Operating instructions

Operation with only one supply frequency inverter

MICROMASTER 420 / 440 – DC link coupling between several

Frequency inverters

A&D SD Page 15/32

In this particular case, the supply inverter (75kW) is fused, on the line side

with the fuses (200A) specified in the Operating Instructions. The frequency

inverters (11kW and 7.5kW) connected to its DC link must be separately

fused as they cannot be protected by the 200A line fuses of the supply

inverter. The two connected inverters are fused through two phases with

40A (11kW frequency inverter) and 32A (7.5kW frequency inverter)

according to Table 2-2. This means that the DC link coupling must be also

directly fused at the DC link output of the 75kW frequency inverter (with 2x

80A fuses). The reason for this is that this also cannot be protected by the

200A line fuses because of the 25mm² cross-section being used. The

cross-section of the DC link coupling depends on the total rated DC link

currents (I

DCtot

= 54A) of the frequency inverters connected to the supply

inverter. Depending on the cable routing type and the ambient temperature,

a cross-section of, e.g. 25mm² can be used (routing type B1, 2 conductors

conducting current, 40° C ambient temperature). The cable coupling

between the DC link connection of the 75kW frequency inverter up to the

fuses of the DC link coupling should be as short as possible and be

implemented and routed so that it is short-circuit proof. As an alternative to

a short circuit-proof implementation and routing, a cable cross-section can

be used for this coupling which is adequately protected using the 200A line

fuses (depending on the line impedance, the DC link current is

approximately 20% higher than the line current).