ABB RED615 Technical Manual page 407

1YHT530004D05 D
615 series
Technical Manual
GUID-46FDF23A-7E78-4B17-A888-8501484AB57A V1 EN
Figure 216: Protection of the power transformer feeding the frequency converter
Transforming ratio correction of CTs
The CT secondary currents often differ from the rated current at the rated load of
the power transformer. The CT transforming ratios can be corrected on both sides
of the power transformer with the CT ratio Cor Wnd 1 and CT ration Cor Wnd 2
settings.
First, the rated load of the power transformer must be calculated on both sides
when the apparent power and phase-to-phase voltage are known.
S
n
=
I
nT
3 × U
n
GUID-B5467DB8-17EB-4D09-A741-1F5BB23466AA V1 EN
I rated load of the power transformer
nT
S rated power of the power transformer
n
U rated phase-to-phase voltage
n
Next, the settings for the CT ratio correction can be calculated.
Section 4
Protection functions
(Equation 51)
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