UV and IR complementary solutions
Corona and arcing activity on power lines and substations are of concern to electrical utilities not only due to the direct damage they may cause and the resulting audio noise (AN) or radio interference (RI) complaints from the public, but also because they are indications of possible defective components. The ability to rapidly identify the exact location of such activity and of the offending component, so that it may be replaced in time, has for a long time been a utility goal.
Ofil's DayCor® technology is today's most advanced and sensitive daytime camera for UV inspection in the utility market. With the help of EPRI it was tailored for the specific needs of the High Voltage utility market. All DayCor® cameras are user friendly and can be operated in full daylight. Ofils' cameras are already in use by hundreds of maintenance teams worldwide and have proven to be an efficient tool in preventing outages and locating sources of audio noise and radio and TV interference complaints.
But why is it still so important to perform maintenance inspection with a corona camera along with an IR camera? Well, the answer is simple; corona can be detected during daytime and only by UV inspection. Corona is not a thermal phenomenon, It produces only little heat, and it is directly related to electrical field (hence to voltage) and not to current however, detecting hot spots requires a flow of current. Having this mentioned, it can be concluded that such different phenomena produce different effects that may be detected by different technologies. Since IR thermography detects hot spots and displays differences in temperature, corona cannot be detected and located by this technology. Corona cameras detect UV emission and as mentioned previously UV emission is voltage related. However, in extreme cases overlapping may be found. In cases of severe arcing activity corona may generate enough heat to be located with IR equipment. This can only mean that the corona problem has already become severe and usually could have been detected at much earlier stage of degradation with a corona camera. We can therefore conclude that corona is a primary indication for electric problem thus an inspection or commissioning only with IR camera, without a UV camera, cannot be flawless and complete. It is now important to mention that when performing an IR inspection usually an increased line load is required for performing a thermovision inspection, which makes this inspection method inconvenient and sometimes not practical. Moreover in those cases where severe corona or arcing evolves temperature gradient weather conditions may set limitation to the inspection efficiency.
In the early days of maintenance procedures, mainly electrical testing measurements were performed. Today the incorporation of optical visualizing techniques is obvious to the maintenance groups. UV and IR cameras became indispensable tools for the maintenance teams both for preventive maintenance and predictive maintenance. The recognition of its benefits and the cost effectiveness when used for preventive and predictive maintenance is growing. The more it is proved that the use of the Daytime UV cameras for inspection can prevent line outages, shutdowns of substations and RF & Audio noise complaints, the acquisition of UV inspection tools like the DayCor® cameras seems more justified to the administrative authorities of the utilities that approve the purchase budgets. IR and the UV inspection technology yield complementary information. Both technologies are therefore required for preventive and predictive maintenance in the sectors of the HV market. The key for a complete and high quality inspection is in the consolidation of data from both UV and IR inspections in order to create a whole analysis and data trending of your electrical asset.
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