24 Planning – basics
Checking the peak AC current at charging
If you only have drives with Type A charging circuits in the common DC system, make sure
that the AC line-side components (fuses, contactors, etc.) can withstand the peak current
at charging. Use the rule of thumb below, or calculate the peak current and compare it to
the allowed peak current data for the AC line-side components.
Rule of thumb:
There can not be more than three drives which are not connected to the AC
power line per one connected drive.
Calculation:
Calculate the peak current with this equation:
Checking the charging energy
Use this method to verify the charging capacity if there are drives with Type B charging
circuit in the common DC system.
The drives that you connect to the AC power line must supply the total charging energy for
all of the DC capacitors in the common DC system at the power up. The charging capacity
must comply with this formula:
E
rconnected
> E
tot
Calculate the charging energy for a drive and the common DC system with these
equations:
E
tot
= E
a
+ …+ E
n
= 1/2 × (C
DCa
+…+C
DCn
) × (1.35 × U
net
)
2
E
1
= 1/2 × C
DCa
× (1.35 × U
net
)
2
I
ac,peak
Peak AC current at charging.
U
ac
AC input voltage.
R
tot
Total charging resistance (see page 23).
E
rconnected
Total energy pulse that the charging resistors of the drives connected to the AC power line
can withstand. See subsection Charging circuit Er values on page 43.
E
tot
Total charging energy of the DC capacitors of all drives in the common DC system.
C
DC
Capacitance of drive DC capacitors. C
DCa
is the capacitance of drive a. See subsection DC
link capacitance values on page 43.
E
a
Charging energy of drive a.
U
net
Main voltage of the AC power line which the common DC system is connected to.
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