Danfoss VT2800 Series Design Manual page 14

RFI 1B/LC filter
The RFI 1B/LC filter contains both an RFI module
that complies with EN 55011-1B and an LC filter
that reduces the acoustic noise.
LC filter
When a motor is controlled by a frequency converter, at
times you will be able to hear the acoustic noise from
the motor. The noise, which is caused by the design of
the motor, is generated every time one of the inverter
contacts in the frequency converter is acti v ated. The
frequency of the acoustic noise therefore corresponds
to the frequency converter's connection frequency.
The filter reduces the voltage's du/dt, the peak voltage
U and ripple current
peak
current and voltage are almost sine-shaped. The
acoustic motor noise is thus reduced to a minimum.
Because of the ripple current in the coils some
noise will be emitted by the coils. This problem
can be solved completely by fitting the filter
inside a cabinet or equi v alent.
Danfoss can supply an LC filter for the frequency
converter, which muffles the acoustic motor noise.
Before the filters are put into use you must ensure that:
- rated current is observed
- mains voltage is 200-480 V
- parameter 412 Variable switching frequency
is set to LC filter attached [3]
- output frequency is max. 120 Hz
See drawing on the next page.
14
I to the motor, so that the
®
VLT 2800 Series
Installation of thermistor (PTC)
The RFI 1B/LC filter has an integral thermistor (PTC),
which is acti v ated if an overtemperature arises. The
frequency converter can be programmed to stop the
motor and acti v atee an alarm via a relay output or
a digital output if the thermistor is acti v ated.
The thermistor must be connected between terminal 50
(+10V) and one of the digital inputs 18, 19, 27 and 29.
In parameter 128 Motor thermal protection Thermistor
warning [1] or Thermistor trip [2] are selected.
The thermistor is connected as follows:
MG.28.E9.02 - VLT is a registered Danfoss trademark