5._Synchronous_Machines_2011

5._Synchronous_Machines_2011 - Synchronous Machines Revised...

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EEL 3211 (© 2011. H. Zmuda) 5. Synchronous Machines 1 Synchronous Machines Revised July 6, 2011
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EEL 3211 (© 2011. H. Zmuda) 5. Synchronous Machines 2 Synchronous Machines: Synchronous machines are AC machines that a field circuit supplied by an external DC source Synchronous generators or alternators are synchronous machines used to convert mechanical energy into electrical energy. Synchronous motors convert electrical energy into mechanical energy.
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EEL 3211 (© 2011. H. Zmuda) 5. Synchronous Machines 3 Synchronous Generators: A DC current is applied to the rotor winding which produces the rotor magnetic field. This rotor is rotated by a prime mover (a steam turbine, for example), which produces as rotating magnetic field in the machine. This rotating field induces a three-phase set of voltages within the stator windings of the generator.
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EEL 3211 (© 2011. H. Zmuda) 5. Synchronous Machines 4 Synchronous Motors: A three-phase set of stator currents produces a rotating magnetic field. This causes the rotor magnetic field to align with it. Since the stator magnetic field is rotating the rotor rotates as it tries to keep up with the moving stator magnetic fields. This supplies mechanical power to a load.
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EEL 3211 (© 2011. H. Zmuda) 5. Synchronous Machines 5 Synchronous Machines: Terminology: Field windings are the windings that produce the main magnetic field in a machine. Armature windings are the windings where the main voltage is induced. For synchronous machines, the field windings are on the rotor, which can be either salient or non-salient in construction. The terms rotor windings and field windings are equivalent. The rotor is essentially a large electromagnet. Similarly, the terms stator windings and armature windings are equivalent.
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EEL 3211 (© 2011. H. Zmuda) 5. Synchronous Machines 6 Synchronous Generators
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EEL 3211 (© 2011. H. Zmuda) 5. Synchronous Machines 7 Synchronous Machines: A DC current must be supplied to the field circuit on the rotor. Since the rotor is rotating a special connection is required: 1. Supply DC power from an external source by means of slip rings and brushes 2. Supply DC power from a DC power source mounted on the rotating shaft of the synchronous machine.
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EEL 3211 (© 2011. H. Zmuda) 5. Synchronous Machines 8 Synchronous Machines: This is for a generator, but the same picture applies. Brushes – made with a low friction carbon compound.
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EEL 3211 (© 2011. H. Zmuda) 5. Synchronous Machines 9 Speed of Rotation of a Synchronous Generator By definition, synchronous generators are termed as such because the electrical frequency produced is synchronized with the mechanical rate of rotation of the generator. Since the rotor magnetic field is produced by a DC current, it forms an electromagnet that is directed in whatever position the rotor happens to be aligned.
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5._Synchronous_Machines_2011 - Synchronous Machines Revised...

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