Power line maintenance, especially of high voltage line with more than 10 km length, is a major stake for electricity infrastructure companies. In Europe, electricity network is mainly aerial compared to undergrounding. Two European countries (Demark and Netherlands) have chosen to bury part of their power line for landscape improvement even if this part remains small (respectively 23% and 10%). Investment cost for underground lines is much higher than for aerial while maintenance cost is ten times less.
With more than 300 000 km of high voltage aerial lines, European maintenance companies need to implement efficient inspection process to ensure 24/7 service rate. Outside Europe, in countries such as the Americas or Asia, to cover long distance, the transmission network largely consists of high-voltage cables with towers to support them. Brazil and China have built power line in the 2000 km range.
The right technologies to detect Corona discharges
Ultra-Violet cameras (UV) and thermal cameras inspection have been selected as the most appropriate ways to detect defaults in an early stage. They could be used in combination to take benefit of the two spectral band to identify more defaults and enlarge the diagnosis capacity.
UV camera operates in the range of 200 to 400 nm. In this range, to avoid sun radiation perturbation, the solar blind UV camera operates between 240 to 280 nm. These cameras are suitable to detect Corona discharges which emit in this region, in day conditions. As corona discharges produce low signal, it’s important to have high sensitivity and capabilities to change integration time.
Thermal camera operates in the range of 8 to 10 µm. This equipment detects the temperature variation of each element of a scene. People with higher temperature (around 37°C) are brighter than the background which is colder. Infrared imaging is able to identify heat elevation and could also be used either in day or night conditions. In the case of power line inspection, thermal systems are used to detect overheated elements, which could be damaged insulators or potential short-circuits.
UltraViolet camera and Thermal camera combination for predictive maintenance in electric lines
The combination of both UV and thermal camera, in addition to a visible one, is the best candidate to perform predictive maintenance. A wide range of defaults can be observed, related, for example, to insulators and solder joints. These systems have usually been developed with friendly user interface to be easily handled by operators. Image processing is one of the big stakes in order to take benefit of the image quality of each sensor. UV camera generally used intensified camera, which is a coupling of UV image intensifier and a CMOS camera while thermal camera uses uncooled microbolometer technology.
These two technologies provide the best sensitivity and contrast required for such kind of application. In addition, technology improvements allow to integrate them in a very small form factor, becoming SWaP (Size Weight and Power), opening the door to aerial integration in UAV or helicopters. Photonis product offers provide both cameras using Smart Tube Management and state-of-the-art electronic, to REVEAL THE INVISIBLE!