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Operating instructions

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Operation with up to three supply inverters
MICROMASTER 420 / 440 – DC link coupling between several
Frequency inverters
5.1 Frequency inverter versions and power ratings which can be
coupled
MICROMASTER 420 and MICROMASTER 440 frequency inverters can be
operated both with one another as well as mixed in a DC link group. In
mixed operation, both frequency inverter types can be used as the supply
frequency inverter connected to the line supply. The DC link coupling is
possible with frequency inverters which can be connected to the following
line supplies:
o 1-ph. 200-240V AC
o 3-ph. 200-240V AC
o 3-ph. 380-480V AC
Note:
o It must be ensured that only frequency inverters having the same
voltage level 1/3-ph. 200-240V AC and 3-ph. 380-480V AC are
connected through the DC links.
Copyright © Siemens AG 2005 All rights reserved
o Only single-phase or three-phase frequency inverters may be used as
supply inverter. It is not permissible to mix 1-ph. AC and 3-ph. AC
frequency inverters
(200-240V drive units) as supply inverter.
o When using single phase frequency inverters (1-ph. 200-240V AC) as
supply inverters, it is extremely important to ensure that all of the supply
inverters are connected to the same line phase (e.g. L1/N), otherwise
the connected frequency inverters could be destroyed.
o When using the DC link coupling, only frequency inverters with a
maximum rated power of 75kW (CT) or 90kW (VT), (housing size F) may
be used.
o The difference between the power ratings of the supply inverters may
not be greater than 1:3 in order that the smaller supply frequency
inverter is not overloaded. This restriction does not apply to the
frequency inverters which are not feeding the drive system. This means
that these frequency inverters can be dimensioned significantly smaller
than the supply inverters.
o The maximum number of supply inverters is 3. A maximum of 7
additional frequency inverters, which are not directly connected to the
line supply, can be connected to the DC link. The sum of the frequency
inverters, coupled through the DC link, may be up to 10 units.
o The supply inverter must be dimensioned by a factor of 1.35 greater
than it would be to cover all of the motoring power connected to the DC
link. The reason for this is the equalization currents which flow between
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