Analysis and treatment of transformer defects caus

2022-07-26
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Analysis and treatment of transformer defects caused by insulating oil Abstract: This paper introduces the analysis and treatment process of a transformer defect caused by the deterioration of insulating oil, and puts forward opinions and suggestions on the analysis and treatment of such defects

key words: the higher the power relevance of transformer insulation oil fault, the transformer plays an important role in the power system. Due to various reasons, transformer insulation defects frequently occur in the power system of our province in recent years. Among these insulation defects, the defect of insulation oil accounts for a large proportion, such as abnormal chromatography, excessive oil dielectric loss, etc. These defects have long tracking and elimination cycles and are difficult to deal with, which seriously threaten the security of the system. The following is an analysis of a transformer defect caused by insulating oil. 1. Transformer defect condition the startup and standby transformer of a power plant is 12a, the model is ttf-55/225, which was manufactured by Alstom in France in 1988. The transformer was deformed and short circuited between turns due to sudden short circuit on may15,1996. Firstly, the main engine was transported to abb transformer factory in Hefei for lantic to expand the product range for repair, and all coils were replaced. On September 29th, 1999, the transformer was subject to routine pre-test. During the test, it was found that the insulation resistance was significantly lower than the factory value, and the dielectric loss of medium voltage winding exceeded 0.8% specified in the preventive test code for power equipment. The test data of insulation resistance and dielectric loss are shown in Table 1 and table 2 respectively. 2 Analysis and treatment

through data analysis, it is considered that the reason for the increase of dielectric loss of transformer body is that the transformer body is damp or the quality of insulating oil is degraded. Since the transformer has been put into operation for a short time, there is basically no oil leakage in the body, and the insulation oil chromatogram and micro water data are normal, the possibility of body insulation moisture can be ruled out. From the electrical performance test of insulating oil, the dielectric loss of insulating oil has increased from 0.2% at the time of delivery to 0.7%. Although it is far less than the 4% specified in the regulations, the growth rate is fast, and the growth rate of oil dielectric loss is basically the same as the decline rate of insulation resistance. The insulating oil used in the transformer is Dalian oil. Some test data of insulating oil are shown in Table 3. In order to confirm that the defect is caused by insulating oil, the insulation resistance of the transformer after oil discharge is measured. After oil discharge, the insulation resistance of the transformer has increased significantly, and the insulation resistance of high, medium and low voltage has increased by an order of magnitude. Through the above test analysis, it is considered that the reason for the decline of insulation characteristics of transformer body is the increase of dielectric loss of insulating oil. The increase of the dielectric loss factor of the insulating oil will cause the decline of the insulation characteristics of the transformer body, and the dielectric loss will cause heat to be generated inside the insulation. The greater the dielectric loss, the 2018 Asian automobile lightweight exhibition will be grandly opened in Shanghai New International Expo Center on July 11. The more heat will be generated inside the insulation, which will further increase the dielectric loss. If this continues, a breakdown will be formed at the insulation defect, affecting the safe operation of the equipment. Therefore, it was decided to replace 12a startup and standby transformer with No. 25 insulating oil produced by Lanzhou Refinery (the dielectric loss of new oil is 0.05%). Measure the insulation resistance and dielectric loss of the transformer 24 hours after the oil change. See Table 4 for insulation test data before and after abstract oil. From the above data, the insulation resistance returned to normal after oil change, but the dielectric loss did not decrease compared with that before oil change. The analysis shows that the main reason for the large dielectric loss data of the main body after oil change is that the insulating material of 12a startup and standby transformer has been thoroughly impregnated with poor quality insulating oil before treatment, so the oil in the insulating material cannot be completely discharged during oil change, but after a period of operation, the poor quality insulating oil in the insulating material has been fully exchanged with the insulating oil in the main body, The dielectric loss of the transformer body is reduced to the qualified range required by the regulations. Three months after the oil change of 12a startup and standby transformer, the insulation resistance and dielectric loss were measured after power failure. The measured data are shown in Table 5. According to the retest data, the insulation data of 12a startup and standby transformer has been qualified. 3 conclusion and discussion

(1) when the insulation resistance, dielectric loss and leakage current of the transformer are worse than 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 of the transformer can be tested after the oil is discharged. According to the test data, it can be analyzed whether it is caused by the dielectric loss of the insulating oil or the damp of the transformer body. If the insulation resistance after oil drainage increases by nearly or more than an order of magnitude compared with that before oil drainage, it is generally considered that the insulation oil is degraded. (2) Strictly control the purchase of abstract oil, especially the oil dielectric loss index of new oil. Although the new oil is qualified if the oil dielectric loss is not less than 0.5%, the oil dielectric loss value at the time of delivery should generally be controlled at about 0.05%. (3) After oil change of transformer, the

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