How to Choose Insulation Materials and Classes When Customizing Oil-Immersed Transformers?

When customizing an oil-immersed transformer, the selection of insulation materials and their class is a critical factor in ensuring the transformer's safe and reliable operation. The primary function of insulation materials is to isolate conductive parts, prevent current leakage and short circuits, and simultaneously withstand electrical, mechanical, and thermal stresses. Below is a detailed analysis of how to choose insulation materials and their classes.

I. Basic Requirements for Insulation Materials

When selecting insulation materials, the following basic requirements must be met:

Electrical Performance: Possess high dielectric strength and voltage withstand capability, able to handle the transformer's rated voltage and overvoltages.

Mechanical Performance: Exhibit good mechanical strength to withstand transformer vibration, shock, and stresses during assembly.

Thermal Performance: Remain stable in the high-temperature environment of transformer operation, possessing a high heat resistance class.

Chemical Stability: Resist chemical reactions in transformer oil and the surrounding environment to avoid aging or degradation.

Environmental Friendliness: Comply with environmental regulations, be free of hazardous substances, and be easy to recycle or dispose of.

II. Common Insulation Materials

Commonly used insulation materials in oil-immersed transformers include:

Insulating Paper: Such as kraft paper, Nomex paper, etc., used for inter-turn and inter-layer insulation in windings.

Insulating Oil: Such as mineral oil, synthetic oil, etc., serving as the primary insulating medium and cooling medium.

Insulating Tape: Such as polyester film tape, polyimide tape, etc., used for fixing and reinforcing insulation.

Insulating Varnish: Used for coating winding surfaces to improve insulation performance.

Insulating Board: Such as epoxy resin boards, phenolic resin boards, etc., used for supporting and isolating structural components.

III. Selection of Insulation Class

The insulation class refers to the maximum temperature that the insulation material can withstand continuously over the long term, typically denoted by a letter. According to International Electrotechnical Commission (IEC) standards, insulation classes are categorized as follows:

Class A (105°C): Materials such as impregnated cotton, paper, etc. Suitable for transformers operating at lower temperatures.

Class E (120°C): Materials such as polyester films, epoxy resins, etc. Suitable for small and medium-sized transformers.

Class B (130°C): Materials such as mica, glass fiber, etc. Suitable for most oil-immersed transformers.

Class F (155°C): Materials such as polyimide, aramid paper, etc. Suitable for high-temperature environments or high-power transformers.

Class H (180°C): Materials such as silicone rubber, polytetrafluoroethylene (PTFE), etc. Suitable for special high-temperature environments.

Class C (>180°C): Materials such as ceramics, mica, etc. Suitable for extreme high-temperature environments.

IV. How to Select the Most Suitable Insulation Class for Your Project?

The selection principle is not "the higher, the better," but rather "matching requirements, economically applicable." You can consider the following dimensions:

1. Operating Environment and Climatic Conditions:

Temperate regions, indoor installation: Class B insulation is an ideal and economical choice, providing sufficient reliability.

Tropical, desert, or high-temperature areas: If the maximum ambient temperature consistently exceeds 40°C, it is strongly recommended to choose Class F or higher insulation. This ensures the transformer has an adequate safety margin in high-temperature environments, preventing premature insulation aging and failure.

High humidity, coastal, or corrosive environments: In these cases, beyond the heat resistance class, attention must also be paid to the moisture resistance, anti-corrosion treatment processes of the insulation materials, and the sealing performance of the transformer.

2. Load Characteristics and Operating Mode:

Stable load: Such as powering urban grids or fixed industrial equipment, Class B insulation is usually sufficient.

Fluctuating or cyclical overload loads: Such as powering mining machinery, rolling mills, or wind/solar grid integration applications where the load frequently changes drastically or planned short-term overloads exist. Choosing Class F insulation can significantly enhance the transformer's overload capacity and extend its service life.

Emergency backup power: Such as data center backup transformers, which mostly remain unloaded or lightly loaded but need to be ready to handle 100% load or even short-term overloads at any time. Higher-class insulation (e.g., Class F) provides them with extremely high starting reliability and lifespan assurance.

3. Lifecycle Cost and Return on Investment:

Initial Cost: Class A < Class B < Class F/H. If the budget is extremely tight and operating conditions are mild, Class A is an option.

Operational and Maintenance Costs: Transformers with higher-class insulation age slower and have lower failure rates, resulting in reduced long-term maintenance costs and lower risk of unexpected downtime. Viewed over the entire lifecycle (20-30 years), choosing Class B or F insulation is often more economical than Class A.

Value Consideration: A slightly higher initial investment brings longer service life, higher overload capacity, and lower failure risk in exchange, which is crucial for ensuring the continuity of your core production.

4. Efficiency Requirements:
High-efficiency transformers (e.g., compliant with IE4 standards) have lower losses and thus generate less heat during operation. This means that even with Class B insulation, the actual operating temperature might be far below the limit, resulting in a longer actual service life. In this case, Class B insulation can adequately meet the needs for high efficiency and long life.

V. Beyond the Class, What Else Requires Attention?

Selecting an insulation system involves more than just the heat resistance class, which is the core but not the entirety. A responsible manufacturer will also ensure quality in the following aspects:

Material Brand and Quality: Using well-known brand insulation materials like Vishay, DuPont, etc., ensures better purity and performance guarantee.

Process Treatment: The drying and oil-impregnation processes for insulation materials are crucial. It is essential to ensure the insulating pressboard is thoroughly dried and oil filling is completed under a vacuum environment to eliminate moisture and air bubbles.

Compatibility: Ensure the selected solid insulation materials have good chemical compatibility with the transformer oil (mineral oil, silicone oil, or ester oil).

Conclusion and Recommendations

In summary, selecting insulation materials and classes when customizing an oil-immersed transformer is a precise balance between performance, lifespan, environmental adaptability, and cost.

For most conventional industrial and general applications: We strongly recommend specifying Class B (130°C) insulation as the standard configuration. It offers the best balance between reliability, lifespan, and cost, making it the common choice in the global market.

For projects with harsh operating environments, fluctuating loads, or special high-reliability requirements: It is advisable to upgrade to Class F (155°C) insulation. This investment acts as valuable "insurance" for your critical power equipment.

For occasions with limited budgets and very mild operating conditions: Class A insulation can be an alternative, but it's important to be fully aware of its limitations regarding service life and overload capacity.

As a professional exporter of transformers, we are pleased to delve deeper into your specific project needs, regional environmental conditions, and operational models. Our technical team, leveraging extensive global project experience, will provide you with the most suitable insulation system solution, ensuring that every transformer you customize is a solid and reliable long-term investment.

Contact us now to get a tailored technical proposal and quotation!

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