An introduction to predictive maintenance - part 5 pptx

8.4 BASIC INFRARED THEORY Infrared energy is light that functions outside the dynamic range of the human eye. Infrared imagers were developed to see and measure this heat. These data are trans- formed into digital data and processed into video images called thermograms. Each pixel of a thermogram has a temperature value, and the image’s contrast is derived from the differences in surface temperature. An infrared inspection is a nondestruc- tive technique for detecting thermal differences that indicate problems with equip- ment. Infrared surveys are conducted with the plant equipment in operation, so production need not be interrupted. The comprehensive information can then be used to prepare repair time/cost estimates, evaluate the scope of the problem, plan to have repair materials available, and perform repairs effectively. 8.4.1 Electromagnetic Spectrum All objects emit electromagnetic energy when heated. The amount of energy is related to the temperature. The higher the temperature, the more electromagnetic energy it emits. The electromagnetic spectrum contains various forms of radiated energy, including X-ray, ultraviolet, infrared, and radio. Infrared energy covers the spectrum of 0.7 micron to 100 microns. The electromagnetic spectrum is a continuum of all electromagnetic waves arranged according to frequency and wavelength. A wave has several characteristics (Figure 8–5). The highest point in the wave is called the crest. The lowest point in the wave is referred to as the trough. The distance from wavecrest to wavecrest is called a wave- length. Frequency is the number of wavecrests passing a given point per second. As the wave frequency increases, the wavelength decreases. The shorter the wavelength, the more energy contained; the longer the wavelength, the less energy. For example, a steel slab exiting the furnace at the hot strip will have short wave- lengths. You can feel the heat and see the red glow of the slab. The wavelengths have 176 An Introduction to Predictive Maintenance Figure 8–4 Electromagnetic spectrum. become shorter crest to crest and the energy being emitted has increased, entering the visible band on the spectrum. By contrast, (infrared energy) when the coil comes off of the coilers it has been cooled. Energy is lost. The wavelength have increased crest to crest and decreased in frequency. 8.4.2 Heat Transfer Concepts Heat is a form of thermal energy. The first law of thermodynamics is that heat given up by one object must equal that taken up by another. The second law is that the trans- fer of heat takes place from the hotter system to the colder system. If the object is cold, it absorbs rather than emits energy. All objects emit thermal energy or infrared energy through three different types or modes: conduction, convection, and radiation. It is important to understand the differences among these three forms. Conduction Conduction is the transfer of energy through or between solid objects. A metal bar heated at one end will, in time, become hot at the other end. When a motor bearing is defective, the heat generated by the bearing is transferred to the motor casing. This is a form of conduction. Convection Convection is the transfer of energy through or between fluids or gases. If you took the same motor mentioned previously and placed a fan blowing directly on the hot bearing, the surface temperature would be different. This is convection cooling. It occurs on the surface of an object. An operator must be careful to identify the true cause and effect. In this case, the difference between good and bad source heating and the surface cooling is caused by convection. Thermography 177 RADIO INFRARED VISIBLE ULTRA- VIOLET X-RAYS GAMMA RAY Figure 8–5 Wavelengths. Radiation Radiation is the transfer of heat by wavelengths of electromagnetic energy. The most common cause of radiation is solar energy. Only radiated energy is detected by an infrared imager. If the aforementioned motor were sitting outside in the slab storage yard with slabs stacked around it, the electromagnetic energy from the sun and from the slabs would increase the temperature. The purpose of the previous example was to make the thermographer aware that other causes of the thermal energy could be found or not found. In this case, was the motor hot because of a bad bearing or because of solar radiation? Was the motor missed and failed later because of the fan blowing on it and causing convection cooling? Con- duction is the only mode that transfers thermal energy from location to location within a solid; however, at the surface of a solid or liquid, and in a gas, it is normal for all three modes to operate simultaneously. Emissivity Emissivity is the percentage of energy emitted by an object. Infrared energy hits an object; the energy is then transmitted, reflected, or absorbed. A common term used in infrared thermography is blackbody. Ablackbody is a perfect thermal emitter. Its emis- sivity is 100 percent. It has no reflection or transmittance. The objects you will be scanning will each have a different emissivity value. A percentage of the total energy will be caused by reflection and transmittance; however, because most of your infrared inspection will be quantitative thermography, the emissivity value will not be as important now. 8.5 INFRARED EQUIPMENT Listed as follows are the criteria used to evaluate infrared equipment. It is important to determine which model best fits your needs before a purchase is made. Some of these points will be important to you and others will not. You will know more about your needs after you have finished reading this book. • Portability. How much portability does your application require? Does weight and size of the instrument affect your data collection? What kind of equipment will you be scanning? • Ease of Use. How much training is required to use the imager? Can it be used easily in your environment? • Qualitative or Quantitative. Does it measure temperatures? If yes, what tem- perature range will be measured? Will you need more than one range? • Ambient or Quantitative Measurements. What are the maximum upper and minimum lower ambient temperatures in which you will be scanning? • Short or Long Wavelengths. Long-wavelength systems offer less solar re- flection and operate in the 8- to 14-micron bandwidth. Short-wavelength systems offer smaller temperature errors when an incorrect emissivity value is entered. The operating bandwidth for a short-wave unit is 2 to 5.6 microns. 178 An Introduction to Predictive Maintenance • Batteries. What is the weight and size of the batteries? How long will they last? Will you need additional batteries? How long do they take to charge? • Interchangeable Lenses. Do the ones available fit your application? What are their costs? • Monitor, Eyepiece, or Both. Will you need to show a live image to others while performing an inspection? • Analog or Digital. How will you process the images? Does the imager have analog, digital, or both capabilities? • Software. Can the software package produce quality reports and store and retrieve images? Do you require colonization and temperature editing? 8.6 INFRARED THERMOGRAPHY SAFETY Equipment included in an infrared thermography inspection is almost always ener- gized. Therefore, a lot of attention must be given to safety. The following are basic rules for safety while performing an infrared inspection: • Plant safety rules must be followed at all times. • Notify area personnel before entering the area for scanning. • A qualified electrician from the area should be assigned to open and close all panels. • Where safe and possible, all equipment to be scanned will be online and under normal load with a clear line of sight to the item. • Equipment whose covers are interlocked without an interlock defect mech- anism should be shut down when allowable. If safe, their control covers should be opened and equipment restarted. 8.7 INFRARED SCANNING PROCEDURES The purpose of an infrared inspection is to identify and document problems in an elec- trical or mechanical system. The information provided by an inspection is presented in an easily and understandable form. A high percentage of problems occur in termi- nation and connections, especially in copper-to-aluminum connections. A splice or a lug connector should not look warmer than its conductors if it has been sized prop- erly. All problem connections should be dismantled, cleaned, reassembled, or replaced as necessary. 8.8 T YPES OF INFRARED PROBLEMS There are three basic types of thermal problems: • Mechanical looseness • Load problems • Component failure Thermography 179 8.8.1 Mechanical Looseness Mechanical looseness occurs most often. A loose connection will result in thermal stress fatigue from overuse. Fuse clips are a good example because the constant heat- up and cooldown creates a poor connection. An accurate temperature measurement, or use of an isotherm, will identify a loose condition. When the isotherm is brought down to a single pixel, or temperature, it will identify the source of the loose condition. 8.8.2 Component Failure Understanding the nomenclature of the problem can identify component failure. Specifically, the actual component will be the heat source. For example, a heat-stressed fuse in a three-phase assembly will appear hotter than the other two fusses. 8.8.3 Common Problems Found and What to Scan Following are examples of what to scan while performing an infrared survey to easily detect common problems. Motor Control and Distribution Centers Have the switchgear panel covers opened or removed by qualified personnel before inspection. Scan cable, cable connections, fuse holders, fuse circuit breakers, and bus. Main Secondary Switchgear Have the switchgear panel covers opened or removed by qualified personnel before inspection. Scan cables, cables connections, circuit breakers (front and back), and bus. Circuit Breaker Distribution Panels Covers on small circuit breaker panels do not have to be removed for scanning. Circuit breakers and conductors are very close to the metal covers. Defective components are usually detectable by the heating of the cover in the area of the problem. If a problem exists, remove the panel cover to locate the problem. Only remove panel covers that can safely be removed. Bus Duct Electrical conductors are very close to the metal “skin” of the duct. Defective joints are usually detectable by the heating of the cover in the vicinity of the problem. Motors Do not scan motors less than 25 horsepower unless they are critical to production. On motors greater than 25 horsepower, scan the “T” boxes, visible conductors, connec- 180 An Introduction to Predictive Maintenance tions, and rotors. Bearing problems can be found by comparing the surface tempera- ture of like motors. Overheating conditions are documented as hot spots on the CRT and are usually found in comparing equipment, end bell and end bell (same type bear- ings), and stator to end bell. Transformer—Oil-Filled Scan transformer, transformer fins, cable connections, bushings, and tap changer. On all transformers, the oil level should be inspected during the survey. During the infrared survey, if a transformer appears exceptionally warm, the cooling radiators are near ambient temperature, and the transformer is above 50 percent of full load, the oil level is too low to circulate the oil and cooling is not taking place. Oil in the trans- formers is cooled by convection; as the load increases, the oil expands and the level increases until it then circulates in the cooling radiators. As a result of repeated oil samples and oil leaks, the reduced volume of oil causes the winding to overheat, thus reducing the life of the transformer. Plugged cooling heaters, isolated radiators, and plugged individual cooling fins can also be detected. Transformers—Dry-Type Scan transfers, cable connections, bushings, and tap changer. Enclosure covers on dry-type transformers should be removed only if there is safe clearance between the transformer connections and the enclosure panels. Some models, especially the newer ones, have screened openings for ventilation. Use these openings for your scanning survey. The iron in these transformers is hot. It will heat the bus work and cause substantial infrared reflection. By increasing the temperature scale and adjusting the level control on the imager, you will be able to get uniform images, which will show hot spots in the secondary bus or the iron. A hot spot in the iron usually indicates a short. Make certain that reflection is not a factor. Compare all windings. If temperatures are over a winding, but there is a difference in temperature of two windings, there may be an unbalanced load. A hot spot on a winding may point to a shorted turn. Transformer Bushings As a scanner moves upward on the transformer main tank and tap changer compart- ment, the bushings, lighting arresters, and their bus connections should be observed. This area is also critical because the integrity of the transformer, substation, or the complete system depends on proper installation and maintenance of each component. A survey of the transformer bushings, comparing one to the other, will reveal any loose connections or bushing problems. With the scanner, you can determine if the connection is loose internally or externally. Thermography 181 Capacitors A capacitor has two conductive surfaces, which are separated by a dielectric barrier. Capacitors usually function as power factor correctors. When energized, all units should have the same temperature if the size is the same. A high uniform temperature is normal. A cold capacitor usually indicates a blown fuse or bad cell. Isolated spots showing a high temperature on a surface of the capacitor may indicate a bad capacitor. High-Voltage Switchgear Scan lighting arresters, insulators, cables, cables connections, bussing, circuit break- ers, and disconnect switches. Load Break Switches In the switch, two metal surfaces act as conductors when they are brought into contact. Usually, problems are restricted to the contact surface. Poor contacts usually show up as hot spots. Fuses A fuse is a metal conductor, which is deliberately melted when an overload of current is forced on it. Major problems affected are loose mechanical stab clips that cause hot spots, corroded or oxidized external contact surfaces, and/or poor internal connec- tions, which are bolted or soldered. Circuit Breakers Circuit breakers serve the same function as a fuse. It is a switching device that breaks an electrical circuit automatically. Problem areas are caused by corroded or oxidized contact surfaces, poor internal connections, poor control circuitry, and/or defective bushings. Conductors The melting points and current-carrying capacity of conductors are determined by the size and base material of the conductors. During a survey, compare between phases and between conductors and connections. An unbalanced load will account for some differences between conductors. Use metering devices already installed to check the differences. The type of load will affect whether the load is balanced. Three-phase motor loads should be balanced; lighting and single-phase loads may be unbalanced. 182 An Introduction to Predictive Maintenance Other Problems • Broken strands. These hot spots are found at the support and at the cable termination. • Spiral heating. This is found on stranded wire, which is heavily oxidized. The problem will show up as a hot spiral from one connection to another. There is a load imbalance between the strands, which results in a poor connection. • Ground conductor. Usually there are no hot spots on a ground conductor. They do show up, however, as hot spots when there is abnormal leakage current to the ground. Be suspicious about such spots. Always point them out in the inspection report. • Parallel feeders. A cold cable indicates a problem when parallel conductors are feeding the same load. APPENDIX 8.1 Abbreviations DT Delta temperature. The delta notation represents the difference in two temperatures. m Electrical units for ohms. Also used to describe microns in the infrared electromagnetic scale. °C Degrees Celsius °F Degrees Fahrenheit APPENDIX 8.2 Glossary A/D conversion The conversion of continuous-type electri- cal signals varying in amplitude, frequency, or phase into proportional, discrete digital signals by means of an analog–digital converter. Absorptivity Ratio of the absorbed to incident electro- magnetic radiation on a surface. Ambient temperature Ambient temperature is the temperature of the air in the immediate neighborhood of the equipment. Analog data Data represented in continuous form, as contrasted with digital data having discrete values. Atmospheric absorption The process whereby some or all of the energy of soundwaves or electromagnetic waves is transferred to the constituents of the atmosphere. Thermography 183 Atmospheric attenuation The process whereby some or all of the energy of the soundwaves or electromag- netic radiation is absorbed and/or scattered when traversing the atmosphere. Atmospheric emission Electromagnetic radiation emitted by the atmosphere. Atmospheric radiance The radiant flux per unit solid angle per unit of projected area of the source in the atmosphere. Atmospheric reflectance Ratio of reflected radiation from the atmos- phere to incident radiation. Band A specification of a spectral range (say, from 0.4 to 0.5 microns) that is used for radiate measurements. The term channel is also in common use, with the same meaning as band. In the electromagnetic spectrum, the term band refers to a specific frequency range, designated as L-Band, S-Band, X- Band, and so on. Bandwidth A certain range of frequencies within a band. Conduction The transfer of heat through or between solids. Convection The transfer of heat through or between fluids. Corona The glow or brush discharge around con- ductors when air is stressed beyond its ion- ization point without developing flashover. Electromagnetic spectrum Electromagnetic radiation is energy propa- gated through space between electrical and magnetic fields. The electromagnetic spec- trum is the extent of that energy ranging from cosmic rays, gamma rays, and X-rays to ultraviolet, visible, and infrared radiation, including microwave energy. Emissivity Consideration of the characteristics of ma- terials, particularly with respect to the ability to absorb, transmit, or reflect infrared energy. 184 An Introduction to Predictive Maintenance Emittance Power radiated per unit area of a radiating surface. Far-infrared Infrared radiation extending approximately from 15 to 100 micrometers. Gamma ray A high-energy photon, especially as emitted by a nucleus in a transition between two energy levels. Hot spot An area of a negative or print revealing excessive light on that part of the subject. Infrared band The band of electromagnetic wavelengths lying between the extreme of the visible (approximately 0.70 micrometer) and the shortest microwaves (approximately 100 micrometers). Infrared radiation Electromagnetic radiation lying in the wavelength interval from 0.7 to 1,000 microns (or roughly between 1 micron and 1 millimeter wavelength). Its lower limit is bounded by visible radiation, and its upper limit by microwave radiation. Isothermal mapping Mapping of all regions with the same temperature. Microwave band The portion of the electromagnetic spec- trum lying between the far-infrared and the conventional radio frequency portion. Although not bounded by definition, it is commonly regarded as extending from 0.1 cm (100 microns) to 30cm in wavelength (1 to 100 gigaHertz frequency). Mid-infrared Infrared radiation extending approximately from 1.3 to 3.0 micrometers and being part of the reflective infrared. Often referred to as short-wavelength infrared radiation (SWIR). Near-infrared Infrared radiation extending approximately from 0.7 to 1.3 micrometers and being part of the radiative infrared. Qualitative infrared thermography The practice of gathering information about a system or process by observing images of infrared radiation and recording and pre- senting that information. Thermography 185 [...]... 100 50 0 1880–3140 Mercury Monel, Ni-Cu Monel, Ni-Cu Monel, Ni-Cu Monel, Ni-Cu Oxidized Monel, Ni-Cu Oxidized at 1110°F °F 38 38–260 25 100 50 0 1000 38 260 53 8 1093 1000–2000 (.000 05 on 00 05 silver) Platinum Platinum, Black Oxidized at 1100°F 53 8–1093 200– 750 93–399 100 50 0 1000 100 50 0 2000 50 0 1000 38 260 53 8 38 260 1093 260 53 8 0. 05 31–.46 0. 05 0.06 0.12 0.19 0.04 0.06 0.1 0.16 59 –.86 16–.17 0. 05 0 .5. .. Type 350 Type 350 Polished Type 446, Polished Type 1 7-7 PH ÊPolished Oxidized Type PH-1 5- 7 MO 75 450 1740 600–2000 150 0–2100 75 450 1740 200–800 300– 150 0 200–800 600–2000 200–800 300–1800 300– 150 0 200–600 300– 150 0 600–2000 300–1200 24 232 949 316–1093 816–1149 24 232 949 93–427 149–8 15 93–427 316–1093 93–427 149–982 149–8 15 93–316 149–8 15 316–1093 149–649 0.27 0 .57 0 .55 74–.87 56 –.81 0.28 0 .57 0.66... An alternator is an AC generator Motor generator A motor generator consists of an AC motor coupled to a generator The utility power energizes the motor to drive the generator, which powers the critical load Motor generators provide protection against noise and spikes, and, if equipped with a heavy flywheel, they may also protect against sags and swells Neutral One of the conductors of a three-phase wye... 25 100 50 0 199 59 9 199 59 9 93 50 4 100 100 100 227 57 7 170 0.02 0.03 0.06 0.11 0.19 0.11 0.19 0.2 0.31 0.09 0.18 0.09 0.04 0.06 0.04 194 An Introduction to Predictive Maintenance Material °F °C Bright Rolled Plate Alloy A3003, Oxidized Alloy A3003, Oxidized Alloy 110 0-0 Alloy 24ST Alloy 24ST, Polished Alloy 75ST Alloy 75ST, Polished 932 600 900 200–800 75 75 75 75 500 316 482 93–427 24 24 24 24 0. 05. .. circuit and/or isolate a circuit from its power source Volt Electrical unit of measure (Current ¥ Resistance) Watt The unit for measuring electrical power or work A watt is the mathematical product of amperes and volts (W = A ¥ V) APPENDIX 8.4 Materials List Material Metals Alloys Aluminum 20-Ni, 24-CR, 55 -FE, Oxidized 20-Ni, 24-CR, 55 -FE, Oxidized 60-Ni, 12-CR, 28-FE, Oxidized 60-Ni, 12-CR, 28-FE, Oxidized... Oxidation Strong Oxidation Liquid 390 1110 212 40 482 27 95 199 59 9 100 104 250 153 5 0.64 0.78 0.21 0. 95 0. 95 0.29 Dull Dull Smooth Polished 77 660 100 100 25 349 38 38 0.94 0.94 0. 35 0.28 Polished Rough 100 50 0 100 53 8 649 760 24 24 90–.96 86–.89 85 .88 0.28 0.42 0 .58 0.19 0.21 Wrought Iron Lead 38–260 38 06–.08 0.43 196 An Introduction to Predictive Maintenance Material Oxidized Oxidized at 1100¡F Gray Oxidized... therefore maintenance costs As a predictive maintenance tool, lubricating oil and spectrographic analysis can be used to schedule oil change intervals based on the actual condition of the oil In midsize to large plants, a reduction in the number of oil changes can amount to a considerable annual reduction in maintenance costs Relatively inexpensive sampling and testing can show when the oil in a machine... and $60,000; therefore, most predictive maintenance programs rely on third-party analysis of oil samples Simple lubricating oil analysis by a testing laboratory will range from about $20 to $50 per sample Standard analysis normally includes viscosity, flash point, total insolubles, total acid number (TAN), total base number (TBN), fuel content, and water content More detailed analysis, using spectrographic... Emissivity Bright, Galvanized Commercial 99.1% Galvanized Oxidized Polished Polished Polished Polished 77 212 932 1832 2732 3632 100 1000 50 00 25 100 50 0 1000 150 0 2000 38 53 8 2760 0.02 0.03 0.07 0. 15 0.23 0.28 0.03 0.11 0. 35 1880 Uranium Oxide Zinc °F 1027 0.79 100 50 0 100 50 0–1000 100 50 0 1000 2000 38 260 38 260 53 8 38 260 53 8 1093 0.23 0. 05 0.28 0.11 0.02 0.03 0.04 0.06 100 32–392 250 0 250 0 199 100–700... 10% Al 26% Al Dow XP-310 Low Gum Varnish (2 coats) Gum Varnish (3 coats) Cellulose Binder (2 coats) All colors Black Black Gloss Camouflage Green Flat Black Flat White Gray-Green Green Lamp Black Red White 75 75 75 75 75 75 75 75 75 75 75 75 75 75 100 100 100 200 24 24 24 24 24 24 24 24 24 24 24 24 42 24 38 38 38 93 70 70 70 200 200 70 1 25 80 80 70 200 209 200 200 21 21 21 93 93 21 52 27 27 21 93 98 93 . problem. Motors Do not scan motors less than 25 horsepower unless they are critical to production. On motors greater than 25 horsepower, scan the “T” boxes, visible conductors, connec- 180 An Introduction. per second). Motor alternator A device that consists of an AC generator mechanically linked to an electric motor, which is driven by utility power or by bat- teries. An alternator is an AC generator. Motor. amperes and volts (W = A ¥ V). APPENDIX 8.4 Materials List Material °F °C Emissivity Metals Alloys 20-Ni, 24-CR, 55 -FE, 392 200 0.9 Oxidized 20-Ni, 24-CR, 55 -FE, 932 50 0 0.97 Oxidized 60-Ni, 12-CR,