New infrared temperature sensors in the power industry

Electricity is the most widely used secondary energy in modern society, and the power industry is an important basic industry and public utility related to the national economy and people's livelihood. It goes without saying that sensors are equivalent to the visual nerves of the power industry, and are an important guarantee for the safe and reliable operation of electricity and the stable supply of quality and quantity. In the process of power production, temperature measurement and control are very important. Accurate measurement of temperature parameters is crucial to the output quality, production efficiency and safe and reliable operation of electric energy. At present, in the process of power production and maintenance, advanced non-traditional temperature sensors such as infrared thermometers have gradually begun to be used to replace traditional thermocouples and thermal resistors. Thermoelectric temperature sensors , thereby realizing the temperature monitoring and control of the power production process or important equipment. Principles and advantages of infrared temperature sensors Infrared radiation, commonly known as infrared rays, refers to electromagnetic waves with a radiation wavelength of approximately 0.75-1000mm in the spectrum range. The physical essence of infrared radiation is thermal radiation. When the temperature of an object is above absolute zero, the thermal motion of the charged particles inside it will emit infrared rays outward. The higher the temperature of the object, the more infrared rays will be radiated, and the stronger the energy of the infrared radiation will be. Infrared thermometers are based on the energy size and wavelength distribution of infrared radiation of an object, the corresponding relationship with the surface temperature of the object, and accurately measure the surface temperature of an object by measuring the infrared energy radiated by the object itself. Compared with conventional temperature sensors such as thermocouples and thermal resistors, infrared thermometers have many advantages such as wide temperature measurement range, long life, reliable performance, extremely fast response and non-contact. In addition, infrared thermometers are particularly suitable for measuring the temperature of corrosive media and moving objects, and will not destroy the temperature field of the object being measured. In recent years, with the rapid development of microprocessor chips and infrared temperature sensing technology, the performance of infrared temperature sensors has been continuously improved, and its scope of application can cover different sections of low, medium and high temperatures. Medium and low temperature infrared temperature sensors in electrical facilities and process measurement and control The PyroCouple M series miniaturized infrared temperature sensors produced by Calex Electronics in the UK have a temperature measurement range of -20℃～+500℃, an accuracy of ±1% of the reading, a repeatability of ±0.5% of the reading, a response time of 200ms, a protection level of IP65, and can be used in an environment with an ambient temperature range of 0℃～70℃ and a relative humidity of 95%, and can output current, voltage or thermocouple signals. In power plants, it is mainly used for non-contact real-time measurement of the temperature of boiler air preheaters, busbars, important circuit breakers, motor bearings, motor windings, transformer windings, UPS or other electrical connectors, and is used to promptly detect hot spots or connection faults in equipment, thereby providing diagnosis, status inspection and maintenance of electrical systems or equipment. Fluke's subsidiary Raytech has newly launched the CM series of small integrated infrared thermometers, whose output signals are 0-5V or J, K type thermocouple continuous signals and switch alarm contact signals, and are equipped with RS232 digital communication interface, probe status and self-diagnosis display LED , which are dedicated to continuous temperature monitoring of industrial manufacturing processes. In places where there is large electromagnetic interference on site, it can be used to replace ordinary thermocouples and thermal resistors that are easily affected. The thermometer has a fast response time of up to 150ms, and can realize real-time monitoring functions in occasions such as drain pipe temperature, drain bag temperature difference water level and exhaust pipe water accumulation detection, which can fully meet the power plant's anti-water ingress protection, as well as the fast response time and reliability requirements of detection. Infrared pyrometers in furnace applications Generally, infrared thermometers that measure high temperatures (above 700℃) have a useful band mainly in the near-infrared region of 0.76 to 3mm, and the optical materials for transmission are mainly optical glass or quartz.

The Marathon series infrared thermometer produced by Raytech is an industrial-grade product designed for harsh industrial environment applications. The temperature range is -40℃～3000℃. This infrared humidity meter has a high-performance optical lens, an optical resolution of up to 300:1, and a response time of 2ms, 60ms and 120ms. It has an IP65 protection level to prevent contamination and damage during installation, setting and use. It also has standard analog, digital and distributed relay outputs, which can simultaneously transmit data, alarm triggers and control signals. It has a built-in intelligent circuit box and an easy-to-use operation interface. In addition, the sturdy stainless steel shell of the infrared thermometer can also ensure safe use in harsh industrial environments.

The temperature of the boiler furnace and the back furnace area of ​​the power plant can not only directly reflect the combustion intensity of the fuel inside and the efficiency of the combustion process, but also indirectly affect the normal operation of the boiler's heating surface and subsequent processes (such as denitrification, ash control, etc.). From the perspective of power plant safety control and efficiency, the temperature of the furnace area is very important and a key parameter that needs to be monitored. In Europe, a considerable number of power plant or boiler manufacturers (such as French Stein boiler) use the above-mentioned type of infrared optical pyrometer to measure the flue gas temperature of the furnace section of a large boiler, and thereby realize the flame detection of the entire furnace of the boiler and the protection function of furnace fire extinguishing. Application advantages of infrared imager In power plants, operators or maintenance personnel not only need to know the average temperature of the surface of the controlled object, but sometimes they also need to know the distribution of the temperature field of the monitored object in order to analyze and study whether the operation is normal and whether there are defects in the internal structure. Unlike the point-type infrared temperature measurement sensor described earlier, the infrared imager uses a surface temperature measurement method, which can intuitively display the distribution of the temperature field of the object in the form of an image to meet the needs of temperature field monitoring. The infrared imager mainly detects the radiation in the infrared electromagnetic spectrum region with a wavelength range of 0.9 to 14 mm. Through thermal imaging technology, the temperature value and temperature field distribution diagram of the thermal radiator are given and converted into a visible thermal image. Most imagers do not use conventional CCD or CMOS sensor elements, but special FPA (focal plane array) to sense longer wavelength bands. The most commonly used FPAs are InSb, InGaAs, HgCdTe and QWIP. At present, the temperature sensitivity of the most advanced infrared imagers in the world can reach up to 0.03℃. When using infrared thermal imagers in practice, you only need to input relevant parameters such as thermal range, thermal level, atmospheric temperature, ambient temperature, emissivity of the object being measured and measurement distance into the instrument's embedded computer to automatically obtain results such as temperature distribution. Infrared imagers can quickly and accurately detect hidden dangers such as loose or poor contact of electrical equipment joints, unbalanced loads, overloads, overheating, etc. (the potential hazards caused by these hidden dangers are arcing, short circuits, equipment ignition or burning, resulting in more serious accidents or fires, etc.). For all equipment that can be seen directly, infrared imagers can determine the thermal hazards of all connection points, and for those parts that cannot be seen directly due to shielding, they can discover their potential hazards based on the heat conduction to the external components. For this situation, there is no better way for traditional detection methods except disassembly inspection. It can be seen that the role of infrared imagers is irreplaceable in the operation test of circuit breakers, conductors, busbars and other components. In addition, infrared imagers can also easily detect overload of transmission or power supply circuits or imbalance of three-phase loads. Detection examples of infrared imagers In the United States, there are dozens of companies that can provide infrared imager inspection services. They can use infrared imagers to inspect all electrical equipment and distribution systems of power customers, including high-voltage contactors, fuse panels, main power circuit breaker panels, contactors, and all distribution lines, motors and transformers, to ensure that all electrical equipment in operation of customers does not have latent thermal hazards and can effectively prevent the occurrence of fire accidents. Figure 4 shows an infrared thermal image that can easily detect abnormal operation of the left fuse using an imager. In addition, infrared imagers can also be used to monitor the flame of the boiler furnace and the water level of the drum to determine whether the equipment cooling pipe is blocked, whether the bearing temperature of the turbine generator set or the fan/pump set/motor is too high, whether the drainage of the drain pipeline is smooth, whether there is internal leakage of the regulating valve/shut-off valve, whether the process pipeline or container is operating normally, whether dangerous or harmful gases are leaking, and other abnormal phenomena. For example, SF6 (sulfur hexafluoride) is a greenhouse gas, and its greenhouse effect is 23,900 times more harmful than CO2 gas. And because it has the advantages of high insulation strength, good thermal conductivity and excellent arc extinguishing performance, SF6 gas is widely used as an insulating and arc extinguishing medium in high-voltage equipment. The GasfindIR LW gas high-sensitivity infrared imager produced by FLIR Corporation of the United States can detect the leakage or emission of more than 20 greenhouse or volatile organic compound gases, and can also be used to detect whether there is SF6 leakage in power equipment in real time, so as to protect the earth environment on which human beings depend for survival.