Application and precautions of infrared thermometer in equipment fault diagnosis
The impact of the operating status of electrical equipment:
Electrical equipment faults are generally caused by heating faults due to current effects (conductive circuit faults - heating power proportional to the square of the load current value), and heating faults caused by voltage effects (insulation medium faults - heating power proportional to the square of the operating voltage). Therefore, the working voltage and load current of the equipment will directly affect the effectiveness of infrared detection and fault diagnosis. The increase in leakage current can cause uneven voltage in some high-voltage equipment. If there is no load running or the load is very low, it will cause the equipment to malfunction and heat up insignificantly. Even if there are more serious faults, they cannot be exposed in the form of characteristic thermal anomalies. Only when the equipment is operating at rated voltage and the load is higher, the heating and temperature rise become more severe, and the characteristic thermal anomalies of the fault point are exposed more clearly. In this way, in order to achieve reliable detection results during infrared detection, it is necessary to ensure that the equipment operates at rated voltage and full load as much as possible. Even if continuous full load operation cannot be achieved, an operation plan should be developed so that the equipment can operate at full load for a period of time before and during the detection process, allowing sufficient heating time for the faulty part of the equipment and ensuring stable temperature rise on its surface. When infrared diagnosis is used for electrical equipment faults, 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 detection, the temperature rise at the fault point of the equipment measured on site should be converted to the temperature rise at rated current.
The influence of device surface emissivity:
Any infrared measuring instrument obtains device temperature information by measuring the infrared radiation power on the surface of electrical equipment. And in the case where the infrared diagnostic instrument receives the same infrared radiation power from the target, different detection results will be obtained due to the different surface emissivity of the target. That is to say, with the same radiation power, the lower the emissivity, the higher the temperature displayed. The emissivity of an object's surface is mainly determined by its material properties and surface state, such as surface oxidation, coating material, roughness, and contamination status. 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 tested target and input this value as an important parameter for calculating temperature into the computer or adjust the ε correction value of the infrared measuring instrument, in order to correct the emissivity of the measured temperature output value. There are two measures to eliminate the influence of emissivity on detection results: when using an infrared thermometer for measurement, the emissivity should be corrected by detecting the emissivity value on the surface of the tested equipment component, in order to obtain reliable temperature measurement results and improve the reliability of detection; For equipment components with frequent malfunctions in infrared detection, in order to ensure good comparability of detection results, the method of applying appropriate paint can be used to increase and stabilize their emissivity values, in order to obtain the true temperature of the surface of the tested equipment.
