SDVeteranOB
Corona Technology Course Instructor & Co-Developer
Level II Infrared Technician
Electrical Power Engineering Tech over 45 years of high voltage experience over 20 years of IR-UV-Visible camera experience
- answers your question's series -
The first question typically is -
What Will Corona See That Infrared Will Not ?
--- Arrow keys to advance slide. --
Copyright 2013 Ox Creek Energy Associates Inc

Corona Camera vs Infrared Camera










Corona Camera vs Infrared Camera
Infrared Camera
Daylight corona camera 
Senses light photons in the range 260-300nm, subject to reflections on water droplets in
 the air.

Electrical - Typically long-wave 8-12 micron (8,000-12,000nm)
Senses heat radiated from objects, subject to reflections from sun, shiny surfaces or holes.
Corona (ultraviolet photon detector image) overlaid onto color visible image, in “real time”.
The corona detector is slaved to the Visible camera typically
 thru at least part of the visible cameras “zoom” range.

Corona cameras ”default field of view” is typically at 100mm, and “zoom” from there.

Infrared image & may have visible image camera.
Infrared cameras do not “zoom”, they focus at a “field of view (FOV)”, then can be adjusted to focus at a different
“distance” with same FOV.
Infrared cameras “default field of view” is typically 35 to 50 mm lens, change lens to “focus at a smaller or larger “field of view”. Lens can cost thousands of dollars..


Corona Camera vs Infrared Camera
Lets consider these statements.

A graph can show the light emission spectrum.

No single sensor can see all of the spectrum.

The Corona Camera sensor is much more sensitive then current
Infrared Camera sensors. With a daylight corona camera I have seen the indication of corona across a mountain valley one mile away.

Everything has a temperature and for our purposes can be seen with an infrared camera.

Long-wave infrared is the choice for outdoor, low-emissivity hardware that electrical inspectors look at, due to less solar reflection which causes erroneous temperature readings.

Companies may select an emissivity standard to use for all infrared scans, typically between 0.85 and 0.95 depending upon the materials they look at and personal choice.






Corona Camera vs Infrared Camera
Lets consider these statements.
Some light sources emit across many wavelengths at different intensities at different times (the sun).
Chemical sources block light in only discrete wavelengths, that are called absorption bands, this can be used to locate gas leaks and identify specific chemicals, such as SF6 gas leaks. A normal infrared camera is not filtered and cannot isolate wavelengths to see these gases because other wavelengths “overpower” the missing signal in the absorption band.
Day-light corona cameras development was enabled because the ozone layer surrounding the earth absorbs the sun light in the 260-300nm wavelengths making these wavelengths on earth pitch black around the clock, except for mostly manmade light sources, such as fire, florescent lights, corona, arcing, arc welding, which all change the state of the nitrogen in the air or emit photons visible in the
260-300 nm band.
Daylight corona cameras were developed to enable scanning of remote electric transmission lines from helicopters, and because a helicopter can scan power lines over crop fields or urban areas without disruption, getting stuck in mud, and much quicker, a rough number can be 90 towers a day on flat land by helicopter versus maybe10 from a vehicle. Scanning from a helo does not replace the need to follow-up from the ground, to do in-plant surveys, R&D, distribution voltage, and more.

Corona Camera vs Infrared Camera

Seeing corona is the first step, which requires a quality lowlight or day-light corona camera dependent upon application.

Understanding the probable causes of corona in that situation
(materials, shape, voltage, …) is the next step. The answer to the question OK You found corona, what does it mean.

From experience deciding if that corona is detrimental and what repair priority or monitoring is needed.

Corona can produce excessive noise resulting in complaints.

Arcing can produce radio/tv interference (RFI) for a mile around that neither infrared or ultrasound can locate. But a daylight corona camera can see from nearly a mile away.

Micro-Arcing (inside connectors) can occur that causes RFI and corona that infrared cannot image.

Corona Camera vs Infrared Camera
S o a corona camera images the ultraviolet light emitted during the change in state of nitrogen in the air due to electrical field intensity or during the initial burning of vegetation.
Electric current flow changes the temperature of electrical equipment and electronic devices.
The electric field intensity around energized equipment can exceed the breakdown strength of air, when this happens corona starts.
S o an infrared camera images the temperature of objects.
The exact voltage to cause corona is dependent upon the shape of the object, the object's proximity to other secondary objects, there shape, applied voltage and polarity, the altitude, wind speed, ambient temperature, humidity -primarily when condensing, when it can act like stepping stones in creating a flashover path, the same occurs when a contaminated object is drying unevenly.
When the temperature of electric equipment exceeds 20 to 50F above ambient temperature (based upon standards) or when compared to the temperature of other phases in the circuit, preferred load is 40% conductor capacity or higher at less then 10mph wind.
So it can be said that an infrared camera displays the temperature of object(s) due to current flow in those object(s.)
So it can be said that a corona camera displays when the relative voltage (electric field intensity) on an object exceeds the relative breakdown strength of air.

Corona Camera vs Infrared Camera

The MultiCAM developed by CSIR (now built by UViRCO Technologies (Pty) Ltd) is the first
-and only- camera to combine the ability to simultaneously image corona and infrared and visible.

This is done by precisely overlaying two images -one corona image overlaid onto one infrared image -of the exact same Field of
View (FOV)- or with the push of one button corona onto a visible image. This is done in real time with a NTSC video output for recording and image storage.







Corona Camera vs Infrared Camera
So at any time the MultiCAM has 3 image's or 3 video streams available for viewing.
Using one push button the operator selects corona overlaid onto infrared or by pushing the button corona overlaid onto visible.
Corona overlaid onto visible is common to all daylight corona cameras.
Scanning with corona overlaid onto infrared should find all problems.
Corona color, selecting a color not in the infrared palette or not blending into the clouds is better for contrast, easier to spot problems.
Scan with corona gain at maximum until an object of interest is located. Then adjust the gain for the best image to tell the story.

Corona Camera vs Infrared Camera

Corona (red blob's) overlaid onto infrared image

Corona overlaid onto visible image

Corona Camera vs Infrared Camera

Corona at maximum gain on infrared

Corona at maximum gain on visible

Corona Camera vs Infrared Camera
In 2000,
I n late 1985,
The CoroCAM IV+ introduced daylight corona cameras.
The CoroCAM 504 became the world's most sensitive corona camera, with it's patented exclusive menu-selected low-light & daylight corona observing capability.

Corona Camera vs Infrared Camera

Corona on generator winding bus bar.

Corona on post insulator cement.

Corona creates porosity in cement, moisture wicks inside, insulator explodes when energized.

Corona Camera vs Infrared Camera

Corona on defective
NCI insulator & tree

Corona on defective
NCI insulator.

Corona Camera vs Infrared Camera

Infrared camera see's isolated “hot spots” in burnt areas.

Corona camera see's direction of fire – new burn.

Corona Camera vs Infrared Camera

Corona on a sprinkler line hangar.

Corona on a cotter pin.

Corona (nitric acid) particulate was falling on enclosures and other insulators below, flash-over hazard.

Corona Camera vs Infrared Camera

Corona on / between conductors can
 be caused by a conductor too small for altitude and/or voltage, new or scuffed conductor, or conductor spacing.

Corona in the center of all insulator strings is bad, and NCI corona is usually over an arcing spot.
NCI corona will kill an insulator with an expected life-span of 80 years, maybe in 10 years.





Corona Camera vs Infrared Camera
This shows three corona problems:

This shows corona on an: frayed wire stub below pistol -grip connector
Over-length bolts on saddle.
NCI insulator to hardware interface, this will destroy the insulator, typically within 10 years.



 undersize conductor, conductor diameter too small for the applied voltage, conductor dragged over stones, new conductor with “die grease”.

Corona Camera vs Infrared Camera
During training a corona
During infrared training, technician must learn what
4 days Level 1, can interfere with getting a reliable image, reading of corona.
4 days Level 2
The Corona Technology Course provides this information in video.
The ESKOM “Corona” manual provides a text.
the technician learns theory, what interferes with imaging and to get a best thermal image from the camera in use.
Corona Camera training is also a necessity to understand camera operation and corona.
Specific camera training and refresher courses are often required annually by the certifying agent.

Corona Camera vs Infrared Camera
In the field -
The corona count is somewhat immaterial, but not to be ignored.
A high corona count can indicate arcing,
A corona blob constantly in one spot can indicate reflection or arcing.
A corona blob suspended over the top of one spot is likely internal arcing, this can occur on NCI, substation PT's,..Not able to image with infrared.
The location of the corona is what matters,
If the corona is on an insulator material vs on hardware.
Is the corona causing a contamination build-up on an insulator, flashover potential.
On metal that doesn't get washed by rain, corona produces nitric acid.
This is written to cover corona in substations, transmission lines, switchgear, HV motors or generators.

SDVeteranOB
3120 S Business Dr, Sheboygan, WI 53081 USA
Tel/Cell: 800-531-6232 Email: cameras@maqs.net
www.specialcamera.com
www.corona-technology-course.com
- answers your question's series -
The first question typically is -
What Will Corona See That Infrared Will Not ?
Copyright 2013 Ox Creek Energy Associates Inc