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INDUSTRIES
INC
Motor Construction
NEMA
Motor Designations
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INCINDUSTRIES
APPLICATION & SELECTION OF MOTORS & STARTERS
The selection of motors and starters for compressor applications involves such basicdecisions as motor enclosure, starter enclosure, and voltage available. This selection
process also involves sizing the motor for the correct horsepower at the worst operatingcondition and determining the type of starter to be applied from the standpoint of fullvoltage or reduced voltage. The first area that we will look at is the enclosure of themotor.
MOTOR ENCLOSURESThe most common enclosure types used in compressor applications are Open DripProof, Weather Protected 1, Weather Protected 2, Totally Enclosed Fan Cooled, andExplosion Proof. We will examine each of these and where they are most often applied.
1. Open Drip Proof Motors (ODP)
Open Drip Proof motors are designed so that the cooling of the motor takes placeby ambient air being pulled through the motor without the use of an external fan.These motors are usually applied in an indoor application where the presence ofmoisture and contaminants is at a minimum. This is the most common type ofmotor used for compressor applications.
2. Weather Protected One (WPI)Weather Protected One motors are actually Open Drip Proof motors withmodifications made for outdoor use in environments that have small amounts ofmoisture and contamination. The modifications made are the addition of screenson all of the openings to prevent anything larger than 3/4 of an inch in diameterfrom entering the motor and angling the openings on the stator frame to minimizethe entrance of rain, snow, or contaminants to the motors internal parts. Thesemotors are applied in outdoor applications where the ambient conditions are notsevere. The addition of space heaters is recommended in this type of motor tokeep condensation out of the motor when it is not operating. This type motor isquite common for compressor applications.
3. Weather Protected Two (WPII)Weather Protected Two motors include a top hat assembly on the motor containingscreens and filters that do not allow any outside air to enter the motor before it
has been filtered and redirected, with 90 degree bends, a minimum of three times.This motor is applied in many outdoor applications where the conditions are severeand there are many contaminants in the air. The advantage for this type motor isthat it can adequately cool the motor and keep out contaminants, much like theTEFC motor, at a reduced price. These motors are common for large outdoorcompressor applications (above 500HP). They are not intended for use inatmospheres containing corrosive fumes or dust.
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INCINDUSTRIES
APPLICATION & SELECTION OF MOTORS & STARTERS
4. Totally Enclosed Fan Cooled (TEFC)Totally Enclosed Fan Cooled motors are designed so that the stator and rotor ofthe motor is enclosed to prevent the entrance of moisture or contaminants to theinternal parts of the motor. The motor has an externally mounted fan to push airover the motor to remove the heat generated during operation of the motor. Thesemotors are used primarily in outdoor applications or applications where moistureand contaminants are a normal occurrence. TEFC motors are often used in division2 hazardous locations.
5. Explosion Proof Motors (XP)Explosion Proof motors are designed for use in hazardous locations as defined byUnderwriters Laboratories (UL). These motors are totally enclosed to insure thatan explosion or flame internal to the motor stays internal. These motors are cooled
by external fans or air to water heat exchangers. The location that an explosionproof motor may be applied is based entirely on the tests completed by eachindividual manufacturer to obtain certification for use in hazardous locations asdetermined by Underwriter Laboratories. Explosion Proof motors require a ULlabel on their nameplate. These motors are used on compressors in petrochemicalapplications or in environments where there are vapors, gasses, or dust presentthat UL has determined explosive.
TEMPERATURE RISE/INSULATION CLASS
The selection of the motor should also include looking at the rated temperature rise andthe insulation class of the motor. The rated temperature rise of a motor is the permissiblerise above ambient when operating under load. The insulation class is a rating determinedby NEMA to handle the temperature rise of the motor. The following are the commonNEMA standard insulation classes:
TEMPERATURE LIMITINSULATION CLASS
ABFH
Motor insulation classes are based on the motor operating in a 40 degree C ambient.Operating temperature of the motor vs insulation class of the motor is the single largestfactor in determining motor life. A general rule is that for every 10 degree C increase inoperating temperature, over the insulation limit, motor life is cut in half. When specifyinga motor you can insure operating tempertatures below insulation class rating by specifyinga class F (155 C) insulation and a class B (130 C) temperature rise. All major motormanufacturers can meet this specification.
105 C (221 F)130 C (275 F)155 C (311 F)180 C (356 F)
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INCINDUSTRIES
APPLICATION & SELECTION OF MOTORS & STARTERS
HORSEPOWER/STARTING TORQUEThe final area that we will look at for motor selection is correct horsepower and startingtorque. The required starting torque is necessary to determine the correct horsepower.This must come from the manufacturer of the driven equipment or in this case thecompressor manufacturer. The starting torque will be given in lb ft values based on thefollowing formula:
When the lb ft values are determined for a motor they are plotted vs the speed of themotor (see enclosed speed vs torque). The same type curve must be supplied by themanufacturer of the driven equipment. When both curves are available, the properselection can be made.
At this time, we must determine the means of staring the motor before we can continuewith our selection. The reason for this is that if reduced voltage starting is required, youmust remember that each type of reduced voltage starter has a different percentage offull-load torque available for accelerating the load.
The most common starting methods for compressors are: Full Voltage (FV) Reduced-Voltage Autotransformer (RVAT) Part-Winding (PW) Wye-Delta (Y-D)
Solid StateEach of these types of starting has a different amount of starting torque available basedon a percentage of full-load torque:
lb ft = HORSEPOWER X 5250
RPM
% FL LB FTSTARTER TYPE
FULL VOLTAGERVAT 80% TAPRVAT 65% TAPPART-WINDINGWYE-DELTA
100%64%42%50%33%
The chart above is strictly based on torque available and does not take into considerationfactors such as equipment being loaded or unloaded at start. The percentages are basedon full load at rated voltage.
The final step in determining which motor is required is comparing the torque availablewith any particular starter with the torque required to accelerate the load. When this hasbeen done, the horsepower of the motor can be determined.
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INCINDUSTRIES
APPLICATION & SELECTION OF MOTORS & STARTERS
EFFICIENCY/POWER FACTORMotor efficiency is defined as the ratio between work performed and the energy consumedto perform that work. To make an accurate decision on the efficiency of a motor, you
must know the exact duty and load cycle. Most purchasing decisions of motors aremade based on full-load efficiency. Motor manufacturers publish efficiencies at fullload, 75% load, and 50% load to allow the user of the motor to make a better selectionbased on his particular duty cycle.
Power Factor is defined as the ratio of true power to apparent power. Power factor is notusually given as much consideration on a motor specification as efficiency because powerfactor can easily be corrected by the use of power factor correction capacitors.
Motor efficiencies and power factors could be the topic of an entire paper, however, forthe basic selection process for motor and starter on a compressor application, I just wantyou to be aware of the availability of high efficiency and high power factor motors.
SUMMARYWhen selecting a motor for any application, you must know the environment to selectthe enclosure, the driven equipment's load characteristics to determine horsepower andspeed, plant distribution loads to determine voltage, and duty and load cycles to makean evaluation of efficiency and power factor. With this information a motor can beproperly selected.
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INCINDUSTRIES
APPLICATION & SELECTION OF MOTORS & STARTERS
OPEN DRIP PROOFThis enclosure is primarily for use in clean, reasonably dry
atmospheres. Incoming air enters through the air inlets inthe bearing brackets. It is then uniformly circulated throughthe motor interior for effective cooling by the cooling fanand discharged from openings on the side of frame.
NEMA WEATHER-PROTECTED
TYPE I (WPI)This is similar to the open drip-proof motor with additionaloutdoor treatment and screens on the air inlets and airdischarge openings. ODP MOTOR
TOTALLY-ENCLOSED,
FAN-COOLED TYPE (TEFCTEFC motors are for installation in locations where dust orharmful gases exist. The external fan installed on the oppositedrive end blows outside air along the cast iron frame fins. Theoutside air then effectively cools the interior air through castiron frame. In this design, there is no free interchange of airbetween the inside and outside of the enclosure. It is alsosuitable for outdoor use and is easily cleaned.
TEFC MOTOR
TYPICAL
CONSTRUCTION
OF
TOTALLY-ENCLOSED,
FAN-COOLED
MOTOR
ENCLOSURES
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INCINDUSTRIES
APPLICATION & SELECTION OF MOTORS & STARTERS
OPEN DRIP PROOF OR
OPEN DRIP PROOF GUARDED TYPEIncoming air enters through the air housing at the motors uppersection, is uniformly circulated through the motor interior foreffective cooling by a high-performance fan.
NEMA WEATHER PROTECTED TYPE 1 (WPI)This is similar to the drip proof guarded motor with additionaloutdoor construction.
NEMA WEATHER PROTECTED TYPE II (WPII)Foreign matter blown into the motor interior by wind, storms, or
other weather influences are prevented from entering the interiorby imparting a right-angle turn to the air flow three times insidethe air housing on the motor top while maintaining an inlet airvelocity of 600 ft/min. or less. Air filters on air inlet openings canbe added environments where dust is a problem.
The TOSMIGHTY M80 series motors utilize a Top Hatstructure which allows easy adaptation to any enclosurerequirement.
TOTALLY ENCLOSED, WATER AIR
COOLED TYPE (TEWAC) (CACW)A water-to-air heat exchanger is installed in the top hat sectionof the motor. Water flowing through the water-to-air heatexchanger effectively cools the motor interior air.
TOTALLY ENCLOSED, FAN COOLED TYPE
(TEFC) (CACA)The outer fan installed on the opposite drive end blows outsideair though tubes, located in the motor top hat. The outside airthen effectively cools hot interior air at the air housing. Thecooling tubes in the air housing can be easily cleaned byremoving the outer fan cover.
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INCINDUSTRIES
APPLICATION & SELECTION OF MOTORS & STARTERS
TYPICAL CONSTRUCTIONFrames 284T - 365T
TYPICAL CONSTRUCTIONFrames 404T - 445T
In addition to the IEEE standard 112A-method B,Toshiba Motors are given a rust-proof test, anti-dust test, and vibration test.
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INCINDUSTRIES
APPLICATION & SELECTION OF MOTORS & STARTERS
TYPICAL CONSTRUCTIONFrames 284T - 445T
ImprovedInsulationSystem
DynamicBalancedRotor
EfficientVentilation
OversizedBearings
Air in
Air in
SpeciallyDesigned LargeConduit Box
DistortionFreeFrame
RuggedCast IronEnd Brackets
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INCINDUSTRIES
APPLICATION & SELECTION OF MOTORS & STARTERS
INSULATION CLASSES
INSULATION CLASS
A
B
F
H
TEMPERATURE
LIMIT
105 C (221 F)
130 C (275 F)
155 C (311 F)
180 C (356 F)
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INCINDUSTRIES
APPLICATION & SELECTION OF MOTORS & STARTERS
TEMP vs INSULATION
1.15 ST - TEFC or ODP
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8
AMBIENT
RISE
TEMPERATURE
180
160
140
120
100
80
60
40
20
0
C O
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
130 O1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
40 O 40 O
115 O
90 O
155 O
B FINSULATION CLASS
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INCINDUSTRIES
APPLICATION & SELECTION OF MOTORS & STARTERS
STARTER TYPES
STARTER TYPE
FULL VOLTAGE
RVAT 80% TAP
RVAT 65% TAP
PART WINDING
WYE-DELTA
% FULL-LOAD
TORQUE
100%
64%
42%
50%
33%
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INCINDUSTRIES
APPLICATION & SELECTION OF MOTORS & STARTERS
VARIOUS METHODS FOR MOTOR STARTINGThe electric motor starter is the important connecting link between the motor and the electricsupply system. Properly applied, the motor starter can reduce the effects of motor startingon the system and on the driven load. The various methods available for starting squirrel-cage motors are described in the following paragraphs.
GENERAL COMPARISONS
STARTERTYPE
MOTORVOLTAGE
MOTORTORQUE
MOTORCURRENT
LINECURRENT
APPROX.COST
Full Voltage
Reduced VoltageAutotransformer
80% Tap65% Tap50% Tap
Primary Resistor80% Tap65% Tap50% Tap
Primary Reactor*Same as PrimaryResistor above*
Reconnectable orIncrementalPart Winding
Low speed
High speed
Wye-Delta
Solid State
1.0
.8.65
.5
.8
.65.5
1.0
1.0
1.0
.4-1.0
1.0
.64
.42
.25
.64
.42.25
.5
.5
.33
.1-1.0
1.0
.8.65
.5
.8
.65.5
.5
.7
.33
.25-1.0
1.0
* .64* .42* .25
.8
.65.5
.5
.7
.33
.25-1.0
1.0
5.0
4.0
2.5
3.5
3.5-5.0
* The magnetizing current of the autotransformer is not included. Typically, this will beapproximately 25% of the motor full load current.
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INCINDUSTRIES
APPLICATION & SELECTION OF MOTORS & STARTERS
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APPLICATION & SELECTION OF MOTORS & STARTERS
SPEED
vsTORQ
UE
PERCENTSPEED
COMPRESSOR
TORQUELB
FT
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INCINDUSTRIES
APPLICATION & SELECTION OF MOTORS & STARTERS
RWB II PLUS ROTARY SCREW COMPRESSOR UNITSENGINEERING DATA
MOTOR SELECTION
AND
STARTING TORQUE
Motors must be sized adequately for all expectedoperating conditions since start-up, pull down, and loadvariations quite often require significantly morehorsepower than nominal design.
Motor starting torque capacity must also beconsidered, especially when other than across-the-line start is employed. Motor starting and pull-uptorque must be at least 20% greater than compressorrequirements at maximum expected start-upconditions. Refer to the torque data.
NOTE: Motor starting torque varies considerably withvarious manufacturers - obtain specific torque datafor the motor being used.
RWBMODEL
STARTING
TORQUE (1)MULTIPLIER
BREAK-AWAY
TORQUE(FT-LB)
(2) (3)
INERTIAWR2, LB-FT2
60
76
100
134
177
222
316
399
0.46
0.58
0.75
1.00
1.27
1.60
2.28
2.87
7
7
10
10
14
14
20
20
3
3.5
7
8
14
17
35
43
(1) High Stage or Booster Application
(2) Including standard compresssor coupling half
(3) Inertia resolved to drive shaft
___________________________________________
___________________________________________
___________________________________________
___________________________________________
___________________________________________
___________________________________________
___________________________________________
RWB SCREW COMPRESSOR
SPEED vs STARTING TORQUE CURVE- FULLY UNLOADED -
HIGH STAGE and BOOSTER
HIGH STAGE BOOSTER
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INCINDUSTRIES
APPLICATION & SELECTION OF MOTORS & STARTERS
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APPLICATION & SELECTION OF MOTORS & STARTERS
SPEED
vsTORQ
UE
FRIC
K
222/350D2
FRICK
222185PSIGP
ERCENTSPEED
350HPD2S/S
*
350D2YD
TORQUELB
FT
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INCINDUSTRIES
APPLICATION & SELECTION OF MOTORS & STARTERS
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APPLICATION & SELECTION OF MOTORS & STARTERS
SPEED
vsTORQ
UE
500HPMOTO
R
460V/FRICK
222
PERC
ENTSPEED
FR
ICK
/222185PSIG
500D2STD
500D2PREM
*
TORQU
ELB
FT
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INCINDUSTRIES
APPLICATION & SELECTION OF MOTORS & STARTERS
EFFICIENCY
OUTPUT
INPUTEFFICIENCY = = INPUT - LOSSES
INPUT
LOSSES
POWER
INPUTPOWER
OUTPUT
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INCINDUSTRIES
APPLICATION & SELECTION OF MOTORS & STARTERS
MOTOR LOSSES
LOSS DESIGN CHANGE
Stator Loss 1) New Slot Geometry
2) Increased Amount of Wire in Slot
3) Decrease Length of Coil Extensions
Rotor Loss 1) New Slot Geometry
2) Increase Flux Density in Air Gap
3) Increase Rotor Bar Size
4) Increase End Ring Size
5) Increase Rotor Bar/End Conductivity
Core Loss 1) Decrease Lamination Thickness
2) Improve Coreplating Process
3) Improve Annealing Process
4) Improve Steel Grade (W / #)
Friction & Windage 1) Optimize Bearing Selection
2) Optimize Fan Design to Increase cfm; Decrease OD
Stray Load Loss 1) Insulate Rotor Bars
2) Increase Air Gap
3) Eliminate Rotor Skew
4) Two Pass Machining
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INCINDUSTRIES
APPLICATION & SELECTION OF MOTORS & STARTERS
SYSTEM POWER FACTOR .75
CONTRACTED POWER FACTOR .90
PENALTY $2000
POWER FACTOR PENALTY
.90$ 10,000 X = $ 12,000.75
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INCINDUSTRIES
APPLICATION & SELECTION OF MOTORS & STARTERS
SUMMARY
NEED TO KNOW
ENVIRONMENT
LOAD
CHARACTERISTICS
PLANT DISTRIBUTION
DUTY & LOAD CYCLES
TO SELECT
ENCLOSURE
HP & SPEED
VOLTAGE
EFFICIENCY &
POWER FACTOR