I am now learning about corona treatment for my research on surface treatment. To understand the basic, i studied electrical discharge in gases. Though i understood about glow, arc and corona discharge, the difference in the definition is in question. Can any one clarify about the difference, especially how the corona is different from Arc discharge.
There is actually a very nice discussion on the distinction between glow and arc discharges following the link below:
http://physics.stackexchange.com/questions/116907/whats-the-relationship-between-glow-and-arc-discharge
I agree with Dustin about the discussion. It's very interesting. I just summarizes that an arc discharge is characterized by a lower voltage than a glow discharge, but has a strong current. Moreover, an electric arc relies on thermionic emission of electrons from the electrodes supporting the arc, while for a glow discharge most charge carriers are produced by secondary electron emission.
Furthermore, the corona discharge occurs at relatively high gas pressures (e.g. at atmospheric pressure) in an electric field which is strongly non-uniform (for example by placing a thin wire inside a metal cylinder having a radius much larger than the wire). The electric field is sufficiently high to cause the ionization of the gas surrounding the wire, but not high enough to cause electrical breakdown or arcing to nearby conductor.
For simplicity:
Take the example of Lightning. It is an arc discharge with rather short duration and high power density. Thease are mainly used in a more controlled way for example for welding, certain types of lamps, high voltage circuit breakers.
Arcs with duration ~ microsecond range are usually called sparks. Even shorter discharges may be created which in fact stop before they are completed in to arcs. These are also called transient discharges and have typical time duration ~ nanoseconds.
There are two methods to create these discharges.
1st method:
A dielectric layer can cover one or two of the electrodes in the discharge gap. At a sufficiently high voltage between the electrodes the discharge starts with the incorporation of gas. It spreads out until it reaches the electrodes but at the dielectric it builds up a space charge that cancel the applied electric field. At that moment the discharge stops. This discharge is usually called dielectric barrier discharge.
2nd method:
One can use an asymmetric electrode pair. Then the discharge develops in the high field region near the sharp electrode and it moves out towards the cathode. Here, there are two possibilities to avoid the transition in to an arc.
First the voltage can be made low enough to stop the spreading of the discharge somewhere before the cathode is reached.
OR Corona discharge
One can stop or lower the voltage when the cathode is reached. In the second way more energy can be put on to the discharge but it is more difficult to make the power supply. This type of discharge is called corona. It is a positive corona when the electrode with the strongest curvature is connected to the positive output of the power supply and a negative corona when this electrode is connected to the negative terminal of the power supply.
In corona discharges at relatively low voltages the discharge stops itself due to the build up of space charge near the sharp electrode. This space charge then disappears due to diffusion and recombination and a new discharge pulse appears. This is the self-repetitive corona and it occurs in the positive and in the negative case.
You may go through literature for more basic understanding. Good luck.
According to Townsend Characteristics (1879) , you can see that current in corona discharge is very very less then glow discharge. Current in arc discharge is maximum. Secondly, both arc discharge and abnormal glow discharge has drooping characteristics. Hence, if you increase current in a discharge, you move from dark discharge to arc discharge via corona and glow discharge.
According to Townsend Characteristics (1879) , you can see that current in corona discharge is very very less then glow discharge. Current in arc discharge is maximum. Secondly, both arc discharge and abnormal glow discharge has drooping characteristics. Hence, if you increase current in a discharge, you move from dark discharge to arc discharge via corona and glow discharge.
According to Townsend Characteristics (1879) , you can see that current in corona discharge is very very less then glow discharge. Current in arc discharge is maximum. Secondly, both arc discharge and abnormal glow discharge has drooping characteristics. Hence, if you increase current in a discharge, you move from dark discharge to arc discharge via corona and glow discharge.
I hope you do not mind if I ask a question related to this topic? There is an atmospheric pressure load (coaxial cylinder and copper wire as main electrode) which high voltage pulses by a Linear transformer driver (LTD) has been released to it. I think a kind of corona discharge will happen in atmospheric load after applying high voltage pulses. Discharge is happening after breakdown by high potential electrode. Question: Why if we release two continuous voltage pulse (50ns, 15kV pulse and then after 100ns another 50ns, 15kV pulse), The peak of discharge current in the first pulse is almost twice than 2nd one? and if we increase the distance between pulses like as (50ns, 15kV pulse then after 1ms another 50ns, 15kV) the peak of discharge current in two pulses are same as each other. Can anyone explain the relation between time and discharge current in this kind of discharge?Why when distance between pulses are far, the discharge currents have same peak?
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science