What does the set of initials with 2 or 4 letters mean to define the cooling system for oil immersed transformer ?
According to the IEC 60076-2, page 9 : * First letter : Internal cooling medium in contact with the windings: O = mineral oil or synthetic insulating liquid with the fire point ≤ 300C K = insulating liquid with fire point > 300C L = insulating liquid with no measurable fire point * Second letter : Circulation mechanism for internal cooling medium: N = natural thermosiphon flow through cooling equipment and windings F = forced circulation through cooling equipment , thermosiphon flow in windings D = forced circulation through cooling equipment, directed from cooling equipment into at least the main windings * Third letter : External cooling medium A = air W = water * Fourth letter : Circulation mechanism for external cooling medium N = natural convection F forced circulation (fans, pumps)
