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Energy Systems Engineering Technology

AC Generators, Transformers, and AC Motors Module

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



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 University’s 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



STEP ONE

AC Generators, Transformers, and AC Motors Course Knowledge

Objectives

Knowledge Terminal Objective (KTO)

KTO 3. 1. ANALYZE AC Generators, Transformers, and AC 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. DESCRIBE what an AC GENERATOR consists of and its principle of

operation.

KEO 3. 2. DESCRIBE how a SINGLE-PHASE AC GENERATOR provides AC Power.

KEO 3. 3. EXPLAIN how 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 VOLTAGE is and how devices can be protected

from High-Level Transients.



KEO 3. 7. DESCRIBE what a TRANSFORMER is and how it effects Voltage.

KEO 3. 8. EXPLAIN what TRANSFORMER LOSSES are and how they can be

minimized.

KEO 3. 9. EXPLAIN how SINGLE-PHASE and THREE PHASE TRANSFORMER

CONNECTIONS are made to include both Primary and Secondary Taps.

KEO 3. 10. EXPLAIN what a CONTROL TRANSFORMER is and how they provide

control voltage lower than the Primary Voltage applied.

KEO 3. 11. DESCRIBE two methods used to TROUBLESHOOT TRANSFORMERS.

KEO 3. 12. DESCRIBE what a SINGLE PHASE AC MOTOR consists of, its construction,

and principle of operation to include advantages they have over DC MOTORS.

KEO 3. 13. DESCRIBE three types of SINGLE PHASE AC MOTORS to include: Shaded-

Pole, Split-Phase, and Capacitor motors.

KEO 3. 14. DESCRIBE what a THREE PHASE AC MOTOR is to include operational

uses, and advantages they have over both DC Motors and AC SINGLE PHASE

Motors.

KEO 3. 15. DESCRIBE SINGLE VOLTAGE and DUAL VOLTAGE THREE PHASE

MOTOR applications to include WYE and DELTA Connections.

KEO 3. 16. DESCRIBE AC MOTOR TROUBLESHOOTING TECHNIQUES to include:

Troubleshooting Single Phase Shaded-Pole, Split-Phase, and Capacitor Motors,

and Three Phase Motors.



AC Generators, Transformers, and AC Motors

KEO 3. 1. DESCRIBE what an AC GENERATOR consists of, its components, and its

principle of operation.

AC GENERATORS convert mechanical energy into electrical energy (the same way a DC

Generator does) by means of electromagnetic induction. AC GENERATORS are actually

referred to as ALTERNATORS because they convert mechanical energy into AC Voltage and

Current (Alternating Current) 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 Field Winding, an Armature (Coil), Slip Rings and Brushes

as depicted in the below picture:

Figure 7-1 page 141

Field Windings are magnets used to produce the magnetic field in a generator. The

magnetic field can be provided by permanent magnets or by Electromagnets. Most AC



Generators have their magnetic field generated by Electromagnets. Electromagnets are

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 the coil(s) are attached to slip rings.

Slip Rings are metallic rings connected to the ends of the armature coils(s) and are used

to connect the induced voltage to the generators brushes. When the armature is rotated in

the 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 current

takes the shape of a sine wave. This is typical of the AC Voltage we have in our homes

and industry throughout the world.



In DC Generators, a commutator is used to provide an output whose current always

flowed in the positive direction as illustrated in the below figure:

Brushes in an AC Generator are the sliding contact that rides against the slip rings and is

used to connect the armature to 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 voltage is obtained at the brushes connected to the slip

rings, and is applied to an external circuit.



KEO 3. 2. DESCRIBE how a SINGLE-PHASE AC GENERATOR provides AC Power.

A SINGLE-PHASE AC GENERATOR provides 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 3600 as it generates continuously changing

AC Sine Wave:

Figure 7-2 page 143



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 “A” to 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 (900 of rotation) of the sine wave.

As the armature rotates from position “B” to position “C”, the current continues in the

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

0 of

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 (1810 – 270

0 of 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 3600 cycle of the sine wave.

KEO 3. 3. EXPLAIN how 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

Generator except that there are there equally spaced armature windings 1200 out of phase with

each other.



The below picture illustrates the differences between a single and a three phase generator

showing how three equally spaced armature windings 1200 out of phase will create three output

voltages 1200 out of phase with each other:

Figure 7-3 page 144

A Single Phase Generator has 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 Three Phase Generator has three separate armature windings so there

are six leads providing power to the intended load.



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



A Delta Connection is 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 Connection appears like the Greek Letter Delta (Δ).

A Wye Connection is 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 Connection appears

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 GENERATORS convert mechanical energy into electrical energy (the same way a

DC Generator does) by means of electromagnetic induction.

AC GENERATORS consists of a Field Winding, an Armature (Coil), Slip Rings and

Brushes.

Field Windings are 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 Rings are metallic rings connected to the ends of the armature coils(s) and are used

to connect the induced voltage to the generators brushes.

Brushes in an AC Generator are the sliding contact that rides against the slip rings and is

used to connect the armature to the external AC Circuit.

A SINGLE-PHASE AC GENERATOR provides 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 the three phase

AC Generator except that there are there equally spaced armature windings 1200 out of

phase with each other.

A Single Phase Generator has two leads providing power to the intended load.

A Three Phase Generator has three separate armature windings so there are six leads

providing power to the intended load.

There are two connections: Delta and Wye; the manner in which they are connected

determines the electrical characteristics of the generators output.

A Delta Connection is a connection that has each coil end connected end-to-end to form

a closed loop

A Wye Connection is a connection that has one end of each coil connected together and

the other end of each coil left open for external connections.



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 Specific 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-Voltage is generally more damaging than an Under-Voltage condition.

Equipment Manufacturers, Utility Companies, and regulating agencies must routinely

compensate for changes in system voltage.

Backup Generators are used to compensate for voltage changes. A Backup Generator can be

powered 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 CHANGES in a system may be categorized as:

Momentary, Temporary, or Sustained as depicted in the below picture:

Figure 7-5 page 146



A Momentary Power Interruption 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 Lightning Strikes Nearby, Utility Grid Switching during a problem (short

on one line, or during Open Circuit Transition Switching (a process in which power is

momentarily disconnected when switching a circuit from one voltage supply or level to

another).

A Temporary Power Interruption is 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 Interruption can also be caused by a time gap

between 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 Interruption is 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, Blown Fuses, and or Damaged 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 Uninterruptable Power System/Supply (UPS) can be utilized. An Uninterruptable Power

System/Supply (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 batteries.



Uninterruptable Power System/Supplies (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 UPS is 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.



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.



SUMMARY:

VOLTAGE CHANGES need to be monitored and controlled.

An Over-Voltage is generally more damaging than an Under-Voltage condition.

Equipment Manufacturers, Utility Companies, and regulating agencies must routinely

compensate for changes in system voltage.

Backup Generators are used to compensate for voltage changes and can be powered by

diesel, gasoline, natural gas, or propane engines connected to the generator.

VOLTAGE CHANGES in a system may be categorized as: Momentary, Temporary, or

Sustained.

A Momentary Power Interruption 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 Interruption is a decrease to 0 Volts on one or more power lines

lasting more than 3 seconds up to 1 minute.

A Sustained Power Interruption is a sustained power interruption when the power

decreases to 0 Volts on all power lines for a period of longer than one minute.

Uninterruptable Power System/Supplies (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.

UPS units have the load running directly from them and are constantly being kept

charged by the facilities main power source.

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.

Portable generators can be used to provide temporary power to essential loads by the

use of extension cords plugged directly to an essential load like a heater or refrigerator

that has been unplugged from the utility powered receptacle.



KEO 3. 6. DESCRIBE a TRANSIENT VOLTAGE is and how devices can be protected

from High-Level Transients.

A TRANSIENT VOLTAGE is 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 Circuits (TVs – Micro Wave Ovens –

Sound Systems etc) require protection against Transient Voltages. 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 Protector is 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/Suppressors can be installed at service entrance panels and individual loads as

depicted in the below picture:

Figure 7-6 page 147



Surge Suppressors power strips as shown above generally will have and on off switch and a

reset 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 61643-11

and 21 , Telcordia Technologies Technical Reference TR-NWT-001011, ANSI / IEEE

C62.xx, or UL) 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 – Mircro Wave Ovens – Sound

Systems etc) require protection against Transient Voltages.

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 Protector is 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 Suppressors power strips generally have and on off switch and a reset button.

When Surge Suppressors 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.

KEO 3. 7. DESCRIBE what a TRANSFORMER is and how it effects Voltage.

A TRANSFORMER is an electrical device that uses electromagnetism to change voltage from

one level to another. In other words, the Voltage is Stepped Up or Stepped 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 High Level for Transmission across the country and then

to decrease that voltage to a Low Level for use to a variety of electrical loads (residential,

commercial, and industrial).

http://en.wikipedia.org/wiki/International_Electrotechnical_Commission

http://en.wikipedia.org/wiki/CENELEC

http://en.wikipedia.org/wiki/Telcordia_Technologies

http://telecom-info.telcordia.com/site-cgi/ido/docs.cgi?ID=SEARCH&DOCUMENT=TR-NWT-001011&

http://en.wikipedia.org/wiki/American_National_Standards_Institute

http://en.wikipedia.org/wiki/Institute_of_Electrical_and_Electronics_Engineers

http://en.wikipedia.org/wiki/Underwriters_Laboratories



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 High 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, providing

additional safety for the circuit operator or technician. Transformers are also used in power

supplies of most electronic equipment to Step-Up or Step-Down the line voltage to provide the

required operating voltage for the equipment.



Transformers have a Primary Winding and a Secondary Winding wound around an Iron Core

as depicted in the below picture:

Figure 7-8 page 148

The Primary Winding is 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 Energy from 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



The following picture also illustrates how Step-Up and Step-Down transformers change the

voltage and current from the Primary Windings to the Secondary Windings as a ratio between

the number of turns of the conductor in the Primary and Secondary sides of the transformer:

Figure 7-10 page 149

The advantage of increasing voltage and reducing current is that power may be transmitted

through smaller gauge wire, thus reducing the cost of larger power lines. Although both voltage

and current can be Stepped-Up or Stepped-Down, these terms when used with transformers,

always apply to the Voltage.



The following picture depicts a High-Voltage Transmission Station where thousands of volts

are received via overhead transmission lines and then transformed to a lower voltage for local

distribution:

Picture page 150



SUMMARY:

A TRANSFORMER is an electrical device that uses electromagnetism to change

voltage from one level to another (the Voltage is Stepped Up or Stepped Down).

TRANSFORMERS are used to increase voltage to a High Level for Transmission

across the country and then to decrease that voltage to a Low Level for use to a variety of

electrical loads (residential, commercial, and industrial).

KEO 3. 8. EXPLAIN what TRANSFORMER LOSSES are and how they can be

minimized.

Many TRANSFORMERS have a secondary coil that has an extra lead (tap) attached to it. A

Tap is a connection brought out of a winding at a point between its endpoints to allow changing

the voltage or current ratio.

Although Transformers are 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 Losses come 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 Current Losses come because iron is 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 Currents, which in turn produce heat. This heat also represents a loss because it

does not useful work.

o Eddy Current Losses are minimized either by making the core of thin sheets

(laminations) which are insulated from each other, or by powered-iron cores

instead of solid blocks of iron.

o The insulation between the laminations of a laminated core break up current

paths within the core and reduces Eddy Currents. This same technique is used to



reduce Eddy Currents in Solenoids and was addressed in: Module # 2 Solenoids

DC Generators and DC Motors.

Hysteresis Loses occur 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 High Silicon Steel and other alloys in

the construction of the core.

All three of these TRANSFORMER LOSSES make 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 should be no odor of burring insulation or varnish, or sings of discoloration or smoke.

Any one of these conditions indicates the transformer is either overloaded or defective and

service is necessary to correct and reduce damage, safety, or fire hazards.

SUMMARY:

A



KEO 3. 9. EXPLAIN how SINGLE-PHASE and THREE PHASE TRANSFORMER

CONNECTIONS are made to include both Primary and Secondary Taps.

SINGLE-PHASE CONNECTIONS utilize 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®:




THREE-PHASE CONNECTIONS utilize 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:





KEO 3. 10. EXPLAIN what a CONTROL TRANSFORMER is and how they provide

control voltage lower than the Primary Voltage applied.

A CONTROL TRANSFORMER is a transformer that is used to Step-Down the voltage to 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




As depicted above, control voltage 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 control circuits. In 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:




Picture Page 153 Control Transformers

Picture Page 154 Autotransformers



KEO 3. 11. DESCRIBE two methods used to TROUBLESHOOT TRANSFORMERS.

Two methods used to TROUBLESHOOT TRANSFORMERS include: Measuring the Input

and Output Voltages, and the Transformer Resistance.

When transformers are installed into a circuit, they generally will operate without failure for a

long time. This is because transformers have no moving parts. If a transformer does fail, it will

appear as either a short circuit or an open circuit in one of its coils.

Measuring Input and output voltages when a transformer is connected in a circuit it

can be tested by measuring the input and output voltages. The transformer is considered

good if the voltages are close to the transformers specifications. If a transformer voltage

does not stay constant, current levels are tested when the transformer is loaded as it may

not be holding up under its expected load.

Checking Transformer Resistance require the voltage to the transformer be removed

from the primary windings (Locked-Out/Tagged-Out) and the secondary windings be

disconnected. Using a DMM set to measure resistance to check for open circuits in coils,

short circuits between coils, or coils shorted to the transformer core.

o To check for open circuits in coils, the resistance of each coil is checked. The

winding is open and the transformer is bad if any coils show an infinite resistance

reading.

o To check for short circuits between primary and secondary coils, the resistance

needs to be checked between primary and secondary coils. If an infinite resistance

is not found between the primary and secondary coils, the coils have shorted and

the transformer is bad.

o To check for coils shorted to the transformer core, the resistance needs to be

checked from each coil to the core. This check is good if the resistance is infinite.

If there is a continuity reading from coil to core, the transformer is bad.



The following picture depicts how using a DMM can be used to test transformers:




SUMMARY:

L

l

KEO 3. 12. DESCRIBE what a SINGLE PHASE AC MOTOR consists of, its construction,

and principle of operation to include advantages they have over DC MOTORS.

A SINGLE PHASE AC MOTOR is an AC motor that uses Alternating Current (AC) to

produce rotation. The main parts of an AC motor are the Rotor, and a Stator. The Rotor is the

rotating part of the motor and the Stator is the stationary part of an AC motor. A typical AC

motor is used in industry because of their Simplicity, Ruggedness, and Reliability and can be

Single Phase, Single Phase Two Speed Single Voltage, and Three Phase Single or Dual

Voltage as depicted below also illustrating typical construction characteristics:




AC motors have several advantages over DC motors in that there are only two bearings that can

wear, and there are No Brushes because the motor does not have a Commutator which 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 Air Furnace Fans, Air Conditioners, Washing

Machines, etc. Single Phase Motors include: Shaded-Pole, Split-Phase, and Capacitor

motors.

KEO 3. 13. DESCRIBE three types of SINGLE PHASE AC MOTORS to include: Shaded-

Pole, Split-Phase, and Capacitor motors.

Shaded-Pole motors are a Single Phase AC Motor that uses a shaded stator pose for

starting the motor as depicted in the picture below:

[ Insert Figure 7-20 page 157 Rockis Book) ]



Shaded-Pole motors utilize the simplest method to start a Single Phase AC Motor. They

are commonly rated at ½ horsepower or less and have low starting torque. Common

applications include small cooling fans found in computers and home entertainment

centers. The Shaded-Pole is 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 900 from the magnetic field of the main Stator Field Pole. This

movement determines the starting direction of a shaded pole motor.

o A shaded-pole motor is a type of AC single-phase induction motor. It is basically

a small squirrel cage motor in which the auxiliary winding is composed of a

copper ring surrounding a portion of each pole. This auxiliary winding is called a

shading coil. Currents in this coil delay the phase of magnetic flux in that part of

the pole enough to provide a rotating magnetic field. The direction of rotation is

from the unshaded side to the shaded (ring) side of the pole. The effect produces

only a low starting torque 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 best

suited to driving fans or other loads that are easily started. Moreover, they are

compatible with TRIAC-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. For

larger motors, other designs offer better characteristics.

Split-Phase motors are Single Phase AC Motors that include a Running (main winding)

and a Starting Winding (auxiliary winding). Split-Phase motors are AC motors of a

fractional horsepower, usually 1/20 to

1/3 HP. They are commonly used to operate washing

machines, oil burners, and small pumps and blowers.

o A Split-Phase motor 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_current

http://en.wikipedia.org/wiki/Single-phase_electric_power

http://en.wikipedia.org/wiki/Induction_motor

http://en.wikipedia.org/wiki/Squirrel_cage_motor

http://en.wikipedia.org/wiki/Phase_(waves)

http://en.wikipedia.org/wiki/Magnetic_flux

http://en.wikipedia.org/wiki/Rotating_magnetic_field

http://en.wikipedia.org/wiki/Torque

http://en.wikipedia.org/wiki/TRIAC



o A Split-Phase motor is depicted in the below picture:


When the Split-Phase starts, both the Running and Start Windings are connected in

parallel. The Start Winding is 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 Split-Phase AC Motor that includes a capacitor in addition to

the running and starting windings. Capacitor Motors range in sizes ranging from 1/8 to 10

HP. Capacitor Motors are used to operate Refrigerators, Compressors, Washing Machines,

and Air Conditioners.



o The Capacitor is wired in series with the Start Winding and provides a Capacitor

Start Motor with the benefit of High Starting Torque. The Capacitor adds an extra

jump start to get the motor to start with loads requiring High Starting Torque. A

Capacitor Start Motor is depicted below:


A Capacitor-Run Motor is a Split-Phase AC Motor with the start winding and the capacitor

connected in series at all times which does not have a centrifugal switch, giving this motor

medium staring torque and somewhat higher running torque than a capacitor start motor as

the capacitor continually charges and discharges while the motor is running.



o A Capacitor-Run Motor is depicted in the below picture:


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 to

start the motor and a smaller one to run it.



o A Capacitor Start-and-Run motor depicted below with a centrifugal switch cutting

out the start capacitor and allowing the run capacitor to stay in the start winding:


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:

.



KEO 3. 14. DESCRIBE what a THREE PHASE AC MOTOR is to include operational

uses, and advantages they have over both DC Motors and AC SINGLE PHASE

Motors.

THREE PHASE AC MOTORS are the most commonly used motors in industrial applications.

Three Phase Ac Motors are used in applications ranging from fractional horsepower to over 500

HP. Three Phase Ac Motors are 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 Phase Ac Motor is the Induction Motor.

The Induction Motor is 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:




o Three Phase Motors are like having three single phase motors connected together to

do more work more efficiently. Each phase is 1200 from the other phases and the

magnetic field is produced in the stator because each phase reaches its peak magnetic

strength 1200 from 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 Motors are designed as either Single-Voltage Motors or Dual-Voltage

Motors.



KEO 3. 15. DESCRIBE SINGLE VOLTAGE and DUAL VOLTAGE THREE PHASE

MOTOR applications to include WYE and DELTA Connections.

SINGLE VOLTAGE THREE PHASE MOTORS is 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 Motors are wired so that the phases are connected in

either a (Y) or a (Δ) configuration as illustrated in the following two pictures:

Three Phase Wye-Connected Motor




o A Wye-Connected Motor has one end of each coil internally connected to the other

phases.

Three Phase Delta-Connected Motor


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 be

connected for either of two voltages. Making motors for two voltages enables the same

motor to be used with two different three phase power supplies.



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 (Δ) configuration as illustrated in the following two

pictures:



Dual Voltage Three Phase Wye-Connected Motor


A Dual Voltage Wye-Connected Motor has each phase coil divided into two equal

parts.



Three Phase Delta-Connected Motor


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:

Troubleshooting Single Phase Shaded-Pole, Split-Phase, and Capacitor Motors,

and Three Phase Motors.

Most problems with AC Motors are related to Single Phase AC Motors dealing with the

Centrifugal 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 than 1/8 HP 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 any

problems 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 motor’s name plate:




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 a

shock 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:




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 motor’s windings from becoming

overheated.

The above methods discussed are preventive maintenance activities that 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 Motors when 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:




To Troubleshoot a Shaded-Pole Single Phase AC Motor, the following procedure may

be used:

1. Visually Inspect the 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 Motors generally 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 automatically

restart at any time. The following picture illustrates how to Troubleshoot Split-Phase Single

Phase AC Motors:




To Troubleshoot a Split-Phase AC Motor, the following procedure may be used:

1. Visually Inspect the 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.



3. If it does not start, Check for 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, turn OFF 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 broken

springs.

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 Motors is similar to troubleshooting Split-Phase Motors. The

only additional device to be tested is the Capacitor. Capacitors have 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).

Capacitors designed 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:




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 Capacitor which 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 Capacitor for any signs of leakage, cracks, or bulges. If any

of these conditions are present, the capacitor will need to be replaced.



5. Carefully Discharge the Capacitor if replacing by using a 20,000 Ὼ 5 Watt

Resistor across the terminals of the capacitor for approximately 5 seconds.

6. After Capacitor has been discharged check its resistance with a DMM. The

DMM indicates the general condition of a discharged capacitor. This test will

verify if the Capacitor is good, shorted, or open.

a. A good capacitor changes the reading of the DMM from Zero to

Infinity. When the meter reaches the halfway point to Infinity,

remove one of the meter leads and wait 30 seconds. When the

meter is reconnected, it should return to the halfway point and

continue to Infinity. This check verifies the capacitor can hold a

charge provided by the DMM (in the Ohm range). If the capacitor

cannot hold a charge, it will return back to Zero and it will need to

be replaced.

b. A Short Capacitor resistance reading changes to Zero and does

not move. The capacitor is bad and needs replacing.

c. An Open Capacitor resistance does not change from Infinity. If

this is the case, the capacitor will need to be replaced.

Troubleshooting Three Phase AC Motors depends on the motor application. Testing is

normally limited to checking the voltage at the motor if a motor us used in an application

that is critical to an operation or production. Motors are assumed to be the problem if the

voltage is not present and is incorrect. Unless the motor is very large, the motor is usually

replaced so production may continue. Further tests on the removed motor or other motors

not in critical operation may be made to determine the exact problem with the motor. The

following picture illustrates steps to perform these tests to determine the motors fault:




To Troubleshoot a Three Phase motor, the following procedure may be used:

1. Measure Voltage at Motor Terminals to 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 is

present 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.



3. Disconnect the Load from the Motor to 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 picture

illustrating 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:



STEP TWO

AC Generators, Transformers, and AC Motors

Skill/Performance Objectives

Skill Knowledge Introduction:

Below are the skill knowledge objectives. How these objectives are performed depend on

equipment and laboratory resources available. With each skill objective it is assumed that a set

of standard test equipment and tools be provided and safety procedures be implemented during

each tasked being performed.

Inspect an AC Motor or Generator for proper operation and identify any defects on

operation

Evaluate the performance of a transformer to determine transformation efficiencies

Disassemble and inspect an motor, transformer or generator and identify service needs

Assemble a motor, transformer or generator replacing normal seals and wearing parts

as specified in the technical manual

Test a service motor to ensure safe and correct operation

Perform a meggaohm test of a motor, generator or transformer and identify any faults

indicated by the test results

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