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College of Technology
Motors and Controls
Module # 3 AC Generators, Transformers, and AC Motors
Document Intent:
The intent of this document is to provide an example of how a subject matter expert might teach
AC Generators, Transformers, and AC Motors. This approach is what Idaho State University
College of Technology is using to teach its Energy Systems Instrumentation and Control
curriculum for AC Generators, Transformers, and AC Motors. The approach is based on a
Systematic Approach to Training where training is developed and delivered in a two step
process. This document depicts the two step approach with knowledge objectives being
presented first followed by skill objectives. Step one teaches essential knowledge objectives to
prepare students for the application of that knowledge. Step two is to let students apply what
they have learned with actual hands on experiences in a controlled laboratory setting.
Examples used are equivalent to equipment and resources available to instructional staff
members at Idaho State University.
Fundamentals of AC Generators, Transformers, and AC Motors Introduction:
This module covers fundamental aspects of AC Generators, Transformers, and AC Motors as
essential knowledge necessary to perform work safely according to national and local standards
on or around electrical power sources that are associated with motors and controls. Students will
be taught the fundamentals of AC Generators, Transformers, and AC Motors using classroom
instruction, demonstration, and laboratory exercises to demonstrate knowledge and skill mastery
of AC Generators, Transformers, and AC Motors. Completion of this module will allow students
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to demonstrate mastery of knowledge and skill objectives by completing a series of tasks
demonstrating safe work practices on or around electrical power sources.
References
This document includes knowledge and skill sections with objectives, information, and examples
of how Motors and Control could be taught in a vocational or industry setting. This document
has been developed by Idaho State Universitys College of Technology. Reference material used
includes information from:
American Technical Publication Electrical Motor Controls for Integrated Systems, Third
Edition, by Gary J. Rockis and Glen A. Mazur, ISBN 0-8269-1207-9 (Chapter 7)
National Electrical Code International Electrical Code Series, NFPA 70TM
, NEC 2008,
ISBN-13: 978-087765790-3
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STEP ONE
AC Generators, Transformers, and AC Motors Course Knowledge
Objectives
Knowledge Terminal Objective (KTO)
KTO 3. 1. ANALYZE AC Generators, Transformers, andAC Motors to compare
advantages and disadvantages to ensure they are correctly selected for applications
according to manufacturing specifications and electrical requirements
Knowledge Enabling Objectives (KEO)
KEO 3. 1. DESCRIBEwhat an AC GENERATORconsists of and its principle of
operation.
KEO 3. 2. DESCRIBEhow a SINGLE-PHASE AC GENERATORprovides AC Power.
KEO 3. 3. EXPLAINhow a three phase AC GENERATOR provides AC Power to
include operational characteristics and how they are connected to power AC
loads.
KEO 3. 4. Place Holder for Lawrence Beaty AC Generator Objective on how it is
taught and differs from Text Book.
KEO 3. 5. EXPLAIN three classifications of VOLTAGE CHANGES to include how they
occur, and how they are compensated.
KEO 3. 6. DESCRIBE a TRANSIENT VOLTAGEis and how devices can be protected
from H igh-L evel Transients.
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KEO 3. 7. DESCRIBEwhat a TRANSFORMERis and how it effects Voltage.
KEO 3. 8. EXPLAINwhat TRANSFORMER LOSSESare and how they can be
minimized.
KEO 3. 9.
EXPLAINhow SINGLE-PHASEand THREE PHASE TRANSFORMER
CONNECTIONS are made to include both Primaryand Secondary Taps.
KEO 3. 10. EXPLAINwhat a CONTROL TRANSFORMERis and how they provide
control voltage lower than the Primary Voltageapplied.
KEO 3. 11. DESCRIBE two methods used to TROUBLESHOOT TRANSFORMERS.
KEO 3. 12. DESCRIBEwhat a SINGLE PHASEAC MOTORconsists of, its construction,
and principle of operation to include advantages they have over DC MOTORS.
KEO 3. 13. DESCRIBEthree types of SINGLE PHASEAC MOTORS to include: Shaded-
Pole, Split-Phase,and Capacitor motors.
KEO 3. 14. DESCRIBEwhat a THREE PHASEAC MOTORis to include operational
uses, and advantages they have over both DC Motorsand AC SINGLE PHASE
Motors.
KEO 3. 15. DESCRIBE SINGLE VOLTAGE and DUAL VOLTAGE THREE PHASE
MOTORapplications to include WYE and DELTAConnections.
KEO 3. 16. DESCRIBE AC MOTOR TROUBLESHOOTING TECHNIQUES to include:
TroubleshootingSingle Phase Shaded-Pole, Split -Phase, and Capacitor M otors,
andThree Phase Motors.
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AC Generators, Transformers, and AC Motors
KEO 3. 1. DESCRIBEwhat an AC GENERATORconsists of, its components, and its
principle of operation.
AC GENERATORSconvert mechanical energy into electrical energy (the same way a DC
Generator does) by means of electromagnetic induction. AC GENERATORSare actually
referred to as ALTERNATORSbecause they convert mechanical energy into AC Vol tageand
Current(Al ternating Curr ent) They are similar to DC Generators in that both generators have
Field Winding and an Armature that rotates in a magnetic field.
AC GENERATORS consists of a F ield Winding, an Armature (Coil), Slip Ringsand Brushes
as depicted in the below picture:
Figure 7-1 page 141
F ield Windingsare magnets used to produce the magnetic field in a generator. The
magnetic field can be provided by permanent magnets or by Electromagnets. Most AC
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Generators have their magnetic field generated by Electromagnets. Electromagnetsare
supplied with an external current to keep the magnetic field at its desired magnetic
strength.
An Armature (Coil) is the movable coil of wire that rotates through the magnetic field.
An Armature (Coil) may consist of many coils (similar to the armature in a DC
generator). The difference between the DC Generator and the AC Generator is:
o In a DC Generators Armature the ends of the coil(s) are attached to a
commutator.
o In n AC Generators Armature the ends of thecoil(s) are attached to slip r ings.
Slip Ringsare metallic rings connected to the ends of the armature coils(s) and are used
to connect the induced voltage to the generator s brushes. When the armature is rotated inthe magnetic field, a voltage is generated in each half of the armature coil. This voltage is
illustrated in the below sine wave of one revolution:
An AC Generator uses slip rings, which will allow the output current and voltage to
oscillate through positive and negative values. This oscillation of voltage and currenttakes the shape of a sine wave. This is typical of the AC Voltage we have in our homes
and industry throughout the world.
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In DC Generators, a commutatoris used to provide an output whose current always
flowed in the positive direction as illustrated in the below figure:
Brushesin an AC Generatorare the sliding contact that rides against the slip rings and is
used to connect the armatureto the external AC Circuit. As the armature is rotated, each
half cuts across the magnetic lines of force at the same speed. Thus the strength of the
voltage induced in one side of the armature is always the same strength of the voltage
induced in the other side of the armature. Each half of the armature cuts the magnetic
lines of force in a different direction. As the armature rotates in the clockwise direction,
the lower half of the coil cuts the magnetic lines of force from the bottom up to the to the
left, while the top half of the coil cuts the magnetic lines of force from the top down to
the right. The voltage induced in one side of the coil, therefore, is opposite to the voltage
induced in the other side of the coil. The voltage in the lower left half of the coil enables
current flow in one direction, and the voltage in the upper half enables current flow in the
opposite direction. This means the voltage and current alternates in both directions as is
why it is called ALTERNATING CURRENT VOLTAGE (AC Voltage).
Since the two halves of the coil(s) are connected in a closed loop, the voltages add to
each other. The result is that the total of a full rotation of the armature is twice the voltage
of each coil(s) half. This total voltageis obtained at the brushesconnected to the slip
rings, and is applied to an external ci rcuit.
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KEO 3. 2. DESCRIBEhow a SINGLE-PHASE AC GENERATORprovides AC Power.
A SINGLE-PHASE AC GENERATORprovides power through each complete rotation of its
armature within its magnetic field coils and produces one complete alternating current cycle. The
following picture depicts how the armature rotates 3600as it generates continuously changing
AC Sine Wave:
Figure 7-2 page 143
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In the above picture, in position A, before the armature begins to rotate in a clockwise
direction, there is no voltage and no current in the external load circuit because the armature is
not cutting across any magnetic lines of force (O0
of rotation).
As the armature rotates from position Ato position B, each half of the armature cuts
across the magnetic lines of force, producing current in the external circuit. The current
increases from zero to maximum value in one direction. This changing value of current is
represented by the first quarter (900of rotation) of the sine wave.
As the armature rotates from position B to position C, the current continues inthe
same direction. The current decreases from its maximum positive value back to zero.
This changing value of current is represented by the second quarter (910- 180
0of
rotation) of the sine wave.
As the armature continues to rotate to position D, each half of the coil cuts across the
magnetic lines of force in the opposite direction. This changes the direction of current.
During this time, the current increases from its maximum negative value. This changing
value of current is shown by the third quarter (1810270
0of rotation) of the sine wave.
As the armature completes its rotation to position E (position A), the current is
deceased to zero, thus completing one 3600cycle of the sine wave.
KEO 3. 3. EXPLAINhow a three phase AC GENERATOR provides AC Power to
include operational characteristics and how they are connected to power AC
loads.
The same principles of a single phase AC Generator are the same for the three phase AC
Generatorexcept that there are there equally spaced armature windings 1200out of phase with
each other.
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The below picture illustrates the differences between a single and a three phase generator
showing how three equally spaced armature windings 1200out of phase will create three output
voltages 1200out of phase with each other:
Figure 7-3 page 144
A Singl e Phase Generatorhas two leads providing power to the intended load. It is alternating
current that flow in both a positive and negative relationship to the (above and below) the 0 volt
reference point. Because a Thr ee Phase Generatorhas three separate armature windings so there
are six leads providing power to the intended load.
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When the six leads are brought out from the Three Phase Generator, they are connected so that
only three leads appear for connection to the three different armature circuits. There are two
connections: Delta and Wye; the manner in which they are connected determines the electrical
characteristics of the generators output. The following picture depicts both the Delta and Wye
connections of a three phase generator:
Figure 7-4 page 145
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A Delta Connectionis a connection that has each coil end connected end-to-end to form
a closed loop. In a Delta Connection, the three windings are all connected in series and
form a closed circuit. A Delta Connectionappears like the Greek Letter Delta ().
A Wye Connectionis a connection that has one end of each coil connected together and
the other end of each coil left open for external connections. A Wye Connectionappears
as the letter Y.
NOTE
The reasoning for the Delta and Wye Connections will be addressed later in this
curriculum as it has to do with AC Power distribution systems and AC Power connections
to three phase motors.
SUMMARY:
AC GENERATORSconvert mechanical energy into electrical energy (the same way aDC Generator does) by means of electromagnetic induction.
AC GENERATORS consists of a F ield Winding, an Armature (Coil), Slip Ringsand
Brushes.
F ield Windingsare magnets used to produce the magnetic field in a generator.
An Armature (Coil) is the movable coil of wire that rotates through the magnetic field.
Slip Ringsare metallic rings connected to the ends of the armature coils(s) and are usedto connect the induced voltage to the generator s brushes.
Brushesin an AC Generatorare the sliding contact that rides against the slip rings and isused to connect the armatureto the external AC Circuit.
A SINGLE-PHASE AC GENERATORprovides power through each complete rotation
of its armature within its magnetic field coils and produces one complete alternating
current cycle.
The same principles of a single phase AC Generator are the same for thethree phaseAC Generatorexcept that there are there equally spaced armature windings 120
0out of
phase with each other.
A Singl e Phase Generatorhas two leads providing power to the intended load.
A Three Phase Generatorhas three separate armature windings so there are six leadsproviding power to the intended load.
There are two connections: Delta and Wye; the manner in which they are connecteddetermines the electrical characteristics of the generators output.
A Delta Connectionis a connection that has each coil end connected end-to-end to forma closed loop
A Wye Connectionis a connection that has one end of each coil connected together and
the other end of each coil left open for external connections.
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KEO 3. 4. Place Holder for Lawrence Beaty AC Generator Objective on how it is
taught and differs from Text Book.
KEO 3. 5. EXPLAIN three classifications of VOLTAGE CHANGES to include how they
occur, and how they are compensated.
VOLTAGE CHANGES need to be monitored and controlled. AC Generators are designed to
produce an out voltage. In addition, all electrical and electronic equipment is rated for operation
at a Specif ic Voltage. The standard rated voltage is a voltage that equipment can operate safely
can vary in a range of +5% to -10%of the equipments voltage requirements. This voltage range
is used because an Over-Voltageis generally more damaging than an Under-Voltagecondition.
Equipment Manufacturers, Utility Companies, and regulating agencies must routinely
compensate for changes in system voltage.
Backup Generatorsare used to compensate for voltage changes. A Backup Generatorcan bepowered by diesel, gasoline, natural gas, or propane engines connected to the generator.
If there is any power interruption in the time period between the loss of main utility power and
when the generator starts providing power, the generator is usually classified as a standby
(emergency) power supply. VOLTAGE CHANGESin a system may be categorized as:
Momentary, Temporar y, orSustainedas depicted in the below picture:
Figure 7-5 page 146
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A Momentary Power I nterr uption is a decrease to 0 Volts on one or more of the three
phase power lines lasting from .5 cycles up to 3 seconds. All power distribution systems
have momentary power interruptions during normal operation. The interruptions can be
caused when L ightn ing Stri kes Nearby, Util ity Grid Switching dur ing a problem(short
on one line, or during Open Cir cuit Tr ansiti on Switching(a process in which power is
momentarily disconnected when switching a circuit from one voltage supply or level to
another).
A Temporary Power I nterr uptionis a decrease to 0 Volts on one or more power lines
lasting more than 3 seconds up to 1 minute. Automatic circuit breakers and other circuit
protection equipment protect all power distribution systems. Circuit protection equipment
is designed to remove faults and to restore power. Automatic circuit breakers normally
take 20 cycles to about 5 seconds to close. If the power is restored, the power interruption
is only temporary. A Temporary Power I nterr uptioncan also be caused by a time gapbetween power interruptions and when a back-up power supply (generator) takes over, or
if someone accidently opens the circuit by switching the wrong circuit breaker and then
turns it back on.
A Sustained Power I nterruptionis a sustained power interruption when the power
decreases to 0 Volts on all power lines for a period of longer than one minute. All power
distribution systems have a complete loss of power at some time. They are caused as a
result of Storms, Tripped Circuit Breakers,Bl own F uses,and orDamaged Equipment.
The effect of a power interruption on a load depends on the load and the application. If a power
interruption could cause equipment, production, and or security problems that are not acceptable,
an Unin terr uptable Power System/Supply (UPS)can be utilized. An Uninterr uptable Power
System/Suppl y (UPS)is a power supply that provides constant power needs when the main
power supply is interrupted. This is accomplished by a network of electronics and batteries such
that the incoming AC power from the main utility is used to convert the AC to DC to keep the
batteries charged and then it inverts the DC back to clean uninterrupted and filtered AC power to
which the facility that utilizes this UPS will not experience a power interruption upon loss of the
main utility power source. A large facility will also have a backup generator with a UPS to pick
up the emergency designated power in the event the UPS main battery(s) lose their ability to
keep their charge. For long power interruption protection (sustained), a combination of a
generator and a UPS are used. For short power interruptions (temporary), a UPS is used. UPS
batteries are generally sealed lead acid batteri es.
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Uninterruptable Power System/Suppl ies (UPS)are also used to keep loads like important
business computing systems and medical equipment powered up at all times in the event of a
power loss. These UPS units have the load running directly from them and are constantly being
kept charged by the facilities main power source. An example of a Common UPSis the power
supply provided to a laptop computer. When the laptop is plugged into a power source, it keeps
the internal battery charged. When the laptop is not plugged into a power source, it is running off
the internal battery. The internal battery provides power to the laptop with or without an outside
power supply as long as the battery can last without being charged.
There are also Portable AC Generators of various sizes used to provide power during temporary
power interruptions as depicted below:
Picture at bottom of page 146
These generators are utilized in Recreational Vehicles to provide AC power when they are not
connected to a power supply in and on construction sites where power has not yet been
established, and in residences for temporary power outages.
NOTE:
Portable generators SHOULD NEVER be connected to a residence or utility power source
to back-feed AC power when the utility power has been lost. This is because the portable
generator and utility power are not synchronized and this could cause a fire and or
explosion, which can cause death or injury as well as serious equipment damage.
AC Backup Generators are designed for temporary or sustained power interruptions. They
are provided with an automatic transfer switch that senses loss of power, starts the
generator, and picks up essential or emergency power loads.
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When the power is restored, the transfer switch automatically resets and allows only the
utility power to be available without a second power loss (this transfer is instantaneous).
When power is initially lost, there is a short interruption of incoming power until the
generator comes up to speed and assumes the load. There is no interruption upon return of
the incoming utility power. The following two pictures are of a backup generator:
Backup 120/240 VAC Natural Gas Generator
Backup Generator Transfer Switch connected to
a residential 120/240 VAC Main Power Panel.
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SUMMARY:
VOLTAGE CHANGES need to be monitored and controlled.
An Over-Voltageis generally more damaging than an Under-Voltagecondition. Equipment Manufacturers, Utility Companies, and regulating agencies must routinely
compensate for changes in system voltage.
Backup Generatorsare used to compensate for voltage changes and can be powered bydiesel, gasoline, natural gas, or propane engines connected to the generator.
VOLTAGE CHANGESin a system may be categorized as: Momentary, Temporary, orSustained.
A Momentary Power I nterr uption is a decrease to 0 Volts on one or more of the three
phase power lines lasting from .5 cycles up to 3 seconds.
A Temporary Power I nterr uptionis a decrease to 0 Volts on one or more power lines
lasting more than 3 seconds up to 1 minute.
A Sustained Power I nterruptionis a sustained power interruption when the powerdecreases to 0 Volts on all power lines for a period of longer than one minute.
Unin terruptable Power System/Suppl ies (UPS)are also used to keep loads likeimportant business computing systems and medical equipment powered up at all times in
the event of a power loss.
UPS units have the load running directly from them and are constantly being kept
charged by the facilities main power source.
Portable generators SHOULD NEVERbe connected to a residence or utility powersource to back-feed AC power when the utility power has been lost. This is because the
portable generator and utility power are not synchronized and this could cause a fire and
or explosion, which can cause death or injury as well as serious equipment damage.
Portable generatorscan be used to provide temporary power to essential loads by theuse of extension cords plugged directly to an essential load like a heater or refrigerator
that has been unplugged from the utility powered receptacle.
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KEO 3. 6. DESCRIBE a TRANSIENT VOLTAGEis and how devices can be protected
from H igh-L evel Transients.
A TRANSIENT VOLTAGEis a temporary, unwanted voltage in an electrical circuit.
Transient Voltages are normally erratic, large voltages or spikes that have a short duration and a
shout rise time. Devices like Computers, Electronic Circui ts (TVsMicro Wave Ovens
Sound Systems etc)require protection against Transient Vol tages. Protection methods usually
include proper wiring to National Electrical Code Requirements, to include grounding, shielding
of the power lines, and use of Surge Protectors.
A Surge Protectoris an electrical device that provides protection from high-level
transient voltages by limiting the level of voltage allowed downstream from the Surge
Protector/Suppressor (more commonly called a Surge Suppressor). Surge
Protector/Suppressorscan be installed at service entrance panels and individual loads as
depicted in the below picture:
Figure 7-6 page 147
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Surge Suppressorspower strips as shown above generally will have and on off switch and areset button. When they trip the power is removed from the loads and the device needs to be
manually reset to restore power to the loads. If the power surge was high enough, it could
actually damage the Suppressor and it will not reset.
Surge Suppressors are under a UL listing and requirements (IEC 61643-1,EN 61643-11and 21 ,Telcordia Technologies Technical ReferenceTR-NWT-001011,ANSI /IEEE
C62.xx, orUL)and mandated that all units manufactured after August 17, 1998 must pass
all test procedures outlined in the second edition of UL1449 to continue to be listed and
labeled as UL1449.
SUMMARY:
Transient Voltages are normally erratic, large voltages or spikes that have a short
duration and a shout rise time.
Devices like Computers, Electronic Circits (TVs
M ir cro Wave Ovens
SoundSystems etc)require protection against Transient Vol tages.
Protection methods usually include proper wiring to National Electrical CodeRequirements, to include grounding, shielding of the power lines, and use of Surge
Protectors.
A Surge Protectoris an electrical device that provides protection from high-level
transient voltages by limiting the level of voltage allowed downstream from the Surge
Protector/Suppressor (more commonly called a Surge Suppressor).
Surge Suppressorspower strips generally have and on off switch and a reset button.
When Surge Suppressorstrip the power is removed from the loads and the device needsto be manually reset to restore power to the loads.
If the Power Surgewas high enough, it could actually damage the Suppressor and it willnot reset.
KEO 3. 7. DESCRIBEwhat a TRANSFORMERis and how it effects Voltage.
A TRANSFORMERis an electrical device that uses electromagnetism to change voltage from
one level to another. In other words, the Voltage is Stepped Up orStepped Down. Transformers
are used in electrical distribution systems to increase or decrease the voltage and current safely
and efficiently.
They are used to increase voltage to a H igh Level for Transmissionacross the country and then
to decrease that voltage to a Low Level for useto a variety of electrical loads (residential,
commercial, and industrial).
http://en.wikipedia.org/wiki/International_Electrotechnical_Commissionhttp://en.wikipedia.org/wiki/CENELEChttp://en.wikipedia.org/wiki/Telcordia_Technologieshttp://telecom-info.telcordia.com/site-cgi/ido/docs.cgi?ID=SEARCH&DOCUMENT=TR-NWT-001011&http://en.wikipedia.org/wiki/American_National_Standards_Institutehttp://en.wikipedia.org/wiki/Institute_of_Electrical_and_Electronics_Engineershttp://en.wikipedia.org/wiki/Underwriters_Laboratorieshttp://en.wikipedia.org/wiki/Underwriters_Laboratorieshttp://en.wikipedia.org/wiki/Institute_of_Electrical_and_Electronics_Engineershttp://en.wikipedia.org/wiki/American_National_Standards_Institutehttp://telecom-info.telcordia.com/site-cgi/ido/docs.cgi?ID=SEARCH&DOCUMENT=TR-NWT-001011&http://en.wikipedia.org/wiki/Telcordia_Technologieshttp://en.wikipedia.org/wiki/CENELEChttp://en.wikipedia.org/wiki/International_Electrotechnical_Commission8/10/2019 Module 3 AC Generators Transformers AC Motors
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An example of how Transformers accomplish this is depicted in the below picture:
Figure 7-7 page 148
Transformers allow power utility companies to distribute large amounts or power at a
reasonable cost. Large Transformers are used for power distribution along city streets and in
large manufacturing or commercial buildings. These distributions are done both above and below
ground locally and mostly overhead for long distances.
The larger transformers are maintained by qualified workers specially trained in H igh Voltage
Transformer Operation and Maintenance. Technicians will often work with small transformers.
Control Transformers are used to isolate the power circuit from the control circuit, providingadditional safety for the circuit operator or technician. Transformersare also used in power
suppliesof most electron ic equipment to Step-Up or Step-Down the l ine voltageto provide the
required operating voltage for the equipment.
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Transformershave a Primary Windingand a Secondary Windingwound around an I ron Core
as depicted in the below picture:
Figure 7-8 page 148
The Primary Windingis the coil that draws the power from its source and the Secondary
Winding is the coil of the transformer that delivers the energy at the transformed or changed
voltage. A Transformer Transfers AC Energyfrom one circuit to another. This transfer is made
magnetically through the iron core as the magnetic field builds up around a wire when AC is
passed through the wire. The magnetic field builds up and collapses each half cycle because the
wire is carrying AC as depicted below:
Figure 7-9 page 149
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The following picture depicts a H igh-Voltage Transmission Stationwhere thousands of volts
are received via overhead transmission lines and then transformed to a lower voltage for local
distribution:
Picture page 150
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SUMMARY:
A TRANSFORMERis an electrical device that uses electromagnetism to changevoltage from one level to another (the Voltage is Stepped Up orStepped Down).
TRANSFORMERS are used to increase voltage to a H igh Level for Transmission
across the country and then to decrease that voltage to a Low Level for useto a variety ofelectrical loads (residential, commercial, and industrial).
KEO 3. 8. EXPLAINwhat TRANSFORMER LOSSESare and how they can be
minimized.
Many TRANSFORMERShave a secondary coil that has an extr a lead (tap)attached to it. A
Tapis a connection brought out of a winding at a point between its endpoints to allow changingthe voltage or current ratio.
Although Transformersare very efficient, they are not perfect. Not all energy delivered to the
primary side by the source is transferred to the secondary load circuit. There is a majority of
energy lost as heat in the transformer. There are three types of TRANSFORMER LOSSES in
an iron core transformer: Resistive Losses, Eddy Current Loses, and Hysteresis Losses.
Resistive Lossescome from the resistance of the coil winding. When current passes
through the winding, the winding will heat up and lose energy that could have been
transferred to the secondary. These losses are inherent and cannot be minimized.
Eddy Cur rent Losses come because iron i s a fair conductor of electricity.This is due to
the varying magnetic field which induces a voltage in the secondary winding that also
induces small voltages in the iron core of the transformer. The small voltages produce
Eddy Cur rents, which in turn produce heat. This heat also represents a loss because it
does not useful work.
o Eddy Cur rent L osses are minimized either by making the core of thin sheets
(laminations) which are insulated from each other, or by powered-iron coresinstead of solid blocks of iron.
o The insulation between the laminationsof a laminated core break up current
paths within the core and reduces Eddy Cur rents. This same technique is used to
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reduce Eddy Cur rents in Solenoids and was addressed in: Module # 2 Solenoids
DC Generators and DC Motors.
Hysteresis Losesoccur each time the magnetizing force produced by the primary side of
a transformer changes, the atoms of the core realign themselves in the direction of the
force. This energy required to realign the iron atoms must be supplied by the input power
and is not transferred to secondary load current.
o Hysteresis Loses are minimized by using H igh Sil icon Steel and other alloys in
the construction of the core.
All three of these TRANSFORMER LOSSESmake the typical iron core transformer hot when
operating under full load. The transformer may be too hot to touch based on its size and load, but
there shoul d be no odor of bur ri ng insulation or varni sh, or sings of discoloration or smoke.
Any one of these conditions indi cates the transformer is either over loaded or defective andservice is necessary to correct and reduce damage, safety, or fir e hazards.
SUMMARY:
A
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KEO 3. 9. EXPLAINhow SINGLE-PHASEand THREE PHASE TRANSFORMER
CONNECTIONS are made to include both Primaryand Secondary Taps.
SINGLE-PHASE CONNECTIONSutilize only one of the three phases of power distributed by
the electrical utility. This Single Phase power is utilized throughout the world in residential
applications and smaller businesses that do not require three phase power. The following picture
depicts how Residential Electrical Power is provided by overhead 3-phase or lateral (under-
ground) service as required by the National Electrical Code:
Figure 7-11 page 151
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THREE-PHASE CONNECTIONSutilize all three phases of power in the same manner where
each phase is Stepped-Down like it is with a single phase using three separate identical
transformers.
The following pictures depict: Transformer Secondary Tap, Centered-Tap, configurations to
obtain a variety of different voltages:
Figure 7-12 page 152
Figure 7-13 page 152
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KEO 3. 10. EXPLAINwhat a CONTROL TRANSFORMERis and how they provide
control voltage lower than the Primary Voltageapplied.
A CONTROL TRANSFORMERis a transformer that is used to Step-Down the voltageto the
control circuit for a system or machine. The most common Control Transformers have two
primary coils and one secondary coil as illustrated in the following three pictures:
Figure 7-14 page 152 Figure 7-15 page 153
Figure 7-16 page 153
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As depicted above, control vol tage can be reduced from 480 VAC to 240 VAC and down to 120
VAC. Control Transformers are also designed to drop a control voltage down to 24 VAC as
well , which is a much safer less hazardous voltage for technicians to work on and
troubleshoot contr ol cir cui ts. I n all cases the Stepped-Down voltage reduces the amount of
voltage used to control a circuit operating on higher voltages.
Transformer specification sheets are used to obtain required information when selecting
the proper transformer for an application as depicted below:
Figure 7-17 page 154
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Picture Page 153 Control Transformers
Picture Page 154 Autotransformers
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The following picture depicts how using a DMM can be used to test transformers:
Figure 7-18 page 155
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SUMMARY:
L
l
KEO 3. 12. DESCRIBEwhat a SINGLE PHASEAC MOTORconsists of, its construction,
and principle of operation to include advantages they have over DC MOTORS.
A SINGLE PHASEAC MOTORis an AC motor that uses Al ternating Cur rent (AC) to
produce rotati on. The main parts of an AC motor are the Rotor, and a Stator. The Rotoris the
rotating part of the motor and the Statoris the stationary part of an AC motor. A typical AC
motor is used in industry because of their Simplicity, Ruggedness, and Reliabilityand can be
Single Phase, Singl e Phase Two Speed Single Voltage, and Three Phase Single or Dual
Voltageas depicted below also illustrating typical construction characteristics:
Figure 7-19 page 156
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AC motors have several advantages over DC motors in that there are only two bearings that can
wear, and there are No Brushesbecause the motor does not have a Commutatorwhich reduces
the need for extra maintenance associated with DC Motors.
Single Phase Motors are commonly used in residential applications for AC Motor
Driven appliances such as:Forced Ai r Furnace Fans, Ai r Conditioners, Washing
Machines, etc.Single Phase Motors include: Shaded-Pole, Spli t-Phase,and Capacitor
motors.
KEO 3. 13. DESCRIBEthree types of SINGLE PHASEAC MOTORS to include: Shaded-
Pole, Split-Phase,and Capacitor motors.
Shaded-Polemotors are a Single Phase AC Motorthat uses a shaded stator pose for
starting the motor as depicted in the picture below:
[ Insert Figure 7-20 page 157 Rockis Book) ]
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Shaded-Polemotors utilize the simplest method to start a Single Phase AC Motor. They
are commonly rated at horsepower or less and have low starting torque. Common
applications include small cooling fans found in computers and home entertainment
centers. The Shaded-Poleis normally a solid single turn of copper wire placed around a
portion of the main pole laminations as indicated in the above picture.
o This shaded pole delays the magnetic field in the area of the pole that is shaded.
This shading causes the magnetic field at the pole area to be positioned
approximately 900from the magnetic field of the main Stator F ield Pole. This
movement determines the starting direction of a shaded pole motor.
o A shaded-pole motor is a type ofACsingle-phaseinduction motor.It is basically
a smallsquirrel cage motor in which the auxiliary winding is composed of a
copper ring surrounding a portion of each pole. This auxiliary winding is called ashading coil. Currents in this coil delay thephase ofmagnetic flux in that part of
the pole enough to provide arotating magnetic field.The direction of rotation isfrom the unshaded side to the shaded (ring) side of the pole. The effect produces
only a low startingtorque compared to other classes of single-phase motors.
o These motors only have one winding, no capacitor nor starting switch, making
them economical and reliable. Because their starting torque is low they are bestsuited to driving fans or other loads that are easily started. Moreover, they are
compatible withTRIAC-based variable-speed controls, which often are used with
fans. They are built in power sizes up to about 1/6 hp or 125 watts output. Forlarger motors, other designs offer better characteristics.
Split-Phasemotors are Single Phase AC M otorsthat include a Running (main winding)and a Starting Winding (auxiliary winding). Split-Phasemotors are AC motors of a
fractional horsepower, usually1/20 to
1/3HP. They are commonly used to operate washing
machines, oil burners, and small pumps and blowers.
o A Split-Phasemotor has a rotating part (rotor), a stationary part consisting of the
running and starting winding (stator), and a centrifugal switch that is located
inside the motor to disconnect the start winding at 60% to 80% of designed full
speed.
http://en.wikipedia.org/wiki/Alternating_currenthttp://en.wikipedia.org/wiki/Single-phase_electric_powerhttp://en.wikipedia.org/wiki/Induction_motorhttp://en.wikipedia.org/wiki/Squirrel_cage_motorhttp://en.wikipedia.org/wiki/Phase_(waves)http://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Rotating_magnetic_fieldhttp://en.wikipedia.org/wiki/Torquehttp://en.wikipedia.org/wiki/TRIAChttp://en.wikipedia.org/wiki/TRIAChttp://en.wikipedia.org/wiki/Torquehttp://en.wikipedia.org/wiki/Rotating_magnetic_fieldhttp://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Phase_(waves)http://en.wikipedia.org/wiki/Squirrel_cage_motorhttp://en.wikipedia.org/wiki/Induction_motorhttp://en.wikipedia.org/wiki/Single-phase_electric_powerhttp://en.wikipedia.org/wiki/Alternating_current8/10/2019 Module 3 AC Generators Transformers AC Motors
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o A Split-Phasemotor is depicted in the below picture:
Figure 7-21 page 158
When the Split-Phasestarts, both the Runningand Start Windingsare connected in
parallel. The Start Windingis used to jump start the motor and then is disconnected by
the centrifugal switch at 60% to 80% of full speed. When the motor is turned off, the
centrifugal switch returns to its normally closed position (at approximately 40% of its full
speed), ready to be used for starting the motor again.
A Capacitor Motor is also a Spli t-Phase AC M otorthat includes a capacitor in addition to
the running and starting windings. Capacitor Motorsrange in sizes ranging from1
/8to 10HP. Capacitor Motors are used to operate Refr igerators, Compressors, Washing Machines,
and Air Conditioners.
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o The Capacitor is wired in ser ies with the Start Winding and provides a Capacitor
Start Motor with the benefi t of H igh Starting Torque. The Capacitor adds an extra
jump start to get the motor to start with loads requiring High Starting Torque. A
Capacitor Start Motoris depicted below:
Figure 7-22 page 159
A Capacitor -Run Motoris aSpli t-Phase AC M otorwith the start winding and the capacitor
connected in series at all times which does not have a centrifugal switch, giving this motormedium staring torque and somewhat higher running torque than a capacitor start motor as
the capacitor continually charges and discharges while the motor is running.
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o A Capacitor-Run Motoris depicted in the below picture:
Figure 7-23 page 160
A Capacitor Start-and-Run motor (used to run refrigerators and compressors) uses two
capacitors with one used to start the motor, and the other one used as a capacitor to allow the
motor to continue operating as a Capacitor Run Motor.This motor uses a larger capacitor tostart the motor and a smaller one to run it.
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o A Capacitor Start-and-Run motordepicted below with a centrifugal switch cutting
out the start capacitor and allowing the run capacitor to stay in the start winding:
Figure 7-24 page 160
A Capacitor Start-and-Run motor has the same starting torque as a capacitor
start motor.
A Capacitor Start-and-Run motor has more running torque that a capacitor-
start motor or a capacitor-run motor.
SUMMARY:
.
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KEO 3. 14. DESCRIBEwhat a THREE PHASEAC MOTORis to include operational
uses, and advantages they have over both DC Motorsand AC SINGLE PHASE
Motors.
THREE PHASEAC MOTORS are the most commonly used motors in industrial applications.
Three PhaseAc Motorsare used in applications ranging from fractional horsepower to over 500
HP. Three PhaseAc Motorsare used in most applications because they are simple in
construction, require little maintenance, and cost less to operate than Single Phase or DC
Motors. The most common Three PhaseAc Motoris the I nduction Motor.
The I nduction Motoris a motor that has three sets of Rotor Coils with each connected a
different phase of the three phase power. These composite windings are the Phase A, B,
and C of the three phase power. An Induction Three Phase Motor is illustrated below
with different colors per phase in the Rotor and in the Voltage Sine Wave:
Figure 7-25page 161
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o Three Phase Motorsare like having three single phase motors connected together to
do more work more efficiently. Each phase is 1200from the other phases and the
magnetic field is produced in the stator because each phase reaches its peak magnetic
strength 1200from the other phases. They are self starting and do not require an
additional starting method because of the rotating magnetic field in the motor.
o Three Phase Motorsare designed as either Single-Voltage Motorsor Dual-Voltage
Motors.
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KEO 3. 15. DESCRIBE SINGLE VOLTAGE and DUAL VOLTAGE THREE PHASE
MOTORapplications to include WYE and DELTAConnections.
SINGLE VOLTAGE THREE PHASE MOTORSis a motor that operates at only one
voltage level. They are less expensive to manufacture than Dual Voltage Motors, but are
limited to locations having the same voltage as the motor.
o Common Single Voltage Three Phase Motors ratings are 230, 460, and 575 VAC.
Other ratings include 200, 208, and 220 VAC.
o All Single Voltage Three Phase Motorsare wired so that the phases are connected in
either a (Y) or a () configuration as illustrated in the following two pictures:
Three Phase Wye-Connected Motor
Figure 7-26 page 162
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o A Wye-Connected Motor has one end of each coil internally connected to the other
phases.
Three Phase Delta-Connected Motor
Figure 7-27 page 163
o A Delta-Connected Motor has each phase coil wired end-to-end to form a
completely closed loop.
A DUAL VOLTAGE THREE PHASE MOTOR is manufactured so that they may beconnected for either of two voltages. Making motors for two voltages enables the same
motor to be used with two different three phase power supplies.
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o The normal dual-voltage rating for three phase motors is 230/460 VAC. In either case
the motor uses the same amount of power and gives the same horsepower output for
either voltage, but as the voltage doubles from 230 VAC to 460 VAC, the current is
cut in half.
o Using a reduced current enables the use of a smaller gauge wire, thus reducing the
cost of installation. Like Single Voltage motors, Dual Voltage motors can also be
connected in either a (Y) or a () configuration as illustrated in the following two
pictures:
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Dual Voltage Three Phase Wye-Connected Motor
Figure 7-28 page 164
A Dual Voltage Wye-Connected Motor has each phase coil divided into two equal
parts.
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Three Phase Delta-Connected Motor
Figure 7-29 page 165
A Dual Voltage Delta-Connected Motor has each phase coil divided into two equal
parts.
KEO 3. 16. DESCRIBE AC MOTOR TROUBLESHOOTING TECHNIQUES to include:
TroubleshootingSingle Phase Shaded-Pole, Split -Phase, and Capacitor M otors,
andThree Phase Motors.
Most problemswith AC Motors are related to Single Phase AC M otors dealing with the
Centr if ugal Switch, Thermal Switch, or Capacitors. These motors are usually serviced and
repaired if the problem is related to the centrifugal switch, thermal switch, or capacitors. If a
motor is less than1/8HP it is usually replaced as the cost to repair can exceed the replacement
cost. As for Three Phase AC Motors, they usually operate for many years without anyproblems as they have fewer components that may malfunction than Single Phase AC or DC
Motors.
AC Motor Maintenance is extremely important and if maintained properly, many motor
failures can be minimized or in some cases prevented. In general, electrical motors are very
dependable and will provide good service under the conditions in which the motor was designed
to operate within. To provide the safest service possible, a technician should check a motor name
plate prior to putting it in service to ensure that the proper voltage and current are being used.
The below picture depicts the type of information found on a motors name plate:
Figure 7-30 page 166
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Any standard motor should not be operated in very damp locations or where water may enter the
motor frame. There are specially designed motors for such locations with enclosures are
available to totally enclose a motor from damp or wet locations.
The frame of a motor should be grounded to prevent anyone receiving an electrical shock in the
event the motor has developed a short. Motors in damp locations are at a greater risk of causing ashock hazard. The reason for grounding motors is that it is common practice for a technician to
feel the motor to see if it has overheated and using a bare hand to feel a motor is done. Using a
temperature indicating device or infrared temperature detector should also be used to check for a
motor that may be overheated.
To prevent an ordinary motor from becoming overheated, keep the air openings on its frame
clear at all times. When oiling motor bearings, be sue not to use excessive oil as it could damage
the motor winding resistance and could cause the motor to collect an excessive amount of dirt
and dust.
When inspecting or replacing a motor, a technician should ensure the enclosure meets the proper
specifications as detailed in the below picture:
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Figure 7-31 page 166
An open motor enclosure allows the air to flow through the motor to cool the windings to
prevent overheating. A totally enclosed motor prevents air from entering the motor and cooling
is provided by other means.
If a motor does not start rotation after the switch has been turned ON, TURN OFF THE MOTOR
and UNPLUG it to prevent any permanent damage to the motors windings from becoming
overheated.
The above methods discussed are preventive maintenance activi tiesthat a facility should have
in place to keep its motors operating safely and efficiently. If done properly, all motors will
provide longer service life and continue to operate efficiently.
Troubleshooting Shaded-Pole Single Phase AC M otorswhen they fail are usually replaced.
The reason for the motor failure needs to be investigated to ensure the replacement motor not
subject due to an overload situation or environmental conditions that may have caused its
failure. To Troubleshoot a Shaded-Pole Motor the following picture illustrates a two step
process:
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Figure 7-32 page 167
To Troubleshoot a Shaded-Pole Single Phase AC Motor, the following procedure may
be used:
1.
Visually Inspectthe motor after turning power off (lock-out and tag-out).
a. Replace the motor if you see any discoloration showing it has been too hot.
b. Replace the motor if the shaft if jammed or lock as the bearings have seized.
c. Replace the motor if there is any sign of damage to the motor.
2. Check Stator Winding as it is the only electrical circuit that may be tested without
taking the motor apart.
a. Measure the resistance of the stator winding at the lowest DMM scale to
verify an infinity reading.
b. Replace the motor if the DMM indicates a zero reading (continuity) even
though the winding may still be good.
c. A final check can also be performed on the coil using a MEGOHMEETER to
verify the coil does not break down with voltage applied.
Troubleshooting Split-Phase Single Phase AC M otorsgenerally looking at a thermal switch
that automatically turns OFF the motor when it has overheated. These thermal switches may
have a manual reset or an automatic reset when the motor has cooled down. Caution must be
taken with any motor that has an automatic reset because the motor may automaticallyrestart at any time. The following picture illustrates how to Troubleshoot Spli t-Phase Single
Phase AC Motors:
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[ Insert Figure 7-33 page 168 Rockis Book) ]
To Troubleshoot a Split-Phase AC Motor, the following procedure may be used:
1. Visually Inspectthe motor after turning OFF the power (lock-out tag-out)
a. Replace the motor if you see any discoloration showing it has been too hot.
b. Replace the motor if the shaft if jammed or lock as the bearings have seized.
c. Replace the motor if there is any sign of damage to the motor.
2. Check for Thermal Switch.
a. With the motor power ON, check to see if a thermal switch exists, if it does,
Reset the switch and turn the motor on if it is a manual reset switch. If it
starts, observe it for normal operation.
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3. If it does not start, Checkfor voltage at the motor terminals using a DMM set to
measure voltage. The voltage should be within 10% of the motor listed voltage. If
voltage in not present or incorrect, continue troubleshooting the voltage problem.
4. If the motor voltage is good, turnOFF the motor (lock-out tag-out) to continue
testing the motor.
5. With power removed, connect a DMM set to resistance to the same motor leads
receiving the power (disconnect the motor leads from the incoming power leads to
ensure accurate measurement of motor leads). A short circuit is present if the
DMM reads Zero and an open circuit is present if the meter reads infinity. In
either case, the motor will need to be replaced and in most cases they are normally
too small for repair to be cost efficient.
6.
Check for Centrifugal Switch if present look for signs of burning or brokensprings.
a. Service or replace the switch if any obvious signs of problems exist.
b. Check the resistance of the switch. If the switch does not indicate it is open,
manually operate the switch with the DMM still connected to verify proper
operation (open and closed). To do this the end-bell on the switch may have to
be removed. The resistance on the DMM decreases if the motor is good. If
problem exists, the resistance will not change.
Troubleshooting Capacitor Motorsis similar to troubleshooting Split-Phase Motors. The
only additional device to be tested is the Capacitor.Capacitorshave a limited life and are
often the problem with Capacitor Motors. They may develop short circuit internally, or
become an open circuit. In either case they need to be tested and replaced as necessary
and they eventually deteriorate to the point when then must be replaced.
Deterioration may also change the value of a Capacitor, which will cause additional
problems. When it shorts out, the winding in the motor could actually burn out and need
to be replaced. When it deteriorates or opens, the motor will have poor starting torque,
which can prevent the motor from starting or more often usually trips the motor overload
devices (interlock switches).
Capacitorsdesigned to be connected to AC Power do not have an established polarity
like in a DC Power circuit. The following picture illustrates the steps on how to
troubleshoot a capacitor motor:
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Figure 7-34 page 169
To Troubleshoot Capacitor Single-Phase AC Motors, the following procedure may be
used:
1. Lock-Out and Tag-Out the handle of the safety switch or combination starter
in the OFF positon.
2. Measure the Voltage at the terminals to ensure the power is off (Zero
Voltage Check)
3. Remove Cover from Capacitorwhich are usually located on the outside of
the motor frame. CAUTION: A good capacitor will hold a charge even
when the power is removed.
4. Visually Inspect Capacitorfor any signs of leakage, cracks, or bulges. If any
of these conditions are present, the capacitor will need to be replaced.
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[ Insert Figure 7-35 page 170 Rockis Book) ]
To Troubleshoot a Three Phase motor, the following procedure may be used:
1. Measure Voltage at Motor Terminalsto verify voltage if present and at the
correct value on all three phases. If all the voltage is not present for all three
phases, the power supply voltage must be checked and restored. If the voltage ispresent and correct but the motor will still not start, proceed to the next step.
2. Lock-Out and Tag-Out the incoming power to the motor and its controls per
proper procedures.
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3. Disconnect the Load from the Motorto see if the motor in not locked by the
load.
4. Restore Power by removing the Lock-Out Tag-Out Tag per proper
procedure and try restarting the motor. If the motor starts, the load needs to be
checked for problems that have caused the motor not to rotate. If the motor does
not start with the load removed, proceed to the next step.
5. Lock-Out and Tag-Out the incoming power to the motor and its controls per
proper procedures.
6. Check the Motor Windings with DMM to measure resistance for any opens, or
short circuits for all coils. This is can be a check across all coils, or to check
indivudal coils, they will need to be isolated as indicated in the above pictureillustrating how to Troubleshoot Three Phase Motors.
a. If checking one coil first to determine its resistance, the basic laws of
series and parallel circuits are applied for series or parallel connected
coils. This can be used to check all coils together and if a problem exists,
then each coil will have to be checked to determine where the problem
may exist.
TECHNICAL FACTS ON 3 PHASE MOTORS:
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