Corona refers to the ionization of air that occurs around an electrical conductor when it is subjected to a high-voltage electric field. This effect produces a faint glow or discharge and may generate heat, audible noise, and electromagnetic interference in high-voltage systems.
In electrical engineering, corona describes a localized discharge phenomenon caused by ionization of air molecules surrounding a conductor. When the electric field intensity exceeds the dielectric strength of air, free electrons collide with neutral molecules, creating ions and photons that emit visible light. While corona discharge may appear faint, it releases energy in the form of heat, sound, and radiation, which can cause measurable power loss and degrade insulation over time.
Corona is primarily a concern in high-voltage power systems such as transmission lines, substations, and large-scale electrical distribution networks. Factors influencing corona include conductor surface roughness, geometry, operating voltage, and the type of surrounding medium. Smooth, polished, and properly insulated conductors are less prone to corona formation, while damaged or uneven surfaces increase discharge intensity. The phenomenon can also lead to radio interference and partial discharges that affect sensitive electronic equipment nearby.
In industrial and commercial cable design, corona is mitigated through the use of high-quality insulation materials such as cross-linked polyethylene (XLPE) or fluoropolymers. These materials provide strong dielectric strength and resist ionization under high electric stress. Although corona rarely affects low-voltage systems like AV, data, or control cables, understanding it is essential for ensuring insulation integrity and system reliability in high-voltage applications.
Corona discharge characteristics and dielectric testing are defined by standards from IEEE (Institute of Electrical and Electronics Engineers), ASTM (American Society for Testing and Materials), and IEC (International Electrotechnical Commission). These organizations establish testing procedures, performance thresholds, and safety limits for high-voltage conductors and insulation systems.
The phenomenon of corona discharge was first observed in the late 19th century with the advent of high-voltage transmission systems. Engineers noted the bluish glow and faint hissing sound emitted from energized power lines, leading to decades of study on ionization and dielectric breakdown. As electrical networks expanded, minimizing corona became a key objective in improving efficiency, reducing interference, and extending cable lifespan.