JF205A synchronous main alternator is a 3 phase, salient pole type machine with two bearings support at both ends and self-ventilated structure. It has features of small size, high voltage, wide voltage regulating ratio, high speed and high insulation class. At the non-driving end, shaft head and spider are shrink fitted to make spider assembly. The spider assembly, cylindrical yoke and short shaft at driving end are connected together to compose the construct rotor yoke with high strengthen bolts. Collecting ring is copper slip ring. The alternator is installed with imported bearing. Bearing NU2230EC4/VA301 is installed at the driving end and bearing NJ326EC4/VA30=HJ326EC is installed at the non-driving end. Stator segment is made of high quality silicon steel plate DW360-50 and stator core is tightened by studs and shrunk on the frame. Stator and rotor are both treated by vacuum pressure impregnation process. There is a centrifugal fan installed at the driving end. The alternator has reasonable design in structure and good performance in technique. It has already been used for 2000 horsepower CKD7 narrow-gauge electric diesel locomotives exported to Myanmar made by Dalian. It can also be used for other occasion.