Basic Electric Motors

1
Chapter 9

• Basic Electric Motors

2
Objectives

• Upon completion of this course, you will be able
  to
• Explain magnetism and the part it plays in the
  operation of electric motors
• Explain torque and the purpose of different types
  of single-phase motors
• Explain the operation of a basic electric motor

3
Objectives (contd.)

• Understand how to operate, install, reverse the
  rotation (if possible), and diagnose problems in
  a shaded-pole motor
• Understand the purpose of capacitors in the
  operation of a single-phase motor and be able to
  explain the difference between a starting and
  running capacitor

4
Objectives (contd.)

• Correctly diagnose the condition of any capacitor
  and, using capacitor rules, be able to substitute
  a capacitor if a direct replacement is not
  available
• Explain how to operate, install, troubleshoot,
  and repair (if possible) split-phase and
  capacitor-start motors

5
Objectives (contd.)

• Explain how to operate, install, troubleshoot,
  and repair (if possible) permanent
  split-capacitor motors
• Explain how to operate, install, troubleshoot,
  and repair (if possible) capacitor-startcapacitor
  -run motors
• Understand how to operate, install, reverse, and
  troubleshoot three-phase motors

6
Objectives (contd.)

• Explain how to operate, install, troubleshoot,
  and repair (if possible) electronically
  commutated motors
• Identify the common, start, and run terminals of
  a single-phase compressor motor

7
Key Terms

• Capacitor
• Capacitor-start motor
• Capacitor-start-capacitor-run motor
• Delta winding

• Electromagnet
• Electronically commutated motor (ECM)
• Flux
• Hermetic compressor
• Induced magnetism

8
Key Terms (contd.)

• Magnetic field
• Magnetism
• Microfarad
• Permanent magnet
• Permanent split-capacitor motor

• Rotor
• Running capacitor
• Shaded-pole motor
• Split-phase motor
• Squirrel cage rotor
• Star winding

9
Key Terms (contd.)

• Starting capacitor
• Stator
• Three-phase motor
• Torque

10
Introduction

• Electric motors
• Change electric energy into mechanical energy
• Used to drive any device needing energy to power
  its movement
• Many types
• Torque strength the motor produces by turning

11
Magnetism

• Physical phenomenon
• Includes attraction of an object for iron
• Exhibited by a permanent magnet or electric
  current
• Produced in many different ways
• Example magnetic fields of the earth
• Compass reaction to earths magnetic fields

12
Magnetism (contd.)

• Magnets have two poles north and south
• North pole of a bar magnet is brought close to
  north pole of another bar magnet
• They will repel
• South pole of a bar magnet is brought close to
  the north pole of bar magnet
• They will attract each other

13
Magnetic Field

• Flux
• Magnetic lines of force of a magnet that flow
  between the north and south poles
• Magnetic field
• Area that the magnetic force operates in
• Can flow through material

14
Induced Magnetism

• Created when a piece of iron is placed in a
  magnetic field
• The closer an object is to the magnet, the
  stronger the magnetic field

Figure 9.5 Magnetic field of an iron core when a
current-carrying conductor is wound around the
core. (Delmar/Cengage Learning)
15
Induced Magnetism (contd.)

• Permanent magnet
• Magnetic material that has been magnetized
• Can hold magnetic strength
• Electromagnet
• Magnet produced through electricity
• Electron flow is in a conductor
• Magnetic field is created around the conductor

16
Basic Electric Motors

• Create a rotating motion and drive components
  that need to be turned
• Electric energy is changed to mechanical energy
  by magnetism
• Based on induced magnetism
• To make an electric motor rotation continuous the
  magnet field must rotate

17
Types of Electric Motors

• All kinds of AC motors are used to rotate many
  different devices
• Different motors are needed
• Not all motors have the same running and starting
  characteristics
• Must use the right motor for the right job

18
Motor Strength

• Generally used to classify motors
• Motors are selected mainly because of starting
  torque required
• General types of motors
• Shaded-pole, split-phase, permanent split-
  capacitor, capacitor-start-capacitor-run,
  capacitor-start, three-phase, and electronically
  commutated

19
Motor Speed

• Formula
• Motor with a load
• Speed (Flow reversals/second x 120)/ Number of
  poles
• Common motor speeds
• Two-pole 3450 rpm
• Four-pole 1750 rpm

• Six-pole 1050 rpm
• Eight-pole 900 rpm

20
Open and Enclosed Motors

• Open motors
• Have a housing
• Rotate a device not enclosed in housing
• Enclosed motors
• Housed within some type of shell
• Most common enclosure completely sealed hermetic
  compressor

21
Motor Dimensions

• Established by National Electrical Manufacturers
  Association (NEMA)

Figure 9.14 Dimension of typical motor frames.
(Delmar/Cengage Learning)
22
Shaded-Pole Motors

• Used when very small starting and running torques
  are required
• Operation current is induced into shaded pole
  from main windings
• Reversing requires disassembly
• Troubleshooting easy to identify because of the
  copper band around shaded pole

23
Capacitors

• Consist of two aluminum plates with an insulator
  between them
• Two types used in the industry
• Electrolytic or starting capacitor
• Oil-filled or running capacitor
• Troubleshooting short capacitor life and
  malfunctions
• Caused by several different factors

24
Split-Phase Motors

• Two general classifications
• Resistance-start-induction-run motor
• Capacitor-start-induction-run motor
• Each has different operating characteristics
• Similar construction
• Use some method of splitting the phase of
  incoming power to produce a second phase

25
Resistance-Start-Induction-Run Motors

• Have starting and running winding
• Most have some method of beginning rotation
• Operation phases are split by makeup of starting
  windings
• Troubleshooting probable areas are the bearings,
  windings, and centrifugal switch

26
Capacitor-Start-Induction-Run Motors

• Produce a high starting torque
• Needed for many applications
• Operate like a split-phase motor
• Except a capacitor is inserted in series with
  centrifugal switch and starting windings
• Types
• Open and enclosed

27
Permanent Split-Capacitor Motors

• Simple design and moderate starting torque
• Operation running capacitor is put in series
  with starting winding
• Troubleshooting usually trouble-free for long
  periods
• Common failures bearings, windings, and capacitor

28
Capacitor-Start-Capacitor-Run Motors

• Produce high starting torque and increase running
  efficiency
• Operation begin on a phase displacement between
  starting and running windings
• Troubleshooting sometimes difficult
• Number of added components

29
Three-Phase Motors

• Rugged, reliable, and more dependable
• Most common squirrel cage induction type
• Operation same principles as single-phase
• Except three-phase displacement
• Troubleshooting ohmmeter is used to check
  resistance

30
Electronically Commutated Motors

• Reverse one-half of each AC cycle to form a
  single directional current
• Construction brushless DC, three-phase motor
  with a permanent magnet rotor
• Two part motor motor and control
• Operation determined by control inputs
• Troubleshooting difficult
• Various interfaces, strategies, and modules

31
Hermetic Compressor Motors

• Induction type motors
• Designed for single- and three-phase current
• Operation enclosed in a shell with refrigerant
  and oil
• Requires special considerations
• Terminal identification common, start, and run
  terminals
• Troubleshooting often difficult

32
Service Call Protocol

• Many types of service procedures are performed
  each day
• Pre-season startups
• Preventive maintenance calls
• Inoperative system calls
• Technicians
• Must always keep in mind the need for service
  calls