Detecting Electrical Problems With Thermal Imaging

Vikram Bhansali, Director, CEM Instruments India

Vikram Bhansali, Director, CEM Instruments India

Vikram holds a demonstrated history of working in the electrical and electronic manufacturing industry. He is skilled in SCADA, Electrical Wiring, Sales Management, Management, and Printed Circuit Board Design.

Thermal Imagers today produce live images of the heat emitting from equipment while being easy to use and much more affordable, thus making them highly practical and worthwhile solutions for even everyday electrical maintenance.

To use a Thermal Imager, a qualified technician or electrician has to point the imager at the equipment in question, scanning the required area for unexpected hot spots, then squeeze the trigger to capture an image. After completion of inspection, the saved images can be uploaded to a system for further analysis, reporting and also future troubleshooting.

For anyone using a thermal imager, the following three points should be given attention:

• Point 1: Loading of Equipment
In order to effectively detect problems with a thermal imager, the electrical equipment being inspected must be under at least 40 percent of the nominal load, and if possible, maximum load conditionsare ideal.

• Point 2: Safety & Protection
Electrical measurement safety standards under NFPA 70E state that Personal Protective Equipment (PPE) is compulsory when standing in front of any open, live electrical panel. PPE should include flame-resistant clothing, leather-over-rubber gloves, leather work boots, arc flash rated face shield, hard hat, hearing protection or a full flash suit, depending on the situation and the incident energy level (Bolted Fault Current) of the system to be scanned.

• Point 3: Emissivity Levels
Emissivity is defined as the relative power of a surface to emit heat by radiation. The emissivity of the panel in question affects how well a thermal imager will be able to accurately measure the object’s surface temperature.

A thermal imager is able to accurately calculate the surface temperature of an object only if the emissivity of the material in question is relatively high and/or the emissivity level setting on the thermal imager is matched closely to the emissivity of the object.

Thermal imaging is a comparative or qualitative process, when undertaken for electrical inspection. Typical temperature measurements are usually not required. Alternatively, one should aim to look for spots that are hotter than similar

equipment under the same load conditions—unexpected spots.

Troubleshooting Electrical Systems
Specific things should be checked when pursuing inspections related to breaker problems or checking on load performance issues. As a rule, after any repair, another follow-up thermal scan should be done. A successful repairing would mean no more unexpected spots along with earlier detected spots to have disappeared.

Keep in mind that not all electrical hot spots that showup are loose connections. For an accurate diagnosis, it is always recommended to have a qualified electrician to either execute the thermal scan or be present while it’s being performed.

For Three-Phase Discrepancies
Capture thermal images of all electrical panels and other high-load connection points such as drives, disconnects and controls. Higher temperatures discovered through hot spots, should be followed, and circuits, associated branches and loads should be examined.

Check for temperature differences by comparing the three phases side-by-side. A cooler-than-normal circuit or leg might also signal failed components. More heavily loaded phases would appear warmer. Hot conductors may be undersized or overloaded. It is important to follow up with electrical or power quality measurements so as to accurately diagnose the problem, since an unbalanced load, an overload, a bad connection and/or harmonics, can all create similar patterns.

Keep in mind that voltage drops across the fuses & switches can also show-up as unbalances at the motor and as excess heat at the root trouble spot. Always double-check current measurements with both the thermal imager and multimeters or clamp meters before assuming the final cause.

Connections & Wiring Issues
Look for connections that have higher temperatures than other similar connections under similar loads. These could indicate loose, over-tightened or corroded connections with increased resistances. Connection-related hot spots usually—but not always— will appear warmest at the spot of resistance, cooling with distance from that spot. Sometimes, a cold component might be abnormal due to current being shunted away from the high-resistance connection. Broken or undersized wires or defective insulation may also be found. The NETA (Inter-National Electrical Testing Association) guidelines advise that when the difference in temperature (DT) between similar components under similar loads exceeds 150 C (~250 F), immediate repairs should be undertaken.

Fuse Issues
In case a fuse shows-up as a hot spot on a thermal scan, it may be at or near its current capacity. Although not all problems show-up as hot spots as sometimes, a blown fuse would be indicated as cooler than normal temperature.

Motor Control Centers (MCC)
While checking an MCC under load, each compartment should be opened, scanned and compared for relative temperatures, incorporating the foregoing guidelines for inspecting connections and fuses, while wanting to identify phase imbalance.

Transformer Scanning
Thermal Imagers can be used to check high and low-voltage for external bushing connections, cooling tubes, cooling fans and pumps, as well as surfaces of critical transformers in oil-filled transformers.

Follow the previously noted guidelines for connections and imbalances. The cooling tubes should appear warm, and when one or more tubes appear comparatively cool, oil flow is probably restricted. Always remember that like an electric motor, a transformer also has a minimum operating temperature that represents the maximum allowable rise in temperature above ambient (typically 400 C). The transformer’s life would probably be reduced by 50 percent with a 100 C rise above the nameplate operating temperature.