Have you ever seen corona? Have you ever been out on a dark, pitch black night and looked up at an electrical pole and noticed a "blue glow"? This is corona.
Have you ever been aboard a ship or sailing vessel and noticed a blue glow atop the mast? This is also corona, sometimes referred to as St. Elmo's Fire.
However, when corona reaches the 300-400 nanometer range within the ultraviolet light spectrum, corona may be seen in the visual spectrum provided there is no interference from background light.
More and more of you now know about corona. But what you have not learned to do is visualize corona or ionization. Why? Because to you and others, what you do not see, is not a problem. You have no mental picture, you have no experience with corona cameras, and we do not see ultraviolet light, so we really have nothing to relate the phenomenon known as "corona" to.
Corona can be a faint glow adjacent to the surface of an electrical conductor at high voltage. It is the result of ionized gases due to high electrical stress. Stress can be caused by contamination, poor insulation values, design defects and/or poor installation. Corona is air, with no ground and therefore no heat buildup. No ground, no heat and no IR signature. This is where the voltage is less than 240 kV.
By going to the bottom of the article and clicking on the link (Figure 1.), you will be taken to my website, where you will again, go to the bottom of the page and click on the "Play Video Link".
Even though the mpeg is from an indoor substation, you can see the corona activity at the corner of the connector and all the corona spray accumulated around it.
Below is picture of an expansion joint (Figure 2.) inside a 550kV Substation as through the corona camera lense.
Now that you have seen it, you can now see how the corona spray resembles those old dime store sparklers we used to set off as kids on the Fourth of July. Sparks are everywhere. Can you imagine reaching into an electrical panel even slightly? The chances of not getting bit are very slim.
You can also imagine how the "white powdery residue" accumulates several inches away from the electrical lugs and connections.
In my Level I Classes and the UST Ultrasound Workshops we discuss corona at length. What are the byproducts of corona?

Do you know?

Here is a list:

All are the results of corona activity.
Corona is not detectable by corona cameras under 3500kV.

Figure 2. Expansion Joint 550kV Substation, as seen with corona camera.

It's not too late to come to the class in Atlanta, October 27-29th. Call me for details or go on-line.
I will also be in Long Beach, California next year at the NETA Conference delivering papers on this very subject. See you there. 
Jim Hall, President
Ultra-Sound Technologies