Danfoss VLT FC Series, Руководство по обслуживанию

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5.3.2 Intermediate Section
Following the rectifier section, voltage passes to the
intermediate section (see
Illustration 5.7 and Illustration 5.8 ).
An LC filter circuit consisting of the DC bus inductor and
the DC bus capacitor bank smooths the rectified voltage.
The DC bus inductor provides series impedance to
changing current. It aids the filtering process while
reducing harmonic distortion to the input AC current
waveform normally present in rectifier circuits.
The DC capacitor bank assembly consists of up to 21
capacitors arranged in series/parallel configuration. The
assembly also contains the bleeder/balance circuitry. This
circuitry maintains equal voltage drops across each
capacitor, and provides a current path for discharging the
capacitors when the drive is powered down.
The intermediate section also includes the high frequency
(HF) filter card. This card contains a high frequency filter
circuit to reduce naturally occurring currents in the HF
range to prevent interference with sensitive equipment
nearby. The circuit, as with other RFI filter circuitry, can be
sensitive to unbalanced phase-to-ground voltages in the 3-
phase AC input line. This sensitivity occasionally results in
nuisance overvoltage alarms. For this reason, the high
frequency filter card contains a set of relay contacts in the
ground connection of the filter capacitors. The relay is tied
to the RFI/HF switch, which can be switched on or off in
parameter 14-50 RFI Filter . This setting disconnects the
ground references to all filters in case unbalanced phase-
to-ground voltages create nuisance overvoltage conditions.
Internal Drive Operation Service Guide
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