3.3.2 Intermediate Section
Following the rectifier section, voltage passes to the
intermediate section (see
). 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. 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 12
capacitors arranged in series/parallel configuration. 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 the adjustable frequency drive is
powered down.
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 interference 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 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
14-50 RFI 1
. This disconnects
the ground references to all filters in case unbalanced
phase-to-ground voltages create nuisance overvoltage
conditions.
Internal Adjustable Frequen...
Service Manual
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Danfoss A/S © Rev. 2014-02-10 All rights reserved.
MG94A222
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Summary of Contents for VLT FC 103
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