Section 4
VARIABLE SPEED DRIVE
25
VARIABLE SPEED DRIVE APPLICATIONS
The most efficient use of a VSD machine in sequencing is to make it always be the trim
machine and always be running. This can be accomplished using the existing Sullair
sequence logic and configuring the machines as follows:
I. SETUP FOR FIXED-SPEED MACHINES NETWORKED TO A VSD MACHINE
The fixed-speed machines must be set up for load/unload operation. If controlled with
Supervisor II controllers, the pressure regulator/s must be made to have no effect by oper-
ating the system below their effective range. If controlled by the Supervisor Controller, the
controls may be programmed for Load/No load operation whereby the Full Load valve is
energized any time the machine is running, thus defeating modulation. Alternately, the Full
Load solenoid valve may be rewired to the Load output with either the Supervisor Controller
or Supervisor II to accomplish the same thing. In any case care must be taken to not over
-
load these compressors by only operating at pressures within the capability of the drive
motor. See the following chart for suggested settings.
SETUP FOR VSD MACHINE
Since this machine is to always be the trim machine, no Full Load action is needed. The
Max Speed input signal should be disabled unless more than one VSD machine is in the
same sequence. Set the fixed-speed compressors to higher COM ID numbers than the VSD
machine.
SEQUENCING WITHOUT AUTO ROTATION OF FIXED-SPEED MACHINES
In this configuration, all machines including the VSD machine are sequenced by Com #. If
rotation of fixed-speed machines is desired, it must be done manually by changing the Com
#s of fixed-speed machines.(Changes must only be made when machines are out of
sequence mode.)
PLEASE NOTE; The sequence may get disrupted if sudden and drastic pressure swings
occur.
SEQUENCING WITH AUTO ROTATION OF FIXED-SPEED MACHINES
In this configuration, only the fixed-speed compressors are sequenced and the VSD is run
with its sequencing disabled. Sequence hours mode can then be used to automatically
rotate the fixed-speed machines. Depending on the application and system demands, the
VSD compressor can either be run continuously or in the AUTO mode to minimize the
unload time to as little as an immediate stop on unload. In this arrangement, the VSD
machine will always be operating as the trim machine because it will restart at a higher pres-
sure than the fixed-speed machines. By adjusting the VSD Unload time in AUTO mode and
the fixed-speed Restart times, rapid cycling and hunting can be minimized.
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