The hazards of overheating of power transformers:
1. Transformer insulation damage is mostly caused by overheating, and temperature rise will reduce the voltage resistance and mechanical strength of the insulating material. According to IEC 354 “Transformer Operation Load Guidelines”, when the hottest point temperature of the transformer reaches 140°C, air bubbles will be generated in the oil, which will reduce the insulation or cause flashover, causing damage to the transformer.
2. The overheating of the transformer has a great influence on its service life. When the insulation heat resistance class of the transformer is Class A, the insulation limit temperature of the pilot holding winding is 105°C. GB 1094 stipulates that the average temperature rise limit of oil-immersed transformer windings is 65K, the top oil temperature rise is 55K, and the iron core and fuel tank are 80K. For the transformer, under the rated load, the hottest spot of the winding is controlled below 98°C, usually the hottest spot is 13°C higher than the upper oil temperature, that is, the upper oil temperature is controlled below 85°C.
Transformer overheating is mainly manifested as an abnormal increase in oil temperature. The main reasons may include:
(1) Transformer overload;
(2) The cooling device fails (or the cooling device is not fully put in);
(3) Internal fault of the transformer;
(4) The temperature indicating device misinforms.
When the transformer oil temperature is found to be abnormally high, the above possible reasons should be checked one by one, and an accurate judgment should be made. The main points of the inspection and treatment are as follows:
(1) If the operating instrument indicates that the transformer is overloaded, the indications of the three-phase thermometers of the single-phase transformer group are basically the same (there may be a few degrees deviation), and the transformer and the cooling device are normal, the oil temperature rise is caused by the overload. The transformer monitors (load, temperature, operating status), and immediately reports to the superior dispatching department. It is recommended to transfer the load to reduce the overload multiple and shorten the overload time.
(2) If the cooling device is not fully put in, it should be put in immediately. If the cooling device is malfunctioning, the cause should be quickly found out, dealt with immediately, and the malfunction is eliminated. If the fault cannot be eliminated immediately, the temperature and load of the transformer must be closely monitored and reported to the superior dispatching department and related production management departments at any time to reduce the transformer operating load and operate according to the corresponding value of the cooling performance and load of the corresponding cooling device.
(3) If the remote temperature measuring device sends out a temperature alarm signal and the indicated temperature value is high, but the on-site thermometer indication is not high, and there is no other fault on the transformer, it may be a false alarm of the remote temperature measuring circuit fault. This type of fault can be Exclude when appropriate.
If the oil temperature of a phase in a three-phase transformer group rises, which is significantly higher than the operating oil temperature of that phase under the same load and cooling conditions in the past, and the cooling device and thermometer are normal, the heat transfer may be caused by the internal transformer. If a certain fault is caused, the professional should be notified to immediately take an oil sample for chromatographic analysis to further investigate the fault. If the chromatographic analysis shows that there is an internal fault in the transformer, or the oil temperature continues to rise under the load and cooling conditions of the transformer, the transformer should be taken out of operation in accordance with the on-site regulations.