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Analysis of Causes for Insulation of Transformer Medium Voltage Side Windings . To analyze the fault of the transformer and find the cause of the problem, we must pass scientific and reasonable test tests to provide effective data information for the fault analysis, so as to perform fault diagnosis.
The outer insulation, main insulation, and ground support portion of the windings are the core components that make up the transformer's medium voltage winding insulation. It is self-healing in the gas-insulated breakdown of the transformer, and the breakdown voltage of this type is usually relatively stable. Generally, there will not be a sudden drop in the voltage value, but the solid insulation device in the transformer is broken down. Under the circumstances, the transformer's own insulation performance will be lost and self-repair will not be possible. Therefore, the problem of solid insulation must be fully considered in the detection of the transformer's medium voltage winding. In order to be able to find the root cause of transformer insulation anomalies, after conducting the AC withstand voltage test on the transformer, perform another test. In the process of measuring the insulation resistance of the transformer, the insulation resistance value test result is 30 MΩ. Insulation resistance values ​​of bushings and other parts are all above 2000 MΩ. Therefore, the insulation resistance of the transformer is not caused by the breakdown of the bushing. Measurement results of the insulation resistance of the iron core and the clamped parts are also normal. After measuring the transformer's withstand voltage, the leakage current of the transformer is measured to be 400μA when the voltage of the transformer is 4kV, and the leakage current of the transformer is 1200μA after the voltage is increased to 6kV. Then the transformer appears. The phenomenon of tripping; the test voltage is 40kV during the transformer withstand voltage test, and the leakage current value of the transformer is measured as 20μA, so the insulation of the transformer side winding is mainly caused by the breakdown of the solid insulation. .
In the investigation of the cause of the failure of the insulation function of the transformer's medium-voltage winding, it was found that it was mainly due to the solid insulation and the problem of the press plate of the bushing, which can be used to determine the lead-out line laminate of the middle bushing of the transformer. Breakdown causes the transformer's medium voltage winding insulation to be lost. Through the transformer manufacturer's inspection found that the casing of the transformer in the transformer lead plate problems, after the separate test of the laminate plate found that the main reason for the transformer winding insulation failure is caused by the loss of insulation properties of the laminate, Through the observation of the laminate, it was found that it had moisture, which led to the enhancement of the electrical conductivity of the laminate, which in turn led to the discharge and the breakdown of the laminate.
After the replacement of the laminate of the transformer is completed, an insulation test is performed on the transformer. The test result shows that the resistance value of the transformer medium-voltage winding is 6000 MΩ, thereby confirming the successful replacement. After that, the transformer was vacuumed and oiled and related operations were performed. After the transformer was placed for 48 hours, the test showed that the oiling test of the transformer complied with industry standards. At this time, the polarization index and AC resistance of the medium voltage side of the transformer were again performed. The relevant test of pressure, the polarization index of the transformer is up to standard, the direct current of leakage of the withstand voltage test is 5μA, at this moment the question of this transformer has been all eliminated. After passing the acceptance inspection, the transformer started normal operation. The transformer was found to be normal through a comprehensive AC withstand voltage test. Therefore, the root cause of this transformer is that the quality of the bushing lead laminate in the transformer is not up to the standard and the transformer appears. The test result is abnormal.