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Transformers in power transmission
Intermediate
High voltage reduces line losses.
Stepping voltage up to 400 kV reduces the current and so I²R losses in lines; it's stepped down for use. For the same power, 10× voltage gives 100× less loss.
1 MW at 10 kV: 100 A, at 100 kV: 10 A.
Reason for AC grids.
In more detail
Power is transmitted at high voltage to reduce current and losses, since power loss is I²R. Transformers step the voltage up at generation and down near consumers.
Real-world uses
- Long-distance power lines operate at hundreds of kilovolts.
- Local distribution steps the voltage down to safe levels for homes.
- Power companies step up voltage to hundreds of kilovolts for transmission, which cuts current and reduces losses in the cables.
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Frequently asked questions
Why not transmit at low voltage?
Losses would be much higher because current would be larger for the same power.
Is high voltage dangerous?
Yes, which is why lines are high in the air and substations are fenced.
Why does high voltage reduce losses?
For the same power, a higher voltage needs less current, and losses depend on the square of the current.
Related topics in AC Circuits & EM Waves
LC oscillations · Parallel resonance · Filters · Three-phase power · Rectification and smoothing · Displacement current