By Ron Newport
In part one of our article, we concentrated on what thermography is, how it works, and why electrical inspections are the main industrial application for infrared thermography. Whether you purchase an instrument, rent or hire an outside service company, the return on investment is amazingly fast. The benefits of establishing an infrared inspection program at most facilities far out weigh the investment. These are:
This month we will look at the more practical side of infrared electrical inspections. We will discuss the sources of thermal patterns on electrical systems. Thermographers beware!! Not all "Hot Spots" are problems....We will then look at a variety of uses and applications, return-on-investment and training.
SOURCES OF THERMAL PATTERN VARIANCES ON ELECTRICAL
SYSTEMS
Thermal energy generated from an electrical component is directly in proportion to the square of the current passing through it multiplied by the components resistance (I2R Loss). As the condition of the component deteriorates, its resistance can increase and generate more heat. Then as the component temperature rises, the resistance increases further. This self propagating process continues until the melting point of the weakest component is reached. By utilizing thermography to inspect electrical systems and components under load the faulty components can be identified and classified by severity. It is interesting to note that because heat loss is proportional to the current, unbalanced or overload conditions can be identified. (I2R Loss)
When performing an infrared inspection of an electrical system, it is important to realize that all of the radiation leaving a surface is not due solely to the temperature of the surface. Unless knowledge, understanding and caution are applied during the analysis portion of the inspection, documentation and interpretation may result in the false conclusion that a fault does or does not exist.
Thermal pattern variations are normally referred to in two ways:
1) Real Temperature Differences: These are thermal patterns caused only by infrared energy exiting the surface of the object.
2) Apparent Temperature Differences: These are patterns which are due to factors other than variations of the target surface.
The causes for thermal pattern variations from electrical components are:
REAL
APPARENT
Of the real thermal pattern variances the only ones which provide true identification of faults on an electrical system are the first four:
The balance of the real and apparent causes of thermal pattern variations are very important to understand for anyone performing infrared electrical inspections. The actual component temperature may or may not change. The variances are not caused by the electrical components themselves but by outside forces creating false anomalies or disguising actual problems. So be careful when performing inspections - it's easy to be fooled.
TRUE FAULTS ARE CAUSED FROM:
Increased Resistance
Overheating of components can have several origins. Low contact pressure may occur when assembling a connection or through wear of the material e.g. decreasing spring tension, worn threads or over-tightened bolts. Another source could be deteriorated conductors of motor windings. As the component continues to deteriorate, the temperature will continue to increase until the melting point of the material is reached and complete failure occurs.
This type of fault can generally be identified because there is a "hottest point" on the thermal image. What this means is, the heat being generated is greatest at the fault point with a tapering off of thermal energy away from the fault.
Load
Load creates resistive heating as well. From a thermographic point of view, load is usually looked at as a different type of problem with specific thermal signatures. As the load on an electrical component rises, so does the temperature. An even load on each phase of a three phase system for example, should result in uniform temperature patterns on all three phases. An anomaly is identified when the overall component and conductor temperature is too high or too low. An unbalanced condition is identified by the phases not displaying a balanced, equal thermal pattern and temperature.
Unbalanced or overloaded components can be generally identified because the temperature remains relatively constant along the conductor or component as long as the object size and mass remain the same.
Harmonics
Harmonics are currents or voltages which are multiples of the basic incoming 60 HZ frequency serving an industrial distribution system. Possibly the most damaging harmonics are the odd harmonics known as triplens. The triplen harmonics add to the basic frequency and can cause severe overvoltage, overcurrent and overheating. Frequency is not the enemy of the electrical system. The real enemy is increased heat caused by higher frequency harmonics.
These triplen harmonics can create drastic overheating and even melting of neutral conductors, connections, contact surfaces, and receptacle strips. Other equipment effected by harmonics are transformers, stand-by generators, motors, telecommunication equipment, electrical panels, circuit breakers and busbars.
Induced Heating
Induced heating is the creation of heat within a material or surface by the induction of currents or fields by an external source. This phenomena will occur in areas of high electromagnetic fields such as high voltage equipment, microwave transmitters, and induction heating equipment. This condition can be induced in ferrous material when an electrically induced electro-magnetic field is present. The field induces eddy current which causes subsequent heating. This phenomena will create true surface temperature changes. Found often in (but not restricted to) ferrous bolts in aluminum electrical bus bar. This is a hard condition to identify and it will appear as something between a faulty component and an emissivity change.
Please Note: It is just as important for a thermographer to understand all the entire eleven reasons for real and apparent temperature variations that can be found on an electrical system as the four true fault conditions. If the thermographer does not understand these, many false anomalies may be reported. Contact the author for more information on real and apparent thermal variations and how they can be dealt with.
ELECTRICAL APPLICATIONS
This could be an enormous list of equipment and processes since virtually every component from generation to low voltage electronic boards can and should be inspected. Suffice it to say, the applications fall within four categories:
Baltimore Gas & Electric company perform infrared electrical inspections on 40,000 miles of distribution lines and 175 substations. The supervisor of the electrical test department is a firm believer in instituting an infrared condition monitoring program for increased reliability. He says, "The infrared equipment allows on-line maintenance with no interruption to service, resulting in continuity of service that avoids about 150,000 customer out-of-service hours a year. The annual inspection tour yields an average of 400 to 450 reports that call for either immediate repair or investigative action, gathered in all types of weather."
It is very difficult to place a dollar value on the benefits realized from an infrared inspection program because the faults are found and repaired before failure. However, companies such as Baltimore Electric, insurance carriers and risk management companies have noted the huge savings received from infrared CM programs. Table 1 itemizes equipment inspected, and in some cases, indicating potential impact and possible savings as reported by various power distribution organizations, industrial plants and insurance companies.
RETURN ON INVESTMENT
The cost of implementing an infrared condition monitoring program and the return on investment, will vary with the size of facility, complexity of the program, and whether infrared equipment will be purchased or a service hired.
Most utilities and industries recognize that infrared electrical inspections are a key element to providing electrical system reliability. For a large organization, purchasing equipment and setting up an in-house infrared condition monitoring program is economically justifiable. Many companies report a complete payback the first time the instrument is used. For example, during the initial inspection at a BC metal smelter, a hot contactor was found in their main substation which, if not found, would have brought much of the process to a halt costing hundreds of thousands of dollars. On the average, the return on investment is approximately 3 months.
Smaller industrial facilities and commercial building owners can set up an infrared inspection program by using an infrared service company. The return on investment in this situation is also excellent. For example, at one hospital, a one-day infrared inspection identified problems that could have cost $12,800.00 Some of the problems were an overheated breaker supplying power to the hospital data processing center; another breaker supplying two elevators; and a badly corroded connection in the breaker of a 50 hp motor.
Another example at a plastics manufacturing plant where an infrared inspection revealed numerous loose, dirty and corroded connections throughout the plant's main electrical distribution system. A "worse case" incident in this plant may have resulted in a $12-22,000 direct damage loss, with a 25 per cent production loss for 3 - 4 days, as compared with several hundred dollars for minor repairs, and a few hours downtime for cleaning, replacing and tightening connections. If this is compared to a typical rate of a one day inspection at $850.00, the payback is substantial.
START THE PROGRAM ON THE RIGHT FOOT
It is simple enough to purchase an infrared instrument - all vendors are willing to accommodate you. There is much more to establishing an effective infrared condition monitoring program than just buying a piece of equipment. We have found that most programs fail because the new untrained and inexperienced operator goes into the plant, finds some "hot spots", misinterprets them as problems, repairs are initiated only to find no problem exists. Both the operator and management lose confidence and the equipment is shelved. For example, a newspaper hired an infrared service company to evaluate the bearings on its printing press. A hot bearing was found and the main printing press was shut-down which severely interrupted production. The bearing was removed and it looked like new! Unfortunately, infrared thermography took the bad rap, not the untrained and unskilled thermographer.
In one of our recent Level I thermography courses, a student was showing some of his reports with "hot spots" on some overhead lines. At the end of the course, we asked the student to show his reports again so the class could evaluate them. He refused . The reason for refusal was he realized most of the "hot spots" were not problems at all but were reflections, solar gain or emittance variations only. He had been doing infrared inspections for 1.5 years prior to taking the course!
TRAINING
If maximum benefits are to be achieved from your investment in this powerful, cost reducing technology, a commitment must be made to provide proper training for the operator. If you are going to hire an outside service you must make sure their operators have received and are continuing to receive training and upgrading, just as you would expect from any one coming to your facility to perform other inspection procedures such as x-ray, ultra sound, liquid penetrant etc. Many companies now require thermographers to have a Level II thermographer standing.
Elements of a typical training course include infrared theory and principles, basic heat transfer theory, operation of infrared equipment, how to conduct inspections in facilities and temperature measurement techniques. Training in how to conduct inspections should include what false anomalies to look out for, how to analyze the information and prepare a report.
With a properly trained individual your infrared condition monitoring program will be off to a great beginning. A trained thermographer will be able to properly diagnose temperature related equipment problems and develop trends to predict equipment failure.
CONCLUSION
If safety, system reliability, product quality and better operating profit is a goal of your organization, then a properly established infrared condition monitoring program will assist in producing the results you are seeking.
Even though savings from this type of program are not always easy to identify, by determining maintenance priorities, avoiding catastrophic failure, enhancing operational safety will save untold dollars and are benefits which contribute to a stronger bottom line with happy employees and customers.
Ron Newport is with the Academy of Infrared Thermography. ET