36
Secondary side
The following diagram represents the secondary side of a step-up system.
I
2
The impedance of the secondary side equals
The system is dimensioned using the nominal current of the motor:
Thus, the minimum voltage for the transformer secondary equals
Primary side
It can be assumed that the primary voltage of the transformer is about 10% lower
than the supply voltage of the drive because of the voltage drop in the sine filter and
the drive. The primary voltage U
• 0.85 × 400 V = 340 V (for 400 V drives)
• 0.87 × 500 V = 435 V (for 500 V drives)
• 0.9 × 690 V = 620 V (for 690 V drives).
Appendix – Step-up applications
R
jX
c
c
R
U
/ sqrt(3)
2
jX
2
(
)
Z
=
R
+
R
+
1
c
m
I
=
I
2
n
⋅
⋅
U
=
3 I
Z
2
2
1
m
U
/ sqrt(3)
n
m
2
(
)
X
+
X
c
m
equals
1