The dedicated frequency converter functionality includes:
•
Start Up
Once the frequency converter has a start
command, the compressor runs up to 3000 RPM
and remains at that speed for 10 s. Once this
initial time is complete, the frequency converter
slowly ramps to the reference speed.
•
Shut Down
The stop command bypasses the normal ramp
time and the frequency converter ramps the
compressor to stop fast.
•
Short Cycle Prevention
The frequency converter has a minimum running
time of 12 s, with an interval between starts of 5
minutes (300 s). The short cycle delay values are
adjustable in parameter group
28-0* Short Cycle
Protection
.
•
Oil Injection
The frequency converter cycles a solenoid valve
via its relay 1. This cycling ensures that the oil is
distributed to the scroll set, improves tightness,
and reduces internal gas leakage during the
compression process.
•
Oil Management
If compressor speed is below 3000 RPM for a
determined amount of time (within 60 minutes),
the boost cycle runs the compressor back to 4200
RPM for a determined amount of time (within 90
s). The maximum time between fixed boosts is
limited to a determined amount of time (within
24 hours).
•
Discharge Temperature Limit
If the discharge temperature exceeds the warning
level of 266
°
F, the compressor drops in speed by
10 Hz for the next 3 minutes. The compressor
continues to drop 10 Hz for each 3 minutes for as
long as the temperature is over the warning level.
If the discharge temperature exceeds the
emergency level of 293
°
C, the compressor is
stops.
•
Crankcase Heater
On VSH088 and VSH117, when the compressor is
stopped, the frequency converter provides a DC
current to the compressor motor. The DC current
keeps the oil warm and an external crankcase
heater is not needed.
VSH170 needs an external crankcase heater
(surface sump heater or belt type).
•
Low Pressure Switch
An LP switch is mandatory with the frequency
converter compressor in any type of application.
•
High Pressure Switch
The high-pressure switch must be connected to
input terminal 37 of the frequency converter in
series with the other safety devices.
1.1.1 Sequence of Operation
All compressor types have strong demands of speed limits
to ensure the oil lubrication of the bearings. Therefore, fast
acceleration from standstill to minimum speed with a
special start ramp is important, when a start command is
given. This is also the reason why the Compressor Drive
trips with an alarm [A49]
Speed Limit
, if the speed falls
below minimum speed e.g. when the current limit
controller reduces the speed due to a high load. This alarm
is reset automatically after 30 s and the compressor
restarts.
If a rotor is blocked, the Compressor Drive trips with an
alarm [A18]
Start failed
, if the speed fails to get above the
minimum speed limit for the compressor within 2 s. This
alarm is reset automatically after 30 s and the compressor
restarts.
The manufacturer sets up the necessary start settings,
motor data and all the other preferred settings for each
compressor type/size. Automatically set up the values by
selecting the actual compressor in
1-13 Compressor
Selection
.
Introduction
Operating Instructions
MG34M422
Danfoss A/S © Rev. 2013-07-03 All rights reserved.
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Summary of Contents for VLT CDS 303
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