Insulation class for oil immersed transformer

The insulation class of an oil-immersed transformer is determined by the temperature withstand capability of the insulating materials used in the transformer, primarily the oil and the solid insulation (such as paper, cellulose, and other materials). The classification of the insulation helps in determining the maximum operating temperature that the transformer can safely handle without the risk of insulation breakdown.

In the case of oil-immersed transformers, the insulation class is typically based on the following temperature ranges:

Common Insulation Classes for Oil-Immersed Transformers:

1. Class A (Maximum temperature 105°C):

   • The insulation can withstand continuous operation at a maximum temperature of 105°C. This is considered a lower-class rating and is typically used for low- and medium-voltage transformers.

2. Class E (Maximum temperature 120°C):

   • This class provides a higher temperature tolerance and is used for transformers that may operate in environments with a higher thermal load.

3. Class B (Maximum temperature 130°C):

   • The insulation materials in this class can operate at temperatures up to 130°C. It is commonly used for medium- and high-voltage transformers.

4. Class F (Maximum temperature 155°C):

   • Transformers with Class F insulation can handle temperatures up to 155°C. This class is suitable for larger transformers and those exposed to higher operating temperatures.

5. Class H (Maximum temperature 180°C):

   • Class H insulation is used in high-power transformers, including those operating in harsher environments or with higher overload capacity. These transformers can handle temperatures up to 180°C.

     Insulation Rating	Insulation class	Average Winding Temperature Rise
     Class 105	A	55 ℃
     Class 130	B	80 ℃
     Class 155	F	115 ℃
     Class 180	H	150 ℃

Temperature Rise:

The actual temperature rise above ambient temperature depends on the transformer design and operating conditions. The insulation class helps to determine the permissible temperature rise during normal operation and under load conditions.

Oil and Solid Insulation:

In oil-immersed transformers, the insulating oil plays a significant role in cooling and insulating the electrical windings. The solid insulation (usually cellulose-based) inside the transformer is impregnated with oil, which improves both dielectric properties and cooling performance.

The choice of insulation class will affect the transformer's design, cost, and operating life. The higher the insulation class, the more expensive the materials, but it also allows for higher temperature operation and better performance in demanding conditions.

Let me know if you need more details on the design or selection of insulation classes for transformers!