ABB Relion 670 Series Applications Manual page 499

1MRK 511 401-UUS F
17.12.4 Setting examples
In order to correctly apply transformer through fault monitoring with proper zero sequence
current, correction is needed for:
• Power transformer phase shift (phase shift compensation)
• Zero sequence current (zero sequence current consideration)
The through fault monitoring is suitable for all standard three-phase power transformers without
any interposing CTs. It is designed with the assumption that all main CTs are wye connected. For
such applications, it is only necessary to enter CT rated data and power transformer data directly
as they are given on the power transformer nameplate. The zero sequence current is then
calculated and included in the winding currents itself unless there is more than one delta winding
configuration.
However, the IED can also be used in applications where some of the main CTs are connected in
delta. In such cases, the ratio for the main CT connected in delta shall be intentionally set to √3 =
1.732 times smaller than the actual ratio of individual phase CTs (for example, set 462/5 instead of
800/5). 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 phase shift shall be set as
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.
17.12.4.1 Typical main CT connections for transformer
Three most typical main CT connections used for transformers are shown in
assumed that the primary phase sequence is A-B-C.
Monitored
Transformer
Winding
ANSI18000079 V1 EN-US
Figure 223: Main CT connections for transformers
Bay control REC670
Application manual
Irrespective of the main CT connections (wye or delta), online reading and
automatic correction for actual load tap changer position can be used in the IED.
CT Wye
Connected DAC Connected
© Copyright 2017 ABB. All rights reserved
CT in Delta CT in Delta
DAB Connected
Section 17
Monitoring
GUID-2AE19CC1-F790-4E98-A75D-65363155E209 v1
Yy0 since the IED shall not
GUID-3179E8A2-D1F8-4EDE-81F9-7A7AF2B8C2D6 v1
Figure 223. It is
IA
A
IB
B
IC
C
ANSI18000079-1-en.vsd
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