Emerson VSG & VSSG Spezifikationen PDF herunterladen (Seite 11)

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Alarm and Shutdown Readings

1. Low Gas Suction Temperature - This point protects

the compressor from suction gas entering the com-

pressor at too low of a temperature, and is activated

by a direct reading from the suction temperature

RTD located in the suction “T”.

2. High Gas Discharge Temperature - This point pro-

tects the compressor against high gas tem-

perature at the discharge of the unit, and is activated

by a direct reading from the RTD located in the

compressor discharge manifold.

3. Low Oil Separator Start Temperature - This point

protects the compressor from starting with low oil

temperature in the separator, and is activated by a

direct reading from the RTD located in the bottom

of the oil separator.

4. Low Oil Separator Run Temperature - Similar to

the Low Oil Separator Start Temperature described

above, however this point only becomes active after

a predetermined period of running time, and uses a

higher setpoint.

5. Low Oil Injection Temperature - This point protects

the compressor from running with cold oil being

injected into the screw housing, and is activated by

a direct reading from the RTD located in the oil injec-

tion line. This point is bypassed for a predetermined

period of time after starting to allow the unit time

to start and warm up.

6. High Oil Injection Temperature - This point protects

the compressor from running with hot oil being

injected into the screw housing, and is activated

by a direct reading from the RTD located in the oil

injection line.

7. Low Suction Pressure - This point protects the

compressor from drawing low suction pressure and

is activated by a direct reading from the suction pres-

sure transducer, which reads the pressure from a tap

located in the suction stop/check valve housing.

8. High Discharge Pressure - This point protects the

compressor from developing high discharge pres-

sure and is activated by a direct reading from the

discharge pressure transducer, which reads the

pressure from a tap located in the oil separator. In

addition to this alarm and shutdown, the compressor

package is ultimately protected from damage due to

over pressurization by at least one discharge pressure

relief valve located on the oil separator. The purpose

of this safety setpoint is to allow for a lower setpoint

to conform to a process requirement, and to prevent

the relief valve from opening.

9. Prelube Oil Pressure - This point acts as a permissive

to start the compressor, and protects against the

compressor starting with no oil lubrication. If, during

a start sequence, the prelube oil pressure fails to rise

above 4.0 PSID, the compressor will fail to start. The

prelube oil pressure is a calculated value obtained

by subtracting the discharge pressure reading from

the oil manifold pressure (oil filter outlet pressure)

reading.

10. Low Oil Pressure - This point protects the com-

pressor from running with insufficient lubrication

pressure, and becomes active after a predetermined

period of running, usually sixty seconds. The oil pres-

sure is a calculated value obtained by subtracting the

suction pressure from the oil manifold pressure (oil

filter outlet pressure) reading, which results in the

actual pressure under which the oil is entering the

screw housing.

11. High Running Oil Filter Differential Pressure - This

point alerts operators to clogging oil filters. When

the oil filters develop a high differential pressure

while running at normal operating temperatures,

it is an indication that they are becoming dirty and

must be changed. An alarm initially warns of dirty

filters; if the situation worsens before the filters are

changed a shutdown will stop the compressor.

The control system for the VSG compressor must protect the

machine from damage caused by running outside of normal

operating conditions by providing operators with alarms

when operating parameters have reached an abnormal

condition, and by automatically stopping the compressor

before these conditions can cause a unit failure. Pressures

and temperatures of the process gas and the oil, as well as

motor amperage and slide positions must all be continuously

monitored to ensure the compressor is operating properly.

In most cases, the safety setpoints described above

will have settings which are dictated by process

requirements, and not necessarily mechanical con-

straints of the compressor. Process pressures and

temperatures may vary considerably depending

on the application of the compressor, and the VSG

compressor is designed to work well in a broad range

of applications.. For this reason, it is impractical

to suggest “initial” setpoints to fit all applications.

Instead, minimum and maximum values for each

safety setpoint are provided, while precise settings

for the safety setpoints must be derived for each

installation.

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