Typical Main Ct Connections For Transformer Differential Protection - ABB RELION 670 SERIES REG670 Applications Manual

Section 7
Differential protection
7.1.4.2
Protected
Transformer
Winding
ANSI06000549 V1 EN-US
Figure 53: Commonly used main CT connections for Transformer differential protection.
144
intentionally set for √(3)=1.732 times smaller than actual ratio of individual phase CTs
(for example, instead of 800/5 set 462/5) In case the ratio is 800/2.88A, often designed
for such typical delta connections, set the ratio as 800/5 in the IED. At the same time
the power transformer vector group shall be set as Yy0 because the IED shall not
internally provide any phase angle shift compensation. The necessary phase angle shift
compensation will be provided externally by delta connected main CT. All other
settings should have the same values irrespective of main CT connections. It shall be
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 53. 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
Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062
CT in Delta
DAC Connected DAB Connected
1MRK 502 071-UUS A
SEMOD167749-5 v3
IA
IB
IC
CT in Delta
en06000549_ansi.vsd
Application manual
A
B
C