KT-420-4 // PDF Download
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Fig. 9: Menu for choosing the VARIPACK frequency inverter in the accessories module of the BITZER SOFTWARE
For further details on the VARIPACK see Operating Instructions
Step 2b: Selecting a frequency inverter of another manufacturer
▶ Allow at least 10% reserve for operating current
The frequency inverter must be able to continuously supply the operating current to the compressor under all ex-
pected operating conditions. At least 10% additional reserve should be planned for, e.g. to be able to compensate
for undervoltage in the network. If the frequency inverter has limiter functions which limit the maximum frequency
under such circumstances to ensure operational safety (such as the BITZER VARIPACK), the reserve can possibly
be selected smaller.
▶ Consider overload capacity for compressor start
Additionally, a compensation factor F
C
for the current during the compressor start must be allowed for. Since the
torque of reciprocating compressors is not constant with the angle of rotation (the higher the number of cylinders,
the more constant the torque), a greater starting torque is required for a smaller number of cylinders. The com-
pensation factors are as follows:
• 2 cylinder compressors for CO
2
: F = 3
• other 2 cylinder compressors: F = 2.0
• 4 cylinder compressors: F = 1.6
• 6 cylinder compressors: F = 1.5
• 8 cylinder compressors: F = 1.4
