By Jim Seffrin, Director, Infraspection Institute
In an effort to reduce the risk of injuries associated with arc flash, many sites have installed infrared (IR) transmissive windows or ports that permit IR inspections of switchgear without the need to open panel covers. Although such devices can provide a measure of safety and help to reduce labor associated with those inspections, they pose unique challenges not associated with direct line-of-sight imaging.
Switchgear windows are typically constructed of a rigid frame with a fixed IR transparent material that enables an imager to view through them. Switchgear ports consist of a rigid frame with small openings through which an imager may be sighted. Depending upon type, some feature a single hole, others incorporate metal screens containing multiple holes.
IR windows will always attenuate infrared energy received by the imager. While this attenuation affects qualitative and quantitative data, the greatest challenge involves temperature measurement. Accurate temperature measurements can’t be obtained through a screened port. Furthermore, the ability to accurately measure temperatures through an IR window is possible only if the following conditions are met.
• The window opening must be larger than the imager’s lens objective.
• The target must be at or beyond the imager’s minimum focus distance.
• Values for window transmittance and target emittance must be known and properly entered into the imager’s computer.
• The imager’s lens must be kept perpendicular to and in contact with the window.
When it is not possible to meet all of the above conditions, imagery should be evaluated only for its qualitative value. As always, any inexplicable hot or cold exceptions should be investigated for cause and appropriate corrective action taken. MT
Words to the Wise: Beware Hidden Electrical Danger
Getting ready for an infrared inspection of electrical equipment often requires manual preparation of switchgear components, which could be a riskier endeavor than many people might think. Unwary thermographers and other personnel can, in fact, be injured through contact with cabinets or component surfaces that have become accidentally or unintentionally energized.
Switchgear enclosures and components are generally designed to prevent their surfaces from becoming energized. Under certain circumstances, however, enclosures and other dielectric surfaces can become unintentionally energized to significant voltage levels. This potentially lethal condition can be caused by improper wiring, faulty equipment, or contamination due to dirt or moisture.
When conducting infrared inspections on or near electrical equipment, always keep the following in mind:
• Only qualified persons should be allowed near energized equipment.
• Treat all devices and enclosures as though they are energized.
• Never touch enclosures or devices without proper PPE (personal protective equipment).
• Do not lean on or use electrical enclosures as work surfaces.
• Always follow appropriate safety rules.
• Know what to do in case of an accident.
Working alone near exposed, energized electrical equipment isn’t just dangerous, it’s a violation of federal law. Thermographers who perform infrared inspections on any electrical equipment should never work alone. Since CPR can’t be self-administered, at least two people trained in first aid and CPR must always be present when working near most exposed, energized equipment. Having a second CPR-trained person along not only satisfies OSHA requirements, it may save your life.
To paraphrase a time-honored electrician’s admonishment, remember that while there are old thermographers and bold thermographers, there are no old, bold ones.
Jim Seffrin, a practicing thermographer with more than 30 years of experience in the field, was appointed to the position of Director of Infraspection Institute (Burlington, NJ), in 2000. This article is based on several of his “Tip of the Week” posts on IRINFO.org. For more information on electrical systems, safety, and other infrared-related issues, as well as various upcoming training and certification opportunities, email firstname.lastname@example.org or visit infraspection.com.