How to Improve the Energy Efficiency of Transformers with Proper Insulation

April 8, 2024

Energy efficiency has become a top priority in the electrical industry, and transformers, key components in any power distribution system, are no exception. One of the main ways to improve transformer performance and reduce energy losses is through the choice of adequate insulation. In this article, we will delve into the role of insulation in transformer efficiency, the most effective materials, and recommended insulation techniques.

The Importance of Insulation in Transformers

Insulation serves multiple critical functions in transformers:

  1. Prevents current flow between primary and secondary windings
  2. Prevents current leakage to the core and metal parts
  3. Protects windings from mechanical stress and vibrations
  4. Contributes to the dissipation of heat generated by losses

Effective insulation not only ensures the safety and integrity of the transformer but also helps reduce energy losses. Losses in transformers can be of two main types:

  1. Copper losses (or Joule losses): caused by winding resistance, proportional to the square of the current
  2. Core losses (or no-load losses): due to hysteresis and eddy currents in the core laminations, present even when the transformer is unloaded

Proper insulation helps minimize both types of losses by reducing current leakage and improving heat dissipation. This results in higher overall transformer efficiency.

Insulation Classes

Transformer insulation materials are classified based on their thermal resistance, i.e., the maximum continuous operating temperature they can withstand without degradation. The main insulation classes according to IEC 60085 standard are:

  • Class A (105°C)
  • Class E (120°C)
  • Class B (130°C)
  • Class F (155°C)
  • Class H (180°C)

The higher the insulation class, the higher the allowed maximum operating temperature. A higher insulation class offers several advantages:

  • Reduces transformer size for a given power rating, thanks to higher current density in the windings
  • Increases power output for a given size, allowing the use of a more compact transformer
  • Extends transformer life, thanks to higher resistance to thermal degradation of insulators

Of course, using higher-class insulation also involves a higher initial cost. The choice of the optimal insulation class will therefore depend on the specific project requirements and a cost-benefit analysis.

High-Performance Insulation Materials

To maximize the energy efficiency of transformers, it is essential to use high-quality insulation materials with high performance. Some of the most effective materials currently available on the market are:

  • Nomex Paper: this aramid paper offers excellent dielectric properties, high resistance to high temperatures (Class H), and outstanding mechanical strength. It is widely used for winding insulation in power transformers.
  • Mylar Film: Mylar is a polyester film that features high dielectric strength, good dimensional stability, and remarkable chemical resistance. It is used as an insulator between winding layers and as a protective barrier.
  • Kapton Film: Kapton is a polyimide film that maintains its dielectric and mechanical properties up to temperatures of 400°C. It is ideal for applications requiring thin, high-temperature resistant insulation.
  • Insulating papers and boards: available in various insulation classes (from A to H), these cellulosic materials offer good dielectric and mechanical performance at affordable costs. They are often used in combination with insulating resins and varnishes to enhance their properties.

In addition to solid insulation materials, insulating liquids such as mineral oil and synthetic fluids also play an important role in the insulation and heat dissipation of power transformers.

Recommended Insulation Techniques

To achieve maximum performance and energy efficiency, it is not enough to choose the right insulation materials; they must also be applied correctly. Some of the recommended insulation techniques for transformers include:

  1. Separate windings: the use of separate primary and secondary windings, with intermediate insulation, reduces parasitic capacitance and associated losses.
  2. Layer insulation: the application of multiple layers of insulating material between turns and between windings increases the overall dielectric strength and reduces the risk of partial discharges.
  3. Vacuum impregnation: impregnating the windings with insulating resins or varnishes under vacuum eliminates air bubbles and ensures a homogeneous, defect-free insulation.
  4. Electrostatic shielding: the use of conductive shields between primary and secondary windings reduces capacitive coupling and associated losses.
  5. Efficient cooling: an adequate cooling system, be it air, oil, or water-cooled, helps dissipate the heat generated by losses and keeps insulators within their operating temperature limits.

Accurate design and implementation of these insulation techniques, together with the choice of high-quality insulation materials, can significantly contribute to improving the energy efficiency of the transformer.


Insulation is a key factor in the energy efficiency of transformers. The choice of high-performance insulation materials, the use of appropriate insulation classes, and the application of optimal insulation techniques can greatly reduce losses, increase power density, and extend the transformer’s life.

To maximize the benefits of insulation, it is important to consider not only the technical specifications of the materials but also their compatibility with the expected operating conditions, such as temperature, humidity, mechanical stresses, and chemical agents present in the installation environment.

Furthermore, regular monitoring of insulation conditions, through visual inspections, insulation resistance measurements, and dissolved gas analysis in oil (for oil-insulated transformers), can help detect early signs of degradation and plan preventive maintenance interventions.

The experts at Guerzoni Insulation Materials can provide specialized advice on the most suitable insulation materials and the most effective insulation techniques for each specific transformer application. With over 30 years of experience in the electromechanical sector, Guerzoni offers a wide range of high-quality insulation products, including papers, boards, films, tapes, and sleevings, to meet the insulation needs of transformers of all power and voltage classes.

Investing in superior quality insulation not only improves the energy efficiency and performance of transformers but also results in long-term operational cost savings, thanks to reduced energy losses and increased component life.

In an era where energy efficiency and sustainability have become essential priorities, optimizing transformer insulation represents a fundamental step towards a greener and more competitive future for the electrical industry.

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