Danfoss VLT HVAC FC 100, Руководство по обслуживанию, Страница: 50 / 220

3.3.2 Intermediate Section
Following the rectifier section, voltage passes to the intermediate section. (see Figure 3-5). This
rectified voltage is smoothed by an LC filter circuit consisting of the DC bus inductor and the DC
bus capacitor bank.
The DC bus inductor provides series impedance to changing current. This aids the filtering process
while reducing harmonic distortion to the input AC current waveform normally inherent in rectifier
circuits.
The DC capacitor bank assembly consists of up to eight capacitors arranged in series/parallel
configuration. Higher power units have two capacitor bank assemblies. Also contained within the
assembly is the bleeder/balance circuitry. This circuitry maintains equal voltage drops across each
capacitor and provides a current path for discharging the capacitors once power has been removed
from the adjustable frequency drive.
Also located in the intermediate section is the high frequency (HF) filter card. It contains a high
frequency filter circuit to reduce naturally occurring currents in the HF range to prevent interfer-
ence with other sensitive equipment in the area. The circuit, as with other RFI filter circuitry, can
be sensitive to unbalanced phase-to-ground voltages in the three-phase AC input line. This can
occasionally result in nuisance overvoltage alarms. For this reason, the high frequency filter card
on 380–500 V range adjustable frequency drives, contains a set of relay contacts in the ground
connection of the filter capacitors. The relay is tied into the RFI/HF switch, which can be switched
on or off in par. 14-50
RFI 1
. This disconnects the ground references to all filters should unbal-
anced phase-to-ground voltages create nuisance overvoltage conditions.
For 525–690 V adjustable frequency drives, there are no relay contacts that disconnect the
grounding.
High Power Service Manual for VLT
®
FC Series
Adjustable Frequency Drives
3 Internal Adjustable Frequency Drive Opera-
tion
MG.90.L1.22 - VLT ® is a registered Danfoss trademark
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