Page 21 - Industrial plants

The complete driver compressor system consisted of:

• Oil flooded screw compressor;
• HSS coupling;
• Gearbox;
• LSS coupling;
• Induction motor.

The operating speed of the screw compressor was
3400 rpm. The operating speed of the
induction motor was 1490 rpm with a gear ratio of ~2.3
(fig. 1). Figure 1

A torsional analysis according to API 619 5th Ed., 2010
was carried out, adopting a lumped parameters model
with a definite number of inertial masses connected
each other by mass-less shaft intervals having proper
torsional stiffness and damping (Tab. 1).

Torsional natural frequencies and relevant vibration
mode shapes were calculated and compared with the
excitation harmonics as shown in Campbell Diagram
(fig. 2):

To avoid resonance during transient phases, an
additional transient calculation was performed to
investigate the response of the system during the Figure 2
following events:
• start-up;
• motor 3-phase short circuit;
• motor 2-phase short circuit;
• motor phase opposition
reclosing.

The four transient events were deeply
evaluated and as a consequence a
special coupling design was adopted.

Table 1

IndustrIal Plants - May 2023
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