What is the structure of the oil immersed transformer?

High-Level Overview: The Two Main Systems
An oil-immersed transformer consists of two fundamental systems housed together:

The Active Part (Core & Windings): The heart of the transformer, where electromagnetic induction and voltage transformation occur.

The Tank and Cooling System: The body and life-support system, which provides insulation, cooling, and protection for the active part.

relationships:

1. The Active Part (Core and Windings)
This is the assembly that is lowered into the main tank.

Core: Made from thin laminations of high-grade silicon steel (grain-oriented). The laminations are insulated from each other to reduce energy losses due to eddy currents.

Function: Provides a low-reluctance path for the magnetic flux, linking the primary and secondary windings.

Shape: Typically a closed core type (like a simple rectangle or "wound core") for better efficiency.

Windings (Coils): These are conductors wound around the core limbs. There are always at least two sets: High Voltage (HV) and Low Voltage (LV).

Conductor Material: Made of copper or aluminum, insulated with paper or enamel.

Arrangement: The LV winding is placed closer to the core, with the HV winding wound concentrically outside it. This reduces the amount of insulation needed between the LV winding and the grounded core.

Insulation: Key spacers and barriers made of pressboard and insulating paper are used to separate the windings from each other and from the core, and to provide mechanical stability.

Tap Changer: A device that allows the number of turns in one of the windings (usually the HV) to be adjusted, thereby changing the voltage ratio.

Off-Load Tap Changer (De-Energized Tap Changer - DETC): Adjustment can only be made when the transformer is de-energized.

On-Load Tap Changer (OLTC): Can adjust taps while the transformer is energized and supplying load. This is a complex component, often housed in a separate compartment from the main tank to prevent contamination of the main oil.

2. The Tank and Cooling System
Main Tank: A robust, welded steel tank that serves as the primary container for the active part and the insulating oil. It is designed to be airtight.

Transformer Oil: A highly refined mineral oil or synthetic ester oil that fills the tank.

Functions:

Insulation: It is a superior dielectric medium, insulating the live windings from each other and from the grounded tank.

Cooling: It circulates by natural convection (or is pumped), absorbing heat from the core and windings and dissipating it through the tank walls and radiators.

Radiators and Tubes: Finned panels or banks of tubes attached to the main tank to increase the surface area for heat dissipation. The oil circulates through these, and heat is transferred to the surrounding air.

Cooling Fans: For larger transformers, fans are mounted on the radiators to force air over them, significantly enhancing the cooling rate. This is known as forced-air cooling.

Oil Pumps: In large transformers, pumps are used to force the circulation of oil, improving the heat transfer efficiency.

3. Protection and Monitoring Accessories
These are crucial for the safe and reliable operation of the transformer.

Conservator (Expansion Tank): A smaller, cylindrical tank mounted above the main tank and connected to it via a pipe. It is only partially filled with oil.

Function: It allows the main tank to be completely filled with oil. As the oil heats up and expands, or cools down and contracts, the oil level in the conservator rises and falls, preventing pressure build-up or a vacuum from forming in the main tank.

Breather: A small container attached to the conservator, filled with a moisture-absorbing material like silica gel. As the transformer "breathes" due to temperature cycles, air passing through the breather is dried, preventing moisture from entering the oil and degrading its insulating properties. The silica gel is blue when dry and turns pink when saturated with moisture.

Buchholz Relay: A very important gas-actuated relay installed in the pipe between the main tank and the conservator.

Function: It detects internal faults. Minor faults generate slow gas bubbles which accumulate in the relay, triggering an alarm. Severe faults cause a sudden surge of oil, which trips the transformer's circuit breakers to disconnect it from the supply. It is a primary protection device.

Sudden Pressure Relay: A modern alternative or supplement to the Buchholz relay that detects rapid pressure waves inside the tank caused by a major internal fault.

Bushings: High-voltage, porcelain, or composite insulators that allow the electrical connections from the HV and LV windings to pass through the tank wall and connect