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White paper: Infrared thermography in Busway

What is infrared thermography, and how does it work?

All objects give off infrared energy, which is electromagnetic radiation in the spectrum above the wavelength of visible light. Infrared cameras utilize special lenses and detector circuitry to convert the infrared energy into color-coded images that make it easy to see temperature differences between objects. Like objects, such as three phases of busway conductor connections with similar load current, should have the same approximate apparent temperature. One conductor showing up “hot” compared to the other two may be indicative of a loose electrical connection with high resistance. 
Electromagnetic spectrum

Why use infrared thermography as a condition-based maintenance tool?

Infrared thermography is a non-intrusive technique that can detect subtle temperature differences between components and be conducted while equipment is energized, ensuring no interruption to your operations. Along with visual inspection and ultrasound, it forms the triumvirate of technologies for assessing electrical equipment health. IR thermography can help you migrate from wasteful calendar- based maintenance to more efficient and effective condition-based maintenance and decision making.

Can actual target object temperatures be taken using an infrared camera?

Hot conductor phase
With care, actual quantitative temperatures of objects can be determined after factoring in for several variables that can otherwise skew readings. Camera settings can adjust for distance to the target, ambient air temperature, relative humidity, target emissivity and transmission rate of IR window (if applicable). Geometry of the targets can also make a difference in the apparent temperature readings. Certified thermographers are trained on how to choose their targets and make these camera adjustments to secure relatively accurate temperature readings.

What is an infrared window and how does it work?

An infrared window is designed to allow safe and efficient access to electrical connections that may be prone to loosening over time and overheating. The IR window must be compliant with several equipment component standards related to mechanical strength, ingress protection rating and flammability and listed or recognized by UL and/or CSA. The IR window keeps the equipment in an “enclosed and guarded” state even when the cover of the window has been opened for taking measurements. The NFPA 70E standard does not require any special Personal Protective Equipment (PPE) to be worn when performing infrared thermography through an IR window but does require PPE if a panel cover is removed or an equipment door is opened exposing live energized components. The IR window utilizes a lens system with a material that will allow most infrared energy to transmit from the source through the lens media to the camera. Most plastics, glass and metals will NOT allow infrared energy to transmit through. The Pow-R-Way III IR joint cover uses a special infrared transmissive reinforced polymer optic lens that has been tested to all the relevant standards and carries a UL listing.
Pow-R-Way III IR Joint measurement

Are IR cameras expensive?  Do I need training to use one?

The cost of Infrared cameras has come down dramatically in the past 10 years. Smartphones with a built-in IR camera with both still and video recording capability are now available for less than $700 while a very good mid-range handheld camera now costs less than $4,000. Low-end cameras may not have all the settings needed to get accurate temperature readings but will allow for good qualitative analysis. A mid-range camera will allow both qualitative and quantitative measurements to be made. It is recommended that personnel attend an accredited level 1 thermography training course before attempting to use an IR camera as the danger of both missing real problems and reporting false positives is possible without proper training.
 

Why can’t I just scan the joints from the outside of the equipment without the special IR joint cover?

Infrared is not x-ray vision-infrared energy will not transmit through solid substances like sheet metal. You can attempt to compare sequential busway joints from their exterior to look for temperature variation but the busway itself has significant thermal mass. A problem that is causing a 50°C temperature rise on a loose connection inside the joint might manifest as only 1-2°C of temperature variance on the exterior of the joint, which can easily be missed. The joint cover, when opened for inspection, allows a direct field of view of the internal connections of the joint ensuring that any problem will be seen immediately.

Scan to detect problems

At a minimum, we recommend annual scanning of busway joints. In critical power applications such as data centers, hospitals, airports and some industrial applications, more frequent inspection may be prudent. In these segments, it is not unusual for inspections to be done on a quarterly basis. Eaton Busway falls under NEMA BU1.1 for all busway maintenance.

Unusual temperature anomaly

Temperature abnormalities constitutes any yearly temperature scans of the same joint showing margins of rise greater than 5°C. During a joint scan, note the ambient temperature of the room for each scan and if any changes were made to the electrical system, as a new load may affect operating temperatures of the busway. Different phases at one joint may also run at higher or lower temperatures than other phase at the same joint, depending on the load incurred by the individual circuit.

What should I do if I detect an anomaly?

Double check your camera settings and record the time, location and temperature values of the suspect busway connection. Note which phase was manifesting as the source of the heat, if applicable. Changes above 5°C of the same joint, during a yearly scan per NEMA BU1.1, would have a recommended action of a visual inspection to check for any changes in the busway during the year and possibly de-energize the busway to check torque values of the busways bridge joints.

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