Theory of Corona, Discharge & Generation

Theory of Corona Formation:

Corona discharge is a process by which a current flows from an electrode with a high potential into a neutral fluid, usually air, by ionizingthat fluid so as to create a region of plasma around the electrode. The ions generated eventually pass charge to nearby areas of lower potential, or recombine to form neutral gas molecules.

Some ionization is always present in atmosphere due to cosmic rays, ultra violet radiation ,and radioactivity. There for normal(low voltage) voltage no any formation of corona, but at the point of high voltage(nearly 30kv) at which corona accrued is called Critical Disruptive Voltage (it is minimum phase to neutral voltage at which corona occurs).

When potential gradient is reach above 30kv per cm value the velocity of electron acquire by electron is sufficient to strike  a neutral molecules with enough force to produce more electron from it. This process is continue with potential gradient, the result of this corona occurs as a spark between conductor. it is called Visual Critical Voltage (it is minimum phase to neutral voltage at which corona glow appears around the conductor).

Photo of Corona Formation:

Large corona discharges (white) around conductors energized by a 1.05 million volt transformer in a U.S. NIST laboratory in 1941

Corona Discharge vs. UV Ozone Generation

Ultraviolet (UV) ozone generation

Ultraviolet lamps have been used for decades to generate ozone.  This lamp emits UV light at 185 nanometers (nm). Light is measured on a scale called an electromagnetic spectrum and its increments are referred to as nanometers. 

Air (usually ambient) is passed over an ultraviolet lamp, which splits oxygen (O₂) molecules in the gas. The resulting oxygen atoms (O^-), seeking stability, attach to other oxygen molecules (O₂), forming ozone (O₃).

Critical to CD ozone systems is proper air preparation. The gas feeding the ozone generator must be very dry (minimum -80 degrees F), because the presence of moisture affects ozone production and leads to the formation of nitric acid. Nitric acid is very corrosive to critical internal parts of a CD ozone generator, which can cause premature failure and will significantly increase the frequency of maintenance.

Advantages of Corona Discharge ozone generation

1. Corona discharge ozone generators can use oxygen preparation thereby doubling the ozone output per given volume vs. dry air
2. Can create a more pure form of ozone without creating other harmful or irritating gases if using dry air or oxygen as a feed gas
3. Can create high quantities of ozone (up to 100-lbs/day)

Disadvantages of UV ozone generation

1. Considerable more electrical energy is required to produce a given quantity of ozone by UV radiation than by corona discharge.
2. UV lamps solarize over time, requiring periodic replacement