Operating instructions

Operation with up to three supply inverters

MICROMASTER 420 / 440 – DC link coupling between several

Frequency inverters

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In this particular case, the five frequency inverters connected to the DC link

are fused with the DC link fuses specified in Table 3-2. The line fuses of the

supply inverters are selected according to the Operating Instructions.

The cable cross-sections to couple the DC link terminals of the inverters to

the DC link fuses are determined corresponding to the downstream DC link

fuses. For the supply inverters, these couplings must be implemented and

routed so that they are short-circuit proof. The couplings after the DC link

fuses are dimensioned for the sum of the rated currents of the line fuses of

the supply inverters multiplied by a factor of 1.2:

DCcross-section

= (80A+50A+35A) * 1.2 = 198A

As a result of this current, a cable cross-section of 95mm² was selected.

The cable cross-section required is also dependent on the routing type and

the ambient temperature. In the example, routing type B1, 2 conductors

conducting current in the cable duct and an ambient temperature of 40° C

were assumed.

Note:

For the DC link couplings, it is also important to observe the plant/system

and country-specific standards and regulations.

5.3.3 Maximum DC link cable lengths

The total length of the DC link couplings is 5m.

5.4 Braking operation of the DC link group

For a DC link coupling, energy is exchanged between the frequency

inverters through the common DC link. If one or several frequency inverters

are in the regenerative mode, then the energy can be provided to the

frequency inverters operating in the motoring mode. If the regenerative

energy is not completely drawn by the connected frequency inverters - or

not at every instant in time - then the energy can be dissipated in a

connected braking resistor using the braking chopper integrated in the

MICROMASTER 440.

In a DC link group, the internal braking chopper may only be activated for

one MICROMASTER 440 frequency inverter. It makes sense if the braking

chopper in the MICROMASTER 440 with the highest power rating in the DC

link group is activated. The braking resistor required can be selected in

accordance with the data in Catalog DA51.2.