Corona vs. Arc
Corona vs. Arc
(OP)
Hello,
I am trying to wrap my mind around what conditions will result in corona discharge, and what will result in an arc.
Is it that, if the potential gradient is high enough, corona discharge will occur? If there happens to be conductive material within the ionized region, a sustained arc will occur?
I am trying to wrap my mind around what conditions will result in corona discharge, and what will result in an arc.
Is it that, if the potential gradient is high enough, corona discharge will occur? If there happens to be conductive material within the ionized region, a sustained arc will occur?






RE: Corona vs. Arc
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Corona vs. Arc
RE: Corona vs. Arc
In a free air arc, the electrical field strength ionizes the air between the conductors. In corona, the gradient of the electrical field ionizes the surrounding air and electrons are blasted off. The field gradient is steeper near a point than near a flat surface. Hence, the practice of using a greater surface radius to reduce or prevent corona.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Corona vs. Arc
In a corona you have ion flow. In an arc you have electron flow through the gas.
The ionization energy of most gasses is around 12 electron-volts (that is the energy imparted to an electron in moving through a field gradient of 12 volts). If the electron hits a molecule before it gains this energy it will lose energy in the collision without ionizing anything. Thus, higher pressure makes molecules closer together so it is more difficult to cause ionization.
Natural radiation or cosmic rays are supposed to create the initial ions and free electrons to allow a corona discharge to start.
RE: Corona vs. Arc
Arcing is a breakdown of the air when the voltage between two points exceeds the dielectric strength of air. Ionization of the air occurs, and a condutive path is formed.
So how does ionization occur from the arc? Is it a cascading effect similar to corona discharge? If so, what is the initial event that causes it?
RE: Corona vs. Arc
Our American cousins tend to use Corona and Partial Discharge interchangeably whereas in the UK we would reserve the term Corona for a partial disharge in the air (or gas) surrounding a conductor.
RE: Corona vs. Arc
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Corona vs. Arc