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Induction Motor Presentation Transcript
1.Induction Motor
2.Learning Outcomes
At the end of the lecture, student should to:
Understand the principle and the nature of 3 phase induction machines.
Perform an analysis on induction machines which is the most rugged and the most widely used machine in industry.
At the end of the lecture, student should to:
Understand the principle and the nature of 3 phase induction machines.
Perform an analysis on induction machines which is the most rugged and the most widely used machine in industry.
3.Contents
Overview of Three-Phase Induction Motor
Construction
Principle of Operation
Equivalent Circuit
Power Flow, Losses and Efficiency
Torque-Speed Characteristics
Speed Control
Overview of Single-Phase Induction Motor
Construction
Principle of Operation
Equivalent Circuit
Power Flow, Losses and Efficiency
Torque-Speed Characteristics
Speed Control
Overview of Single-Phase Induction Motor
4.Overview of Three-Phase Induction Motor
Induction motors are used worldwide in many residential, commercial, industrial, and utility applications.
Induction Motors transform electrical energy into mechanical energy.
It can be part of a pump or fan, or connected to some other form of mechanical equipment such as a winder, conveyor, or mixer.
Induction motors are used worldwide in many residential, commercial, industrial, and utility applications.
Induction Motors transform electrical energy into mechanical energy.
It can be part of a pump or fan, or connected to some other form of mechanical equipment such as a winder, conveyor, or mixer.
5.Introduction
General aspects
A induction machine can be used as either a induction generator or a induction motor.
Induction motors are popularly used in the industry
Focus on three-phase induction motor
Main features: cheap and low maintenance
Main disadvantages: speed control is not easy
6.The three basic parts of an AC motor are the rotor, stator, and enclosure.
The stator and the rotor are electrical circuits that perform as electromagnets.
7.Squirrel Cage Rotor
General aspects
A induction machine can be used as either a induction generator or a induction motor.
Induction motors are popularly used in the industry
Focus on three-phase induction motor
Main features: cheap and low maintenance
Main disadvantages: speed control is not easy
6.The three basic parts of an AC motor are the rotor, stator, and enclosure.
The stator and the rotor are electrical circuits that perform as electromagnets.
7.Squirrel Cage Rotor
8.Construction (Stator construction)
9.The rotor is the rotating part of the electromagnetic circuit.
It can be found in two types:
Squirrel cage
Wound rotor
However, the most common type of rotor is the “squirrel cage” rotor.
It can be found in two types:
Squirrel cage
Wound rotor
However, the most common type of rotor is the “squirrel cage” rotor.
10.Induction motor types:
Squirrel cage type:
Rotor winding is composed of copper bars embedded in the rotor slots and shorted at both end by end rings
Simple, low cost, robust, low maintenance
Wound rotor type:
Rotor winding is wound by wires. The winding terminals can be connected to external circuits through slip rings and brushes.
Easy to control speed, more expensive.
11.Wound Rotor
Squirrel cage type:
Rotor winding is composed of copper bars embedded in the rotor slots and shorted at both end by end rings
Simple, low cost, robust, low maintenance
Wound rotor type:
Rotor winding is wound by wires. The winding terminals can be connected to external circuits through slip rings and brushes.
Easy to control speed, more expensive.
11.Wound Rotor
12.The enclosure consists of a frame (or yoke) and two end brackets (or bearing housings). The stator is mounted inside the frame. The rotor fits inside the stator with a slight air gap separating it from the stator. There is NO direct physical connection between the rotor and the stator.
13.The enclosure also protects the electrical and operating parts of the motor from harmful effects of the environment in which the motor operates. Bearings, mounted on the shaft, support the rotor and allow it to turn. A fan, also mounted on the shaft, is used on the motor shown below for cooling.
14.Rotating Magnetic Field
When a 3 phase stator winding is connected to a 3 phase voltage supply, 3 phase current will flow in the windings, which also will induced 3 phase flux in the stator.
These flux will rotate at a speed called a Synchronous Speed, ns. The flux is called as Rotating magnetic Field
Synchronous speed: speed of rotating flux
When a 3 phase stator winding is connected to a 3 phase voltage supply, 3 phase current will flow in the windings, which also will induced 3 phase flux in the stator.
These flux will rotate at a speed called a Synchronous Speed, ns. The flux is called as Rotating magnetic Field
Synchronous speed: speed of rotating flux
15.AC Machine Stator
16.MMF Due to ‘a’ phase current
17.Slip Ring Rotor
18.Slip and Rotor Speed
19.Slip and Rotor Speed
20.Principle of Operation
21.Direction of Rotor Rotates
22.Equivalent Circuit of Induction Machines
Conventional equivalent circuit
Note:
Never use three-phase equivalent circuit. Always use per- phase equivalent circuit.
The equivalent circuit always bases on the Y connection regardless of the actual connection of the motor.
Induction machine equivalent circuit is very similar to the single-phase equivalent circuit of transformer. It is composed of stator circuit and rotor circuit
Conventional equivalent circuit
Note:
Never use three-phase equivalent circuit. Always use per- phase equivalent circuit.
The equivalent circuit always bases on the Y connection regardless of the actual connection of the motor.
Induction machine equivalent circuit is very similar to the single-phase equivalent circuit of transformer. It is composed of stator circuit and rotor circuit
23.Equivalent Circuit of Induction Machines
24.Equivalent Circuit of Induction Machines
25.Efficiency
26.Torque-Equation
27.Speed Control
28.Varying rotor resistance
For wound rotor only
Speed is decreasing
Constant maximum torque
The speed at which max torque occurs changes
Disadvantages:
large speed regulation
Power loss in Rext – reduce the efficiency
For wound rotor only
Speed is decreasing
Constant maximum torque
The speed at which max torque occurs changes
Disadvantages:
large speed regulation
Power loss in Rext – reduce the efficiency
29.Maximum torque changes
The speed which at max torque occurs is constant (at max torque, XR=RR/s
Relatively simple method – uses power electronics circuit for voltage controller
Suitable for fan type load
Disadvantages :
Large speed regulation since ~ ns
30.Varying supply voltage and supply frequency
The best method since supply voltage and supply frequency is varied to keep V/f constant
Maintain speed regulation
uses power electronics circuit for frequency and voltage controller
Constant maximum torque
The speed which at max torque occurs is constant (at max torque, XR=RR/s
Relatively simple method – uses power electronics circuit for voltage controller
Suitable for fan type load
Disadvantages :
Large speed regulation since ~ ns
30.Varying supply voltage and supply frequency
The best method since supply voltage and supply frequency is varied to keep V/f constant
Maintain speed regulation
uses power electronics circuit for frequency and voltage controller
Constant maximum torque
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