Liquid Immersed Transformer Cooling Class Letter Designations are specified using four letters.
- 1st Letter: It provides information about the internal cooling medium in contact with the windings of the transformer
- 2nd Letter: It indicates the circulation mechanism for the internal cooling medium
- 3rd Letter: It indicate the external cooling medium
- 4th Letter: It indicates the circulation method used for that medium
Good to know: IEEE (Institute of Electrical and Electronics Engineers) standard C57.12.00 specifies liquid-immersed transformer kVA ratings.
Liquid Immerse Transformer Cooling Class Letter Chart
|First Letter (Cooling Medium)||O||Mineral oil or synthetic Liquid with a flash point less than or equal to 300°C|
|K||Insulating Liquid with a flash point greater than 300°C|
|L||Liquid with no measurable flash point|
|Second Letter (Cooling mechanism)||N||Natural convection through cooling equipment and windings|
|F||Forced circulation through cooling equipment, natural convection in windings|
|D||Forced circulation through cooling equipment, directed flow in man windings|
|Third letter (Cooling medium)||A||Air|
|Fourth letter (Cooling medium)||N||Natural convection|