Seeing what is invisible to the naked eye

Visually displaying the corona discharge around a defective, high-voltage electrical installation is a problem that  researchers at the CSIR have long since overcome – of that the worldwide success of its CoroCAM designs are proof. The CoroCAM range of products was licensed to UViRCO Technologies, a CSIR spin-off, staffed by ex-CSIR personnel, in 2008.

Power utilities worldwide are experiencing pressure to manage their available power efficiently. Preventative maintenance can reduce blackouts and power loss on high voltage equipment, which results in minimising power losses. Under high load on transmission and distribution infrastructure, localised hot spots limit capacity and can cause black-outs due to failure. Power-loss causes can be minimised through inspection to verify that lines are installed as designed. It is for these inspections that the CSIR developed CoroCAM has become irreplaceable.

The first CoroCAM was an ultraviolet (UV) imaging camera that could detect and display the UV discharges that indicate high-voltage equipment problems – discharges that are not normally possible to spot with the naked eye as they fall below the range of visible light that humans can detect. This camera could only spot the resulting corona at night and the request soon came for a device that could do exactly the same thing, but during the day.

Four models followed, with the CoroCAM 504 being the current and very popular version with the ability to detect faults  during night and day. According to Riaan Rossouw, UViRCO’s marketing manager, more than 150 units of  he CoroCAM 504 have been sold internationally, the majority of which have gone to China, Russia and the USA.

“However, while the CoroCAM can visually show power utilities and large industrial users of electricity where corona discharge creating equipment faults are located, it cannot showthem the severity of the problem.

This still requires a human operator,” says Rossouw. UViRCO is about to release the CoroCAM 6D, the latest addition to the CoroCAM family.

The CoroCAM 6D was developed in-house by UViRCO and introduces a number of new features which the market demanded, that is, on-board recording and a simplified user interface.

The CoroCAM 6D leveraged optimised electronics and mechanical design to effect a reduction in production cost.

The technology behind CoroCAM
When looking at an object such as a high-voltage electrical wirethrough the UV detecting camera, the incoming light is split into two pathways. One path passes the visible light through to a standard video camera which records the images of the object being inspected in order to create a background image. The second path takes its light through a 240-280 nm wavelength solar blind filter to a camera which is sensitive to UV light.

The UV image is overlaid on the background image to provide a final picture which shows the location of UV corona discharges on the object being inspected.

Other developments
Apart from the CoroCAM, the CSIR, which now acts as research and development (R&D) partner for UViRCO, also developed a product called MultiCAM. This camera can detect both UV and infrared (IR) wavelengths and visually display these images for the easy identification of high voltage equipment problems.

Jeremy Wallis, competence area manager for the sensor science and technology group at the CSIR, says that by adding the IR ability to the UV function, the MultiCAM can show differences in temperature as well as faults that radiate a corona. “Having both the thermal and corona image allows the operator to eliminate possible causes of a problem and get to the real problem (and solution) faster.”

With the MultiCAM, an IR dimension as well as the normal visible spectrum can be recorded at the same time as the UV
spectrum. The UV image can be overlaid on top of either the IR or background image, showing a final image with temperature differences as well as coronas on the object being inspected.

This camera too has been transferred to UViRCO and the CSIR is currently applying for funding to develop a fully radiometric MultiCAM.

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