•
Oil Injection
The frequency converter cycles a solenoid valve
via its relay 1. This ensures that the oil is
distributed to the scroll set, improves tightness,
and reduces internal gas leakage during the
compression process.
•
Oil Management
If the speed of the compressor 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 130
°
C, the compressor drops in speed by
10 Hz for the next 3 minutes, then 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 145
°
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 to keep the oil
warm and to avoid needing an external crankcase
heater.
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 27 of the frequency converter in
series with the other safety devices.
1.1.1 Sequence of Operation
All compressor types have strong demands to speed limits
to ensure the oil lubrication of the bearings. This is the
main reason for accelerating from standstill to minimum
speed as fast as possible with a special start ramp 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 will be reset automatically after 30 s and
the compressor will restart.
In case of a blocked rotor, 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 will be reset automatically after 30 s and the
compressor will restart.
The necessary start settings, motor data and all the other
preferred settings for each compressor type/size are set up
by the manufacturer and are automatically set up by
selecting the actual compressor in
1-13 Compressor
Selection
.
Introduction
Operating Instructions VLT
®
CDS302 and CDS303
MG34M302 - VLT
®
is a registered Danfoss trademark/Commercial Compressor
5
1
1
