Johnson Controls SABROE Unisab III Control, Engineering Manual

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Engineering manual - UniSAB III 1.10.8
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001930 en 2021.06
Alarms and shutdowns
2.2.24 Watch the oil pressure
The alarm will be activated if the oil pump for oil charging is started by means of the picture Timers/Oil
charging and the compressor is in operation at the same time.
2.2.25 Low lubricating pressure monitoring (screw compressor)
The reason for this shutdown is that the differential pressure across the compressor and thus the effec-
tive lubricating pressure are too low. The differential pressure is calculated the following way: Absolute
oil pressure - 1.1 x Absolute suction pressure.
The differential pressure must be higher than the set shutdown limit for low oil pressure, see Fig. 7.
An alarm will be issued after 25 seconds and a shutdown after 120 seconds.
2.2.26 Oil log shutdown
GSV/RWF/SGC compressors with oil pump
This shutdown protects against overcharging the compressor with oil. The oil pump is started at com-
pressor start-up if the capacity slide is above 5%. The purpose of this is to increase oil pressure and
thereby run the slide into minimum position. If capacity is not below 5% before the
oil log shutdown timer
runs out, a shutdown will be issued for the Oil log shutdown . Note that there is a risk of overcharging the
compressor with oil which may damage it at next start-up if the timer is set too high.
2.2.27 Vi position error
The shutdown will only be activated if UniSAB III is configured for automatic Vi regulation, i.e. Volume ra-
tio is set to Auto in picture Configuration/compressor block . The shutdown indicates that the shown ca-
pacity in connection with automatic Vi regulation is incorrect. The real capacity of the compressor is
lower than the one shown in the display.
2.2.28 Vi slide position error (screw compressors)
This alarm is released if the Vi slide is not positioned correctly. The Vi position is supervised when the
compressor is running at a capacity above minimum capacity and the
Auto Vi control is enabled.
The alarm is set if the deviation between the Vi slide position and Vi actual set point is above 10% and
after the
Vi position alarm delay has timed out. The alarm is reset when the deviation between Vi slide
position and Vi actual set point is below 10%, and after the Vi position alarm delay has timed out.
2.2.29 Slide calibration error
This alarm is released if the capacity slide and/or Vi slide is not calibrated correctly. The slide calibration
is checked when the compressor should run at full capacity i.e. 100%.
The alarm is set if the capacity shown is above 104%. The alarm is also set if the capacity shown is be-
low 96% and the compressor should be running at 100% capacity, meaning the
Capacity set point is
100% and the capacity slide is moving less than 2% per 0.5 second in up direction.
The alarm is reset when the capacity is between 96% and 104% at the time where the compressor
should be running at 100% capacity.
2.2.30 Insufficient main oil pressure shutdown
SGC compressors (SAB 120 → → 151 and SAB 193 → → 355)
This shutdown is released if the main oil pressure < 1 bar and at the same time the capacity slide is
above 50%. The shutdown delay is 180 seconds. When the oil pressure is too low, this function limits ca-
pacity to max. 50% and the capacity cannot increase if it is between 40 and 50%. For screws with both
capacity slide and frequency converter the limitation only affects the capacity slide not the VSD. See
Fig. 8. The main oil pressure is calculated as
main oil pressure = P
oil, abs
- 1.50 x P
suction, abs
.