The delayed alarms are described in section 6.5. Timers.
Running
After the starting sequence and during normal running operation the following SSSTV limiters
will be active: high torque, low oil pressure and high internal suction pressure. See subsection
3.2.3. Special limiters for more information.
Stopping sequence
At normal stop (to avoid back-spin) the SSSTV valve is closed for the time stated in the timer
SSSTV delay before the compressor is stopped. The default setting is 40 seconds but it is ad-
justable between 0 and 60 seconds.
Note: The SSSTV timer starts counting after the stop delay timer has run out. This means
that the compressor will not stop immediately even though the stop key is pressed or the in-
stant stop digital input is removed.
After compressor stop the SSSTV valve is kept closed for 60 seconds, not adjustable, and the
internal water cooling pump will have a stop delay of 10 seconds. The stop delay for the water
cooling pump can be set in the menu Timers/Motor fan/Run timer SP.
At shutdown the frequency converter is stopped immediately and the SSSTV valve is closed
immediately.
Vi ratio regulation
Unisab III regulates the Vi ratio in three steps according to the actual pressure ratio. Before
switching from one Vi step to another, the actual Vi ratio for the compressor must have been
present for at least the time indicated in timer 34 Vi-pause (60 seconds). Otherwise the
change of the Vi step will be cancelled.
Vi ratio .../Capacity/Vi ratio
Vi low range setting Vi high range setting Dig. output 12 (Vi)
1.9 2.6 Off
3.2 4.8 On
3.3.21 SAB 157HR
The SAB 157HR compressor is a frequency regulated high pressure (HPSH) screw compressor
without 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 frequency 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 3.2.3. Spe-
cial limiters.
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 stopped with a shutdown.
Compressor control and surveillance
Engineering manual - Unisab III 1.10
001930 en 2014.09
111/319
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