ABB RELION RET670, Applications Manual

Page: 154 / 1016

1. Input CT channels on the transformer input modules.
2. General settings for the transformer differential protection where specific data
about protected power transformer shall be entered.
Finally the setting for the differential protection characteristic will be given for all
presented applications.
Example 1: Wye-delta connected power transformer without on-load
tap-changer
SEMOD167854-110 v5
Single line diagrams for two possible solutions for such type of power transformer with
all relevant application data are given in figure
50 .
CT 300/5
in Delta
(DAC)
CT 800/5
Wye
20.9 MVA
69/12.5 kV
YNd1
(YD
AC
)
CT 300/5
Wye
CT 800/5
Wye
20.9 MVA
69/12.5 kV
YNd1
(YD
AC
)
en06000554_ansi.vsd
ANSI06000554 V1 EN-US
Figure 50: Two differential protection solutions for wye-delta connected power
transformer
For this particular power transformer the 69 kV side phase-to-ground no-load voltages
lead by 30 degrees the 12.5 kV side phase-to- ground no-load voltages. Thus when
external phase angle shift compensation is done by connecting main HV CTs in delta,
as shown in the right-hand side in figure
50 , it must be ensured that the HV currents
Section 7
1MRK 504 163-UUS A
Differential protection
148 Transformer protection RET670 2.2 ANSI
Application manual