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Electric Motors
UNEP 2006
ical Equipment/ctric Motors
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Agenda: Electric Motors
IntroductionTypes of electric motorsAssessment of electric motorsEnergy efficiency opportunities
ical Equipment/ctric Motors
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UNEP 2006
Introduction
Electromechanical device that converts
electrical energy to mechanical energy Mechanical energy used to e.g.
o Rotate pump impeller, fan, blowero Drive compressorso Lift materials
Motors in industry: 70% of electrical load
What is an Electric Motor?
ical Equipment/ctric Motors
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Introduction
How Does an Electric Motor Work?
ical Equipment/ctric Motors
(Nave, 2005)
1
2
3
4
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Introduction
Three types of Motor Load
ical Equipment/ctric Motors
Motor loads Description Examples
Constanttorque loads
Output power variesbut torque is constant
Conveyors, rotary kilns,constant-displacementpumps
Variabletorque loads
Torque varies withsquare of operationspeed
Centrifugal pumps, fans
Constantpower loads
Torque changesinversely with speed
Machine tools
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Training Agenda: Electric Motors
IntroductionTypes of electric motorsAssessment of electric motorsEnergy efficiency opportunities
ical Equipment/ctric Motors
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Type of Electric Motors
Classification of Motors
ical Equipment/ctric Motors
Electric Motors
Alternating Current(AC) Motors
Direct Current (DC)Motors
Synchronous Induction
Three-PhaseSingle-Phase
Self ExcitedSeparately
Excited
Series ShuntCompound
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Type of Electric Motors
Field poleo North pole and south poleo Receive electricity to form
magnetic field Armature
o Cylinder between the poleso Electromagnet when current goes througho Linked to drive shaft to drive the load
Commutatoro Overturns current direction in armature
DC Motors Components
ical Equipment/ctric Motors
(Direct Industry, 1995)
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Type of Electric Motors
Speed control without impact powersupply qualityo Changing armature voltageo Changing field current
Restricted useo Few low/medium speed applicationso
Clean, non-hazardous areas
Expensive compared to AC motors
DC motors
ical Equipment/ctric Motors
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Type of Electric Motors
Relationship between speed, field fluxand armature voltage
DC motors
ical Equipment/ctric Motors
Back electromagnetic force: E = K NTorque: T = K Ia
E = electromagnetic force developed at armature terminal (volt)= field flux which is directly proportional to field current
N = speed in RPM (revolutions per minute)T = electromagnetic torqueIa = armature currentK = an equation constant
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Type of Electric Motors
Separately excited DC motor: field currentsupplied from a separate force
Self-excited DC motor: shunt motor
ical Equipment/ctric Motors
Field winding parallelwith armaturewinding
Current = fieldcurrent + armaturecurrent
Speed constantindependent of loadup to certain torque
Speed control:insert resistancein armature orfield current
DC motors
(Rodwell Int.
Corporation, 1999)
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Type of Electric Motors
Self-excited DC motor: series motor
ical Equipment/ctric Motors
DC motors
(Rodwell Int.
Corporation, 1999)
Field winding inseries with armaturewinding
Field current =armature current
Speed restrictedto 5000 RPM Avoid running
with no load:speeduncontrolled
Suited for high
starting torque:cranes, hoists
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Type of Electric Motors
DC compound motor
ical Equipment/ctric Motors
DC motors
Field winding inseries and parallelwith armaturewinding
Good torque and
stable speed
Higher %compound in
series = highstarting torque
Suited for high
starting torque if high% compounding:cranes, hoists
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Type of Electric Motors
Classification of Motors
ical Equipment/ctric Motors
Electric Motors
Alternating Current(AC) Motors
Direct Current (DC)Motors
Synchronous Induction
Three-PhaseSingle-Phase
Self ExcitedSeparatelyExcited
Series ShuntCompound
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Type of Electric Motors
Electrical current reverses direction Two parts: stator and rotor
o Stator: stationary electrical componento Rotor: rotates the motor shaft
Speed difficult to control Two types
o Synchronous motoro Induction motor
AC Motors
ical Equipment/ctric Motors
(Integrated Publishing, 2003)
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Type of Electric Motors
Constant speed fixed by systemfrequency
DC for excitation and low startingtorque: suited for low load applications
Can improve power factor: suited forhigh electricity use systems
Synchronous speed (Ns):
ical Equipment/ctric Motors
AC Motors Synchronous motor
Ns = 120 f / PF = supply frequencyP = number of poles
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Type of Electric Motors
Most common motors in industry Advantages:
o Simple designo Inexpensiveo High power to weight ratioo Easy to maintaino Direct connection to AC power source
ical Equipment/ctric Motors
AC Motors Induction motor
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Type of Electric Motors
ical Equipment/ctric Motors
Components Rotor
o Squirrel cage:conducting barsin parallel slots
o Wound rotor: 3-phase, double-layer,distributed winding
AC Motors Induction motor
Statoro Stampings with slots to carry 3-phase windingso
Wound for definite number of poles
(Automated Buildings)
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Type of Electric Motors
ical Equipment/ctric Motors
AC Motors Induction motor
How induction motors work Electricity supplied to stator Magnetic field generated that moves around rotor Current induced in rotor
Electromagnetics
Stator
Rotor
Rotor produces secondmagnetic field thatopposes stator magneticfield
Rotor begins to rotate (Reliance)
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Type of Electric Motors
ical Equipment/ctric Motors
AC Motors Induction motor
Single-phase induction motoro One stator windingo Single-phase power supplyo Squirrel cage rotoro Require device to start motoro 3 to 4 HP applicationso Household appliances: fans, washing machines,
dryers
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Type of Electric Motors
ical Equipment/ctric Motors
AC Motors Induction motor
Three-phase induction motoro Three-phase supply produces magnetic fieldo Squirrel cage or wound rotoro Self-startingo High power capabilitieso 1/3 to hundreds HP applications: pumps,
compressors, conveyor belts, grinderso 70% of motors in industry!
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Type of Electric Motors
ical Equipment/ctric Motors
AC Motors Induction motor
Speed and slip Motor never runs at synchronous
speed but lower base speed Difference is slip Install slip ring to avoid this Calculate % slip:
% Slip = Ns Nb x 100Ns
Ns = synchronous speed in RPMNb = base speed in RPM
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Type of Electric Motors
ical Equipment/ctric Motors
AC Motors Induction motor
Relationship load, speed and torque
At start: highcurrent and lowpull-up torque
At start: highcurrent and lowpull-up torque
At 80% of full
speed: highestpull-outtorque andcurrent drops
At full speed:torque andstator currentare zero
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Training Agenda: Electric Motors
IntroductionTypes of electric motorsAssessment of electric motorsEnergy efficiency opportunitiesical Equipment/
ctric Motors
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Assessment of Electric Motors
Motors loose energy when serving a load
Fixed loss
Rotor loss Stator loss Friction and rewinding
Stray load loss
Efficiency of Electric Motors
ical Equipment/ctric Motors
(US DOE)
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Factors that influence efficiency
Age
Capacity Speed Type
Temperature
Rewinding Load
Efficiency of Electric Motors
ical Equipment/ctric Motors
Assessment of Electric Motors
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Motor part load efficiency Designed for 50-100% load
Most efficient at 75% load
Rapid drop below 50% load
Efficiency of Electric Motors
ical Equipment/ctric Motors
(US DOE)
Assessment of Electric Motors
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Motor load is indicator of efficiency Equation to determine load:
Motor Load
ical Equipment/ctric Motors Load = Pi x HP x 0.7457
= Motor operating efficiency in %HP = Nameplate rated horse powerLoad = Output power as a % of rated powerPi = Three phase power in kW
Assessment of Electric Motors
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Three methods for individual motors Input power measurement
o Ratio input power and rate power at 100%loading Line current measurement
o Compare measured amperage with ratedamperage
Slip methodo Compare slip at operation with slip at full load
Motor Load
ical Equipment/ctric Motors
Assessment of Electric Motors
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Input power measurement Three steps for three-phase motors
Step 1. Determine the input power:
Motor Load
ical Equipment/ctric Motors
Pi = Three Phase power in kWV = RMS Voltage, mean line toline of 3 PhasesI = RMS Current, mean of 3phasesPF = Power factor as Decimal
Assessment of Electric Motors
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Input power measurementStep 2. Determine the rated power:
Step 3. Determine the percentage load:
Motor Load
ical Equipment/ctric Motors
Load = Output Power as a % of RatedPowerPi = Measured Three Phase power inkWPr = Input Power at Full Rated load inkW
Pr = Input Power at Full Rated load inkWhp = Name plate Rated Horse Power
r = Efficiency at Full Rated Load
Assessment of Electric Motors
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Result1. Significantly
oversized andunderloaded
2. Moderatelyoversized andunderloaded
3. Properly sized butstandard efficiency
Motor Load
ical Equipment/ctric Motors
Action Replace with more efficient,
properly sized models Replace with more efficient,
properly sized models whenthey fail
Replace most of these with
energy-efficient models whenthey fail
Assessment of Electric Motors
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Training Agenda: Electric Motors
IntroductionTypes of electric motorsAssessment of electric motorsEnergy efficiency opportunitiesical Equipment/
ctric Motors
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1.Use energy efficient motors2.Reduce under-loading (and avoid over-
sized motors)3.Size to variable load4.Improve power quality5.Rewinding6.Power factor correction by capacitors7.Improve maintenance8.Speed control of induction motor
ical Equipment/ctric Motors
Energy Efficiency Opportunities
O
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Reduce intrinsic motor losses Efficiency 3-7% higher Wide range of ratings More expensive but
rapid payback Best to replace when
existing motors fail
Use Energy Efficient Motors
ical Equipment/ctric Motors
(Bureau of Indian Standards)
Energy Efficiency Opportunities
E Effi i O i i
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ical Equipment/ctric Motors
Power Loss Area Efficiency Improvement
1. Fixed loss (iron) Use of thinner gauge, lower loss core steel reduces eddycurrent losses. Longer core adds more steel to the design,
which reduces losses due to lower operating flux densities.
2. Stator I2R Use of more copper & larger conductors increases crosssectional area of stator windings. This lower resistance (R)of the windings & reduces losses due to current flow (I)
3 Rotor I2R Use of larger rotor conductor bars increases size of crosssection, lowering conductor resistance (R) & losses due to
current flow (I)
4 Friction & Winding Use of low loss fan design reduces losses due to airmovement
5. Stray Load Loss Use of optimized design & strict quality control proceduresminimizes stray load losses
(BEE India, 2004)
Use Energy Efficient Motors
Energy Efficiency Opportunities
E Effi i O t iti
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Energy Efficiency Opportunities
Reasons for under-loadingo Large safety factor when selecting motoro Under-utilization of equipmento Maintain outputs at desired level even at low
input voltageso High starting torque is required
Consequences of under-loadingo Increased motor losseso Reduced motor efficiencyo Reduced power factor
2. Reduce Under-loading
ical Equipment/ctric Motors
E Effi i O t iti
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Energy Efficiency Opportunities
Replace with smaller motoro If motor operates at
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Energy Efficiency Opportunities
Motor selection based ono Highest anticipated load: expensive and risk of
under-loadingo Slightly lower than highest load: occasional
overloading for short periods But avoid risk of overheating due to
o Extreme load changeso
Frequent / long periods of overloading
o Inability of motor to cool down
3. Sizing to Variable Load
ical Equipment/ctric Motors
X
Motors haveservice factor
of 15% aboverated load
Energy Efficiency Opportunities
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Energy Efficiency Opportunities
Motor performance affected by Poor power quality: too high fluctuations in
voltage and frequency Voltage unbalance: unequal voltages to threephases of motor
4. Improve Power Quality
ical Equipment/ctric Motors
Example 1 Example 2 Example 3
Voltage unbalance (%) 0.30 2.30 5.40
Unbalance in current (%) 0.4 17.7 40.0
Temperature increase (oC) 0 30 40
Energy Efficiency Opportunities
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Energy Efficiency Opportunities
Keep voltage unbalance within 1% Balance single phase loads equally
among three phases Segregate single phase loads and
feed them into separate
line/transformer
4. Improve Power Quality
ical Equipment/ctric Motors
Energy Efficiency Opportunities
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Energy Efficiency Opportunities
Rewinding: sometimes 50% of motors Can reduce motor efficiency Maintain efficiency after rewinding byo Using qualified/certified firm
o Maintain original motor designo Replace 40HP, >15 year old motors instead of
rewindingo
Buy new motor if costs are less than 50-65% ofrewinding costs
5. Rewinding
ical Equipment/ctric Motors
Energy Efficiency Opportunities
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Energy Efficiency Opportunities
Use capacitors for induction motors Benefits of improved PF
o Reduced kVAo Reduced losseso Improved voltage regulationo Increased efficiency of plant electrical system
Capacitor size not >90% of no-load
kVAR of motor
6. Improve Power Factor (PF)
ical Equipment/ctric Motors
Energy Efficiency Opportunities
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Energy Efficiency Opportunities
Checklist to maintain motor efficiency Inspect motors regularly for wear, dirt/dust
Checking motor loads for over/under loading
Lubricate appropriately Check alignment of motor and equipment Ensure supply wiring and terminal box and
properly sized and installed Provide adequate ventilation
7. Maintenance
ical Equipment/ctric Motors
Energy Efficiency Opportunities
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Energy Efficiency Opportunities
Multi-speed motorso Limited speed control: 2 4 fixed speeds
Wound rotor motor driveso Specifically constructed motoro Variable resistors to control torque performanceo >300 HP most common
8. Speed Control of Induction Motor
ical Equipment/ctric Motors
Energy Efficiency Opportunities
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Energy Efficiency Opportunities
Variable speed drives (VSDs)o Also called inverterso Several kW to 750 kWo Change speed of induction motorso Can be installed in existing systemo Reduce electricity by >50% in fans and pumpso Convert 50Hz incoming power to variable
frequency and voltage: change speedo Three types
8. Speed Control of Induction Motor
ical Equipment/ctric Motors
Energy Efficiency Opportunities
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Energy Efficiency Opportunities
Direct Current Drives Oldest form of electrical speed control Consists of
o DC motor: field windings and armatureo Controller: regulates DC voltage to armature
that controls motor speedo Tacho-generator: gives feedback signal to
controlled
ical Equipment/ctric Motors
8. Speed Control of Induction Motor
Training Session on Energy
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Equipment
Electric MotorsTHANK YOU
FOR YOUR ATTENTION
UNEP 2006
ical Equipment/ctric Motors
Disclaimer and References
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rical Systems/ctric motors
UNEP 2006
Disclaimer and References
This PowerPoint training session was prepared aspart of the project Greenhouse Gas EmissionReduction from Industry in Asia and the Pacific(GERIAP). While reasonable efforts have been madeto ensure that the contents of this publication are
factually correct and properly referenced, UNEP doesnot accept responsibility for the accuracy orcompleteness of the contents, and shall not be liablefor any loss or damage that may be occasioneddirectly or indirectly through the use of, or reliance
on, the contents of this publication. UNEP, 2006.
The GERIAP project was funded by the SwedishInternational Development Cooperation Agency (Sida)
Full references are included in the textbook chapterthat is available on www.energyefficiencyasia.org