MIKE Shekhtman from Goodyear has written on how thermal imagers can help detect electrical problems.
The thermal imagers of today produce live images of heat emitted from equipment, and are rugged, easy to use, and affordable, making them cost-effective for everyday electrical maintenance.
The technician or electrician points the imager at the equipment in question, scanning for unexpected hot spots, and squeezing the trigger to capture a specific image.
When technicians have finished the inspections, they can upload the saved images to a computer for closer analysis, reporting and future trending. Of course, the process is much more effective if the user understands electrical measurement and the equipment being inspected.
Three points are important when using a thermal imager in this way: loading, safety and emissivity.
The electrical equipment being inspected should be running with at least 40% if not 100% of nominal load in order to reliably detect problems with a thermal imager.
Even though the personnel are not in contact with the equipment being inspected, electrical measurement safety standards still apply. Technicians should don personal protective equipment when standing in front of an open and live electrical panel.
The emissivity of the equipment and material describes how well they emit infrared energy or heat. This can affect the accuracy of the thermal imager. The higher the emissivity of the equipment, the more accurate the thermal imagery will be.
However, thermal imaging for electrical inspection is often a comparative process, so users do not need specific temperature measurements. Instead, they should look for spots which are hotter than similar equipment under the same load condition.
All thermal anomalies should be followed up with electrical or power quality measurements, by following circuits and looking at associated branches and loads.
Abnormally hot fuses may be at or near its current capacity. Where a cooler than normal temperature is detected, the fuse may be blown.
Motor control centres should be evaluated under load. Technicians should open each compartment and compare the relative temperatures of the key components.
For oil-filled transformers, technicians should use a thermal imager to look at high- and low-voltage external bushing connections, cooling tubes, and cooling fans and pumps, as well as the surfaces of critical transformers. Cooling tubes should appear warm. A comparatively cool tube could be an indication of restricted oil flow.
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