ABB RET670 Applications Manual page 115

1MRK504116-UUS C
Protected
Transformer
Winding
ANSI06000549 V1 EN
Figure 26: Commonly used main CT connections for Transformer differential protection.
Application manual
noted that irrespective of the main CT connections (wye or delta) on-line reading and
automatic compensation for actual load tap changer position can be used in the IED.
Typical main CT connections for transformer differential protection
Three most typical main CT connections used for transformer differential protection
are shown in figure 26. It is assumed that the primary phase sequence is A-B-C.
CT Wye
Connected
For wye connected main CTs, secondary currents fed to the IED:
• are directly proportional to the measured primary currents
• are in phase with the measured primary currents
• contain all sequence components including zero sequence current component
For wye connected main CTs, the main CT ratio shall be set as it is in actual
application. The "WyePoint" parameter, for the particular wye connection shown in
figure 26, shall be set ToObject. If wye connected main CTs have their wye point away
from the protected transformer this parameter should be set FromObject.
For delta DAC connected main CTs, secondary currents fed to the IED:
CT in Delta
DAC Connected DAB Connected
Section 3
IED application
IA
IB
IC
CT in Delta
en06000549_ansi.vsd
A
B
C
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