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Transcript of NEMA 1 hoja
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NEMA MG 2 - 2001
6.3 ProperSelection of
Machines
Machines shouldbe properly
selected withrespect to their
usual or unusualservice conditions,
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both ofwhich
involve theenvironmental and
operatingconditions towhich the
machine issubjected.
Machinesconforming to the Scope of
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this publication
are designed foroperation in
accordance withtheir ratingsunderusual service
conditions. Sometypical
applications formotors of
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standard Design
types are giveninTable 3. Typical
speed torquecharacteristics areshown in Figure 4.
Some machinesmay also be
capableofoperating in
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accordance with
their ratings underone or more
unusual serviceconditions.Definite-purpose
or special-purposemachines may be
required for someunusual
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conditions.Good
energymanagement is
the successfulapplication of themotor controller,
motor, and thedrivencomponents
that results in theleast consumption
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of energy. Since
all motors do nothave the
sameefficiency,carefulconsideration
must be given totheir selection and
application. Forfurther
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informationand
guidance, see MG10EnergyManagementGuide for
Selection and Useof Fixed
FrequencyMedium AC
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Squirrel-Cage
PolyphaseInduction Motors
.Serviceconditions, otherthan those
specified as usual,may involve some
degree of hazard.Theadditional
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hazard depends
upon the degreeof departure from
usual operatingconditions and theseverityof the
environment towhich the
machine isexposed. The
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additional hazard
results from suchthings
asoverheating,mechanicalfailure, abnormal
deterioration ofthe insulation
system, corrosion,fire,
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orexplosion.Althou
gh pastexperience of the
user may often bethe best guide, themanufacturer of
the drivenordriving
equipment or themachine
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manufacturer, or
both, should beconsulted for
furtherinformationregarding any unusual
service conditionswhich increase
the mechanical orthermal duty of
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the machineand,
as a result,increase the
chances for failureand consequenthazard. This
further informationshouldbe
considered by theuser, his
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consultants, or
others mostfamiliar with the
details of theapplicationinvolved when making
the final decision.6.3.1 Variation
From RatedVoltage and
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Rated
Frequency6.3.1.1Induction
Motors6.3.1.1.1RunningMotors will
operatesuccessfully under
running conditionsat rated load with
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a variation in the
voltage orthefrequency up
to the following:a)Plus or minus 10percent of rated
voltage with ratedfrequency.b) Plus
or minus 5percent of rated
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frequency with
rated voltage.c) Acombined
variation involtage andfrequency of 10
percent (sum ofabsolute values)
of the ratedvalues,provided the
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frequency
variation does notexceed plus or
minus 5 percent ofratedfrequency.Perform
ance within thesevoltage and
frequencyvariations will not
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necessarily be in
accordance withthestandards
established foroperation at ratedvoltage and
frequency.6.3.1.1.2 StartingThe limitingvalues of voltage
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and frequency
under which amotor will
successfully startand acceleratetorunning speed
depend on themargin between
the speed-torquecurve of the motor
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at rated voltage
andfrequency andthe speed-torque
curve of the loadunder startingconditions. Since
the torquedeveloped bythe
motor at anyspeed is
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approximately
proportional to thesquare of the
voltage andinverselyproportional to the square
of the frequency, itis generally
desirable todetermine what
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voltage
andfrequencyvariations will
actually occur ateach installation,taking into
account anyvoltage drop
resultingfrom thestarting current
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drawn by the
motor. Thisinformation and
the torquerequirements ofthe drivenmachine
define the motorspeed torque-
curve, at ratedvoltage and
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frequency, which
is adequate fortheapplication.