Ct Earthing Direction - ABB REG670 Applications Manual

Section 7
Differential protection
7.4.2.6
7.4.3
7.4.3.1
180
REFPDIF
I3PW1CT1
I3P
IdN/I
I3PW1CT2
IEC09000113-3 V2 EN
Figure 76: Connection of Restricted earth fault, low impedance function
REFPDIF in multi-breaker arrangements

CT earthing direction

To make the restricted earth fault protection REFPDIF operate correctly, the main
CTs are always supposed to be star -connected. The main CT's neutral (star) formation
can be positioned in either way, ToObject or FromObject. However, internally
REFPDIF always uses reference directions towards the protected transformers, as
shown in Figure 76. Thus the IED always measures the primary currents on all sides
and in the neutral of the power transformer with the same reference direction towards
the power transformer windings.
The earthing can be freely selected for each of the involved current transformers.
Setting guidelines
Setting and configuration
Recommendation for analog inputs
I3P: Neutral point current ( All analog inputs connected as 3Ph groups in ACT).
I3PW1CT1: Phase currents for winding 1 first current transformer set.
I3PW1CT2: Phase currents for winding1 second current transformer set for multi-
breaker arrangements. When not required configure input to "GRP-OFF".
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
1MRK 502 071-UEN -
Protected
winding
IEC09000113-3.vsd
Application manual