Uvirco:Outsourcing_book_temp.qxd 24/08/2009 15:35 Page 66
The Role of CoroCAM and MultiCAM in the Development of High-voltage Defect Visualisation
corona emissions below the 280nm wavelength at which solar
Figure 1: Spectral Irradiance of Corona (UVA, UVB and UVC
Wavebands) and Solar Energy
energy ceases, finally allowed accurate inspections to take place
during the day. It also provided some relative quantification of the
Solar
number of UV photon events being detected. The most recent
Corona
x 10,000
daylight UV detection camera, the CoroCAM 504, has a removable
UV
solar-blind filter on the UV channel and near-IR filter on the visible
CBA
channel, allowing the same system to be used with increased
sensitivity in indoor situations or in very low light conditions.
To allow the solar-blind filter to block the UV wavelengths from the
sun, the incoming image is split and digitised, resulting in the UV
200 300 400 500 600 700 800
image becoming a series of pixels superimposed on the visible
Electromagnetic spectrum wavelength (nm)
daylight image forming the final output. This has the advantage of
giving ample opportunity for the UV image to be enhanced through
Figure 2: Defects Visible in the Same and in Different Locations on an
image processing, if required, allowing the user a number of optionsInsulator by Overlaying the Ultraviolet and Infrared Images
in displaying the UV image to best advantage. These include image
coloration contrasting the UV with the background, frame
integration to remove background noise, photon counting for UV
quantification and high-definition zoom to see the discharge
location more clearly.
Generally, the lower voltage limit for daylight detection of  high-
voltage faults is around 11kV, depending on the distance from the
object and the severity of the problem. This can be reduced to
around 3kV with the solar-blind filter removed.
Thermal Hotspot Visualisation
IR detection technology has been around for longer than UV
visualisation and is  accepted as a standard method of detecting
mechanical faults on high-voltage systems that may lead to power
failures. Unfortunately, the IR tells only part of the story as it does
Figure 3: Different Defects Are Sometimes Visible in Only One
Particular Spectrum Due to the Nature of the Problem
not detect surface discharges where heat is not generated,
generally related to voltage differences indicating areas with a
potential for flash-over and subsequent power outages. The
opposite applies to UV detection, which does not detect hidden or
current-related faults from which UV photons cannot escape but
which may produce hotspots.
Both phenomena provide much-needed information on the
integrity of the line and its associated hardware. Thus, both
visualisation technologies are required together in order to see the
whole picture. Where this can be done in one instrument, such as
the MultiCAM with a visible spectrum image, the inspection process
becomes much more efficient (see Figures 2 and 3). This also
ensures that the picture shows both phenomena under exactly the
same climatic conditions and instrument settings, eliminating many
of the variables encountered in comparing survey results from
greater sensitivity than previous photographic methods and extended separate instruments.
the usage window into pre-sunrise and post-sunset low-light
conditions. These systems are still widely used where manpower or Visualisation Applications
power system availability inhibits daylight surveys or where the Now that the visualisation technologies are available, there are
application is indoors, away from the effects of natural sunlight. several ways of deploying those technologies depending on the
application. For small areas, such as substations, surveys on foot
User need soon required cameras for use during daylight hours for using handheld CoroCAM systems are suitable. For transmission and
manpower efficiency and safety reasons, however, as well as much- distribution line surveys, mounting the CoroCAM UV visualisation
improved background imaging via a visible channel. The system into a motor vehicle for cross-country transmission lines, a
development of the daylight solar-blind CoroCAM IV+ around train for railway lines or a helicopter for long-line or inhospitable
2000–2001, although constrained by extremely low levels of UVC terrain becomes necessary.
MODERN ENERGY REVIEW VOLUME 1
66
Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84