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Audio:
Building Operator Certification Level I
Audio: This Building Operator Certification Level 1 lesson is made possible thanks to the following organizations.
Reading Assignment for this Lesson
If you have not already done so, below is the reading assignment you
should complete before starting this lesson.
BOC 103
If you do not have the required reading material,
please contact XXXX.
Audio: You should have completed the following reading assignment prior to starting this lesson.
Welcome to Motors
A
B
D
C
Audio: Motors are some of the biggest energy users in a facility, powering everything from HVAC systems, to
factory conveyor belts, to the power tools used to make building repairs. In fact, motors consume
approximately 70% of all electricity used in manufacturing!
The Importance of Efficiency
A
A
A
3.5
3
B
2.5
D
2
Efficiency
Cost
1.5
1
0.5
C
0
Audio: Because motors are one of a facility’s biggest energy users, their efficient operation can greatly influence
costs. Even a small increase in efficiency can have a large payback, decreasing the energy budget.
Benefits of Energy-Efficient Motors
A
C
C
B
Benefits of Energy-Efficient Motors
•Reduced current on customer's distribution system
•Less heat load on building air conditioning system
•Environmental awareness - Less Greenhouse Gas
emissions
•Utility rebates and tax credits may be available
Audio: A motor performs more efficiently when maintained and properly used. Besides the reduced operating costs
already mentioned, energy-efficient motors provide many additional benefits. Take a minute to read through
them.
Lesson Topics
•
•
•
•
Section
Section
Section
Section
1:
2:
3:
4:
Principles of Motors
Motor Maintenance
Efficiency
Motor Formulas
Remember, you don’t have to complete the entire
lesson in one sitting. You may stop and come back to
the lesson and pick up from where you left off.
Audio: In order to learn how to make motors as efficient as possible, we will cover the following topics in this
lesson. After you’ve reviewed the topics, click Next and let’s get started!
Section 1: Principles of Motors
This section provides an overview of how motors
are put together and operated, and introduces the
specifications included on a motor nameplate.
We’ll talk about:
•
Basic construction of motors
•
AC and DC motors
•
Single-phase vs. three-phase motors
•
Nameplate data
•
Starters
Audio: Before we can delve too deeply into the specifics of motor maintenance and efficiency, we need to
investigate some basic concepts of motors. This section will help us do that. Let’s begin with how motors
function.
Basic Construction of Motors
D
C
How an Electric Motor Works:
•
Motor with a permanently
magnetized stator
•
Electricity applied to the rotor
creates a strong magnetic
field in rotor
•
Force in the rotor will rotate
the rotor
A
B
"How an Electric Motor Works", via eHow.com
Audio: Here is an example of a DC motor. Read through the key points of its operation, then click Next to
continue. To watch a five-minute video on how electric motors work, click the link at the bottom of the page.
Typical Electric Motor Construction
The STATOR is
the stationary
part of the
motor.
A
A
B
C
D
The BEARINGS
support the
shaft and allow
it to spin freely.
The FAN cools
the motor; it’s
attached to the
shaft.
The
ARMETURE
rotates to
provise energy
to the shaft.
CONDUCTORS
help transfer
power
throughout the
motor.
B
E
C
WINDINGS
create the
rotating
magnetic field
which induces
current.
D
E
F
F
G
The FAN cools
the motor; it’s
attached to the
shaft.
G
FYI – this is
known as a
squirrel-cage
motor because a
squirrel cage
housing
surrounds the
rotor.
Audio: Induction motors are the most common types of motors. In fact, they account for 90% of all AC motors.
Here is a cutaway view of a typical induction motor. Click on the parts to review what each does.
Close-up of a Stator
Close-Up View of the Stator
Audio: Let’s look specifically at a cutaway of the stator for a minute. Remember that the stator is the stationary
part of the motor, and its squirrel cage design helps with induction. Click each star to reveal the components of
a stator. Once you are finished reviewing, click Next to continue.
Comparing Motor Types
AC Motors
DC Motors
•Coils rotate in a magnetic field
•Coils rotate in a magnetic field
•Current passes through stator; stator induces
movement in the rotor which is attached to shaft
•Current passes through coils
•No commutator
•Somewhat less expensive than a DC motor (with
same power)
•Single-phase and three-phase
• Polarity flipped by commutator
•Easily-varied speed
•Used in many power tools
•Require a bit more maintenance than
comparable AC Motor
Audio: While electric motors are generally similar in their functions and construction, there are some interesting
distinctions to be made between the two types of induction motors. Read through this comparison chart to
discover some similarities and differences between AC and DC motors. Once you are finished, click Next to
continue.
Motors Types and Efficiency
A
B
Audio: You learned earlier that efficiency was going to be a key component of this course. To that end, there is
one more quick distinction to be made between single-phase and three-phase motors. Imagine that a singlephase motor (A) is a merry-go-round being pushed by one child. By contrast, a three-phase motor (B) is like
having three children pushing. Which merry-go-round is more efficient? Of course, the one with three times the
power! A three-phase motor is able to work more efficiently than a single-phase motor.
Motor Nameplates
D
A
B
C
http://www.pdhonline.org/courses/e156/e156content.pdf
Audio: This is a generic motor nameplate. Most of you will be familiar with its contents. It contains the motor’s
electrical and performance specifications, as well as the manufacturer and model number. The National Electrical
Manufacturers Association, or NEMA, defines some basic parameters for what should be coded onto a motor
nameplate, and manufacturers often include additional information to further define some key motor features. If
you would like to take a closer look at NEMA’s nameplate specifications, click the link at the bottom of the page.
Now, let’s take a closer look at some common nameplate information.
Basic Electric Motor Nameplate Data







HP - mechanical work produced at the shaft
 1 HP = 746 watts
Required Voltage for motor operation
Phases (single or 3-phase)
Rated Amps
 LRA - Locked Rotor Amps – Motor is not turning
 RLA – Rated Load Amps – Running at Rated HP
 FLA - Full load Amps – Amps/current drawn when the motor is at 100% load
Efficiency
 83 - 88% Standard, >90% Premium
 Eff = work output / energy input
Type (torque characteristics in relation to current)
 Type B - general duty, most common
 Type B limits inrush of current
 Type A does not, which can cause problems with sizing the starter
Frame
 NEMA dimensions for replacement across manufacturers
 Frame size sets important mounting dimensions such as foot hole mounting pattern,
shaft diameter, and shaft height
 NEMA standards do not set some dimensions that can turn out to be important if the
motor must fit into a confined space
Audio: Click each of the bullet points to reveal common nameplate information and abbreviations. Once you have
finished reading, click Next to continue.
Basic Electric Motor Nameplate Data





D


A
HP - mechanical work produced at the shaft
 1 HP = 746 watts
B
Required Voltage for motor operation
Phases (single or 3-phase)
Rated Amps
C
 LRA - Locked Rotor Amps – Motor is not turning
 RLA – Rated Load Amps – Running at Rated HP
 FLA - Full load Amps – Amps/current drawn when the motor is at 100% load
Efficiency
E
 83 - 88% Standard, >90% Premium
F
 Eff = work output / energy input
Type (torque characteristics in relation to current)
 Type B - general duty, most common
 Type B limits inrush of current
 Type A does not, which can cause problems with sizing the starter
Frame
 NEMA dimensions for replacement across manufacturers
 Frame size sets important mounting dimensions such as foot hole mounting pattern,
shaft diameter, and shaft height
 NEMA standards do not set some dimensions that can turn out to be important if the
motor must fit into a confined space
KNOWLEDGE
TO - DO
84%
Audio: You may be asking yourself “I can read a nameplate. Why is this extra information important?” It’s
important for a couple of reasons. First, so you understand motors and their ratings. Second, you will need to
pull this information off of one nameplate of a motor at your school. Add this information to your project file.
One more note – a key concept of this course is the idea of efficiency. The standard efficiency range of 83-88%
is known as the “average scale”. Therefore, while a motor with an efficiency of 84% sounds fairly efficient, it is
actually on the low end of the average scale.
Motor Starters
A
B
C
D
• Soft start: starts a motor gently; regulates
power “rushing” into motor so as not to be
abrupt. This reduces motor wear and
power usage
• A solid state reduced voltage starter is
designed to control the current supplied to
an induction motor
 Starters protect against
• Thermal overloads
• Excessive load conditions
• Low-voltage conditions
• Transients
•Watch out for
 Corrosion on contacts (high
resistance)
 Frequent trips and cycling
Motor Starter
Audio: So far, we have talked about the basic construction and function of motors. However, we have not discussed
the specifics about actually turning a motor on! When a motor is first started, power is pulled in via an
electromagnetic coil on call from a lower voltage control circuit. The motor starter helps to regulate power
inrush and motor wear-and-tear, typically through soft-start and solid-state technologies. Additionally, a starter
serves to protect a motor and lengthen its life. Just be mindful of warning signs of starter malfunction! Once
you are finished reviewing these bullet points, click Next to continue and we’ll quickly look at a visual of this
power regulation.
Three-Phase Motor Starter Schematic
A
B
1
C
D
E
2
3
Audio: Here is a 3-phase motor starter. When the motor is started, power enters through each of the three lead
connections and moves through the contacts of the breaker. Next it hits the contacts of the overload device and
then the temperature sensors before finally reaching the motor.
And with that, you have completed Section 1!
Check Your Knowledge
Read the question, then select the best answer.
1. You need to calculate the amount of power a motor draws. You know that Power
(Watts) = Volts x Current (Amps). The maximum power a motor can draw is Volts
x Maximum current. What information do you need from the motor nameplate?
a) Horsepower
Feedback: Multiplying Rated Voltage and
b) Rated Voltage
Rated Current will give you the motor’s
c) Rated Current
power draw.
d) A and B
e) B and C
Feedback: DC motors have commutators;
2. An AC motor has a commutator .
AC motors have stators.
a) True
b) False
3. A squirrel cage is part of the:
a) Bearings
b) Housing
c) Stator
d) Starter
Feedback: The squirrel cage is part of the
stator; it helps with induction.
4. NEMA is the organization that defines basic design and dimensional parameters for
motors.
Feedback: NEMA provides design
a) True
parameters and abbreviations for motor
b) False
nameplates.
Audio: Let’s take a moment to check your understanding of what we’ve covered so far. Answer these questions to
the best of your ability. Your answers for these reviews are not “scored.”
Back on the job…
Your supervisor has asked you to pull information from your HVAC motor’s
nameplate. Fill out the clipboard by dragging nameplate information onto the
correct line.
Feedback:
Model # = 5K254AK205
Serial # = 1105842
Phase Type = 3
Efficiency = 91.7%
Frame = 254T
Horsepower = 15
Audio: Throughout the lesson, we’ll present you with opportunities to apply what you’ve learned to real-world
situations. We call these “Back on the job.”
Section 2: Motor Maintenance
This section discusses reasons for motor failure and
the typical checklists, schedules, and replacement
plans necessary to keep motors maintained and
running efficiently.
We’ll talk about:
•
Causes of motor failure
•
Maintenance checklists
•
Motor schedules
•
Replacement plans
Audio: The better maintained a motor is, the more efficiently it will perform. Sometimes, though, maintenance is
not enough, and a motor needs to be replaced. This section will investigate some best practices for motor
maintenance as well as the process to replace motors when they are no longer functional.
Common Causes of Early Motor Failure
A
• Overheating – excessive
start/stop, poor air
flow/blockage from dirt
and dust, phase
imbalance, loose
connections
C
• Improper lubrication of B
bearings
• Poor alignment to fan or
pump – this wastes
energy in addition to
shortening motor life
• Movement and vibration in
motor supports
Audio: Here is a list of the most common reasons a motor fails. Take a minute to read through them. Of these four,
overheating is the highest priority to fix. In fact, any motor that won’t let you comfortably rest your hand on it is
too hot!
Key Maintenance Practices for Motors
 Check load conditions to ensure that the motor is not
over or under loaded. Check for rated ‘Amps’ using a clampon Ampmeter.
 Lubricate appropriately. Manufacturers generally give
recommendations for how and when to lubricate.
 Inspect the connections at the motor and starter regularly to
be sure that they are clean and tight. (A thermograph scan
may help detect leaks).
 Provide adequate ventilation and keep motor cooling ducts
clean to help dissipate heat to reduce excessive losses.
For every 20°F increase in motor operating
temperature, motor life is estimated to be halved
Audio: So overheating, lubrication, alignment, movement and vibration are causes of motor failure. How do we
prevent these issues from happening? Click each check mark to learn prevention strategies. Then, click next to
take a look at how often these and other common maintenance checks should be performed to keep your motors
in top shape.
Maintenance Checklist
B
C
A
D
Audio: This is a great example of a maintenance checklist. Notice that most tasks are performed monthly, but
there are some that are done daily, others weekly, and still others that are only done once a year. To download
a copy of this checklist for your own records, click the link at the bottom of the page.
http://www1.eere.energy.gov/femp/pdfs/OM_9.pdf
D
E
F
Managing Motors
Sample Motor Performance Graph – Illustrative Only
A
B
C
Years
Audio: While proper maintenance will go a long way toward prolonging the life of motors, and ensuring that they
perform as efficiently as possible, there will come a time when a motor will need to be replaced. There are a few
ways to prepare for that, so replacement is as quick and easy as possible. Let’s take a look at some of these
ideas.
Managing Motors
LOAD
Bill – would you please provide, via email, a line or 2 of
appropriate information for the Motor schedule, so we can have
it “filled out” as students read this slide…
LOCATION, DESCRIPTION
HP
V
A
Ph
KW,
connected
TIME OF OPER
KW, onpeak
OPER HRS/YR
KWH /YR
A A Motor Schedule will help you:
•
•
•
•
Identify trends in motor usage B
Develop an inventory of building motors
Speed motor replacement
D
Select best replacement options E
C
Audio: One way is to keep a Motor Schedule. The information you collect will help you identify trends in energy
consumption, peak demand, and operating hours. In addition, a Motor Schedule will allow you to develop an
inventory of building motors and their specifications. Having an inventory on hand will allow you to quickly
replace a motor when needed and select the best replacement motor for your needs..
Managing Motors
A
B •
MotorMaster
–
–
–
–
•
Free software provided through
the Department of Energy
Database of 25,000 available
electric motors, efficiencies, and
prices
User enters current motor
inventory and utility rates
MotorMaster recommends
replacement units based on
lifecycle savings
Copper.org
–
–
–
C
Entire section devoted to Premium
Efficiency Motors
In addition to a nice summary of
motor information, it has:
Tables showing payback time
when moving from a standard to
premium motor
Link to MotorMaster Software
Link to Copper.org Motor Payback Tables
Audio: The Internet provides access to other tools that are invaluable when preparing for motor replacement,
especially when there is pushback to moving toward premium efficiency motors. Click the MotorMaster and
Copper.org headings to read more about each site’s offerings. Then, to explore the sites on your own, click the
links at the bottom of the page.
Check Your Knowledge
Read the question, then select the best answer.
1.For every ____ increase in motor operating temperature, motor life is estimated to
be halved.
a) 10° F
b) 20° F
Feedback: Every 20 ° increase in
c) 30° F
temperature causes an estimated 50%
d) 40° F
reduction in motor life.
2.In addition to shortening a motor’s life, poor alignment will also ____.
a) cause excessive noise
b) overheat the motor
Feedback: Poor alignment between a motor
c) short out the starter
and its fan or pump will waste energy.
d) waste energy
3.Improper lubrication is one of the common causes of early motor failure.
a) True
Feedback: If bearings are not properly
b) False
lubricated, a motor will burn out.
4.Match
a)
b)
c)
d)
each maintenance task with how often it should be performed.
Check alignment (monthly)
Check bearings (annually)
Check motor condition (weekly)
Check motor sequencing (daily)
Audio: So we’ve completed Section 2. Let’s take a moment to check your understanding of what we’ve covered so
far. Answer these questions to the best of your ability. Remember, your answers for these reviews are not
Back on the job…
•
While performing routine motor maintenance, you need to
ensure the motor is not overloaded for its size. How do you
do this?
Feedback: Use a Clamp On Amp meter to
check that the current to the motor does
not exceed the rated ‘Amps’ of the motor.
•
A trainee asks you what would happen to a motor that is
blocked with dust or has no air circulation through it. What
would you tell them?
Feedback: The motor will overheat and, if
left this way, eventually burn out.
Audio: Let’s take a look at this, back on the job…
Section 3: Motor Efficiency
This section outlines the importance of efficient
motor operations and then covers efficiency
specifications for motors at various loads and power
levels.
We’ll talk about:
•
Benefits of motor efficiency
•
Efficiency specifications
•
Load efficiencies
•
FEMP guidelines for efficient motor operation
Audio: Now we have arrived at the heart of the course – efficiency. This section will revisit the benefits of energyefficient motors and look at how efficiency is measured and used. First, let’s look at efficiency in a context that is
familiar to most of us.
Putting Motor Efficiency in Perspective
C
A
B
D
E
Audio: When you buy a car, you go to a lot of effort to select a car with high efficiency to save on the cost of gas.
But consider this…the cost of gas is a relatively small part of the cost of car ownership. By contrast, fuel costs
are a much larger chunk of expenses for a motor, so it would make even more sense to choose high-efficiency
motors for your facility.
Putting Motor Efficiency in Perspective
A
1.
C
25
2.
mpg
$2600
B
20%
D
86%
1.
$4640
F
G
E
2.
4%
Audio: Let’s look at this another way. Upgrading your car’s mileage from 25 miles per gallon to 30 miles per gallon
will result in a twenty percent increase in efficiency. That’s pretty good! In fact, it results in a savings of twentysix hundred dollars over the lifetime of the car. However, upgrading a motor that is 86% efficient to one that is
90% efficient – a difference of only 4% - results in a savings of over forty-six hundred dollars over the motor’s
The Benefits of Energy-Efficient Motors
A
The Benefits of Energy-Efficient Motors
•
•
•
•
•
•
•
•
•
Reduced current on customer's distribution system
Fewer motors needed in building inventory
Lower Peak Demand
Less heat load on building air conditioning system
Lower operating expenses
Greater power consumption for building
Environmental awareness - Less Greenhouse Gas emissions
Reduced operating hours
Utility rebates and tax credits may be available
Feedback: These are the benefits of
energy-efficient motors.
Audio: If you recall, we looked at some benefits of energy-efficient motors back in the Introduction. Let’s take a
minute to review them. Here is a list of statements – click on each one you believe to be a benefit of efficient
motors. When you have finished, click the Submit button to check your answers.
Energy Specifications
1. What is the NEMA Premium Efficiency standard for a 20 HP, 1800 RPM motor? (93)
2. What is the NEMA Premium Efficiency standard for a 5 HP, 1200 RPM motor? (89.5)
3. What is the NEMA Premium Efficiency standard for a 50 HP, 3600 RPM motor? (93.0)
Audio: This chart shows the efficiencies required by the EPA for different size motors as well as available
efficiencies for NEMA premium efficiency motors. Remember, even a small increase in efficiency can save a
Energy at Full and Partial Loads – Comparison Charts
Efficiency at Full and Partial Loads – ODP Motors
A
Audio: We have been looking at the various benefits of energy efficient motors. Here are two visual depictions of
those benefits – the chart and graph each show the efficiencies of different sized motors when partially loaded.
Take a few minutes to study them. You will notice that the larger horsepower motors reach their highest
efficiencies with less of a load than the smaller motors.
FEMP Guidelines for Efficient Operation of Motors
FEMP 9.10.15 – Cost and Energy Efficiency
 Turn off unneeded motors
Reduce motor system usage, reducing load in building
 Efficiency of mechanical systems affects motor run-time
 For example, reducing solar load on a building will reduce the amount
of time the air handler motors would need to operate
Check ventilation systems for excessive air
 Re-sheave fan if air is excessive
 Downsize motors, if possible
 Repair air duct leaks
Improve compressed air systems by finding and repairing leaks
Replace motors with more energy-efficient versions
Audio: The Cost and Energy Efficiency section of the Federal Energy Management Program, or FEMP, covers some
best practices for efficient motor operations. Click the check marks to read through them. When you have
finished, click Next to continue.
FEMP Guidelines for Sizing Motors
FEMP 9.10.15 – Cost and Energy Efficiency
 Do not assume an existing motor is properly sized for its load, especially
when replacing motors.
 Many motors operate most efficiently at 75% to 85% of full load rating.
 Under-sizing or over-sizing reduces efficiency.
 For large motors, facility managers may want to seek professional help in
determining proper sizes and actual loadings of existing motors.
 There are several ways to estimate actual motor loading: the kilowatt
technique, the amperage ratio technique, and the less reliable slip
technique.
 All three are supported in the MotorMaster+ software.
Link to MotorMaster Software
Audio: When it comes to the motors themselves, sizing is the most important concept discussed in the FEMP
guidelines. The MotorMaster software you looked at in the prior section actually provides a number of ways to
estimate motor loading. Read through the sizing guidelines shown here, then click the link at the bottom of the
page to investigate how MotorMaster can assist you. When you have finished, click Next to continue.
Check Your Knowledge
Read the question, then select the best answer.
1. A small increase in motor efficiency will have no impact on the energy budget.
a) True
Feedback: Even a small increase in efficiency will
b) False
have a significant impact on the energy budget.
2. One of the easiest FEMP guidelines of increasing efficiency to implement is to
____.
a) improve compressed air systems
b) downsize motors
c) replace motors with more efficient ones
d) turn off unneeded motors
Feedback: Turning off motors that are not
needed is the quickest and easiest way to
boost efficiency.
Audio: Let’s take a moment to check your understanding of what the information you’ve covered in Section 3.
Answer these questions to the best of your ability. Remember, your answers for these reviews are not “scored.”
Check Your Knowledge, Continued
Read the question, then select the best answer.
Here is a snapshot of the EPA Efficiency Requirements chart you looked at
earlier. Use this to answer the next two questions.
3. What is the NEMA requirement for a 2 HP motor at 1800 RPMs?
a) 87.5
Feedback: A 2 HP motor at 1800 RPMs needs to
b) 86.5
be 86.5 efficient.
c) 85.5
d) 84.0
4.
What is the NEMA requirement for a 3 HP motor at 3600 RPMs?
a)
86.5
Feedback: A 3 HP motor at 3600 RPMs needs to
b) 88.5
be 85.5 efficient.
c)
89.5
d) 85.5
Back on the job…
3
Feedback:
1. The US Motors – Premium operates
with94.6% efficiency at 50% load.
2. The Reliance XE motor is 87.6%
efficient while 25% loaded.
3. The US Motors – Premium motor is
96.1% efficient at 75% of load.
1
2
It is time to replace some of your facility’s motors. Identify the best replacement
option in each of these scenarios by clicking on the motor name:
1. A 40 HP motor that would operate at 50% load
2. A 10 HP motor that would operate at 25% load
3. A 100 HP motor that would operate at 75% load
Audio: Let’s take a look at efficiency back on the job….
Section 4: Quantifications
This section provides a basic review of motor load
and sizing, then addresses a basic method of
calculating energy use that will be useful on the
job.
We’ll talk about:
•
Motor load
•
Converting HP to Kilowatt hours
•
The Herzog Method
Audio: We have arrived at the final section of the course. It’s short, but important. In this section, we will review
the importance of motor loading and look at a calculation to help convert horsepower to Kilowatt hours. This
conversion is the most basic one used in calculating efficiencies, energy use, and savings. Let’s get started.
Reviewing Motor Load
Load Factor = how much load a motor is carrying right now
relative to its full rated power
A
25hp
D
C
C
25%
B
B
E
100hp
F
G
7 amps
10 amps
G
70% G
Audio: If you recall, the term “load factor” refers to how much load a motor is carrying relative to its full rated
power. A motor carrying a 25 horsepower load when it is rated for 100 horsepower is at a 25% load factor.
You can test this by using an amp meter. For example, you use an amp meter on a motor rated for 10 amps;
the meter reads 7 amps. The motor’s load factor is 70%.
Reviewing Motor Load – Key Points
Load Factor = how much load a motor is carrying right now
relative to its full rated power
•
•
•
•
Motors are almost always oversized for their load
Many loads are not constant, due to changing conditions, peak
demands, etc.
A motor sized for the maximum load will be further oversized
for many/most operating conditions
Use of full rated power or incorrect estimation of load factor
can be a major source of error in energy audits
A
Audio: Here are some key points to keep in mind when dealing with motor load. Read through them, and click Next
when you are ready to move on.
Quantification
A Rated Power = motor HP x [(.745 x Load Factor) / Efficiency]
.745 is the conversion factor from HP to kW
(1HP = .745 kW)
B
C
D
For a 20 HP fan motor with a 62% load factor and 84% efficiency:
E 20HP x [ (.745 x .62LF) / .84 Efficiency] = 10.99 kW
J
F .745 x .62 = 0.4619
G 0.4619 / .84 = 0.54988
H
0.54988 x 20 = 10.99
I
Audio: S So being able to size motors appropriately is a key component of efficiency. The remainder of this section
will set the stage for various motor energy calculations you will study in another course. Let’s take a look at a
formula for converting nameplate horsepower to Kilowatt hours. “Point seven four five” is the conversion factor
from horsepower to kilowatts, where one horsepower is equal to point seven four five kilowatts, assuming a
100% load. Here’s an example of a fairly typical motor scenario First, we multiply our kilowatt hour conversion
The Herzog Method
Rated Power = motor HP x [(.745 x Load Factor) / Efficiency]
B The Herzog Method
A kW = HP x 0.55kW per HP
C
C
C
Audio: So being able to size motors appropriately is a key component of efficiency. The remainder of this section
will set the stage for various motor energy calculations you will study in another course. Here, though, we will
look at a quick formula for converting nameplate horsepower to Kilowatt hours. It is called the Herzog method.
Herzog Method, Continued
Rated Power = motor HP x [(.745 x Load Factor) / Efficiency]
A
.745 is the conversion factor from HP to kW
(1HP = .745 kW)
For a 20 HP fan motor, 62% load factor , 84% efficiency:
20HP x [ (.745 x .62LF) / .84 Efficiency] = 10.99 kW
B
C
E
Herzog rule of thumb:
HP x .55kW
20HP x .55kW = 11kW
E
D
Audio: Here is what we just solved. Now, let’s solve the same scenario using the Herzog rule of thumb. Twenty
horsepower is multiplied by the Herzog conversion of point five five kilowatts, which gives us a result of 11.
That’s basically identical to the answer we arrived at in the original equation!
Herzog Method, Continued
Rated Power = motor HP x [(.745 x Load Factor) / Efficiency]
A
F
.745 is the conversion
factor from HP to kW
(1HP = .745 kW)
For a 20 HP fan motor, 62% load factor , 84% efficiency:
20HP x [ (.745 x .62LF) / .84 Efficiency] = 10.99 kW
B
C
E
Herzog rule of thumb:
HP x .55kW
20HP x .55kW = 11kW
E
D
Audio: So being able to size motors appropriately is a key component of efficiency. The remainder of this section
will set the stage for various motor energy calculations you will study in another course. Here, though, we will
look at a quick formula for converting nameplate horsepower to Kilowatt hours. It is called the Herzog method.
One important point to keep in mind, though – motor efficiency and load factor will vary from case to case, so
the Herzog calculations may vary more greatly from the example seen here. However, Herzog remains a fairly
accurate simplification, so it’s a great formula to remember.
Check Your Knowledge
Read the question, then select the best answer.
1.For every ____ increase in motor operating temperature, motor life is estimated to
be halved.
a) 10° F
b) 20° F
Feedback: Every 20 ° increase in
c) 30° F
temperature causes an estimated 50%
d) 40° F
reduction in motor life.
2.In addition to shortening a motor’s life, poor alignment will also ____.
a) cause excessive noise
b) overheat the motor
Feedback: Poor alignment between a motor
c) short out the starter
and its fan or pump will waste energy.
d) waste energy
3.Improper lubrication is one of the common causes of early motor failure.
a) True
Feedback: If bearings are not properly
b) False
lubricated, a motor will burn out.
4.Match
a)
b)
c)
d)
each maintenance task with how often it should be performed.
Check alignment (monthly)
Check bearings (annually)
Check motor condition (weekly)
Check motor sequencing (daily)
Audio: So we’ve completed Section 2. Let’s take a moment to check your understanding of what we’ve covered so
far. Answer these questions to the best of your ability. Remember, your answers for these reviews are not
Back on the job…
•
While performing routine motor maintenance, you need to
ensure the motor is not overloaded for its size. How do you
do this?
Feedback: Use a Clamp On Amp meter to
check that the current to the motor does
not exceed the rated ‘Amps’ of the motor.
•
A trainee asks you what would happen to a motor that is
blocked with dust or has no air circulation through it. What
would you tell them?
Feedback: The motor will overheat and, if
left this way, eventually burn out.
Audio: Let’s take a look at this, back on the job…