ABB 615 series Technical Manual page 524

Section 4
Protection functions
518
GUID-46FDF23A-7E78-4B17-A888-8501484AB57A V1 EN
Figure 259: 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 V
×
n
GUID-B5467DB8-17EB-4D09-A741-1F5BB23466AA-ANSI V1 EN
I rated load of the power transformer
nT
S rated power of the power transformer
n
V rated phase-to-phase voltage
n
1MAC059074-MB A
(Equation 89)
615 series ANSI
Technical Manual