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VLT
®
6000 HVAC
37
MG.60.B1.02 - VLT is a registered Danfoss trademark
Introduction to
HV
AC
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LC filters for VLT 6000 HVAC
When a motor is controlled by a frequency converter,
resonance noise will be heard from the motor. This
noise, which is caused by the design of the motor,
occurs each time one of the inverter switches in the
frequency converter is activated. Consequently, the
resonance noise frequency corresponds to the
switching frequency of the frequency converter.
For the VLT 6000 HVAC, Danfoss offers a LC filter to
dampen the acoustic motor noise.
This filter reduces the voltage rise time, the peak
voltage U
PEAK
and the ripple current
∆
I to the motor,
thereby making current and voltage almost sinusoidal.
The acoustic motor noise is therefore reduced to a
minimum.
Because of the ripple current in the coils, there will be
some noise from the coils. This problem can be solved
entirely by integrating the filter in a cabinet or similar.
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Examples of the use of LC filters
Submersible pumps
For small motors with up to and including 5.5 kW
rated motor power, use a LC filter, unless the motor is
equipped with phase separation paper. This applies
e.g. to all wet running motors. If these motors are
used without LC filter in connection with a frequency
converter, the motor windings will short-circuit. If in
doubt, ask the motor manufacturer whether the
motor in question is equipped with phase separation
paper.
Long motor cables
If screened/armoured motor cables longer than 150
m or unscreened/unarmoured motor cables longer
than 300 m are used, a LC filter should be applied.
The LC filter reduces the capacitive earth leakage
currents and the voltage peak loads.
NB!:
If a VLT frequency converter controls several
motors in parallel, the motor cables must be
added up to give the total cable length.
Well pumps
If immersion pumps are used, e.g. submerged pumps
or well pumps, the supplier should be contacted for
clarification of requirements. It is recommended to
use a LC filter if a VLT frequency converter is used for
immersion operations.