GE Industrial Solutions AF-600 FP High Power (460V_575V 150HP and above) - Manual (Page 38)

3.3.2 Intermediate Section
Following the rectifier section, voltage passes to the intermediate section. (see Illustration 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 as-
semblies. 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 frequency converter.
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-earth 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 frequency converters, contains a set of relay contacts in the earth connection of the filter capacitors. The relay is tied into the RFI/HF switch,
which can be switched on or off in par. SP-50 RFI Filter. This disconnects the earth references to all filters should unbalanced phase-to-earth voltages create
nuisance overvoltage conditions.
For 525–690 V frequency converters, there are no relay contacts that disconnect the earthing.
AF-650 GP and AF-600 FP High Power Service Manual
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