Oil-cooled a.c. generators for aircraft ¿present trends

Oil-cooled generators for aircraft were first developed in Britain about nine years ago, and, for the first seven years, attention was focused on indirectly liquid-cooled machines, in which the coolant was confined within oil galleries during its route through the machine. More recently, directly liquid-cooled machines have been developed in which the cooling oil is sprayed within the generator directly on to the rotor and stator windings and other components to be cooled. Large savings in weight are possible by using direct liquid cooling because of the improved heat transfer and the consequent reduction in active material (iron and copper).