1. When replacing the insulating parts, the performance of the insulating parts should be guaranteed
During processing, test the performance of the replaced insulation and use it only if it meets the requirements. In particular, attention should be paid to the insulation of the wood block of the lead bracket. The wood block should be placed in the thermal transformer oil at about 80°C for a period of time before installation to ensure the insulation of the wood block.
2. The transformer insulation test should be carried out after the transformer is filled with oil for 24 hours
Because some damp insulating parts are soaked in hot oil for a long time, the moisture will diffuse to the insulating surface, so the insulation defect cannot be detected after the test after oil filling. For example, a 31.5MVA 110kv power transformer low-voltage side replaced a 10kV copper bar bracket block during processing. After the transformer was filled with oil, the test was normal, and the 10kV low-voltage side's insulation resistance to the iron core, clamps and ground was reduced to about 1 MΩ. After the inspection of the hanging hood, it was found that the insulation of the support wooden blocks of the 10 kV copper bar was very low. Therefore, the insulation test should be carried out after the transformer is filled with oil for 24 hours to be more reliable.
3. Pay attention to its sharp corners when reassembling the iron core
When the iron core is reinstalled on the iron yoke, attention should be paid to the sharp corners of the core chips, and the insulation between the oil passages should be measured in time, especially the sharp corners of the chips at the oil passages should be paid attention to, so as to prevent the core from being grounded at multiple points by lapping of the chips. For example, for a 120MVA 220kv power transformer, when replacing the winding on the low-voltage side and reinstalling the iron yoke, because the sharp corners of the chip were not paid attention to during reassembly, and the insulation between the oil passages was not measured in time, the insulation between the oil passages was measured as 0, it took a long time to find it in the end because the sharp corner of the core chip shorted the oil passage.
4. Replace the winding material with stronger short-circuit resistance
The mechanical strength of the improved structure transformer winding is mainly determined by the following two aspects:
① One is the mechanical strength of the winding determined by the structure of the winding itself;
② The second is the mechanical strength determined by the support on the inner diameter side of the winding, the axial compression structure of the winding, and the manufacturing process of pull plates and clamps. At present, most transformer manufacturers use semi-hard copper wire or self-adhesive transposition wire to improve the short-circuit resistance of the winding itself, and use better quality cardboard tubes or increase the number of stays to improve the radial force of the winding. And use pull plate or spring pressure nail to improve the ability of winding to bear axial force.
As the technical department of the chinese transformer manufacturers, when the technical demonstration before signing the transformer sales contract and when the transformer winding is replaced, the short-circuit resistance capability of the winding should be fully investigated and paid enough attention to.
5. Drying of the transformer
After the transformer is impacted by a short circuit, it generally takes a long time to carry out maintenance. In order to prevent the transformer from being damp, two measures can be taken:
① One is to buckle the cover of the transformer before closing work every day, and use a vacuum pump to evacuate the transformer to remove free water on the surface of the transformer body. When starting work the next day, use dry nitrogen or dry air to release the vacuum. It can be put into operation directly after 24 hours of hot oil circulation after maintenance.
② The second is to take rainproof measures for the transformer after work is over every day. After all the work is completed, the transformer is dried by spraying hot oil. This method generally takes 7 to 10 days.
6. Other matters that should be paid attention to
After a transformer short-circuit accident occurs, in addition to testing the transformer according to routine items, the nature of the fault should be judged and analyzed based on the test results of transformer oil, gas in the gas relay, winding DC resistance, winding capacitance, and winding deformation measurement, and check The deformation of the winding, the displacement and looseness of the iron core and the clamp, and then determine the treatment plan for the transformer and the preventive measures that should be taken. When the winding is seriously deformed due to a transformer short-circuit accident and needs to be replaced, attention should be paid to the reassembly of the core chip, the drying of all insulating parts, the treatment of the transformer oil, and the overall drying of the transformer.