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Kuliah TE-091237-TEKNIK TENAGA LISTRIK - TEKNIKMESIN

Dosen : Ir.SYARIFFUDDIN MAHMUDSYAH,M.Eng.

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Sub Bahasan : The Magic Of Electricity-The Principles ofElectrical Motors 72

MOTORS

Device to convert electrical energy to mechanical energy



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SomeData OnMotor UseElectrical Consumption Of MotorsTypes Of Motors In Use

Sizes Of Motors In UseLoad Factors Of Motors In UsePerformance Data For Motors



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DCMotors DC Motors Fundamental characteristics

Basic function

Types and applications Series Shunt Combination Torque characteristics

Modelling



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Fundamental characteristics of DC Motors

End viewTime 0

End viewTime 0+

Shifting magnetic field in rotor causes rotor to be forced to turn



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Natureof commutation

Power is applied to armaturewindings From V+ Through the +brush Through the commutator

contacts Through the armature (rotor)

winding

Through the brush To V-

Rotation of the armaturemoves the commutator,switching the armature windingconnections

Stator may be permanent orelectromagnet



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DC motorwiring topologies



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SeriesWound DC Motors

Armature and field connected in a series circuit. Apply for high torque loads that do not require precise speed

regulation. Useful for high breakaway torque loads. locomotives, hoists, cranes, automobile starters

Starting torque 300% to as high as 800% of full load torque.

Load increase results in both armature and field current increase Therefore torque increases by the square of a current increase.

Speed regulation Less precise than in shunt motors

Diminished load reduces current in both armature and fieldresulting in a greater increase in speed than in shunt motors.

No load results in a very high speed which may destroy the motor. Small series motors usually have enough internal friction to prevent

high-speed breakdown, but larger motors require external safetyapparatus.



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Shunt wound DC motors

Field coil in parallel (shunt) with the armature. Current through field coil is independant of the armature. Result = excellent speed control.

Apply where starting loads are low fans, blowers, centrifugal pumps, machine tools

Starting torque 125% to 200% full load torque (300 for short periods).



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CompoundWound DCmotors Performance is roughly between series-wound and shunt-wound Moderately high starting torque Moderate speed control Inherently controlled no-load speed

safer than a series motor where load may be disconnected e.g. cranes



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Permanentmagnet DCmotors



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PermanentMagnet DCMotors

Have permanent magnets rather than field windings but withconventional armatures. Power only to armature. Short response time Linear Torque/Speed characteristics similar to shunt wound

motors. Field magnetic flux is constant Current varies linearly with torque.

Self-braking upon disconnection of electrical power

Need to short + to supply, May need resistance to dissipate heat. Magnets lose strength over time and are sensitive to heating.

Lower than rated torque. Not suitable for continuous duty May have windings built into field magnets to re-magnetize.

Best applications for high torque at low speed intermittent duty. Servos, power seats, windows, and windshield wipers.



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ModelingDC Motors

A linear speed/torque curvecan be used to model DCmotors. This works well forPM and compound designsand can be used for controlmodels for narrow ranges forthe other configurations

Model will assume! Linearity Constant thermal

characteristics No armature inductance No friction in motor



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DCMotor Modeling

] / [ A NmK t

b E IRV

eb K E

I K T t

Motor equations

From the circuit

et

K RK

T V

RK K

T K V

t et

Substituting the above:

R

V K T es

t n K

V

For stalled rotor torque

And no-load speed

T K K

R

t en

In terms of no-load speedtorque/speed equation is:

2T K K

RT T P

t en

Power is:

Max power is:V

P4

2

max

] / [ rad VsK e

Units:



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Application

Use motor voltage and no-load speed to calculate K t Kt = Ke in SI units Use stalled rotor torque, V, and K e to find R

Note, R varies with speed and cannot be measured at rest

See web download for explanation of K t, Ke :http://biosystems.okstate.edu/home/mstone/4353/downloads/

Development of Electromotive Force.pdf



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DC motorcontrol H-bridge

Switches control direction A switches closed for

clockwise B switches for counter-

clockwise

PWM for speed control As duty cycle for clockwise

speed Bs duty cycle for counter-

clockwise speed

Can be configured to brake Bottom B and A to brake



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H-Bridgeimplementation

Elements in box areavailable as single IC



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Brushlessdesigns

Commutation is doneelectronically Encoder activated switching Hall effect activated switching Back EMF driven switching

PM armature Wound/switched fields

Application Few wearing parts (bearings) Capable of high speed Fractional HP

Servos Low EMC



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StepperMotors

Description Generally a two phase motor permanent magnet rotor and wound fields Rotor normally has many poles

200 poles = 1.8 degrees per step Used primarily for position or velocity control Typically no position feedback

Torques are managed so that an intended step is always achieved Accelerations, decelerations and loads must be managed intelligently

Two general types of windings Unipolar Bi-polar



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WindingConfigurations

Bi-polar design 6 wire

Unipolar design 4 wire



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An Electric Motorn Electric Motor

The commutator and coils rotates between twoThe commutator and coils rotates between two

magnets. This is a three pole motormagnets. This is a three pole motor



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Brushless Outrunner Motorrushless Outrunner Motor

The coils are stationary the casing for theThe coils are stationary the casing for themagnets around the periphery rotates.magnets around the periphery rotates.

By Torcmany Torcman



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Brushless Outrunner Motorrushless Outrunner Motor

Torcman MotorTorcman Motor 14 magnets = 14 Poles14 magnets = 14 PolesMagnetic field goes around 7 times for 1 rev ofMagnetic field goes around 7 times for 1 rev of OutrunnerOutrunnerOutrunnerOutrunner type motors have more torque than same size brushed motortype motors have more torque than same size brushed motor



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ACMotors

AC Motors Fundamental characteristics Types

Fractional horsepower (single phase) Integral

Single phase (Cap start Induction run) Three phase

NEMA Torque characteristics Modelling



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FractionalHorsepower Designs

Shaded Pole (low starting torque, simple, cheap) uses a short circuited coil embedded in face of field to cause oneside of field to be magnetized before the other

Split phase (low starting torque) Two windings (2-phase), one with high resistance hence different

RL and phase Centrifugal switch on starting winding

Capacitor Start Induction Run (medium starting torque) Two windings (2-phases) Capacitor used on second winding to create leading phase Centrifugal switch on starting winding

Universal? (intermittent use, brushes!) DC motor with inductance managed to allow AC operation

Synchronous (clocks, synchronization)

Permanent magnet rotor always in phase with AC



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ACMotor Model

mm

L f E

I 2 f

E w I k T

22

wms I I I



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ACMotors

Relationship between number of poles and motor synchronousspeed f=60 c/s

Squirrel cage motors must operate with some slip .5 to 8% to allowthe rotor to be magnetized. Actual speed is synchronous speed reduced by the slip.

P f

N s120

12006

18004

36002

SynchronousSpeed(RPM)

Poles

100

)%100( slip N N s



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Squirrel Cage Rotor Induction Motor



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Inducingmagnetism inthe rotor

Difference betweenangular velocity of rotorand angular velocity ofthe field magnetismcauses squirrel cagebars to cut the fieldmagnetic field inducingcurrent into squirrel cagebars.

This current in turnmagnetizes the rotor



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Torque/speedcurve



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Typical starting current



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Motorcharacteristics

Enclosure / frame Voltage / frequency

3 or 1 phase Poles / speed Service factor

Fraction of rated HP that motor can be operated at

Insulation class/ Temp rise (operating temperature compatible)

NEMA Design A,B,C,D, etc. (Torque curve type) See next page

Efficiency

575

220/380460

425230

400200

380115

50 Hz60 Hz



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NEMA Torque characteristics summarized

High Punch PressHigh-------LowVery highD

Loaded compressorLoaded conveyorNormalLowNormalHighC

Same as Design "A"NormalNormalNormalNormalB

Mach. Tools, FansLowHighHighNormalA

TYPICALAPPLICATIONS

FULLLOADSLIP

BREAK-DOWN

TORQUESTARTINGCURRENT

STARTINGTORQUE

NEMADESIGN



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NEMA Motor Characteristics

High

Low

Med

Med-High

Med-High

Efficiency

0.5-3800-1000160-20060-14074-190E

5-8600-700275NA275D

1-5600-700190-225140-195200-285C

0.5-5600-700175-30065-19070-275B(mostcommon)

0.5-5NA175-30065-19070-275A

Slip%

LockedRotor

Current% FL

BreakdownTorque

% FL

Pull-upTorque

% FL

LockedRotor

Torque% FL

Design



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PWMVariable FrequencyDrives

Variable frequency drives use AC to DC converter then aDC to AC converter (inverter) Inverter frequency and voltage output can be varied to allow

motor speed to be varied. Very efficient and cost effective variable speed for 1 HP and up



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Money SavingO pportunities InMotor And DriveAppl ications

Make sure the job being done by themotor is the right jobCorrectly size motor for the loadUse energy efficient motorsUse effective belts and drivesUse adjustable speed drives



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Energy Efficient Motors

What makes an efficient motorWhy buy an efficient motor

Economic analysis of purchasePotential problems



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Electric Motor Fundamentals

(Losses)Stator

Windings (IR)Stator Laminations (Eddy

Current)

Bearing

(Friction)

External Fan(Windage)

Rotor or ArmatureWindage-Lam)

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EconomicAnaly sis of Motor UsePurchase costOperating costSimple payback periodLife cycle cost



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Purchase Price

Annual Use

Efficiency

Fuel/Energy Cost

Annual Operating Cost

Operating Cost as a %

of Purchase Price

Automobile

$18,00012,000 miles/yr

30 miles/gallon

$2.80/gallon

$440/yr

2%

60 HP Motor

$4,0004,000 hours

89.2%

5.6 cents/ kwh

$10,036

250%

Automobile vs. 60H P Motor



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14K

12K

10K

8K

6K

4K

2K

0

$

Motor A95%

Efficiency

Motor B91.6%

Efficiency

Purchase Price (100 HP, 1800RPM, TEFC)

Net Present Worth cost oflosses @ .05/kwh and 10% costof capital, motor life assumed40,000 hrs

Option A: Purchase price $3,660;NPW of losses $5,686

Option B: Purchase price of$3,150; NPW of losses $9,552



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KW Required

Monthly KWh

Monthly Demand Costs

Monthly Energy Costs

Total Monthly Savings

Payback

8.1 KW

4860 kwh

$72.09

$170.10

$17.24

12 Months

8.5 KW

5100 kwh

$75.65

$178.50

$5.28

22 Months

8.7 KW

5200 kwh

$77.43

$182.00

$0

-

$ 2 6 0

$ 3 7 5

$ 4 7 5

Rewound Standard86% Efficiency

New Standard 88%Efficiency

New High-Efficiency92% Efficiency



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Projected Energy Savings based on continuous operation

(8,760 hr/yr) with motor operating at full load

Projected Energy Savings

HP

10

25

50

100

HIGH

93.2

93.0

93.6

95.4

STD.

88.5

90.2

90.2

91.0

Efficiency .04/kwh .06/kwh .08/kwh .10/kwh .12/kwh

$149

$218

$526

$1,325

$223

$327

$790

$1,987

$298

$436

$1,053

$2,650

$372

$545

$1,316

$3,312

$447

$654

$1,579

$3,975



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The following formula, based on the relationship between the efficiency of the oldmotor and replacement motor, can be used to calculate electricity cost savings.

S = 0.746 x hp x LF x C x H [ (1/E old ) (1/E new )]

Where,

S = annual savings in electricity

hp = motor horsepower

0.746 = conversion of hp to kW

L = loading in percent, typically assumed tobe 100 percent

C = cost of electricity, dollars/kWh

H = number of operating hours/year (8000 forcontinuous)

Eold = efficiency of old motor. Generally, motorslose some efficiency when re-wound (1.5 percentloss is assumed)

Enew = efficiency of new motor.

For a 150 hp, 1800 rpm TEFC motor, thevalues might be:

S = 0.746 x 150 x 1 x 0.04 x 8000 x

x [(1/0.905) (1/0.958)]

= $2,191 saved per year

To calculate the time required torecover the extra initial investment of anew motor, we use the followingformula:

Payback = (motor cost utility rebate estimated rewind cost) / savings peryear

For the example, the payback might be:

Payback = ($6,756 - $1,352 - $874) /$2,191 = 2.07 years



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MotorEfficienciesTable



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Motor Failures

Most motor failures are caused by:Bearing failureWinding failureNeed to develop a motor plan to deal withfailures and replacements in the best wayDecide on rewinding in advance



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Dealing with Motor FailuresMotor Failure

AnalyzeFailure

AnalyzeDamage

Check Winding Bearings Starter Wiring Miscellaneous problems

WashdownLoad Problems

Take Care ofProblem

AnalyticalTools

Surge test Growler Core Loss Test Vibration Test

MajorWindingBearingsEnd bellsShaftRotorStatorBalance

MinorWindingBearingsBalance

Is it aCritical

Application?YES

Running 8000 +hours/year?

YES

NO

NO

Rebuild OldMotor

Purchase NewMotor

Do electricalacceptancetest

Do vibrationacceptance test

Install TrackingNumber on Motor

* Consider Purchasing energy-efficientmotors if estimated costs of rebuild are65% of the cost of a new motor.

For motors under 7.5 hp, considerpurchasing a new motor in any failure .



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Rewound versus Premium Efficiency Motors

0.50

0.60

0.70

0.80

0.90

1.00

0 1 1 . 5

2 3 5 7 . 5 1

0 1 5

2 0

2 5

3 0

4 0

5 0

6 0

7 5

1 0 0

1 2 5

1 5 0

2 0 0

2 5 0

HP

E f f i c

i e n c y

Premium

Rewound

MotorsEfficiencies



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Replace Failed Motors

Failed Motor(50 hp)

Rewind Motor

Premium Efficiency Motor

Top-Premium Motor

High Efficiency Motor

Std. Efficiency Motor

EPACT Efficiency Motor

???



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Motor Rewinding

Rewinding motors that have failed is verycommon since the initial cost is quite lowHowever, rewound motors are most often less

efficient than new motors, and may bedamaged further in the rewinding processMotors should be tested before and afterrewinding



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Factors To ConsiderIn Rewinding

The cost difference between rewinding andbuying a new energy efficient motorThe motor might not be as efficient as the user

expects when it returns from the repair shopThe rewound motor is typically about 1.5% lessefficient than a new standard motor



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When To Rewind

When it is a special purpose motorWhen the motor is not used muchWhen it is a very large motorIn most other cases, buy a new highefficiency motor



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Transmission Of Motor Power

30 - 50% have shaft couplings10 - 30% have gears34% have belt drives

6% have chains



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Motor Belts And Drives

Standard V-belts slip and flexCogged V-belts offer some improvement -about 2-3%Synchronous belts are the most efficient -about 5% better than standard v-belts



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Install Variable Frequency Drives

Cooling Water(inlet)

Chiller

Cooling Water(outlet)

CoolingTower

Cooling TowerFan Variable Frequency

Drive

Cooling WaterTemperature

signal

VFD signal

Air

- Regulate cooling tower fan speed according to outlet water temperature.

- Energy savings comes from reduced motor speeds especially duringwinter time

- Less wear on motor since no longer turning on and off several times.



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Effects ofvariable speed(inverter)controls ofcentrifugal pumpsystems drivenby premium-efficiency motors



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DOMOARIGATO

GOZAIMASU !

003-TTL-Kuliah-3

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