Chapter3-AC machine Fundamentals 《Electric Machinery 电机学（英汉双语）》课件.ppt

Chapter 3 AC Machine Fundamentals Brief Content 3.1 Operation Principles of the Three-Phase Synchronous Generator 3.2 AC Windings 3.3 Induced EMF of AC Winding 3.4 Operation Principles of the Three-Phase Induction Motor 3.5 MMF of AC 3.1 Operation Principles of the Three-Phase Synchronous Generator the radial distribution of the air-gap flux density B is shown. As the rotor rotates, the flux waveform sweeps by the six coil sides. The resulting coil voltage is a time function which has the same waveform as the spatial distribution B. And there are six sinusoidal waveforms of emf are induced in the six coil sides respectively, they have the same magnitude. the space phase differences between two adjacent conductors are 60?, therefore, the induced emf time phase differences between two adjacent conductors are 60?, and the induced emf phasor-diagram of the six coil sides is shown. The set of three-phase stator windings can be connected to wye (Y) connection or delta (?) connection. In a three-phase synchronous generator, a DC current is applied to a rotor winding, which will produce a rotor magnetic field. When the rotor is driven by a prime mover at a constant speed, there will be a rotating magnetic field in the machine. This rotating magnetic field induces a set of three-phase voltages within the stator windings of the generator. If the three-phase windings of the generator are connected to those three identical loads; there will be three sets of currents flowing though the windings and the loads. Eventually, the mechanical power from the prime mover is converted into an ac electric power to loads. 3.2 AC Windings AC windings can be classified as single-layer windings and double-layer windings according to the number of layers that are placed in the slots. 3.2.1 The basic concept of ac windings 1. Electrical angle ?e the relationship between the electrical angle ?e and the mechanical angle ?m is ?e =p ×?m 2. Coils Coil is the basic element of