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42 Operation principle and hardware description
Weak supply networks
In weak supply networks with a short-circuit ratio less than 8, ABB recommends to
equip the supply unit with BAMU auxiliary measurement unit (option +G442). If it is
not included, there is a risk of nuisance DC overvoltage trippings due to disturbances
caused by high-voltage THD in the supply voltage. Short-circuit ratio is defined as the
supply network's apparent short-circuit power S
apparent power S
n
SCR
= S
/ S
, where
net
k,net
n
•
SCR
= short-circuit ratio of the supply network
net
•
S
= supply network's apparent short-circuit power
k,net
•
S
= nominal apparent power of the drive.
n
If a generator is used as a supply: The recommendation for ACS880 IGBT supply unit
with generator supply is:
•
always use BAMU auxiliary measurement unit
•
short-circuit ratio of the supply network SCR
•
short-circuit ratio of the generator SCR
•
xk = relative short-circuit reactance
generator nominal power P
•
•
P
= generator nominal power (output)
gen
P
•
= typical power of the IGBT supply unit in no-overload use.
N,ISU
1
Generator. SCR
gen
2
Supply network. SCR
3
LCL filter
4
IGBT supply module
:
> 0.3 × P
gen
1
2
> 2
> 3
net
divided by the drive's nominal
k,net
> 3
net
= 1/xk > 2, where
gen
, where
N,ISU
3
4
AC
DC
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