Section 9
VARIABLE SPEED DRIVE APPLICATIONS
33
9.1 DESCRIPTION OF COMPONENTS
Refer to Figures 9-1A, 9-1B, 9-1C and 9-1D. The
components and assemblies of the air compressor
are clearly shown. The complete package includes
compressor, electric motor, variable speed
drive, Supervisor™ Controller, compressor inlet
system, compressor discharge system, com-
pressor lubrication and cooling system, capaci-
ty control system, instrument panel, aftercooler,
and combination separator and trap, all mounted
on a heavy gauge steel frame.
On air-cooled models, a fan draws air over the
motor and forces it out through the combined after-
cooler and fluid cooler thereby removing the com-
pression heat from the compressed air and the
cooling fluid.
On water-cooled models, a shell and tube heat
exchanger is mounted on the compressor frame.
Fluid is piped into the heat exchanger where com-
pression heat is removed from the fluid. Another
similar heat exchanger cools the compressed air.
Both air-cooled and water-cooled versions have
easily accessible items such as the fluid filters and
control valves. The inlet air filter is also easily
accessible for servicing.
9.2 CONTROL SYSTEM, FUNCTIONAL DESCRIP-
TION
Refer to Figures 2-5B and 2-5C. The purpose of the
compressor control system is to regulate the
amount of the air being compressed to match the
amount of compressed air being used. The
Capacity Control System consist of variable
speed drive, solenoid valve, regulating valve,
and the inlet valve. The functional description of
the control system is described below in six distinct
phases of operation. The following description text
applies to V200TS series variable speed drive com-
pressors with Supervisor Controller. Depending on
the model, the compressor can be operated at a
setpoint pressure from 60 to 175 psig (4.1 to
12.1 bar). Refer to the nameplate for operating
pressure range. The Supervisor Controller will
automatically set the frequency range based on
the selected pressure. For explanatory purposes,
this description will apply to a compressor with an
operating pressure of 100 psig (6.9 bar). A com-
pressor with any other pressure range would oper-
ate in the same manner except stated pressures.
START MODE- 0 – 50 PSIG (0 TO 3.5 BAR)
When the Supervisor Controller (START) button
is depressed, the VSD ramps the motor to full
speed and the sump pressure will quickly rise from
0 to 50 psig ( 0-3.4 bar). During this period, both the
regulator and solenoid valves are closed, the inlet
valve is fully open and the air-end delivers full
capacity to the sump tank. The rising compressor
air pressure is isolated from the service line in this
phase by the minimum pressure valve set at
approximately 50 psig (3.4 bar).
FULL LOAD MODE- 50 TO 100 PSIG (3.4 TO 6.9
BAR)
When the compressed air pressure rises over 50
psig (3.4 bar) the minimum pressure valve opens
allowing compressed air to flow into the service line.
From this point on the line pressure is continually
monitored by the Supervisor Controller, which con-
trols the variable speed drive. The pressure regula-
tor and solenoid valve remain closed with the inlet
valve fully open running at 100 psig (6.9 bar) or
below.
VARIABLE SPEED DRIVE PART LOAD CON-
TROL
If less than rated capacity of compressed air is
being used, the service line pressure will rise
above 100 psig (6.9 bar). Consequently, the
Variable Speed Drive will begin to decelerate the
motor, thereby reducing the output capacity to
match demand. The drive will continuously adjust
the motor speed (accelerate or decelerate) to main-
tain a line pressure of 100 psig (6.9 bar). In this
mode the VSD will operate within the appropriate
frequency range determined by the Supervisor
Controller.
MODULATING MODE WITH SPIRAL VALVE:
As demand decreases, the variable speed drive
reduces motor speed to maintain the set point pres-
sure. When the speed approaches the minimum
setting, a solenoid valve opens feeding air pressure
to the spiral valve actuator. This in turn expands the
diaphragm and engages the pinion mounted on the
spiral valve shaft assembly, resulting in a rotary
motion and full opening of the spiral valve, effec-
tively reducing the rotor length by 50%. Excess air
will be returned back internally to the suction side of
the compressor unit. In this mode, the VSD will
modulate the motor speed within a specified range
to maintain the set point pressure as follows:
Increasing demand condition:
If demand increases, the VSD increases the motor
speed until the set point pressure is achieved. If set
point pressure is not achieved while at maximum
speed, the controller will close the spiral valve,
thereby eliminating internal air bypass.
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