ABB RELION REX640 Technical Manual page 615

1MRS759142 C
REX640
Technical Manual
GUID-0BCC5A98-15E9-4025-8E80-2CFF512127DD V1 EN
Figure 339: 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-BEC5B6EB-3302-490B-B99E-D9B2EBEFA644 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
Section 4
Protection functions
(Equation 112)
609