1. The performance of the insulation should be guaranteed when replacing the insulation.
The replaced insulation shall be tested for performance and shall be used in accordance with the requirements. In particular, the insulation of the lead frame wood block should be taken seriously. The wooden block should be immersed in the thermal transformer oil of about 80 °C for a period of time before installation to ensure the insulation of the wooden block.
2. The transformer insulation test should be carried out 24 hours after the transformer is oiled.
Since some moisture-insulated parts are immersed in hot oil for a long time, the moisture will spread to the surface of the insulation. If the test is done after oiling, the insulation defects will not be detected. For example, a 31.5MVA 110kV transformer low-voltage side replaces a bracket wood block of the kV copper bar during processing. After the transformer is oiled, the test is normal. The 10kV low-voltage side reduces the insulation resistance of the core, the clamp and the ground to about 1mΩ. After inspection by the hood, it was found that the insulation of the 10kV copper platoon was very low. Therefore, the insulation test should be carried out more reliably after the transformer is oiled for 24 hours.
3, iron core reload should pay attention to its sharp corner
When reloading the iron yoke, pay attention to the sharp corner of the iron core chip, and measure the insulation between the oil passages in time, especially pay attention to the sharp corner of the chip at the oil passage, to prevent the chip from overlapping and causing the iron core to be grounded at multiple points. For example, a 120MV 220kV transformer, when replacing the winding iron yoke on the low-voltage side, because there is no attention to the chip angle when reloading, and the oil-to-tank insulation is not measured in time, the insulation between the oil channels is measured after installation. Finally, it took a long time to find out because the core of the core chip shorted the oil passage.
4. Replace the winding material with strong resistance to short circuit and improve the structure.
The mechanical strength of the transformer winding is mainly determined by the following two aspects: one is the mechanical strength of the winding determined by the structure of the winding itself; the other is the support on the inner diameter side of the winding and the axial compression structure of the winding, the pull plate, the clamp, etc. The mechanical strength determined by the manufacturing process. Currently, most transformer manufacturers use semi-hard copper wire or self-adhesive transposition wires to improve the winding's own short-circuit resistance. The better quality cardboard cylinders or the number of struts are used to increase the radial force of the windings. The pulling plate or the spring pressing nail is used to improve the axial force of the winding. As the technical department of the power transformer, when the technical demonstration before the transformer sales contract is signed and when the transformer winding is replaced, the short-circuit resistance of the winding should be fully investigated and given sufficient attention.
5, the drying of the transformer
Since the transformer generally takes a long time to be repaired after being short-circuited, two measures can be taken to prevent the transformer from getting wet:
First, the transformer is buckled before the daily work, vacuum pump is used to vacuum the transformer to remove the free water on the surface of the transformer body. When the next day starts, the vacuum is released by using dry nitrogen or dry air. After the hot oil cycle, it can be put into operation directly in 24 hours.
Second, after the daily work, the rain protection measures are taken on the transformer. After the work is completed, the transformer is dried by the hot oil spray method. This method generally takes 7-10 days.
In addition, after the transformer has a short-circuit fault, in addition to testing the transformer according to the conventional project, the test results of the transformer oil, gas relay gas, winding DC resistance, winding capacity and winding deformation measurement should be combined to judge the nature of the fault. Also check the deformation of the winding, the displacement and looseness of the core and the clamp, and then determine the treatment plan for the transformer and the precautions to be taken. When the winding is severely deformed due to a short-circuit fault of the transformer, it is necessary to pay attention to the replacement of the core chip, the drying of all the insulating parts, the processing of the transformer oil and the overall drying of the transformer.
