What insulation materials are used in transformers?

Insulation is one of the most important characteristics of transformers and it is responsible for providing better performance when the transformer is in operation. In fact, the durability and stability of the transformer largely depends on the proper use of insulation materials in the transformer. This means that in addition to metal components such as silicon steel and copper, there are other important insulation materials used in power transformers to perform better.

Insulating Oil

Insulating oil is one of the most important components in transformers, which acts as an electrical insulator as well as a coolant to dissipate heat. This oil is found in transformers of 11kV or higher voltages and is placed in the tank where the transformer core is placed. Insulating oil is not required for low voltage transformers as the heat dissipation of such transformers is very low. Insulating oil is obtained by fractional distillation and subsequent processing of crude oil.

Insulating Paper

Insulating paper is made of plant fibers that are felted together to form a sheet of paper. These fibers come from plants such as cotton, straw, hemp, abaca, and conifers. When this insulating paper is placed in insulating oil under vacuum, it acquires extremely high electrical strength.

Insulating Tape

As the name suggests, insulating tape can be used for a variety of tape purposes. Insulating tapes are available in various forms like cotton tapes, braided tapes, glass braided tapes and phenol laminated paper base sheets. These tapes are used in areas where high strength is required. They are also used for bundling of transformer cores.

Pressboards

Paperboards are used for electrical, mechanical and thermal design of transformers and are also made of plant fibers containing a high amount of cellulose. These paperboards can be molded into any shape for use in transformers; the most common shapes are corner rings and caps.

Wood laminates

Wood laminates are made from selected veneers obtained from various wood species. The veneers are first dried and then partially/completely naturally impregnated. Such laminates are used in areas where high mechanical strength and low electrical strength are required. They are used to make various components like coil clamping rings, cores, yokes and brackets.

All these insulating materials used in transformers are based on their temperature resistance capabilities. They are classified into classes A, B, C, E, F, H and Y. Let us understand all these classes in detail.

• Class A materials are those that have a maximum hot spot temperature of 105°C. These materials include cotton, silk and impregnated paper.
• Class B materials are materials with a maximum hot spot temperature of 130°C. These materials include fiberglass, mica, and asbestos with suitable impregnating or coating substances.
• Class C materials are materials with a maximum hot spot temperature of 180°C. These materials include glass, mica, asbestos, porcelain, and quartz (with or without inorganic binders).
• Class E materials are materials with a maximum hot spot temperature of 120°C. These materials include electrical wire and enameled wire.
• Class F materials are materials with a maximum hot spot temperature of 155°C. These materials include glass, mica, and asbestos with suitable bonding impregnating or coating substances.
• Class H materials have a maximum hot spot temperature of 180°C. These materials are a combination of materials such as fiberglass, asbestos, and mica that are properly bonded together.
• Class Y materials are materials with a maximum hot spot temperature of 90°C. These materials include cotton, silk, paper, and unimpregnated wood.