For Altivar ATV930 drives that share the same DC bus, there are several rules regarding connections, fuse selection, and operation. All details are explained in the DC bus sharing technical note, (document PHA25028, attached).

For braking resistor selection there are a few criteria in the form:
- Min braking power. The requirement for braking power must come from application needs (load, load cycle, number of concurrent drives braking, etc.)
- min resistance of braking resistor. The resistance of the braking resistor must always be equal to or greater than min allowed resistance required by the connected device (drive or braking unit).

If several ATV930 drives share the same DC bus and there is a requirement to dissipate energy to the braking resistor in case of braking, the braking resistor does not need to be connected to each drive. The resistor can be only one, but this resistor and associated unit (braking unit or associated ATV connected to the resistor) must be able to transfer braking power for the worst case that can occur in the application. For example, a situation when no drive on a DC bus consumes power at the time, but all drives are braking at the moment.

If a braking resistor is used with the braking unit, then the braking unit gets active (dissipates energy from the DC bus to the resistor) as soon as the DC bus voltage increases to 780V providing that the associated drive connected to the braking unit via control link is in ready (RDY) or RUN.

If the braking resistor is directly connected to a drive that has a built-in braking transistor, then the parameter of the drive has to be: parameter “brC” must be set to “yes” to enable operation of the braking IGBT and parameter “brA" must be set to "No". Altivar ATV900 can activate its braking transistor even in RDY state, so no need to force the drive to RUN. Other drives on the same DC bus (and without braking resistor) must have bra=no and brC=No.

Bear in mind that if Altivar that has a braking resistor connected gets into a fault state, it cannot provide braking. Consequences for other drives must be considered unless there is another drive on the DC bus able to dissipate all braking power.
Also, consider that for vertical movement (hoist) it is less safe to use a braking resistor connected to another drive. For hoists, it is recommended to use a braking resistor either directly on the hoist drive or to use a braking unit.

Gepubliceerd voor: Schneider Electric Belgium