What is corona?

• A. A phenomenon around high-voltage conductors when the electric field ionizes the surrounding air, causing a partial electrical discharge
• B. A coating on insulation
• C. A unit of electrical resistance
• D. A method of grounding

Answer: (A)

Corona is the partial electrical discharge that happens around high-voltage conductors when the electric field is strong enough to ionize the surrounding air, but not to cause a full arc. In practice you’ll often notice a faint glow around sharp points or edges and may hear a soft crackling or see an ozone-like smell. It becomes more likely at higher voltages, with conductors that have sharp geometries, long spans, or surfaces that are moist or dirty, all of which intensify the surface electric field. Corona wastes energy, can cause radio interference, and over time may contribute to insulation aging due to ozone and chemical effects, so engineers design to minimize it by smoothing conductors, increasing conductor diameter, and keeping insulators clean and dry. It is not a coating on insulation, not a unit of resistance, and not a grounding method.