Corona is partial breakdown of air next to a high-voltage conductor where the surface field exceeds about 30 kV/cm at sea level, especially at sharp points, burrs and small-diameter wires. It produces a hiss or crackle, ozone, radio interference and power loss, and gets worse in rain, fog and at altitude. Transmission lines use bundled conductors and large, smooth fittings with grading rings to keep surface stress below corona onset.
You can hear the corona on the 400 kV in this fog, sounds like frying bacon, but the UV camera only lights up at the damaged spacer.
Line crews use UV cameras to see corona in daylight; a bright spot on a fitting usually means a missing or badly fitted corona ring.
Also heard as
- corona discharge
Related terms
Partial discharge
Tiny discharge in a void, on a surface or at a sharp edge that never spans the whole insulation, an early sign of decay.
Flashover
Disruptive discharge over or around insulation that creates a short circuit through the air.
Tracking
Conductive carbon trail that leakage arcs through dirt and moisture gradually burn across an insulating surface.