Rotatune (Vsd) - Johnson Controls SABROE UniSAB III Engineering Manual

3.3.26

Rotatune (VSD)

A screw compressor can be fitted with a frequency converter (VSD) for additional capacity control. In
documentation from Johnson Controls Denmark, this unit type is called a "Rotatune".
The cooling capacity can be a combination of the rotation speed set by the frequency converter and the
capacity slide position. This is the case if the compressor is equipped with capacity slide control. For
compressors not equipped with capacity slide control, the cooling capacity is given only by the rotation
speed set by the frequency converter.
See the compressor descriptions in section 3.3 for more information about the screw compressor types
covered by UniSAB III.
Most screw types have capacity slide control for regulation purposes and for start-up torque relief. Some
types do not have a capacity slide but e.g. a relief valve handling start-up torque relief.
Check the following parameters to set up a screw compressor for VSD operation
The following Rotatune parameters must be configured in the Setup/Configuration/Drive menu (see
subsection 6.4.1 Drive):
• Rotatune and Drive Com is set to define VSD and operation.
• Motor rpm min and Motor rpm max are set to define minimum and maximum motor speed.
Depending on the compressor type, the default settings and the min. and max. settings are as listed
here; default value [min., max.]:
Compressor
SABflex
SABCube
SAB 157 HR
SAB 273 S
Screw (std.)
• Forced speed is set to ensure sufficient oil pressure at compressor start-up.
• Drive cap limit is only set in special cases.
The minimum slide position during operation must be configured to ensure sufficient oil pressure at low
speed (see subsection 6.4.3 Compressor block).
• Manual zero - is set automatically for some compressor types.
The Capacity signal parameter must be configured in the Setup/Configuration/Measuring menu (see
subsection 6.4.7 Measuring).
• Capacity signal - is set automatically for some compressor types.
Set the Ramp function in the frequency drive in a proper way.
Set the capacity regulator parameters in UniSAB III to values which are appropriate for the actual proc-
ess (see subsection 3.1.7 Regulator settings).
• Decrease or increase the proportional band - to make the regulator respond faster or slower.
This will affect both the capacity slide and the speed control.
Adjust the throttling valves in the capacity block in a proper way (see subsection 3.7.1 Capacity slide).
• Adjusting slide speed - to fit the capacity regulator Run time settings.
UniSAB III can handle VSD operation in both manual and auto/remote operation
In manual operation, when the start button is pushed the compressor will start and the drive will jump
to 'Forced Speed' to achieve oil pressure. At the same time the capacity slide valve will move up to the
manual zero point which is, say, mechanical 30%.
Motor rpm min.
1000 [0,12000]
1000 [0,12000]
1000 [600,1500]
1000 [600,1500]
1000 [0,12000]
124/346
Compressor control and surveillance
Motor rpm max.
6000 [0,12000]
5800 [0,12000]
6000 [3000,6000]
3000 [3000,3600]
3600 [0,12000]
Engineering manual - UniSAB III 1.10.8
001930 en 2021.06