How to correctly diagnose equipment failure with infrared thermometer

The core issue of infrared diagnosis of equipment failure requires accurate acquisition of the temperature distribution of the equipment under test or the temperature value and temperature rise value of the fault-related points. This temperature information is not only the basis for judging whether the equipment has a fault, but also the objective basis for judging the fault attributes, location, and severity. Therefore, the calculation and reasonable correction of the temperature of the fault-related parts of the equipment under test is the key link to improve the accuracy of the surface temperature of the detection equipment. However, when the infrared detection of equipment is carried out on site, due to the changes in the detection conditions and the influence of the environment, the same equipment may get different results due to different detection conditions. Therefore, in order to improve the accuracy of infrared detection, it is necessary to take corresponding countermeasures and measures or select good detection conditions or make reasonable corrections to the detection results during the on-site detection process or in the analysis and processing of the detection results. Generally, we need to apply the infrared thermometer according to the following conditions and influences: 
　　
　　Influence of the operating status of electrical equipment:
　　
　　Electrical equipment failure is generally a heating failure caused by current effect (conductive circuit failure-heating power is proportional to the square of the load current value), and a heating failure caused by voltage effect (insulating medium failure-heating power is proportional to the square of the operating voltage). Therefore, the working voltage and load current of the equipment will directly affect the effect of infrared detection and fault diagnosis. The increase of leakage current can cause uneven voltage in some high-voltage equipment. If there is no load or the load is very low, the heating of the equipment failure will not be obvious. Even if there is a serious fault, it is impossible to expose it in the form of characteristic thermal anomalies. Only when the equipment is running at rated voltage and the load is greater, the heating and temperature rise will be more serious, and the characteristic thermal anomaly of the fault point will be more obvious. In this way, when conducting infrared detection, in order to obtain reliable detection results, the equipment should be operated at rated voltage and full load as much as possible. Even if it is not possible to operate at full load continuously, an operation plan should be prepared so that the equipment can be operated at full load for a period of time before and during the detection, so that the fault part of the equipment has enough heating time and its surface can reach a stable temperature rise. When diagnosing electrical equipment faults by infrared, the fault judgment standard is often based on the temperature rise of the equipment at rated current. Therefore, when the actual operating current is less than the rated current during the detection, the temperature rise of the equipment fault point actually measured on site should be converted into the temperature rise of the rated current.

Infrared measuring instruments for equipment surfaces obtain equipment temperature information by measuring the infrared radiation power on the surface of electrical equipment. And when the infrared diagnostic instrument receives the same infrared radiation power from the target, different test results will be obtained due to different surface emissivity of the target. In other words, for the same radiation power, the lower the emissivity, the higher the temperature will be displayed. The surface emissivity of an object is mainly determined by the material properties and surface conditions (such as surface oxidation, coating materials, roughness, and contamination conditions, etc.). Therefore, in order to accurately measure the temperature of electrical equipment using infrared measuring instruments, it is necessary to know the emissivity value of the target being tested, and input this value into the computer as an important parameter for calculating the temperature, or adjust the ε correction value of the infrared measuring instrument, so as to make emissivity corrections to the measured temperature output value. Two countermeasures to eliminate the influence of emissivity on the test results: When using an infrared thermometer for measurement, the emission must be corrected, and the emissivity value of the surface of the device under test must be found and corrected, so as to obtain reliable temperature measurement results and improve the reliability of the test; for infrared detection of equipment parts with frequent failures, in order to make the test results have good comparability, the method of applying appropriate paint can be used to increase and stabilize its emissivity value, so as to obtain the true temperature of the surface of the device under test.

Influence of atmospheric attenuation:

• The infrared radiation energy on the surface of the electrical equipment under test is transmitted to the infrared detection instrument through the atmosphere, which will be affected by the absorption attenuation of gas molecules such as water vapor, carbon dioxide, carbon monoxide in the atmospheric combination and the scattering attenuation of suspended particles in the air.
  　　
  　　The attenuation of the equipment radiation energy transmission will reduce the transmittance of the radiation of the equipment under test as the distance between the detection instrument and the equipment under test, so its attenuation increases with the increase of distance. Reducing the radiation contrast between the faulty part and the normal part of the equipment under test will also reduce the target energy received by the infrared instrument, making the temperature displayed by the instrument lower than the actual temperature value of the fault point under test, resulting in missed detection or misdiagnosis, especially for equipment failures with low temperature rise. As the detection distance increases, the influence of the atmospheric combination will become greater and greater. In this way, in order to obtain the accuracy of the target temperature, it is necessary to try to choose a season when the ambient atmosphere is relatively dry and clean for detection; shorten the detection distance as much as possible without affecting safety, and at the same time, it is necessary to make a reasonable distance correction to the temperature measurement result in order to measure the actual temperature value.
  　　
  　　Influence of meteorological conditions:
  　　
  　　bad meteorological environment (rain, snow, fog and strong wind, etc.) will have an adverse effect on equipment temperature detection and often give false fault phenomena. In order to reduce the impact of meteorological conditions, it is best to conduct the test on a rainless, fogless, windless night with a relatively stable ambient temperature.
  　　
  　　Influence of environmental and background radiation:
  　　
  　　When the infrared thermometer is used for infrared detection of outdoor power equipment, the infrared radiation received by the detection instrument includes not only the radiation emitted by the corresponding parts of the equipment under test, but also the reflection of other parts of the equipment and the background, as well as the direct solar radiation. These radiations will interfere with the temperature of the equipment to be tested and bring errors to fault detection. In order to reduce the impact of environmental and background radiation, when conducting on-site infrared detection of outdoor electrical equipment, it is best to choose to conduct it on a cloudy day or at sunset when there is no light. This can prevent the impact of direct incident, reflected and scattered solar radiation; for indoor equipment, the lighting can be turned off and the impact of other radiation can be avoided. For highly reflective equipment surfaces, appropriate measures should be taken to reduce the impact of solar radiation and radiation from surrounding high-temperature objects, or the detection angle should be changed to find the best angle to avoid reflection for detection. In order to reduce the impact of solar radiation and the surrounding high-temperature background radiation, appropriate shielding measures should be taken during detection, or appropriate infrared filters should be installed on the infrared measuring instrument to filter out solar and other background radiation. Select an instrument with appropriate parameters and detection distance for detection so that the device under test is within the instrument's field of view, thereby reducing interference from background radiation.