Engineering manual - SAB 193-233-283 S A-frame (including ATEX)
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008831 en 2020.10
Technical data
Fig. 69: Starting torque curves, booster
Starting torque for specific compressor
Multiply the starting torque value from high-stage or booster curves at 100% of normal run speed
by starting torque multiplier for appropriate compressor size.
6.9 Motor/compressor torque
Ensure that the motor starting and minimum pull-up torque capabilities will exceed the compres-
sor requirements at the anticipated condition that will be experienced during normal starting.
Note: Star-delta and auto transformer (reduced voltage) motor starting methods drastically ef-
fect the starting torque available from motors as indicated:
Across-the-line
100% torque
Auto transformer
25-64% torque
Star-delta
33% torque
Fig. 70: Motor/compressor torque
136
122
108
95
81
68
54
41
27
14
100
90
80
70
60
50
40
30
20
10
0
Nm
[Ft-lb]
50
100
75
Discharge pressure
0
25
55
45
35
25
15
10
3.8
3.1
2.4
1.7
1.0
0.7
[Psig]
Bar
S t a r t i n g t o r q u e
Percentage of normal run speed
Speed vs starting torque curve fully unloaded
Speed
25
50
75
100%
T or
que
M
otor B
Compressor
Motor A
M
otor A: Adequate to start the compressor
Motor B: Will not start the compressor
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