Engineering manual - UniSAB III 1.10.8
94/346
001930 en 2021.06
Compressor control and surveillance
Low oil pressure limiter (SABflex and SABCube)
If the oil pressure is lower than the low alarm limit the load is released by throttling the (S)SSTV valve.
The (S)SSTV valve is closed and opened by issuing a pulse modulated signal to it. The period time of
this signal can be set with the parameter
Run Time
found in the picture
Control values/Suction/Internal
pressure/Control
.
The low alarm limit for the oil pressure is set in the picture
Control values/Oil/Pressure/Limits
. If the oil
pressure is below the high alarm limit the (S)SSTV valve will start to close. The size of the closing signal,
i.e. the pulse/pause ratio, is proportional to the difference between the alarm limit and the actual oil pres-
sure. The valve will close completely when there is a constant ON signal to the valve, i.e. when the ac-
tual oil pressure has been lower than the alarm limit for a while.
If the oil pressure is above the high alarm limit the (S)SSTV valve will start to close. The size of the clos-
ing signal, i.e. the pulse/pause ratio, is proportional to the difference between the alarm limit and the ac-
tual oil pressure. The valve will close completely when there is a constant OFF signal to the valve, i.e.
when the actual oil pressure has been higher than the alarm limit for a while.
Start-up RPM limiter (SAB 157 HR)
This limiter will limit the speed during compressor start-up. If the suction pressure is higher than the
High
alarm
limit for suction pressure, this limiter will during the start-up phase limit speed to minimum speed,
default 1,000 [rpm].
To leave the
Start-up RPM limiter
the suction pressure must be well below the suction pressure alarm
limit. The neutral zone used is 1.0 Bar.
The start-up limiter can maximum be active for the time set in the timer
Start RPM limiter
(default 300
seconds). When the limiter is active the
Start RPM limiter
timer is running and a
Start up RPM limiter
alarm is shown. If the
Start RPM limiter
timer runs out while the limiter is still active the compressor is
stopped by a shutdown
Start RPM limiter error
.
Start-up limiter (SABflex and SABCube)
This limiter will throttle the (S)SSTV valve and limit the speed during compressor start-up, if:
•
The internal suction pressure is higher than the High alarm limit for internal suction pressure or
the oil pressure is lower than the low alarm limit curve Y', then this limiter will, during the start-up
phase, limit the SABCube speed to 1,000 [rpm].
•
The external suction pressure is higher than the High alarm limit for internal suction pressure or
the oil pressure is lower than the low alarm limit curve Y, then this limiter will too, during the
start-up, keep the (S)SSTV valve closed.
To leave the “Start-up limiter”, and then slowly open (S)SSTV valve, the external suction pressure must
be well below the internal suction pressure alarm limit and the oil pressure must be well over the oil pres-
sure alarm curve Y.
The start-up limiter is left when both these two conditions are fulfilled
P
suct
< ‘High Alarm limit’ – NZ
suct,int
for P
suct,int
and P
oil,rel
> ‘Low Alarm curve’ Y + NZ
oil,rel
for P
oil,rel
The neutral zone NZ
suct,int
is found in the
../Suction/Internal Pressure/Control picture
.
The neutral zone NZ
oil,rel
is found in the
../Oil/ Pressure/Control
picture.
The ‘High Alarm limit’ value for P
suct,int
is found in the
../Suction/Internal Pressure/Limits
picture.
The ‘Low Alarm curve’ Y value for P
oil,rel
is found in the
../Oil/ Pressure/Control
picture.
The start-up limiter can maximum be active for the time set in timer “Max. start-up time” (default 600
sec.) When the “Max. start-up time” timer is running the “Start-up limiter” alarm is shown. If the “Max.
start-up time” timer runs out the compressor is stopped by a shutdown.
Summary of Contents for SABROE Unisab III Control
Page 1: ...UniSAB III control Version 1 10 8 Engineering manual EN...
Page 2: ......
Page 347: ......
