6
SECTION 3 — CONTROL FEATURES AND FUNCTIONS
STANDARD FEATURES AND
FUNCTIONALITY
The Ingersoll Rand 302 drive is an external device that is
wired to the compressor’s motors through the starter
panel. The Intellisys controller on the compressor still
starts and stops the compressor, while the Ingersoll Rand
302 Series VFD’s controller varies the compressor’s
motor speed to regulate constant system pressure. The
Ingersoll Rand 302 Series VFD operates in two different
setups:
1) In Setup 1, the Ingersoll Rand 302 Series VFD runs at
constant minimum speed and the compressor is
unloaded.
2) In Setup 2, the Ingersoll Rand 302 Series VFD
regulates a constant pressure and the compressor is
loaded.
The Intellisys controller logic determines which setup the
Ingersoll Rand 302 Series VFD operates.
See Intellisys and Ingersoll Rand 302 Series VFD
Controllers Interface Logic Diagram
As always, the Intellisys controller, set to On / Off Line
mode, will load and unload the compressor, depending
on the system pressure relative to the pressure band
limits. The Ingersoll Rand 302 Series VFD, however, tries
to keep the system pressure within the pressure band as
long as possible.
When the system pressure rises above the target
pressure, the drive will slow the compressor’s motors so
that the compressor supplies less air to the system and
allows the pressure to fall. Likewise, when the system
pressure falls, the drive increases the compressor’s
motor speed so that the compressor supplies more air to
the system.
The compressor with the Ingersoll Rand 302 Series VFD
will only load and unload at minimum speed, unless the
system pressure swings outside the Intellisys pressure
band faster than the drive can react. When the system
pressure rises above the Off Line pressure setpoint, the
blowdown valve opens and the inlet valve closes to
unload the compressor. The load relay, 2CR,
simultaneously opens to switch the drive to Setup 1
(constant, minimum speed).
Conversely, when the system pressure falls below the On
Line pressure setpoint, the blowdown valve closes and
the inlet valve opens to load the compressor. The load
relay, 2CR, simultaneously closes to switch the drive to
Setup 2 (pressure regulation).
Even with the Ingersoll Rand 302 Series VFD wired to
the compressor, the Start button on the Intellisys
controller initiates the full-voltage or star-delta starters.
When the 1M contactor closes, the start relay, 1CR,
closes to start the Ingersoll Rand 302 Series VFD. On
air-cooled, SSR units, the contactors have no power
flowing through them. However, the 1M contactor does
provide power to the constant-speed fan (for a water-
cooled unit) and the oil pump (on Sierra units only). After
the Start process is completed, the compressor will
automatically load and the Ingersoll Rand 302 Series
VFD will try to regulate the pressure.
On SSR air cooled units, the Ingersoll Rand 302 Series
VFD controls the main drive motor and the cooling fan
motor.
On SSR water cooled units, the Ingersoll Rand 302
Series VFD controls the main drive motor. The small
enclosure fan motor gets its power from the compressor
starter.
On Sierra units, the air cooled and water cooled units are
configured the same as the SSR units, except the
externally driven oil pump gets its power from the
compressor starter.
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