Large power transformers:

1- The input, output, and star point bushing connections of the transformer are opened.

2- The fan motors that cool the transformer's oil radiators are removed.

3- The oil valves of the oil cooler radiators are closed, and the radiators are removed under vacuum.

4- The silica gel tanks, which dry the moisture in the transformer oil, are removed under vacuum after their oil valves are closed.

5- The silica gel tube, which indicates the moisture content in the transformer oil, is removed.

6- The oil expansion tank is removed.

7- Transformer protective relays (Buholtz, differential, contact thermometer, thermal relay inside the oil tank) are removed.

8- Current transformers are removed from their locations. They are then placed in a protected area to prevent exposure to moisture, dust, etc.

9- The transformer's input, output, and star terminal bushings are removed. They are then protected from moisture, dust, etc.

Important: When removing the components listed in items 3, 4, 5, 6, 7, 8, 9, and 10, precautions must be taken to prevent moisture from entering the transformer (blind flanges must be installed according to the hole dimensions).

10- The oil inside the contactor tank that changes the voltage level is drained.

11- A transformer oil sample is taken and subjected to chemical and dielectric breakdown voltage tests.

12- The transformer needs to be heated without draining the oil from the transformer tank. For this, the oil level inside the transformer is lowered by 15-20 cm.

13- The oil inside the transformer tank needs to be heated.

a- This is done by applying DC current through the transformer input bushings. (The applied current should not be greater than the transformer winding current)

b- A vacuum pump is connected between the transformer's bottom valve and top valve, circulating the transformer oil within itself.

14- To drain the oil from the transformer, a vacuum pump is connected to the bottom valve of the transformer, and the pump's outlet is connected to a clean tank where the oil will be drained.

15- The oil inside the transformer is drained by opening the bleed bolt on the top of the transformer.

16- A program is prepared for the dismantling of the transformer bell. Within 16-20 hours, the bell will be opened, the connection points of the primary and secondary windings will be checked and tightened with the appropriate torque, and the transformer bell will be closed. During the work, precautions will be taken against dust, moisture, and foreign objects in the transformer.

17- Maintenance of components removed from the transformer is performed taking into account the transformer's instructions (instructions, catalog, project specifications) and they are reinstalled in their place in the correct order.

18- The insulation resistance and winding resistance of the primary and secondary windings of the transformer, as well as the transformation ratios, are measured.

19-The protective relays are tested.

20-The information written about the transformer only describes the main points. Maintenance instructions, catalogs, project specifications, and previously established maintenance protocols are taken into account when completing the work.