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Transcript of Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational...
![Page 1: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/1.jpg)
![Page 2: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/2.jpg)
Chapter 13
AC Motors
![Page 3: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/3.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Objectives
• Discuss the operation of an induction motor.
• Identify and explain the operation of various three-phase motors.
• Explain how a split-phase condition is created.
![Page 4: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/4.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Objectives
• Discuss the purpose of ac motor protection circuits.
• List the common causes of motor failure.
• Explain basic troubleshooting techniques for ac motors.
![Page 5: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/5.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Induction Motors
• Three-phase motor– Rotation of magnetic field inside a stator– Rotor inside stator housing– Squirrel cage rotor
![Page 6: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/6.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Synchronous Speed
• Dependent on frequency and number of poles
• As the number of coils or poles per phase increases, the rpm of the motor decreases
poles of pairs ofNumber
seconds 60 hertz ofNumber minute)per srevolution(in speed sSynchronou
![Page 7: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/7.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Slip
• Rotor travels slower than synchronous speed of magnetic field
• 4%–5% of motor’s rpm
• Rotor’s rpm depends on number and size of rotor bars
• As slip increases, greater current circulates, leading to greater torque
![Page 8: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/8.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Types of Induction Motors
• Three-phase synchronous motor• Wound rotor motor• Dual-voltage motor• Single-phase induction motor• Capacitor start, capacitor run motor• Repulsion-induction motor• Shaded-pole motor• Stepping motor
![Page 9: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/9.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Three-Phase Synchronous Motors
• Motor and magnetic field rotate at same speed
• Rotor windings are energized, so rotor is an electromagnet
• No slip to maintain
• Used where constant speeds exist under changing mechanical loads
![Page 10: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/10.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Wound Rotor Motors
• Use three sets of windings wrapped around soft iron laminations
• Can be brought to near synchronous speed
• Varying induced current in rotor windings
• Rotor speed can be adjusted
![Page 11: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/11.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Dual-Voltage Motors
• Stator coils arranged in pairs
• Three-phase motors• Economical motors
![Page 12: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/12.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Single-Phase Induction Motors
• Splitting phases• Used in home
appliances
![Page 13: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/13.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Inductive Reactance Phase Splitting
• Starting windings• Running windings
![Page 14: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/14.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Capacitor Phase Splitting
• Larger phase displacement
• High starting torque
![Page 15: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/15.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Capacitor Start, Capacitor Run Motors
• Heavy mechanical load conditions
• Similar to capacitor start motors
• Single-phase air-conditioning equipment
![Page 16: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/16.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Repulsion-Induction Motors
• Resemble dc motors
• Brushes connected to each other, not power source
• Rotation started by repulsion
• Currents displaced by brushes
• New poles opposing stator poles
![Page 17: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/17.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Shaded-Pole Motors
• Shading the pole• Shading coils• Induced current
opposes change in magnetic field of field coil
![Page 18: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/18.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Stepping Motors
• Rotate in steps
• Gear teeth inside motor
• Pulses of power, not continuous
• Speed of power pulses determines rotor speed
• Used in robots and disk drive systems
![Page 19: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/19.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Selsyn Units
• Synchros• Two motor units• Energized by ac
power supply• Transmitter and
receiver
![Page 20: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/20.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Review
What is the stator in a motor?
Stationary windings in a circular pattern inside a housing
![Page 21: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/21.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Review
What differentiates a squirrel cage from other rotors?
It is common in the three-phase induction motor, used to produce rotation instead of just vibration
![Page 22: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/22.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Review
What is synchronous speed?
The speed of the stator’s rotating magnetic field
![Page 23: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/23.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Review
What happens to the rpm of a motor as the number of coils or poles per phase increases?
The rpm decreases
![Page 24: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/24.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Review
Which kind of motor has stator coils arranged in pairs?
The dual-voltage motor
![Page 25: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/25.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Review
What is the single turn of wire in a shaded-pole motor called?
Shading coil
![Page 26: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/26.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Motor Protection
• Dedicated line• Branch circuit protecti
on
![Page 27: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/27.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Motor Protection (Cont.)
• Run protection
• Service factor– Based on percentage of normal current under
full load condition– (Percentage of current – 1) × 100
![Page 28: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/28.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Motor Failure
• Excessive bearing wear
• Mechanical overload
• Single-phasing condition
• Locked rotor condition
• Low voltage
![Page 29: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/29.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Excessive Bearing Wear
• Most common cause of failure
• Some bearings should be lubricated
• Dry bearings cause friction
• Causes motor to go into overload condition
![Page 30: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/30.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Mechanical Overload
• Affects small ac motors
• Overheating can cause irreversible damage
• Can produce short between windings
![Page 31: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/31.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Single-Phasing Condition
• Affects three-phase motors
• Power supply to one line is lost to open or blown fuse
• Increased current will damage motor
• Thermo protection prevents overheating
![Page 32: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/32.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Locked Rotor Condition
• Causes severe damage
• Caused by mechanical failure in the system
• Excessive current in windings
![Page 33: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/33.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Low Voltage
• Excessive motor current in windings
• Causes the rotor to lock
• Motor should be under mechanical load
![Page 34: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/34.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Troubleshooting Motors
• Clamp-on ammeters– Used only for ac circuits– Circuit does not have to be opened for
ammeter to be connected
• Current should be below motor’s rating• Compare all three lines of a three-phase
motor• Megohmmeters
![Page 35: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/35.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Review
What is a dedicated line?
A circuit used for only one purpose
![Page 36: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/36.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Review
What is the ability of a motor to withstand or avoid damage from an overload condition?
Service factor
![Page 37: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/37.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Review
In a case where the motor is energized, but the rotor is not turning, what component can be most severely damaged?
The motor windings
![Page 38: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/38.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
Review
What is the most common cause of motor failure?
Excessive bearing wear
![Page 39: Chapter 13 AC Motors © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Discuss the operation of an induction.](https://reader035.fdocuments.in/reader035/viewer/2022062307/551c47bf550346b1458b4880/html5/thumbnails/39.jpg)
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.
For Discussion
• Why does an overloaded motor heat up?
• Why are motor starters necessary on heavy-duty motors?
• Compare an induction motor to a transformer.