The following is an example of sequencing compressors:
On System Start-up - The first available compressor
in the order of A, B, C and D will start if the capacity is
greater than or equal to the Start setpoint for it’s Start
Delay time period. If A is not available then B will start
when it’s Start Delay has timed out. If B is not
available then C will start when it’s Start Delay has
timed out. If C is not available then D will start when
it’s Start Delay has timed out.
On an initial or cold start-up (no compressors are
running) and Load Limiting has been enabled, then
the first compressor started will load to the Load
Limiting Slide Valve Position setpoint and remain
there until the Load Limiting Duration Time has timed
out or until the current reading of the process variable
falls below the Start setpoint.
Load Rises - If the current reading continues to be
greater than or equal to the Capacity Control setpoint
plus the Upper Dead Band setpoint, then the first
compressor in the order of A, B, C, and D that is
running will be loaded to 100%, followed by the next
running compressor in the sequencing. When at
100%, the load signal will be sent to that compressor
every minute to insure the compressor remains fully
loaded.
If all running compressors are loaded greater than
90% slide valve position, then the next available
compressor in the order of A, B, C, and D will be
started if the current reading of the process variable is
greater than the Start setpoint for it’s Start Delay time.
Load Falls - If the current reading of the process
variable falls to or below the Stop setpoint, then the
last compressor in the order of A, B, C, and D that is
running will be unloaded to its Min. Slide Valve
Position setpoint, followed by the next running
compressor in reverse sequencing. For example, if A
and B are running, B is unloaded to it’s Min. Slide
Valve Position setpoint and then A is unloaded to it’s
Min. Slide Valve Position setpoint.
Only the last two running compressors may unload to
their Min. Slide Valve Position setpoint while any
other running compressor will remain loaded. If a
running compressor drops below its Min. Slide Valve
Position setpoint it will be given a load pulse every 15
seconds to bring it back to the Min. Slide Valve
Position. If more than one compressor is running and
the compressors have unloaded to their Min. Slide
Valve Position setpoint, then the last compressor in
the sequence will be stopped if the Current Value is
less than the Stop setpoint for the Stop Delay time
and the compressor has run for longer than it’s Min.
Run Time setpoint.
If only one compressor is running, then this
compressor may unload completely and stop when
the current reading of the process variable is less
than the Stop setpoint.
FRICK
QUANTUM™ COMPRESSOR CONTROL PANEL S90-010 O
OPERATION Page 53
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