Do you know the main components of an oil-immersed transformer?

The oil-immersed transformer, as a commonly used Transformer Equipment in the power system, has an additional special component related to insulation and cooling oil on top of the core components of ordinary transformers. The main components can be classified into three categories: electromagnetic core components, oil tank and cooling system, and insulation and protection components. The details are as follows:
1. Electromagnetic Core Components (Energy Conversion Core)
Iron Core
Function: Forms the magnetic circuit and is the medium for electromagnetic induction. It realizes the energy transfer between the primary and secondary windings through high magnetic conductivity, and through special design reduces hysteresis loss and eddy current loss.
Material: Made by stacking oriented silicon steel sheets (with a thickness usually ranging from 0.23 to 0.3 mm), with insulating paint applied between the sheets to prevent eddy current generation; for large transformers, the iron core may also adopt a multi-level joint structure to further optimize the magnetic circuit.
Structure: Commonly in a core-type structure (with windings surrounding the iron core column), or in a shell-type structure (with the iron core surrounding the windings) in some special scenarios.
Windings (Coils)
Function: The primary winding supplies electrical energy to generate an alternating magnetic field, and the secondary winding, in the magnetic field, induces an electric field to generate electrical energy, achieving voltage and current transformation.
Material: Mainly composed of high conductivity copper wires (for some low-voltage small-capacity transformers, aluminum wires are used), with the wire surface covered by insulating materials such as insulating paper, cotton yarn, or epoxy paint to ensure insulation between windings and between windings and the iron core.
Structure: According to voltage levels, they are divided into high-voltage windings and low-voltage windings. Usually, the high-voltage windings have more turns and thinner wires, while the low-voltage windings have fewer turns and thicker wires; the winding winding method includes layer type (with clear insulation between layers, suitable for low voltage) and cake type (good heat dissipation, suitable for high voltage).
2. Oil Tank and Cooling System (Insulation and Heat Dissipation Core)
Oil Tank
Function: As the shell of The Transformer, it contains insulating oil inside and supports the iron core and windings, isolating the external environment (preventing dust and moisture).
Structure: Made by welding steel plates, large transformers' oil tanks may be designed as bell-shaped (with the upper cover able to be lifted for easy maintenance) or barrel-shaped; the surface of the oil tank is often welded with heat dissipation tubes or heat dissipation plates to enhance the heat dissipation effect.
Insulating Oil
Function: Dual functions - insulation (separating windings, iron core and oil tank, etc., to increase insulation strength) and cooling (through convection transferring the heat generated by the windings and iron core to the oil tank wall or heat exchanger).
Requirements: It should have high insulation strength, low viscosity (facilitating convection), low freezing point (adapted to low-temperature environments), and good chemical stability (not prone to oxidation and deterioration).
Cooling Device
Function: Enhances heat dissipation. According to capacity and cooling requirements, it is divided into:
Natural Cooling (ONAN): Only through natural convection of the oil tank wall and heat dissipation plates for cooling, suitable for small-capacity transformers;
Forced Oil Circulation Cooling (OFAF/OFWF): Through the oil pump to make the insulating oil flow through the heat exchanger, or combined with fans to accelerate air flow (air cooling) or water cooling (water cooling), suitable for large-capacity transformers.
3. Insulation and Protection Components (Safety Operation Guarantee)
Insulation Bushings
Function: Expose the high and low-voltage windings inside the transformer to the outside of the oil tank, and realize insulation between the windings and the oil tank (grounding).
Structure: Composed of porcelain bushings (or silicone rubber) and internal conductive rods, classified by voltage levels as low-voltage bushings (ceramic or bakelite) and high-voltage bushings (mostly ceramic, filled with oil or insulating paper tubes).
Tap Switch
Function: Adjust the output voltage of the transformer by changing the turns of the high-voltage winding, compensating for voltage fluctuations in the power grid (such as ±5% or ±2.5% voltage regulation range).
Type: Divided into no-excursion tap switch (operated without power interruption, suitable for small and medium-capacity) and on-load tap switch (operated with power on, suitable for large-capacity, high voltage stability requirements scenarios).
Protection Devices Oil reservoir (oil pillow): Connected above the oil tank, it compensates for the volume expansion / contraction of the insulating oil due to temperature changes, and reduces the contact between the oil and air (delaying oxidation). An oil level gauge is also installed inside.
Absorber (breather): Connected to the oil reservoir, it absorbs moisture from the air entering the oil pillow through silica gel to prevent the insulating oil from getting damp.
Safety vent (explosion-proof tube): When a short circuit or other faults occur inside the transformer causing a sudden increase in pressure, the oil and gas can be released through the explosion-proof tube to prevent the oil tank from bursting (modern large transformers mostly use pressure relief valves instead).
Gas relay (gas relay): Installed on the connecting pipe between the oil tank and the oil reservoir, it issues an alarm signal when a minor fault occurs internally (gas generation) and automatically cuts off the power supply when a serious fault occurs (oil flow impact), and is the core protective component of oil-immersed transformers.