Liquid Immersed Transformer Cooling Class Letter Designations are specified using four letters.
Where:
- 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
| Position | Letter | Description |
|---|---|---|
| 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 |
| W | Water | |
| Fourth letter (Cooling medium) | N | Natural convection |
| F | Forced circulation |