Safer inspection of high-energy control panels

Jon Chynoweth
Vice President
Mikron Infrared
Oakland, N.J.

It can be a frustrating question if you're a plant manager worried about electrical hardware. Today's higher equipment use rates and lower staffing levels at many plants call for aggressive preventive maintenance on electrical panels.

Until now, however, standard methods for safely IR scanning electrical panels and cabinets to find hot spots and pinpoint future failures have not been appealing. Removing or opening electrical panels always poses a risk when high energy levels are involved. Human error, equipment failure, and other factors can quickly turn stable conditions in a cabinet into a dangerous environment for the inspector and anyone nearby.

Closed-door inspections are safer and a better use of manpower. They let thermographers work without electricians and with much-less protective clothing. But these inspections traditionally require cabinets with costly and fragile IR-transparent windows (or sight glasses), which let a small portion of the cabinet interior be viewed through a camera. Metal-mesh ports are also used.

IR sight glasses of crystalline materials screen out much of the IR light and are typically made of calcium fluoride, germanium, sodium fluoride, or zinc selenide, which are expensive. Just a few square inches cost hundreds or thousands of dollars. Worse, they're extremely fragile and prone to vandalism by disgruntled employees. Most are also highly susceptible to scratching and damage from UV light and corrosive fumes, and require an overlay or coating to protect against breakage and degradation. Unlike glass or acrylic, IR windows shatter easily under pressure. The most common material, calcium fluoride, is also hygroscopic and has a reputation for dissolving in humid environments, leaving gaping holes in cabinet doors.

IR windows and metal screens add an unpredictable amount of IR attenuation or transmission loss, so temperature measurements taken by a thermographer cannot be considered accurate. And metal screens also break and can fall into the cabinet, creating a hazard of their own.

IR windows, even with wide-angle lenses, restrict thermographers to seeing only a portion of the cabinet interior. It can take four or more sight glasses (at a cost of about $200 to 300 apiece) to scan the entire inside of a panel. Sight glasses also mount in relatively large holes in cabinet doors, a safety hazard if the window breaks.

An alternative has recently been developed for closed-door inspections that requires no IRtransparent or metal-mesh windows. It lets a thermographer scan a panel by looking through a 0.62-in. opening in the door. This new system, SpyGlass, combines a viewport and a mating fisheye lens.

This combination of windowfree port and fisheye lens makes company-wide standardization feasible and affordable because the cost comes down as the number of ports ordered goes up. (Prices start at about $50.) Industry leaders such as GE, Exxon Mobil, Boeing, DuPont, and Cargill have installed thousands of these UL-approved ports.

Spyglass lets thermographers inspect energized electrical switch gear without opening the panel. Therefore panels maintain original safety ratings. The device works on cabinets energized with 480 to 13,200 V, as well as motor junction boxes with 4,160 V.

The viewport uses only a 0.62-in. aperture covered by a screw-on cap to maintain cabinet integrity and safety rating when not in use. An optional lock for the cap prevents unauthorized access to the cabinet. The viewport is unaffected by moisture, dirt, UV, and corrosive environments, and it never needs cleaning or replacement.

The viewport mates with the coneshaped tip of a special lens barrel for an IR camera. The plastic-tipped barrel prevents the lens from touching the port or cabinet, and provides a layer of insulation to eliminate a path-to-ground hazard. By contrast, the metal rim of a camera lens touching an IR window might easily damage the window.

In addition to the lens' wide field of view, its tip fits into the viewport like a ball-and-socket joint, letting the camera swivel to look up, down, and to the sides, as well as straight ahead.

The fisheye lens in the viewport has a relatively wide field of view (53° horizontal by 40° vertical, or 66° diagonal). It provides temperature measurement accuracies of ±3°C. The fisheye lens, with a focus range of 4 in. to infinity. (10 cm to infinity) and large depth of field reduces the need to refocus for electrical cabinets with different depths.

The viewport is UL approved for installation at the OEM level or as a retrofit in the field on NEMA-Type 1, 2, 3, 3R, 4, 5, 12, 12K, and 13 enclosures. It is suitable for indoor and outdoor cabinets, as well as vertically and horizontally mounted cabinets.