Section 11
VARIABLE SPEED DRIVE APPLICATIONS
59
being used, the service line pressure will rise
above 100 psig (6.9 bar). Once 101.5 psig (7.0 bar)
is reached, the Variable Speed Drive will begin to
decelerate the motor, thereby reducing the output
capacity to match demand. The drive will continu-
ously adjust the motor speed (accelerate or decel-
erate) to maintain a line pressure of 101.5 psig (7.0
bar). In this mode the VSD will operate within the
frequency range specified.
MODULATING MODE- 101.5 (7.0 BAR) PSIG TO
106 PSIG (7.3 BAR)
During low demand periods and with the Variable
Speed Drive at minimum speed, the line pressure
can rise above 101.5 psig (7.0 bar). In this case the
pressure regulator valve gradually opens, directing
air pressure to the inlet control valve piston, this
causes the inlet valve to partially close further
reducing the air entering the compressor until it
matches the amount of air being used. The control
system functions continually in this manner
between the limits of > 101.5 psig (7.0 bar) to 106
psig (7.3 bar) in response to varying flow demands.
The pressure regulator has an orifice which vents a
small amount of air to the atmosphere when the
Figure 11-2 Variable Speed Drive Control System with Supervisor Controller
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