Engineering manual - UniSAB III 1.10.8
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001930 en 2021.06
Compressor control and surveillance
When the compressor has been stopped, the capacity slide will be moved below 5% slide capacity. The
solenoid valves for decreasing capacity and Vi position are activated for maximum 300 seconds. If the
capacity slide is not below 5% within the 300 seconds, a Capacity error shutdown will be issued.
Balance piston
For SAB 193 H - 355 H, the AUX output is dedicated for control of the balance piston. Choose the AUX
output to be activated At bal. cap. in the menu Compressor control – user functions and set the Signal
high limit and the Signal low limit.
For more information about the AUX output function, see also subsection 3.5.6 Aux. output.
3.3.24 SABflex
The SABflex compressor is a frequency-regulated screw compressor without capacity slide but with au-
tomatic Vi-control. A demand driven oil pump is optional.
Starting sequence
Once the compressor has received permission to start, UniSAB III will send a start signal to the fre-
quency converter and to the cooling fan.
When the compressor starts up, the SSTV valve will close in order to reduce the internal suction pres-
sure and quickly increase the oil pressure. When the timer Start unload has run out, the Start-up limiter
is activated and the timer Max. start-up time is started.
The SSTV valve is kept closed until the oil pressure is above the low alarm curve Y’ + a neutral zone
(NZ
oil,rel
) and the suction pressure is below high alarm limit for internal suction pressure - a neutral zone
(NZ
suct,int
).
Speed will remain at 1,000 rpm until the oil pressure is above the low alarm curve Y’ and the internal
suction pressure is below high alarm limit for internal suction pressure. If the timer Max. start-up time
runs out before the oil and suction pressure is inside the alarm limits, the compressor is stopped with a
shutdown.
After this forced start-up period, where oil and suction pressures are inside the alarm limits, the com-
pressor is now in normal operation. The SSTV limiters for High torque, high internal suction pressure
and low oil pressure will now be active too.
The default setting for the timer Start unload is 15 seconds and for Max. start-up time it is 600 seconds.
Alarm surveillance
During start-up the following alarms are delayed:
Low oil pressure 15 sec.
High filter diff. pressure 300 sec.
Low superheat 300 sec.
High superheat 300 sec.
Low/high oil temperature
300 sec.
The delayed alarms are described in section 6.5 Timers.
Running
After the starting sequence and during normal running operation the following SSTV limiters will be ac-
tive: high torque, low oil pressure and high internal suction pressure. See subsection 3.2.3 Special limit-
ers for more information.
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