Example - ABB ACS800 User Manual

At frequency f, the normally required voltage equals
f
⋅
--- - U
U =
U/F
f
n
Thus, the required boost equals
U
--------------------------------------------- - 100%
BOOST =
The transformer is dimensioned according to the specified voltage boost.

Example

In this example, the voltage boost (BOOST) is calculated for a 50% torque. The
motor data etc. are as above.
I =
USED
The voltage drop on the secondary side equals (assumed motor stator resistance
0.3 ohm, assumed transformer resistance 0.19 ohm)
U =
drop,phase
On the primary side, the voltage drop equals
U
drop,primary
For 2 Hz, the normal U/F curve gives the following result:
2
----- - 690 V = 27.6 V
U =
U/F
50
Thus, the required voltage boost for 50% equals
41,4
-------------------------- - 100% = 250%
BOOST =
The transformer should, according to the above calculations, withstand 250%
voltage at 2 Hz frequency. The calculated boost value is to be forwarded to the
manufacturer of the transformer.
input
+ U
drop,primary U/F
⋅
U
U/F
2
2
( ⋅ )
1 0,82 – 106 +
⋅ (
74,63 0,19 + 1,35
620
⋅ ⋅
----------- -
= 3 137.3 V = 41.4 V
3560
⋅
+ 27,6
⋅
27,6
2
50
⎛ ⎞
⋅ ⋅
-------- - 0,82 106
A
⎝ ⎠
100
) V = 137.3 V
+ 0,3
Appendix – Step-up applications
= 74,63 A
41