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Analysis and Treatment of Power Transformer Defects Caused by Insulating Oil


Release time:

2018-07-27

Looking back, the "better start" of the excellent answer left such an appraisal: the first half of the whole society electricity consumption increased by 9.4 percent year-on-year, the first five months of the country's new coal power installed capacity decreased by more than 40 percent year-on-year, abandoned wind abandoned light rate to achieve "double down", to achieve a new round of electricity reform pilot full coverage ...... July 26, "out" of the national energy "mid-year exam" gold content.

Power transformers play an important role in the power system, due to various reasons. In recent years, transformer insulation defects occur frequently in the power system of our province, and the defects of insulating oil occupy a large proportion of these insulation defects. Such as abnormal chromatography, excessive oil dielectric loss, etc. These defects tracking and defect elimination cycle is long, difficult to deal with, a serious threat to the security of the system. The following is an analysis of a transformer defect caused by insulating oil.
 
1 Analysis and processing
 
Through the analysis of the data, it is believed that the reason for the increase of the dielectric loss of the transformer body is the moisture of the transformer body or the deterioration of the insulating oil. Since the transformer is put into operation for a short time, and the body is basically free of oil leakage, the insulating oil chromatography and micro water data are normal. Therefore, the possibility of moisture in the body insulation can be ruled out. From the electrical performance test of insulating oil, the dielectric loss of insulating oil increased from 0.2 at the factory to 0.7. Although it is far less than the 4% stipulated in the regulations, the growth rate is faster, and the growth rate of the dielectric loss of the oil is basically the same as the decline rate of the insulation resistance. The insulating oil used in this transformer is Dalian oil. Source: http://www.tede.cn Source: http://www.tede.cn
 
In order to confirm that the defect was caused by the insulating oil, the insulation resistance of the transformer was measured after the oil was released. The insulation resistance of the transformer increased significantly after the oil was released, and the insulation resistance of high, medium and low voltages increased by an order of magnitude. Through the above test analysis, it is believed that the reason for the decline of the insulation characteristics of the transformer body is the increase of the dielectric loss of the insulating oil.
 
The increase of the media loss factor of insulating oil will cause the decrease of the insulation characteristics of the transformer body, the media loss will generate heat inside the insulation, the greater the media loss, the more heat generated inside the insulation, thus causing the media loss to increase. If this continues, a breakdown will be formed at the insulation defect, which will affect the safe operation of the equipment. Therefore, it is decided to change the oil of 12A standby transformer and replace it with No. 25 insulating oil (the dielectric loss of the new oil is 0.05).
 
After the oil change is stopped for 24h, the insulation resistance and dielectric loss of the transformer shall be measured.
 
From the above data, the insulation resistance returned to normal after the oil change, but the dielectric loss did not decrease before the oil change. According to the analysis, the main reason for the large dielectric loss data of the body after oil change is that the insulating material has been completely impregnated with poor quality insulating oil before treatment of the 12A start-up transformer, and the oil in the insulating material cannot be completely discharged during oil change. However, after a period of operation, the poor quality insulating oil in the insulating material is fully exchanged with the insulating oil in the body, the dielectric loss of the transformer body is reduced to the qualified range required by the regulations.
 
After 3 months of oil change, insulation resistance and dielectric loss were measured during power failure. Judging from the retest data, the insulation data of 12A start-up standby transformer is qualified.
 
2 Conclusion and discussion
 
(1) When the insulation resistance, dielectric loss and leakage current of the transformer tend to deteriorate compared with the historical data and the transformer itself has no obvious oil leakage, when analyzing the causes of the defects, the insulation resistance and dielectric loss test of the transformer can be carried out after oil drainage, and whether it is caused by dielectric loss of insulating oil or damp of the transformer body can be analyzed according to the test data. If the insulation resistance after oil release is nearly or more than one order of magnitude higher than before oil release, it can be generally considered as the deterioration of insulating oil. Information to (2) When abstracting oil, we should strictly control the procurement, especially the oil loss index of new oil. Although the new oil is qualified if the oil dielectric loss is less than 0.5, the oil dielectric loss value when the oil leaves the factory should generally be controlled at about 0.05.
 
(3) after the transformer oil change, the insulation resistance will be quickly restored, but the change of the body dielectric loss may take some time, the experience obtained at present, in 1~6 months, pay close attention to the change trend of the oil dielectric loss, if necessary, can be cut off to measure the body dielectric loss.
 
(4) The method of oil change has a higher probability of success in dealing with such defects, but the cost of oil change is higher, and the time for preparation and oil change is longer. Therefore, when using this method, we should also consider various factors such as economy and power supply reliability.

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