Guide to daytime corona cameras

2 min read

Ofil attributes its established market superiority to customers' appreciation and to its cameras' guaranteed sensitivity to ultraviolet. Corona discharge is a weak UV emitter; as a result sensitivity is the most important property of any optical corona detector.

Daytime corona cameras aim at detecting and displaying corona partial discharge during daytime, and to be able to fulfill their intended use they must satisfy three basic criteria: high sensitivity to UV; high accuracy; ongoing reliable operation.

High sensitivity

Three elements determine the sensitivity of a DayCor camera:

Collecting area

The lens’ area that collects UV light from the source (corona in this case) needs to be large. The larger the collecting area of the UV lens, the more UV light gets in and the more sensitive is the corona camera. The UV lenses of the DayCor camera have about four times larger UV light collection area than commercial UV lenses. The lenses were designed by Ofil and are Ofil's proprietary.

UV filter quality

The filter must have maximum transmittance in the 250-280nm (UVc) range while blocking absolutely any sun radiation from outside this transmission band. Ofil's top quality filters absorb and prevent sun radiation from reaching the UV detector. As a result, background "noise" of solar radiation is diminished and the DayCor camera can operate at very high gains in full daylight.

Image intensifier

The quality of the UV image intensifier that creates the bright UV image from the very faint UV emission source must be very high.

Ofil tests its cameras at RWE facilities, a reputable unbiased institute (Germany) that runs tests according to acceptable strict standards. The tests' results are written on a formal signed certificate, mentioning the true actual results of the tests.

Customers should check the manufacturer's claimed sensitivity values and look for a valid certificate. It is unacceptable to refer to a calculated extrapolated figure as real validated values. Corona cameras are not linear in their performance and therefore only real tests can validate their sensitivity.

Frames integration (Long integration - LI)

As a means to get clearer & conspicuous signals, corona cameras other than Ofil's, deploy this feature by default. Frames integration means merging UV signals from consecutive frames creating a distinctive spot. A clear disadvantage of LI is the "cruising" effect where spots seem floating and often detached from the emitting sources, in particular a delay is noticeable when the camera moves.

Ofil's corona cameras, due to their unique high sensitivity, operate by default without integrating frames and display accurate images of the corona and the emitting sources. The available LI feature in Ofil's cameras can be switched on in noisy areas with welding sparks where integrating assists distinguishing between flashing corona and sporadic sparks. Upon enabling LI the high sensitivity of Ofil's cameras increases even more.

Customers should check whether the corona camera under consideration uses only LI, as a means to enhance sensitivity, or like Ofil's cameras that have a switchable LI that is turned on only when needed.

Continuous operation without overheating

A corona camera should operate continuously throughout inspection sessions as long as power is supplied. A camera that overheats has limited operation duration, and imposes unplanned breaks during inspection.

Ofil's corona cameras are electronically designed to withstand long operating hours under extreme weather conditions. No ventilation is needed, and no overheating is expected.

Customers should inquire whether the corona camera under consideration overheats. It is necessary to explicitly ask and insist on getting answers because such information is often concealed.

Ofil's corona cameras are being used worldwide by electrical utilities, research institutes, high voltage laboratories, manufactures, services contractors and others since 2000. Ofil keeps on developing its cameras for the sake of its customers experience and for the sake of improving the reliability of power systems. Ofil's corona cameras are sturdy, stable, reliable, innovative and ergonomic. Ofil believes in the need for equipment that are easy to operate, precise and with the exact features that match their intended use.