Jiangsu DFSai Optoelectronic Co.,LTD.
Add：No.68, xinkang road cloud courtyard, north high-tech zone, nantong city, jiangsu province
The transformer casing is abnormal due to internal damage, abnormal joint, leakage of insulator and so on. The application of infrared thermal imager to transformer casing can find out whether the casing is in good working condition in time, detect problems in time, improve work efficiency and avoid accidents.
The main reasons for the abnormal heating of transformer casing are as follows
1. The casing will contact the external wiring board or internal conductive rod;
2. Oil filling sleeve;
3. Defects in the casing cause heat.
Description of thermal defect of transformer casing
1. The most common occurrence of abnormal heat in transformer bushing is due to the improper contact between the military cap and external wiring board or internal conductive rod. In this case, the surface temperature is higher than the other two at the top of the casing. (see casing figure 3 below).
2. The internal oil shortage of transformer oil filled casing can also be observed by infrared thermal imager. Because of the difference between the heat capacity of the transformer oil and the air, the speed of the two mediums in the heat absorption and heat dissipation is different. Using the infrared thermal imager to observe the outer wall of the oil filled casing, you can see a temperature dividing line - the line is the oil level line in the casing (as shown in the casing figure 4).
3. If there is a defect in the casing, it may also cause the casing to be unusually hot. In this case, the overall temperature of the failure casing is generally higher than that of other normal two phases (the infrared thermograph is shown in the casing diagram 5).
4. If there is a bad contact between the internal or external joint of the casing, or if the contact is oxidized, it may lead to the temperature anomaly of the casing contact point. In this case, the contact point of the failure casing will show that the temperature of the contact is significantly higher than that of other normal points or lines or cannulas (FIG. 6).
Application of infrared thermal imager for transformer casing thermal defects
According to the judgment of DL/T 664-2008 9.1 current heating equipment, the casing will contact the external wiring board or the external wiring board or the internal conductive rod, which is caused by the thermal failure of the current, and the judgment is based on the following:
The defects in the casing are more complicated: it may be caused by the voltage induced thermal failure, or it may be caused by the casing mechanical damage. The following are the diagnostic criteria for the thermal defects of the casing voltage in the application of infrared thermal imager:
However, the casing outer wall is an insulating ceramic with poor thermal conductivity. By measuring the surface temperature, it is difficult to obtain the real temperature inside the device. In general, we recommend a three-phase comparison to measure whether the casing is unusually hot.
For the case of casing oil shortage, it is a voltage - induced thermal failure. This kind of failure is a great danger to the safety production of power department. In the actual operation, the detection personnel should pay attention to the observation, in order to avoid significant loss. The following is the diagnostic criteria for casing shortage:
Suggestions for thermal defect treatment of transformer casing
1. If the abnormal heat is caused by contact with external terminal or internal conductive rod. It is recommended to measure the dc resistance of the casing in case of power failure. In general, the dc resistance of an unusually hot phase is higher than that of the other two phases. This proves that the high pressure casing has a bad contact. Replacement of defective parts should be replaced.
2. If it is an internal defect of the casing, it may be caused by mechanical damage to the casing or casing internal parts. The transformer oil in the casing is recommended for the analysis of the defects.
3. If the casing is short of oil. The site of the leak is recommended. Repair or replace the oil spill site when the power failure is available, and add transformer oil to the casing.
How to use the thermograph to test the transformer casing?
The casing is usually installed directly outside (also partially installed in the indoor), and it is subject to external environmental interference more, we suggest:
1) the infrared thermal imager should be careful to avoid direct sunlight, especially to avoid shooting at noon.
2) if the thermal image is not clear in the automatic mode, the temperature range of the oil pillow can be measured by automatic mode. Then manually set the level and span, set the temperature range to the minimum, and contain the temperature range of the previous measurements (the minimum temperature range of each device is different).
3) there are usually three - phase cannula in the field, and the working condition is similar, which can be used to compare the temperature of the same position of different phases, so that the failure of the casing heating can be found quickly.