Power transformers play an important role in the power system. Due to various reasons, transformer insulation defects have occurred frequently in the power system of our province in recent years. In these insulation defects, the defects of insulating oil occupy a large proportion. such as Chromatographic anomalies.oil dielectric loss exceeded the standard,These defect tracking and elimination cycles are long and difficult to handle,which seriously threatens the security of the system. The following is an analysis of a transformer defect caused by insulating oil.The following is an analysis of a transformer defect caused by insulating oil.

 

1 analysis and processing

 

According to the analysis of the data, the cause of the increase in the dielectric loss of the transformer body is that the transformer body is wet or the oil quality of the insulating oil is deteriorated. Since the transformer has a short commissioning time and the body is substantially free of oil leakage, the insulating oil chromatogram and the micro water data are normal. so the possibility of the body insulation being wetted can be excluded. From the electrical performance test of insulating oil, the dielectric loss of insulating oil increased from 0.2% at the time of shipment to 0.7%. Although it is much smaller than the 4% specified in the regulations, the growth rate is faster, and the rate of oil dielectric loss growth is The falling speed of the insulation resistance is basically the same. The insulating oil used in this transformer is Dalian Oil. Source of information: http://www.tede.cn

 

In order to confirm that the defect was caused by the insulating oil, the insulation resistance of the transformer after oil discharge was measured. After the oil is discharged, the insulation resistance of the transformer increases significantly, and the insulation resistance of the high, medium and low voltages increases by an order of magnitude. Through the above test analysis, it is believed that the cause of the decrease in the insulation properties of the transformer body is due to the increase in dielectric loss of the insulating oil.due to the increase in dielectric loss of the insulating oil.

The dielectric loss factor of the insulating oil increases, which causes the insulation property of the transformer body to decrease. The dielectric loss causes heat to be generated inside the insulation. The greater the dielectric loss, the more heat is generated inside the insulation, which in turn causes the dielectric loss to increase. If this continues, it will form a breakdown at the insulation defect, which will affect the safe operation of the equipment. Therefore, it was decided to change the oil for the 12A starter and replace it with the No. 25 insulating oil (the new oil loss is 0.05%).

 

After the oil change is stopped for 24 hours, the insulation resistance and dielectric loss of the transformer are measured.

 the insulation resistance and dielectric loss of the transformer are measured.

From the above data, the insulation resistance returned to normal after 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 after oil change is that the insulation material has been completely impregnated by the poor quality insulating oil before the treatment of 12A, and the oil in the insulation material cannot be completely discharged during the oil change process. However, after a period of operation, the insulating oil with poor quality in the insulating material is fully exchanged with the insulating oil in the body, and the dielectric loss of the transformer body is reduced to within the qualified range required by the regulations.

 

After the 12A was changed, the insulation resistance and dielectric loss were measured after power failure for 3 months. From the data of the retest, the insulation data of the 12A change has passed.

 

2 conclusions 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 leakage oil, the transformer can be insulated after the oil is drained when the cause of the defect is analyzed. Resistance and dielectric loss test, according to the test data to analyze is caused by the dielectric loss of the insulating oil, or caused by the moisture of the transformer body. If the insulation resistance after oil discharge rises by nearly one order or more before the oil discharge, it is generally considered that the oil quality of the insulation oil is deteriorated. Information (2) When concentrating oil, it is necessary to strictly control the procurement, especially the oil dielectric loss index of the new oil should be strictly controlled. Although the oil loss of the new oil is not as high as 0.5%, the oil dielectric loss value of the oil should be controlled at about 0.05%.

 

(3) After the oil is changed, the insulation resistance will recover quickly, but the change of the bulk dielectric loss may take some time. With the current experience, within 1 to 6 months, pay close attention to the change trend of oil dielectric loss. If necessary, the power loss can be measured by power failure.

 

(4) The probability of success in handling such defects by oil change is higher, but the cost of oil change is higher, and the time for preparation and oil change is longer. Therefore, the economy should be considered comprehensively while adopting this method. Factors such as sex, power supply reliability and so on.