Oil-Immersed Transformer Structures Oil-immersed transformers are widely used in power distribution and transmission systems due to their efficient cooling, insulation, and durability. The core structure consists of several key components, each playing a critical role in ensuring reliable operation. 1. Core The transformer core is typically made of laminated silicon steel sheets to minimize eddy current losses. The core provides a low-reluctance magnetic path for the flux generated by the windings. Common core configurations include: - Shell-type: Windings are surrounded by the core, offering better mechanical strength and reduced leakage flux. - Core-type: The core surrounds the windings, providing easier maintenance and better cooling. 2. Windings Windings are usually made of copper or aluminum conductors, insulated with paper or polymer materials. They are classified into: - Primary winding: Receives input voltage from the power source. - Secondary winding: Delivers transformed voltage to the load. Windings can be arranged concentrically (cylindrical layers) or disc-type (stacked sections) to optimize performance. 3. Insulating Oil Mineral oil is the most common insulating and cooling medium. It serves multiple purposes: - Electrical insulation: Prevents arcing between windings and the core. - Heat dissipation: Transfers heat from the core and windings to the tank walls. - Protection: Inhibits oxidation and moisture absorption. 4. Tank and Cooling System The transformer tank houses the core, windings, and oil. Cooling methods include: - Radiators: Finned tubes or panels increase surface area for natural convection. - Cooling fans: Forced air cooling in larger transformers. - Oil pumps: Used in high-capacity transformers for directed oil flow. 5. Bushings Bushings are insulated terminals that connect internal windings to external circuits. They are made of porcelain or composite materials to withstand high voltages. 6. Conservator and Buchholz Relay - Conservator: An auxiliary oil tank that compensates for oil expansion/contraction due to temperature changes. - Buchholz relay: A protective device that detects internal faults (e.g., gas accumulation from arcing) and triggers alarms or disconnects the transformer. 7. Tap Changer An on-load or off-load tap changer adjusts the turns ratio to regulate output voltage under varying load conditions. 8. Pressure Relief Device Prevents tank rupture by releasing excess pressure caused by internal faults or overheating. Advantages of Oil-Immersed Transformers - High efficiency and long service life. - Effective cooling due to oil circulation. - Robust insulation against high voltages. Disadvantages - Fire risk if oil leaks or degrades. - Requires regular maintenance (oil testing, filtration). In summary, oil-immersed transformers are essential in power systems, combining efficient magnetic coupling, insulation, and cooling to ensure stable electricity supply. Their design prioritizes reliability, safety, and adaptability to varying operational demands.