Operating instructions

Operation with up to three supply inverters

MICROMASTER 420 / 440 – DC link coupling between several

Frequency inverters

The required supply power of 75kW can, for example, be split-up as follows:

Motor power of the Required power of the

supply inverters: supply inverters:

11kW => 15kW (overdimensioned by a factor of 1.35)

15kW => 30kW 1)

22kW => 30kW (overdimensioned by a factor of 1.35)

Overdimensioned by more than a factor of 1.35 as a frequency inverter

which is not a supply inverter operates in the motoring mode and the total

supply power must be at least 1.35 times larger than the sum of the

motoring powers in the drive group.

The frequency inverters connected to the DC link do not have to be

overdimensioned. This means that 2 frequency inverters, each with a

7.5kW power rating can be used.

5.2 Options which are required at the line supply input of the supply

inverters

The fuses, circuit-breaker and a possible externally mounted EMC filter

should be used, according to Catalog DA51.2 at the line side of the supply

inverter just the same as for the individually operated frequency inverters.

The supply inverters must be overdimensioned by a factor of 1.35. This

means that the line-side options also have to be dimensioned for a higher

rating. In turn this means that the line-side options can be selected

corresponding to the power rating of the supply inverters. In order to limit

the equalization currents between the supply inverters it is absolutely

necessary that each supply inverter has its own line reactor which matches

the power rating of the supply inverter. In order to achieve a symmetrical

pre-charging of the frequency inverters, the supply inverters must be

simultaneously switched-in using a common line contactor.

We recommend that the line-side fuses of the frequency inverter are

monitored so that the complete drive group can be powered-down when a

fuse ruptures.

Otherwise the frequency inverters still connected to the line supply would

have to compensate for the disconnected supply inverter and could

therefore be possibly overloaded.

Frequency inverters with integrated radio suppression filters can also be

used as supply inverters. For frequency inverters connected to the DC link,

an integrated EMC filter makes no sense and is not necessary.

A&D SD Page 23/32