kilovolt
Voltageexact by definition
The kilovolt is one thousand volts. It is the unit of transmission and distribution engineering, of X-ray tube settings, and of ignition and insulation testing, where distribution feeders run at a few kilovolts and long-haul lines at hundreds. The factor of 1000 is exact, being an SI prefix.
Watch out: High-voltage ratings are quoted several different ways: RMS versus peak, phase-to-phase versus phase-to-ground, and continuous versus impulse withstand. A bare kilovolt figure on a nameplate is not enough to compare two pieces of equipment.
| 1 | 1,000 |
About the kilovolt
The kilovolt appears in daily life mostly as a spark. Dry air breaks down at roughly 3 kV per millimetre, so the length of a spark reads out the voltage that made it: the snap from a doorknob after walking on carpet is 5 to 15 kV across a few millimetres, and a car ignition coil fires its plug gap with tens of kilovolts. Those shocks are harmless despite the impressive figure because the charge behind them is microcoulombs, a reminder that volts alone are not a hazard rating.
The professional home of the unit is the grid, and the reason transmission runs at hundreds of kilovolts is one line of the site's power solvers. For a fixed delivery , raising the voltage tenfold cuts the current tenfold, and resistive line loss then falls a hundredfold. Every transformer between a 500 kV line and a 120 or 230 V outlet is spending that arithmetic in reverse. The record for the trade is China's Changji to Guquan link, which moves power at ±1100 kV over roughly 3300 km, the highest transmission voltage in commercial service anywhere.
In an X-ray room the kilovolt turns directly into photon energy: electrons falling through 80 kV strike the anode at 80 keV, so the tube's kV setting is literally the energy of the hardest photon in the beam, a correspondence the electron volt entries on this site carry from the other side.