starter. All reduced voltage starters will reduce
the motor starting torque, so the designer should
evaluate the load characteristics to ensure that
motor torque will be sufficient under all starting
conditions. If reduced-kVA starters are required,
EM 1110-2-3105 should be consulted for further
guidance.
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Starting and accelerating torque shall be sufficient to start the pump and
accelerate it against all torques experienced in passing to the pull-in
speed under maximum head conditions and with rated excitation current and a
terminal voltage equal to [90 percent of rated value] [the output of a
closed-transition autotransformer type reduced-voltage starter supplied at
90 percent of rated voltage and connected on its [80] [65] percent tap].
The pull-in torque shall exceed that required by the pump under maximum
head conditions but shall not be less than 100 percent of motor full-load
torque, with a terminal voltage equal to 90 percent of rated value.
Pull-out torque shall not be less than 150 percent of motor full-load
torque for one minute minimum and with a terminal voltage equal to 90
percent of rated value.
2.1.2.2
Locked-Rotor Current
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NOTE: The objective of this specification is to
limit the locked-rotor current to a value
sufficiently low to permit full-voltage starting.
The motor horsepower rating is to be a minimum of
110 percent of the maximum pump load at a service
factor of 1.0. Manufacturer's standard is to limit
locked-rotor current to 600 percent of full load
current. However, local utilities may have
additional limitations on inrush currents and should
be consulted. Motor design will permit some
reduction in inrush current in which case 500
percent should be used. If this is not sufficient,
reduced-voltage starting should be used. The inrush
current limit should be specified whenever possible.
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The locked-rotor current shall not exceed [600] [500] percent of rated
nameplate full load running current. [The locked-rotor current shall not
exceed [_____] amperes at 90 percent of rated voltage during any point in
the starting cycle under worst case starting conditions. For
autotransformer reduced voltage starting, the above criteria shall apply to
primary side and at any prescribed tap.]
2.1.2.3
Starting Capability
Each motor, when operating at rated voltage and frequency and on the basis
of the connected pump load inertia, Wk2, and the speed-torque
characteristics of the maximum load during starting conditions as furnished
by the pump manufacturer, shall be capable of making the starts required in
NEMA MG 1 paragraph 21.43. A starting information nameplate setting forth
the starting capabilities shall be provided on each motor in accordance
with NEMA MG 1 paragraph 21.43.3. This nameplate shall also include the
minimum time at standstill and the minimum running time prior to an
additional start.
SECTION 16222A
Page 14
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