Oil-Immersed Transformers: The Silent Cornerstone of the Power World

In every corner of modern society, from the glittering lights of bustling cities to the scattered illumination of remote villages, the stable transmission of electricity relies on a crucial yet often overlooked device—the oil-immersed transformer. As the most widely used and technologically mature type of transformer in power systems, it acts like a low-profile “energy distribution master,” quietly safeguarding the safety and efficiency of the grid.

1. What Is an Oil-Immersed Transformer?

As the name suggests, an oil-immersed transformer is a power device in which the main structure (core and windings) is immersed in special transformer oil. Its core working principle is based on electromagnetic induction, which enables efficient long-distance transmission and rational distribution of electrical energy by altering the voltage level of alternating current.

A typical oil-immersed transformer consists of the following components:

1. Core and Windings: The core, laminated from silicon steel sheets, and the windings, wound from copper or aluminum wire, form the core components that enable electromagnetic energy conversion.
2. Tank: The transformer’s outer shell, used to house the core, windings, and transformer oil. It is typically welded from steel plates with sufficient mechanical strength.
3. Transformer Oil: Not ordinary oil, but specially treated mineral oil or synthetic ester oil. It plays multiple critical roles: insulation, heat dissipation, and arc suppression.
4. Conservator (Oil Expension Tank): Connected to the main tank, it adjusts the volume expansion and contraction of the transformer oil due to temperature changes, reducing oil-air contact and preventing oil aging and moisture absorption.
5. Cooling Equipment: Includes radiators, cooling tubes, or fans, which increase the heat dissipation area, accelerate the circulation of transformer oil, and dissipate heat generated during operation into the air.
6. Safety Protection Devices:
   • Buchholz Relay (Gas Relay): Installed in the pipe between the tank and the conservator. It triggers an alarm or trip signal when internal faults produce gas or severe faults cause sudden oil flow, making it one of the most important protective devices for the transformer.
   • Pressure Relief Device: Rapidly releases pressure in case of a sudden internal pressure surge due to a fault, preventing tank explosion.
7. Insulating Bushing: Allows the leads of the high- and low-voltage windings to safely pass through the tank cover while maintaining reliable insulation to ground.

2. Core Advantages: Why Has It Endured?

Despite advancements in technologies like dry-type transformers, oil-immersed transformers still dominate in specific fields due to their unparalleled advantages:

• Excellent Insulation and Heat Dissipation Properties: Transformer oil has a much higher dielectric strength than air, ensuring safe operation under high voltage. Additionally, oil has a high specific heat capacity and good fluidity, enabling efficient heat transfer from the core and windings to the tank walls and radiators.
• High Reliability and Long Service Life: Mature design, robust construction, and the protective nature of the oil allow oil-immersed transformers to operate stably for decades with proper maintenance, typically with a design life of 20–30 years or more.
• Strong Overload Capacity: The high thermal capacity of oil enables the transformer to withstand short-term overloads without immediate critical damage.
• Cost-Effectiveness: Compared to dry-type transformers of equivalent voltage and capacity, oil-immersed transformers have lower manufacturing costs, offering significant economic advantages, especially in high-capacity, high-voltage applications (e.g., 35kV and above).

3. Wide Range of Applications

Oil-immersed transformers are the backbone of power networks and are commonly used in:

• Power Plants: Stepping up the voltage of electricity generated by generators to extra-high voltage levels to reduce losses during long-distance transmission.
• Transmission Networks: stepping voltage up or down at substations of various voltage levels.
• Distribution Networks: Serving as distribution transformers, reducing voltage to 10kV/400V to directly supply factories, commercial centers, and residential areas.
• Industrial and Mining Enterprises: Acting as dedicated power transformers for large electrical equipment.

4. Operation, Maintenance, and Environmental Considerations

Maintenance Is Key: Regular maintenance inspections are essential to ensure safe operation, including:

• Periodic oil sampling for chromatographic analysis to diagnose internal latent faults by detecting characteristic dissolved gases (e.g., acetylene, hydrogen). This is a critical predictive maintenance tool.
• Checking oil level and temperature for abnormalities.
• Listening for unusual operating noises.
• Inspecting bushings and the tank for oil leaks.

Environmental and Safety Considerations: Traditional mineral oil is flammable, and leaks can impact the environment. To address this, the industry is actively promoting the use of high-fire-point, biodegradable synthetic ester insulating oils and enhancing sealing designs with fully sealed structures to reduce maintenance needs and environmental impact.

Conclusion

The oil-immersed transformer, a classic design that has stood the test of time, remains an indispensable foundation of the global power industry. Whether hidden behind substation fences or mounted on utility poles in the wilderness, its stable, efficient, and reliable operation is fundamental to our modern, convenient lives. With advancements in new materials, processes, and online monitoring technologies, this “veteran of the power industry” continues to evolve, silently supporting the future of smart grids.