This is Part 1 of a two-part series on the use of infrared thermographic surveys in predictive and preventive maintenance programs. Part 2 (http://www.plantservices.com/articles/2009/125.html )explains ways to reduce data errors in IR surveys.
The use of infrared (IR) cameras in preventive and predictive maintenance (PPM) is well established. These cameras produce thermographic images and capture the temperature measurements that provide an early warning of potential equipment failures and unsafe working conditions. In some applications they’re used in stationary installations to record critical equipment images and temperature data automatically. However, most PPM programs involve an operator conducting an equipment survey manually on a standard schedule. Most mechanical, electrical, hydraulic and pneumatic equipment will benefit from their use in a PPM program.
Infrared surveys are particularly important for electrical equipment because it’s usually critical to an enterprise’s mission. Moreover, certain kinds of electrical failures pose life-threatening risks to workers.
Importance of a standard schedule
[pullquote]The IR survey frequency and scheduling often are overlooked as a standard operating procedure. Most infrared thermographers consider a standard schedule to be a generally accepted best practice. Nevertheless, plant thermographers often perform other tasks, dealing with emergency situations and unforeseen breakdowns. This often results in the IR survey schedule being viewed as optional. Such a view is understandable because IR trend data is collected over a relative long period of time, whereas equipment breakdowns and other crises must be handled immediately.
Still, skipping an IR survey can lead to equipment problems that produce their own crises, which further postpones the already-delayed survey. Such a breakdown in the IR survey routine can put the plant back into a reactionary maintenance mode. Failing to recognize this can make the IR program seem ineffective. Having a standard schedule and sticking to it whenever possible avoids this situation, while still allowing some flexibility for emergencies. Consistent IR surveys are the only way to make thermography an effective tool in preventing avoidable equipment failures (Figure 1).
Figure 1 also highlights the importance of timely repair. The thermographic image reveals a significant overheating problem. Failure of this connection would force the associated distribution control center to switch to a backup feed, and possibly force a transfer to backup generators. With all systems functioning properly, such a transfer would be seamless for most of the data and control systems. Conversely, should this component fail catastrophically, the resulting arc flash could destroy the entire feed cabinet circuitry. A catastrophic failure of this sort would cost at least 10 times more to repair than fixing the problem as found.
Figure 1. This 200-ampere terminator connector is in an electrical cabinet feeding a distribution facility. In a visible-light image, it appears normal. A thermographic image reveals abnormally high temperatures, indicating an impending failure. (Lighter colors indicate higher temperatures.)
For many installations, the IR survey schedule should start at the time the equipment is first commissioned to establish baseline data. This promotes safety, ensures proper installation, identifies OEM defects, and ensures service continuity.
Following the initial survey, a good guideline is to conduct another one within one year. However, certain equipment types warrant more frequent surveys. On the other hand, highly reliable electrical components might not require another survey for as long as three years, provided that the one-year survey reveals no problems or disturbing trends.
Establishing an IR survey plan also includes safety considerations, operational reliability, optimization of maintenance costs and communicating the results. By recognizing the importance of, and developing, a standard equipment schedule and IR survey plan, thermographers can contribute real value to their plant’s PPM program.
Safety is of utmost concern in every industry. This is particularly true in electric power distribution. Making IR thermography an effective PPM tool not only prevents equipment failure, it also improves safety for maintenance personnel. In fact, the first step in a thermographer’s survey should be to use the IR camera to sweep the entire survey area, looking for major problems that pose safety hazards. If none are found, the routine survey can begin. If a potential hazard is present, it should be documented and appropriate maintenance personnel notified immediately. In some cases, the thermographer should leave the area immediately.
Sticking to an established survey schedule and recording results ensures employees and management that any equipment on the route is in safe working order and problems are reported. In the latter case, the exception report forewarns employees of a potential hazard before they go to the area to perform their assigned duties.
Get the word out
Clearly, communication is important. In fact, many believe communication represents 70% to 80% of the effort of any good predictive program. A standard part of a thermographer’s job description includes the report generation that documents problems, their severity and potential safety hazards. Report routing also is important for alerting relevant personnel to problems. If they aren’t reported, problems won’t be fixed.
A good example of effective reporting is illustrated by what happened when the problem in Figure 1 was found. The thermographer immediately called the problem to the distribution field supervisor’s attention. The thermographer followed up with a written report to document the findings. The problem was fixed the same day, thereby preventing a catastrophic outage.
The initial IR survey, performed after equipment commissioning and startup, can identify problems related to improper installation. Figure 2 shows visual and IR images from an in-service startup survey. An improper installation of two of three terminators produced an abnormal thermal pattern.
Figure 2. A thermograph (right) of a 750 kcmil terminator on the left side of the cabinet shows excessive heat (yellow-orange color) below the fluted part of the insulator, indicating improper installation. The terminator on the right was installed correctly and isn’t overheating (the entire terminator appears nearly black).
Identifying this type of installation problem contributes to continuity of electrical service. IR surveys at startup also can identify the need for employee training that can prevent improper future installations.
Temperature trend analysis is another technique for monitoring minor problems and fixing them before they grow. Trending also provides data for determining IR survey frequency. IR camera manufacturers can supply analysis software,which provides many other functions that support effective PPM.
Timing the survey plans
Timing is important. Too frequent and you’re wasting resources; not frequent enough and you’re likely to have equipment failures. Deciding on the frequency requires a good deal of thought about usage patterns and what drives them. For example, electrical systems don’t get hot in the absence of electrical load (current). The load depends on how many pieces of equipment are tied to a system, the number in use at any one time, peak loading and other factors. In the case of electrical distribution systems, the load is customer- and weather-dependent, which relates to the time of the year. Providing reliable service to the end user is of paramount importance, so it’s a good idea to perform the IR survey when equipment is under maximum load stress.
For outdoor equipment, weather conditions affect the integrity of IR surveys. Temperature, wind speed, humidity and cloud cover are important variables when planning a survey. This is particularly true for electrical equipment, which is affected by seasonal differences.
For instance, the summer peak load occurs at a different time of day than the winter peak. Solar loading affects outdoor equipment and makes IR surveys difficult during peak summer loads unless the day is cloudy. IR cameras require a difference in either temperature or emissivity between the target object and the background. Clouds provide a better background than the sky when examining components that are located well above ground level. Clouds also reduce solar heating of target objects.
Condensation on outdoor equipment when the air temperature is below the dew point can provide cooling. With little or no wind, its affect on electrical insulators can lead to some “head scratching” hot spots. Hot spots can appear on terminators, probably caused by “tracking” or current leakage. When terminators dry out, the hot spots disappear. Trend analysis can help determine whether a problem is moisture- or defect-related.
Another consideration is gaining access to restricted areas when an escort is required. Access to secure facilities often requires several days notice and detailed documentation. Normal working hours are typically preferred to facilitate access to secure areas.
Still, such difficulties should not deter critical equipment IR surveys. Figure 3 shows a severely overheated (260°F) fuse cutout. This feeds a pharmaceutical plant that runs 24/7. An outage would severely affect the plant’s production and revenue generation. This facility has no backup generation, and there’s no way to get power to it automatically.
Figure 3. This fuse cutout shows a severe thermal problem that could produce an outage for a pharmaceutical manufacturer that operates 24/7.
Safety of maintenance personnel, equipment users and other employees is a primary consideration when conducting IR surveys. IR surveys enhance safety by identifying dangerous equipment conditions. Thermography is a powerful PPM tool that helps keep equipment operating reliably. However, to be effective, there needs to be a plan, and the plan needs to be followed. This means scheduling routine IR surveys, considering the factors that control survey timing, and communicating IR survey results to key personnel in a timely fashion. Ultimately, company management needs to recognize the value of IR surveys, and become an advocate for these programs.
William K. (Ken) Leonard is a Licensed NC Electrician at Progress Energy Carolinas in Cary, NC. Contact him at [email protected] and (919) 481-6151. Robert P. Madding is Director, ITC at FLIR Systems, Inc., N. Billerica, Mass. Contact him at [email protected]. Additional information is available at www.goinfrared.com/IRsurveys.