Insulation Class for Transformer

Oil Immersed Transformer

The insulation rating is the maximum permissible winding (hot spot) temperature of a transformer operating at an ambient temperature of 40°C. Insulation systems are classified by temperature class.

The insulation is available in the following recognised grades.

Class A

Insulation Class A consists of materials such as cotton, silk and paper which have been suitably impregnated or coated, or immersed in an insulating liquid (e.g. oil). Other materials or combinations of materials may be included in this class if experience or tests show that they are capable of operating at Class A temperatures.

Maximum permissible temperature: (IEC 60034-1 & NEMA MG1-12.43): 105C, 221F.

Dry Type Transformer     

Class B

Class B insulation consists of materials or combinations of materials such as mica, glass fibre, asbestos with a suitable bonding, impregnating or coating substance (note some older applications where asbestos was used). Other materials or combinations of materials, not necessarily inorganic, may be included in this category if they are shown by experience or testing to be capable of operating at Class B temperatures.

Maximum allowable temperature: (IEC 60034-1 & NEMA MG1-12.43): 130C, 266F.

Class C

Class C insulation consists of materials or combinations of materials such as mica, porcelain, glass, quartz, with or without inorganic binders (note some older applications using asbestos). Other materials or combinations of materials may be included in this category if it can be demonstrated from experience or testing that they are capable of operating at temperatures above the limits of Class H. Specific materials or combinations of materials in this category will have temperature limits depending on their physical, chemical and electrical properties.

Maximum permissible temperature: (IEC60034-1 only): >180C, 356F.

H-Class Dry-Type Power Transformer   

Class E

Class E insulation consists of materials or combinations of materials that can be demonstrated by experience or testing to operate at Class E temperatures (materials with a degree of thermal stability that allows them to operate at temperatures up to 15 degrees Celsius higher than Class E) a material).

Maximum permissible temperature: (IEC60034-1 only): 120C, 248F.

Class F

Class F insulation consists of materials or combinations of materials such as mica, glass fibre, asbestos, etc., with suitable bonding, impregnating or coating substances, and other materials or combinations of materials, not necessarily inorganic, which can be demonstrated by experience or testing to be capable of operating at Class F temperatures (the materials have a degree of thermal stability which allows them to operate at temperatures up to 25 degrees Celsius higher than Class B materials).

Maximum allowable temperature: (IEC 60034-1 & NEMA MG1-12.43): 155C, 311F.

 SG (B) 10 series Non-encapsulated H-class Dry-type Power Transformers

Class H

Class H insulation consists of a combination of materials such as silicone elastomers and materials such as mica, glass fibre, asbestos, etc. with a suitable bonding, impregnating or coating substance, e.g. a suitable silicone resin. Other materials or combinations of materials may be included in this class if it has been shown by experience or testing that they are capable of operating at Class H temperatures.

Maximum permissible temperature: (IEC 60034-1 & NEMA MG1-12.43): 180C, 356F.

Class h transformer

SG (B) 10 series of non-encapsulated class h transformers adopt the special process technology of German (MORA) dry-type transformers to ensure that the products fully meet the requirements such as fire prevention, waterproof, environmental protection. It is the ideal product for distribution systems and is widely used in the subway, shipbuilding, mining, chemical, power companies and personnel-intensive buildings as well as other special requirements of the occasion for safety.

Zhongyi Transformers is one of the most trusted transformer manufacturers, known for its high safety standards, reliability and utmost commitment to quality. Our products are tested to meet the stringent standards of a wide range of industries. Contact us to learn more about how we can get your product to market faster!