Fluke has produced this handy guide to help professionals in the electrical industry understand the benefits of thermal imaging technology. Today’s thermal imagers are rugged, easy to use, and much more affordable than even just a few years ago. They have become a realistic solu¬tion for everyday electrical maintenance. To use, a qualified technician or electrician points the ther­mal imager at the equipment in question and scans the immedi­ate area, looking for unexpected hot spots. The imager produces a live image of the heat emit­ted from the equipment and with the quick squeeze of the trigger, a thermal image is captured. When the inspection is complete, upload the images to a computer, Apple, iPhone or iPad for closer analysis, reporting, and future trending. While the imagers are easy to use, they are most effec­tive in the hands of a qualified technician who understands electrical measurement and the equipment being inspected. The following three points are especially important. Point one: loading The electrical equipment being inspected must be under at least 40 % of nominal load in order to detect problems with a thermal imager. Maximum load conditions are ideal, if possible. Point two: safety Standing in front of an open, live electrical panel requires personal protective equipment (PPE). Depending on the situation and the inci­dent energy level (Bolted Fault Current) of the equipment being scanned, this may include:

• Flame resistant clothing
• Leather-over-rubber gloves
• Leather work boots
• Arc flash rated face shield, hard hat and hearing protec­tion or a full flash suit

Point three: emissivity Emissivity describes how well an object emits infrared energy or heat. This affects how well a thermal imager can accurately measure the object’s surface temperature. Different materials emit infrared energy in different ways. Every object and material has a specific emissivity that is rated on a scale of 0 to 1.0. For thermal imagers to report accu­rate temperatures, the higher emissivity, the better. Objects that have high emis­sivity emit thermal energy well and are not usually very reflective. Materials that have low emissivity are usually fairly reflective and do not emit ther­mal energy well. This can cause confusion and incorrect analysis of the situation if you are not careful. A thermal imager can only accurately calculate the surface temperature of an object if the emissivity of the material is relatively high, and/or the emissivity level on the imager is set close to the emissivity of the object. Most painted objects have a high emissivity of about 0.90 to 0.98. Ceramic, rubber, and most electrical tape and conductor insulation have relatively high emissivities as well. Aluminium bus, however, is very reflective, and so are copper and some kinds of stainless steel. The good news is that most thermal imaging performed for electrical inspection purposes is a comparative, or qualita­tive, process. You don’t usually need a specific temperature measurement. Instead, look for a spot that is hotter than similar equipment under the same load conditions... spots that you do not expect. Troubleshooting electrical systems If you’re chasing breaker prob­lems or load performance issues, here’s what to check. Once you’ve completed your repairs, take another thermal scan. If the repair was successful, the hot spot you first detected should have gone away. Note: Not all electrical hot spots are loose connections. For a correct diagnosis, it’s smart to have a qualified electrician either perform the thermal scan or be present while it’s done. Three-phase imbalance Capture thermal images of all electrical panels and other high-load connection points such as drives, disconnects, controls, and so on. Wherever you discover higher tempera­tures, follow that circuit and examine associated branches and loads. Compare all three phases side-by-side and check for temperature differences. A cooler-than-normal circuit or leg might signal a failed com­ponent. More heavily loaded phases will appear warmer. Hot conductors may be undersized or overloaded. However, an unbalanced load, an overload, a bad connection, and harmonics can all create a similar pattern, so follow up with electrical or power quality measurements to diagnose the problem. Note: Voltage drops across the fuses and switches can also show up as unbalance at the motor and excess heat at the root trouble spot. Before you assume the cause has been found, double-check with both a thermal imager and a multimeter or clamp meter current measurements. Connections and wiring Look for connections that have higher temperatures than other similar connections under similar loads. That could indi­cate a loose, over-tightened, or corroded connection with increased resistance. Connec­tion-related hot spots usually, but not always, appear warmest at the spot of resistance, cool­ing with distance from that spot. In some cases, a cold component is abnormal due to the current being shunted away from the high-resistance connection. You may also find broken or under­sized wires or defective insulation. Fuses If a fuse shows up hot on a ther­mal scan, it may be at or near its current capacity. However, not all problems are hot. A blown fuse, for example, would produce a cooler than normal temperature. Motor control centres (MCC) To evaluate an MCC under load, open up each compartment and compare the relative tem­peratures of key components: bus bars, controllers, starters, contactors, relays, fuses, break­ers, disconnects, feeders, and transformers. Incorporate the guidelines above for inspect­ing connections and fuses and identifying phase imbalance. Tip: Measure the load at the time of each scan, so that you can properly evaluate your measurements against normal operating conditions. Transformers For oil-filled transformers, 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 (Dry transformers have coil temperatures so much higher than ambient, it’s difficult to detect problems with ther­mal imagery). Incorporate the guidelines above for connec­tions and imbalances. The cooling tubes should appear warm. If one or more tubes are comparatively cool, oil flow is probably restricted. Keep in mind that like an electric motor, a transformer has a minimum operating temperature that rep­resents the maximum allowable rise in temperature above ambi­ent (typically 40 °C). A 10 °C rise above the nameplate oper­ating temperature will probably reduce the transformer’s life by 50%. Source: https://www.voltimum.co.uk/articles/solving-electrical-problems-thermal