Rfi 1B/Lc Filter - Danfoss VLT 2800 Design Manual

Introduction to VLT 2800

1.7.11 RFI 1B/LC Filter

The RFI 1B/LC filter contains both an RFI module that
complies with EN 55011-1B, and a LC filter that reduces
the acoustic noise.
LC filter
Illustration 1.4 LC Filter
When a motor is controlled by a frequency converter,
acoustic noise may be heard 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 activated. 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 ΔI to the motor, so that the
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 is
emitted by the coils. This problem can be solved
completely by fitting the filter inside a cabinet or
equivalent.
Danfoss can supply an LC filter for the VLT series 2800,
which muffles the acoustic motor noise. Before the filters
are put into use, ensure that:
•
Rated current is observed.
•
Mains voltage is 200-480 V.
•
Parameter 412 Variable switching frequency is set
to [3] LC filter attached.
•
Output frequency is max. 120 Hz.
Refer to Illustration 1.7 for a connection example of LC
filter.
Installation of thermistor (PTC)
The RFI 1B/LC filter has an integral thermistor (PTC), which
is activated if an overtemperature arises. The frequency
converter can be programmed to stop the motor and
activate an alarm via a relay output or a digital output if
the thermistor is activated.
MG27E402
Design Guide
Illustration 1.5 Thermistor Installation
The thermistor must be connected between terminal 50
(+10 V) and one of the digital inputs 18, 19, 27 and 29.
In parameter 128 Thermal motor protection, [1] Thermistor
warning or [2] Thermistor trip is selected.
Illustration 1.7 shows the thermistor connection.
Illustration 1.6 Thermistor Connection
To comply with EN 55011-1B, the RFI 1B filter module must
be fitted to a VLT 2800 with integral 1A RFI filter.
NOTICE
The 1B/LC filter is not suitable for 200 V devices due to
the high 1Ø input current.
Danfoss A/S © Rev. May/2014 All rights reserved.
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