VLT
®
2800 Series
■ 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 reduce s the acoustic noise.
LC filter
When a m otor is c ontrolled by a frequency converter, at
times you will be able to hear the acoustic noise from
the m otor. The noise, which is caused by the design of
the motor, is generated ever y time one of the inverter
contacts in the frequency converter is activated. The
frequency of the acousti c noise therefore corresponds
to the freque ncy converter’s connection frequency.
The filter reduces the voltage’s du/dt, the peak voltage
U
peak
and ripple current Itothemotor,sothatthe
current and voltage are almost sine-shaped. The
acoustic motor noise is thus reduced to a minimum.
Becauseoftheripplecurrentinthecoilssome
noisewillbeemittedbythecoils. Thisproblem
can be solved completely by fitting the filter
inside a cabinet or equivalent.
Danfoss can supply an LC filter for the frequency
converter, which m uffles the acoustic motor noise.
Beforethefiltersareputintouseyoumustensurethat:
- rated current is observed
- ma ins voltage is 200-480 V
- parameter 412 Variable sw itching frequency
is set to LC filter attached [3]
- output frequency is max. 120 Hz
See drawing on the next page.
Installation of thermistor (PTC)
The RFI 1B/LC filter has an integral thermistor (PTC),
which is activated if an overtemperature arises. The
frequency c onverter can be programmed to stop the
motor and activatee an alarm via a relay output or
a digital output if the the rmistor is act ivated.
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
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