how to fill oil in transformer?

To fill oil in a transformer, first ensure the transformer is de-energized and isolated from the power supply. Use a vacuum pump to remove air and moisture from the transformer. Connect an oil filling apparatus to the transformer’s oil filling port. Gradually fill the transformer with the appropriate insulating oil, monitoring the oil level through the sight glass or gauge. Finally, check for leaks and ensure all connections are secure before re-energizing the transformer.