Thanks to today’s economic climate, the only thing that facility directors and engineering managers have seen diminish more than their general maintenance budget is their pro-active or preventive maintenance budget. With that in mind, thermography, now more than ever, is an excellent way to economically assess the health and welfare of a facility’s electrical distribution system. But how do you best assess which piece of equipment to include in your survey? And how do you successfully select a themographic contractor who will provide you with a successful site scan? Understanding the basic concepts of thermography and touching on what it can and can’t do is a good starting point.
Thermomagraphy defined. Thermographic scans of equipment are noncontact, nondestructive surveys. Unlike an arbitrary system torque and tightening procedure, a thermographic scan doesn’t require you to de-energize equipment, which will save you losses in production or increases in payroll from scheduling the work during overtime hours.
In the area of equipment, modern thermographic cameras have accuracy in the neighborhood of 3°C to 5°C. Today’s longwave cameras are non-cooled and very compact, unlike older equipment, which was powered by several large external batteries and required an external cooling source, such as liquid nitrogen. Because of these advances in technology, greater numbers of power distribution equipment can now be surveyed in the same amount of time. And after all, time is money.
In order to fully understand what thermography can do, you also need to understand what it can’t do. Thermography is not x-ray technology. You can’t expect thermography to see through covers or dead-fronts. Every object, including our own bodies, emits photon radiation. This is what the thermal junctions in the camera detect. The electronics in the camera then convert this radiation pattern into a recognizable image that may be stored in the camera or used later in a report.
It’s important to note that cameras, however, only “read” the temperature on a piece of equipment to a surface depth of three microns. Therefore, if covers or dead-fronts aren’t removed during the site scan, you’ll be missing a large number of connections in your survey.
For example, if you surveyed a branch circuit panel with the panel cover and dead front in place, you would only be able to see the bodies of the breakers. This is the wrong method for several reasons. First of all, you couldn’t see the panel feeder connections to the main lugs or main breaker. In addition, you wouldn’t be able to see the panel busses, breaker-to-bus connections, load wire-to-breaker connections, or neutral-to-bus connections. In many respects, such a survey could be viewed as a total waste of time and expense.
The basic concept and theory used to detect system anomalies is differential temperature, or Delta T. You should look for and compare like objects under like loads. In the case of a branch circuit panel, you may note that some breakers may be operating at higher temperatures than others. However, this may or may not be a problem. If one 20A breaker looks hotter than another, you should then take an amp probe reading to determine if there is more connected load on that breaker than the other. Any load over 80% of rating is considered an overloaded circuit.
The proper comparison wouldn’t be breaker to breaker, but breaker to buss and branch circuit connection, or surface temperature of the conductor insulation near the field connection to the surface temperature of the conductor insulation a few inches away. In a perfect world, if all connections were tight and had no resistance, the temperatures throughout this path would be at equilibrium and you wouldn’t have a Delta T. This same method is applied to all equipment, no matter what its type.
The most common differential temperature criteria used by thermographers today are those in NFPA 70B. This standard sets forth guidelines for differential temperature analysis and lists recommended actions based on those Delta-Ts. A Delta T of 7.3°F to 14.4°F (4.1°C to 8.0°C) falls into the alert category. In such cases, you should take action during the next scheduled maintenance cycle. The next level, 14.5°F to 27°F (8.1°C to 15°C), is classified as severe. This calls for a repair before the next scheduled maintenance cycle, and/or in a timely manner. A Delta T greater than 27°F (15.1°C) is classified as critical, which calls for an immediate repair.
Preparing for the big scan. Now that you understand the benefits and limitations of thermography, it’s time to develop a plan of action for your facility. As facilities manager or engineering director, your first step is to perform a mental inventory of your electrical system. Picture those pieces of equipment or sections of power distribution system that are critical to your facility operations, and make a few notes. Grab a copy of the plant’s one-line diagram, walk through the facility, and prioritize equipment as most critical to least critical. You should also note the number of items surveyed versus your thermographic budget. This step is useful on two levels. First, it will help you get an accurate bid from your contractors. Second, if the selected contractor can complete the identified list of most critical equipment in the time allotted, they can easily continue surveying the less critical pieces of equipment noted on your priority list until they run out of time.
It’s also important to carefully choose the time of year and time of day your equipment is surveyed. Thermography is only effective if the equipment is operating under normal working conditions. Thus, determine what time of year your facility is operating at its most normal peak loads. Also, note what time of day each piece of equipment operates under full load and try to schedule the scan during that general time frame. It serves no value to scan equipment that may be energized, but sitting idle.
Finding a qualified contractor. Where do you find a competent thermographic contractor? A good first step might be to check with facility directors of local area hospitals and hotels. These facilities regularly test their systems to maintain high levels of reliability. They should be able to provide you with a good reference. Another good source is the Professional Thermographers Association, which maintains a directory of consulting companies on its Web site at www.prothermographer.com.
As you begin to contact your potential list of contractors, ask them to supply you with a list of their clients and samples of their reports. When reviewing their reports, ask yourself these important questions:
Are the reports professionally prepared?
Are they easy to read and understand?
Do they contain all pertinent information to allow your staff or your preferred electrical contractor to make the necessary repairs with ease?
You should also inquire about the level of formal training, certifications, and years of experience of the thermographer that they would send to your facility. Many infrared equipment manufacturers offer their own excellent certification programs through their own internal training networks.
It’s also important to keep in mind that some thermographic contractors use licensed electricians as certified thermographers, while others don’t. This fact becomes important on a number of levels. If thermographers are licensed electricians, then they’re qualified to remove and replace equipment covers as needed throughout the scan. If, however, they aren’t qualified electricians, you’ll have to assign your own maintenance personnel to accompany the thermographer during the scan. Companies who use non-qualified electricians as thermographers won’t allow their employees to remove covers on their own. Secondly, if thermographers understand electrical installation and service practices, they’ll most likely be able to provide a more in-depth explanation of the problem and recommend a repair.
Preparing for the survey. Once you’ve secured a qualified contractor to perform the survey, there are a few preliminary steps you should take care of before the survey begins. First, provide the contractor with an accurate list of items you need surveyed. Then, select a competent person on your staff whom the contractor may report problems to if needed. If you’re unable to provide maintenance personnel as an escort during the survey, it’s important to provide the contractor with a photocopy layout of your facility with the equipment locations clearly marked. It’s also important that you note if any of these areas are secured or locked, and that arrangements are made to allow them timely access to these areas. Other items to note include the proper entrance and exit locations throughout the facility and typical lunch periods, in case you’re providing maintenance personnel to assist with the scan. As a final note, you need to make your facility staff aware of the upcoming thermographic survey. This step is important so that upon their arrival, the thermographer’s work may commence without lost time.
Once the thermography crew is on-site, be sure to tell them to check in every morning and give you an idea of the areas within the plant they’ll be working. Each evening as they check out they should provide you with a review of any anomalies they detected during the day’s survey that fell into the alert and severe categories. Critical category anomalies would have been reported at the time of detection.
Upon completion of the project, the contractor should provide a complete copy of the report in an agreed-upon and timely manner. The report should include the thermographer’s contact information, in case you have any questions you might need answered regarding the report.
The preceding information is by no means meant to serve as a complete guide to planning your thermographer’s visit. It is, however, a great start. If you take these suggestions and tailor them to your specific facility, you should minimize any downtime or confusion once the thermographic study at your site begins and be able to realize a maximum number of scans in a given timeframe.
McNabb is a FLIR / ITC Level II Certified Thermographer with U.S. Electrical, a TEGG Service provider, in Lenexa, Kan.