Application of Infrared Thermometer in Operating Electrical Equipment
Infrared temperature measurement diagnostic methods mainly include surface temperature judgment method, relative temperature difference judgment method, similar comparison method, thermogram analysis method, and file analysis method. Among them, the surface temperature judgment method is a method commonly used by current production test personnel. This method is based on the measured surface temperature value of the equipment and compared with the relevant regulations. , the importance of the equipment and the magnitude of the mechanical stress the equipment bears to determine the nature of the equipment defect, and most production personnel often simply judge whether the equipment is defective and the degree of defect based on whether the equipment generates heat and the absolute temperature of the heat. The subjective determination of the method is too strong, and the criterion lacks reliability, which often leads to misjudgment. The author personally thinks that the relative temperature difference judgment method and similar comparison method are more objective and correct in field judgment.
The relative temperature difference method, as the name implies, is a method of judging based on the relative temperature difference. Relative temperature difference is the percentage of the ratio of the temperature difference between two corresponding measuring points to the temperature rise of the hotter point.
Temperature rise——the difference between the surface temperature of the measured object and the ambient temperature and the surface temperature of the reference body measured successively by the same testing instrument.
Temperature difference - the temperature difference between different measured objects or different parts of the same measured object successively measured by the same testing instrument.
Ambient temperature reference body - the object used to collect the ambient temperature is called the ambient temperature reference body. It may not have the real ambient temperature at that time, but it has similar physical properties to the measured object and is in a similar environment as the measured object. For current-heating equipment, if it is found that the thermal state of the conduction part of the equipment is abnormal, the relative temperature difference is calculated after accurate temperature measurement, and the nature of the equipment defect is judged according to the provisions in the above table. When the temperature rise of the heating point is less than 10K, it is not appropriate to determine the nature of the equipment defect according to the above provisions. For equipment with small load rate and small temperature rise but large relative temperature difference, if conditions change the load rate, the load current can be increased and retested to determine the nature of equipment defects. When this kind of retest cannot be carried out, it can be tentatively determined as a general defect, and attention should be paid to monitoring.
The similar comparison method is to compare equipment of the same model and the same manufacturer. The similar comparison method can be divided into current heating type equipment and voltage heating type equipment comparison. In the same electrical circuit, when the three-phase current is symmetrical and the three-phase (or two-phase) equipment is the same, by comparing the temperature rise of the corresponding parts of the three-phase (or two-phase) current heating type (such as current transformer) equipment, it can be judged Whether the equipment is normal. If the three-phase equipment is abnormal at the same time, it can be compared with similar equipment in the same circuit. When the three-phase load current is asymmetrical, the influence of the load current should be considered. For voltage-heating equipment (such as arresters) with the same model and specification, it can be judged whether the equipment is normal according to the difference in temperature rise at the corresponding points. Defects of voltage-induced heating equipment should be determined on the basis of allowable temperature rise or similar allowable temperature difference. Generally, when the temperature difference of the same type exceeds 30% of the allowable temperature rise, it shall be regarded as a major defect. When the three-phase voltage is asymmetrical, the influence of the working voltage should be considered.
The thermogram analysis method is to judge whether the equipment is normal or not based on the difference between the thermograms of the same equipment in the normal state and the abnormal state. The file analysis method is to analyze the detection data (such as temperature rise, relative temperature difference, and thermogram) of the same equipment in different periods to find out the trend and rate of change of the heating parameters of the equipment, so as to judge whether the equipment is normal.
