Which statement correctly describes corona?

• A. It occurs only in DC
• B. A phenomenon around high-voltage conductors due to ionization of surrounding air
• C. It is a property of insulating oil
• D. It prevents arcing

Answer: (B)

Corona is the ionization of the air surrounding a high‑voltage conductor caused by a strong electric field. When the field around the conductor is high enough, electrons are ripped from air molecules, creating a small plasma region that glows, can produce ozone, and may cause audible noise. This effect isn’t limited to DC; it occurs in high‑voltage systems with AC or DC fields, especially at sharp points or irregularities where the field concentrates. It isn’t a property of insulating oil, and it doesn’t prevent arcing—if anything, corona indicates stress in the insulation and can contribute to deterioration and eventual arcing. So the statement describing corona as a phenomenon around high‑voltage conductors due to ionization of surrounding air is the accurate description.