Power Systems — Distribution
Three-phase power, transformers, why transmission is high-voltage, feeder voltage drop, and PF penalties.
Between the generator and your outlet sits a machine the size of a continent. Its design reduces to a few formulas: three-phase bookkeeping, transformer ratios, and an endless war against I²R — losses that grow with the square of current.
- 01 Three-phase power Three sine waves, 120° apart: their power sum is constant (no flicker), conductors share return paths (less copper), and motors start themselves. The…
- 02 Transformers — the reason AC won Two coils on shared iron: voltage scales with the turns ratio, current scales inversely, power (almost) passes through untouched. This single device is why…
- 03 Why transmission is high-voltage Line loss is I²R — current squared. Move the same power at 20× the voltage and current drops 20×, so losses drop 400×. That arithmetic, not convenience, is why…
- 04 Feeder voltage drop Copper isn't free and neither is distance: a long feeder drops voltage on the way. Codes cap the drop (≈3% for branches). A 240 V single-phase feeder, 60 m…
- 05 The power-factor penalty A poor PF means the wires carry current that does no work — and the utility pays for those I²R losses, so they bill you for it. The current saved by correcting…