Application Examples - ABB RELION 670 Series Applications Manual

Section 6
Differential protection
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 34, shall be set
ToObject . If star connected main CTs have their star point away from the protected
transformer this parameter should be set
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 34.
For delta DAB connected main CTs, secondary currents fed to the IED:
• are increased √3 times (1.732 times) in comparison with star connected CTs
• lead by 30° the primary winding currents (this CT connection rotates currents by 30° in
anti-clockwise direction)
• do not contain zero sequence current component
For DAB delta connected main CT ratio shall be set for √3 times smaller in RET 670 then the
actual ratio of individual phase CTs. The "StarPoint" parameter, for this particular connection
shall be set
exactly as shown in figure 34.
For more detailed info regarding CT data settings please refer to the three application
examples presented in section
6.1.4.3

Application Examples

Three application examples will be given here. For each example two differential protection
solutions will be presented:
• First solution will be with all main CTs star connected.
• Second solution will be with delta connected main CT on Y (that is, star) connected sides
of the protected power transformer.
For each differential protection solution the following settings will be given:
1. Input CT channels on the transformer input modules.
2. General settings for the transformer differential protection where specific data about
protected power transformer shall be entered.
Finally the setting for the differential protection characteristic will be given for all presented
applications.
108
ToObject . It shall be noted that delta DAB connected main CTs must be connected
"Application
FromObject .
Examples".
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