nema motor designations.pdf

7/28/2019 NEMA motor designations.pdf

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INC

Motor Construction

NEMA

Motor Designations


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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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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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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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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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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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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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TYPICAL CONSTRUCTIONFrames 284T - 365T


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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ImprovedInsulationSystem

DynamicBalancedRotor

EfficientVentilation

OversizedBearings

Air in

Air in

SpeciallyDesigned LargeConduit Box

DistortionFreeFrame

RuggedCast IronEnd Brackets


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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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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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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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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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SPEED

vsTORQ

UE

PERCENTSPEED

COMPRESSOR

TORQUELB

FT


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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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SPEED

vsTORQ

UE

FRIC

K

222/350D2

FRICK

222185PSIGP

ERCENTSPEED

350HPD2S/S

*

350D2YD

TORQUELB

FT


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SPEED

vsTORQ

UE

500HPMOTO

R

460V/FRICK

222

PERC

ENTSPEED

FR

ICK

/222185PSIG

500D2STD

500D2PREM

*

TORQU

ELB

FT


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EFFICIENCY

OUTPUT

INPUTEFFICIENCY = = INPUT - LOSSES

INPUT

LOSSES

POWER

INPUTPOWER

OUTPUT


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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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SYSTEM POWER FACTOR .75

CONTRACTED POWER FACTOR .90

PENALTY $2000

POWER FACTOR PENALTY

.90$ 10,000 X = $ 12,000.75


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SUMMARY

NEED TO KNOW

ENVIRONMENT

LOAD

CHARACTERISTICS

PLANT DISTRIBUTION

DUTY & LOAD CYCLES

TO SELECT

ENCLOSURE

HP & SPEED

VOLTAGE

EFFICIENCY &

POWER FACTOR

nema motor designations.pdf

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