Evaluation of a Charged Coupled Device Camera for the Detection of Ultraviolet Emissions by Corona Discharges

摘要

The current state of the art is UV cameras that use photomultiplier tube technology to make the comparatively weak UV emissions visible. These camera systems have a fixed lens with a fixed focal length, making it impossible to zoom or vary the focal length. In the application scenario of an overhead line inspection flight by helicopter, the cameras, which are available on the market, are approaching their limits. The inspector normally uses the available camera(s) during an inspection flight in parallel to the visual inspection, but this is often not possible due to the fixed focal length and resolution of the camera system. Hence, an adopted flight route would be advantageous for such UV cameras. As a result separate flights are needed for a visual inspection and corona detection. In this paper a compact camera with a Charged Coupled Device Sensor (short: CCD sensor), which covers a spectral working range of 190 nm-1100 nm was investigated within the scope of a research project. The camera is able to detect the UV emissions of corona discharges in the range of 250 nm to 400 nm. Another advantage of the front side illuminated CCD sensor is the high resolution of 1.4 megapixels and the dynamic range of 14-bit. The camera core offers the possibility to mount any lens with the appropriate focal length for the respective application. This circumstance allows a flexible use in helicopters for an overhead inspection flight. Laboratory performance tests of the camera system are promising and prove the feasibility. The use of the camera requires a preselection of the spectral range in order to take full advantage of the dynamics of the camera and to avoid overloading the sensor. For this purpose, filters with different bandpass characteristics were investigated. Finally the UV sensitivity of the camera at different intensities of corona surface discharges and in tip-plate arrangements was determined.