ABB REG670 Applications Manual page 144

Section 7
Differential protection
Protected
Transformer
Winding
IEC06000549 V1 EN
Figure 54: Commonly used main CT connections for Transformer differential protection.
138
CT Star
Connected
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
• contain all sequence components including zero sequence current component
For star connected main CTs, the main CT ratio shall be set as it is in actual
application. The "StarPoint" parameter, for the particular star connection shown in
figure 54, shall be set ToObject. If star connected main CTs have their star point away
from the protected transformer this parameter should be set FromObject.
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)
• do not contain zero sequence current component
For DAC delta connected main CTs, ratio shall be set for √3 times smaller than the
actual ratio of individual phase CTs. The "StarPoint" parameter, for this particular
connection shall be set ToObject. It shall be noted that delta DAC connected main CTs
must be connected exactly as shown in figure 54.
For delta DAB connected main CTs, secondary currents fed to the IED:
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
CT in Delta
DAC Connected
1MRK 502 071-UEN -
IL1
IL2
IL3
CT in Delta
DAB Connected
en06000549.vsd
Application manual
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