Pull-up Torque
Pull-up torque is the minimum torque
developed from stand-still to the pull-in point.
The pull-up torque must exceed the load torque
(torque required by the driven machine) by
enough margin to maintain a satisfactory rate of
acceleration from stand-still to pull-in under the
minimum expected voltage condition.
Net Accelerating Torque
Net accelerating torque is the margin by
which the motor torque exceeds the load torque
from stand-still to the pull-in point.
In the case of high inertia loads, it is important
that the starting time be determined so proper
relaying action of overcurrent relays and
amortisseur winding protective relays, etc., can be
obtained.
Accelerating time from standstill to the pull-in
point can be approximated by applying the
following relationship:
Accelerating time t = WK2 x ∆rpm (seconds) 308T
WK2 = total inertia of the load and the
motor in lb.ft.2
∆rpm = the change in speed (rpm2 - rpm1)
308 = a constant
T = net accelerating torque, lb.ft. from
rpm1 to rpm2
t = the time increment to accelerate
from rpm1 to rpm2
Note the motor torque as a function of speed,
the load torque as a function of speed, and the
Pull-up TorquePull-up torque is the minimum torquedeveloped from stand-still to the pull-in point.The pull-up torque must exceed the load torque(torque required by the driven machine) byenough margin to maintain a satisfactory rate ofacceleration from stand-still to pull-in under theminimum expected voltage condition.Net Accelerating TorqueNet accelerating torque is the margin bywhich the motor torque exceeds the load torquefrom stand-still to the pull-in point.In the case of high inertia loads, it is importantthat the starting time be determined so properrelaying action of overcurrent relays andamortisseur winding protective relays, etc., can beobtained.Accelerating time from standstill to the pull-inpoint can be approximated by applying thefollowing relationship:Accelerating time t = WK2 x ∆rpm (seconds) 308TWK2 = total inertia of the load and themotor in lb.ft.2∆rpm = the change in speed (rpm2 - rpm1)308 = a constantT = net accelerating torque, lb.ft. fromrpm1 to rpm2t = the time increment to acceleratefrom rpm1 to rpm2Note the motor torque as a function of speed,the load torque as a function of speed, and the
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Pull-up Torque
Pull-up torque is the minimum torque
developed from stand-still to the pull-in point.
The pull-up torque must exceed the load torque
(torque required by the driven machine) by
enough margin to maintain a satisfactory rate of
acceleration from stand-still to pull-in under the
minimum expected voltage condition.
Net Accelerating Torque
Net accelerating torque is the margin by
which the motor torque exceeds the load torque
from stand-still to the pull-in point.
In the case of high inertia loads, it is important
that the starting time be determined so proper
relaying action of overcurrent relays and
amortisseur winding protective relays, etc., can be
obtained.
Accelerating time from standstill to the pull-in
point can be approximated by applying the
following relationship:
Accelerating time t = WK2 x ∆rpm (seconds) 308T
WK2 = total inertia of the load and the
motor in lb.ft.2
∆rpm = the change in speed (rpm2 - rpm1)
308 = a constant
T = net accelerating torque, lb.ft. from
rpm1 to rpm2
t = the time increment to accelerate
from rpm1 to rpm2
Note the motor torque as a function of speed,
the load torque as a function of speed, and the
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