Engineering manual - SAB 355 Screw compressor unit (including ATEX)
004100 en 2020.10
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Technical description
4.1.5 Variable speed drive (VSD)
The compressor can be VSD driven as long as the rpm limits are not exceeded. For standard and
total unloading compressors, UniSAB III controls the VSD combined with the mechanical capacity
control in the most efficient way considering both energy consumption and wear.
It should be noted that compressors running variable speed (VSD) are at higher risk of facing vi-
brational problems than similar fixed-speed applications. Johnson Controls Denmark and the
Sabroe Factory have gained comprehensive experience in VSD, and we are integrating this
knowledge into both the mechanical design and the control systems of our products. For this rea-
son, we cannot accept liability for any damage related to vibrations or variable speed drive on
non-factory-built equipment. This includes both mechanical and electrical equipment, meaning
that VSD equipment must be purchased as complete factory-built and tested packages to ensure
optimum reliability and to attain full factory warranty coverage. It should be noted that vibrations
may appear as structural vibrations in for instance frames, piping and instrumentation, or as tor-
sional vibrations in rotating equipment: compressor shaft, coupling and motor rotor.
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