Within the past year development has taken place at a feverish pace in Israel to bring the DayCor corona cameras to market. Dr's Malka and Pinhas Lindner, both chemical engineers, had an idea that they knew would have an application. They knew they could develop a "solar blind filter", a filter that would only transmit the ultraviolet "C" (UVc) band of wavelengths.

The sun radiates a lot of energy in many wavelengths toward the earth every day. By using an appropriate UV imager coupled to this "solar blind filter" on earth one can look at the sun and not see it, but strike a match 100's of yards away and see the lit match while looking at the sun.

The ozone layer surrounding the earth, which makes it possible for us to survive, absorbs the suns radiation in the UVc range preventing it from reaching the earth. The filter the Dr's Lindner developed can only see between 240 and 280 nm in the UVc range. The UVc band of wavelengths is inactive except for primarily man-made energy sources. How can we use this new technology?

Lighting:
These light sources include florescent lights (may look like a snowstorm), some high intensity spotlights (have a UVc beam ahead of them), some typically old incandescent bulbs give off a shower of UVc. UV why do I care? Well UVc may cause cataracts in human eyes, UVc does cause clothing and colored candy in stores exposed to florescent lights and some other lights to fade. The DayCor cameras can be used to inspect buildings for UVc sources to reduce damage to humans (premature gray hair?) and products.

High Voltage Electricity:
The electric utility transmission and distribution organization EPRI played a significant role in bringing the DayCor cameras into the USA and in funding developments of the DayCor cameras for use by utility personnel in troubleshooting electrical corona. Corona is caused by the high voltage electrical breakdown into the air surrounding a cable, insulator, or electric motor winding. The chemical reaction that results produces nitric acid, ozone, and ultraviolet light which the DayCor camera can see in the UVc 240 to 280 nm range during bright daylight due to its unique solar-blind filter. By using the DayCor camera the technician can identify specifically where the problem is on a tall transmission tower. Click here to see images generated with DayCor.

Certain conditions help to create corona such as sharp points (broken cable strands, icicles during winter), contamination on cable or bus conductors, connectors, and insulators from refinery soot, railroad dirt, ore mining and manufacturing, bird droppings, design of the insulator (insulators that don't self-clean when it rains), lineman connector practices such as a stub left out of connector, design of the connector such as sharp points or bolts protruding, vertical conductors ("bird caging" where the strands untwist), broken or surface fractured insulators (this may lead to distribution pole fires or outages), high humidity levels cause the air to become more conductive and a lack of rain means more contaminant build-up on insulators and conductors.

Corona on non-ceramic insulators may lead to rapid strain load capacity reduction and shear failure.

Electric motor high voltage winding insulation testing standards are that corona must be observed in a darkened room (requiring expensive minutes to wait for test technicians eyes to adjust to the darkness.) DayCor can see the corona during daylight or a future "NightCor" will immediately see the corona in a red-lighted room or inside a sealed electric motor immediately.

Corona produces light as discrete lines across a broad band of the ultraviolet and slightly into the visible but the corona signal is weak in comparison to the sun and can't be seen during daylight but it may be heard sometimes with the human ear and more frequently with an ultrasonic detector. The drawback to the ultrasonic detector is it can't see like a camera can. The ultrasonic detector may get you to the right pole but after you replace everything on the pole you may still have corona if it was a design problem or maybe it was something benign on a bolt where it wouldn't cause damage for 50 years but keeps the neighbors up at night.

Infrared cameras which sense temperature radiating from an object are widely used for utility predictive testing (current flow causes heat, unequal heat for the same current flow means there is a problem). But a corona camera senses the ultraviolet light produced by a (over) voltage problem. The infrared camera can't see a corona problem but the corona camera may see a problem the infrared camera couldn't, if the current flow in a conductor with broken strands is too low to cause heating you would not see a problem with an infrared camera but might see corona from the broken strands. The corona and infrared cameras are complementary technologies.

Corona can also occur in enclosed high voltage switchgear, the minimum voltage for corona is about 1,000 volts.

Some people question what corona is unacceptable. The current solar-blind corona cameras can see about a 20pC (picoCoulumb) discharge at a distance of 6 meters and about a 200 pC discharge at the typical field distance of 25 meters. Compare this to a new high quality test equipment specification of 2 to 5 pC partial discharge. Thus if you can image corona with a camera it should be fixed.

Corona discharge at high intensity may be heard by humans, other high voltage defect electro-magnetic radiation may cause radio/television interference (RFI/TVI).

Flame Detection:
The world of racing has used alcohol fuel for years in midgets and IRL/CART racing cars. Many people have seen the images recently of a driver after a crash running for the infield to roll in the grass to smother the invisible flames of an alcohol fire. Other drivers in midgets especially seem to get upside down and while hanging in there seat belts can't get them to unlatch and have died in the invisible flames.

The DayCor can see the UVc part of the alcohol flame warning the fire crew before they get to the car of the danger to the driver.

The DayCor can also see hydrogen flame and  rocket plumes.

Conclusion:
This is the beginning of another technology wave in imaging. The ultraviolet light that is emitted and used in processes around us for our purposes, sometimes can warn us of problems and potentially can harm us by injuring our eyes without knowing of the exposure. Store and factory workers are subjected to UVc daily for extended periods of time and a thin sheet of plastic (clear plastic report cover thickness coated to stop UV) can stop the UV from a florescent light reducing product damage due to UV.

About the author:

Dan Ninedorf, President/Sales Rep. of Ox Creek Energy Assoc Inc. of Montello, WI USA is a "DayCor" UVc camera Importer, North American Distributor, and an Upper Midwest USA Manufacturers Sales Rep. He can be contacted at 1-800-531-6232 or oxcreek@maqs.net where technology is our future at www.ox-creek-energy.com. 

The author wishes to thank Dr. Pinhas Lindner of Ofil, Ltd. of Nes Ziona, Israel for reviewing this article for accuracy.

Click here to see the images captured with the DayCor Camera

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