Question

32-2 Power transmission

Why do power transmission lines use high voltage? An electric power station sends out a fixed 40 MW of power. The cross-country power line wires from the power station to the city has a total resistance of 7 Ω. Assume the circuit consists of the power station, the line wire (resistor), the city (resistor), and a storage battery.

Find the power loss (in kW) in the wires using a line voltage of

a) 500 kV

b) 20 kV

All are rms values. Eq. (32.40), (32.36)

Answer 1

given source power of the power station is 40 MW

a) For 500 kV, the current through the wire is source power divided the line voltage

The power loss is

b) For 20 kV,, the current through the wire is source power divided the line voltage

The power loss is

Clearly, the power loss using high voltage is less!