E283C7 - EEEB344 Electromechanical Devices Chapter 7...

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EEEB344 Electromechanical Devices Chapter 7 CHAPTER 7 – INDUCTION MOTOR Summary: 1. Induction Motor Construction 2. Basic Induction Motor Concepts - The Development of Induced Torque in an Induction Motor. - The Concept of Rotor Slip. - The Electrical Frequency on the Rotor. 3. The Equivalent Circuit of an Induction Motor. - The Transformer Model of an induction Motor. - The Rotor Circuit Model. - The Final Equivalent Circuit. 4. Powers and Torque in Induction Motor. - Losses and Power-Flow diagram - Power and Torque in an Induction Motor. - Separating the Rotor Copper Losses and the Power Converted in an Induction Motor’s Equivalent Circuit. 5. Induction Motor Torque-Speed Characteristics - Induced Torque from a Physical Standpoint. - The Derivation of the Induction Motor Induced-Torque Equation. - Comments on the Induction Motor Torque Speed Curve. - Maximum (Pullout) Torque in an Induction Motor. 6. Variations in Induction Motor Toque-Speed Characteristics - Control of Motor Characteristics by Cage Rotor Design. - Deep-Bar and Double-Cage rotor design. - Induction Motor Design Classes. 7. Starting Induction Motors 8. Speed Control of Induction Motor - Induction Motor Speed Control by Pole Changing. - Speed Control by Changing the Line Frequency. - Speed Control by Changing the Line Voltage. - Speed Control by Changing the Rotor Resistance. 9. Determining Circuit Model Parameters - The No-Load Test - The DC Test - The Locked-Rotor Test 1
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Cutaway diagram of a typical large cage rotor induction motor Sketch of cage rotor EEEB344 Electromechanical Devices Chapter 7 Induction machine – the rotor voltage that produces the rotor current and the rotor magnetic field is induced in the rotor windings rather than being physically connected by wires. No dc field current is required to run the machine. 1. Induction Motor Construction There are basically 2 types of rotor construction: a) Squirrel Cage - no windings and no slip rings b) Wound rotor - It has 3 phase windings, usually Y connected, and the winding ends are connected via slip rings. Wound rotor are known to be more expensive due to its maintenance cost to upkeep the slip rings, carbon brushes and also rotor windings. 2
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EEEB344 Electromechanical Devices Chapter 7 3 Typical wound rotor for induction motors. Cutaway diagram of a wound rotor induction motor.
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EEEB344 Electromechanical Devices Chapter 7 2. Basic Induction Motor Concepts The Development of Induced Torque in an Induction Motor When current flows in the stator, it will produce a magnetic field in stator as such that B s (stator magnetic field) will rotate at a speed: 120 e sync f n P = Where f e is the system frequency in hertz and P is the number of poles in the machine. This rotating magnetic field B s passes over the rotor bars and induces a voltage in them. The voltage induced in the rotor is given by: e ind = ( v x B ) l Hence there will be rotor current flow which would be lagging due to the fact that the rotor has an inductive element. And this rotor current will produce a magnetic field at the rotor,
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This note was uploaded on 03/03/2010 for the course POWER 332 taught by Professor Dr during the Spring '10 term at Ain Shams University.

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E283C7 - EEEB344 Electromechanical Devices Chapter 7...

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