Johnson Controls SAB 355 - Motor Selection and Starting Torque

Engineering manual - SAB 355 Screw compressor unit (including ATEX)
86/156
004100 en 2020.10
Technical data
Fig. 62: Operating limits for SAB 355 using R717
6.7 Motor selection and starting torque
Motors must be sized adequately for all expected operating conditions as start-up, pull down and
load variations quite often require significantly more horsepower than nominal design.
Motor starting torque capacity must also be considered, especially when across-the-line start is
not used. Motor starting and pull-up torque must be at least 20% greater than compressor re-
quirements at maximum expected start-up conditions. See the torque data.
Note: Motor starting torque varies considerably with various manufacturers - therefore, obtain
specific torque data for the motor being used.
Unit
Starting
torque
(1)
multiplier
Breakaway
torque
(ft-lb)
Breakaway
torque
(Nm)
(2)(3)
Mass
moment of
inertia
(lb-ft
2
)
(2)(3)
Mass
moment of
inertia
(Kg m
2
)
SAB 355 S 3.71 25 34 102.7 4.33
SAB 355 L 5.08 25 34 116.5 4.91
SAB 355 E 6.45 25 34 135.1 5.69
SAB 355 X 8.99 25 34 145.0 6.11
1. High-stage or booster application.
2. Including standard compressor coupling half.
3. Inertia resolved to drive shaft.
-40
0
20
40
60
C
5
-20
-80-70-60-50-40-30-20-10
20
30
-60
010
TC
TE
C
5
Condensing temperature (deg. C)
Evaporating temperature (deg. C)
Oil pump required