1 accelerating thermal limit (loci): The time-current
relationship limit based on the allowable temperature limit of the rotor during
the accelerating (starting) process.
2 accelerating time-current curve: The characteristic
starting current vs. time curve representing the motor acceleration at a given
applied voltage.
3 accelerating torque: The net torque between the motor
capability torque and load torque during the
starting process, which accelerates the motor and load to
operating speed.
4 breakdown torque: The maximum torque that a motor will
develop with rated voltage at rated frequency, where an abrupt drop in speed
will not occur.
5 damper winding limited: A synchronous motor that is
thermally limited by its damper winding.
6 field winding: The rotor circuit on an ac synchronous
motor, which consists of winding connected to a dc source and produces the main
electromagnetic field of the motor.
7 high-inertia load: A load that has a moment of inertia
that exceeds normal values, as described in NEMA MG-1-1993, and for which the
motor needs to be designed to have both thermal and mechanical capability to
accelerate the load to operating speed without exceeding its limits.
8 load torque: The torque required by mechanically driven
equipment across the operating speed range.
9 locked-rotor current: The steady-state motor current with
the rotor locked, when supplied from a
source at rated voltage and frequency.
10 locked-rotor impedance: The impedance at the motor terminals
during the locked-rotor condition.
11 locked-rotor thermal limit (permissible locked-rotor
time): The maximum permissible safe time vs. locked-rotor current flowing in
the windings at rated voltage and frequency.
12 locked-rotor torque: The minimum torque that a motor will
develop at rest, for all angular positions of the rotor, at rated voltage and
frequency.
13 loss of synchronism (out of step): A condition that
exists when the synchronous machine has lost synchronism with respect to the
supply system.
14 motor torque capability: The torque capability of the
motor, supplied with rated voltage and frequency across the operating speed
range, during the starting and running processes.
15 pull-in torque: The maximum constant torque of a
synchronous motor under which the motor will pull its connected inertia load
into synchronism, at rated voltage and frequency, when its field excitation is
applied.
16 pull-up torque: The minimum torque developed by the motor
during the period of acceleration from rest to the speed at which breakdown
torque occurs.
17 rotor: The rotating component of an ac motor that
contains the field winding, which may be wound or of the squirrel-cage type. In
the case of the synchronous motor, the field winding may be energized from a dc
source.
18 rotor limited: A motor that is thermally limited by its
rotor system.
19 running thermal capability: A plot of maximum permissible
time vs. percent of rated current flowing in the motor winding when the motor
is running.
20 service factor: A multiplier which, when applied to the
rated horsepower, indicates a permissible
horsepower loading that may be carried under the conditions
specified for the service factor.
21 slip cycle: When a synchronous motor slips out of step
(loss of synchronism) a complete 360°
with respect to the supply source.
22 slip frequency: The frequency of a induction motor
rotor’s voltage and current when the rotor is rotating at some value of slip.
23 starting current: The current required by the motor
during the starting process to accelerate the motor and load to operating
speed. Maximum starting current at rated voltage is drawn at the time of
energizing.
24 starting time: The time required to accelerate the load
to operating speed.
25 starting torque: The rated motor torque capability during
start at rated voltage and frequency.
26 stator: The stationary component of an ac motor that
contains the armature winding and stator core.
27 stator-limited: A motor that is thermally limited by its
stator system.
28 squirrel-cage winding: A rotor circuit that consists of
conducting bars, connected with an end ring on each end, which constitute the
rotor winding. Voltages are induced on this circuit which, in turn, produces
current flow. Interaction between the stator and rotor fields creates the
electromagnetic torque of the motor.
29 thermal limit curve (cold): A plot of maximum permissible
time vs. percent of rated current flowing in the motor winding when the motor
is started from ambient temperature.
30 thermal limit curve (hot): A plot of maximum permissible
time vs. percent of rated current flowing in the motor winding when the motor
is started from rated operating temperature.
31 wound rotor winding: The rotor circuit on a wound rotor
induction motor, which consists of a
polyphase winding that
carries the alternating current produced by induction.
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