The oil immersed transformer is one of the most widely used transformer types in power systems. Its core structural design directly determines operational efficiency, safety, and service life. Whether you are a power engineering professional or a procurement decision‑maker selecting the right transformer for your project, understanding the core structures of an oil immersed transformer is essential foundational knowledge. In this article, Xinhong Electrical provides a detailed breakdown of these core components and compares them with cast resin transformers and dry transformers, helping you make a more informed choice.
I. Core Structure Overview of Oil Immersed Transformers
The basic design philosophy of an oil immersed transformer is to fully immerse the active part (core and windings) in insulating oil. The transformer oil simultaneously provides electrical insulation and heat dissipation. The main structural systems include: the active part (core and windings), the tank, the cooling system, protective devices, and bushing assemblies.
II. Core Structure 1: The Magnetic Core – The Magnetic Circuit
The core forms the magnetic circuit of the transformer and generates hysteresis losses and eddy currents during operation. It is typically laminated from high‑permeability silicon steel sheets to reduce losses and improve efficiency. Depending on the design, cores can be multi‑step stepped or wound without joints – the latter helps reduce magnetic reluctance, lower no‑load losses, and decrease noise levels.
Together with the windings, the core constitutes the “active part” – the electromagnetic heart of the transformer. The quality of the core directly affects no‑load losses and overall performance, making it a critical indicator of a high‑quality oil immersed transformer.
III. Core Structure 2: Windings – The Electrical Circuit
The windings are the electrical circuit of the transformer and perform the core function of voltage transformation. They are typically wound from copper or aluminium conductors and insulated with pressboard, barriers, and spacers between layers. In an oil immersed transformer, both high‑voltage and low‑voltage windings are submerged in insulating oil. The oil medium not only provides excellent electrical insulation – effectively isolating HV from LV windings and preventing arcing – but also rapidly carries away the heat generated during operation.
IV. Core Structure 3: The Tank – The Enclosure and Container
The tank is the outer casing of the oil immersed transformer, fabricated from welded steel plates, and houses the core, windings, and transformer oil. For larger capacity units, radiators or cooling tubes are mounted externally to increase the heat‑dissipation surface. The tank is also equipped with an oil drain valve, earthing bolts, nameplate, and rolling wheels. The sealing integrity and structural strength of the tank are directly related to operational safety and longevity, and are key quality focus areas for oil immersed transformer manufacturers.
V. Core Structure 4: Insulating Bushings – The Connection Between Internal and External Circuits
The terminals of each winding are brought out through insulating bushings to the outside of the tank for connection to external lines. These bushings must safely lead high‑voltage currents out while maintaining reliable insulation from the tank. Both high‑voltage and low‑voltage bushings are essential components of the outlet assembly.
VI. Core Structure 5: Protective and Cooling Devices – Safeguarding Reliable Operation
Oil immersed transformers are also equipped with a range of protective and cooling devices, including:
Conservator (oil expansion tank) – compensates for oil volume changes due to temperature fluctuations
Buchholz relay (gas relay) – detects internal faults and triggers alarms or trip signals
Silica gel breather (dehydrating breather) – filters moisture and impurities from air entering the conservator
Radiators – accelerate heat exchange between the oil and the surrounding environment
Tap changer – allows voltage adjustment without interrupting the load
Thermometer and oil level gauge – provide real‑time monitoring of oil temperature and level
Together, these devices form a complete protection system, ensuring safe and reliable operation under various working conditions.
VII. Oil Immersed Transformer vs Cast Resin – How to Choose?
When selecting a transformer, the comparison of oil immersed transformer vs cast resin is frequently discussed. Each type has its own advantages and suits different applications.
Advantages of Oil Immersed Transformer:
Higher cooling efficiency, suitable for large‑capacity and high‑load applications
Excellent heat dissipation, allowing higher power ratings and longer overload operation
Generally higher overall efficiency than dry‑type transformers
Advantages of Cast Resin Transformer:
Oil‑free operation – no risk of oil leakage, simpler maintenance
Superior fire safety – ideal for hospitals, airports, commercial areas, and other fire‑sensitive locations
Epoxy resin encapsulation provides excellent moisture and pollution resistance
Better short‑circuit withstand capability and impulse voltage strength
Where Dry Transformers Fit In:
Dry transformers (including cast resin transformers) are typically used for indoor installations, where fire safety is critical, or where special environmental conditions exist. In contrast, the oil immersed transformer is better suited for outdoor installation, large‑capacity transmission, and distribution applications.
VIII. Xinhong Electrical – A Trusted Oil Immersed Transformer Manufacturer
Xinhong Electrical (Jiangsu Xinhong Electrical Equipment Co., Ltd.) is a comprehensive enterprise integrating R&D, manufacturing, trading, and services, with deep expertise in industrial electrical equipment. Xinhong Electrical offers a full range of three‑phase oil‑immersed power transformers from 50 kVA to 3000 kVA, covering both standard models and customised 20 kV specifications to meet diverse customer requirements.
Xinhong Electrical’s oil immersed transformer product line is renowned for high efficiency, energy savings, stability, and reliability, and is widely used in power distribution systems, industrial plants, and infrastructure projects. As a quality supplier to the State Grid of China, Xinhong Electrical consistently earns market trust through superior quality and professional service.
Conclusion
The core structures of an oil immersed transformer – the core, windings, tank, bushings, and protective/cooling systems – together form the complete system of this classic power device. Whether you are evaluating oil immersed transformer China offerings or deciding between oil immersed transformer vs cast resin, understanding the working principles and performance characteristics of these core components is a critical first step.
Xinhong Electrical is committed to providing high‑quality oil immersed transformer solutions to customers worldwide. For more product information or professional selection guidance, please visit the Xinhong Electrical official website or contact our sales team.
