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Unformatted text preview: 1-1ECE 320 Energy Conversion and Power Electronics Spring 2009 Instructor: Tim Hogan (Notes from Prof. Elias Strangas) Chapter 5: Three Phase Windings (Textbook Sections 4.3-4.7) Chapter Objectives Flux linkage plays a crucial role in the operation of both DC and AC machines. In this chapter, the geometry and the operation of windings in AC machines is discussed. The flux varies in time, and can also vary in position, or be stationary. To understand how these machines operate, the concept of space vectors(or space phasors) is introduced. 5.1 IntroductionElectric machines often have defined an armature winding which is the winding that is power producing, and a field winding that generates the magnetic field. Either could be on the stator or rotor depending on the specific motor or generator; however it is more common with AC machines such as synchronous or induction machines that the armature winding is on the stator (the stationary portion of the motor). Synchronous machines have field windings on the rotor that is excited by direct current delivered to the rotor windings by slip rings or collector rings by carbon brushes. The field winding produces the north and south poles, thus the image shown in Figure 1 is for a two-pole, single phase (one armature winding) synchronous generator. The magnetic axis for the armature winding is perpendicular to the area defined by the armature winding (armature winding is the perimeter of this area). Figure 1. Figures 4.4 and 4.5 from your textbook showing a simple two-pole, single phase synchronous generator, the spatial distribution of the magnetic field relative to the magnetic axis of the armature winding, and the time dependent induced voltage in the armature winding . 1-2In a three phase device, the armature has three coils each with a magnetic axis that is rotated spatially by 120º as shown in Figure 2. Figure 2. A three-phase, two-pole synchronous generator as shown in Figure 4.12(a) in your textbook . More poles for the field winding and more armature windings are also possible as shown in Figure 3. Such a configuration can deliver three phase power by interconnecting the armature windings in a Y connection configuration as an example. Figure 3. A four-pole synchronous generator with multiple armature windings that can be wired together in a three-phase Y connection is shown (from Figure 4.12(b) and 4.12(c) in your textbook ). 5.2 Control of the Magnetomotive Force DistributionAs generators, the synchronous machines typically use the stator windings as a source of electrical power. As motors, the stator (or armature) windings are commonly supplied electrical power to generate a spatially varying field (we will consider the time variation of these fields later)....
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- Spring '09
- Flux, Magnetic Field, air gap, space vector