is Ploss = I²R. For constant transmitted power P = VI, higher voltage means lower current. Since loss depends on I², reducing current by increasing voltage dramatically reduces losses. This is why transmission uses hundreds of kilovolts.

Q2: Doubling the transmission voltage for a given power halves the current and reduces line losses to one-quarter of the original value.

Answer: TRUE

TRUE. If V doubles, I halves (since P = VI is constant). Power loss Ploss = I²R becomes (I/2)²R = I²R/4, one-quarter of original. This quadratic relationship explains why high-voltage transmission is so effective at reducing losses.

Q3: Australian household power is supplied at 230 volts, which is the same voltage at which electricity is transmitted over long distances.

Answer: FALSE

FALSE. Households receive 230 V, but long-distance transmission uses much higher voltages (up to 500 kV in Australia). High voltage minimizes transmission losses (I²R). Step-down transformers progressively reduce voltage from 500 kV to 230 V through substations.