Types and Functions of Transformer Insulating Oil

Basic Structure and Main Components of Transformers

Electrical insulating oil is a liquid dielectric medium widely used in electrical power transmission equipment such as transformers, instrument transformers, switchgear, rectifiers, cables, and capacitors. Among these, transformer oil used in transformers, instrument transformers, oil switches, and rectifiers accounts for more than 98% of total insulating oil consumption.

A power transformer is a crucial electrical device used to convert electrical energy from one voltage and current to another at the same frequency. Transformer oil, specifically designed as an insulating and cooling medium, offers excellent insulation properties, thermal stability, oxidation resistance, and electrical performance. It ensures long-term operation under high voltage fields and effectively prevents faults such as arcing, discharges, and explosions.

With the development of power resources and the increasing demand for power transmission equipment, the usage of transformers, as key transmission equipment, continues to grow, leading to a steady rise in transformer oil demand.

Based on the source of base oil, transformer oil can be classified into the following four types:

1. Mineral Oil Transformer Oil

2. Vegetable Oil Transformer Oil

3. Silicone Oil Transformer Oil

4. Synthetic Ester Transformer Oil

Main Types of Transformer Oil

1. Mineral Oil Transformer Oil

Mineral oil transformer oil has been used for nearly a century due to its excellent electrical and thermal performance, making it an ideal choice for ultra-high voltage and extra-high voltage transformers.

The components of mineral oil include straight-chain alkanes, isoalkanes, cycloalkanes, and aromatic hydrocarbons, each playing a distinct role in transformer oil:

· Straight-Chain Alkanes: High freezing point and prone to generating hydrogen; rarely used directly in transformer oil production.

· Isoalkanes: Low freezing point, low acid value, and good oxidation stability make them suitable as the main component of transformer oil.

· Cycloalkanes: Low freezing point and good electrical properties make them a core component of transformer oil.

· Aromatic Hydrocarbons: Mono-aromatic hydrocarbons have good gas release properties for ultra-high voltage use, but poly-aromatics are unstable and should be removed.

2. Vegetable Oil Transformer Oil

Vegetable oil transformer oil is derived from natural oilseeds and has advantages such as high flash point, renewability, and biodegradability. Its main component is triglycerides.

Advantages: Biodegradable, environmentally friendly, with good electrical performance and high flash point.

Limitations:High viscosity, poor low-temperature performance, prone to hydrolysis that generates acidic substances.

3. Silicone Oil Transformer Oil

Silicone oil offers excellent electrical properties and a high flash point, suitable for transformers under 35kV. However, it has low stability under repeated discharges.

Characteristics: High flash point and fire resistance, but less environmentally friendly and costly, with usage declining globally and limited to niche areas (e.g., tunnel boring machine transformers).

4. Synthetic Ester Transformer Oil

Synthetic ester transformer oil excels in environmental friendliness, biodegradability, and moisture resistance, making it particularly suitable for environmentally sensitive areas like offshore wind farms.

Characteristics: Highly biodegradable and maintains high breakdown voltage under high humidity conditions.

Functions of Transformer Oil

1. Insulation

Transformer oil serves as an electrical insulating medium, effectively isolating different potentials between conductors, preventing current leakage, and enhancing equipment safety and reliability.

2. Cooling

Transformers generate significant heat during operation. Transformer oil circulates, carrying heat to cooling systems, preventing overheating and equipment damage.

3.  Arc Suppression

During switching operations, arcs can damage equipment or cause fires. Transformer oil suppresses arcs with its rapid cooling ability.

4.  Protection Against Corrosion and Moisture

Antioxidant additives in transformer oil prevent metal corrosion and isolate equipment from moisture.

Conclusion

Transformer oil is indispensable in power equipment, serving as an insulating, cooling, and protective medium. Understanding the characteristics and applications of different types of transformer oil helps select the optimal solution for power systems.