Six Judgment Methods of Infrared Defect
In dlt_664-2008_ application specification for infrared diagnosis of live equipment, there are six methods to determine infrared defects, which are as follows:
1. Surface temperature judgment method
The defect is directly judged according to the temperature threshold. When the temperature reaches the threshold point, it is set as the defect, which is the easiest one of all defects to be judged. In most cases, it is used for current - induced thermal defects.
2. Comparative judgment of the same kind
Similar comparison refers to the comparison of similar tested equipment. The so-called similar equipment means that their model, working condition, environmental temperature and background thermal noise are the same and comparable equipment.
The specific method is to compare the temperature values of the corresponding parts of similar equipment, but the possibility of simultaneous thermal failure should not be excluded. This method is mostly used for the comparison between three-phase equipment. Generally, the comparison between ABC three-phase equipment is carried out because the working conditions of three-phase equipment are basically the same. If one side of the thermal image is obviously different from the other two terms, it can be judged that the phase is a suspected defect.
3. Image feature judgment method
Image feature judgment is usually used to determine the voltage - induced thermal defects of a method. Since similar image features always appear when defects of the same reason occur, such defects are considered to occur when similar image features are found. Image feature judgment method can help power detection personnel to find defects in the field work, and at the same time to provide solutions.
If the B phase of a current transformer is caused by internal defects, resulting in uneven temperature, we can not only judge the defects of the equipment, but also find reasons to eliminate them from the equipment.
4. Relative temperature difference judgment method
The relative temperature difference judgment method refers to the temperature difference between two corresponding measuring points in the same or basically the same condition of two devices (refers to the equipment model, installation location, environmental temperature, surface condition and load size), and the percentage of the temperature rise ratio of the relative thermal measuring point. It is to eliminate the influence of different equipment load and ambient temperature on infrared detection and diagnosis results.
For example, the B phase of a blade brake overheats, with a maximum temperature of 103.9 degrees Celsius and a minimum temperature of 52.4 degrees Celsius. The maximum relative temperature difference reached 107%, which is a critical defect. If only according to the hot spot temperature judgment method, it is a serious defect, so this method can help us judge the real defect condition of the equipment before the load reaches the peak.
5. Archive analysis and judgment method
Archival analysis is a diagnostic method that compares the measurement results with the infrared diagnostic technology files of the equipment. In general, we usually need to use the database to make comprehensive judgment.
6. Real-time analysis and judgment method
In general, the defects of equipment are easy to change with the change of load. When the load of equipment is low, the defects are not easy to be exposed or even disappear; when the load is high, the defects are easy to be exposed or even more serious. So we can use some online monitoring equipment to monitor important equipment for a long time.