Seeking advice on transformer maintenance

This is something that professional maintenance personnel do

I just want to propose a simple plan to the company, and then hire professionals to implement it

A couple of days ago, we had our 10KV dry-type transformer serviced. It’s absolute nonsense – apart from a few tests, they didn’t even clean it; they were asked to do it all over again…

It’s too unprofessional; I need to pay more attention to this aspect

Dear sea friend, I’m not sure whether you use oil-based or dry-based products. If it’s oil-based, it’s a bit more complicated. I’ll upload two tables for oil-based options for your reference – it will be clear at a glance! It can be divided into major repairs and minor repairs; it is recommended to carry out a major repair after 8 to 10 years of operation, as this is considered more reliable (refer to DLT 573-2010 Guidelines for the Maintenance of Power Transformers) ； For the rest, it can be handled as a minor repair! Contents and technical standards for the major overhaul of 10kV transformers √ Serial number, Inspection contents, Technical standards, References, Inspection results, Signature of the person in charge 1 Transport of the transformer: Remove the primary and secondary leads of the transformer, and transport it from the 10kV compartment to an open outdoor area. Take proper measures to prevent rain, moisture, dust, and fire. Maintenance Guidelines 2: Transformer Core Lifting. When inspecting the transformer core, it is necessary to choose good weather conditions. Use an oil filter to drain all the oil from the unit into a clean oil tank that has been prepared in advance. Remove all components connected to it and the large cover bolts. The lifting rope should be attached to the transformer-specific lifting device, with the angle between it and the device not exceeding 60 degrees. During lifting, the rising or descending speed should not be too fast; ropes should be tied to the four corners of the core, and a dedicated person should assist to maintain stability, ensuring that there is no collision between the device body and the box walls. After the core is lifted out, a suitable location should be selected in advance, sleepers should be laid, and the core should be lowered slowly and carefully. Maintenance Guidelines 3: Body Maintenance. The time the body remains in the air (from the start of oil extraction to the start of oil injection) is 16 hours when the relative humidity is ≤65%, and 12 hours when the relative humidity is ≤75%. The core should remain flat and free of deformation, with no peeling of the insulating paint coating. Use a clean cloth to wipe away the oil and debris accumulated on the top of the iron yoke and the bottom of the lower iron yoke. Check the tightness and insulation of the core, upper and lower clamps, square iron pieces, coil pressure plates, and core-penetrating bolts; measure their insulation resistance using a megohmmeter and compare it with previous values to ensure there are no significant changes. The exposed parts of the core grounding tabs should be insulated to prevent short circuits in the core, and the core should not have multiple grounding points. The surface of the coil should remain clean and free from deformation; the entire coil should not be tilted, and the radial wires should not protrude. The shims in various parts of the coil should be arranged neatly, provide firm support, and have an appropriate degree of compression. The shielding screen is clean, undamaged, and properly secured; there are no signs of heating or tree discharge at the outlets of the tap leads. The partition plates are securely fixed in place. The insulating material at the lead wrapping area should be in good condition, without any deformation or brittleness, and the leads should have no broken strands. The leads are firmly welded at the lead joints, with no signs of welding failure or overheating. The wooden support has no signs of damage, cracks, bending, deformation, or scorching. All fixing bolts must be equipped with anti-loosening caps. Maintenance Guidelines 4: Tank Maintenance – Clean the bottom of the tank with qualified insulating oil, ensuring that no debris remains. The valves on the box walls should open and close smoothly, with correct indication. The fuel tank is well-sealed with no leaks. The exterior parts such as the fuel tank and the cover are rust-removed and painted. Maintenance Guidelines 5: Maintenance of tap changers – The mechanical parts should rotate smoothly, the bearings should be properly sealed, and there should be no sticking. The indicated position at the top should match the actual contact position at the bottom. The surfaces of the moving and stationary contacts are clean, without any signs of oxidation, discoloration, or damage. The springs and fasteners are not loose, and the surfaces of the insulating components are clean, without any signs of cracking, deformation, or moisture damage. Check whether the U-shaped fork of the insulation operating rod is in good contact. Maintenance Guidelines 6 Appendix: Maintenance. The inner and outer walls of the oil storage tank should be clean, with a uniform paint coating; all seals must be in good condition, with no leaks. The respirator’s glass cover is in good condition and has been cleaned; the discolored or ineffective desiccant has been replaced, and insulating oil has been poured into the air filter cover at the bottom. Replace the sealing gaskets in various parts of the transformer. Maintenance Guidelines 7: Core Reset – Fit the sealing gasket along the box edges, place it firmly in position, and secure it with U-shaped clamps. The core should descend smoothly to the correct position, paying attention to the distance between the device body and the box walls. Prevent damage to various components. When the core is lowered to near the edge of the box, care should be taken to align the screw holes on all sides, install the bolts, remove the U-shaped clamps, and tighten them evenly. All sealing gaskets have been replaced; their dimensions meet the requirements, and they are compressed evenly under stress – it is advisable to compress them to 2/3 of their original thickness. Maintenance Guidelines 8: Oil Filling – Use the conventional oil filling method to replace the insulation oil with qualified material. Maintenance Guidelines 9: Measurement and Testing – Tests for the overall sealing of the transformer, analysis of insulating oil in various components, and insulation tests of the transformer itself. Maintenance Guidelines 10: Rehandling of Transformers – After lifting the core of the transformer, check that there is no oil leakage from the tank and clean the exterior; rust removal and painting may be necessary if required. Move the transformer back from the outside area into the 10kV bay. Reconnect the primary and secondary leads. Maintenance Guidelines: Work Contents and Technical Standards for Minor Repairs of 10kV Transformers √ Serial Number Maintenance Content Technical Standards References Results of Maintenance Signatory 1 Transformer maintenance Remove dust and oil deposits from the outside of the transformer to keep its enclosure clean; ensure that the grounding wires are in good condition. Check the tightness of the connections on the primary and secondary sides, and make sure that all connection bolts are present and tight ； Check whether the oil level in the tank is normal, and top up the insulating oil if necessary. Replace the color-changing silica gel. Maintenance Guidelines 2 – Preventive Testing: Measurements and tests shall be carried out in accordance with the relevant provisions of the \"Guidelines for the Maintenance of Power Transformers,\" ensuring compliance with the requirements of the testing standards. Maintenance Guidelines