Engineering manual - UniSAB III 1.10.8
001930 en 2021.06
125/346
Compressor control and surveillance
When main oil pressure has been achieved, the speed will fall back to minimum speed. The slide valve
should now have increased to the set
Manual zero
point and the display will show 0%. When the '
Cap
Up
' button is pushed, the slide valve will start to move up against maximum capacity slide position. The
speed will stay at minimum until the capacity slide is at maximum, then the drive will start to increase
speed.
Note that some screw compressors do not have the '
Forced Speed
' function nor any capacity slide. In
that case the compressor will start at minimum speed and then the VSD will be released for speed con-
trol between min. and max. speed.
In
auto/remote operation
the compressor starts on demand and the drive increases to '
Forced Speed
'
to achieve oil pressure. At the same time the capacity slide valve starts to move up to the
Manual zero
point
. When main oil pressure is achieved and there is a positive demand. Expect the drive to stay on
the '
Forced Speed
' value until the capacity slide valve gets to 100%. Then the drive is released to in-
crease speed. This initial phase depends on demand, and if it means that the capacity gets too high be-
cause of the capacity increase from the slide valve moving up, the drive will decrease speed to
compensate. Otherwise, during normal operation, the capacity slide will stay at 100% and capacity is
controlled by speed. At very low capacity with minimum speed, the capacity slide will move back.
Note that some screw compressors do not have the '
Forced Speed
' function nor a capacity slide. In that
case the compressor will start at minimum speed and the VSD will be released for speed control be-
tween min. and max. speed.
If during operation the VSD/motor is overloaded, UniSAB III will reduce the capacity slide position to un-
load the compressor and reduce the torque/current. Torque reduction cannot be done by reducing
speed. Some screw types without capacity slide are equipped with a relief valve which in case of over-
load will unload the compressor and reduce the torque/current.
3.3.27
Oil heating
Oil heating is
not
a configuration point, but it has various functions depending on whether the compres-
sor in question is configured as a reciprocating or a screw compressor.
For screw compressors the heating element will be connected while the compressor is not in operation.
Except for SAB 120-151, SAB 193-355, SAB 193 H-355 H, SAB 157 HR and SAB 273 S there is no tem-
perature regulation.
SAB 120-151, SAB 193-355, SAB 193 H-355 H, SAB 157 HR and SAB 273 S
When the compressor is not in operation, UniSAB III will control the heating element in the oil separator.
If the temperature is lower than the set point the heating element will be activated. The set point and
neutral zone can be set in the in the menu
Control values/Oil/Separator temp/Control
.
Normal setting for SAB 120-151, SAB 193-355, SAB 193 H-355 H, SAB 157 HR and SAB 273 S
Set point 1 = 50
°
C
Neutral zone = 2
°
C
Regardless of oil separator temperature, the heating element will be deactivated when the compressor
is running.
Summary of Contents for SABROE Unisab III Control
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