Dielectric Properties of Insulating Liquids in Power Transformers

Insulating liquids within power transformers serve the dual purpose of electrical insulation and thermal regulation. Their dielectric performance is characterised by parameters such as dielectric strength, relative permittivity, dissipation factor and conductivity, which govern breakdown phenomena, field distribution and ageing behaviour. Mineral oil has dominated the market for decades but faces challenges under ultra-high voltage operation, environmental concerns and accelerated degradation. Alternative formulations—including natural and synthetic esters, bio-derived triglyceride oils and dielectric nanofluids—have emerged to address safety, sustainability and enhanced dielectric and thermal characteristics. Molecular structure, moisture content, dissolved gases and particulate contaminants interact to influence microscopic polarisation mechanisms and trap states within the fluid, thereby affecting macroscopic properties. Advances in materials science and simulation techniques have deepened understanding of interfacial charge transport and heat transfer under transient and steady-state conditions. This knowledge underpins the design of insulating systems that meet stricter global demands for reliability, fire safety and reduced environmental impact. Practical applications range from improved flood-filled transformers to retrofit solutions in existing infrastructure, ensuring operational resilience and longevity of power grids worldwide.

Research from Nature Portfolio

No recent Nature Portfolio content available.

Dielectric Properties of Insulating Liquids in Power Transformers publication trend

The graph below shows the total number of articles in dielectric properties of insulating liquids in power transformers across all publications each year (not limited to Nature Index journals).

Technical terms

Dielectric strength: The maximum electric field a fluid can withstand without electrical breakdown, typically expressed in kV/mm.

Relative permittivity: The ratio of the permittivity of a fluid to that of vacuum, indicating its ability to store electrical energy in an electric field.

Dielectric dissipation factor: A measure of dielectric losses within a fluid under alternating electric fields, representing energy converted to heat.

Nanofluid: A stable suspension of nanoscale particles in a base insulating liquid, designed to enhance electrical and thermal properties.

Ester-based insulating fluid: A biodegradable or synthetic oil containing ester groups, offering improved fire safety and environmental compatibility compared with mineral oil.

References

1. Contribution to the use of palm kernel oil methyl esters as liquid bio-insulators in distribution transformers: Experimentation and simulation of heat transfer. Results in Engineering (2024).
2. Alternative Dielectric Fluids for Transformer Insulation System: Progress, Challenges, and Future Prospects. IEEE Access (2019).
3. A Review on Properties, Opportunities, and Challenges of Transformer Oil‐Based Nanofluids. Journal of Nanomaterials (2016).
4. Photoluminescence Spectroscopy Measurements for Effective Condition Assessment of Transformer Insulating Oil. Processes (2021).