KT-420-4 // PDF Download
61
– voltage
– frequency
– number of motor poles
– (motor speed)
– (power)
– (cos φ)
• control logic: U/f (proportional)
• switching frequency of the converter in the frequency inverter: use approx. 3 kHz as standard
– Low switching frequencies reduce the strain on the isolation of the motor windings, in summary this results in
higher efficiency.
– Higher switching frequencies may cause less motor sound, slightly reduced motor losses and motor heat-up.
On the other hand, they lead to higher losses and thus a higher temperature in the frequency inverter (pos-
sibly consider degrading, i.e. the output load decreases with rising ambient temperature).
• Activate the “Autotune” function of the frequency inverter, if available.
• Define the start and stop sequences.
With BITZER VARIPACK frequency inverters, not all of these steps are necessary, since they are pre-configured
and may be adapted to system requirements via the BEST SOFTWARE (see Operating instructions
).
Vibrations
!
!
NOTICE
Danger of material fatigue and damage caused by vibrations in the system due to FI speed drive!
Check the whole system carefully at all possible operating frequencies for vibrations and resonances.
Blend out frequencies which cause resonances by appropriate parameter setting at the inverter!
If a vibration problem is identified at a certain speed or combination of speeds, it may be possible to modify or rein-
force the piping design to correct it. After any such changes, the system should be retested across the entire speed
range to make sure that solving the problem at one speed does not create a problem at another.
Alternatively, most inverters have the ability to program “gap” speed ranges (frequency bypass areas): While the
compressor will be permitted to pass through the gap speed range, it will not be allowed to dwell within that range.
Any frequency ranges where vibration or sound problems are identified can be “excluded” in this manner.
For further questions, please contact BITZER.
7.2
Cycling rate and minimum running times
The maximum cycling rates (minimum pause times, maximum starts per hour) of the compressors which are given
in the respective Operating Instructions also apply to frequency inverter operation. At low motor speeds, the min-
imum running times may be longer – pay special attention to the oil return.
For work on the compressor once it has been commissioned:
WARNING
The compressor is under pressure!
Serious injuries are possible.
Depressurize the compressor!
Wear safety goggles!
