2.10
General functional description
element will result in noise and vibration. Anti-vibration
mountings reside below the air end and the motor. This
configuration reduces the transmission of vibration from
airend and motor to the structure, reducing noise and
ensuring reliability of mounted parts on the structure.
2.4.4 Control system
Load - Unload
Depending on the demand for compressed air from the
application at a particular time, the compressor needs to
respond accordingly. The compressor, therefore operates
in either loading or unloading mode to meet this
requirement. The primary objective of these modes is to
save energy and reduce wear and tear on the machine.
The control system ensures a smooth start without
overloading the motor. The compressor is started in star
mode, during which most of the compressed air is vented
to the atmosphere. This mechanism helps prevent
overloading the motor. In delta mode the motor speed
stabilizes, the solenoid valve energizes after 10 seconds of
change-over to reduce load on the motor, the blow-down
valve is closes, and the compressor starts loading.
When the receiver pressure reaches the maximum limit, a
signal arrives the solenoid valve from the control system.
Next, the inlet valve actuates and closes, and the
compressor runs in unloading mode. If unloading mode
continues for more than 5 minutes, i.e., compressed air is
consumed and thus no decrease in pressure occurs, the
system stops and switches to standby mode. If a drop in
pressure occurs in the receiver, the compressor returns to
loading mode automatically.
Suction modulation
When you operate a compressor without VFD, capacity
control occurs via a pressure regulator (for selected
models). When the consumption of air is less than the FAD
of the compressor, the line pressure will start increasing.
Whenever the line pressure goes up constantly beyond the
set pressure, the pressure regulator bleeds the excess air
to the atmosphere thereby reducing the amount of flow
into the actuator. The actuator is spring loaded, which, in
turn, closes the intake valve slightly and enables capacity
control. Similarly when the consumption of air is more
than the FAD, the line pressure starts decreasing and the
actuator progressively opens the intake valve. This
regulation is called intake modulation by throttling.
VFD modulation
VFD is an efficient way of controlling capacity as per
demand. In a compressor with VFD the power of
compressor varies proportionally with capacity reduction.
The VFD tunes the frequency, thereby adjusting the speed
based on the change in line pressure. The incoming flow
will automatically reduce because of reduced speed of the
motor. Conversely speed increases when line pressure
goes down below working pressure.
2.4.5 For retro-fitment of Standalone VFD
with Compressor (C) version in field
1. Change the bearings to insulated type for motors
>=90kw at Non Drive End side of Motor
2. Turndown only upto 50% for conversion models
(considering the motor speed) i.e. motor frequency range
is 50 - 25 Hz for 50Hz variant and 60 - 30Hz for 60Hz
variant. No pressure turndown is applicable
3. Run the compressor in the VFD operating range (50 to
25Hz) and skip the frequency in VFD controller (within +/-
1Hz) if abnormal noise / vibration is observed
4. Change the thermal element from 65°C to 75°C
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