ABB Relion 670 Series Applications Manual page 525

1MRK 511 401-UEN Rev. K
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 vector group shall be set as
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.
18.12.4.1 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 L1-L2-L3.
Monitored
Transformer
Winding
IEC18000079 V1 EN-US
Figure 252: Main CT connections for transformers
For star 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
• Contains all sequence components including zero sequence current component
For star connected main CTs, the main CT ratio shall be set as it is in the actual application.
StarPoint parameter, for the particular star connection shown in
The
ToObject . If star connected main CTs have their star point away from the protected
transformer, this parameter shall be set as
For delta DAC connected main CTs, secondary currents fed to the IED:
• Are increased √3 times (1.732 times) in comparison with star connected CTs
• Lag by 30° the primary winding currents (this CT connection rotates currents by 30° in
clockwise direction)
• Does not contain zero sequence current component and consequently winding currents
are not properly measured for all types of faults
Bay control REC670
Application manual
Irrespective of the main CT connections (star or delta), online reading and
automatic correction for actual load tap changer position can be used in the
IED.
CT Star
Connected DAC Connected
© Copyright 2017 Hitachi Power Grids. All rights reserved
CT in Delta CT in Delta
DAB Connected
FromObject .
Section 18
Monitoring
Yy0 since the IED shall
GUID-3179E8A2-D1F8-4EDE-81F9-7A7AF2B8C2D6 v1
Figure 252. It is
IL1
L1
IL2
L2
IL3
L3
IEC18000079-1-en.vsd
Figure 252, shall be set as
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