Johnson Controls SABROE Unisab III Control, Инструкция по эксплуатации

Страница: 98 / 348

Engineering manual - UniSAB III 1.10.8
98/346
001930 en 2021.06
Compressor control and surveillance
rate limiter, which prevents the regulator from reducing Δ Yield/sec. (Yield change per second) with a
higher rate than set in the following parameter:
• Yield rate down limitation [%/sec]
The Yield decrease rate limiter must limit the regulator decrease rate in Auto and Remote mode and the
decrease rate in Manual mode. See subsection 6.4.7 Measuring , 8: Yield rate down limitation.
In addition to the decrease rate limiter , an increase rate limiter is defined and can be adjusted too, it is
set in the following parameter:
• Yield rate up limitation [%/sec]
See subsection 6.4.7 Measuring , 7: Yield rate up limitation .
Forced speed active
Note that for SAB 120-151, SAB 193-355, SAB 193 H-355 H, SAB 157 HR and SAB 273 S with fre-
quency converter you may experience a problem with low oil pressure at compressor start-up at low
rpm.
To avoid this problem UniSAB III will increase the speed in the frequency converter (“forced speed”) to
make it regulate up to, and stay at, a predefined speed set between
Motor rpm min. and Motor rpm max.
for as long as the main oil pressure is low. An alarm Forced speed active will be issued.
When the main oil pressure (P
oil
abs - P
suct
abs x 1.5) is above a defined minimum limit of 1 bar the
forced speed regulation is deactivated. The speed is then decreased to minimum speed in Manual or
the speed is set free to be controlled by the capacity regulator in Auto .
Plug valve limiters (SAB 157 HR)
The high-pressure (HPSH) screw compressor type SAB 157 HR is equipped with a relief valve for un-
loading. This relief or plug valve is used for start relief and torque reduction. The following limiter func-
tions will unload the plug valve.
Low lube pressure (SAB 157 HR)
To secure the bearing (Lube) oil pressure at start-up UniSAB III will start with unloaded plug valve. Under
operation the plug valve will unload if the lube oil pressure is lower than a predefined limit.
If P
oil,abs
< P
suct,abs
* 1.25 + 1.0: unload plug valve
If P
oil,abs
> P
suct,abs
* 1.30 + 1.0: allow loading plug valve
When the plug valve is unloaded, a Lube pressure unload alarm is given.
Insufficient main oil pressure (SAB 157 HR)
To secure main oil pressure at start-up and during operation the plug valve will unload if the absolute oil
pressure is too low compared to the absolute suction pressure.
If P
oil,abs
< P
suct,abs
* 1.50 + 1.0: unload plug valve
If P
oil,abs
> P
suct,abs
* 1.50 + 1.1: allow loading plug valve
When the plug valve is unloaded a Low main oil pressure alarm is given with a 180 second delay.
See also Fig. 9: Insufficient main oil pressure during low differential pressure, SAB 157 HR in subsection
2.2.54 Oil pressure diagrams .
High suction pressure (SAB 157 HR)
If the suction pressure is higher than the high alarm limit, unload the plug valve. When the suction pres-
sure is lower than the high alarm limit – 1.0 bar, allow loading the plug valve.