Restrictions; Selecting The Brake Resistor - ABB ACS880-104 Hardware Manual

330 Resistor braking using frames R1i...R4i inverter modules
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Restrictions

• Internal brake choppers are only available for frame R1i...R4i, ACS880-104-xxxxx-3
and ACS880-104-xxxxx-5 inverter module types.
• The maximum number of modules doing the braking is 12 frame R1i...R2i modules or
6 frame R3i...R4i modules, ie. the number of modules that can be mounted into a 800
mm wide Rittal TS 8 cubicle.
• Each inverter module must have its own resistor(s).
• In case the braking power of the modules is not sufficient, a separate brake chopper
must be used. It is not allowed to use the internal brake choppers simultaneously with
a separate brake chopper.
• The cubicle with the braking modules must be next in the line-up to the inverter that
needs to be braked.
• The internal brake choppers cannot be used if the system has an IGBT (regenerative)
supply unit.
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Selecting the brake resistor

Ratings (page 335) lists an example brake resistor for each inverter type. These resistors
are available from ABB.
When sourcing a resistor from a third party, make sure that:
1. The resistance of the custom resistor is greater or equal than the minimum allowed
resistance:
R ≥ R
min
where
R Resistance of the custom resistor.
R Minimum allowed resistance of the brake resistor. See section Ratings.
min
2. The load capacity of the custom resistor is higher than the instantaneous maximum
power consumption of the resistor when it is connected to the DC link voltage by the
chopper:
where
P Load capacity of the custom resistor
r
U Drive DC link voltage.
DC
1.35 · 1.25 · 415 V DC (when supply voltage is 380 to 415 V AC) or
1.35 · 1.25 · 500 V DC (when supply voltage is 440 to 500 V AC)
R Resistance of the custom resistor
WARNING! Never use a brake resistor with a resistance smaller than Rmin. The in-
verter module and the chopper are not able to handle the overcurrent caused by the
low resistance.