Infrared thermometers in pre-maintenance and diagnosis in the electrical/ power industry

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This post was last edited by Wang Tianze on 2017-5-23 at 11:02 —— High-precision and high-repeatability infrared thermometers can accurately measure the temperature of abnormal areas and key electrical equipment. http://bbs.dqccc.com/upload/2017/5/20/6af319d9-3bcb-4efd-931d-e075f50b006a.pngOverview: Infrared thermometers/thermal cameras can measure the surface temperature of objects from a safe distance away from them, which makes them essential tools for electrical maintenance. By detecting thermal defects in electrical equipment and circuits, it is possible to identify, address them promptly, and prevent the occurrence of major accidents. The guidelines on the application of infrared diagnostic techniques for live equipment state that during testing, an imager is generally used first to conduct a comprehensive scan of all areas that need to be inspected, in order to identify those with abnormal operating conditions; thereafter, accurate temperature measurements are taken of these abnormal areas as well as of key electrical equipment. The F572-2 series and the F56X-2 series are the best choices for accurate measurements. Concept: Thermal defects in electrical equipment/wires: Generally refer to the heating phenomenon caused by internal or external factors. Based on the different causes of defects, they can be classified into three types: The first type involves components that have been exposed to the air for a long time; poor contact occurs due to the effects of temperature and humidity or surface scaling, or damage to the components results from external forces, which in turn leads to a reduction in the conductive cross-sectional area and subsequent heat generation. If the joint is not properly connected, the bolts and washers are not tightened enough ； Corrosion oxidation under long-term operation ； Corrosion caused by active gases and dust in the atmosphere ； Poor quality of components and inadequate processing and installation techniques lead to damage to the conductors ； Reduction in the actual cross-sectional area of the conductor due to various factors such as mechanical vibration ； Unstable load current or exceeding limits, etc. The second reason is a fault within the electrical appliance itself, such as excessive resistance caused by poor contact of internal connection components ； Aging, cracking, and peeling of insulating materials ； The internal components become damp, resulting in increased component loss ； Blockages in the cooling medium pipelines, and so on. The third type is the eddy current loss caused by leakage magnetic flux. The scope of diagnosis includes the stator winding bar connections, core, brushes, end caps, and cooling system of generators; rotating motors, transformers, bushings, circuit breakers, disconnectors, instrument transformers, wave arresters, power capacitors, surge arresters, power cables, busbars, wire connections, composite electrical apparatus, insulator strings, low-voltage electrical equipment, as well as the secondary circuits of devices that exhibit heating effects due to current or voltage or other types of heating effects. Judgment methods: 1. Surface temperature judgment method; 2. Relative temperature difference judgment method. For current-heating type devices, accurate temperature measurement is required to calculate the relative temperature and determine the nature of the defects. 3. Comparative method of the same type A. Within the same electrical circuit, compare the temperature rise at corresponding locations when the three-phase currents are symmetric and the three-phase equipment is identical, in order to determine whether the operating conditions are normal ； B. For voltage-heating devices of the same model, it is possible to determine whether the device is functioning properly by examining the differences in temperature rise at the corresponding points. 4. Thermogram analysis 5. Archival analysis – Data analysis for different periods (temperature, temperature rise, relative temperature difference, and thermograms). Specific diagnostic methods: 1. Infrared thermometers can directly measure the temperature of visible equipment and components, thereby enabling quick and effective detection of any thermal issues at the connection points. 2. For those parts that cannot be seen directly due to obstruction, analysis can be conducted based on the temperature changes resulting from heat transfer to the external components. By taking into account the actual conditions on site, such as the current temperature, wind volume, and load, appropriate judgments can be made depending on the specific circumstances. For example, in the case of Level 1 danger: Is the temperature difference between these phases greater than 24°C? Is the absolute temperature 94°C, or is it higher than the reliable measurement being used? Is there any visible sign indicating that the metal or insulation layer has melted or changed color significantly? To prevent equipment failures and unexpected shutdowns, it is recommended to follow the following comprehensive preventive maintenance procedures: Connectors are typically subjected to alternating current loads, and changes in ambient temperature cause them to heat up (expand) and cool down (contract) repeatedly. Over time, the connectors become loose, and since loose connectors present high impedance to electric current, this results in power consumption and heat generation. Similarly, dirt, carbon deposits, and corrosion on the connector can also cause high impedance. When checking connectors, it is important to know the temperature difference between the connector and the ambient temperature; if the ambient temperature is unknown, it can be measured quickly using a non-contact thermometer. If the connector is 10°C higher than the ambient temperature, it indicates a poor connection, a short circuit to ground in the circuit, or an unbalanced load. More experts agree that if its temperature reading is 30°C or more higher than the ambient temperature, it indicates a serious problem. In motor manufacturing plants, there are usually hundreds of polyphase motors in operation. To ensure the service life of these motors, it is necessary to monitor their temperature in order to maintain a balanced power distribution among the phases and an appropriate operating temperature. NEMA—the International Electrotechnical Manufacturing Association—recommends maintaining a power balance of ±1% to prevent damage or burning out of the motor. An infrared thermometer can be used to check whether the temperatures of the power connector and the circuit breaker (or fuse) are the same. When motor bearings are damaged and cause vibration in the motor or a deviation of the axis, heat is usually generated; an infrared thermometer can be used to measure the temperature of the bearings. Infrared thermometers enable maintenance engineers to detect hot spots before equipment fails, allowing for timely routine repairs or replacements. If the operating temperature of the motor winding insulation exceeds the specified maximum value, the lifespan of that insulation will be **reduced; the normal service life of the armature winding insulation is approximately 10 years. The table below illustrates the effect of operating temperature on the insulation life of windings: http://bbs.dqccc.com/upload/2017/5/20/a55f82c8-21c3-4f80-8623-fecfc5e2f093.png Research by electrical maintenance professionals shows that the surface temperature of windings is 10°C lower than that inside them. When the thermal overload protection device fails to function and the motor stops, an infrared thermometer can effectively locate the fault. Phase-to-phase measurement in three-phase circuits: High-voltage three-phase power circuits are commonly used in industrial power systems. For induction motors, large computers, and other equipment, it is important to maintain phase-to-phase power balance; a power imbalance caused by overload or short grounding can lead to damage or shutdown. Use a non-contact infrared thermometer to check whether the temperatures between the cables and connectors are equal; if the measured temperature difference is 5°C or more, it indicates a problem immediately. Transformers usually have the maximum operating temperature indicated on them. The windings of air-cooled devices can be measured with an infrared thermometer to check for excessive temperatures, as any hot spots indicate damage to the transformer windings. Wires and cables can be monitored using an infrared thermometer to detect overheating caused by breaks, corrosion, aging, etc. By comparing the two cables, it can be determined which one is carrying a higher current, as it is the cable with the higher temperature. The connections between the DC batteries in an uninterruptible power supply can become loose or corroded, which generates additional heat. An infrared thermometer can be used to identify hot spots in the connections on the UPS output filter, while cold spots indicate that the DC filter circuit is disconnected. Low-voltage batteries should be checked using a contactless temperature sensor to ensure proper connections; poor connections between the batteries in a battery pack can cause the wiring terminals to burn out. The aged electrical components of a ballast can cause the lighting fixture to overheat, and an overheating ballast can be detected using an infrared thermometer before it starts to smoke. The electrical system is on-site, and infrared thermometers help to quickly identify hot spots in connections, wire joints, transformers, and other equipment, thus helping to save costs effectively. Because regular temperature monitoring can prevent huge costs resulting from equipment damage and unexpected system shutdowns. In these areas, managing electrical systems involves regularly measuring the temperature of transformers, wires, or components installed at high heights above the ground or in other hard-to-reach locations. It explains how to determine the actual source of the problem once a temperature reading is obtained This requires making a judgment by combining the experience of the repair and maintenance technicians with regard to the equipment, and the rated values provided by the manufacturers of the electrical components being monitored. Electronic device manufacturers usually specify a maximum allowable temperature. Related products: Infrared cameras of the Ti series; Infrared thermometers of the F572-2 series; Infrared thermometers of the F56X-2 series. http://bbs.dqccc.com/upload/2017/5/20/9a05e7d6-83c0-49b2-b4bf-c8a852b18b9d.png
Features of the F-572-2 infrared thermometer: High testing accuracy (up to 1% for F570/MX); high distance ratio (D:S) (up to 60:1 for F570/MX); high testing repeatability (up to 0.5%); short response time (up to 250ms for F570/MX); adjustable emissivity; powerful and durable design.
Instructions for using the instrument: 1. Select an appropriate environmental temperature reference body; 2. Set the instrument’s emissivity correctly; 3. Ensure an appropriate testing distance; 4. Perform compensation for environmental parameters