Engineering manual - UniSAB III 1.10.8
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001930 en 2021.06
Compressor control and surveillance
3.3.21
SAB 157 HR
The SAB 157 HR compressor is a frequency-regulated high-pressure (HPSH) screw compressor with-
out capacity slide and volume slide. The screw compressor is for heat pump (NH
3
) and CO
2
operation.
There is a relief valve for unloading and the compressor is available with a number of fixed Vi ratios. The
compressor has no oil pump.
Starting sequence
Once the compressor has received permission to start, UniSAB III will send a start signal to the fre-
quency converter. When the compressor starts up, the relief valve will open in order to reduce torque
and internal pressure. It will close when speed is above minimum speed + 200 rpm.
The relief valve will unload i. e. be kept open until a number of conditions for oil, suction and internal
pressure are fulfilled; see the description
Plug valve limiters
in subsection
Motor speed will remain at 1,000 rpm until the suction pressure is below the high alarm limit. If the timer
Start RPM limiter
runs out before the suction pressure is inside the alarm limits, the compressor is stop-
ped with a shutdown.
After this start-up period where oil, suction and internal pressure are inside the alarm limits, the com-
pressor is now in normal operation. The relief valve will be closed and there will be no restrictions on
speed regulation.
Alarm surveillance
During start the following alarms are delayed:
Low oil pressure: 45 sec.
High filter diff. pressure: 600 sec.
Low superheat: 300 sec.
High superheat: 300 sec.
Low/high oil temperature: 300 sec.
The delayed alarms are described in section
Running
After the starting sequence and during normal running operation the following relief valve limiters will be
active:
•
low oil pressure
•
low main oil pressure
•
high suction pressure
•
high internal pressure
•
high torque
•
low Vi ratio
See subsection
for more information.
Stopping sequence
At normal stop, the speed will be reduced to minimum speed which will stop the frequency converter. At
shutdown, the frequency converter is stopped immediately.
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