coronaontlading

Coronaontlading, or corona discharge, describes a partial electrical breakdown of the insulating medium around a conductor carrying high voltage. It occurs when the local electric field is strong enough to ionize surrounding gas molecules but not so strong as to create a sustained arc. The phenomenon is common around sharp conductors, points, or stressed surfaces, and is frequently observed in high-voltage equipment such as power lines, transformers, insulators, and bushings.

The discharge produces a faint glow, often blue or violet, and can be accompanied by a hissing or crackling sound. It also generates ozone and other reactive species, and can cause energy losses, radio interference, and gradual chemical aging of insulation with long-term exposure. Corona is more pronounced at higher field concentrations, rough surfaces, or contaminants, and can occur with both alternating and direct current.

Corona must be distinguished from arcing or complete breakdown. In corona, no continuous conductive path forms across the gap; ionization remains localized near the surface or around sharp edges. Engineers monitor corona using indicators such as corona inception voltage, corona extinction voltage, UV imaging, acoustic sensors, and measurements of ozone or related byproducts.

Prevention and design strategies aim to minimize high-field concentrations. These include increasing conductor diameter or smoothing surfaces, adding corona rings or grading devices, improving insulation spacing, encapsulation, and controlling environmental conditions to reduce ionization. Standards define acceptable corona levels to ensure reliability and limit insulation aging in high-voltage systems.