UAVs have great potential in the energy sector for technical aerial inspection, mapping and monitoring. In the Czech Republic, Upvision has carried out various kinds of testing of UAVs, including inspecting insulated power lines for the largest Czech electricity provider CEZ.
Very often, damage occurs to the insulation of isolated power lines in difficult, inaccessible terrain, primarily in forests from falling branches. It has been impossible until now to check and identify the sites of damage, because it must be done from above the power line.
Upvision tested various UAVs and techniques of aerial inspections along a more than 4km stretch of power lines in the forested area on the border of the Czech Republic and Germany.
The site selected for inspection meant that only three different types of professional UAV with various outputs could be used, but the UAVs that offered the best options for moving in heavily accessible terrain when flying in visual range of the pilot were used.
The following outputs of aerial inspection were tested:
• Orthogonal photos with overlaps at low altitude (about 10-15m) over the power line
• Aerial video documentation
• Mapping (orthophoto and digital surface model)
To map the power lines in millimetre resolution, we used the medium-sized Geodrone 6 to map smaller areas or line structures. This was designed for the inspections based on the German Mikrokopter platform, with our own modifications. The camera mounted on the UAV was a professional SLR Canon EOS 700D with interchangeable lenses (four different focuses).
This UAV can image the required area automatically using a flight plan, which can be activated after take-off. Alternatively, mapping can be done manually, with photos manually taken from the UAVs or using an auto-exposure time series determined by the airspeed and the overlap needed between photos.
The creation of aerial images with overlaps over power lines from a UAV is one of the best possible outcomes with respect to the use of professional cameras with interchangeable lenses of various focuses for zooming the resulting images. At the same time, this is the best possible method to accurately synchronise the GPS positions of the photos taken. Professional UAVs are designed to record the GPS location mapping centres of each photograph; it is therefore then easy to trace the position of possibly damage.
The output of this method are the original aerial images overlaid on each other and coordinate centres (external orientation) for all the images. For the best quality aerial images, the RAW format is used, which can be further improved during post-processing to deal with bad weather conditions, eliminate shadows, improve sharpness, increased brightness and so on.
In addition, the UAV can be piloted by one person while another controls the recording of images and the degree to which they overlap. The method is also appropriate for the challenging terrain, as all UAVs in the Czech Republic and the rest of the EU must be operated within sight of the pilot.
We also tested aerial video documentation of the power lines using a bigger UAV: the DJI S1000, with a camera and special lens for recording in 4K resolution. This provides both high resolution and detail, although the quality is inferior to photos taken using a professional SLR camera. In addition, while the recorded video can be exported to individual photos, these images suffer more from motion blur so are more suitable for use on open exterior sections and for monitoring at a lower altitude over power lines.