be programmed to prevent staging until the system load
has stabilized and normal control established.
When the Pack Controller is enabled and running normally,
and the frequency converter issues a trip alarm, the system
head pressure is maintained by staging and destaging
fixed speed compressors. To prevent frequent staging and
destaging and minimize load fluctuations, a wider Fixed
Speed Bandwidth is used instead of the Staging
bandwidth.
3.5.2 System Status and Operation
When the pack controller is enabled, the operation status
for each compressor and the pack controller is displayed
on the Local Control Panel. Information displayed includes:
•
Compressor Status, is a read out of the status for
the relays assigned to each compressor. The
display shows compressors that are disabled, off,
running on the frequency converter or running
on the mains
•
Pack Status, is a read out of the status for the
Pack Controller. The display shows the Pack
Controller is disabled, all compressors are off, and
emergency has stopped all compressors, all
compressors are running, fixed speed
compressors are being staged/destaged.
•
If a no load need occurs then destaging ensures
that all fixed speed compressors are stopped
individually followed by the variable speed
compressor.
3.5.3 Pack Compressor Wiring Diagram
The wiring diagram shows an example with the built in
BASIC cascade controller with one variable speed
compressor (lead) and two fixed speed compressors, a 4-20
mA transmitter and System Safety Interlock.
L1/L2/L3
L1/L2/L3
L1/L2/L3
Po
w
er S
ec
tion
RELA
Y 1
RELA
Y 2
130BA376.10
Illustration 3.31
How to Install
Operating Instructions VLT
®
CDS302 and CDS303
MG34M302 - VLT
®
is a registered Danfoss trademark/Commercial Compressor
35
3
3
