1 Solving electrical problems with thermal imaging Application Note This article describes how to identify problems is complete, upload the images within the electrical distribution system, both when to a computer for closer analysis, trouble has already hit and in advance, through reporting, and future trending. While the imagers are easy to routine preventive maintenance. use, they are most effective in the hands of a qualified techni- Basic how-tos: To use it, a qualified technician cian who understands electrical electrical load, safety, or electrician points the ther- measurement and the equipment and emissivity mal imager at the equipment in being inspected. The follow- question and scans the immedi- ing three points are especially Today's thermal imagers are rug- ate area, looking for unexpected important. ged, easy to use, and much more hot spots. The imager produces affordable than even just a few Point one: loading a live image of the heat emitted The electrical equipment being years ago.
2 That's making them from the equipment. To capture a inspected must be under at least a realistic solution for everyday specific thermal image, squeeze electrical maintenance. 40 % of nominal load in order to the trigger. When the inspection detect problems with a thermal imager. Maximum load conditions are ideal, if possible. Point two: safety electrical measurement safety standards still apply, under NFPA 70E*. Standing in front of an open, live electrical panel requires personal protective equipment (PPE). Depending upon the situation and the inci- dent 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 protec- tion 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.
3 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 For thermal imagers to report accu- When scanning a live electrical panel, wear appropriate 70E personal protective equipment for arc rate temperatures, the higher flash and stand at least four feet away. emissivity, the better. From the Fluke Digital Library @ Objects that have high emissiv- Most painted objects have a load, an overload, a bad con- ity emit thermal energy well and high emissivity of about to nection, and harmonics can all are not usually very reflective. Ceramic, rubber, and most create a similar pattern, so follow Materials that have low emis- electrical tape and conductor up with electrical or power qual- sivity are usually fairly reflective insulation have relatively high ity measurements to diagnose and do not emit thermal energy emissivities as well. the problem .
4 Well. This can cause confusion Aluminum bus, however, is Note: Voltage drops across the fuses and and incorrect analysis of the very reflective, and so are copper switches can also show up as unbalance at situation if you are not care- and some kinds of stainless steel. the motor and excess heat at the root trouble spot. Before you assume the cause has been ful. A thermal imager can only The good news is that most found, double-check with both the thermal accurately calculate the surface thermal imaging performed for imager and a multimeter or clamp meter cur- temperature of an object if the electrical inspection purposes rent measurements. emissivity of the material is rela- is a comparative, or qualitative, Connections and wiring tively high, and/or the emissivity process. You don't usually need Look for connections that have level on the imager is set close to a specific temperature measure- higher temperatures than other the emissivity of the object.
5 Ment. Instead, look for a spot similar connections under simi- that is hotter than similar equip- lar loads. That could indicate ment under the same load con- a loose, over tightened, or cor- spots that you do not roded connection with increased expect. resistance. Connection-related hot spots usually, but not always, 1050 C Troubleshooting appear warmest at the spot of 1922 F. electrical systems resistance, cooling with distance If you're chasing breaker prob- from that spot. In some cases lems or load performance issues, a cold component is abnormal 842 F. here's what to check. Once due to the current being shunted 850 C. you've completed your repairs, away from the high-resistance 1562 F. take another thermal scan. If the connection. You may also find repair was successful, the hot broken or undersized wires or spot you first detected should defective insulation. The NETA. have gone away. (InterNational electrical Testing 650 C Association) guidelines say that 1202 F Note: Not all electrical hot spots are loose connections.
6 For a correct diagnosis, it's when the difference in tem- smart to have a qualified electrician either perature (DT) between similar perform the thermal scan or be present components under similar loads while it's done. exceeds 15 C (~25 F), immedi- 450 C Three-phase imbalance ate repairs should be undertaken. 842 F. Capture thermal images of all -150 C. electrical panels and other high- load connection points such as drives, disconnects, controls, and 250 C so on. Wherever you discover 482 F higher temperatures, follow that circuit and examine associated branches and loads. 650 C. Compare all three phases 50 C side-by-side and check for tem- 122 F perature differences. A cooler- than-normal circuit or leg might signal a failed component. More heavily loaded phases will 0 C appear warmer. Hot conductors 32 F may be undersized or over- loaded. However, an unbalanced When evaluating an electrical hot spot, notice whether the heat con- -50 C tinues back along the wire toward the load (load releated problem ) or -58 F.
7 Is isolated to the connection (connection-related problem ). 2 Fluke Corporation Solving electrical problems with thermal imaging Fuses Transformers If a fuse shows up hot on a ther- For oil-filled transformers, use a mal scan, it may be at or near its thermal imager to look at high- current capacity. However, not all and low-voltage external bush- problems are hot. A blown fuse, ing connections, cooling tubes, for example, would produce a and cooling fans and pumps, as cooler than normal temperature. well as the surfaces of critical transformers. (Dry transformers have coil temperatures so much Tip: Measure the load at the higher than ambient, it's difficult time of each scan, so that you to detect problems with thermal can properly evaluate your mea- imagery.) Incorporate the guide- surements against normal oper- lines above for connections and ating conditions. imbalances. The cooling tubes should appear warm. If one or more tubes is comparatively cool, oil flow is probably restricted.
8 Motor control centers (MCC) Keep in mind that like an electric To evaluate an MCC under load, motor, a transformer has a mini- open up each compartment mum operating temperature that and compare the relative tem- represents the maximum allow- peratures of key components: able rise in temperature above bus bars, controllers, starters, ambient (typically 40 C). A 10 C. contactors, relays, fuses, break- rise above the nameplate operat- ers, disconnects, feeders, and ing temperature will probably transformers. Incorporate the reduce the transformer's life by guidelines above for inspecting 50 percent. connections and fuses and iden- tifying phase imbalance. Note: For a thermal imager to detect an internal transformer problem , the malfunction must generate enough heat to be detectable on the * For PPE guidelines, reference NFPA (National Fire Protection outside. That means that a malfunctioning bushing connection, for Association) Standard 70E Tables (c)(9)(a), (c)(10), (c)(11).
9 Example, will be much hotter than the surface temperatures read by the imager. Fluke. Keeping your world up and running.. Fluke Corporation PO Box 9090, Everett, WA 98206 Fluke Europe PO Box 1186, 5602 BD. Eindhoven, The Netherlands For more information call: In the (800) 443-5853 or Fax (425) 446-5116. In Europe/M-East/Africa +31 (0) 40 2675 200 or Fax +31 (0) 40 2675 222. In Canada (800)-36-FLUKE or Fax (905) 890-6866. From other countries +1 (425) 446-5500 or Fax +1 (425) 446-5116. Web access: 2008 Fluke Corporation. Specifications subject to change without notice. Printed in 7/2008 3359026 A-EN-N Rev A. Modification of this document is not permitted without written permission from Fluke Corporation. 3 Fluke Corporation Solving electrical problems with thermal imaging