12: Electromagnetic Induction

12.3 Transmission of Electrical Power

Infra-red camera image of power lines:

Transmission of Electrical Power

Power Loss in Transmission Cables

Rate of energy loss in transmission lines is determined by the rms current and the resistance of the wires:

Also remember that the wire resistance is given by...

P = I2RP = Power loss (W)I = rms current (A)R = Total wire resistance (Ω)

R = ρl A

ρ = Resistivity (Ωm)l = Total length of both wires (m)A = CS Area of wire (m2)

Example

Electricity is generated in a power station at 30kV and 400W of power. The voltage is stepped up to 105kV for transmission and then down to 220V in a town. If the wires between the power station and town have a total resistance of 5Ω...

a. What current flows in the wires?

b. How much power is lost in the cables?

c. What is this as a percentage of the total power?

d. If the voltage were stepped up to 195kV, what would be the new percentage of power lost?

Power Lines and Your Health

Read the article form Harvard medical School and make notes / highlight text.

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