Connecting
6.1 Instructions for EMC-compliant drive installation
SINAMICS DCM DC Converter
Operating Instructions, 12/2018, A5E34763375A
105
The fundamental component of current I
1
as a reference variable is calculated using the
following formula
I
1
= g × 0.817 × I
d
where I
d
is the DC current of the operating point under investigation and
where g is the fundamental factor (see previous table)
The harmonic currents calculated according to the previous table
apply for:
I.) Short-circuit power S
K
at the location where the converter is connected
S
K
= U
2
v0
/ X
N
(VA)
with
X
N
= X
K
- X
D
= 0.03526 × U
v0
/ I
d
- 2Ï€f
N
× L
D
(Ω)
and
U
v0
No-load voltage on the power unit terminal V
I
d
Direct current of the operating point examined in A
f
N
Line frequency in Hz
L
D
Inductance of the commutating reactors used in H
X
D
Impedance of the commutating reactor
X
N
Impedance of the line
X
K
Impedance at the unit terminals
II.) Armature inductance L
a
L
a
= 0.0488 × U
v0
/ (f
N
× I
d
) (H)
If the actual values for the short-circuit power S
K
and/or armature inductance L
a
deviate from
the values calculated using the previous formulas, a separate calculation procedure will need
to be carried out.
Let us assume a drive with the following data:
U
v0
= 400 V
I
d
= 150 A
f
N
= 50 Hz
L
D
= 0.169 mH (4EU2421-7AA10 with I
Ln
= 125 A)
With
X
N
= 0.03536 × 400 / 150 - 2π × 50 × 0.169 × 10
-3
= 0.0412 Ω
the network short-circuit power at the converter unit terminal is as follows:
S
K
= 400
2
/ 0.0412 = 3.88 MVA
and the armature inductance of the motor is as follows:
L
a
= 0.0488 × 400 / (50 × 150) = 2.60 mH
The harmonic currents I
ν
(with I
1
= g × 0.817 × I
d
for firing angles α = 20° and α = 60°) that
can be taken from the tables,
apply for the values S
K
and L
a
that have been calculated
in this way. If the actual values deviate from these, a separate calculation will have to be
made.
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