3Phase-Synchronous Motors.pdf - ISTANBUL TECHNICAL...

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ISTANBUL TECHNICAL UNIVERSITY FACULTY OF MECHANICAL ENGINEERING ELK 226E HOMEWORK 4 Three Phase Synchronous Machines Lecturer: Ali Sinan ÇABUK Prepared By: 030120251 Fatih YAMAK
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1. Introduction An alternator driven at a constant speed produces an alternating voltage at a fixed frequency dependent on the number of poles in the machine. A machine designed to be connected to the supply and run at synchronous speed is referred to as a synchronous machine. The description applies to both motors and generators. 2. Construction The electromechanical energy conversion occurs whenever a change in flux is associated with mechanical motion. In synchronous machines field winding is the primary source of flux. The field winding and the armature winding are placed on a common magnetic circuit composed of two parts which stator and rotor. 2.1. Stator The stator is a stationary member. It is the annular potion of a cylinder inside which the rotor rotates. A sufficient air gap is provided between the stator and the rotor. The armature winding are housed in the slots cut in the stator 2.2. Rotor There are two types of rotor constructions employed in the synchronous motors. They are cylindrical type rotor and salient pole or projecting pole type rotor. The cylindrical pole rotor has the DC field winding embedded in them. Cylindrical rotor provides greater mechanical strength and permits more accurate dynamic balancing. It is particularly used in high speed turbo generators. The second type of synchronous motor is the salient pole rotors which has projecting poles in it. These projecting poles lessen its mechanical strength. This type of rotor construction is used for low speed applications such as hydroelectric generators. Large number of poles in the rotor makes the rotor larger in diameter and smaller in length.
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The rotor axle is carried on two bearings which a housed on the two end covers bolted on the two sides of the rotor. The stator and rotor are made up of silicon steel, a high permeability magnetic material. The field winding is supplied with a separate DC supply from the exciter, through a pair of carbon brushes. The exciter may be an external DC source or a
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