Chapter 9 Basic Electric Motors

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

Objectives (cont’d.) 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

Objectives (cont’d.) 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

Objectives (cont’d.) 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-start–capacitor-run motors Understand how to operate, install, reverse, and troubleshoot three-phase motors

Objectives (cont’d.) 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

Key Terms Capacitor Capacitor-start motor Capacitor-start-capacitor-run motor Delta winding Electromagnet Electronically commutated motor (ECM) Flux Hermetic compressor Induced magnetism

Key Terms (cont’d.) Magnetic field Magnetism Microfarad Permanent magnet Permanent split-capacitor motor Rotor Running capacitor Shaded-pole motor Split-phase motor Squirrel cage rotor Star winding

Key Terms (cont’d.) Starting capacitor Stator Three-phase motor Torque

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

Magnetism Physical phenomenon Produced in many different ways 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 earth’s magnetic fields

Magnetism (cont’d.) 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

Magnetic Field Flux Magnetic field 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

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)

Induced Magnetism (cont’d.) 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

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

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

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

Motor Speed Formula Common motor speeds 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

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

Motor Dimensions Established by National Electrical Manufacturers’ Association (NEMA) Figure 9.14 Dimension of typical motor frames. (Delmar/Cengage Learning)

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

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

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

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

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

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

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

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

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

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

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