Safety information
page 18
ELTROPLAN-REVCON
Length of the DC-connection
The maximum inductivity of the DC-connection between output B6 bridge of
the inverter and the power feedback device mustn't exceed a certain level, as
this inductivity inducts an additional voltage to the DC-bus, when the IGBT’s
are switched off . To avoid an overload to the components of the power feed-
back unit, this additional voltage must not exceed 100V. Resulting from this
and other relevant characteristics of the power feedback unit (DC-capacity and
absolute maximum value of the grid current) the maximum inductivity
(
)
2
2
max
ˆ
i
U
C
L
GL
∆
⋅
=
can be calculated. This inductivity always has to be higher
or equal than the sum of the DC-bus inductivity of the frequency inverter and
the conductor inductivity of the DC connection. The DC-bus inductivity of the
frequency inverter has only to be considered, if it is placed between the inverter
B6 bridge and the power feed-back unit. The cables, which are normally used
for power applications, have an inductance per unit length of about 0,6µH/m. If
the values of the input capacitance C, the during power backfeeding maximum
allowed rise of the DC-voltage
∆
U
GL
=100V, the top level of the AC-current of
the device (=2xI
eff
), the inductance per unit length L´ and the inductance of the
DC-bus ´choke
L
ZKD
are known the maximum longitude of the conductors can
be calculated with the following equation:
L
L
L
i
U
C
l
ZKD
GL
′
−
′
⋅
∆
⋅
=
2
2
max
ˆ
Typical capacitance of the DC-connection inside the power feedback unit
:
REVCON
®
-type Power
DC-capacitance
SVC
7-45kW
100
µ
F
70-135kW
200µF
160-200kW 420µF
Table 2.6.1
Example:
C=200µF,
∆
U
GL
=100V, i=271A, a=80mm, r=8,5mm, µ
0
=1,257
.
10
-6
H/m
⇒
l
max
=26m
For longer DC-Bus-wires additional capacitors have to be installed (please get
in contact with our application-department if the occasion arrises).