Johnson Controls SABROE Unisab III Control User Manual

2.1.9 Suction gas superheat, shutdown
The suction gas superheat shutdown is a shutdown which in many cases will protect the com-
pressor against liquid slugging. However, many aspects may affect superheating and there-
fore this shutdown must not be considered full protection against liquid slugging.
If the superheat falls below the set value, the compressor stops. However, on R717 pump cir-
culation plants with a short distance between liquid separator and compressor, the suction
gas superheat may drop down to 0 K during normal operation. In such cases adjust Low shut-
down to 0.0 thus making it inactive.
2.1.10 User input 1 (4-20 mA)
The shutdown and alarm limits are activated when Ext. Input Signal has been selected under
Setup/Configuration/External input.
2.1.11 Oil pressure alarm (SABflex and SABCube)
The alarm indicates that the oil pressure for a SAB 109-159 is below the alarm limit curve
Y [bar] = Y
1
+K
1
x P
suction, abs
under normal operation
Y’ [bar] = Y
1
+K
1
x P
suction, int, abs
when the start-up limiter is active
Y [bar] = Y
1
+K
1
x P
suction, abs
when the start-up limiter is active, but where only the SSSTV
valve is limited (i.e. closed)
Where Y1 is the low alarm limit from Table 8, and the constant K1 is the low alarm coefficient
also found in Table 8.
P
suction, abs
is the external (plant) suction pressure, and P
suction, int, abs
is the internal suction
pressure, both measured absolute.
The alarm is only active when the compressor is running and the Start unload timer has run
out.
2.1.12 Oil pressure shutdown (SABflex and SABCube)
The shutdown indicates that the oil pressure for a SAB 109-159 is below the shutdown limit
curve.
Z’ [bar] = Z
1
+K
1
x P
suction, int, abs
under normal operation
Z’ [bar] = Z
1
when the start-up limiter is active
Z’ [bar] = Z
1
+K
1
x P
suction, int, abs
when the Start-up limiter is active but where only the SSSTV
valve is limited (i.e. closed).
Where Z
1
is the low shutdown limit from Table 8 and the constant K
1
is the low alarm coeffi-
cient also found in Table 8.
The shutdown is only active when the compressor is running and the Start unload timer has
run out. As long as the start-up limiter is active, the shutdown limit curve (where the limit is a
function of the internal suction pressure) is not activated. In this case the shutdown limit is
equal to the low oil pressure shutdown limit, i.e. the constant Z
1
in above equation.
Alarms and shutdowns
Engineering manual - Unisab III 1.10
001930 en 2014.09
47/319

Johnson Controls SABROE Unisab III Control Specifications

General

Brand	Johnson Controls
Model	SABROE Unisab III Control
Category	Control Systems
Language	English