March 30, 2006
Alcoa has key(hole) to fast, safe infrared inspections of switchgear without "NASA suit" PPE
$50 UL-approved port lets thermographer inspect through closed door with minimal PPE. Costs one-tenth of an IR window, transmits full IR spectrum.
April 2006, Newburgh, IN – Alcoa does not like surprises, specifically unplanned downtime that interrupts power from its Warrick Power Plant in Newburgh, Indiana. Like other global leaders, Alcoa is building its bottom line with an aggressive reliability program aimed at elimination of unplanned downtime. But it’s hard to eliminate unplanned downtime without thermographic surveys of switchgear in a generating station where the newest unit dates to 1970.
The days of opening panel doors for those surveys ended with the plant’s adoption of Alcoa’s Electrical High Voltage Safety Standard 32.60, which is even more stringent than NFPA 70E. But Senior Power Reliability Engineer Brent Welz found an inexpensive and clever workaround: the Mikron Infrared Viewport, a simple 0.50” opening that’s UL approved and uses no IR-transparent window. Like a keyhole, a Viewport allows a thermographer with Mikron’s SpyGlass lens to do infrared scans with the doors closed, eliminating the need for “NASA suit” PPE. The $50 port is significantly less expensive than the $300-600 unit cost for IR transparent windows, the only other alternative for closed-door inspections. “With 60 PORTS installed, we’ve saved more than $20,000 over the cost of IR windows,” says Welz.
The Warrick Power Plant is a four-unit, 742 megawatt (MW), coal-fired, steam-electric generating facility. Units 1, 2 and 3, rated at 144 MW each, and one-half of the 300 MW Unit 4 are owned by Alcoa. Vectren, an Indiana gas and electric utility, owns the other half of Unit 4. All of the units were placed in service between 1960 and 1970. Of the Alcoa-owned generation, nearly all of the power is provided to Warrick Operations, an integrated smelting and fabricating facility that produces aluminum sheet for beverage and food can ends and tabs, along with other flat-rolled products.
"Our two options for open-door inspection of medium-voltage switchgear under the Alcoa safety standard are to wear 100-calorie protective gear or operate the infrared camera remotely from a safe distance,” says Welz. “The suit imposes physical limits on what a thermographer can do and see while using the IR camera, not to mention that it can be intolerably hot inside that suit. Remote operation of the camera eliminates the suit, but adds its own hurdles to camera setup and aiming.”
IR surveys have proven their worth for Alcoa, so Welz explored IR-transparent windows as a solution to allow “closed door” inspections. IR windows are made of various crystalline materials, all of which reduce to some degree the amount of infrared energy getting to the camera’s detector. The windows used on electrical cabinets typically transmit IR energy only in the wavelength of 0.13 to 10 microns. However, the “sweet spot” for an infrared camera is 8-14 microns. If the window cuts off at 10.0 microns, then the camera misses more than 70% of the energy emitted by the target. This reduction of energy on the detector results in lower image quality and severely compromises temperature values computed with camera algorithms established for the 8-14 micron range.
"The reduction in transmitted IR energy is critical when you’re looking at switchgear,” Welz explains. “Switchgear is usually oversized for the load, so it runs cool. This means the IR camera must detect subtle temperature differences in an environment with very low levels of emitted infrared. This makes it difficult to identify what you’re seeing in the camera so you can verify you’re scanning the correct targets. Anything that attenuates the energy reaching the camera’s detector is going to compromise results.”
IR windows have other practical issues as well. The hygroscopic crystal materials of the window absorb moisture over time, reducing image quality. The crystal material is also easily scratched or cracked, so a camera lens barrel cannot be pushed against it. Any removal of the heavy bolt-on cabinet doors risks breaking the window if the panel flexes or absorbs an impact. And, any window will attract dirt and oils over time, which creates a dilemma for cleaning the inside surface.
"The greater concern for us was the cost of the windows – $300-600 each,” Welz states. “Using a camera’s standard lens, you’d need more than one window for each cabinet, or with a wide angle lens, you’d probably need a larger, more expensive window because the wide angle usually has a larger-diameter front optic. We swallowed hard and were planning to try some windows, but then learned about Mikron Infrared’s Viewport as an alternative. At $50 for a non-locking port and $85 for the locking version, it was an easy decision to change direction. The Viewport is part of a system that requires a special wide angle lens, but our thermography service has the lens.”
The Viewport uses no IR window, so there’s no reduction in the infrared energy that reaches the camera. The port allows a wide-angle lens known as a SpyGlass, to scan the interior of a cabinet through an opening just 0.50” diameter. The patented port is UL approved for NEMA Type 1, 2, 3, 3R, 4, 5, 12, 12K and 13 enclosures. The lens/port system enables closed-door thermal inspections of connected electrical switchgear, while maintaining the original safety rating on cabinets energized with up to 15,000 volts.
The Viewport is designed to “dock” with the cone-shaped tip of the SpyGlass barrel. The tip works with the port like a ball-and-socket joint, allowing the camera to be rocked at different angles to look up, down and to the sides, as well as straight ahead. When not in use, the port is covered by a sealed, screw-on or lockable cap. The SpyGlass lens has a wide field of view (53° horizontal by 40° vertical, or 66° diagonal) and provides temperature measurement accuracy of ±3°C. Focusing as close as 2” and providing great depth of field, it is ideal for situations where components are crowded or near the door.
"We currently have about 60 ports installed, and we add more during scheduled outages,” Welz explains. “With the port and the lens, there’s a defined area you can view at a certain distance, and we position the port to adequately cover the cabinet interior. We’ve been using one port per cabinet. Had we used windows it probably would have required more than one. Standard IR camera lenses don’t have a 54° field of view and they focus to only 12”. You can’t press the lens on the window anyway, so when you back the camera away from the door surface, you never get your full field of view inside the cabinet.” Coverage and image quality are as good today as when the cabinet doors used to be removed, he adds. “And an entire unit’s switchgear can be scanned in about 45 minutes with the port, compared to 4-5 hours if we removed the doors and worked the camera remotely or with the required PPE.”
The only PPE needed when scanning switchgear through the Viewport is what Alcoa classifies as Level 2: hardhat, safety glasses, ear plugs and no synthetic fabrics. “It’s a big step down from the 100-calorie suit, and makes the job fast and easy,” Welz adds. “The ports may be even more valuable as we apply them on our 480V equipment where the cramped nature of the cabinet makes a close-focusing, wide-angle lens valuable. We think the ports will also facilitate our use of ultrasound detection, which we’re currently implementing. Eventually, we may have enough of them installed to justify buying a SpyGlass lens for our own Mikron 7515 camera, which we use for day to day work and verification of our repairs, etc.”
For additional information on the Viewport/SpyGlass system, contact Mikron Infrared at 888-506-3900 or email
