he slots. Note that the basic two-pole pattern of Fig.5.2(a) is repeated twice, indicating that the three-phase winding is designed for four poles. The rotor either is cylindrical and equipped with a distributed winding or else has salient poles with a coil wound on each leg as depicted in Fig.5.3. The cylindrical construction is used exclusively for turbo-generators, which operate at high speeds. On the other hand the salient-pole construction is used exclusively for synchronous motors operating at speeds of 1800 r · min -1 or less. When operated asa generator the synchronous machine receives mechanical energy from a prime mover ( 机械原动力, 牵引机) such as a steam turbine ( 蒸汽涡轮) and is driven at some fixed speed. Also, the rotor winding is energized from a DC source, thereby furnishing a field
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