Influence of Emissivity and Distance in High Voltage Equipments Thermal Imaging

Thermographic inspection is a very safe and noninvasive monitoring technique, widely used in electrical substations and other power plants. Using an infrared camera, a thermal image can be obtained presenting abnormal heating regions on power equipment. The heating can indicate a failure on this system/equipment or an unusual electrical situation as over voltage or a poor contact. The precision of an infrared cam is based on some parameters that must be evaluated during the inspection. This work presents a study done with thermal images obtained from different materials. Different values measured when the correct emissivities and distance are not used during inspection and/or analysis of the thermal image. The results show that differences larger than 10% can be obtained for the temperature when the emissivity varies in a range from 1 to 0.75, which includes the value of 0,85 used for most companies.