Automation Direct Stellar SR55 Series, User Manual

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Appendix B: Soft Starter Application Considerations
Page B–9 Stellar
®
SR55 Series Soft Starter User Manual – 1st Ed, Rev F – 09/18/2019
b.3.2 – T
he
i
nduCTion
m
oTor
(
ConTinued
0
f
igure
b.3.2.1: T
orque
/s
peed
C
urve
– i
nduCTion
m
oTor
Pull Out Torque ( M
K
)
TORQUE
Full Load Torque ( FLT, M
A
)
Pull-up Torque
Synchronous speed
Torque/Speed Curve – Induction Motor
Locked Rotor Torque
( LRT, M
A
)
0 SPEED S
f
igure
b.3.2.2: T
orque
/s
peed
C
urve
– C
oupled
l
oad
Each load coupled to an induction motor has its own speed/torque curve:
Pull Out Torque ( M
K
)
TORQUE
Pull-up Torque
Full Load Torque ( FLT, M
N
)
Synchronous speed
0 SPEED S
Torque/Speed Curve – Coupled Load
Locked Rotor Torque
( LRT, M
A
)
f
igure
b.3.2.3: T
orque
/s
peed
C
urve
– a
CCeleraTing
T
orque
The acceleration of a motor-load system is caused by the difference between the developed
torque (motor) and the absorbed torque (load), and is shown by the shaded area in the next
figure:
0 SPEED S
Locked Rotor Torque
( LRT, M
A
)
Pull Out Torque ( M
K
)
Pull-up Torque
Full Load Torque ( FLT, M
N
)
Synchronous speed
Torque/Speed Curve – Accelerating Torque
TORQUE