Is The Hotspot You See Really a Real Hotspot?

Electrical thermographic inspection is a contact-free predictive maintenance method that uses infrared cameras to detect heat variations in electrical components. By observing the heat patterns in operational system components, faults can be located and their seriousness evaluated. However, not every hotspot that appears on the thermal image is a sign of a problem. Sometimes, what looks like a hotspot is actually a reflection of infrared radiation from another source. This can lead to false alarms and unnecessary repairs. Therefore, it is important for thermographers to take every measure possible to reduce the chance of detecting false hotspots due to IR reflection and to increase the chance of detecting real hotspots due to faults.

How to reduce false hotspots due to IR reflection

IR reflection is a phenomenon where infrared radiation is bounced off a surface, similar to how visible light is reflected by a mirror. IR reflection can occur on any surface, but it is more likely on shiny or metallic surfaces, such as copper wires, steel pipes, or aluminum foil. One of the common mistakes that thermographers made is misinterpreting reflections as faults. IR reflection can create false hotspots on the thermal image, because the camera cannot distinguish between the emitted and the reflected radiation. To reduce the chance of detecting false hotspots due to IR reflection, thermographers should understand this:

1. Be extra careful when inspecting shiny or metallic surfaces. Emissivity is a measure of how efficiently a surface radiates infrared energy. Most metallic or shiny materials like metal have low emissivity and they are usually a good IR reflector. Since most inspection is qualitative, the emissivity setting is usually fixed to a value like 0.95. This means that the thermographer should be extra careful when inspecting shiny or metallic surfaces, as they may have lower emissivity and higher reflection than the camera assumes. There are several additional factors that can affect emissivity, therefore understanding what emissivity is and how to correctly account for it will ensure you do not make this mistake.
2. Change the viewing angle. If the camera is facing a reflective surface at a certain angle, it may capture the reflection of another heat source, such as the sun, a light bulb, or the thermographer’s body. Stand in front of a copper connection and chances are any hotspots you see on the image will be your own body heat reflecting back at the camera. By changing the viewing angle, the thermographer can avoid or distinguish the reflection and see the true temperature of the surface. Thermographers should be aware of the sources of reflection and how to reduce or eliminate them. It might be helpful to capture the image at a slight angle, not perpendicular to the surface of the target object to reduce the chance of capturing own’s body heat. Thermographers can move around to the right or left, in order to change the viewing angle and see if the hotspot is due to reflection.

What can be done to increase the chance of detecting real hotspot

Faults in electrical components can cause overheating, which can lead to fire, equipment damage, or power outage. Therefore, it is crucial for thermographers to detect and locate the real hotspots due to faults by conducting a routine inspection at least once a year. Good thermographers not only need to take measures to reduce false hotspot but also take measures to increase detection of real hotspot:

1. It may seem obvious, but one of the frequent errors that thermographers commit is not surveying under load. The system should be inspected under normal load, as the temperature difference between a faulty and a normal component is more evident when the system is operating at its normal capacity. This way, the thermographer can increase the accuracy of the thermal image and spot the hotspots more easily. Without load, the system will not generate any heat and faults will not be visible. Surveying under load allows the thermographer to see the true condition of the system and detect any faults. If inspecting under nominal load is not possible, thermographers may need to consider making corrections or extrapolations when doing thermal analysis.
2. Another frequent error that thermographers make is not opening the panel door. Thermal cameras cannot see through objects and they don’t operate like an X-ray camera do. They only detect the heat radiated from the surface of the object they are looking at. Without a clear view, most faults will be overlooked. Health and safety restrictions may prevent panel doors from being opened, so in this case other options may need to be explored, such as infrared viewing windows. It’s also common when removing panel cover is possible, there are presence of plastic or acrylic shields inside the panels. These shields are often used to protect the personnel from arc flash, which is a dangerous explosion of electricity that can cause severe injuries or death. However, they can also interfere by not allowing line of sight inspection. Therefore, thermographers should remove these shields whenever possible before taking the thermal image. However, thermographers should also be extra careful when removing the shields and take safety precautions like wearing appropriate personal protective equipment and follow safety procedures. It’s also advisable to allow certified and trained personnel to remove covers and shields.

Conclusion

Thermographic inspection is not a simple snap and go process. It requires careful preparation, execution, and analysis to ensure reliable and accurate results. Electrical thermographic inspection is a valuable technique for preventive maintenance and fault detection. However, it is not a foolproof method. Thermographers need to be aware of the potential sources of error and take every measure possible to reduce the chance of detecting false hotspots due to IR reflection and to increase the chance of detecting real hotspots due to faults. Clients who need electrical thermographic inspection must hire certified thermographers who have the necessary qualifications and skills to conduct the inspection according to the standards and best practices. Certified thermographers can provide high-quality reports that can help clients identify and prevent potential problems and save costs and time.